One document matched: draft-ietf-httpbis-p2-semantics-21.xml
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<rfc obsoletes="2616" updates="2817" category="std" ipr="pre5378Trust200902" docName="draft-ietf-httpbis-p2-semantics-21">
<front>
<title abbrev="HTTP/1.1 Semantics and Content">Hypertext Transfer Protocol (HTTP/1.1): Semantics and Content</title>
<author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
<organization abbrev="Adobe">Adobe Systems Incorporated</organization>
<address>
<postal>
<street>345 Park Ave</street>
<city>San Jose</city>
<region>CA</region>
<code>95110</code>
<country>USA</country>
</postal>
<email>fielding@gbiv.com</email>
<uri>http://roy.gbiv.com/</uri>
</address>
</author>
<author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
<organization abbrev="greenbytes">greenbytes GmbH</organization>
<address>
<postal>
<street>Hafenweg 16</street>
<city>Muenster</city><region>NW</region><code>48155</code>
<country>Germany</country>
</postal>
<email>julian.reschke@greenbytes.de</email>
<uri>http://greenbytes.de/tech/webdav/</uri>
</address>
</author>
<date month="October" year="2012" day="4"/>
<workgroup>HTTPbis Working Group</workgroup>
<abstract>
<t>
The Hypertext Transfer Protocol (HTTP) is an application-level protocol for
distributed, collaborative, hypertext information systems. This document
defines the semantics of HTTP/1.1 messages, as expressed by request
methods, request header fields, response status codes, and response header
fields, along with the payload of messages (metadata and body content) and
mechanisms for content negotiation.
</t>
</abstract>
<note title="Editorial Note (To be removed by RFC Editor)">
<t>
Discussion of this draft takes place on the HTTPBIS working group
mailing list (ietf-http-wg@w3.org), which is archived at
<eref target="http://lists.w3.org/Archives/Public/ietf-http-wg/"/>.
</t>
<t>
The current issues list is at
<eref target="http://tools.ietf.org/wg/httpbis/trac/report/3"/> and related
documents (including fancy diffs) can be found at
<eref target="http://tools.ietf.org/wg/httpbis/"/>.
</t>
<t>
The changes in this draft are summarized in <xref target="changes.since.20"/>.
</t>
</note>
</front>
<middle>
<section title="Introduction" anchor="introduction">
<t>
Each Hypertext Transfer Protocol (HTTP) message is either a request or a
response. A server listens on a connection for a request, parses each
message received, interprets the message semantics in relation to the
identified request target, and responds to that request with one or more
response messages. A client constructs request messages to communicate
specific intentions, and examines received responses to see if the
intentions were carried out and determine how to interpret the results.
This document defines HTTP/1.1 request and response semantics in terms of
the architecture defined in <xref target="Part1"/>.
</t>
<t>
HTTP provides a uniform interface for interacting with a resource
(<xref target="resource"/>), regardless of its type, nature, or
implementation, and for transferring content in message payloads in the
form of a representation (<xref target="representation"/>).
</t>
<t>
HTTP semantics include the intentions defined by each request method
(<xref target="methods"/>), extensions to those semantics that might be
described in request header fields (<xref target="request.header.fields"/>),
the meaning of status codes to indicate a machine-readable response
(<xref target="status.codes"/>), and the meaning of other control data
and resource metadata that might be given in response header fields
(<xref target="response.header.fields"/>).
</t>
<t><iref item="content negotiation"/>
This document also defines representation metadata that describe how a
payload is intended to be interpreted by a recipient, the request header
fields that might influence content selection, and the various selection
algorithms that are collectively referred to as
"content negotiation" (<xref target="content.negotiation"/>).
</t>
<section title="Conformance and Error Handling" anchor="conformance">
<t>
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in <xref target="RFC2119"/>.
</t>
<t>
Conformance criteria and considerations regarding error handling
are defined in Section 2.5 of <xref target="Part1"/>.
</t>
</section>
<section title="Syntax Notation" anchor="notation">
<t>
This specification uses the Augmented Backus-Naur Form (ABNF) notation
of <xref target="RFC5234"/> with the list rule extension defined in
Section 1.2 of <xref target="Part1"/>. <xref target="imported.abnf"/> describes rules imported from
other documents. <xref target="collected.abnf"/> shows the collected ABNF
with the list rule expanded.
</t>
</section>
</section>
<section title="Resource" anchor="resource">
<t>
The target of each HTTP request is called a resource.
HTTP does not limit the nature of a resource; it merely
defines an interface that might be used to interact with resources.
Each resource is identified by a Uniform Resource Identifier (URI), as
described in Section 2.7 of <xref target="Part1"/>.
</t>
<t>
When a client constructs an HTTP/1.1 request message, it sends the
"target URI" in one of various forms, as defined in
(Section 5.3 of <xref target="Part1"/>). When a request is received, the server reconstructs
an "effective request URI" for the target resource
(Section 5.5 of <xref target="Part1"/>).
</t>
<t>
One design goal of HTTP is to separate resource identification from
request semantics, which is made possible by vesting the request
semantics in the request method (<xref target="methods"/>) and a few
request-modifying header fields (<xref target="request.header.fields"/>).
Resource owners SHOULD NOT include request semantics within a URI,
such as by specifying an action to invoke within the path or query
components of the effective request URI, unless those semantics are
disabled when they are inconsistent with the request method.
</t>
</section>
<section title="Representation" anchor="representation">
<iref item="representation"/>
<t>
If we consider that a resource could be anything, and that the uniform
interface provided by HTTP is similar to a window through which one
can observe and act upon such a thing only through the communication of
messages to some independent actor on the other side, then we need an
abstraction to represent ("take the place of") the current or desired state
of that thing in our communications. We call that abstraction a
"representation" <xref target="REST"/>.
</t>
<t>
For the purposes of HTTP, a representation is information
that reflects the current or desired state of a given resource, in a format
that can be readily communicated via the protocol, consisting of a set of
representation metadata and a potentially unbounded stream of
representation data.
</t>
<section title="Representation Metadata" anchor="representation.metadata">
<t>
Representation header fields provide metadata about the representation.
When a message includes a payload body, the representation header fields
describe how to interpret the representation data enclosed in the payload
body. In a response to a HEAD request, the representation header fields
describe the representation data that would have been enclosed in the
payload body if the same request had been a GET.
</t>
<t>
The following header fields are defined to convey representation metadata:
</t>
<texttable align="left">
<ttcol>Header Field Name</ttcol>
<ttcol>Defined in...</ttcol>
<c>Content-Type</c> <c><xref target="header.content-type"/></c>
<c>Content-Encoding</c> <c><xref target="header.content-encoding"/></c>
<c>Content-Language</c> <c><xref target="header.content-language"/></c>
<c>Content-Location</c> <c><xref target="header.content-location"/></c>
<c>Expires</c> <c>Section 7.3 of <xref target="Part6"/></c>
</texttable>
<section title="Data Type" anchor="data.type">
<section title="Media Types" anchor="media.types">
<t>
HTTP uses Internet Media Types <xref target="RFC2046"/> in the
<xref target="header.content-type" format="none">Content-Type</xref> (<xref target="header.content-type"/>)
and <xref target="header.accept" format="none">Accept</xref> (<xref target="header.accept"/>) header fields in
order to provide open and extensible data typing and type negotiation.
</t>
<figure><iref primary="true" item="Grammar" subitem="media-type"/><iref primary="true" item="Grammar" subitem="type"/><iref primary="true" item="Grammar" subitem="subtype"/><artwork type="abnf2616"><![CDATA[
media-type = type "/" subtype *( OWS ";" OWS parameter )
type = token
subtype = token
]]></artwork></figure>
<t anchor="rule.parameter">
The type/subtype MAY be followed by parameters in the form of
attribute/value pairs.
</t>
<figure><iref primary="true" item="Grammar" subitem="parameter"/><iref primary="true" item="Grammar" subitem="attribute"/><iref primary="true" item="Grammar" subitem="value"/><artwork type="abnf2616"><![CDATA[
parameter = attribute "=" value
attribute = token
value = word
]]></artwork></figure>
<t>
The type, subtype, and parameter attribute names are case-insensitive.
Parameter values might or might not be case-sensitive, depending on the
semantics of the parameter name. The presence or absence of a parameter might
be significant to the processing of a media-type, depending on its
definition within the media type registry.
</t>
<t>
A parameter value that matches the <xref target="imported.abnf" format="none">token</xref> production can be
transmitted as either a token or within a quoted-string. The quoted and
unquoted values are equivalent.
</t>
<t>
Media-type values are registered with the Internet Assigned Number
Authority (IANA). The media type registration process is
outlined in <xref target="RFC4288"/>. Use of non-registered media types is
discouraged.
</t>
</section>
<section title="Character Encodings (charset)" anchor="character.sets">
<t>
HTTP uses charset names to indicate the character encoding of a
textual representation.
</t>
<t anchor="rule.charset">
A character encoding is identified by a case-insensitive token. The
complete set of tokens is defined by the IANA Character Set registry
(<eref target="http://www.iana.org/assignments/character-sets"/>).
</t>
<figure><iref primary="true" item="Grammar" subitem="charset"/><artwork type="abnf2616"><![CDATA[
charset = token
]]></artwork></figure>
<t>
Although HTTP allows an arbitrary token to be used as a charset
value, any token that has a predefined value within the IANA
Character Set registry MUST represent the character encoding defined
by that registry. Applications SHOULD limit their use of character
encodings to those defined within the IANA registry.
</t>
<t>
HTTP uses charset in two contexts: within an <xref target="header.accept-charset" format="none">Accept-Charset</xref>
request header field (in which the charset value is an unquoted token) and
as the value of a parameter in a <xref target="header.content-type" format="none">Content-Type</xref> header field
(within a request or response), in which case the parameter value of the
charset parameter can be quoted.
</t>
<t>
Implementers need to be aware of IETF character set requirements <xref target="RFC3629"/>
<xref target="RFC2277"/>.
</t>
</section>
<section title="Canonicalization and Text Defaults" anchor="canonicalization.and.text.defaults">
<t>
Internet media types are registered with a canonical form. A
representation transferred via HTTP messages MUST be in the
appropriate canonical form prior to its transmission except for
"text" types, as defined in the next paragraph.
</t>
<t>
When in canonical form, media subtypes of the "text" type use CRLF as
the text line break. HTTP relaxes this requirement and allows the
transport of text media with plain CR or LF alone representing a line
break when it is done consistently for an entire representation. HTTP
applications MUST accept CRLF, bare CR, and bare LF as indicating
a line break in text media received via HTTP. In
addition, if the text is in a character encoding that does not
use octets 13 and 10 for CR and LF respectively, as is the case for
some multi-byte character encodings, HTTP allows the use of whatever octet
sequences are defined by that character encoding to represent the
equivalent of CR and LF for line breaks. This flexibility regarding
line breaks applies only to text media in the payload body; a bare CR
or LF MUST NOT be substituted for CRLF within any of the HTTP control
structures (such as header fields and multipart boundaries).
</t>
<t>
If a representation is encoded with a content-coding, the underlying
data MUST be in a form defined above prior to being encoded.
</t>
</section>
<section title="Multipart Types" anchor="multipart.types">
<t>
MIME provides for a number of "multipart" types — encapsulations of
one or more representations within a single message body. All multipart
types share a common syntax, as defined in Section 5.1.1 of <xref target="RFC2046"/>,
and include a boundary parameter as part of the media type
value. The message body is itself a protocol element; a sender MUST
generate only CRLF to represent line breaks between body-parts.
</t>
<t>
In general, HTTP treats a multipart message body no differently than
any other media type: strictly as payload. HTTP does not use the
multipart boundary as an indicator of message body length.
<!-- jre: re-insert removed text pointing to caching? -->
In all other respects, an HTTP user agent SHOULD follow the same or similar
behavior as a MIME user agent would upon receipt of a multipart type.
The MIME header fields within each body-part of a multipart message body
do not have any significance to HTTP beyond that defined by
their MIME semantics.
</t>
<t>
A recipient MUST treat an unrecognized multipart subtype
as being equivalent to "multipart/mixed".
</t>
<t><list>
<t>
Note: The "multipart/form-data" type has been specifically defined
for carrying form data suitable for processing via the POST
request method, as described in <xref target="RFC2388"/>.
</t>
</list></t>
</section>
<section title="Content-Type" anchor="header.content-type">
<iref primary="true" item="Content-Type header field"/>
<t>
The "Content-Type" header field indicates the media type of the
representation, which defines both the data format and how that data
SHOULD be processed by the recipient (within the scope of the request
method semantics) after any <xref target="header.content-encoding" format="none">Content-Encoding</xref> is decoded.
For responses to the HEAD method, the media type is
that which would have been sent had the request been a GET.
</t>
<figure><iref primary="true" item="Grammar" subitem="Content-Type"/><artwork type="abnf2616"><![CDATA[
Content-Type = media-type
]]></artwork></figure>
<t>
Media types are defined in <xref target="media.types"/>. An example of the field is
</t>
<figure><artwork type="example"><![CDATA[
Content-Type: text/html; charset=ISO-8859-4
]]></artwork></figure>
<t>
A sender SHOULD include a Content-Type header field in a message
containing a payload body, defining the media type of the enclosed
representation, unless the intended media type is unknown to the sender.
If a Content-Type header field is not present, recipients MAY either
assume a media type of
"application/octet-stream" (<xref target="RFC2046"/>, Section 4.5.1)
or examine the representation data to determine its type.
</t>
<t>
In practice, resource owners do not always properly configure their origin
server to provide the correct Content-Type for a given representation,
with the result that some clients will examine a payload's content
and override the specified type.
Clients that do so risk drawing incorrect conclusions, which might expose
additional security risks (e.g., "privilege escalation"). Furthermore,
it is impossible to determine the sender's intent by examining the data
format: many data formats match multiple media types that differ only in
processing semantics. Implementers are encouraged to provide a means of
disabling such "content sniffing" when it is used.
</t>
</section>
</section>
<section title="Data Encoding" anchor="data.encoding">
<section title="Content Codings" anchor="content.codings">
<iref primary="true" item="content coding"/>
<iref primary="true" item="compress (content coding)"/>
<iref primary="true" item="x-compress (content coding)"/>
<iref primary="true" item="deflate (content coding)"/>
<iref primary="true" item="gzip (content coding)"/>
<iref primary="true" item="x-gzip (content coding)"/>
<t>
Content coding values indicate an encoding transformation that has
been or can be applied to a representation. Content codings are primarily
used to allow a representation to be compressed or otherwise usefully
transformed without losing the identity of its underlying media type
and without loss of information. Frequently, the representation is stored in
coded form, transmitted directly, and only decoded by the recipient.
</t>
<figure><iref primary="true" item="Grammar" subitem="content-coding"/><artwork type="abnf2616"><![CDATA[
content-coding = token
]]></artwork></figure>
<t>
All content-coding values are case-insensitive and SHOULD be registered
within the HTTP Content Coding registry, as defined in
<xref target="content.coding.registry"/>. They are used in the
<xref target="header.accept-encoding" format="none">Accept-Encoding</xref> (<xref target="header.accept-encoding"/>)
and <xref target="header.content-encoding" format="none">Content-Encoding</xref> (<xref target="header.content-encoding"/>)
header fields.
</t>
<t>
The following content-coding values are defined by this specification:
<list>
<t>compress (and x-compress): See Section 4.2.1 of <xref target="Part1"/>.</t>
<t>deflate: See Section 4.2.2 of <xref target="Part1"/>.</t>
<t>gzip (and x-gzip): See Section 4.2.3 of <xref target="Part1"/>.</t>
</list>
</t>
</section>
<section title="Content-Encoding" anchor="header.content-encoding">
<iref primary="true" item="Content-Encoding header field"/>
<t>
The "Content-Encoding" header field indicates what content codings
have been applied to the representation, beyond those inherent in the media
type, and thus what decoding mechanisms have to be applied in order to
obtain data in the media type referenced by the <xref target="header.content-type" format="none">Content-Type</xref>
header field.
Content-Encoding is primarily used to allow a representation's data to be
compressed without losing the identity of its underlying media type.
</t>
<figure><iref primary="true" item="Grammar" subitem="Content-Encoding"/><artwork type="abnf2616"><![CDATA[
Content-Encoding = 1#content-coding
]]></artwork></figure>
<t>
An example of its use is
</t>
<figure><artwork type="example"><![CDATA[
Content-Encoding: gzip
]]></artwork></figure>
<t>
If multiple encodings have been applied to a representation, the content
codings MUST be listed in the order in which they were applied.
Additional information about the encoding parameters MAY be provided
by other header fields not defined by this specification.
</t>
<t>
Unlike Transfer-Encoding (Section 3.3.1 of <xref target="Part1"/>), the codings listed
in Content-Encoding are a characteristic of the representation; the
representation is defined in terms of the coded form, and all other
metadata about the representation is about the coded form unless otherwise
noted in the metadata definition. Typically, the representation is only
decoded just prior to rendering or analogous usage.
</t>
<t>
A transforming proxy MAY modify the content coding if the
new coding is known to be acceptable to the recipient, unless the
"no-transform" cache-control directive is present in the message.
</t>
<t>
If the media type includes an inherent encoding, such as a data format
that is always compressed, then that encoding would not be restated as
a Content-Encoding even if it happens to be the same algorithm as one
of the content codings. Such a content coding would only be listed if,
for some bizarre reason, it is applied a second time to form the
representation. Likewise, an origin server might choose to publish the
same payload data as multiple representations that differ only in whether
the coding is defined as part of <xref target="header.content-type" format="none">Content-Type</xref> or
Content-Encoding, since some user agents will behave differently in their
handling of each response (e.g., open a "Save as ..." dialog instead of
automatic decompression and rendering of content).
</t>
<t>
If the content-coding of a representation in a request message is not
acceptable to the origin server, the server SHOULD respond with a
status code of 415 (Unsupported Media Type).
</t>
</section>
</section>
<section title="Audience Language" anchor="audience.language">
<section title="Language Tags" anchor="language.tags">
<t>
A language tag, as defined in <xref target="RFC5646"/>, identifies a
natural language spoken, written, or otherwise conveyed by human beings for
communication of information to other human beings. Computer languages are
explicitly excluded. HTTP uses language tags within the
<xref target="header.accept-language" format="none">Accept-Language</xref> and <xref target="header.content-language" format="none">Content-Language</xref> fields.
</t>
<t>
In summary, a language tag is composed of one or more parts: A primary
language subtag followed by a possibly empty series of subtags:
</t>
<figure><iref primary="true" item="Grammar" subitem="language-tag"/><artwork type="abnf2616"><![CDATA[
language-tag = <Language-Tag, defined in [RFC5646], Section 2.1>
]]></artwork></figure>
<t>
White space is not allowed within the tag and all tags are case-insensitive.
The name space of language subtags is administered by the IANA (see
<eref target="http://www.iana.org/assignments/language-subtag-registry"/>).
</t>
<figure>
<preamble>Example tags include:</preamble>
<artwork type="example"><![CDATA[
en, en-US, es-419, az-Arab, x-pig-latin, man-Nkoo-GN
]]></artwork>
</figure>
<t>
See <xref target="RFC5646"/> for further information.
</t>
</section>
<section title="Content-Language" anchor="header.content-language">
<iref primary="true" item="Content-Language header field"/>
<t>
The "Content-Language" header field describes the natural
language(s) of the intended audience for the representation. Note that this might
not be equivalent to all the languages used within the representation.
</t>
<figure><iref primary="true" item="Grammar" subitem="Content-Language"/><artwork type="abnf2616"><![CDATA[
Content-Language = 1#language-tag
]]></artwork></figure>
<t>
Language tags are defined in <xref target="language.tags"/>. The primary purpose of
Content-Language is to allow a user to identify and differentiate
representations according to the user's own preferred language. Thus, if the
content is intended only for a Danish-literate audience, the
appropriate field is
</t>
<figure><artwork type="example"><![CDATA[
Content-Language: da
]]></artwork></figure>
<t>
If no Content-Language is specified, the default is that the content
is intended for all language audiences. This might mean that the
sender does not consider it to be specific to any natural language,
or that the sender does not know for which language it is intended.
</t>
<t>
Multiple languages MAY be listed for content that is intended for
multiple audiences. For example, a rendition of the "Treaty of
Waitangi", presented simultaneously in the original Maori and English
versions, would call for
</t>
<figure><artwork type="example"><![CDATA[
Content-Language: mi, en
]]></artwork></figure>
<t>
However, just because multiple languages are present within a representation
does not mean that it is intended for multiple linguistic audiences.
An example would be a beginner's language primer, such as "A First
Lesson in Latin", which is clearly intended to be used by an
English-literate audience. In this case, the Content-Language would
properly only include "en".
</t>
<t>
Content-Language MAY be applied to any media type — it is not
limited to textual documents.
</t>
</section>
</section>
<section title="Identification" anchor="identification">
<section title="Identifying a Representation" anchor="identifying.payload">
<t>
When a complete or partial representation is transferred in a message
payload, it is often desirable for the sender to supply, or the recipient
to determine, an identifier for a resource corresponding to that
representation.
</t>
<t>
The following rules are used to determine such a URI for the payload of a
request message:
<list style="symbols">
<t>If the request has a <xref target="header.content-location" format="none">Content-Location</xref> header field,
then the sender asserts that the payload is a representation of the
resource identified by the Content-Location field-value. However,
such an assertion cannot be trusted unless it can be verified by
other means (not defined by HTTP). The information might still be
useful for revision history links.</t>
<t>Otherwise, the payload is unidentified.</t>
</list>
</t>
<t>
The following rules, to be applied in order until a match is found, are
used to determine such a URI for the payload of a response message:
<list style="numbers">
<t>If the request is GET or HEAD and the response status code is
<xref target="status.200" format="none">200 (OK)</xref>,
<xref target="status.204" format="none">204 (No Content)</xref>,
206 (Partial Content), or
304 (Not Modified),
the payload's identifier is the effective request URI
(Section 5.5 of <xref target="Part1"/>).</t>
<t>If the request is GET or HEAD and the response status code is
<xref target="status.203" format="none">203 (Non-Authoritative Information)</xref>, the payload is a
potentially modified representation of the target resource; as such,
the effective request URI might only act as an identifier for the
payload's representation when a request is made via the same chain
of intermediaries.</t>
<t>If the response has a <xref target="header.content-location" format="none">Content-Location</xref> header field
and its field-value is a reference to the same URI as the effective
request URI, the payload's identifier is the effective request URI.</t>
<t>If the response has a <xref target="header.content-location" format="none">Content-Location</xref> header field
and its field-value is a reference to a URI different from the
effective request URI, then the sender asserts that the payload is a
representation of the resource identified by the Content-Location
field-value. However, such an assertion cannot be trusted unless
it can be verified by other means (not defined by HTTP).</t>
<t>Otherwise, the payload is unidentified.</t>
</list>
</t>
</section>
<section title="Content-Location" anchor="header.content-location">
<iref primary="true" item="Content-Location header field"/>
<t>
The "Content-Location" header field references a URI that can be used
as a specific identifier for the representation in this message payload.
In other words, if one were to perform a GET on this URI at the time
of this message's generation, then a <xref target="status.200" format="none">200 (OK)</xref> response would
contain the same representation that is enclosed as payload in this message.
</t>
<figure><iref primary="true" item="Grammar" subitem="Content-Location"/><artwork type="abnf2616"><![CDATA[
Content-Location = absolute-URI / partial-URI
]]></artwork></figure>
<t>
The Content-Location value is not a replacement for the effective
Request URI (Section 5.5 of <xref target="Part1"/>). It is representation metadata.
It has the same syntax and semantics as the header field of the same name
defined for MIME body parts in Section 4 of <xref target="RFC2557"/>.
However, its appearance in an HTTP message has some special implications
for HTTP recipients.
</t>
<t>
If Content-Location is included in a <xref target="status.2xx" format="none">2xx (Successful)</xref>
response message and its value refers (after conversion to absolute form)
to a URI that is the same as the effective request URI, then the response
payload SHOULD be considered a current representation of that resource.
For a GET or HEAD request, this is the same as the default semantics
when no Content-Location is provided by the server. For a state-changing
request like PUT or POST, it implies that the server's response contains
the new representation of that resource, thereby distinguishing it from
representations that might only report about the action (e.g., "It worked!").
This allows authoring applications to update their local copies without
the need for a subsequent GET request.
</t>
<t>
If Content-Location is included in a <xref target="status.2xx" format="none">2xx (Successful)</xref>
response message and its field-value refers to a URI that differs from the
effective request URI, then the origin server claims that the field-value
is an identifier for the payload's representation. Such a claim can only be
trusted if both identifiers share the same resource owner, which cannot be
programmatically determined via HTTP.
<list style="symbols">
<t>For a response to a GET or HEAD request, this is an indication that the
effective request URI identifies a resource that is subject to content
negotiation and the Content-Location field-value is a more specific
identifier for the selected representation.</t>
<t>For a <xref target="status.201" format="none">201 (Created)</xref> response to a state-changing method,
a Content-Location field-value that is identical to the
<xref target="header.location" format="none">Location</xref> field-value indicates that this payload is a
current representation of the newly created resource.</t>
<t>Otherwise, such a Content-Location indicates that this payload is a
representation reporting on the requested action's status and that the
same report is available (for future access with GET) at the given URI.
For example, a purchase transaction made via a POST request might
include a receipt document as the payload of the <xref target="status.200" format="none">200 (OK)</xref>
response; the Content-Location field-value provides an identifier for
retrieving a copy of that same receipt in the future.</t>
</list>
</t>
<t>
If Content-Location is included in a request message, then it MAY
be interpreted by the origin server as an indication of where the
user agent originally obtained the content of the enclosed
representation (prior to any subsequent modification of the content
by that user agent). In other words, the user agent is providing
the same representation metadata that it received with the original
representation. However, such interpretation MUST NOT be used to
alter the semantics of the method requested by the client. For
example, if a client makes a PUT request on a negotiated resource
and the origin server accepts that PUT (without redirection), then the
new set of values for that resource is expected to be consistent with
the one representation supplied in that PUT; the Content-Location
cannot be used as a form of reverse content selection that
identifies only one of the negotiated representations to be updated.
If the user agent had wanted the latter semantics, it would have applied
the PUT directly to the Content-Location URI.
</t>
<t>
A Content-Location field received in a request message is transitory
information that SHOULD NOT be saved with other representation
metadata for use in later responses. The Content-Location's value
might be saved for use in other contexts, such as within source links
or other metadata.
</t>
<t>
A cache cannot assume that a representation with a Content-Location
different from the URI used to retrieve it can be used to respond to
later requests on that Content-Location URI.
</t>
</section>
</section>
</section>
<section title="Representation Data" anchor="representation.data">
<t>
The representation data associated with an HTTP message is
either provided as the payload body of the message or
referred to by the message semantics and the effective request
URI. The representation data is in a format and encoding defined by
the representation metadata header fields.
</t>
<t>
The data type of the representation data is determined via the header fields
<xref target="header.content-type" format="none">Content-Type</xref> and <xref target="header.content-encoding" format="none">Content-Encoding</xref>.
These define a two-layer, ordered encoding model:
</t>
<figure><artwork type="example"><![CDATA[
representation-data := Content-Encoding( Content-Type( bits ) )
]]></artwork></figure>
</section>
<section title="Payload Semantics" anchor="payload">
<iref item="payload"/>
<t>
Some HTTP messages transfer a complete or partial representation as the
message "payload". In some cases, a payload might only
contain the associated representation's header fields (e.g., responses to
HEAD) or only some part(s) of the representation data
(e.g., the 206 (Partial Content) status code).
</t>
<t>
The purpose of a payload in a request is defined by the method semantics.
In a response, the payload's purpose is defined by both the request method
and the response status code.
</t>
<t>
For example, a representation in the payload of a PUT request
(<xref target="PUT"/>) represents the desired state of the target resource
if the request is successfully applied, whereas a representation in the
payload of a POST request (<xref target="POST"/>) represents an anonymous
resource for providing data to be processed, such as the information that
a user entered within an HTML form.
</t>
<t>
Likewise, the payload of a <xref target="status.200" format="none">200 (OK)</xref> response to GET
(<xref target="GET"/>) contains a representation of the target resource,
as observed at the time of the message origination date
(<xref target="header.date"/>), whereas the same status code in a response
to POST might contain either a representation of the processing result or
a current representation of the target resource after applying the
processing. Response messages with an error status code usually contain
a representation that describes the error and what next steps are suggested
for resolving it.
</t>
<t>
Header fields that specifically describe the payload, rather than the
associated representation, are referred to as "payload header fields".
Payload header fields are defined in other parts of this specification,
due to their impact on message parsing.
</t>
<texttable align="left">
<ttcol>Header Field Name</ttcol>
<ttcol>Defined in...</ttcol>
<c>Content-Length</c> <c>Section 3.3.2 of <xref target="Part1"/></c>
<c>Content-Range</c> <c>Section 5.2 of <xref target="Part5"/></c>
<c>Transfer-Encoding</c> <c>Section 3.3.1 of <xref target="Part1"/></c>
</texttable>
</section>
<section title="Content Negotiation" anchor="content.negotiation">
<t>
HTTP responses include a representation which contains information for
interpretation, whether by a human user or for further processing.
Often, the server has different ways of representing the
same information; for example, in different formats, languages,
or using different character encodings.
</t>
<t>
HTTP clients and their users might have different or variable
capabilities, characteristics or preferences which would influence
which representation, among those available from the server,
would be best for the server to deliver. For this reason, HTTP
provides mechanisms for "content negotiation" — a process of
allowing selection of a representation of a given resource,
when more than one is available.
</t>
<t>
This specification defines two patterns of content negotiation;
"proactive", where the server selects the representation based
upon the client's stated preferences, and "reactive" negotiation,
where the server provides a list of representations for the client to
choose from, based upon their metadata. In addition, there are
other patterns: some applications use an "active content" pattern,
where the server returns active content which runs on the client
and, based on client available parameters, selects additional
resources to invoke. "Transparent Content Negotiation" (<xref target="RFC2295"/>)
has also been proposed.
</t>
<t>
These patterns are all widely used, and have trade-offs in applicability
and practicality. In particular, when the number of preferences or
capabilities to be expressed by a client are large (such as when many
different formats are supported by a user-agent), proactive
negotiation becomes unwieldy, and might not be appropriate. Conversely,
when the number of representations to choose from is very large,
reactive negotiation might not be appropriate.
</t>
<t>
Note that, in all cases, the supplier of representations has the
responsibility for determining which representations might be
considered to be the "same information".
</t>
<section title="Proactive Negotiation" anchor="proactive.negotiation">
<t>
If the selection of the best representation for a response is made by
an algorithm located at the server, it is called proactive
negotiation. Selection is based on the available representations of
the response (the dimensions over which it can vary; e.g., language,
content-coding, etc.) and the contents of particular header fields in
the request message or on other information pertaining to the request
(such as the network address of the client).
</t>
<t>
Proactive negotiation is advantageous when the algorithm for
selecting from among the available representations is difficult to
describe to the user agent, or when the server desires to send its
"best guess" to the client along with the first response (hoping to
avoid the round-trip delay of a subsequent request if the "best
guess" is good enough for the user). In order to improve the server's
guess, the user agent MAY include request header fields (<xref target="header.accept" format="none">Accept</xref>,
<xref target="header.accept-language" format="none">Accept-Language</xref>, <xref target="header.accept-encoding" format="none">Accept-Encoding</xref>, etc.) which describe its
preferences for such a response.
</t>
<t>
Proactive negotiation has disadvantages:
<list style="numbers">
<t>
It is impossible for the server to accurately determine what
might be "best" for any given user, since that would require
complete knowledge of both the capabilities of the user agent
and the intended use for the response (e.g., does the user want
to view it on screen or print it on paper?).
</t>
<t>
Having the user agent describe its capabilities in every
request can be both very inefficient (given that only a small
percentage of responses have multiple representations) and a
potential violation of the user's privacy.
</t>
<t>
It complicates the implementation of an origin server and the
algorithms for generating responses to a request.
</t>
<t>
It might limit a public cache's ability to use the same response
for multiple user's requests.
</t>
</list>
</t>
<t>
Proactive negotiation allows the user agent to specify its preferences,
but it cannot expect responses to always honor them. For example, the origin
server might not implement proactive negotiation, or it might decide that
sending a response that doesn't conform to them is better than sending a <xref target="status.406" format="none">406
(Not Acceptable)</xref> response.
</t>
<t>
HTTP/1.1 includes the following header fields for enabling
proactive negotiation through description of user agent
capabilities and user preferences: <xref target="header.accept" format="none">Accept</xref>
(<xref target="header.accept"/>), <xref target="header.accept-charset" format="none">Accept-Charset</xref>
(<xref target="header.accept-charset"/>), <xref target="header.accept-encoding" format="none">Accept-Encoding</xref>
(<xref target="header.accept-encoding"/>), <xref target="header.accept-language" format="none">Accept-Language</xref>
(<xref target="header.accept-language"/>), and <xref target="header.user-agent" format="none">User-Agent</xref>
(<xref target="header.user-agent"/>).
However, an origin server is not limited to these dimensions and MAY vary
the response based on any aspect of the request, including aspects
of the connection (e.g., IP address) or information within extension
header fields not defined by this specification.
</t>
<t><list>
<t>
Note: In practice, <xref target="header.user-agent" format="none">User-Agent</xref> based negotiation is fragile,
because new clients might not be recognized.
</t>
</list></t>
<t>
The <xref target="header.vary" format="none">Vary</xref> header field (<xref target="header.vary"/>) can be
used to express the parameters the server uses to select a representation
that is subject to proactive negotiation.
</t>
</section>
<section title="Reactive Negotiation" anchor="reactive.negotiation">
<t>
With reactive negotiation, selection of the best representation
for a response is performed by the user agent after receiving an
initial response from the origin server. Selection is based on a list
of the available representations of the response included within the
header fields or body of the initial response, with each
representation identified by its own URI. Selection from among the
representations can be performed automatically (if the user agent is
capable of doing so) or manually by the user selecting from a
generated (possibly hypertext) menu.
</t>
<t>
Reactive negotiation is advantageous when the response would vary
over commonly-used dimensions (such as type, language, or encoding),
when the origin server is unable to determine a user agent's
capabilities from examining the request, and generally when public
caches are used to distribute server load and reduce network usage.
</t>
<t>
Reactive negotiation suffers from the disadvantage of needing a
second request to obtain the best alternate representation. This
second request is only efficient when caching is used. In addition,
this specification does not define any mechanism for supporting
automatic selection, though it also does not prevent any such
mechanism from being developed as an extension and used within
HTTP/1.1.
</t>
<t>
This specification defines the <xref target="status.300" format="none">300 (Multiple Choices)</xref> and
<xref target="status.406" format="none">406 (Not Acceptable)</xref> status codes for enabling reactive
negotiation when the server is unwilling or unable to provide a varying
response using proactive negotiation.
</t>
</section>
</section>
</section>
<section title="Product Tokens" anchor="product.tokens">
<t>
Product tokens are used to allow communicating applications to
identify themselves by software name and version. Most fields using
product tokens also allow sub-products which form a significant part
of the application to be listed, separated by whitespace. By
convention, the products are listed in order of their significance
for identifying the application.
</t>
<figure><iref primary="true" item="Grammar" subitem="product"/><iref primary="true" item="Grammar" subitem="product-version"/><artwork type="abnf2616"><![CDATA[
product = token ["/" product-version]
product-version = token
]]></artwork></figure>
<t>
Examples:
</t>
<figure><artwork type="example"><![CDATA[
User-Agent: CERN-LineMode/2.15 libwww/2.17b3
Server: Apache/0.8.4
]]></artwork></figure>
<t>
Product tokens SHOULD be short and to the point. They MUST NOT be
used for advertising or other non-essential information. Although any
token octet MAY appear in a product-version, this token SHOULD
only be used for a version identifier (i.e., successive versions of
the same product SHOULD only differ in the product-version portion of
the product value).
</t>
</section>
<section title="Request Methods" anchor="methods">
<section title="Overview" anchor="method.overview">
<t>
The request method token is the primary source of request semantics;
it indicates the purpose for which the client has made this request
and what is expected by the client as a successful result. The request
semantics MAY be further specialized by the semantics of some header
fields when present in a request (<xref target="request.header.fields"/>)
if those additional semantics do not conflict with the method.
</t>
<figure><iref primary="true" item="Grammar" subitem="method"/><artwork type="abnf2616"><![CDATA[
method = token
]]></artwork></figure>
<t>
HTTP was originally designed to be usable as an interface to distributed
object systems. The request method was envisioned as applying
semantics to a target resource in much the same way as invoking a defined
method on an identified object would apply semantics. The method token
is case-sensitive because it might be used as a gateway to object-based
systems with case-sensitive method names.
</t>
<t>
Unlike distributed objects, the standardized request methods in HTTP are
not resource-specific, since uniform interfaces provide for better
visibility and reuse in network-based systems <xref target="REST"/>.
Once defined, a standardized method MUST have the same semantics when
applied to any resource, though each resource determines for itself
whether those semantics are implemented or allowed.
</t>
<t>
This specification defines a number of standardized methods that are
commonly used in HTTP, as outlined by the following table. By convention,
standardized methods are defined in all-uppercase ASCII letters.
</t>
<texttable align="left" suppress-title="true" anchor="table.of.methods">
<ttcol>Method</ttcol>
<ttcol>Description</ttcol>
<ttcol>Sec.</ttcol>
<c>GET</c>
<c>Transfer a current representation of the target resource.</c>
<c><xref target="GET" format="counter"/></c>
<c>HEAD</c>
<c>Same as GET, but do not include a message body in the response.</c>
<c><xref target="HEAD" format="counter"/></c>
<c>POST</c>
<c>Perform resource-specific processing on the request payload.</c>
<c><xref target="POST" format="counter"/></c>
<c>PUT</c>
<c>Replace all current representations of the target resource with
the request payload.</c>
<c><xref target="PUT" format="counter"/></c>
<c>DELETE</c>
<c>Remove all current representations of the target resource.</c>
<c><xref target="DELETE" format="counter"/></c>
<c>CONNECT</c>
<c>Establish a tunnel to the server identified by the target resource.</c>
<c><xref target="CONNECT" format="counter"/></c>
<c>OPTIONS</c>
<c>Describe the communication options for the target resource.</c>
<c><xref target="OPTIONS" format="counter"/></c>
<c>TRACE</c>
<c>Perform a message loop-back test along the path to the target resource.</c>
<c><xref target="TRACE" format="counter"/></c>
</texttable>
<t>
The methods GET and HEAD MUST be supported by all general-purpose
servers. All other methods are OPTIONAL.
When implemented, a server MUST implement the above methods according
to the semantics defined for them in <xref target="method.definitions"/>.
</t>
<t>
Additional methods MAY be used in HTTP; many have already been
standardized outside the scope of this specification and registered
within the HTTP Method Registry maintained by IANA, as defined in
<xref target="method.registry"/>.
</t>
<t>
The set of methods allowed by a target resource can be listed in an
<xref target="header.allow" format="none">Allow</xref> header field (<xref target="header.allow"/>).
However, the set of allowed methods can change dynamically.
When a request message is received that is unrecognized or not implemented
by an origin server, the origin server SHOULD respond with the
<xref target="status.501" format="none">501 (Not Implemented)</xref> status code.
When a request message is received that is known by an origin server but
not allowed for the target resource, the origin server SHOULD respond
with the <xref target="status.405" format="none">405 (Method Not Allowed)</xref> status code.
</t>
</section>
<section title="Common Method Properties" anchor="method.properties">
<section title="Safe Methods" anchor="safe.methods">
<iref item="safe" primary="true"/>
<t>
Request methods are considered "safe" if
their defined semantics are essentially read-only; i.e., the client does
not request, and does not expect, any state change on the origin server
as a result of applying a safe method to a target resource. Likewise,
reasonable use of a safe method is not expected to cause any harm,
loss of property, or unusual burden on the origin server.
</t>
<t>
This definition of safe methods does not prevent an implementation from
including behavior that is potentially harmful, not entirely read-only,
or which causes side-effects while invoking a safe method. What is
important, however, is that the client did not request that additional
behavior and cannot be held accountable for it. For example,
most servers append request information to access log files at the
completion of every response, regardless of the method, and that is
considered safe even though the log storage might become full and crash
the server. Likewise, a safe request initiated by selecting an
advertisement on the Web will often have the side-effect of charging an
advertising account.
</t>
<t>
The GET, HEAD, OPTIONS, and TRACE request methods are defined to be safe.
</t>
<t>
The purpose of distinguishing between safe and unsafe methods is to
allow automated retrieval processes (spiders) and cache performance
optimization (pre-fetching) to work without fear of causing harm.
In addition, it allows a user agent to apply appropriate constraints
on the automated use of unsafe methods when processing potentially
untrusted content.
</t>
<t>
A user agent SHOULD distinguish between safe and unsafe methods when
presenting potential actions to a user, such that the user can be made
aware of an unsafe action before it is requested.
</t>
<t>
When a resource is constructed such that parameters within the effective
request URI have the effect of selecting an action, it is the resource
owner's responsibility to ensure that the action is consistent with the
request method semantics.
For example, it is common for Web-based content editing software
to use actions within query parameters, such as "page?do=delete".
If the purpose of such a resource is to perform an unsafe action, then
the resource MUST disable or disallow that action when it is accessed
using a safe request method. Failure to do so will result in
unfortunate side-effects when automated processes perform a GET on
every URI reference for the sake of link maintenance, pre-fetching,
building a search index, etc.
</t>
</section>
<section title="Idempotent Methods" anchor="idempotent.methods">
<iref item="idempotent" primary="true"/>
<t>
Request methods are considered
"idempotent" if the intended effect
of multiple identical requests is the same as for a single request.
PUT, DELETE, and all safe request methods are idempotent.
</t>
<t>
Like the definition of safe, the idempotent property only applies to
what has been requested by the user; a server is free to log each request
separately, retain a revision control history, or implement other
non-idempotent side-effects for each idempotent request.
</t>
<t>
Idempotent methods are distinguished because the request can be repeated
automatically if a communication failure occurs before the client is
able to read the server's response. For example, if a client sends a PUT
request and the underlying connection is closed before any response is
received, then it can establish a new connection and retry the idempotent
request because it knows that repeating the request will have the same
effect even if the original request succeeded. Note, however, that
repeated failures would indicate a problem within the server.
</t>
</section>
<section title="Cacheable Methods" anchor="cacheable.methods">
<iref item="cacheable" primary="true"/>
<t>
Request methods are considered
"cacheable" if it is possible and useful
to answer a current client request with a stored response from a prior
request. GET and HEAD are defined to be cacheable. In general, safe
methods that do not depend on a current or authoritative response are
cacheable, though the overwhelming majority of caches only support
GET and HEAD. HTTP requirements for cache behavior and cacheable responses
are defined in <xref target="Part6"/>.
</t>
</section>
</section>
<section title="Method Definitions" anchor="method.definitions">
<section title="GET" anchor="GET">
<iref primary="true" item="GET method"/>
<t>
The GET method requests transfer of a current representation of
the target resource.
</t>
<t>
If the target resource is a data-producing process, it is the
produced data which shall be returned as the representation in the response and not
the source text of the process, unless that text happens to be the output of
the process.
</t>
<t>
The semantics of the GET method change to a "conditional GET" if the
request message includes an If-Modified-Since,
If-Unmodified-Since, If-Match,
If-None-Match, or If-Range header field
(<xref target="Part4"/>). A conditional GET requests that the representation
be transferred only under the circumstances described by the conditional
header field(s). The conditional GET request is intended to reduce
unnecessary network usage by allowing cached representations to be refreshed
without requiring multiple requests or transferring data already held by the
client.
</t>
<t>
The semantics of the GET method change to a "partial GET" if the request
message includes a Range header field (<xref target="Part5"/>).
A partial GET requests that only part of the representation be transferred,
as described in Section 5.4 of <xref target="Part5"/>. The partial GET request is intended to reduce
unnecessary network usage by allowing partially-retrieved representations to
be completed without transferring data already held by the client.
</t>
<t>
A payload within a GET request message has no defined semantics;
sending a payload body on a GET request might cause some existing
implementations to reject the request.
</t>
<t>
The response to a GET request is cacheable and MAY be used to satisfy
subsequent GET and HEAD requests (see <xref target="Part6"/>).
</t>
<t>
See <xref target="encoding.sensitive.information.in.uris"/> for security considerations when used for forms.
</t>
</section>
<section title="HEAD" anchor="HEAD">
<iref primary="true" item="HEAD method"/>
<t>
The HEAD method is identical to GET except that the server MUST NOT
return a message body in the response. The metadata contained
in the HTTP header fields in response to a HEAD request SHOULD be identical
to the information sent in response to a GET request. This method can
be used for obtaining metadata about the representation implied by the
request without transferring the representation data. This method is
often used for testing hypertext links for validity, accessibility,
and recent modification.
</t>
<t>
The response to a HEAD request is cacheable and MAY be used to satisfy
a subsequent HEAD request. It also has potential side effects on
previously stored responses to GET; see Section 5 of <xref target="Part6"/>.
</t>
<t>
A payload within a HEAD request message has no defined semantics;
sending a payload body on a HEAD request might cause some existing
implementations to reject the request.
</t>
</section>
<section title="POST" anchor="POST">
<iref primary="true" item="POST method"/>
<t>
The POST method requests that the origin server accept the
representation enclosed in the request as data to be processed by the
target resource. POST is designed to allow a uniform method to cover the
following functions:
<list style="symbols">
<t>
Annotation of existing resources;
</t>
<t>
Posting a message to a bulletin board, newsgroup, mailing list,
or similar group of articles;
</t>
<t>
Providing a block of data, such as the result of submitting a
form, to a data-handling process;
</t>
<t>
Extending a database through an append operation.
</t>
</list>
</t>
<t>
The actual function performed by the POST method is determined by the
server and is usually dependent on the effective request URI.
</t>
<t>
The action performed by the POST method might not result in a resource that
can be identified by a URI. In this case, either <xref target="status.200" format="none">200 (OK)</xref> or
<xref target="status.204" format="none">204 (No Content)</xref> is the appropriate response status
code, depending on whether or not the response includes a representation
that describes the result.
</t>
<t>
If a resource has been created on the origin server, the response
SHOULD be <xref target="status.201" format="none">201 (Created)</xref> and contain a representation which
describes the status of the request and refers to the new resource, and a
<xref target="header.location" format="none">Location</xref> header field (see <xref target="header.location"/>).
</t>
<t>
Responses to POST requests are only cacheable when they include explicit
freshness information (see Section 4.1.1 of <xref target="Part6"/>). A cached POST response with a
<xref target="header.content-location" format="none">Content-Location</xref> header field (see
<xref target="header.content-location"/>) whose value is the effective Request URI MAY
be used to satisfy subsequent GET and HEAD (not POST) requests.
</t>
<t>
Note that POST caching is not widely implemented.
However, the <xref target="status.303" format="none">303 (See Other)</xref> response can be used to direct
the user agent to retrieve a cacheable representation of the resource.
</t>
</section>
<section title="PUT" anchor="PUT">
<iref primary="true" item="PUT method"/>
<t>
The PUT method requests that the state of the target resource
be created or replaced with the state defined by the representation
enclosed in the request message payload. A successful PUT of a given
representation would suggest that a subsequent GET on that same target
resource will result in an equivalent representation being returned in
a <xref target="status.200" format="none">200 (OK)</xref> response. However, there is no guarantee that
such a state change will be observable, since the target resource might be
acted upon by other user agents in parallel, or might be subject to dynamic
processing by the origin server, before any subsequent GET is received.
A successful response only implies that the user agent's intent was
achieved at the time of its processing by the origin server.
</t>
<t>
If the target resource does not have a current representation and
the PUT successfully creates one, then the origin server MUST inform
the user agent by sending a <xref target="status.201" format="none">201 (Created)</xref> response. If the
target resource does have a current representation and that representation is
successfully modified in accordance with the state of the enclosed
representation, then either a <xref target="status.200" format="none">200 (OK)</xref> or <xref target="status.204" format="none">204 (No Content)</xref>
response SHOULD be sent to indicate successful completion of the request.
</t>
<t>
Unrecognized header fields SHOULD be ignored (i.e., not saved
as part of the resource state).
</t>
<t>
An origin server SHOULD verify that the PUT representation is
consistent with any constraints which the server has for the target
resource that cannot or will not be changed by the PUT. This is
particularly important when the origin server uses internal
configuration information related to the URI in order to set the
values for representation metadata on GET responses. When a PUT
representation is inconsistent with the target resource, the origin
server SHOULD either make them consistent, by transforming the
representation or changing the resource configuration, or respond
with an appropriate error message containing sufficient information
to explain why the representation is unsuitable. The
<xref target="status.409" format="none">409 (Conflict)</xref> or <xref target="status.415" format="none">415 (Unsupported Media Type)</xref>
status codes are suggested, with the latter being specific to constraints on
<xref target="header.content-type" format="none">Content-Type</xref> values.
</t>
<t>
For example, if the target resource is configured to always have a
<xref target="header.content-type" format="none">Content-Type</xref> of "text/html" and the representation being PUT
has a Content-Type of "image/jpeg", then the origin server SHOULD do one of:
<list style="letters">
<t>reconfigure the target resource to reflect the new media type;</t>
<t>transform the PUT representation to a format consistent with that
of the resource before saving it as the new resource state; or,</t>
<t>reject the request with a <xref target="status.415" format="none">415 (Unsupported Media Type)</xref>
response indicating that the target resource is limited to "text/html",
perhaps including a link to a different resource that would be a
suitable target for the new representation.</t>
</list>
</t>
<t>
HTTP does not define exactly how a PUT method affects the state
of an origin server beyond what can be expressed by the intent of
the user agent request and the semantics of the origin server response.
It does not define what a resource might be, in any sense of that
word, beyond the interface provided via HTTP. It does not define
how resource state is "stored", nor how such storage might change
as a result of a change in resource state, nor how the origin server
translates resource state into representations. Generally speaking,
all implementation details behind the resource interface are
intentionally hidden by the server.
</t>
<t>
The fundamental difference between the POST and PUT methods is
highlighted by the different intent for the target resource.
The target resource in a POST request is intended to handle the
enclosed representation as a data-accepting process, such as for
a gateway to some other protocol or a document that accepts annotations.
In contrast, the target resource in a PUT request is intended to
take the enclosed representation as a new or replacement value.
Hence, the intent of PUT is idempotent and visible to intermediaries,
even though the exact effect is only known by the origin server.
</t>
<t>
Proper interpretation of a PUT request presumes that the user agent
knows what target resource is desired. A service that is intended
to select a proper URI on behalf of the client, after receiving
a state-changing request, SHOULD be implemented using the POST
method rather than PUT. If the origin server will not make the
requested PUT state change to the target resource and instead
wishes to have it applied to a different resource, such as when the
resource has been moved to a different URI, then the origin server
MUST send a <xref target="status.301" format="none">301 (Moved Permanently)</xref> response; the user
agent MAY then make its own decision regarding whether or not to redirect
the request.
</t>
<t>
A PUT request applied to the target resource MAY have side-effects
on other resources. For example, an article might have a URI for
identifying "the current version" (a resource) which is separate
from the URIs identifying each particular version (different
resources that at one point shared the same state as the current version
resource). A successful PUT request on "the current version" URI might
therefore create a new version resource in addition to changing the
state of the target resource, and might also cause links to be added
between the related resources.
</t>
<t>
An origin server SHOULD reject any PUT request that contains a
Content-Range header field (Section 5.2 of <xref target="Part5"/>), since
it might be misinterpreted as partial content (or might be partial content
that is being mistakenly PUT as a full representation). Partial content
updates are possible by targeting a separately identified resource with
state that overlaps a portion of the larger resource, or by using a
different method that has been specifically defined for partial
updates (for example, the PATCH method defined in
<xref target="RFC5789"/>).
</t>
<t>
Responses to the PUT method are not cacheable. If a PUT request passes
through a cache that has one or more stored responses for the effective
request URI, those stored responses will be invalidated (see
Section 6 of <xref target="Part6"/>).
</t>
</section>
<section title="DELETE" anchor="DELETE">
<iref primary="true" item="DELETE method"/>
<t>
The DELETE method requests that the origin server delete the target
resource. This method MAY be overridden by
human intervention (or other means) on the origin server. The client cannot
be guaranteed that the operation has been carried out, even if the
status code returned from the origin server indicates that the action
has been completed successfully. However, the server SHOULD NOT
indicate success unless, at the time the response is given, it
intends to delete the resource or move it to an inaccessible
location.
</t>
<t>
A successful response SHOULD be <xref target="status.200" format="none">200 (OK)</xref> if the response
includes a representation describing the status, <xref target="status.202" format="none">202 (Accepted)</xref>
if the action has not yet been enacted, or <xref target="status.204" format="none">204 (No Content)</xref> if
the action has been enacted but the response does not include a representation.
</t>
<t>
A payload within a DELETE request message has no defined semantics;
sending a payload body on a DELETE request might cause some existing
implementations to reject the request.
</t>
<t>
Responses to the DELETE method are not cacheable. If a DELETE request
passes through a cache that has one or more stored responses for the
effective request URI, those stored responses will be invalidated (see
Section 6 of <xref target="Part6"/>).
</t>
</section>
<section title="CONNECT" anchor="CONNECT">
<iref primary="true" item="CONNECT method"/>
<t>
The CONNECT method requests that the proxy establish a tunnel
to the request-target and, if successful, thereafter restrict its behavior
to blind forwarding of packets until the connection is closed.
</t>
<t>
When using CONNECT, the request-target MUST use the authority form
(Section 5.3 of <xref target="Part1"/>); i.e., the request-target consists of only the
host name and port number of the tunnel destination, separated by a colon.
For example,
</t>
<figure><artwork type="message/http; msgtype="request""><![CDATA[
CONNECT server.example.com:80 HTTP/1.1
Host: server.example.com:80
]]></artwork></figure>
<t>
Any <xref target="status.2xx" format="none">2xx (Successful)</xref> response to a CONNECT request indicates that the
proxy has established a connection to the requested host and port,
and has switched to tunneling the current connection to that server
connection.
The tunneled data from the server begins immediately after the blank line
that concludes the successful response's header block.
</t>
<t>
A server SHOULD NOT send any Transfer-Encoding or
Content-Length header fields in a successful response.
A client MUST ignore any Content-Length or Transfer-Encoding header
fields received in a successful response.
</t>
<t>
Any response other than a successful response indicates that the tunnel
has not yet been formed and that the connection remains governed by HTTP.
</t>
<t>
Proxy authentication might be used to establish the
authority to create a tunnel:
</t>
<figure><artwork type="message/http; msgtype="request""><![CDATA[
CONNECT server.example.com:80 HTTP/1.1
Host: server.example.com:80
Proxy-Authorization: basic aGVsbG86d29ybGQ=
]]></artwork></figure>
<t>
A payload within a CONNECT request message has no defined semantics;
sending a payload body on a CONNECT request might cause some existing
implementations to reject the request.
</t>
<t>
Similar to a pipelined HTTP/1.1 request, data to be tunneled from client
to server MAY be sent immediately after the request (before a response
is received). The usual caveats also apply:
data can be discarded if the eventual response is negative, and the
connection can be reset with no response if more than one TCP segment
is outstanding.
</t>
<t>
It might be the case that the proxy itself can only reach the requested
origin server through another proxy. In this case, the first proxy
SHOULD make a CONNECT request of that next proxy, requesting a tunnel
to the authority. A proxy MUST NOT respond with any <xref target="status.2xx" format="none">2xx</xref> status code
unless it has either a direct or tunnel connection established to the
authority.
</t>
<t>
If at any point either one of the peers gets disconnected, any
outstanding data that came from that peer will be passed to the other
one, and after that also the other connection will be terminated by
the proxy. If there is outstanding data to that peer undelivered,
that data will be discarded.
</t>
<t>
An origin server which receives a CONNECT request for itself MAY
respond with a <xref target="status.2xx" format="none">2xx</xref> status code to indicate that a connection is
established. However, most origin servers do not implement CONNECT.
</t>
</section>
<section title="OPTIONS" anchor="OPTIONS">
<iref primary="true" item="OPTIONS method"/>
<t>
The OPTIONS method requests information about the
communication options available on the request/response chain
identified by the effective request URI. This method allows a client to
determine the options and/or requirements associated with a resource,
or the capabilities of a server, without implying a resource action
or initiating a resource retrieval.
</t>
<t>
Responses to the OPTIONS method are not cacheable.
</t>
<t>
If the OPTIONS request includes a payload,
then the media type MUST be indicated by a <xref target="header.content-type" format="none">Content-Type</xref>
field. Although this specification does not define any use for such a body,
future extensions to HTTP might use the OPTIONS body to make more detailed
queries on the server.
</t>
<t>
If the request-target (Section 5.3 of <xref target="Part1"/>) is an asterisk ("*"),
the OPTIONS request is
intended to apply to the server in general rather than to a specific
resource. Since a server's communication options typically depend on
the resource, the "*" request is only useful as a "ping" or "no-op"
type of method; it does nothing beyond allowing the client to test
the capabilities of the server. For example, this can be used to test
a proxy for HTTP/1.1 conformance (or lack thereof).
</t>
<t>
If the request-target is not an asterisk, the OPTIONS request applies
only to the options that are available when communicating with that
resource.
</t>
<t>
A <xref target="status.200" format="none">200 (OK)</xref> response SHOULD include any header fields that
indicate optional features implemented by the server and applicable to that
resource (e.g., <xref target="header.allow" format="none">Allow</xref>), possibly including extensions not
defined by this specification. The response payload, if any, SHOULD also
include information about the communication options. The format for such a
payload is not defined by this specification, but might be defined by
future extensions to HTTP. Content negotiation MAY be used to select
the appropriate representation. If no payload body is included, the
response MUST include a Content-Length field with a
field-value of "0".
</t>
<t>
The <xref target="header.max-forwards" format="none">Max-Forwards</xref> header field MAY be used to target a
specific proxy in the request chain (see <xref target="header.max-forwards"/>).
If no Max-Forwards field is present in the request, then the forwarded
request MUST NOT include a Max-Forwards field.
</t>
</section>
<section title="TRACE" anchor="TRACE">
<iref primary="true" item="TRACE method"/>
<t>
The TRACE method requests a remote, application-level loop-back
of the request message. The final recipient of the request
SHOULD reflect the message received back to the client as the message body
of a <xref target="status.200" format="none">200 (OK)</xref> response. The final recipient is either the
origin server or the first proxy to receive a <xref target="header.max-forwards" format="none">Max-Forwards</xref>
value of zero (0) in the request (see <xref target="header.max-forwards"/>).
A TRACE request MUST NOT include a message body.
</t>
<t>
TRACE allows the client to see what is being received at the other
end of the request chain and use that data for testing or diagnostic
information. The value of the Via header field (Section 5.7 of <xref target="Part1"/>)
is of particular interest, since it acts as a trace of the request chain.
Use of the <xref target="header.max-forwards" format="none">Max-Forwards</xref> header field allows the client to
limit the length of the request chain, which is useful for testing a chain of
proxies forwarding messages in an infinite loop.
</t>
<t>
If the request is valid, the response SHOULD have a
<xref target="header.content-type" format="none">Content-Type</xref> of "message/http" (see Section 7.3.1 of <xref target="Part1"/>)
and contain a message body that encloses a copy of the entire request message.
Responses to the TRACE method are not cacheable.
</t>
</section>
</section>
</section>
<section title="Request Header Fields" anchor="request.header.fields">
<t>
A client sends request header fields to provide more information about
the request context, make the request conditional based on the target
resource state, suggest preferred formats for the response, supply
authentication credentials, or modify the expected request processing.
These fields act as request modifiers, similar to the parameters on a
programming language method invocation.
</t>
<section title="Controls" anchor="request.controls">
<t>
Controls are request header fields that direct specific handling of the
request.
</t>
<texttable align="left">
<ttcol>Header Field Name</ttcol>
<ttcol>Defined in...</ttcol>
<c>Host</c> <c>Section 5.4 of <xref target="Part1"/></c>
<c>Max-Forwards</c> <c><xref target="header.max-forwards"/></c>
<c>Expect</c> <c><xref target="header.expect"/></c>
<c>Range</c> <c>Section 5.4 of <xref target="Part5"/></c>
</texttable>
<section title="Max-Forwards" anchor="header.max-forwards">
<iref primary="true" item="Max-Forwards header field"/>
<t>
The "Max-Forwards" header field provides a mechanism with the
TRACE (<xref target="TRACE"/>) and OPTIONS (<xref target="OPTIONS"/>)
methods to limit the number of times that the request is forwarded by
proxies. This can be useful when the client is attempting to
trace a request which appears to be failing or looping mid-chain.
</t>
<figure><iref primary="true" item="Grammar" subitem="Max-Forwards"/><artwork type="abnf2616"><![CDATA[
Max-Forwards = 1*DIGIT
]]></artwork></figure>
<t>
The Max-Forwards value is a decimal integer indicating the remaining
number of times this request message can be forwarded.
</t>
<t>
Each recipient of a TRACE or OPTIONS request
containing a Max-Forwards header field MUST check and update its
value prior to forwarding the request. If the received value is zero
(0), the recipient MUST NOT forward the request; instead, it MUST
respond as the final recipient. If the received Max-Forwards value is
greater than zero, then the forwarded message MUST contain an updated
Max-Forwards field with a value decremented by one (1).
</t>
<t>
The Max-Forwards header field MAY be ignored for all other request
methods.
</t>
</section>
<section title="Expect" anchor="header.expect">
<iref primary="true" item="Expect header field"/>
<t>
The "Expect" header field is used to indicate that particular
server behaviors are required by the client.
</t>
<figure><iref primary="true" item="Grammar" subitem="Expect"/><iref primary="true" item="Grammar" subitem="expectation"/><iref primary="true" item="Grammar" subitem="expect-param"/><iref primary="true" item="Grammar" subitem="expect-value"/><iref primary="true" item="Grammar" subitem="expect-name"/><artwork type="abnf2616"><![CDATA[
Expect = 1#expectation
expectation = expect-name [ BWS "=" BWS expect-value ]
*( OWS ";" [ OWS expect-param ] )
expect-param = expect-name [ BWS "=" BWS expect-value ]
expect-name = token
expect-value = token / quoted-string
]]></artwork></figure>
<t>
If all received Expect header field(s) are syntactically valid but contain
an expectation that the recipient does not understand or cannot comply with,
the recipient MUST respond with a <xref target="status.417" format="none">417 (Expectation Failed)</xref> status code. A
recipient of a syntactically invalid Expectation header field MUST respond
with a <xref target="status.4xx" format="none">4xx</xref> status code other than 417.
</t>
<t>
The only expectation defined by this specification is:
</t>
<t><iref primary="true" item="100-continue (expect value)"/><iref primary="true" item="Expect Values" subitem="100-continue"/>
100-continue
<list>
<t>
The "100-continue" expectation is defined below. It does not support
any expect-params.
</t>
</list>
</t>
<t>
Comparison is case-insensitive for names (expect-name), and case-sensitive
for values (expect-value).
</t>
<t>
The Expect mechanism is hop-by-hop: the above requirements apply to any
server, including proxies. However, the Expect header field itself is
end-to-end; it MUST be forwarded if the request is forwarded.
</t>
<t>
Many older HTTP/1.0 and HTTP/1.1 applications do not understand the Expect
header field.
</t>
<section title="Use of the 100 (Continue) Status" anchor="use.of.the.100.status">
<t>
The purpose of the <xref target="status.100" format="none">100 (Continue)</xref> status code
(<xref target="status.100"/>)
is to allow a client that is sending a request message with a payload
to determine if the origin server is willing to accept the request
(based on the request header fields) before the client sends the payload
body. In some cases, it might either be inappropriate or highly
inefficient for the client to send the payload body if the server will
reject the message without looking at the body.
</t>
<t>
Requirements for HTTP/1.1 clients:
<list style="symbols">
<t>
If a client will wait for a <xref target="status.100" format="none">100 (Continue)</xref> response before
sending the payload body, it MUST send an <xref target="header.expect" format="none">Expect</xref> header
field with the "100-continue" expectation.
</t>
<t>
A client MUST NOT send an <xref target="header.expect" format="none">Expect</xref> header field with
the "100-continue" expectation if it does not intend to send a payload
body.
</t>
</list>
</t>
<t>
Because of the presence of older implementations, the protocol allows
ambiguous situations in which a client might send "Expect: 100-continue"
without receiving either a <xref target="status.417" format="none">417 (Expectation Failed)</xref>
or a <xref target="status.100" format="none">100 (Continue)</xref> status code. Therefore, when a client sends this
header field to an origin server (possibly via a proxy) from which it
has never seen a <xref target="status.100" format="none">100 (Continue)</xref> status code, the client SHOULD NOT
wait for an indefinite period before sending the payload body.
</t>
<t>
Requirements for HTTP/1.1 origin servers:
<list style="symbols">
<t> Upon receiving a request which includes an <xref target="header.expect" format="none">Expect</xref> header
field with the "100-continue" expectation, an origin server MUST
either respond with <xref target="status.100" format="none">100 (Continue)</xref> status code and continue to read
from the input stream, or respond with a final status code. The
origin server MUST NOT wait for the payload body before sending
the <xref target="status.100" format="none">100 (Continue)</xref> response. If it responds with a final status
code, it MAY close the transport connection or it MAY continue
to read and discard the rest of the request. It MUST NOT
perform the request method if it returns a final status code.
</t>
<t> An origin server SHOULD NOT send a <xref target="status.100" format="none">100 (Continue)</xref> response if
the request message does not include an <xref target="header.expect" format="none">Expect</xref> header
field with the "100-continue" expectation, and MUST NOT send a
<xref target="status.100" format="none">100 (Continue)</xref> response if such a request comes from an HTTP/1.0
(or earlier) client. There is an exception to this rule: for
compatibility with <xref target="RFC2068"/>, a server MAY send a <xref target="status.100" format="none">100 (Continue)</xref>
status code in response to an HTTP/1.1 PUT or POST request that does
not include an Expect header field with the "100-continue"
expectation. This exception, the purpose of which is
to minimize any client processing delays associated with an
undeclared wait for <xref target="status.100" format="none">100 (Continue)</xref> status code, applies only to
HTTP/1.1 requests, and not to requests with any other HTTP-version
value.
</t>
<t> An origin server MAY omit a <xref target="status.100" format="none">100 (Continue)</xref> response if it has
already received some or all of the payload body for the
corresponding request.
</t>
<t> An origin server that sends a <xref target="status.100" format="none">100 (Continue)</xref> response MUST
ultimately send a final status code, once the payload body is
received and processed, unless it terminates the transport
connection prematurely.
</t>
<t> If an origin server receives a request that does not include an
<xref target="header.expect" format="none">Expect</xref> header field with the "100-continue" expectation,
the request includes a payload body, and the server responds
with a final status code before reading the entire payload body
from the transport connection, then the server SHOULD NOT close
the transport connection until it has read the entire request,
or until the client closes the connection. Otherwise, the client
might not reliably receive the response message. However, this
requirement ought not be construed as preventing a server from
defending itself against denial-of-service attacks, or from
badly broken client implementations.
</t>
</list>
</t>
<t>
Requirements for HTTP/1.1 proxies:
<list style="symbols">
<t> If a proxy receives a request that includes an <xref target="header.expect" format="none">Expect</xref>
header field with the "100-continue" expectation, and the proxy
either knows that the next-hop server complies with HTTP/1.1 or
higher, or does not know the HTTP version of the next-hop
server, it MUST forward the request, including the Expect header
field.
</t>
<t> If the proxy knows that the version of the next-hop server is
HTTP/1.0 or lower, it MUST NOT forward the request, and it MUST
respond with a <xref target="status.417" format="none">417 (Expectation Failed)</xref> status code.
</t>
<t> Proxies SHOULD maintain a record of the HTTP version
numbers received from recently-referenced next-hop servers.
</t>
<t> A proxy MUST NOT forward a <xref target="status.100" format="none">100 (Continue)</xref> response if the
request message was received from an HTTP/1.0 (or earlier)
client and did not include an <xref target="header.expect" format="none">Expect</xref> header field with
the "100-continue" expectation. This requirement overrides the
general rule for forwarding of <xref target="status.1xx" format="none">1xx</xref> responses
(see <xref target="status.100"/>).
</t>
</list>
</t>
</section>
</section>
</section>
<section title="Conditionals" anchor="request.conditionals">
<t>
Conditionals are request header fields that indicate a precondition to be
tested before applying the method semantics to the target resource.
Each precondition is based on metadata that is expected to change if the
selected representation of the target resource is changed. The HTTP/1.1
conditional request mechanisms are defined in <xref target="Part4"/>.
</t>
<texttable align="left">
<ttcol>Header Field Name</ttcol>
<ttcol>Defined in...</ttcol>
<c>If-Match</c> <c>Section 3.1 of <xref target="Part4"/></c>
<c>If-None-Match</c> <c>Section 3.2 of <xref target="Part4"/></c>
<c>If-Modified-Since</c> <c>Section 3.3 of <xref target="Part4"/></c>
<c>If-Unmodified-Since</c> <c>Section 3.4 of <xref target="Part4"/></c>
<c>If-Range</c> <c>Section 5.3 of <xref target="Part5"/></c>
</texttable>
</section>
<section title="Content Negotiation" anchor="request.conneg">
<texttable align="left">
<ttcol>Header Field Name</ttcol>
<ttcol>Defined in...</ttcol>
<c>Accept</c> <c><xref target="header.accept"/></c>
<c>Accept-Charset</c> <c><xref target="header.accept-charset"/></c>
<c>Accept-Encoding</c> <c><xref target="header.accept-encoding"/></c>
<c>Accept-Language</c> <c><xref target="header.accept-language"/></c>
</texttable>
<section title="Quality Values" anchor="quality.values">
<t>
Many of the request header fields for proactive content negotiation
use a common parameter, named "q" (case-insensitive), to assign a relative
"weight" to the preference for that associated kind of content.
This weight is referred to as a "quality value" (or "qvalue") because
the same parameter name is often used within server configurations to
assign a weight to the relative quality of the various representations
that can be selected for a resource.
</t>
<t>
The weight is normalized to a real number in the range 0 through 1,
where 0.001 is the least preferred and 1 is the most preferred;
a value of 0 means "not acceptable". If no "q" parameter is present,
the default weight is 1.
</t>
<figure><iref primary="true" item="Grammar" subitem="weight"/><iref primary="true" item="Grammar" subitem="qvalue"/><artwork type="abnf2616"><![CDATA[
weight = OWS ";" OWS "q=" qvalue
qvalue = ( "0" [ "." 0*3DIGIT ] )
/ ( "1" [ "." 0*3("0") ] )
]]></artwork></figure>
<t>
A sender of qvalue MUST NOT generate more than three digits after the
decimal point. User configuration of these values ought to be limited in
the same fashion.
</t>
</section>
<section title="Accept" anchor="header.accept">
<iref primary="true" item="Accept header field"/>
<t>
The "Accept" header field can be used by user agents to specify
response media types that are acceptable. Accept header fields can be used to
indicate that the request is specifically limited to a small set of desired
types, as in the case of a request for an in-line image.
</t>
<figure><iref primary="true" item="Grammar" subitem="Accept"/><iref primary="true" item="Grammar" subitem="media-range"/><iref primary="true" item="Grammar" subitem="accept-params"/><iref primary="true" item="Grammar" subitem="accept-ext"/><artwork type="abnf2616"><![CDATA[
Accept = #( media-range [ accept-params ] )
media-range = ( "*/*"
/ ( type "/" "*" )
/ ( type "/" subtype )
) *( OWS ";" OWS parameter )
accept-params = weight *( accept-ext )
accept-ext = OWS ";" OWS token [ "=" word ]
]]></artwork></figure>
<t>
The asterisk "*" character is used to group media types into ranges,
with "*/*" indicating all media types and "type/*" indicating all
subtypes of that type. The media-range MAY include media type
parameters that are applicable to that range.
</t>
<t>
Each media-range MAY be followed by one or more accept-params,
beginning with the "q" parameter for indicating a relative weight,
as defined in <xref target="quality.values"/>.
The first "q" parameter (if any) separates the media-range
parameter(s) from the accept-params.
</t>
<t><list>
<t>
Note: Use of the "q" parameter name to separate media type
parameters from Accept extension parameters is due to historical
practice. Although this prevents any media type parameter named
"q" from being used with a media range, such an event is believed
to be unlikely given the lack of any "q" parameters in the IANA
media type registry and the rare usage of any media type
parameters in Accept. Future media types are discouraged from
registering any parameter named "q".
</t>
</list></t>
<t>
The example
</t>
<figure><artwork type="example"><![CDATA[
Accept: audio/*; q=0.2, audio/basic
]]></artwork></figure>
<t>
SHOULD be interpreted as "I prefer audio/basic, but send me any audio
type if it is the best available after an 80% mark-down in quality".
</t>
<t>
A request without any Accept header field implies that the user agent
will accept any media type in response.
If an Accept header field is present in a request and none of the
available representations for the response have a media type that is
listed as acceptable, the origin server MAY either honor the Accept
header field by sending a <xref target="status.406" format="none">406 (Not Acceptable)</xref> response
or disregard the Accept header field by treating the response as if
it is not subject to content negotiation.
</t>
<t>
A more elaborate example is
</t>
<figure><artwork type="example"><![CDATA[
Accept: text/plain; q=0.5, text/html,
text/x-dvi; q=0.8, text/x-c
]]></artwork></figure>
<t>
Verbally, this would be interpreted as "text/html and text/x-c are
the preferred media types, but if they do not exist, then send the
text/x-dvi representation, and if that does not exist, send the text/plain
representation".
</t>
<t>
Media ranges can be overridden by more specific media ranges or
specific media types. If more than one media range applies to a given
type, the most specific reference has precedence. For example,
</t>
<figure><artwork type="example"><![CDATA[
Accept: text/*, text/plain, text/plain;format=flowed, */*
]]></artwork></figure>
<t>
have the following precedence:
<list style="numbers">
<t>text/plain;format=flowed</t>
<t>text/plain</t>
<t>text/*</t>
<t>*/*</t>
</list>
</t>
<t>
The media type quality factor associated with a given type is
determined by finding the media range with the highest precedence
which matches that type. For example,
</t>
<figure><artwork type="example"><![CDATA[
Accept: text/*;q=0.3, text/html;q=0.7, text/html;level=1,
text/html;level=2;q=0.4, */*;q=0.5
]]></artwork></figure>
<t>
would cause the following values to be associated:
</t>
<texttable align="left">
<ttcol>Media Type</ttcol><ttcol>Quality Value</ttcol>
<c>text/html;level=1</c> <c>1</c>
<c>text/html</c> <c>0.7</c>
<c>text/plain</c> <c>0.3</c>
<c>image/jpeg</c> <c>0.5</c>
<c>text/html;level=2</c> <c>0.4</c>
<c>text/html;level=3</c> <c>0.7</c>
</texttable>
<t>
Note: A user agent might be provided with a default set of quality
values for certain media ranges. However, unless the user agent is
a closed system which cannot interact with other rendering agents,
this default set ought to be configurable by the user.
</t>
</section>
<section title="Accept-Charset" anchor="header.accept-charset">
<iref primary="true" item="Accept-Charset header field"/>
<t>
The "Accept-Charset" header field can be used by user agents to
indicate what character encodings are acceptable in a response
payload. This field allows
clients capable of understanding more comprehensive or special-purpose
character encodings to signal that capability to a server which is capable of
representing documents in those character encodings.
</t>
<figure><iref primary="true" item="Grammar" subitem="Accept-Charset"/><artwork type="abnf2616"><![CDATA[
Accept-Charset = 1#( ( charset / "*" ) [ weight ] )
]]></artwork></figure>
<t>
Character encoding values (a.k.a., charsets) are described in
<xref target="character.sets"/>. Each charset MAY be given an
associated quality value which represents the user's preference
for that charset, as defined in <xref target="quality.values"/>.
An example is
</t>
<figure><artwork type="example"><![CDATA[
Accept-Charset: iso-8859-5, unicode-1-1;q=0.8
]]></artwork></figure>
<t>
The special value "*", if present in the Accept-Charset field,
matches every character encoding which is not mentioned elsewhere in the
Accept-Charset field. If no "*" is present in an Accept-Charset field,
then any character encodings not explicitly mentioned in the field are
considered "not acceptable" to the client.
</t>
<t>
A request without any Accept-Charset header field implies that the user
agent will accept any character encoding in response.
</t>
<t>
If an Accept-Charset header field is present in a request and none of the
available representations for the response have a character encoding that
is listed as acceptable, the origin server MAY either honor the
Accept-Charset header field by sending a <xref target="status.406" format="none">406 (Not Acceptable)</xref> response or
disregard the Accept-Charset header field by treating the response as if
it is not subject to content negotiation.
</t>
</section>
<section title="Accept-Encoding" anchor="header.accept-encoding">
<iref primary="true" item="Accept-Encoding header field"/>
<t>
The "Accept-Encoding" header field can be used by user agents to
indicate what response content-codings (<xref target="content.codings"/>)
are acceptable in the response. An "identity" token is used as a synonym
for "no encoding" in order to communicate when no encoding is preferred.
</t>
<figure><iref primary="true" item="Grammar" subitem="Accept-Encoding"/><iref primary="true" item="Grammar" subitem="codings"/><artwork type="abnf2616"><![CDATA[
Accept-Encoding = #( codings [ weight ] )
codings = content-coding / "identity" / "*"
]]></artwork></figure>
<t>
Each codings value MAY be given an associated quality value which
represents the preference for that encoding, as defined in <xref target="quality.values"/>.
</t>
<t>
For example,
</t>
<figure><artwork type="example"><![CDATA[
Accept-Encoding: compress, gzip
Accept-Encoding:
Accept-Encoding: *
Accept-Encoding: compress;q=0.5, gzip;q=1.0
Accept-Encoding: gzip;q=1.0, identity; q=0.5, *;q=0
]]></artwork></figure>
<t>
A server tests whether a content-coding for a given representation is
acceptable, according to an Accept-Encoding field, using these rules:
<list style="numbers">
<t>The special "*" symbol in an Accept-Encoding field matches any
available content-coding not explicitly listed in the header
field.</t>
<t>If the representation has no content-coding, then it is acceptable
by default unless specifically excluded by the Accept-Encoding field
stating either "identity;q=0" or "*;q=0" without a more specific
entry for "identity".</t>
<t>If the representation's content-coding is one of the content-codings
listed in the Accept-Encoding field, then it is acceptable unless
it is accompanied by a qvalue of 0. (As defined in <xref target="quality.values"/>, a
qvalue of 0 means "not acceptable".)</t>
<t>If multiple content-codings are acceptable, then the acceptable
content-coding with the highest non-zero qvalue is preferred.</t>
</list>
</t>
<t>
An Accept-Encoding header field with a combined field-value that is empty
implies that the user agent does not want any content-coding in response.
If an Accept-Encoding header field is present in a request and none of the
available representations for the response have a content-coding that
is listed as acceptable, the origin server SHOULD send a response
without any content-coding.
</t>
<t>
A request without an Accept-Encoding header field implies that the user
agent will accept any content-coding in response.
</t>
<t><list>
<t>
Note: Most HTTP/1.0 applications do not recognize or obey qvalues
associated with content-codings. This means that qvalues will not
work and are not permitted with x-gzip or x-compress.
</t>
</list></t>
</section>
<section title="Accept-Language" anchor="header.accept-language">
<iref primary="true" item="Accept-Language header field"/>
<t>
The "Accept-Language" header field can be used by user agents to
indicate the set of natural languages that are preferred in the response.
Language tags are defined in <xref target="language.tags"/>.
</t>
<figure><iref primary="true" item="Grammar" subitem="Accept-Language"/><iref primary="true" item="Grammar" subitem="language-range"/><artwork type="abnf2616"><![CDATA[
Accept-Language = 1#( language-range [ weight ] )
language-range =
<language-range, defined in [RFC4647], Section 2.1>
]]></artwork></figure>
<t>
Each language-range can be given an associated quality value which
represents an estimate of the user's preference for the languages
specified by that range, as defined in <xref target="quality.values"/>. For example,
</t>
<figure><artwork type="example"><![CDATA[
Accept-Language: da, en-gb;q=0.8, en;q=0.7
]]></artwork></figure>
<t>
would mean: "I prefer Danish, but will accept British English and
other types of English".
(see also Section 2.3 of <xref target="RFC4647"/>)
</t>
<t>
For matching, Section 3 of <xref target="RFC4647"/> defines
several matching schemes. Implementations can offer the most appropriate
matching scheme for their requirements.
</t>
<t><list>
<t>
Note: The "Basic Filtering" scheme (<xref target="RFC4647"/>, Section 3.3.1) is identical to the matching scheme that was
previously defined in Section 14.4 of <xref target="RFC2616"/>.
</t>
</list></t>
<t>
It might be contrary to the privacy expectations of the user to send
an Accept-Language header field with the complete linguistic preferences of
the user in every request. For a discussion of this issue, see
<xref target="privacy.issues.connected.to.accept.header.fields"/>.
</t>
<t>
As intelligibility is highly dependent on the individual user, it is
recommended that client applications make the choice of linguistic
preference available to the user. If the choice is not made
available, then the Accept-Language header field MUST NOT be given in
the request.
</t>
<t><list>
<t>
Note: When making the choice of linguistic preference available to
the user, we remind implementers of the fact that users are not
familiar with the details of language matching as described above,
and ought to be provided appropriate guidance. As an example, users
might assume that on selecting "en-gb", they will be served any
kind of English document if British English is not available. A
user agent might suggest in such a case to add "en" to get the
best matching behavior.
</t>
</list></t>
</section>
</section>
<section title="Authentication Credentials" anchor="request.auth">
<texttable align="left">
<ttcol>Header Field Name</ttcol>
<ttcol>Defined in...</ttcol>
<c>Authorization</c> <c>Section 4.1 of <xref target="Part7"/></c>
<c>Proxy-Authorization</c> <c>Section 4.3 of <xref target="Part7"/></c>
</texttable>
</section>
<section title="Context" anchor="request.context">
<texttable align="left">
<ttcol>Header Field Name</ttcol>
<ttcol>Defined in...</ttcol>
<c>From</c> <c><xref target="header.from"/></c>
<c>Referer</c> <c><xref target="header.referer"/></c>
<c>TE</c> <c>Section 4.3 of <xref target="Part1"/></c>
<c>User-Agent</c> <c><xref target="header.user-agent"/></c>
</texttable>
<section title="From" anchor="header.from">
<iref primary="true" item="From header field"/>
<t>
The "From" header field, if given, SHOULD contain an Internet
e-mail address for the human user who controls the requesting user
agent. The address SHOULD be machine-usable, as defined by "mailbox"
in Section 3.4 of <xref target="RFC5322"/>:
</t>
<figure><iref primary="true" item="Grammar" subitem="From"/><artwork type="abnf2616"><![CDATA[
From = mailbox
mailbox = <mailbox, defined in [RFC5322], Section 3.4>
]]></artwork></figure>
<t>
An example is:
</t>
<figure><artwork type="example"><![CDATA[
From: webmaster@example.org
]]></artwork></figure>
<t>
This header field MAY be used for logging purposes and as a means for
identifying the source of invalid or unwanted requests. It SHOULD NOT
be used as an insecure form of access protection. The interpretation
of this field is that the request is being performed on behalf of the
person given, who accepts responsibility for the method performed. In
particular, robot agents SHOULD include this header field so that the
person responsible for running the robot can be contacted if problems
occur on the receiving end.
</t>
<t>
The Internet e-mail address in this field MAY be separate from the
Internet host which issued the request. For example, when a request
is passed through a proxy the original issuer's address SHOULD be
used.
</t>
<t>
The client SHOULD NOT send the From header field without the user's
approval, as it might conflict with the user's privacy interests or
their site's security policy. It is strongly recommended that the
user be able to disable, enable, and modify the value of this field
at any time prior to a request.
</t>
</section>
<section title="Referer" anchor="header.referer">
<iref primary="true" item="Referer header field"/>
<t>
The "Referer" [sic] header field allows the client to specify the
URI of the resource from which the target URI was obtained (the
"referrer", although the header field is misspelled.).
</t>
<t>
The Referer header field allows servers to generate lists of back-links to
resources for interest, logging, optimized caching, etc. It also allows
obsolete or mistyped links to be traced for maintenance. Some servers use
Referer as a means of controlling where they allow links from (so-called
"deep linking"), but legitimate requests do not always
contain a Referer header field.
</t>
<t>
If the target URI was obtained from a source that does not have its own
URI (e.g., input from the user keyboard), the Referer field MUST either be
sent with the value "about:blank", or not be sent at all. Note that this
requirement does not apply to sources with non-HTTP URIs (e.g., FTP).
</t>
<figure><iref primary="true" item="Grammar" subitem="Referer"/><artwork type="abnf2616"><![CDATA[
Referer = absolute-URI / partial-URI
]]></artwork></figure>
<t>
Example:
</t>
<figure><artwork type="example"><![CDATA[
Referer: http://www.example.org/hypertext/Overview.html
]]></artwork></figure>
<t>
If the field value is a relative URI, it SHOULD be interpreted
relative to the effective request URI. The URI MUST NOT include a fragment. See
<xref target="encoding.sensitive.information.in.uris"/> for security considerations.
</t>
</section>
<section title="User-Agent" anchor="header.user-agent">
<iref primary="true" item="User-Agent header field"/>
<t>
The "User-Agent" header field contains information about the user
agent originating the request. User agents SHOULD include this field with
requests.
</t>
<t>
Typically, it is used for statistical purposes, the tracing of protocol
violations, and tailoring responses to avoid particular user agent
limitations.
</t>
<t>
The field can contain multiple
product tokens (<xref target="product.tokens"/>)
and comments (Section 3.2 of <xref target="Part1"/>) identifying the agent and its
significant subproducts. By convention, the product tokens are listed in
order of their significance for identifying the application.
</t>
<t>
Because this field is usually sent on every request a user agent makes,
implementations are encouraged not to include needlessly fine-grained
detail, and to limit (or even prohibit) the addition of subproducts by third
parties. Overly long and detailed User-Agent field values make requests
larger and can also be used to identify ("fingerprint") the user against
their wishes.
</t>
<t>
Likewise, implementations are encouraged not to use the product tokens of
other implementations in order to declare compatibility with them, as this
circumvents the purpose of the field. Finally, they are encouraged not to
use comments to identify products; doing so makes the field value more
difficult to parse.
</t>
<figure><iref primary="true" item="Grammar" subitem="User-Agent"/><artwork type="abnf2616"><![CDATA[
User-Agent = product *( RWS ( product / comment ) )
]]></artwork></figure>
<t>
Example:
</t>
<figure><artwork type="example"><![CDATA[
User-Agent: CERN-LineMode/2.15 libwww/2.17b3
]]></artwork></figure>
</section>
</section>
</section>
<section title="Response Status Codes" anchor="status.codes">
<t>
The status-code element is a 3-digit integer result code of the attempt to
understand and satisfy the request.
</t>
<t>
HTTP status codes are extensible. HTTP applications are not required
to understand the meaning of all registered status codes, though such
understanding is obviously desirable. However, applications MUST
understand the class of any status code, as indicated by the first
digit, and treat any unrecognized response as being equivalent to the
x00 status code of that class, with the exception that an
unrecognized response MUST NOT be cached. For example, if an
unrecognized status code of 431 is received by the client, it can
safely assume that there was something wrong with its request and
treat the response as if it had received a 400 status code. In such
cases, user agents SHOULD present to the user the representation enclosed
with the response, since that representation is likely to include human-readable
information which will explain the unusual status.
</t>
<t>
The first digit of the status-code defines the class of response. The
last two digits do not have any categorization role. There are 5
values for the first digit:
<list style="symbols">
<t>
<xref target="status.1xx" format="none">1xx (Informational)</xref>: Request received, continuing process
</t>
<t>
<xref target="status.2xx" format="none">2xx (Successful)</xref>: The action was successfully received,
understood, and accepted
</t>
<t>
<xref target="status.3xx" format="none">3xx (Redirection)</xref>: Further action needs to be taken in order to
complete the request
</t>
<t>
<xref target="status.4xx" format="none">4xx (Client Error)</xref>: The request contains bad syntax or cannot
be fulfilled
</t>
<t>
<xref target="status.5xx" format="none">5xx (Server Error)</xref>: The server failed to fulfill an apparently
valid request
</t>
</list>
</t>
<t>
For most status codes the response can carry a payload, in which case a
<xref target="header.content-type" format="none">Content-Type</xref> header field indicates the payload's media type
(<xref target="header.content-type"/>).
</t>
<section title="Overview of Status Codes" anchor="overview.of.status.codes">
<t>
The status codes listed below are defined in this specification,
Section 4 of <xref target="Part4"/>, Section 3 of <xref target="Part5"/>, and Section 3 of <xref target="Part7"/>.
The reason phrases listed here are only recommendations — they can be
replaced by local equivalents without affecting the protocol.
</t>
<texttable align="left">
<ttcol>status-code</ttcol>
<ttcol>reason-phrase</ttcol>
<ttcol>Defined in...</ttcol>
<c>100</c> <c>Continue</c> <c><xref target="status.100"/></c>
<c>101</c> <c>Switching Protocols</c> <c><xref target="status.101"/></c>
<c>200</c> <c>OK</c> <c><xref target="status.200"/></c>
<c>201</c> <c>Created</c> <c><xref target="status.201"/></c>
<c>202</c> <c>Accepted</c> <c><xref target="status.202"/></c>
<c>203</c> <c>Non-Authoritative Information</c> <c><xref target="status.203"/></c>
<c>204</c> <c>No Content</c> <c><xref target="status.204"/></c>
<c>205</c> <c>Reset Content</c> <c><xref target="status.205"/></c>
<c>206</c> <c>Partial Content</c> <c>Section 3.1 of <xref target="Part5"/></c>
<c>300</c> <c>Multiple Choices</c> <c><xref target="status.300"/></c>
<c>301</c> <c>Moved Permanently</c> <c><xref target="status.301"/></c>
<c>302</c> <c>Found</c> <c><xref target="status.302"/></c>
<c>303</c> <c>See Other</c> <c><xref target="status.303"/></c>
<c>304</c> <c>Not Modified</c> <c>Section 4.1 of <xref target="Part4"/></c>
<c>305</c> <c>Use Proxy</c> <c><xref target="status.305"/></c>
<c>307</c> <c>Temporary Redirect</c> <c><xref target="status.307"/></c>
<c>400</c> <c>Bad Request</c> <c><xref target="status.400"/></c>
<c>401</c> <c>Unauthorized</c> <c>Section 3.1 of <xref target="Part7"/></c>
<c>402</c> <c>Payment Required</c> <c><xref target="status.402"/></c>
<c>403</c> <c>Forbidden</c> <c><xref target="status.403"/></c>
<c>404</c> <c>Not Found</c> <c><xref target="status.404"/></c>
<c>405</c> <c>Method Not Allowed</c> <c><xref target="status.405"/></c>
<c>406</c> <c>Not Acceptable</c> <c><xref target="status.406"/></c>
<c>407</c> <c>Proxy Authentication Required</c> <c>Section 3.2 of <xref target="Part7"/></c>
<c>408</c> <c>Request Time-out</c> <c><xref target="status.408"/></c>
<c>409</c> <c>Conflict</c> <c><xref target="status.409"/></c>
<c>410</c> <c>Gone</c> <c><xref target="status.410"/></c>
<c>411</c> <c>Length Required</c> <c><xref target="status.411"/></c>
<c>412</c> <c>Precondition Failed</c> <c>Section 4.2 of <xref target="Part4"/></c>
<c>413</c> <c>Request Representation Too Large</c> <c><xref target="status.413"/></c>
<c>414</c> <c>URI Too Long</c> <c><xref target="status.414"/></c>
<c>415</c> <c>Unsupported Media Type</c> <c><xref target="status.415"/></c>
<c>416</c> <c>Requested range not satisfiable</c> <c>Section 3.2 of <xref target="Part5"/></c>
<c>417</c> <c>Expectation Failed</c> <c><xref target="status.417"/></c>
<c>426</c> <c>Upgrade Required</c> <c><xref target="status.426"/></c>
<c>500</c> <c>Internal Server Error</c> <c><xref target="status.500"/></c>
<c>501</c> <c>Not Implemented</c> <c><xref target="status.501"/></c>
<c>502</c> <c>Bad Gateway</c> <c><xref target="status.502"/></c>
<c>503</c> <c>Service Unavailable</c> <c><xref target="status.503"/></c>
<c>504</c> <c>Gateway Time-out</c> <c><xref target="status.504"/></c>
<c>505</c> <c>HTTP Version not supported</c> <c><xref target="status.505"/></c>
</texttable>
<t>
Note that this list is not exhaustive — it does not include
extension status codes defined in other specifications.
</t>
</section>
<section title="Informational 1xx" anchor="status.1xx">
<iref primary="true" item="1xx Informational (status code class)"/>
<iref primary="true" item="Status Codes Classes" subitem="1xx Informational"/>
<t>
This class of status code indicates a provisional response,
consisting only of the status-line and optional header fields, and is
terminated by an empty line. There are no required header fields for this
class of status code. Since HTTP/1.0 did not define any 1xx status
codes, servers MUST NOT send a 1xx response to an HTTP/1.0 client
except under experimental conditions.
</t>
<t>
A client MUST be prepared to accept one or more 1xx status responses
prior to a regular response, even if the client does not expect a <xref target="status.100" format="none">100
(Continue)</xref> status message. Unexpected 1xx status responses MAY be
ignored by a user agent.
</t>
<t>
Proxies MUST forward 1xx responses, unless the connection between the
proxy and its client has been closed, or unless the proxy itself
requested the generation of the 1xx response. (For example, if a
proxy adds an "Expect: 100-continue" field when it forwards a request,
then it need not forward the corresponding <xref target="status.100" format="none">100 (Continue)</xref>
response(s).)
</t>
<section title="100 Continue" anchor="status.100">
<iref primary="true" item="100 Continue (status code)"/>
<t>
The client SHOULD continue with its request. This interim response is
used to inform the client that the initial part of the request has
been received and has not yet been rejected by the server. The client
SHOULD continue by sending the remainder of the request or, if the
request has already been completed, ignore this response. The server
MUST send a final response after the request has been completed.
See <xref target="use.of.the.100.status"/> for detailed discussion of the
use and handling of this status code.
</t>
</section>
<section title="101 Switching Protocols" anchor="status.101">
<iref primary="true" item="101 Switching Protocols (status code)"/>
<t>
The server understands and is willing to comply with the client's request,
via the Upgrade message header field (Section 6.3 of <xref target="Part1"/>), for
a change in the application protocol being used on this connection. The
server will switch protocols to those defined by the response's Upgrade
header field immediately after the empty line which terminates the 101
response.
</t>
<t>
The protocol SHOULD be switched only when it is advantageous to do
so. For example, switching to a newer version of HTTP is advantageous
over older versions, and switching to a real-time, synchronous
protocol might be advantageous when delivering resources that use
such features.
</t>
</section>
</section>
<section title="Successful 2xx" anchor="status.2xx">
<iref primary="true" item="2xx Successful (status code class)"/>
<iref primary="true" item="Status Codes Classes" subitem="2xx Successful"/>
<t>
This class of status code indicates that the client's request was
successfully received, understood, and accepted.
</t>
<section title="200 OK" anchor="status.200">
<iref primary="true" item="200 OK (status code)"/>
<t>
The request has succeeded. The payload returned with the response
is dependent on the method used in the request, for example:
<list style="hanging">
<t hangText="GET">
a representation of the target resource is sent in the response;
</t>
<t hangText="HEAD">
the same representation as GET, except without the message body;
</t>
<t hangText="POST">
a representation describing or containing the result of the action;
</t>
<t hangText="TRACE">
a representation containing the request message as received by the
end server.
</t>
</list>
</t>
<t>
Caches MAY use a heuristic (see Section 4.1.2 of <xref target="Part6"/>) to determine
freshness for 200 responses.
</t>
</section>
<section title="201 Created" anchor="status.201">
<iref primary="true" item="201 Created (status code)"/>
<t>
The request has been fulfilled and has resulted in one or more new resources
being created.
</t>
<t>
Newly created resources are typically linked to from the response payload,
with the most relevant URI also being carried in the <xref target="header.location" format="none">Location</xref>
header field. If the newly created resource's URI is the same as the
Effective Request URI, this information can be omitted (e.g., in the case of
a response to a PUT request).
</t>
<t>
The origin server MUST create the resource(s) before returning the 201 status
code. If the action cannot be carried out immediately, the server SHOULD
respond with <xref target="status.202" format="none">202 (Accepted)</xref> response instead.
</t>
<t>
A 201 response MAY contain an ETag response header field
indicating the current value of the entity-tag for the representation of the
resource identified by the <xref target="header.location" format="none">Location</xref> header field or, in case
the Location header field was omitted, by the Effective Request URI (see
Section 2.3 of <xref target="Part4"/>).
</t>
</section>
<section title="202 Accepted" anchor="status.202">
<iref primary="true" item="202 Accepted (status code)"/>
<t>
The request has been accepted for processing, but the processing has
not been completed. The request might or might not eventually be
acted upon, as it might be disallowed when processing actually takes
place. There is no facility for re-sending a status code from an
asynchronous operation such as this.
</t>
<t>
The 202 response is intentionally non-committal. Its purpose is to
allow a server to accept a request for some other process (perhaps a
batch-oriented process that is only run once per day) without
requiring that the user agent's connection to the server persist
until the process is completed. The representation returned with this
response SHOULD include an indication of the request's current status
and either a pointer to a status monitor or some estimate of when the
user can expect the request to be fulfilled.
</t>
</section>
<section title="203 Non-Authoritative Information" anchor="status.203">
<iref primary="true" item="203 Non-Authoritative Information (status code)"/>
<t>
The representation in the response has been transformed or otherwise
modified by a transforming proxy (Section 2.3 of <xref target="Part1"/>). Note that the
behavior of transforming intermediaries is controlled by the no-transform
Cache-Control directive (Section 7.2 of <xref target="Part6"/>).
</t>
<t>
This status code is only appropriate when the response status code would
have been <xref target="status.200" format="none">200 (OK)</xref> otherwise. When the status code before
transformation would have been different, the 214 Transformation Applied
warn-code (Section 7.5 of <xref target="Part6"/>) is appropriate.
</t>
<t>
Caches MAY use a heuristic (see Section 4.1.2 of <xref target="Part6"/>) to determine
freshness for 203 responses.
</t>
</section>
<section title="204 No Content" anchor="status.204">
<iref primary="true" item="204 No Content (status code)"/>
<t>
The 204 (No Content) status code indicates that the server has
successfully fulfilled the request and that there is no additional
content to return in the response payload body. Metadata in the
response header fields refer to the target resource and its current
representation after the requested action.
</t>
<t>
For example, if a 204 status code is received in response to a PUT
request and the response contains an ETag header field, then
the PUT was successful and the ETag field-value contains the entity-tag for
the new representation of that target resource.
</t>
<t>
The 204 response allows a server to indicate that the action has been
successfully applied to the target resource while implying that the
user agent SHOULD NOT traverse away from its current "document view"
(if any). The server assumes that the user agent will provide some
indication of the success to its user, in accord with its own interface,
and apply any new or updated metadata in the response to the active
representation.
</t>
<t>
For example, a 204 status code is commonly used with document editing
interfaces corresponding to a "save" action, such that the document
being saved remains available to the user for editing. It is also
frequently used with interfaces that expect automated data transfers
to be prevalent, such as within distributed version control systems.
</t>
<t>
The 204 response MUST NOT include a message body, and thus is always
terminated by the first empty line after the header fields.
</t>
</section>
<section title="205 Reset Content" anchor="status.205">
<iref primary="true" item="205 Reset Content (status code)"/>
<t>
The server has fulfilled the request and the user agent SHOULD reset
the document view which caused the request to be sent. This response
is primarily intended to allow input for actions to take place via
user input, followed by a clearing of the form in which the input is
given so that the user can easily initiate another input action.
</t>
<t>
The message body included with the response MUST be empty. Note that
receivers still need to parse the response according to the algorithm defined
in Section 3.3 of <xref target="Part1"/>.
</t>
</section>
</section>
<section title="Redirection 3xx" anchor="status.3xx">
<iref primary="true" item="3xx Redirection (status code class)"/>
<iref primary="true" item="Status Codes Classes" subitem="3xx Redirection"/>
<t>
This class of status code indicates that further action needs to be
taken by the user agent in order to fulfill the request. If the required
action involves a subsequent HTTP request, it MAY be carried out by the
user agent without interaction with the user if and only if the method used
in the second request is known to be "safe", as defined in
<xref target="safe.methods"/>.
</t>
<t>
There are several types of redirects:
<list style="numbers">
<t>
Redirects of the request to another URI, either temporarily or
permanently. The new URI is specified in the <xref target="header.location" format="none">Location</xref>
header field. In this specification, the status codes <xref target="status.301" format="none">301
(Moved Permanently)</xref>, <xref target="status.302" format="none">302 (Found)</xref>, and
<xref target="status.307" format="none">307 (Temporary Redirect)</xref> fall under this category.
</t>
<t>
Redirection to a new location that represents an indirect response to
the request, such as the result of a POST operation to be retrieved
with a subsequent GET request. This is status code <xref target="status.303" format="none">303 (See
Other)</xref>.
</t>
<t>
Redirection offering a choice of matching resources for use by
reactive content negotiation (<xref target="reactive.negotiation"/>). This
is status code <xref target="status.300" format="none">300 (Multiple Choices)</xref>.
</t>
<t>
Other kinds of redirection, such as to a cached result (status code 304
(Not Modified), see Section 4.1 of <xref target="Part4"/>).
</t>
</list>
</t>
<t><list>
<t>
Note: In HTTP/1.0, only the status codes <xref target="status.301" format="none">301 (Moved Permanently)</xref>
and <xref target="status.302" format="none">302 (Found)</xref> were defined for the first type of redirect,
and the second type did not exist at all (<xref target="RFC1945"/>, Section 9.3).
However it turned out that web forms using POST expected redirects to change
the operation for the subsequent request to retrieval (GET). To address this
use case, HTTP/1.1 introduced the second type of redirect with the status
code <xref target="status.303" format="none">303 (See Other)</xref> (<xref target="RFC2068"/>, Section 10.3.4).
As user agents did not change their behavior to maintain backwards
compatibility, the first revision of HTTP/1.1 added yet another status code,
<xref target="status.307" format="none">307 (Temporary Redirect)</xref>, for which the backwards
compatibility problems did not apply (<xref target="RFC2616"/>, Section 10.3.8).
Over 10 years later, most user agents still do method rewriting for status codes
<xref target="status.301" format="none">301</xref> and <xref target="status.302" format="none">302</xref>, therefore this specification makes that behavior
conformant in case the original request was POST.
</t>
</list></t>
<t>
A <xref target="header.location" format="none">Location</xref> header field on a 3xx response indicates that a
client MAY automatically redirect to the URI provided; see
<xref target="header.location"/>.
</t>
<t>
Note that for methods not known to be "safe", as defined in <xref target="safe.methods"/>,
automatic redirection needs to done with care, since the redirect might
change the conditions under which the request was issued.
</t>
<t>
Clients SHOULD detect and intervene in cyclical redirections (i.e.,
"infinite" redirection loops).
</t>
<t><list>
<t>
Note: An earlier version of this specification recommended a
maximum of five redirections (<xref target="RFC2068"/>, Section 10.3).
Content developers need to be aware that some clients might
implement such a fixed limitation.
</t>
</list></t>
<section title="300 Multiple Choices" anchor="status.300">
<iref primary="true" item="300 Multiple Choices (status code)"/>
<t>
The target resource has more than one
representation, each with its own specific location, and reactive
negotiation information (<xref target="content.negotiation"/>) is being provided so that
the user (or user agent) can select a preferred representation by
redirecting its request to that location.
</t>
<t>
Unless it was a HEAD request, the response SHOULD include a representation
containing a list of representation metadata and location(s) from
which the user or user agent can choose the one most appropriate. Depending
upon the format and the capabilities of
the user agent, selection of the most appropriate choice MAY be
performed automatically. However, this specification does not define
any standard for such automatic selection.
</t>
<t>
If the server has a preferred choice of representation, it SHOULD
include the specific URI for that representation in the <xref target="header.location" format="none">Location</xref>
field; user agents MAY use the Location field value for automatic
redirection.
</t>
<t>
Caches MAY use a heuristic (see Section 4.1.2 of <xref target="Part6"/>) to determine
freshness for 300 responses.
</t>
</section>
<section title="301 Moved Permanently" anchor="status.301">
<iref primary="true" item="301 Moved Permanently (status code)"/>
<t>
The target resource has been assigned a new permanent URI and any
future references to this resource SHOULD use one of the returned
URIs. Clients with link editing capabilities ought to automatically
re-link references to the effective request URI to one or more of the new
references returned by the server, where possible.
</t>
<t>
Caches MAY use a heuristic (see Section 4.1.2 of <xref target="Part6"/>) to determine
freshness for 301 responses.
</t>
<t>
The new permanent URI SHOULD be given by the <xref target="header.location" format="none">Location</xref> field
in the response. A response payload can contain a short hypertext note with a
hyperlink to the new URI(s).
</t>
<t><list>
<t>
Note: For historic reasons, user agents MAY change the
request method from POST to GET for the subsequent request. If this
behavior is undesired, status code <xref target="status.307" format="none">307 (Temporary Redirect)</xref>
can be used instead.
</t>
</list></t>
</section>
<section title="302 Found" anchor="status.302">
<iref primary="true" item="302 Found (status code)"/>
<t>
The target resource resides temporarily under a different URI.
Since the redirection might be altered on occasion, the client SHOULD
continue to use the effective request URI for future requests.
</t>
<t>
The temporary URI SHOULD be given by the <xref target="header.location" format="none">Location</xref> field in
the response. A response payload can contain a short hypertext note with a
hyperlink to the new URI(s).
</t>
<t><list>
<t>
Note: For historic reasons, user agents MAY change the
request method from POST to GET for the subsequent request. If this
behavior is undesired, status code <xref target="status.307" format="none">307 (Temporary Redirect)</xref>
can be used instead.
</t>
</list></t>
</section>
<section title="303 See Other" anchor="status.303">
<iref primary="true" item="303 See Other (status code)"/>
<t>
The 303 status code indicates that the server is redirecting the
user agent to a different resource, as indicated by a URI in the
<xref target="header.location" format="none">Location</xref> header field, that is intended to provide an indirect
response to the original request. In order to satisfy the original
request, a user agent SHOULD perform a retrieval request using the
Location URI (a GET or HEAD request if using HTTP), which
can itself be redirected further, and present the eventual result as an
answer to the original request.
Note that the new URI in the Location header field is not considered
equivalent to the effective request URI.
</t>
<t>
This status code is generally applicable to any HTTP method. It is
primarily used to allow the output of a POST action to redirect
the user agent to a selected resource, since doing so provides the
information corresponding to the POST response in a form that
can be separately identified, bookmarked, and cached independent
of the original request.
</t>
<t>
A 303 response to a GET request indicates that the requested
resource does not have a representation of its own that can be
transferred by the server over HTTP. The <xref target="header.location" format="none">Location</xref> URI
indicates a resource that is descriptive of the target resource, such that
the follow-on representation might be useful to recipients without
implying that it adequately represents the target resource.
Note that answers to the questions of what can be represented, what
representations are adequate, and what might be a useful description
are outside the scope of HTTP and thus entirely determined by the
URI owner(s).
</t>
<t>
Except for responses to a HEAD request, the representation of a 303
response SHOULD contain a short hypertext note with a hyperlink
to the <xref target="header.location" format="none">Location</xref> URI.
</t>
</section>
<section title="305 Use Proxy" anchor="status.305">
<iref primary="true" item="305 Use Proxy (status code)"/>
<t>
The 305 status code was defined in a previous version of this specification
(see <xref target="changes.from.rfc.2616"/>), and is now deprecated.
</t>
</section>
<section title="306 (Unused)" anchor="status.306">
<iref primary="true" item="306 (Unused) (status code)"/>
<t>
The 306 status code was used in a previous version of the
specification, is no longer used, and the code is reserved.
</t>
</section>
<section title="307 Temporary Redirect" anchor="status.307">
<iref primary="true" item="307 Temporary Redirect (status code)"/>
<t>
The target resource resides temporarily under a different URI.
Since the redirection can change over time, the client SHOULD
continue to use the effective request URI for future requests.
</t>
<t>
The temporary URI SHOULD be given by the <xref target="header.location" format="none">Location</xref> field in
the response. A response payload can contain a short hypertext note with a
hyperlink to the new URI(s).
</t>
<t><list>
<t>
Note: This status code is similar to <xref target="status.302" format="none">302 (Found)</xref>, except
that it does not allow rewriting the request method from POST to GET. This
specification defines no equivalent counterpart for <xref target="status.301" format="none">301 (Moved
Permanently)</xref> (<xref target="status-308"/>,
however, defines the status code 308 (Permanent Redirect) for this purpose).
</t>
</list></t>
</section>
</section>
<section title="Client Error 4xx" anchor="status.4xx">
<iref primary="true" item="4xx Client Error (status code class)"/>
<iref primary="true" item="Status Codes Classes" subitem="4xx Client Error"/>
<t>
The 4xx class of status code is intended for cases in which the
client seems to have erred. Except when responding to a HEAD request,
the server SHOULD include a representation containing an explanation of the
error situation, and whether it is a temporary or permanent
condition. These status codes are applicable to any request method.
User agents SHOULD display any included representation to the user.
</t>
<section title="400 Bad Request" anchor="status.400">
<iref primary="true" item="400 Bad Request (status code)"/>
<t>
The server cannot or will not process the request, due to a client error (e.g.,
malformed syntax).
</t>
</section>
<section title="402 Payment Required" anchor="status.402">
<iref primary="true" item="402 Payment Required (status code)"/>
<t>
This code is reserved for future use.
</t>
</section>
<section title="403 Forbidden" anchor="status.403">
<iref primary="true" item="403 Forbidden (status code)"/>
<t>
The server understood the request, but refuses to authorize it. Providing
different user authentication credentials might be successful, but any
credentials that were provided in the request are insufficient. The request
SHOULD NOT be repeated with the same credentials.
</t>
<t>
If the request method was not HEAD and the server wishes to make
public why the request has not been fulfilled, it SHOULD describe the
reason for the refusal in the representation. If the server does not wish to
make this information available to the client, the status code <xref target="status.404" format="none">404
(Not Found)</xref> MAY be used instead.
</t>
</section>
<section title="404 Not Found" anchor="status.404">
<iref primary="true" item="404 Not Found (status code)"/>
<t>
The server has not found anything matching the effective request URI. No
indication is given of whether the condition is temporary or
permanent. The <xref target="status.410" format="none">410 (Gone)</xref> status code SHOULD be used if the server
knows, through some internally configurable mechanism, that an old
resource is permanently unavailable and has no forwarding address.
This status code is commonly used when the server does not wish to
reveal exactly why the request has been refused, or when no other
response is applicable.
</t>
</section>
<section title="405 Method Not Allowed" anchor="status.405">
<iref primary="true" item="405 Method Not Allowed (status code)"/>
<t>
The method specified in the request-line is not allowed for the target
resource. The response MUST include an <xref target="header.allow" format="none">Allow</xref> header field
containing a list of valid methods for the requested resource.
</t>
</section>
<section title="406 Not Acceptable" anchor="status.406">
<iref primary="true" item="406 Not Acceptable (status code)"/>
<t>
The resource identified by the request is only capable of generating
response representations which have content characteristics not acceptable
according to the <xref target="header.accept" format="none">Accept</xref> and Accept-* header fields sent in
the request.
</t>
<t>
Unless it was a HEAD request, the response SHOULD include a representation
containing a list of available representation characteristics and location(s)
from which the user or user agent can choose the one most
appropriate. Depending upon the format and the
capabilities of the user agent, selection of the most appropriate
choice MAY be performed automatically. However, this specification
does not define any standard for such automatic selection.
</t>
<t><list>
<t>
Note: HTTP/1.1 servers are allowed to return responses which are
not acceptable according to the accept header fields sent in the
request. In some cases, this might even be preferable to sending a
406 response. User agents are encouraged to inspect the header fields of
an incoming response to determine if it is acceptable.
</t>
</list></t>
<t>
If the response could be unacceptable, a user agent SHOULD
temporarily stop receipt of more data and query the user for a
decision on further actions.
</t>
</section>
<section title="408 Request Timeout" anchor="status.408">
<iref primary="true" item="408 Request Timeout (status code)"/>
<t>
The client did not produce a request within the time that the server
was prepared to wait. The client MAY repeat the request without
modifications at any later time.
</t>
</section>
<section title="409 Conflict" anchor="status.409">
<iref primary="true" item="409 Conflict (status code)"/>
<t>
The request could not be completed due to a conflict with the current
state of the resource. This code is only allowed in situations where
it is expected that the user might be able to resolve the conflict
and resubmit the request. The payload SHOULD include enough
information for the user to recognize the source of the conflict.
Ideally, the response representation would include enough information for the
user or user agent to fix the problem; however, that might not be
possible and is not required.
</t>
<t>
Conflicts are most likely to occur in response to a PUT request. For
example, if versioning were being used and the representation being PUT
included changes to a resource which conflict with those made by an
earlier (third-party) request, the server might use the 409 response
to indicate that it can't complete the request. In this case, the
response representation would likely contain a list of the differences
between the two versions.
</t>
</section>
<section title="410 Gone" anchor="status.410">
<iref primary="true" item="410 Gone (status code)"/>
<t>
The target resource is no longer available at the server and no
forwarding address is known. This condition is expected to be
considered permanent. Clients with link editing capabilities SHOULD
delete references to the effective request URI after user approval. If the
server does not know, or has no facility to determine, whether or not
the condition is permanent, the status code <xref target="status.404" format="none">404 (Not Found)</xref>
SHOULD be used instead.
</t>
<t>
The 410 response is primarily intended to assist the task of web
maintenance by notifying the recipient that the resource is
intentionally unavailable and that the server owners desire that
remote links to that resource be removed. Such an event is common for
limited-time, promotional services and for resources belonging to
individuals no longer working at the server's site. It is not
necessary to mark all permanently unavailable resources as "gone" or
to keep the mark for any length of time — that is left to the
discretion of the server owner.
</t>
<t>
Caches MAY use a heuristic (see Section 4.1.2 of <xref target="Part6"/>) to determine freshness
for 410 responses.
</t>
</section>
<section title="411 Length Required" anchor="status.411">
<iref primary="true" item="411 Length Required (status code)"/>
<t>
The server refuses to accept the request without a defined
Content-Length. The client MAY repeat the request if it
adds a valid Content-Length header field containing the length of the
message body in the request message.
</t>
</section>
<section title="413 Request Representation Too Large" anchor="status.413">
<iref primary="true" item="413 Request Representation Too Large (status code)"/>
<t>
The server is refusing to process a request because the request
representation is larger than the server is willing or able to process. The
server MAY close the connection to prevent the client from continuing
the request.
</t>
<t>
If the condition is temporary, the server SHOULD include a
<xref target="header.retry-after" format="none">Retry-After</xref> header field to indicate that it is temporary and
after what time the client MAY try again.
</t>
</section>
<section title="414 URI Too Long" anchor="status.414">
<iref primary="true" item="414 URI Too Long (status code)"/>
<t>
The server is refusing to service the request because the effective request URI
is longer than the server is willing to interpret. This rare
condition is only likely to occur when a client has improperly
converted a POST request to a GET request with long query
information, when the client has descended into a URI "black hole" of
redirection (e.g., a redirected URI prefix that points to a suffix of
itself), or when the server is under attack by a client attempting to
exploit security holes present in some servers using fixed-length
buffers for reading or manipulating the request-target.
</t>
</section>
<section title="415 Unsupported Media Type" anchor="status.415">
<iref primary="true" item="415 Unsupported Media Type (status code)"/>
<t>
The server is refusing to service the request because the request
payload is in a format not supported by this request method on the
target resource.
</t>
</section>
<section title="417 Expectation Failed" anchor="status.417">
<iref primary="true" item="417 Expectation Failed (status code)"/>
<t>
The expectation given in an <xref target="header.expect" format="none">Expect</xref> header field (see
<xref target="header.expect"/>) could not be met by this server, or, if the
server is a proxy, the server has unambiguous evidence that the request
could not be met by the next-hop server.
</t>
</section>
<section title="426 Upgrade Required" anchor="status.426">
<iref primary="true" item="426 Upgrade Required (status code)"/>
<t>
The request can not be completed without a prior protocol upgrade. This
response MUST include an Upgrade header field
(Section 6.3 of <xref target="Part1"/>) specifying the required protocols.
</t>
<figure>
<preamble>Example:</preamble>
<artwork type="message/http; msgtype="response""><![CDATA[
HTTP/1.1 426 Upgrade Required
Upgrade: HTTP/3.0
Connection: Upgrade
Content-Length: 53
Content-Type: text/plain
This service requires use of the HTTP/3.0 protocol.
]]></artwork></figure>
<t>
The server SHOULD include a message body in the 426 response which
indicates in human readable form the reason for the error and describes any
alternative courses which might be available to the user.
</t>
</section>
</section>
<section title="Server Error 5xx" anchor="status.5xx">
<iref primary="true" item="5xx Server Error (status code class)"/>
<iref primary="true" item="Status Codes Classes" subitem="5xx Server Error"/>
<t>
Response status codes beginning with the digit "5" indicate cases in
which the server is aware that it has erred or is incapable of
performing the request. Except when responding to a HEAD request, the
server SHOULD include a representation containing an explanation of the
error situation, and whether it is a temporary or permanent
condition. User agents SHOULD display any included representation to the
user. These response codes are applicable to any request method.
</t>
<section title="500 Internal Server Error" anchor="status.500">
<iref primary="true" item="500 Internal Server Error (status code)"/>
<t>
The server encountered an unexpected condition which prevented it
from fulfilling the request.
</t>
</section>
<section title="501 Not Implemented" anchor="status.501">
<iref primary="true" item="501 Not Implemented (status code)"/>
<t>
The server does not support the functionality required to fulfill the
request. This is the appropriate response when the server does not
recognize the request method and is not capable of supporting it for
any resource.
</t>
</section>
<section title="502 Bad Gateway" anchor="status.502">
<iref primary="true" item="502 Bad Gateway (status code)"/>
<t>
The server, while acting as a gateway or proxy, received an invalid
response from the upstream server it accessed in attempting to
fulfill the request.
</t>
</section>
<section title="503 Service Unavailable" anchor="status.503">
<iref primary="true" item="503 Service Unavailable (status code)"/>
<t>
The server is currently unable to handle the request due to a
temporary overloading or maintenance of the server.
</t>
<t>
The implication is that this is a temporary condition which will be
alleviated after some delay. If known, the length of the delay MAY be
indicated in a <xref target="header.retry-after" format="none">Retry-After</xref> header field
(<xref target="header.retry-after"/>). If no Retry-After is given, the
client SHOULD handle the response as it would for a <xref target="status.500" format="none">500 (Internal
Server Error)</xref> response.
</t>
<t><list>
<t>
Note: The existence of the 503 status code does not imply that a
server has to use it when becoming overloaded. Some servers might wish
to simply refuse the connection.
</t>
</list></t>
</section>
<section title="504 Gateway Timeout" anchor="status.504">
<iref primary="true" item="504 Gateway Timeout (status code)"/>
<t>
The server, while acting as a gateway or proxy, did not receive a
timely response from the upstream server specified by the URI (e.g.,
HTTP, FTP, LDAP) or some other auxiliary server (e.g., DNS) it needed
to access in attempting to complete the request.
</t>
<t><list>
<t>
Note to implementers: some deployed proxies are known to
return <xref target="status.400" format="none">400 (Bad Request)</xref> or <xref target="status.500" format="none">500 (Internal Server
Error)</xref> when DNS lookups time out.
</t>
</list></t>
</section>
<section title="505 HTTP Version Not Supported" anchor="status.505">
<iref primary="true" item="505 HTTP Version Not Supported (status code)"/>
<t>
The server does not support, or refuses to support, the protocol
version that was used in the request message. The server is
indicating that it is unable or unwilling to complete the request
using the same major version as the client, as described in Section 2.6 of <xref target="Part1"/>,
other than with this error message. The response SHOULD contain
a representation describing why that version is not supported and what other
protocols are supported by that server.
</t>
</section>
</section>
</section>
<section title="Response Header Fields" anchor="response.header.fields">
<t>
The response header fields allow the server to pass additional
information about the response which cannot be placed in the status-line.
These header fields give information about the server and about
further access to the target resource (Section 5.5 of <xref target="Part1"/>).
</t>
<section title="Control Data" anchor="response.control.data">
<t>
Response header fields can supply control data that supplements the
status code or instructs the client where to go next.
</t>
<texttable align="left">
<ttcol>Header Field Name</ttcol><ttcol>Defined in...</ttcol>
<c>Age</c> <c>Section 7.1 of <xref target="Part6"/></c>
<c>Date</c> <c><xref target="header.date"/></c>
<c>Location</c> <c><xref target="header.location"/></c>
<c>Retry-After</c> <c><xref target="header.retry-after"/></c>
</texttable>
<section title="Origination Date" anchor="origination.date">
<section title="Date/Time Formats" anchor="http.date">
<t>
HTTP applications have historically allowed three different formats
for date/time stamps. However, the preferred format is a fixed-length subset
of that defined by <xref target="RFC1123"/>:
</t>
<figure><artwork type="example"><![CDATA[
Sun, 06 Nov 1994 08:49:37 GMT ; RFC 1123
]]></artwork></figure>
<t>
The other formats are described here only for compatibility with obsolete
implementations.
</t>
<figure><artwork type="example"><![CDATA[
Sunday, 06-Nov-94 08:49:37 GMT ; obsolete RFC 850 format
Sun Nov 6 08:49:37 1994 ; ANSI C's asctime() format
]]></artwork></figure>
<t>
HTTP/1.1 clients and servers that parse a date value MUST accept
all three formats (for compatibility with HTTP/1.0), though they MUST
only generate the RFC 1123 format for representing HTTP-date values
in header fields.
</t>
<t>
All HTTP date/time stamps MUST be represented in Greenwich Mean Time
(GMT), without exception. For the purposes of HTTP, GMT is exactly
equal to UTC (Coordinated Universal Time). This is indicated in the
first two formats by the inclusion of "GMT" as the three-letter
abbreviation for time zone, and MUST be assumed when reading the
asctime format. HTTP-date is case sensitive and MUST NOT include
additional whitespace beyond that specifically included as SP in the
grammar.
</t>
<figure><iref primary="true" item="Grammar" subitem="HTTP-date"/><artwork type="abnf2616"><![CDATA[
HTTP-date = rfc1123-date / obs-date
]]></artwork></figure>
<t anchor="preferred.date.format">
Preferred format:
</t>
<figure><iref primary="true" item="Grammar" subitem="rfc1123-date"/><iref primary="true" item="Grammar" subitem="date1"/><iref primary="true" item="Grammar" subitem="time-of-day"/><iref primary="true" item="Grammar" subitem="hour"/><iref primary="true" item="Grammar" subitem="minute"/><iref primary="true" item="Grammar" subitem="second"/><iref primary="true" item="Grammar" subitem="day-name"/><iref primary="true" item="Grammar" subitem="day-name-l"/><iref primary="true" item="Grammar" subitem="day"/><iref primary="true" item="Grammar" subitem="month"/><iref primary="true" item="Grammar" subitem="year"/><iref primary="true" item="Grammar" subitem="GMT"/><artwork type="abnf2616"><![CDATA[
rfc1123-date = day-name "," SP date1 SP time-of-day SP GMT
; fixed length subset of the format defined in
; Section 5.2.14 of [RFC1123]
day-name = %x4D.6F.6E ; "Mon", case-sensitive
/ %x54.75.65 ; "Tue", case-sensitive
/ %x57.65.64 ; "Wed", case-sensitive
/ %x54.68.75 ; "Thu", case-sensitive
/ %x46.72.69 ; "Fri", case-sensitive
/ %x53.61.74 ; "Sat", case-sensitive
/ %x53.75.6E ; "Sun", case-sensitive
date1 = day SP month SP year
; e.g., 02 Jun 1982
day = 2DIGIT
month = %x4A.61.6E ; "Jan", case-sensitive
/ %x46.65.62 ; "Feb", case-sensitive
/ %x4D.61.72 ; "Mar", case-sensitive
/ %x41.70.72 ; "Apr", case-sensitive
/ %x4D.61.79 ; "May", case-sensitive
/ %x4A.75.6E ; "Jun", case-sensitive
/ %x4A.75.6C ; "Jul", case-sensitive
/ %x41.75.67 ; "Aug", case-sensitive
/ %x53.65.70 ; "Sep", case-sensitive
/ %x4F.63.74 ; "Oct", case-sensitive
/ %x4E.6F.76 ; "Nov", case-sensitive
/ %x44.65.63 ; "Dec", case-sensitive
year = 4DIGIT
GMT = %x47.4D.54 ; "GMT", case-sensitive
time-of-day = hour ":" minute ":" second
; 00:00:00 - 23:59:59
hour = 2DIGIT
minute = 2DIGIT
second = 2DIGIT
]]></artwork></figure>
<t>
The semantics of <xref target="preferred.date.format" format="none">day-name</xref>, <xref target="preferred.date.format" format="none">day</xref>,
<xref target="preferred.date.format" format="none">month</xref>, <xref target="preferred.date.format" format="none">year</xref>, and <xref target="preferred.date.format" format="none">time-of-day</xref> are the
same as those defined for the RFC 5322 constructs
with the corresponding name (<xref target="RFC5322"/>, Section 3.3).
</t>
<t anchor="obsolete.date.formats">
Obsolete formats:
</t>
<figure><iref primary="true" item="Grammar" subitem="obs-date"/><artwork type="abnf2616"><![CDATA[
obs-date = rfc850-date / asctime-date
]]></artwork></figure>
<figure><iref primary="true" item="Grammar" subitem="rfc850-date"/><artwork type="abnf2616"><![CDATA[
rfc850-date = day-name-l "," SP date2 SP time-of-day SP GMT
date2 = day "-" month "-" 2DIGIT
; day-month-year (e.g., 02-Jun-82)
day-name-l = %x4D.6F.6E.64.61.79 ; "Monday", case-sensitive
/ %x54.75.65.73.64.61.79 ; "Tuesday", case-sensitive
/ %x57.65.64.6E.65.73.64.61.79 ; "Wednesday", case-sensitive
/ %x54.68.75.72.73.64.61.79 ; "Thursday", case-sensitive
/ %x46.72.69.64.61.79 ; "Friday", case-sensitive
/ %x53.61.74.75.72.64.61.79 ; "Saturday", case-sensitive
/ %x53.75.6E.64.61.79 ; "Sunday", case-sensitive
]]></artwork></figure>
<figure><iref primary="true" item="Grammar" subitem="asctime-date"/><artwork type="abnf2616"><![CDATA[
asctime-date = day-name SP date3 SP time-of-day SP year
date3 = month SP ( 2DIGIT / ( SP 1DIGIT ))
; month day (e.g., Jun 2)
]]></artwork></figure>
<t><list>
<t>
Note: Recipients of date values are encouraged to be robust in
accepting date values that might have been sent by non-HTTP
applications, as is sometimes the case when retrieving or posting
messages via proxies/gateways to SMTP or NNTP.
</t>
</list></t>
<t><list>
<t>
Note: HTTP requirements for the date/time stamp format apply only
to their usage within the protocol stream. Clients and servers are
not required to use these formats for user presentation, request
logging, etc.
</t>
</list></t>
</section>
<section title="Date" anchor="header.date">
<iref primary="true" item="Date header field"/>
<t>
The "Date" header field represents the date and time at which
the message was originated, having the same semantics as the Origination
Date Field (orig-date) defined in Section 3.6.1 of <xref target="RFC5322"/>.
The field value is an HTTP-date, as defined in <xref target="http.date"/>;
it MUST be sent in rfc1123-date format.
</t>
<figure><iref primary="true" item="Grammar" subitem="Date"/><artwork type="abnf2616"><![CDATA[
Date = HTTP-date
]]></artwork></figure>
<t>
An example is
</t>
<figure><artwork type="example"><![CDATA[
Date: Tue, 15 Nov 1994 08:12:31 GMT
]]></artwork></figure>
<t>
Origin servers MUST include a Date header field in all responses,
except in these cases:
<list style="numbers">
<t>If the response status code is <xref target="status.100" format="none">100 (Continue)</xref> or
<xref target="status.101" format="none">101 (Switching Protocols)</xref>, the response MAY include a
Date header field, at the server's option.</t>
<t>If the response status code conveys a server error, e.g., <xref target="status.500" format="none">500
(Internal Server Error)</xref> or <xref target="status.503" format="none">503 (Service Unavailable)</xref>,
and it is inconvenient or impossible to generate a valid Date.</t>
<t>If the server does not have a clock that can provide a
reasonable approximation of the current time, its responses
MUST NOT include a Date header field.</t>
</list>
</t>
<t>
A received message that does not have a Date header field MUST be
assigned one by the recipient if the message will be cached by that
recipient.
</t>
<t>
Clients can use the Date header field as well; in order to keep request
messages small, they are advised not to include it when it doesn't convey
any useful information (as is usually the case for requests that do not
contain a payload).
</t>
<t>
The HTTP-date sent in a Date header field SHOULD NOT represent a date and
time subsequent to the generation of the message. It SHOULD represent
the best available approximation of the date and time of message
generation, unless the implementation has no means of generating a
reasonably accurate date and time. In theory, the date ought to
represent the moment just before the payload is generated. In
practice, the date can be generated at any time during the message
origination without affecting its semantic value.
</t>
</section>
</section>
<section title="Location" anchor="header.location">
<iref primary="true" item="Location header field"/>
<t>
The "Location" header field MAY be sent in responses to refer to
a specific resource in accordance with the semantics of the status
code.
</t>
<figure><iref primary="true" item="Grammar" subitem="Location"/><artwork type="abnf2616"><![CDATA[
Location = URI-reference
]]></artwork></figure>
<t>
For <xref target="status.201" format="none">201 (Created)</xref> responses, the Location is the URI of the
new resource which was created by the request. For <xref target="status.3xx" format="none">3xx (Redirection)</xref>
responses, the location SHOULD indicate the server's preferred URI for
automatic redirection to the resource.
</t>
<t>
The field value consists of a single URI-reference. When it has the form
of a relative reference (<xref target="RFC3986"/>, Section 4.2),
the final value is computed by resolving it against the effective request
URI (<xref target="RFC3986"/>, Section 5). If the original URI, as
navigated to by the user agent, did contain a fragment identifier, and the
final value does not, then the original URI's fragment identifier is added
to the final value.
</t>
<figure>
<preamble>For example, the original URI "http://www.example.org/~tim", combined with a field value given as:</preamble><!--DO NOT DARE changing the vertical spacing below, it's necessary this way for xml2rfc-->
<artwork type="example"><![CDATA[
Location: /pub/WWW/People.html#tim
]]></artwork>
<postamble>would result in a final value of "http://www.example.org/pub/WWW/People.html#tim"</postamble>
</figure>
<figure>
<preamble>An original URI "http://www.example.org/index.html#larry", combined with a field value given as:</preamble><!--DO NOT DARE changing the vertical spacing below, it's necessary this way for xml2rfc-->
<artwork type="example"><![CDATA[
Location: http://www.example.net/index.html
]]></artwork>
<postamble>would result in a final value of "http://www.example.net/index.html#larry", preserving the original fragment identifier.</postamble>
</figure>
<t><list>
<t>
Note: Some recipients attempt to recover from Location fields
that are not valid URI references. This specification does not mandate or
define such processing, but does allow it.
</t>
</list></t>
<t>
There are circumstances in which a fragment identifier in a Location URI
would not be appropriate. For instance, when it appears in a <xref target="status.201" format="none">201
(Created)</xref> response, where the Location header field specifies the
URI for the entire created resource.
</t>
<t><list>
<t>
Note: The <xref target="header.content-location" format="none">Content-Location</xref> header field
(<xref target="header.content-location"/>) differs from Location in that the
Content-Location identifies the most specific resource corresponding to the
enclosed representation. It is therefore possible for a response to contain
header fields for both Location and Content-Location.
</t>
</list></t>
</section>
<section title="Retry-After" anchor="header.retry-after">
<iref primary="true" item="Retry-After header field"/>
<t>
The header "Retry-After" field can be used with a <xref target="status.503" format="none">503 (Service
Unavailable)</xref> response to indicate how long the service is expected to
be unavailable to the requesting client. This field MAY also be used
with any <xref target="status.3xx" format="none">3xx (Redirection)</xref> response to indicate the minimum time the
user-agent is asked to wait before issuing the redirected request.
</t>
<t>
The value of this field can be either an HTTP-date or an integer number
of seconds (in decimal) after the time of the response.
</t>
<figure><iref primary="true" item="Grammar" subitem="Retry-After"/><artwork type="abnf2616"><![CDATA[
Retry-After = HTTP-date / delta-seconds
]]></artwork></figure>
<t anchor="rule.delta-seconds">
Time spans are non-negative decimal integers, representing time in
seconds.
</t>
<figure><iref primary="true" item="Grammar" subitem="delta-seconds"/><artwork type="abnf2616"><![CDATA[
delta-seconds = 1*DIGIT
]]></artwork></figure>
<t>
Two examples of its use are
</t>
<figure><artwork type="example"><![CDATA[
Retry-After: Fri, 31 Dec 1999 23:59:59 GMT
Retry-After: 120
]]></artwork></figure>
<t>
In the latter example, the delay is 2 minutes.
</t>
</section>
</section>
<section title="Selected Representation Header Fields" anchor="selected.representation">
<t><iref primary="true" item="selected representation"/>
We use the term "selected representation" to refer to the
the current representation of a target resource that would have been
selected in a successful response if the same request had used the
method GET and excluded any conditional request header fields.
</t>
<t>
Additional header fields define metadata about the selected
representation, which might differ from the representation included
in the message for responses to some state-changing methods.
The following header fields are defined as selected representation
metadata:
</t>
<texttable align="left">
<ttcol>Header Field Name</ttcol>
<ttcol>Defined in...</ttcol>
<c>ETag</c> <c>Section 2.3 of <xref target="Part4"/></c>
<c>Last-Modified</c> <c>Section 2.2 of <xref target="Part4"/></c>
<c>Vary</c> <c><xref target="header.vary"/></c>
</texttable>
<section anchor="header.vary" title="Vary">
<iref item="Vary header field" primary="true"/>
<t>
The "Vary" header field conveys the set of header fields
that were used to select the representation.
</t>
<t>
Caches use this information as part of determining whether a stored
response can be used to satisfy a given request (Section 4.3 of <xref target="Part6"/>).
</t>
<t>
In uncacheable or stale responses, the Vary field value advises the user
agent about the criteria that were used to select the representation.
</t>
<figure><iref primary="true" item="Grammar" subitem="Vary"/><artwork type="abnf2616"><![CDATA[
Vary = "*" / 1#field-name
]]></artwork></figure>
<t>
The set of header fields named by the Vary field value is known as the
selecting header fields.
</t>
<t>
A server SHOULD include a Vary header field with any cacheable response
that is subject to proactive negotiation. Doing so allows a cache to
properly interpret future requests on that resource and informs the user
agent about the presence of negotiation on that resource. A server MAY
include a Vary header field with a non-cacheable response that is subject
to proactive negotiation, since this might provide the user agent with
useful information about the dimensions over which the response varies at
the time of the response.
</t>
<t>
A Vary field value of "*" signals that unspecified parameters not limited
to the header fields (e.g., the network address of the client), play a
role in the selection of the response representation; therefore, a cache
cannot determine whether this response is appropriate. A proxy MUST NOT
generate the "*" value.
</t>
<t>
The field-names given are not limited to the set of standard header
fields defined by this specification. Field names are case-insensitive.
</t>
</section>
</section>
<section title="Authentication Challenges" anchor="response.auth">
<t>
Authentication challenges indicate what mechanisms are available for the
client to provide authentication credentials in future requests.
</t>
<texttable align="left">
<ttcol>Header Field Name</ttcol><ttcol>Defined in...</ttcol>
<c>WWW-Authenticate</c> <c>Section 4.4 of <xref target="Part7"/></c>
<c>Proxy-Authenticate</c> <c>Section 4.2 of <xref target="Part7"/></c>
</texttable>
</section>
<section title="Informative" anchor="response.inform">
<t>
The remaining response header fields provide more information about
the target resource for potential use in later requests.
</t>
<texttable align="left">
<ttcol>Header Field Name</ttcol><ttcol>Defined in...</ttcol>
<c>Accept-Ranges</c> <c>Section 5.1 of <xref target="Part5"/></c>
<c>Allow</c> <c><xref target="header.allow"/></c>
<c>Server</c> <c><xref target="header.server"/></c>
</texttable>
<section title="Allow" anchor="header.allow">
<iref primary="true" item="Allow header field"/>
<t>
The "Allow" header field lists the set of methods advertised as
supported by the target resource. The purpose of this field is strictly to
inform the recipient of valid request methods associated with the resource.
</t>
<figure><iref primary="true" item="Grammar" subitem="Allow"/><artwork type="abnf2616"><![CDATA[
Allow = #method
]]></artwork></figure>
<t>
Example of use:
</t>
<figure><artwork type="example"><![CDATA[
Allow: GET, HEAD, PUT
]]></artwork></figure>
<t>
The actual set of allowed methods is defined by the origin server at the
time of each request.
</t>
<t>
A proxy MUST NOT modify the Allow header field — it does not need to
understand all the methods specified in order to handle them according to
the generic message handling rules.
</t>
</section>
<section title="Server" anchor="header.server">
<iref primary="true" item="Server header field"/>
<t>
The "Server" header field contains information about the
software used by the origin server to handle the request.
</t>
<t>
The field can contain multiple
product tokens (<xref target="product.tokens"/>) and
comments (Section 3.2 of <xref target="Part1"/>) identifying the server and any significant
subproducts. The product tokens are listed in order of their significance
for identifying the application.
</t>
<figure><iref primary="true" item="Grammar" subitem="Server"/><artwork type="abnf2616"><![CDATA[
Server = product *( RWS ( product / comment ) )
]]></artwork></figure>
<t>
Example:
</t>
<figure><artwork type="example"><![CDATA[
Server: CERN/3.0 libwww/2.17
]]></artwork></figure>
<t>
If the response is being forwarded through a proxy, the proxy application
MUST NOT modify the <xref target="header.server" format="none">Server</xref> header field. Instead, it
MUST include a Via field (as described in Section 5.7 of <xref target="Part1"/>).
</t>
<t><list>
<t>
Note: Revealing the specific software version of the server might
allow the server machine to become more vulnerable to attacks
against software that is known to contain security holes. Server
implementers are encouraged to make this field a configurable
option.
</t>
</list></t>
</section>
</section>
</section>
<section title="IANA Considerations" anchor="IANA.considerations">
<section title="Method Registry" anchor="method.registry">
<t>
The HTTP Method Registry defines the name space for the request method
token (<xref target="methods"/>).
The method registry is maintained at
<eref target="http://www.iana.org/assignments/http-methods"/>.
</t>
<section title="Procedure" anchor="method.procedure">
<t>
HTTP method registrations MUST include the following fields:
<list style="symbols">
<t>Method Name (see <xref target="methods"/>)</t>
<t>Safe ("yes" or "no", see <xref target="safe.methods"/>)</t>
<t>Idempotent ("yes" or "no", see <xref target="idempotent.methods"/>)</t>
<t>Pointer to specification text</t>
</list>
</t>
<t>
Values to be added to this name space require IETF Review
(see <xref target="RFC5226"/>, Section 4.1).
</t>
</section>
<section title="Considerations for New Methods" anchor="considerations.for.new.methods">
<t>
Standardized methods are generic; that is, they are potentially
applicable to any resource, not just one particular media type, kind of
resource, or application. As such, it is preferred that new methods
be registered in a document that isn't specific to a single application or
data format, since orthogonal technologies deserve orthogonal specification.
</t>
<t>
Since message parsing (Section 3.3 of <xref target="Part1"/>) needs to be independent of method
semantics (aside from responses to HEAD), definitions of new methods
cannot change the parsing algorithm or prohibit the presence of a message
body on either the request or the response message.
Definitions of new methods can specify that only a zero-length message body
is allowed by requiring a Content-Length header field with a value of "0".
</t>
<t>
New method definitions need to indicate whether they are safe (<xref target="safe.methods"/>), idempotent (<xref target="idempotent.methods"/>),
cacheable (<xref target="cacheable.methods"/>), and what
semantics are to be associated with the payload body if any is present
in the request. If a method is cacheable, the method definition ought
to describe how, and under what conditions, a cache can store a response
and use it to satisfy a subsequent request.
</t>
</section>
<section title="Registrations" anchor="method.registration">
<t>
The HTTP Method Registry shall be populated with the registrations below:
</t>
<!--AUTOGENERATED FROM extract-method-defs.xslt, do not edit manually-->
<texttable align="left" suppress-title="true" anchor="iana.method.registration.table">
<ttcol>Method</ttcol>
<ttcol>Safe</ttcol>
<ttcol>Idempotent</ttcol>
<ttcol>Reference</ttcol>
<c>CONNECT</c>
<c>no</c>
<c>no</c>
<c>
<xref target="CONNECT"/>
</c>
<c>DELETE</c>
<c>no</c>
<c>yes</c>
<c>
<xref target="DELETE"/>
</c>
<c>GET</c>
<c>yes</c>
<c>yes</c>
<c>
<xref target="GET"/>
</c>
<c>HEAD</c>
<c>yes</c>
<c>yes</c>
<c>
<xref target="HEAD"/>
</c>
<c>OPTIONS</c>
<c>yes</c>
<c>yes</c>
<c>
<xref target="OPTIONS"/>
</c>
<c>POST</c>
<c>no</c>
<c>no</c>
<c>
<xref target="POST"/>
</c>
<c>PUT</c>
<c>no</c>
<c>yes</c>
<c>
<xref target="PUT"/>
</c>
<c>TRACE</c>
<c>yes</c>
<c>yes</c>
<c>
<xref target="TRACE"/>
</c>
</texttable>
<!--(END)-->
</section>
</section>
<section title="Status Code Registry" anchor="status.code.registry">
<t>
The HTTP Status Code Registry defines the name space for the response
status-code token (<xref target="status.codes"/>).
The status code registry is maintained at
<eref target="http://www.iana.org/assignments/http-status-codes"/>.
</t>
<t>
This section replaces the registration procedure for HTTP Status Codes
previously defined in Section 7.1 of <xref target="RFC2817"/>.
</t>
<section title="Procedure" anchor="status.code.procedure">
<t>
Values to be added to the HTTP status code name space require IETF Review
(see <xref target="RFC5226"/>, Section 4.1).
</t>
</section>
<section title="Considerations for New Status Codes" anchor="considerations.for.new.status.codes">
<t>
When it is necessary to express semantics for a response that are not
defined by current status codes, a new status code can be registered.
HTTP status codes are generic; they are potentially applicable to
any resource, not just one particular media type, "type" of resource, or
application. As such, it is preferred that new status codes be
registered in a document that isn't specific to a single application.
</t>
<t>
New status codes are required to fall under one of the categories
defined in <xref target="status.codes"/>. To allow existing parsers to
properly handle them, new status codes cannot disallow a payload,
although they can mandate a zero-length payload body.
</t>
<t>
A definition for a new status code ought to explain the request
conditions that produce a response containing that status code (e.g.,
combinations of request header fields and/or method(s)) along with any
dependencies on response header fields (e.g., what fields are required
and what fields can modify the semantics). A response that can transfer a
payload ought to specify expected cache behavior (e.g., cacheability and
freshness criteria, as described in <xref target="Part6"/>) and whether the payload has
any implied association with an identified resource
(<xref target="identifying.payload"/>).
</t>
</section>
<section title="Registrations" anchor="status.code.registration">
<t>
The HTTP Status Code Registry shall be updated with the registrations below:
</t>
<!--AUTOGENERATED FROM extract-status-code-defs.xslt, do not edit manually-->
<texttable align="left" suppress-title="true" anchor="iana.status.code.registration.table">
<ttcol>Value</ttcol>
<ttcol>Description</ttcol>
<ttcol>Reference</ttcol>
<c>100</c>
<c>Continue</c>
<c>
<xref target="status.100"/>
</c>
<c>101</c>
<c>Switching Protocols</c>
<c>
<xref target="status.101"/>
</c>
<c>200</c>
<c>OK</c>
<c>
<xref target="status.200"/>
</c>
<c>201</c>
<c>Created</c>
<c>
<xref target="status.201"/>
</c>
<c>202</c>
<c>Accepted</c>
<c>
<xref target="status.202"/>
</c>
<c>203</c>
<c>Non-Authoritative Information</c>
<c>
<xref target="status.203"/>
</c>
<c>204</c>
<c>No Content</c>
<c>
<xref target="status.204"/>
</c>
<c>205</c>
<c>Reset Content</c>
<c>
<xref target="status.205"/>
</c>
<c>300</c>
<c>Multiple Choices</c>
<c>
<xref target="status.300"/>
</c>
<c>301</c>
<c>Moved Permanently</c>
<c>
<xref target="status.301"/>
</c>
<c>302</c>
<c>Found</c>
<c>
<xref target="status.302"/>
</c>
<c>303</c>
<c>See Other</c>
<c>
<xref target="status.303"/>
</c>
<c>305</c>
<c>Use Proxy</c>
<c>
<xref target="status.305"/>
</c>
<c>306</c>
<c>(Unused)</c>
<c>
<xref target="status.306"/>
</c>
<c>307</c>
<c>Temporary Redirect</c>
<c>
<xref target="status.307"/>
</c>
<c>400</c>
<c>Bad Request</c>
<c>
<xref target="status.400"/>
</c>
<c>402</c>
<c>Payment Required</c>
<c>
<xref target="status.402"/>
</c>
<c>403</c>
<c>Forbidden</c>
<c>
<xref target="status.403"/>
</c>
<c>404</c>
<c>Not Found</c>
<c>
<xref target="status.404"/>
</c>
<c>405</c>
<c>Method Not Allowed</c>
<c>
<xref target="status.405"/>
</c>
<c>406</c>
<c>Not Acceptable</c>
<c>
<xref target="status.406"/>
</c>
<c>408</c>
<c>Request Timeout</c>
<c>
<xref target="status.408"/>
</c>
<c>409</c>
<c>Conflict</c>
<c>
<xref target="status.409"/>
</c>
<c>410</c>
<c>Gone</c>
<c>
<xref target="status.410"/>
</c>
<c>411</c>
<c>Length Required</c>
<c>
<xref target="status.411"/>
</c>
<c>413</c>
<c>Request Representation Too Large</c>
<c>
<xref target="status.413"/>
</c>
<c>414</c>
<c>URI Too Long</c>
<c>
<xref target="status.414"/>
</c>
<c>415</c>
<c>Unsupported Media Type</c>
<c>
<xref target="status.415"/>
</c>
<c>417</c>
<c>Expectation Failed</c>
<c>
<xref target="status.417"/>
</c>
<c>426</c>
<c>Upgrade Required</c>
<c>
<xref target="status.426"/>
</c>
<c>500</c>
<c>Internal Server Error</c>
<c>
<xref target="status.500"/>
</c>
<c>501</c>
<c>Not Implemented</c>
<c>
<xref target="status.501"/>
</c>
<c>502</c>
<c>Bad Gateway</c>
<c>
<xref target="status.502"/>
</c>
<c>503</c>
<c>Service Unavailable</c>
<c>
<xref target="status.503"/>
</c>
<c>504</c>
<c>Gateway Timeout</c>
<c>
<xref target="status.504"/>
</c>
<c>505</c>
<c>HTTP Version Not Supported</c>
<c>
<xref target="status.505"/>
</c>
</texttable>
<!--(END)-->
</section>
</section>
<section title="Header Field Registry" anchor="header.field.registry">
<t>
HTTP header fields are registered within the Message Header Field Registry
located at <eref target="http://www.iana.org/assignments/message-headers/message-header-index.html"/>,
as defined by <xref target="RFC3864"/>.
</t>
<section title="Considerations for New Header Fields" anchor="considerations.for.new.header.fields">
<t>
Header fields are key:value pairs that can be used to communicate data about
the message, its payload, the target resource, or the connection
(i.e., control data). See Section 3.2 of <xref target="Part1"/> for a general definition
of header field syntax in HTTP messages.
</t>
<t>
The requirements for header field names are defined in
Section 4.1 of <xref target="RFC3864"/>. Authors of specifications
defining new fields are advised to keep the name as short as practical, and
not to prefix them with "X-" if they are to be registered (either
immediately or in the future).
</t>
<t>
New header field values typically have their syntax defined using ABNF
(<xref target="RFC5234"/>), using the extension defined in Appendix B of <xref target="Part1"/>
as necessary, and are usually constrained to the range of ASCII characters.
Header fields needing a greater range of characters can use an encoding
such as the one defined in <xref target="RFC5987"/>.
</t>
<t>
Because commas (",") are used as a generic delimiter between field-values,
they need to be treated with care if they are allowed in the field-value's
payload. Typically, components that might contain a comma are protected with
double-quotes using the quoted-string ABNF production (Section 3.2.4 of <xref target="Part1"/>).
</t>
<t>
For example, a textual date and a URI (either of which might contain a comma)
could be safely carried in field-values like these:
</t>
<figure><artwork type="example"><![CDATA[
Example-URI-Field: "http://example.com/a.html,foo",
"http://without-a-comma.example.com/"
Example-Date-Field: "Sat, 04 May 1996", "Wed, 14 Sep 2005"
]]></artwork></figure>
<t>
Note that double-quote delimiters almost always are used with the
quoted-string production; using a different syntax inside double-quotes
will likely cause unnecessary confusion.
</t>
<t>
Many header fields use a format including (case-insensitively) named
parameters (for instance, <xref target="header.content-type" format="none">Content-Type</xref>, defined in
<xref target="header.content-type"/>). Allowing both unquoted (token) and quoted
(quoted-string) syntax for the parameter value enables recipients to use
existing parser components. When allowing both forms, the meaning of a
parameter value ought to be independent of the syntax used for it (for an
example, see the notes on parameter handling for media types in
<xref target="media.types"/>).
</t>
<t>
Authors of specifications defining new header fields are advised to consider
documenting:
<list style="symbols">
<t>Whether the field is a single value, or whether it can be a list
(delimited by commas; see Section 3.2 of <xref target="Part1"/>).<vspace blankLines="1"/>If it does not use the list syntax, document how to treat messages
where the header field occurs multiple times (a sensible default would
be to ignore the header field, but this might not always be the right
choice).<vspace blankLines="1"/>Note that intermediaries and software libraries might combine
multiple header field instances into a single one, despite the header
field not allowing this. A robust format enables recipients to discover
these situations (good example: "Content-Type", as the comma can only
appear inside quoted strings; bad example: "Location", as a comma can
occur inside a URI).</t>
<t>Under what conditions the header field can be used; e.g., only in
responses or requests, in all messages, only on responses to a particular
request method.</t>
<t>Whether it is appropriate to list the field-name in the
Connection header field (i.e., if the header field is to
be hop-by-hop, see Section 6.1 of <xref target="Part1"/>).</t>
<t>Under what conditions intermediaries are allowed to modify the header
field's value, insert or delete it.</t>
<t>How the header field might interact with caching (see
<xref target="Part6"/>).</t>
<t>Whether the header field is useful or allowable in trailers (see
Section 4.1 of <xref target="Part1"/>).</t>
<t>Whether the header field ought to be preserved across redirects.</t>
</list>
</t>
</section>
<section title="Registrations" anchor="header.field.registration">
<t>
The Message Header Field Registry shall be updated with the
following permanent registrations:
</t>
<!--AUTOGENERATED FROM extract-header-defs.xslt, do not edit manually-->
<texttable align="left" suppress-title="true" anchor="iana.header.registration.table">
<ttcol>Header Field Name</ttcol>
<ttcol>Protocol</ttcol>
<ttcol>Status</ttcol>
<ttcol>Reference</ttcol>
<c>Accept</c>
<c>http</c>
<c>standard</c>
<c>
<xref target="header.accept"/>
</c>
<c>Accept-Charset</c>
<c>http</c>
<c>standard</c>
<c>
<xref target="header.accept-charset"/>
</c>
<c>Accept-Encoding</c>
<c>http</c>
<c>standard</c>
<c>
<xref target="header.accept-encoding"/>
</c>
<c>Accept-Language</c>
<c>http</c>
<c>standard</c>
<c>
<xref target="header.accept-language"/>
</c>
<c>Allow</c>
<c>http</c>
<c>standard</c>
<c>
<xref target="header.allow"/>
</c>
<c>Content-Encoding</c>
<c>http</c>
<c>standard</c>
<c>
<xref target="header.content-encoding"/>
</c>
<c>Content-Language</c>
<c>http</c>
<c>standard</c>
<c>
<xref target="header.content-language"/>
</c>
<c>Content-Location</c>
<c>http</c>
<c>standard</c>
<c>
<xref target="header.content-location"/>
</c>
<c>Content-Type</c>
<c>http</c>
<c>standard</c>
<c>
<xref target="header.content-type"/>
</c>
<c>Date</c>
<c>http</c>
<c>standard</c>
<c>
<xref target="header.date"/>
</c>
<c>Expect</c>
<c>http</c>
<c>standard</c>
<c>
<xref target="header.expect"/>
</c>
<c>From</c>
<c>http</c>
<c>standard</c>
<c>
<xref target="header.from"/>
</c>
<c>Location</c>
<c>http</c>
<c>standard</c>
<c>
<xref target="header.location"/>
</c>
<c>MIME-Version</c>
<c>http</c>
<c>standard</c>
<c>
<xref target="mime-version"/>
</c>
<c>Max-Forwards</c>
<c>http</c>
<c>standard</c>
<c>
<xref target="header.max-forwards"/>
</c>
<c>Referer</c>
<c>http</c>
<c>standard</c>
<c>
<xref target="header.referer"/>
</c>
<c>Retry-After</c>
<c>http</c>
<c>standard</c>
<c>
<xref target="header.retry-after"/>
</c>
<c>Server</c>
<c>http</c>
<c>standard</c>
<c>
<xref target="header.server"/>
</c>
<c>User-Agent</c>
<c>http</c>
<c>standard</c>
<c>
<xref target="header.user-agent"/>
</c>
<c>Vary</c>
<c>http</c>
<c>standard</c>
<c>
<xref target="header.vary"/>
</c>
</texttable>
<!--(END)-->
<t>
The change controller for the above registrations is:
"IETF (iesg@ietf.org) - Internet Engineering Task Force".
</t>
</section>
</section>
<section title="Content Coding Registry" anchor="content.coding.registry">
<t>
The HTTP Content Coding Registry defines the name space for content
coding names (Section 4.2 of <xref target="Part1"/>).
The content coding registry is maintained at
<eref target="http://www.iana.org/assignments/http-parameters"/>.
</t>
<section title="Procedure" anchor="content.coding.procedure">
<t>
Content Coding registrations MUST include the following fields:
<list style="symbols">
<t>Name</t>
<t>Description</t>
<t>Pointer to specification text</t>
</list>
</t>
<t>
Names of content codings MUST NOT overlap with names of transfer codings
(Section 4 of <xref target="Part1"/>), unless the encoding transformation is identical (as
is the case for the compression codings defined in
Section 4.2 of <xref target="Part1"/>).
</t>
<t>
Values to be added to this name space require IETF Review
(see Section 4.1 of <xref target="RFC5226"/>), and MUST
conform to the purpose of content coding defined in this section.
</t>
</section>
<section title="Registrations" anchor="content.coding.registration">
<t>
The HTTP Content Codings Registry shall be updated with the registrations
below:
</t>
<texttable align="left" suppress-title="true" anchor="iana.content.coding.registration.table">
<ttcol>Name</ttcol>
<ttcol>Description</ttcol>
<ttcol>Reference</ttcol>
<c>compress</c>
<c>UNIX "compress" program method</c>
<c>
Section 4.2.1 of <xref target="Part1"/>
</c>
<c>deflate</c>
<c>"deflate" compression mechanism (<xref target="RFC1951"/>) used inside
the "zlib" data format (<xref target="RFC1950"/>)
</c>
<c>
Section 4.2.2 of <xref target="Part1"/>
</c>
<c>gzip</c>
<c>Same as GNU zip <xref target="RFC1952"/></c>
<c>
Section 4.2.3 of <xref target="Part1"/>
</c>
<c>identity</c>
<c>reserved (synonym for "no encoding" in <xref target="header.accept-encoding" format="none">Accept-Encoding</xref>
header field)</c>
<c>
<xref target="header.accept-encoding"/>
</c>
</texttable>
</section>
</section>
</section>
<section title="Security Considerations" anchor="security.considerations">
<t>
This section is meant to inform application developers, information
providers, and users of the security limitations in HTTP/1.1 as
described by this document. The discussion does not include
definitive solutions to the problems revealed, though it does make
some suggestions for reducing security risks.
</t>
<section title="Transfer of Sensitive Information" anchor="security.sensitive">
<t>
Like any generic data transfer protocol, HTTP cannot regulate the
content of the data that is transferred, nor is there any a priori
method of determining the sensitivity of any particular piece of
information within the context of any given request. Therefore,
applications SHOULD supply as much control over this information as
possible to the provider of that information. Four header fields are
worth special mention in this context: <xref target="header.server" format="none">Server</xref>,
Via, <xref target="header.referer" format="none">Referer</xref> and <xref target="header.from" format="none">From</xref>.
</t>
<t>
Revealing the specific software version of the server might allow the
server machine to become more vulnerable to attacks against software
that is known to contain security holes. Implementers SHOULD make the
<xref target="header.server" format="none">Server</xref> header field a configurable option.
</t>
<t>
Proxies which serve as a portal through a network firewall SHOULD
take special precautions regarding the transfer of header information
that identifies the hosts behind the firewall. In particular, they
SHOULD remove, or replace with sanitized versions, any Via
fields generated behind the firewall.
</t>
<t>
The <xref target="header.referer" format="none">Referer</xref> header field allows reading patterns to be
studied and reverse links drawn. Although it can be very useful, its power
can be abused if user details are not separated from the information
contained in the Referer. Even when the personal information has been
removed, the Referer header field might indicate a private document's URI
whose publication would be inappropriate.
</t>
<t>
The information sent in the <xref target="header.from" format="none">From</xref> field might conflict with
the user's privacy interests or their site's security policy, and hence it
SHOULD NOT be transmitted without the user being able to disable,
enable, and modify the contents of the field. The user MUST be able
to set the contents of this field within a user preference or
application defaults configuration.
</t>
<t>
We suggest, though do not require, that a convenient toggle interface
be provided for the user to enable or disable the sending of
<xref target="header.from" format="none">From</xref> and <xref target="header.referer" format="none">Referer</xref> information.
</t>
<t>
The <xref target="header.user-agent" format="none">User-Agent</xref> (<xref target="header.user-agent"/>) or
<xref target="header.server" format="none">Server</xref> (<xref target="header.server"/>) header fields can
sometimes be used to determine that a specific client or server has a
particular security hole which might be exploited. Unfortunately, this same
information is often used for other valuable purposes for which HTTP
currently has no better mechanism.
</t>
<t>
Furthermore, the <xref target="header.user-agent" format="none">User-Agent</xref> header field might contain enough
entropy to be used, possibly in conjunction with other material, to uniquely
identify the user.
</t>
<t>
Some request methods, like TRACE (<xref target="TRACE"/>), expose information
that was sent in request header fields within the body of their response.
Clients SHOULD be careful with sensitive information, like Cookies,
Authorization credentials, and other header fields that might be used to
collect data from the client.
</t>
</section>
<section title="Encoding Sensitive Information in URIs" anchor="encoding.sensitive.information.in.uris">
<t>
Because the source of a link might be private information or might
reveal an otherwise private information source, it is strongly
recommended that the user be able to select whether or not the
<xref target="header.referer" format="none">Referer</xref> field is sent. For example, a browser client could
have a toggle switch for browsing openly/anonymously, which would
respectively enable/disable the sending of Referer and From
information.
</t>
<t>
Clients SHOULD NOT include a <xref target="header.referer" format="none">Referer</xref> header field in a
(non-secure) HTTP request if the referring page was transferred with a secure
protocol.
</t>
<t>
Authors of services SHOULD NOT use GET-based forms for the submission of
sensitive data because that data will be placed in the request-target. Many
existing servers, proxies, and user agents log or display the request-target
in places where it might be visible to third parties. Such services can
use POST-based form submission instead.
</t>
</section>
<section title="Location Header Fields: Spoofing and Information Leakage" anchor="location.spoofing-leakage">
<t>
If a single server supports multiple organizations that do not trust
one another, then it MUST check the values of <xref target="header.location" format="none">Location</xref> and
<xref target="header.content-location" format="none">Content-Location</xref> header fields in responses that are
generated under control of said organizations to make sure that they do not
attempt to invalidate resources over which they have no authority.
</t>
<t>
Furthermore, appending the fragment identifier from one URI to another
one obtained from a <xref target="header.location" format="none">Location</xref> header field might leak
confidential information to the target server — although the fragment
identifier is not transmitted in the final request, it might be visible to
the user agent through other means, such as scripting.
</t>
</section>
<section title="Security Considerations for CONNECT">
<t>
Since tunneled data is opaque to the proxy, there are additional
risks to tunneling to other well-known or reserved ports.
A HTTP client CONNECTing to port 25 could relay spam
via SMTP, for example. As such, proxies SHOULD restrict CONNECT
access to a small number of known ports.
</t>
</section>
<section title="Privacy Issues Connected to Accept Header Fields" anchor="privacy.issues.connected.to.accept.header.fields">
<t>
Accept header fields can reveal information about the user to all
servers which are accessed. The <xref target="header.accept-language" format="none">Accept-Language</xref> header field
in particular can reveal information the user would consider to be of a
private nature, because the understanding of particular languages is often
strongly correlated to the membership of a particular ethnic group.
User agents which offer the option to configure the contents of an
Accept-Language header field to be sent in every request are strongly
encouraged to let the configuration process include a message which
makes the user aware of the loss of privacy involved.
</t>
<t>
An approach that limits the loss of privacy would be for a user agent
to omit the sending of Accept-Language header fields by default, and to ask
the user whether or not to start sending Accept-Language header fields to a
server if it detects, by looking for any <xref target="header.vary" format="none">Vary</xref> header fields
generated by the server, that such sending could improve the quality
of service.
</t>
<t>
Elaborate user-customized accept header fields sent in every request,
in particular if these include quality values, can be used by servers
as relatively reliable and long-lived user identifiers. Such user
identifiers would allow content providers to do click-trail tracking,
and would allow collaborating content providers to match cross-server
click-trails or form submissions of individual users. Note that for
many users not behind a proxy, the network address of the host
running the user agent will also serve as a long-lived user
identifier. In environments where proxies are used to enhance
privacy, user agents ought to be conservative in offering accept
header field configuration options to end users. As an extreme privacy
measure, proxies could filter the accept header fields in relayed requests.
General purpose user agents which provide a high degree of header field
configurability SHOULD warn users about the loss of privacy which can
be involved.
</t>
</section>
</section>
<section title="Acknowledgments" anchor="acks">
<t>
See Section 9 of <xref target="Part1"/>.
</t>
</section>
</middle>
<back>
<references title="Normative References">
<reference anchor="Part1">
<front>
<title>Hypertext Transfer Protocol (HTTP/1.1): Message Syntax and Routing</title>
<author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
<organization abbrev="Adobe">Adobe Systems Incorporated</organization>
<address><email>fielding@gbiv.com</email></address>
</author>
<author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
<organization abbrev="greenbytes">greenbytes GmbH</organization>
<address><email>julian.reschke@greenbytes.de</email></address>
</author>
<date month="October" year="2012"/>
</front>
<seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p1-messaging-21"/>
</reference>
<reference anchor="Part4">
<front>
<title>Hypertext Transfer Protocol (HTTP/1.1): Conditional Requests</title>
<author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
<organization abbrev="Adobe">Adobe Systems Incorporated</organization>
<address><email>fielding@gbiv.com</email></address>
</author>
<author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
<organization abbrev="greenbytes">greenbytes GmbH</organization>
<address><email>julian.reschke@greenbytes.de</email></address>
</author>
<date month="October" year="2012"/>
</front>
<seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p4-conditional-21"/>
</reference>
<reference anchor="Part5">
<front>
<title>Hypertext Transfer Protocol (HTTP/1.1): Range Requests</title>
<author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
<organization abbrev="Adobe">Adobe Systems Incorporated</organization>
<address><email>fielding@gbiv.com</email></address>
</author>
<author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
<organization abbrev="W3C">World Wide Web Consortium</organization>
<address><email>ylafon@w3.org</email></address>
</author>
<author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
<organization abbrev="greenbytes">greenbytes GmbH</organization>
<address><email>julian.reschke@greenbytes.de</email></address>
</author>
<date month="October" year="2012"/>
</front>
<seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p5-range-21"/>
</reference>
<reference anchor="Part6">
<front>
<title>Hypertext Transfer Protocol (HTTP/1.1): Caching</title>
<author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
<organization abbrev="Adobe">Adobe Systems Incorporated</organization>
<address><email>fielding@gbiv.com</email></address>
</author>
<author initials="M." surname="Nottingham" fullname="Mark Nottingham" role="editor">
<organization>Akamai</organization>
<address><email>mnot@mnot.net</email></address>
</author>
<author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
<organization abbrev="greenbytes">greenbytes GmbH</organization>
<address><email>julian.reschke@greenbytes.de</email></address>
</author>
<date month="October" year="2012"/>
</front>
<seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p6-cache-21"/>
</reference>
<reference anchor="Part7">
<front>
<title>Hypertext Transfer Protocol (HTTP/1.1): Authentication</title>
<author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
<organization abbrev="Adobe">Adobe Systems Incorporated</organization>
<address><email>fielding@gbiv.com</email></address>
</author>
<author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
<organization abbrev="greenbytes">greenbytes GmbH</organization>
<address><email>julian.reschke@greenbytes.de</email></address>
</author>
<date month="October" year="2012"/>
</front>
<seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p7-auth-21"/>
</reference>
<reference anchor="RFC1950">
<front>
<title>ZLIB Compressed Data Format Specification version 3.3</title>
<author initials="L.P." surname="Deutsch" fullname="L. Peter Deutsch">
<organization>Aladdin Enterprises</organization>
<address><email>ghost@aladdin.com</email></address>
</author>
<author initials="J-L." surname="Gailly" fullname="Jean-Loup Gailly"/>
<date month="May" year="1996"/>
</front>
<seriesInfo name="RFC" value="1950"/>
<!--<annotation>
RFC 1950 is an Informational RFC, thus it might be less stable than
this specification. On the other hand, this downward reference was
present since the publication of <xref target="RFC2068" x:fmt="none">RFC 2068</xref> in 1997,
therefore it is unlikely to cause problems in practice. See also
<xref target="BCP97"/>.
</annotation>-->
</reference>
<reference anchor="RFC1951">
<front>
<title>DEFLATE Compressed Data Format Specification version 1.3</title>
<author initials="P." surname="Deutsch" fullname="L. Peter Deutsch">
<organization>Aladdin Enterprises</organization>
<address><email>ghost@aladdin.com</email></address>
</author>
<date month="May" year="1996"/>
</front>
<seriesInfo name="RFC" value="1951"/>
<!--<annotation>
RFC 1951 is an Informational RFC, thus it might be less stable than
this specification. On the other hand, this downward reference was
present since the publication of <xref target="RFC2068" x:fmt="none">RFC 2068</xref> in 1997,
therefore it is unlikely to cause problems in practice. See also
<xref target="BCP97"/>.
</annotation>-->
</reference>
<reference anchor="RFC1952">
<front>
<title>GZIP file format specification version 4.3</title>
<author initials="P." surname="Deutsch" fullname="L. Peter Deutsch">
<organization>Aladdin Enterprises</organization>
<address><email>ghost@aladdin.com</email></address>
</author>
<author initials="J-L." surname="Gailly" fullname="Jean-Loup Gailly">
<address><email>gzip@prep.ai.mit.edu</email></address>
</author>
<author initials="M." surname="Adler" fullname="Mark Adler">
<address><email>madler@alumni.caltech.edu</email></address>
</author>
<author initials="L.P." surname="Deutsch" fullname="L. Peter Deutsch">
<address><email>ghost@aladdin.com</email></address>
</author>
<author initials="G." surname="Randers-Pehrson" fullname="Glenn Randers-Pehrson">
<address><email>randeg@alumni.rpi.edu</email></address>
</author>
<date month="May" year="1996"/>
</front>
<seriesInfo name="RFC" value="1952"/>
<!--<annotation>
RFC 1952 is an Informational RFC, thus it might be less stable than
this specification. On the other hand, this downward reference was
present since the publication of <xref target="RFC2068" x:fmt="none">RFC 2068</xref> in 1997,
therefore it is unlikely to cause problems in practice. See also
<xref target="BCP97"/>.
</annotation>-->
</reference>
<reference anchor="RFC2045">
<front>
<title abbrev="Internet Message Bodies">Multipurpose Internet Mail Extensions (MIME) Part One: Format of Internet Message Bodies</title>
<author initials="N." surname="Freed" fullname="Ned Freed">
<organization>Innosoft International, Inc.</organization>
<address><email>ned@innosoft.com</email></address>
</author>
<author initials="N.S." surname="Borenstein" fullname="Nathaniel S. Borenstein">
<organization>First Virtual Holdings</organization>
<address><email>nsb@nsb.fv.com</email></address>
</author>
<date month="November" year="1996"/>
</front>
<seriesInfo name="RFC" value="2045"/>
</reference>
<reference anchor="RFC2046">
<front>
<title abbrev="Media Types">Multipurpose Internet Mail Extensions (MIME) Part Two: Media Types</title>
<author initials="N." surname="Freed" fullname="Ned Freed">
<organization>Innosoft International, Inc.</organization>
<address><email>ned@innosoft.com</email></address>
</author>
<author initials="N." surname="Borenstein" fullname="Nathaniel S. Borenstein">
<organization>First Virtual Holdings</organization>
<address><email>nsb@nsb.fv.com</email></address>
</author>
<date month="November" year="1996"/>
</front>
<seriesInfo name="RFC" value="2046"/>
</reference>
<reference anchor="RFC2119">
<front>
<title>Key words for use in RFCs to Indicate Requirement Levels</title>
<author initials="S." surname="Bradner" fullname="Scott Bradner">
<organization>Harvard University</organization>
<address><email>sob@harvard.edu</email></address>
</author>
<date month="March" year="1997"/>
</front>
<seriesInfo name="BCP" value="14"/>
<seriesInfo name="RFC" value="2119"/>
</reference>
<reference anchor="RFC3986">
<front>
<title abbrev="URI Generic Syntax">Uniform Resource Identifier (URI): Generic Syntax</title>
<author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
<organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
<address>
<email>timbl@w3.org</email>
<uri>http://www.w3.org/People/Berners-Lee/</uri>
</address>
</author>
<author initials="R." surname="Fielding" fullname="Roy T. Fielding">
<organization abbrev="Day Software">Day Software</organization>
<address>
<email>fielding@gbiv.com</email>
<uri>http://roy.gbiv.com/</uri>
</address>
</author>
<author initials="L." surname="Masinter" fullname="Larry Masinter">
<organization abbrev="Adobe Systems">Adobe Systems Incorporated</organization>
<address>
<email>LMM@acm.org</email>
<uri>http://larry.masinter.net/</uri>
</address>
</author>
<date month="January" year="2005"/>
</front>
<seriesInfo name="STD" value="66"/>
<seriesInfo name="RFC" value="3986"/>
</reference>
<reference anchor="RFC4647">
<front>
<title>Matching of Language Tags</title>
<author initials="A." surname="Phillips" fullname="Addison Phillips" role="editor">
<organization>Yahoo! Inc.</organization>
<address><email>addison@inter-locale.com</email></address>
</author>
<author initials="M." surname="Davis" fullname="Mark Davis" role="editor">
<organization>Google</organization>
<address><email>mark.davis@macchiato.com</email></address>
</author>
<date year="2006" month="September"/>
</front>
<seriesInfo name="BCP" value="47"/>
<seriesInfo name="RFC" value="4647"/>
</reference>
<reference anchor="RFC5234">
<front>
<title abbrev="ABNF for Syntax Specifications">Augmented BNF for Syntax Specifications: ABNF</title>
<author initials="D." surname="Crocker" fullname="Dave Crocker" role="editor">
<organization>Brandenburg InternetWorking</organization>
<address>
<email>dcrocker@bbiw.net</email>
</address>
</author>
<author initials="P." surname="Overell" fullname="Paul Overell">
<organization>THUS plc.</organization>
<address>
<email>paul.overell@thus.net</email>
</address>
</author>
<date month="January" year="2008"/>
</front>
<seriesInfo name="STD" value="68"/>
<seriesInfo name="RFC" value="5234"/>
</reference>
<reference anchor="RFC5646">
<front>
<title>Tags for Identifying Languages</title>
<author initials="A." surname="Phillips" fullname="Addison Phillips" role="editor">
<organization>Lab126</organization>
<address><email>addison@inter-locale.com</email></address>
</author>
<author initials="M." surname="Davis" fullname="Mark Davis" role="editor">
<organization>Google</organization>
<address><email>mark.davis@google.com</email></address>
</author>
<date month="September" year="2009"/>
</front>
<seriesInfo name="BCP" value="47"/>
<seriesInfo name="RFC" value="5646"/>
</reference>
</references>
<references title="Informative References">
<reference anchor="REST" target="http://roy.gbiv.com/pubs/dissertation/top.htm">
<front>
<title>Architectural Styles and the Design of Network-based Software Architectures</title>
<author initials="R.T." surname="Fielding" fullname="Roy T. Fielding">
</author>
<date month="September" year="2000"/>
</front>
<seriesInfo name="Doctoral Dissertation, University of California, Irvine" value=""/>
</reference>
<reference anchor="RFC1123">
<front>
<title>Requirements for Internet Hosts - Application and Support</title>
<author initials="R." surname="Braden" fullname="Robert Braden">
<organization>University of Southern California (USC), Information Sciences Institute</organization>
<address><email>Braden@ISI.EDU</email></address>
</author>
<date month="October" year="1989"/>
</front>
<seriesInfo name="STD" value="3"/>
<seriesInfo name="RFC" value="1123"/>
</reference>
<reference anchor="RFC1945">
<front>
<title abbrev="HTTP/1.0">Hypertext Transfer Protocol -- HTTP/1.0</title>
<author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
<organization>MIT, Laboratory for Computer Science</organization>
<address><email>timbl@w3.org</email></address>
</author>
<author initials="R.T." surname="Fielding" fullname="Roy T. Fielding">
<organization>University of California, Irvine, Department of Information and Computer Science</organization>
<address><email>fielding@ics.uci.edu</email></address>
</author>
<author initials="H.F." surname="Nielsen" fullname="Henrik Frystyk Nielsen">
<organization>W3 Consortium, MIT Laboratory for Computer Science</organization>
<address><email>frystyk@w3.org</email></address>
</author>
<date month="May" year="1996"/>
</front>
<seriesInfo name="RFC" value="1945"/>
</reference>
<reference anchor="RFC2049">
<front>
<title abbrev="MIME Conformance">Multipurpose Internet Mail Extensions (MIME) Part Five: Conformance Criteria and Examples</title>
<author initials="N." surname="Freed" fullname="Ned Freed">
<organization>Innosoft International, Inc.</organization>
<address><email>ned@innosoft.com</email></address>
</author>
<author initials="N.S." surname="Borenstein" fullname="Nathaniel S. Borenstein">
<organization>First Virtual Holdings</organization>
<address><email>nsb@nsb.fv.com</email></address>
</author>
<date month="November" year="1996"/>
</front>
<seriesInfo name="RFC" value="2049"/>
</reference>
<reference anchor="RFC2068">
<front>
<title>Hypertext Transfer Protocol -- HTTP/1.1</title>
<author initials="R." surname="Fielding" fullname="Roy T. Fielding">
<organization>University of California, Irvine, Department of Information and Computer Science</organization>
<address><email>fielding@ics.uci.edu</email></address>
</author>
<author initials="J." surname="Gettys" fullname="Jim Gettys">
<organization>MIT Laboratory for Computer Science</organization>
<address><email>jg@w3.org</email></address>
</author>
<author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
<organization>Digital Equipment Corporation, Western Research Laboratory</organization>
<address><email>mogul@wrl.dec.com</email></address>
</author>
<author initials="H." surname="Nielsen" fullname="Henrik Frystyk Nielsen">
<organization>MIT Laboratory for Computer Science</organization>
<address><email>frystyk@w3.org</email></address>
</author>
<author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
<organization>MIT Laboratory for Computer Science</organization>
<address><email>timbl@w3.org</email></address>
</author>
<date month="January" year="1997"/>
</front>
<seriesInfo name="RFC" value="2068"/>
</reference>
<reference anchor="RFC2076">
<front>
<title abbrev="Internet Message Headers">Common Internet Message Headers</title>
<author initials="J." surname="Palme" fullname="Jacob Palme">
<organization>Stockholm University/KTH</organization>
<address><email>jpalme@dsv.su.se</email></address>
</author>
<date month="February" year="1997"/>
</front>
<seriesInfo name="RFC" value="2076"/>
</reference>
<reference anchor="RFC2277">
<front>
<title abbrev="Charset Policy">IETF Policy on Character Sets and Languages</title>
<author initials="H.T." surname="Alvestrand" fullname="Harald Tveit Alvestrand">
<organization>UNINETT</organization>
<address><email>Harald.T.Alvestrand@uninett.no</email></address>
</author>
<date month="January" year="1998"/>
</front>
<seriesInfo name="BCP" value="18"/>
<seriesInfo name="RFC" value="2277"/>
</reference>
<reference anchor="RFC2295">
<front>
<title abbrev="HTTP Content Negotiation">Transparent Content Negotiation in HTTP</title>
<author initials="K." surname="Holtman" fullname="Koen Holtman">
<organization>Technische Universiteit Eindhoven</organization>
<address>
<email>koen@win.tue.nl</email>
</address>
</author>
<author initials="A.H." surname="Mutz" fullname="Andrew H. Mutz">
<organization>Hewlett-Packard Company</organization>
<address>
<email>mutz@hpl.hp.com</email>
</address>
</author>
<date year="1998" month="March"/>
</front>
<seriesInfo name="RFC" value="2295"/>
</reference>
<reference anchor="RFC2388">
<front>
<title abbrev="multipart/form-data">Returning Values from Forms: multipart/form-data</title>
<author initials="L." surname="Masinter" fullname="Larry Masinter">
<organization>Xerox Palo Alto Research Center</organization>
<address><email>masinter@parc.xerox.com</email></address>
</author>
<date year="1998" month="August"/>
</front>
<seriesInfo name="RFC" value="2388"/>
</reference>
<reference anchor="RFC2557">
<front>
<title abbrev="MIME Encapsulation of Aggregate Documents">MIME Encapsulation of Aggregate Documents, such as HTML (MHTML)</title>
<author initials="F." surname="Palme" fullname="Jacob Palme">
<organization>Stockholm University and KTH</organization>
<address><email>jpalme@dsv.su.se</email></address>
</author>
<author initials="A." surname="Hopmann" fullname="Alex Hopmann">
<organization>Microsoft Corporation</organization>
<address><email>alexhop@microsoft.com</email></address>
</author>
<author initials="N." surname="Shelness" fullname="Nick Shelness">
<organization>Lotus Development Corporation</organization>
<address><email>Shelness@lotus.com</email></address>
</author>
<author initials="E." surname="Stefferud" fullname="Einar Stefferud">
<address><email>stef@nma.com</email></address>
</author>
<date year="1999" month="March"/>
</front>
<seriesInfo name="RFC" value="2557"/>
</reference>
<reference anchor="RFC2616">
<front>
<title>Hypertext Transfer Protocol -- HTTP/1.1</title>
<author initials="R." surname="Fielding" fullname="R. Fielding">
<organization>University of California, Irvine</organization>
<address><email>fielding@ics.uci.edu</email></address>
</author>
<author initials="J." surname="Gettys" fullname="J. Gettys">
<organization>W3C</organization>
<address><email>jg@w3.org</email></address>
</author>
<author initials="J." surname="Mogul" fullname="J. Mogul">
<organization>Compaq Computer Corporation</organization>
<address><email>mogul@wrl.dec.com</email></address>
</author>
<author initials="H." surname="Frystyk" fullname="H. Frystyk">
<organization>MIT Laboratory for Computer Science</organization>
<address><email>frystyk@w3.org</email></address>
</author>
<author initials="L." surname="Masinter" fullname="L. Masinter">
<organization>Xerox Corporation</organization>
<address><email>masinter@parc.xerox.com</email></address>
</author>
<author initials="P." surname="Leach" fullname="P. Leach">
<organization>Microsoft Corporation</organization>
<address><email>paulle@microsoft.com</email></address>
</author>
<author initials="T." surname="Berners-Lee" fullname="T. Berners-Lee">
<organization>W3C</organization>
<address><email>timbl@w3.org</email></address>
</author>
<date month="June" year="1999"/>
</front>
<seriesInfo name="RFC" value="2616"/>
</reference>
<reference anchor="RFC2817">
<front>
<title>Upgrading to TLS Within HTTP/1.1</title>
<author initials="R." surname="Khare" fullname="R. Khare">
<organization>4K Associates / UC Irvine</organization>
<address><email>rohit@4K-associates.com</email></address>
</author>
<author initials="S." surname="Lawrence" fullname="S. Lawrence">
<organization>Agranat Systems, Inc.</organization>
<address><email>lawrence@agranat.com</email></address>
</author>
<date year="2000" month="May"/>
</front>
<seriesInfo name="RFC" value="2817"/>
</reference>
<reference anchor="RFC3629">
<front>
<title>UTF-8, a transformation format of ISO 10646</title>
<author initials="F." surname="Yergeau" fullname="F. Yergeau">
<organization>Alis Technologies</organization>
<address><email>fyergeau@alis.com</email></address>
</author>
<date month="November" year="2003"/>
</front>
<seriesInfo name="STD" value="63"/>
<seriesInfo name="RFC" value="3629"/>
</reference>
<reference anchor="RFC3864">
<front>
<title>Registration Procedures for Message Header Fields</title>
<author initials="G." surname="Klyne" fullname="G. Klyne">
<organization>Nine by Nine</organization>
<address><email>GK-IETF@ninebynine.org</email></address>
</author>
<author initials="M." surname="Nottingham" fullname="M. Nottingham">
<organization>BEA Systems</organization>
<address><email>mnot@pobox.com</email></address>
</author>
<author initials="J." surname="Mogul" fullname="J. Mogul">
<organization>HP Labs</organization>
<address><email>JeffMogul@acm.org</email></address>
</author>
<date year="2004" month="September"/>
</front>
<seriesInfo name="BCP" value="90"/>
<seriesInfo name="RFC" value="3864"/>
</reference>
<reference anchor="RFC4288">
<front>
<title>Media Type Specifications and Registration Procedures</title>
<author initials="N." surname="Freed" fullname="N. Freed">
<organization>Sun Microsystems</organization>
<address>
<email>ned.freed@mrochek.com</email>
</address>
</author>
<author initials="J." surname="Klensin" fullname="J. Klensin">
<address>
<email>klensin+ietf@jck.com</email>
</address>
</author>
<date year="2005" month="December"/>
</front>
<seriesInfo name="BCP" value="13"/>
<seriesInfo name="RFC" value="4288"/>
</reference>
<reference anchor="RFC5226">
<front>
<title>Guidelines for Writing an IANA Considerations Section in RFCs</title>
<author initials="T." surname="Narten" fullname="T. Narten">
<organization>IBM</organization>
<address><email>narten@us.ibm.com</email></address>
</author>
<author initials="H." surname="Alvestrand" fullname="H. Alvestrand">
<organization>Google</organization>
<address><email>Harald@Alvestrand.no</email></address>
</author>
<date year="2008" month="May"/>
</front>
<seriesInfo name="BCP" value="26"/>
<seriesInfo name="RFC" value="5226"/>
</reference>
<reference anchor="RFC5322">
<front>
<title>Internet Message Format</title>
<author initials="P." surname="Resnick" fullname="P. Resnick">
<organization>Qualcomm Incorporated</organization>
</author>
<date year="2008" month="October"/>
</front>
<seriesInfo name="RFC" value="5322"/>
</reference>
<reference anchor="RFC5789">
<front>
<title>PATCH Method for HTTP</title>
<author initials="L." surname="Dusseault" fullname="L. Dusseault">
<organization>Linden Lab</organization>
</author>
<author initials="J." surname="Snell" fullname="J. Snell"/>
<date year="2010" month="March"/>
</front>
<seriesInfo name="RFC" value="5789"/>
</reference>
<reference anchor="RFC5987">
<front>
<title>Character Set and Language Encoding for Hypertext Transfer Protocol (HTTP) Header Field Parameters</title>
<author initials="J. F." surname="Reschke" fullname="Julian F. Reschke">
<organization abbrev="greenbytes">greenbytes GmbH</organization>
<address>
<postal>
<street>Hafenweg 16</street>
<city>Muenster</city><region>NW</region><code>48155</code>
<country>Germany</country>
</postal>
<email>julian.reschke@greenbytes.de</email>
<uri>http://greenbytes.de/tech/webdav/</uri>
</address>
</author>
<date month="August" year="2010"/>
</front>
<seriesInfo name="RFC" value="5987"/>
</reference>
<reference anchor="RFC6151">
<front>
<title>Updated Security Considerations for the MD5 Message-Digest and the HMAC-MD5 Algorithms</title>
<author initials="S." surname="Turner" fullname="S. Turner"/>
<author initials="L." surname="Chen" fullname="L. Chen"/>
<date year="2011" month="March"/>
</front>
<seriesInfo name="RFC" value="6151"/>
</reference>
<reference anchor="RFC6266">
<front>
<title abbrev="Content-Disposition in HTTP">Use of the Content-Disposition Header Field
in the Hypertext Transfer Protocol (HTTP)</title>
<author initials="J. F." surname="Reschke" fullname="Julian F. Reschke">
<organization abbrev="greenbytes">greenbytes GmbH</organization>
<address>
<email>julian.reschke@greenbytes.de</email>
</address>
</author>
<date month="June" year="2011"/>
</front>
<seriesInfo name="RFC" value="6266"/>
</reference>
<reference anchor="status-308">
<front>
<title abbrev="HTTP Status Code 308">The Hypertext Transfer Protocol (HTTP) Status Code 308 (Permanent Redirect)</title>
<author initials="J. F." surname="Reschke" fullname="Julian F. Reschke">
<organization abbrev="greenbytes">greenbytes GmbH</organization>
<address>
<email>julian.reschke@greenbytes.de</email>
</address>
</author>
<date month="March" year="2012"/>
</front>
<seriesInfo name="Internet-Draft" value="draft-reschke-http-status-308-07"/>
</reference>
</references>
<section title="Differences between HTTP and MIME" anchor="differences.between.http.and.mime">
<t>
HTTP/1.1 uses many of the constructs defined for Internet Mail (<xref target="RFC5322"/>) and the Multipurpose Internet Mail Extensions (MIME <xref target="RFC2045"/>) to
allow a message body to be transmitted in an open variety of
representations and with extensible mechanisms. However, RFC 2045
discusses mail, and HTTP has a few features that are different from
those described in MIME. These differences were carefully chosen
to optimize performance over binary connections, to allow greater
freedom in the use of new media types, to make date comparisons
easier, and to acknowledge the practice of some early HTTP servers
and clients.
</t>
<t>
This appendix describes specific areas where HTTP differs from MIME.
Proxies and gateways to strict MIME environments SHOULD be
aware of these differences and provide the appropriate conversions
where necessary. Proxies and gateways from MIME environments to HTTP
also need to be aware of the differences because some conversions
might be required.
</t>
<section title="MIME-Version" anchor="mime-version">
<iref primary="true" item="MIME-Version header field"/>
<t>
HTTP is not a MIME-compliant protocol. However, HTTP/1.1 messages MAY
include a single MIME-Version header field to indicate what
version of the MIME protocol was used to construct the message. Use
of the MIME-Version header field indicates that the message is in
full conformance with the MIME protocol (as defined in <xref target="RFC2045"/>).
Proxies/gateways are responsible for ensuring full conformance (where
possible) when exporting HTTP messages to strict MIME environments.
</t>
<figure><iref primary="true" item="Grammar" subitem="MIME-Version"/><artwork type="abnf2616"><![CDATA[
MIME-Version = 1*DIGIT "." 1*DIGIT
]]></artwork></figure>
<t>
MIME version "1.0" is the default for use in HTTP/1.1. However,
HTTP/1.1 message parsing and semantics are defined by this document
and not the MIME specification.
</t>
</section>
<section title="Conversion to Canonical Form" anchor="conversion.to.canonical.form">
<t>
MIME requires that an Internet mail body-part be converted to
canonical form prior to being transferred, as described in Section 4 of <xref target="RFC2049"/>.
<xref target="canonicalization.and.text.defaults"/> of this document describes the forms
allowed for subtypes of the "text" media type when transmitted over
HTTP. <xref target="RFC2046"/> requires that content with a type of "text" represent
line breaks as CRLF and forbids the use of CR or LF outside of line
break sequences. HTTP allows CRLF, bare CR, and bare LF to indicate a
line break within text content when a message is transmitted over
HTTP.
</t>
<t>
Where it is possible, a proxy or gateway from HTTP to a strict MIME
environment SHOULD translate all line breaks within the text media
types described in <xref target="canonicalization.and.text.defaults"/>
of this document to the RFC 2049 canonical form of CRLF. Note, however, that
this might be complicated by the presence of a <xref target="header.content-encoding" format="none">Content-Encoding</xref>
and by the fact that HTTP allows the use of some character encodings which do
not use octets 13 and 10 to represent CR and LF, respectively, as is the case
for some multi-byte character encodings.
</t>
<t>
Conversion will break any cryptographic
checksums applied to the original content unless the original content
is already in canonical form. Therefore, the canonical form is
recommended for any content that uses such checksums in HTTP.
</t>
</section>
<section title="Conversion of Date Formats" anchor="conversion.of.date.formats">
<t>
HTTP/1.1 uses a restricted set of date formats (<xref target="http.date"/>) to
simplify the process of date comparison. Proxies and gateways from
other protocols SHOULD ensure that any <xref target="header.date" format="none">Date</xref> header field
present in a message conforms to one of the HTTP/1.1 formats and rewrite
the date if necessary.
</t>
</section>
<section title="Introduction of Content-Encoding" anchor="introduction.of.content-encoding">
<t>
MIME does not include any concept equivalent to HTTP/1.1's
<xref target="header.content-encoding" format="none">Content-Encoding</xref> header field. Since this acts as a modifier
on the media type, proxies and gateways from HTTP to MIME-compliant
protocols MUST either change the value of the <xref target="header.content-type" format="none">Content-Type</xref>
header field or decode the representation before forwarding the message.
(Some experimental applications of Content-Type for Internet mail have used
a media-type parameter of ";conversions=<content-coding>" to perform
a function equivalent to Content-Encoding. However, this parameter is
not part of the MIME standards).
</t>
</section>
<section title="No Content-Transfer-Encoding" anchor="no.content-transfer-encoding">
<iref item="Content-Transfer-Encoding header field"/>
<t>
HTTP does not use the Content-Transfer-Encoding field of MIME.
Proxies and gateways from MIME-compliant protocols to HTTP MUST
remove any Content-Transfer-Encoding
prior to delivering the response message to an HTTP client.
</t>
<t>
Proxies and gateways from HTTP to MIME-compliant protocols are
responsible for ensuring that the message is in the correct format
and encoding for safe transport on that protocol, where "safe
transport" is defined by the limitations of the protocol being used.
Such a proxy or gateway SHOULD label the data with an appropriate
Content-Transfer-Encoding if doing so will improve the likelihood of
safe transport over the destination protocol.
</t>
</section>
<section title="MHTML and Line Length Limitations" anchor="mhtml.line.length">
<t>
HTTP implementations which share code with MHTML <xref target="RFC2557"/> implementations
need to be aware of MIME line length limitations. Since HTTP does not
have this limitation, HTTP does not fold long lines. MHTML messages
being transported by HTTP follow all conventions of MHTML, including
line length limitations and folding, canonicalization, etc., since
HTTP transports all message-bodies as payload (see <xref target="multipart.types"/>) and
does not interpret the content or any MIME header lines that might be
contained therein.
</t>
</section>
</section>
<section title="Additional Features" anchor="additional.features">
<t>
<xref target="RFC1945"/> and <xref target="RFC2068"/> document protocol elements used by some
existing HTTP implementations, but not consistently and correctly
across most HTTP/1.1 applications. Implementers are advised to be
aware of these features, but cannot rely upon their presence in, or
interoperability with, other HTTP/1.1 applications. Some of these
describe proposed experimental features, and some describe features
that experimental deployment found lacking that are now addressed in
the base HTTP/1.1 specification.
</t>
<t>
A number of other header fields, such as Content-Disposition and Title,
from SMTP and MIME are also often implemented (see <xref target="RFC6266"/>
and <xref target="RFC2076"/>).
</t>
</section>
<section title="Changes from RFC 2616" anchor="changes.from.rfc.2616">
<t>
Remove base URI setting semantics for "<xref target="header.content-location" format="none">Content-Location</xref>" due to
poor implementation support, which was caused by too many broken servers emitting
bogus Content-Location header fields, and also the potentially undesirable effect
of potentially breaking relative links in content-negotiated resources.
(<xref target="header.content-location"/>)
</t>
<t>
Clarify definition of POST.
(<xref target="POST"/>)
</t>
<t>
Remove requirement to handle all Content-* header fields; ban use of
Content-Range with PUT.
(<xref target="PUT"/>)
</t>
<t>
Take over definition of CONNECT method from <xref target="RFC2817"/>.
(<xref target="CONNECT"/>)
</t>
<t>
Restrict "<xref target="header.max-forwards" format="none">Max-Forwards</xref>" header field to OPTIONS and TRACE
(previously, extension methods could have used it as well).
(<xref target="header.max-forwards"/>)
</t>
<t>
The ABNF for the "<xref target="header.expect" format="none">Expect</xref>" header field has been both fixed
(allowing parameters for value-less expectations as well) and simplified
(allowing trailing semicolons after "100-continue" when they were invalid
before).
(<xref target="header.expect"/>)
</t>
<t>
Remove ISO-8859-1 special-casing in <xref target="header.accept-charset" format="none">Accept-Charset</xref>.
(<xref target="header.accept-charset"/>)
</t>
<t>
Allow "<xref target="header.referer" format="none">Referer</xref>" field value of "about:blank" as alternative to
not specifying it.
(<xref target="header.referer"/>)
</t>
<t>
Broadened the definition of <xref target="status.203" format="none">203 (Non-Authoritative Information)</xref>
to include cases of payload transformations as well.
(<xref target="status.203"/>)
</t>
<t>
Status codes <xref target="status.301" format="none">301</xref>, <xref target="status.302" format="none">302</xref>, and <xref target="status.307" format="none">307</xref>:
removed the normative requirements on both response payloads and user interaction.
(<xref target="status.3xx"/>)
</t>
<t>
Failed to consider that there are many other request methods that are safe
to automatically redirect, and further that the user agent is able to make
that determination based on the request method semantics.
Furthermore, allow user agents to rewrite the method from POST to GET
for status codes <xref target="status.301" format="none">301</xref> and <xref target="status.302" format="none">302</xref>.
(Sections <xref format="counter" target="status.301"/>,
<xref format="counter" target="status.302"/> and
<xref format="counter" target="status.307"/>)
</t>
<t>
Deprecate <xref target="status.305" format="none">305 (Use Proxy)</xref> status code, because user agents did
not implement it. It used to indicate that the target resource needs to be
accessed through the proxy given by the <xref target="header.location" format="none">Location</xref> field. The
Location field gave the URI of the proxy. The recipient was expected to
repeat this single request via the proxy.
(<xref target="status.305"/>)
</t>
<t>
Define status <xref target="status.426" format="none">426 (Upgrade Required)</xref> (this was incorporated
from <xref target="RFC2817"/>).
(<xref target="status.426"/>)
</t>
<t>
Correct syntax of "<xref target="header.location" format="none">Location</xref>" header field to allow URI
references (including relative references and fragments), as referred symbol
"absoluteURI" wasn't what was expected, and add some clarifications as to
when use of fragments would not be appropriate.
(<xref target="header.location"/>)
</t>
<t>
Reclassify "<xref target="header.allow" format="none">Allow</xref>" as response header field, removing the
option to specify it in a PUT request.
Relax the server requirement on the contents of the Allow header field and
remove requirement on clients to always trust the header field value.
(<xref target="header.allow"/>)
</t>
<t>
In the description of the "<xref target="header.server" format="none">Server</xref>" header field, the
"Via" field was described as a SHOULD. The requirement was and
is stated correctly in the description of the Via header field in
Section 5.7 of <xref target="Part1"/>.
(<xref target="header.server"/>)
</t>
<t>
Clarify contexts that charset is used in.
(<xref target="character.sets"/>)
</t>
<t>
Remove the default character encoding of "ISO-8859-1" for text media types; the
default now is whatever the media type definition says.
(<xref target="canonicalization.and.text.defaults"/>)
</t>
<t>
Registration of Content Codings now requires IETF Review
(<xref target="content.coding.registry"/>)
</t>
<t>
Remove definition of "Content-MD5 header" field because it was inconsistently
implemented with respect to partial responses, and also because of known
deficiencies in the hash algorithm itself (see <xref target="RFC6151"/> for details).
</t>
<t>
Introduce Method Registry.
(<xref target="method.registry"/>)
</t>
<t>
Take over the Status Code Registry, previously defined in
Section 7.1 of <xref target="RFC2817"/>.
(<xref target="status.code.registry"/>)
</t>
<t>
Remove reference to non-existant identity transfer-coding value tokens.
(<xref target="no.content-transfer-encoding"/>)
</t>
<t>
Remove discussion of Content-Disposition header field, it is now defined
by <xref target="RFC6266"/>.
(<xref target="additional.features"/>)
</t>
</section>
<section title="Imported ABNF" anchor="imported.abnf">
<t>
The following core rules are included by
reference, as defined in Appendix B.1 of <xref target="RFC5234"/>:
ALPHA (letters), CR (carriage return), CRLF (CR LF), CTL (controls),
DIGIT (decimal 0-9), DQUOTE (double quote),
HEXDIG (hexadecimal 0-9/A-F/a-f), HTAB (horizontal tab), LF (line feed),
OCTET (any 8-bit sequence of data), SP (space), and
VCHAR (any visible US-ASCII character).
</t>
<t>
The rules below are defined in <xref target="Part1"/>:
</t>
<figure><artwork type="abnf2616"><![CDATA[
BWS = <BWS, defined in [Part1], Section 3.2.1>
OWS = <OWS, defined in [Part1], Section 3.2.1>
RWS = <RWS, defined in [Part1], Section 3.2.1>
URI-reference = <URI-reference, defined in [Part1], Section 2.7>
absolute-URI = <absolute-URI, defined in [Part1], Section 2.7>
comment = <comment, defined in [Part1], Section 3.2.4>
field-name = <comment, defined in [Part1], Section 3.2>
partial-URI = <partial-URI, defined in [Part1], Section 2.7>
quoted-string = <quoted-string, defined in [Part1], Section 3.2.4>
token = <token, defined in [Part1], Section 3.2.4>
word = <word, defined in [Part1], Section 3.2.4>
]]></artwork></figure>
</section>
<section title="Collected ABNF" anchor="collected.abnf">
<figure>
<artwork type="abnf" name="p2-semantics.parsed-abnf"><![CDATA[
Accept = [ ( "," / ( media-range [ accept-params ] ) ) *( OWS "," [
OWS ( media-range [ accept-params ] ) ] ) ]
Accept-Charset = *( "," OWS ) ( ( charset / "*" ) [ weight ] ) *( OWS
"," [ OWS ( ( charset / "*" ) [ weight ] ) ] )
Accept-Encoding = [ ( "," / ( codings [ weight ] ) ) *( OWS "," [ OWS
( codings [ weight ] ) ] ) ]
Accept-Language = *( "," OWS ) ( language-range [ weight ] ) *( OWS
"," [ OWS ( language-range [ weight ] ) ] )
Allow = [ ( "," / method ) *( OWS "," [ OWS method ] ) ]
BWS = <BWS, defined in [Part1], Section 3.2.1>
Content-Encoding = *( "," OWS ) content-coding *( OWS "," [ OWS
content-coding ] )
Content-Language = *( "," OWS ) language-tag *( OWS "," [ OWS
language-tag ] )
Content-Location = absolute-URI / partial-URI
Content-Type = media-type
Date = HTTP-date
Expect = *( "," OWS ) expectation *( OWS "," [ OWS expectation ] )
From = mailbox
GMT = %x47.4D.54 ; GMT
HTTP-date = rfc1123-date / obs-date
Location = URI-reference
MIME-Version = 1*DIGIT "." 1*DIGIT
Max-Forwards = 1*DIGIT
OWS = <OWS, defined in [Part1], Section 3.2.1>
RWS = <RWS, defined in [Part1], Section 3.2.1>
Referer = absolute-URI / partial-URI
Retry-After = HTTP-date / delta-seconds
Server = product *( RWS ( product / comment ) )
URI-reference = <URI-reference, defined in [Part1], Section 2.7>
User-Agent = product *( RWS ( product / comment ) )
Vary = "*" / ( *( "," OWS ) field-name *( OWS "," [ OWS field-name ]
) )
absolute-URI = <absolute-URI, defined in [Part1], Section 2.7>
accept-ext = OWS ";" OWS token [ "=" word ]
accept-params = weight *accept-ext
asctime-date = day-name SP date3 SP time-of-day SP year
attribute = token
charset = token
codings = content-coding / "identity" / "*"
comment = <comment, defined in [Part1], Section 3.2.4>
content-coding = token
date1 = day SP month SP year
date2 = day "-" month "-" 2DIGIT
date3 = month SP ( 2DIGIT / ( SP DIGIT ) )
day = 2DIGIT
day-name = %x4D.6F.6E ; Mon
/ %x54.75.65 ; Tue
/ %x57.65.64 ; Wed
/ %x54.68.75 ; Thu
/ %x46.72.69 ; Fri
/ %x53.61.74 ; Sat
/ %x53.75.6E ; Sun
day-name-l = %x4D.6F.6E.64.61.79 ; Monday
/ %x54.75.65.73.64.61.79 ; Tuesday
/ %x57.65.64.6E.65.73.64.61.79 ; Wednesday
/ %x54.68.75.72.73.64.61.79 ; Thursday
/ %x46.72.69.64.61.79 ; Friday
/ %x53.61.74.75.72.64.61.79 ; Saturday
/ %x53.75.6E.64.61.79 ; Sunday
delta-seconds = 1*DIGIT
expect-name = token
expect-param = expect-name [ BWS "=" BWS expect-value ]
expect-value = token / quoted-string
expectation = expect-name [ BWS "=" BWS expect-value ] *( OWS ";" [
OWS expect-param ] )
field-name = <comment, defined in [Part1], Section 3.2>
hour = 2DIGIT
language-range = <language-range, defined in [RFC4647], Section 2.1>
language-tag = <Language-Tag, defined in [RFC5646], Section 2.1>
mailbox = <mailbox, defined in [RFC5322], Section 3.4>
media-range = ( "*/*" / ( type "/*" ) / ( type "/" subtype ) ) *( OWS
";" OWS parameter )
media-type = type "/" subtype *( OWS ";" OWS parameter )
method = token
minute = 2DIGIT
month = %x4A.61.6E ; Jan
/ %x46.65.62 ; Feb
/ %x4D.61.72 ; Mar
/ %x41.70.72 ; Apr
/ %x4D.61.79 ; May
/ %x4A.75.6E ; Jun
/ %x4A.75.6C ; Jul
/ %x41.75.67 ; Aug
/ %x53.65.70 ; Sep
/ %x4F.63.74 ; Oct
/ %x4E.6F.76 ; Nov
/ %x44.65.63 ; Dec
obs-date = rfc850-date / asctime-date
parameter = attribute "=" value
partial-URI = <partial-URI, defined in [Part1], Section 2.7>
product = token [ "/" product-version ]
product-version = token
quoted-string = <quoted-string, defined in [Part1], Section 3.2.4>
qvalue = ( "0" [ "." *3DIGIT ] ) / ( "1" [ "." *3"0" ] )
rfc1123-date = day-name "," SP date1 SP time-of-day SP GMT
rfc850-date = day-name-l "," SP date2 SP time-of-day SP GMT
second = 2DIGIT
subtype = token
time-of-day = hour ":" minute ":" second
token = <token, defined in [Part1], Section 3.2.4>
type = token
value = word
weight = OWS ";" OWS "q=" qvalue
word = <word, defined in [Part1], Section 3.2.4>
year = 4DIGIT
]]></artwork>
</figure>
</section>
<section title="Change Log (to be removed by RFC Editor before publication)" anchor="change.log">
<section title="Since RFC 2616">
<t>
Extracted relevant partitions from <xref target="RFC2616"/>.
</t>
</section>
<section title="Since draft-ietf-httpbis-p2-semantics-00">
<t>
Closed issues:
<list style="symbols">
<t>
<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/5"/>:
"Via is a MUST"
(<eref target="http://purl.org/NET/http-errata#via-must"/>)
</t>
<t>
<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/6"/>:
"Fragments allowed in Location"
(<eref target="http://purl.org/NET/http-errata#location-fragments"/>)
</t>
<t>
<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/10"/>:
"Safe Methods vs Redirection"
(<eref target="http://purl.org/NET/http-errata#saferedirect"/>)
</t>
<t>
<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/17"/>:
"Revise description of the POST method"
(<eref target="http://purl.org/NET/http-errata#post"/>)
</t>
<t>
<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/35"/>:
"Normative and Informative references"
</t>
<t>
<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/42"/>:
"RFC2606 Compliance"
</t>
<t>
<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/65"/>:
"Informative references"
</t>
<t>
<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/84"/>:
"Redundant cross-references"
</t>
</list>
</t>
<t>
Other changes:
<list style="symbols">
<t>
Move definitions of 304 and 412 condition codes to <xref target="Part4"/>
</t>
</list>
</t>
</section>
<section title="Since draft-ietf-httpbis-p3-payload-00">
<t>
Closed issues:
<list style="symbols">
<t>
<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/8"/>:
"Media Type Registrations"
(<eref target="http://purl.org/NET/http-errata#media-reg"/>)
</t>
<t>
<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/14"/>:
"Clarification regarding quoting of charset values"
(<eref target="http://purl.org/NET/http-errata#charactersets"/>)
</t>
<t>
<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/16"/>:
"Remove 'identity' token references"
(<eref target="http://purl.org/NET/http-errata#identity"/>)
</t>
<t>
<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/25"/>:
"Accept-Encoding BNF"
</t>
<t>
<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/35"/>:
"Normative and Informative references"
</t>
<t>
<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/46"/>:
"RFC1700 references"
</t>
<t>
<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/55"/>:
"Updating to RFC4288"
</t>
<t>
<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/65"/>:
"Informative references"
</t>
<t>
<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/66"/>:
"ISO-8859-1 Reference"
</t>
<t>
<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/68"/>:
"Encoding References Normative"
</t>
<t>
<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/86"/>:
"Normative up-to-date references"
</t>
</list>
</t>
</section>
<section title="Since draft-ietf-httpbis-p2-semantics-01">
<t>
Closed issues:
<list style="symbols">
<t>
<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/21"/>:
"PUT side effects"
</t>
<t>
<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/91"/>:
"Duplicate Host header requirements"
</t>
</list>
</t>
<t>
Ongoing work on ABNF conversion (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/36"/>):
<list style="symbols">
<t>
Move "Product Tokens" section (back) into Part 1, as "token" is used
in the definition of the Upgrade header field.
</t>
<t>
Add explicit references to BNF syntax and rules imported from other parts of the specification.
</t>
<t>
Copy definition of delta-seconds from Part6 instead of referencing it.
</t>
</list>
</t>
</section>
<section title="Since draft-ietf-httpbis-p3-payload-01">
<t>
Ongoing work on ABNF conversion (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/36"/>):
<list style="symbols">
<t>
Add explicit references to BNF syntax and rules imported from other parts of the specification.
</t>
</list>
</t>
</section>
<section title="Since draft-ietf-httpbis-p2-semantics-02" anchor="changes.since.02">
<t>
Closed issues:
<list style="symbols">
<t>
<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/24"/>:
"Requiring Allow in 405 responses"
</t>
<t>
<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/59"/>:
"Status Code Registry"
</t>
<t>
<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/61"/>:
"Redirection vs. Location"
</t>
<t>
<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/70"/>:
"Cacheability of 303 response"
</t>
<t>
<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/76"/>:
"305 Use Proxy"
</t>
<t>
<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/105"/>:
"Classification for Allow header field"
</t>
<t>
<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/112"/>:
"PUT - 'store under' vs 'store at'"
</t>
</list>
</t>
<t>
Ongoing work on IANA Message Header Field Registration (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/40"/>):
<list style="symbols">
<t>
Reference RFC 3984, and update header field registrations for header
fields defined in this document.
</t>
</list>
</t>
<t>
Ongoing work on ABNF conversion (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/36"/>):
<list style="symbols">
<t>
Replace string literals when the string really is case-sensitive (method).
</t>
</list>
</t>
</section>
<section title="Since draft-ietf-httpbis-p3-payload-02" anchor="changes.3.since.02">
<t>
Closed issues:
<list style="symbols">
<t>
<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/67"/>:
"Quoting Charsets"
</t>
<t>
<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/105"/>:
"Classification for Allow header field"
</t>
<t>
<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/115"/>:
"missing default for qvalue in description of Accept-Encoding"
</t>
</list>
</t>
<t>
Ongoing work on IANA Message Header Field Registration (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/40"/>):
<list style="symbols">
<t>
Reference RFC 3984, and update header field registrations for header
fields defined in this document.
</t>
</list>
</t>
</section>
<section title="Since draft-ietf-httpbis-p2-semantics-03" anchor="changes.since.03">
<t>
Closed issues:
<list style="symbols">
<t>
<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/98"/>:
"OPTIONS payload bodies"
</t>
<t>
<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/119"/>:
"Description of CONNECT should refer to RFC2817"
</t>
<t>
<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/125"/>:
"Location Content-Location reference request/response mixup"
</t>
</list>
</t>
<t>
Ongoing work on Method Registry (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/72"/>):
<list style="symbols">
<t>
Added initial proposal for registration process, plus initial
content (non-HTTP/1.1 methods to be added by a separate specification).
</t>
</list>
</t>
</section>
<section title="Since draft-ietf-httpbis-p3-payload-03" anchor="changes.3.since.03">
<t>
Closed issues:
<list style="symbols">
<t>
<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/67"/>:
"Quoting Charsets"
</t>
<t>
<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/113"/>:
"language tag matching (Accept-Language) vs RFC4647"
</t>
<t>
<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/121"/>:
"RFC 1806 has been replaced by RFC2183"
</t>
</list>
</t>
<t>
Other changes:
<list style="symbols">
<t>
<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/68"/>:
"Encoding References Normative" — rephrase the annotation and reference
BCP97.
</t>
</list>
</t>
</section>
<section title="Since draft-ietf-httpbis-p2-semantics-04" anchor="changes.since.04">
<t>
Closed issues:
<list style="symbols">
<t>
<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/103"/>:
"Content-*"
</t>
<t>
<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/132"/>:
"RFC 2822 is updated by RFC 5322"
</t>
</list>
</t>
<t>
Ongoing work on ABNF conversion (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/36"/>):
<list style="symbols">
<t>
Use "/" instead of "|" for alternatives.
</t>
<t>
Introduce new ABNF rules for "bad" whitespace ("BWS"), optional
whitespace ("OWS") and required whitespace ("RWS").
</t>
<t>
Rewrite ABNFs to spell out whitespace rules, factor out
header field value format definitions.
</t>
</list>
</t>
</section>
<section title="Since draft-ietf-httpbis-p3-payload-04" anchor="changes.3.since.04">
<t>
Closed issues:
<list style="symbols">
<t>
<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/132"/>:
"RFC 2822 is updated by RFC 5322"
</t>
</list>
</t>
<t>
Ongoing work on ABNF conversion (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/36"/>):
<list style="symbols">
<t>
Use "/" instead of "|" for alternatives.
</t>
<t>
Introduce new ABNF rules for "bad" whitespace ("BWS"), optional
whitespace ("OWS") and required whitespace ("RWS").
</t>
<t>
Rewrite ABNFs to spell out whitespace rules, factor out
header field value format definitions.
</t>
</list>
</t>
</section>
<section title="Since draft-ietf-httpbis-p2-semantics-05" anchor="changes.since.05">
<t>
Closed issues:
<list style="symbols">
<t>
<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/94"/>:
"reason-phrase BNF"
</t>
</list>
</t>
<t>
Final work on ABNF conversion (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/36"/>):
<list style="symbols">
<t>
Add appendix containing collected and expanded ABNF, reorganize ABNF introduction.
</t>
</list>
</t>
</section>
<section title="Since draft-ietf-httpbis-p3-payload-05" anchor="changes.3.since.05">
<t>
Closed issues:
<list style="symbols">
<t>
<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/118"/>:
"Join "Differences Between HTTP Entities and RFC 2045 Entities"?"
</t>
</list>
</t>
<t>
Final work on ABNF conversion (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/36"/>):
<list style="symbols">
<t>
Add appendix containing collected and expanded ABNF, reorganize ABNF introduction.
</t>
</list>
</t>
<t>
Other changes:
<list style="symbols">
<t>
Move definition of quality values into Part 1.
</t>
</list>
</t>
</section>
<section title="Since draft-ietf-httpbis-p2-semantics-06" anchor="changes.since.06">
<t>
Closed issues:
<list style="symbols">
<t>
<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/144"/>:
"Clarify when Referer is sent"
</t>
<t>
<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/164"/>:
"status codes vs methods"
</t>
<t>
<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/170"/>:
"Do not require "updates" relation for specs that register status codes or method names"
</t>
</list>
</t>
</section>
<section title="Since draft-ietf-httpbis-p3-payload-06" anchor="changes.3.since.06">
<t>
Closed issues:
<list style="symbols">
<t>
<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/80"/>:
"Content-Location isn't special"
</t>
<t>
<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/155"/>:
"Content Sniffing"
</t>
</list>
</t>
</section>
<section title="Since draft-ietf-httpbis-p2-semantics-07" anchor="changes.since.07">
<t>
Closed issues:
<list style="symbols">
<t>
<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/27"/>:
"Idempotency"
</t>
<t>
<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/33"/>:
"TRACE security considerations"
</t>
<t>
<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/110"/>:
"Clarify rules for determining what entities a response carries"
</t>
<t>
<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/140"/>:
"update note citing RFC 1945 and 2068"
</t>
<t>
<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/182"/>:
"update note about redirect limit"
</t>
<t>
<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/191"/>:
"Location header field ABNF should use 'URI'"
</t>
<t>
<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/192"/>:
"fragments in Location vs status 303"
</t>
<t>
<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/198"/>:
"move IANA registrations for optional status codes"
</t>
</list>
</t>
<t>
Partly resolved issues:
<list style="symbols">
<t>
<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/171"/>:
"Are OPTIONS and TRACE safe?"
</t>
</list>
</t>
</section>
<section title="Since draft-ietf-httpbis-p3-payload-07" anchor="changes.3.since.07">
<t>
Closed issues:
<list style="symbols">
<t>
<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/13"/>:
"Updated reference for language tags"
</t>
<t>
<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/110"/>:
"Clarify rules for determining what entities a response carries"
</t>
<t>
<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/154"/>:
"Content-Location base-setting problems"
</t>
<t>
<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/155"/>:
"Content Sniffing"
</t>
<t>
<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/188"/>:
"pick IANA policy (RFC5226) for Transfer Coding / Content Coding"
</t>
<t>
<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/189"/>:
"move definitions of gzip/deflate/compress to part 1"
</t>
</list>
</t>
<t>
Partly resolved issues:
<list style="symbols">
<t>
<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/148"/>:
"update IANA requirements wrt Transfer-Coding values" (add the
IANA Considerations subsection)
</t>
<t>
<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/149"/>:
"update IANA requirements wrt Content-Coding values" (add the
IANA Considerations subsection)
</t>
</list>
</t>
</section>
<section title="Since draft-ietf-httpbis-p2-semantics-08" anchor="changes.since.08">
<t>
Closed issues:
<list style="symbols">
<t>
<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/10"/>:
"Safe Methods vs Redirection" (we missed the introduction to the <xref target="status.3xx" format="none">3xx</xref>
status codes when fixing this previously)
</t>
</list>
</t>
</section>
<section title="Since draft-ietf-httpbis-p3-payload-08" anchor="changes.3.since.08">
<t>
Closed issues:
<list style="symbols">
<t>
<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/81"/>:
"Content Negotiation for media types"
</t>
<t>
<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/181"/>:
"Accept-Language: which RFC4647 filtering?"
</t>
</list>
</t>
</section>
<section title="Since draft-ietf-httpbis-p2-semantics-09" anchor="changes.since.09">
<t>
Closed issues:
<list style="symbols">
<t>
<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/43"/>:
"Fragment combination / precedence during redirects"
</t>
</list>
</t>
<t>
Partly resolved issues:
<list style="symbols">
<t>
<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/185"/>:
"Location header field payload handling"
</t>
<t>
<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/196"/>:
"Term for the requested resource's URI"
</t>
</list>
</t>
</section>
<section title="Since draft-ietf-httpbis-p3-payload-09" anchor="changes.3.since.09">
<t>
Closed issues:
<list style="symbols">
<t>
<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/122"/>:
"MIME-Version not listed in P1, general header fields"
</t>
<t>
<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/143"/>:
"IANA registry for content/transfer encodings"
</t>
<t>
<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/155"/>:
"Content Sniffing"
</t>
<t>
<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/200"/>:
"use of term "word" when talking about header field structure"
</t>
</list>
</t>
<t>
Partly resolved issues:
<list style="symbols">
<t>
<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/196"/>:
"Term for the requested resource's URI"
</t>
</list>
</t>
</section>
<section title="Since draft-ietf-httpbis-p2-semantics-10" anchor="changes.since.10">
<t>
Closed issues:
<list style="symbols">
<t>
<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/69"/>:
"Clarify 'Requested Variant'"
</t>
<t>
<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/109"/>:
"Clarify entity / representation / variant terminology"
</t>
<t>
<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/139"/>:
"Methods and Caching"
</t>
<t>
<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/190"/>:
"OPTIONS vs Max-Forwards"
</t>
<t>
<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/199"/>:
"Status codes and caching"
</t>
<t>
<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/220"/>:
"consider removing the 'changes from 2068' sections"
</t>
</list>
</t>
</section>
<section title="Since draft-ietf-httpbis-p3-payload-10" anchor="changes.3.since.10">
<t>
Closed issues:
<list style="symbols">
<t>
<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/69"/>:
"Clarify 'Requested Variant'"
</t>
<t>
<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/80"/>:
"Content-Location isn't special"
</t>
<t>
<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/90"/>:
"Delimiting messages with multipart/byteranges"
</t>
<t>
<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/109"/>:
"Clarify entity / representation / variant terminology"
</t>
<t>
<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/136"/>:
"confusing req. language for Content-Location"
</t>
<t>
<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/167"/>:
"Content-Location on 304 responses"
</t>
<t>
<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/183"/>:
"'requested resource' in content-encoding definition"
</t>
<t>
<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/220"/>:
"consider removing the 'changes from 2068' sections"
</t>
</list>
</t>
<t>
Partly resolved issues:
<list style="symbols">
<t>
<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/178"/>:
"Content-MD5 and partial responses"
</t>
</list>
</t>
</section>
<section title="Since draft-ietf-httpbis-p2-semantics-11" anchor="changes.since.11">
<t>
Closed issues:
<list style="symbols">
<t>
<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/229"/>:
"Considerations for new status codes"
</t>
<t>
<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/230"/>:
"Considerations for new methods"
</t>
<t>
<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/232"/>:
"User-Agent guidelines" (relating to the 'User-Agent' header field)
</t>
</list>
</t>
</section>
<section title="Since draft-ietf-httpbis-p3-payload-11" anchor="changes.3.since.11">
<t>
Closed issues:
<list style="symbols">
<t>
<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/123"/>:
"Factor out Content-Disposition"
</t>
</list>
</t>
</section>
<section title="Since draft-ietf-httpbis-p2-semantics-12" anchor="changes.since.12">
<t>
Closed issues:
<list style="symbols">
<t>
<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/43"/>:
"Fragment combination / precedence during redirects" (added warning
about having a fragid on the redirect might cause inconvenience in
some cases)
</t>
<t>
<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/79"/>:
"Content-* vs. PUT"
</t>
<t>
<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/88"/>:
"205 Bodies"
</t>
<t>
<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/102"/>:
"Understanding Content-* on non-PUT requests"
</t>
<t>
<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/103"/>:
"Content-*"
</t>
<t>
<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/104"/>:
"Header field type defaulting"
</t>
<t>
<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/112"/>:
"PUT - 'store under' vs 'store at'"
</t>
<t>
<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/137"/>:
"duplicate ABNF for reason-phrase"
</t>
<t>
<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/180"/>:
"Note special status of Content-* prefix in header field registration procedures"
</t>
<t>
<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/203"/>:
"Max-Forwards vs extension methods"
</t>
<t>
<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/213"/>:
"What is the value space of HTTP status codes?" (actually fixed in
draft-ietf-httpbis-p2-semantics-11)
</t>
<t>
<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/224"/>:
"Header Field Classification"
</t>
<t>
<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/225"/>:
"PUT side effect: invalidation or just stale?"
</t>
<t>
<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/226"/>:
"proxies not supporting certain methods"
</t>
<t>
<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/239"/>:
"Migrate CONNECT from RFC2817 to p2"
</t>
<t>
<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/240"/>:
"Migrate Upgrade details from RFC2817"
</t>
<t>
<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/267"/>:
"clarify PUT semantics'"
</t>
<t>
<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/275"/>:
"duplicate ABNF for 'Method'"
</t>
<t>
<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/276"/>:
"untangle ABNFs for header fields"
</t>
</list>
</t>
</section>
<section title="Since draft-ietf-httpbis-p3-payload-12" anchor="changes.3.since.12">
<t>
Closed issues:
<list style="symbols">
<t>
<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/224"/>:
"Header Field Classification"
</t>
<t>
<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/276"/>:
"untangle ABNFs for header fields"
</t>
<t>
<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/277"/>:
"potentially misleading MAY in media-type def"
</t>
</list>
</t>
</section>
<section title="Since draft-ietf-httpbis-p2-semantics-13" anchor="changes.since.13">
<t>
Closed issues:
<list style="symbols">
<t>
<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/276"/>:
"untangle ABNFs for header fields"
</t>
<t>
<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/251"/>:
"message body in CONNECT request"
</t>
</list>
</t>
</section>
<section title="Since draft-ietf-httpbis-p3-payload-13" anchor="changes.3.since.13">
<t>
Closed issues:
<list style="symbols">
<t>
<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/20"/>:
"Default charsets for text media types"
</t>
<t>
<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/178"/>:
"Content-MD5 and partial responses"
</t>
<t>
<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/276"/>:
"untangle ABNFs for header fields"
</t>
<t>
<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/281"/>:
"confusing undefined parameter in media range example"
</t>
</list>
</t>
</section>
<section title="Since draft-ietf-httpbis-p2-semantics-14" anchor="changes.since.14">
<t>
Closed issues:
<list style="symbols">
<t>
<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/255"/>:
"Clarify status code for rate limiting"
</t>
<t>
<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/294"/>:
"clarify 403 forbidden"
</t>
<t>
<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/296"/>:
"Clarify 203 Non-Authoritative Information"
</t>
<t>
<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/298"/>:
"update default reason phrase for 413"
</t>
</list>
</t>
</section>
<section title="Since draft-ietf-httpbis-p3-payload-14" anchor="changes.3.since.14">
<t>
None.
</t>
</section>
<section title="Since draft-ietf-httpbis-p2-semantics-15" anchor="changes.since.15">
<t>
Closed issues:
<list style="symbols">
<t>
<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/285"/>:
"Strength of requirements on Accept re: 406"
</t>
<t>
<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/303"/>:
"400 response isn't generic"
</t>
</list>
</t>
</section>
<section title="Since draft-ietf-httpbis-p3-payload-15" anchor="changes.3.since.15">
<t>
Closed issues:
<list style="symbols">
<t>
<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/285"/>:
"Strength of requirements on Accept re: 406"
</t>
</list>
</t>
</section>
<section title="Since draft-ietf-httpbis-p2-semantics-16" anchor="changes.since.16">
<t>
Closed issues:
<list style="symbols">
<t>
<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/160"/>:
"Redirects and non-GET methods"
</t>
<t>
<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/186"/>:
"Document HTTP's error-handling philosophy"
</t>
<t>
<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/231"/>:
"Considerations for new header fields"
</t>
<t>
<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/310"/>:
"clarify 303 redirect on HEAD"
</t>
</list>
</t>
</section>
<section title="Since draft-ietf-httpbis-p3-payload-16" anchor="changes.3.since.16">
<t>
Closed issues:
<list style="symbols">
<t>
<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/186"/>:
"Document HTTP's error-handling philosophy"
</t>
</list>
</t>
</section>
<section title="Since draft-ietf-httpbis-p2-semantics-17" anchor="changes.since.17">
<t>
Closed issues:
<list style="symbols">
<t>
<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/185"/>:
"Location header field payload handling"
</t>
<t>
<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/255"/>:
"Clarify status code for rate limiting" (change backed out because
a new status code is being defined for this purpose)
</t>
<t>
<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/312"/>:
"should there be a permanent variant of 307"
</t>
<t>
<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/325"/>:
"When are Location's semantics triggered?"
</t>
<t>
<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/327"/>:
"'expect' grammar missing OWS"
</t>
<t>
<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/329"/>:
"header field considerations: quoted-string vs use of double quotes"
</t>
</list>
</t>
</section>
<section title="Since draft-ietf-httpbis-p3-payload-17" anchor="changes.3.since.17">
<t>
Closed issues:
<list style="symbols">
<t>
<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/323"/>:
"intended maturity level vs normative references"
</t>
</list>
</t>
</section>
<section title="Since draft-ietf-httpbis-p2-semantics-18" anchor="changes.since.18">
<t>
Closed issues:
<list style="symbols">
<t>
<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/227"/>:
"Combining HEAD responses"
</t>
<t>
<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/238"/>:
"Requirements for user intervention during redirects"
</t>
<t>
<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/250"/>:
"message-body in CONNECT response"
</t>
<t>
<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/295"/>:
"Applying original fragment to 'plain' redirected URI"
</t>
<t>
<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/302"/>:
"Misplaced text on connection handling in p2"
</t>
<t>
<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/331"/>:
"clarify that 201 doesn't require Location header fields"
</t>
<t>
<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/332"/>:
"relax requirements on hypertext in 3/4/5xx error responses"
</t>
<t>
<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/333"/>:
"example for 426 response should have a payload"
</t>
<t>
<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/336"/>:
"drop indirection entries for status codes"
</t>
</list>
</t>
</section>
<section title="Since draft-ietf-httpbis-p3-payload-18" anchor="changes.3.since.18">
<t>
Closed issues:
<list style="symbols">
<t>
<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/330"/>:
"is ETag a representation header field?"
</t>
<t>
<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/338"/>:
"Content-Location doesn't constrain the cardinality of representations"
</t>
<t>
<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/346"/>:
"make IANA policy definitions consistent"
</t>
</list>
</t>
</section>
<section title="Since draft-ietf-httpbis-p2-semantics-19 and draft-ietf-httpbis-p3-payload-19" anchor="changes.since.19">
<t>
Closed issues:
<list style="symbols">
<t>
<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/312"/>:
"should there be a permanent variant of 307"
</t>
<t>
<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/347"/>:
"clarify that 201 can imply *multiple* resources were created"
</t>
<t>
<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/351"/>:
"merge P2 and P3"
</t>
<t>
<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/361"/>:
"ABNF requirements for recipients"
</t>
<t>
<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/364"/>:
"Capturing more information in the method registry"
</t>
<t>
<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/368"/>:
"note introduction of new IANA registries as normative changes"
</t>
</list>
</t>
</section>
<section title="Since draft-ietf-httpbis-p2-semantics-20" anchor="changes.since.20">
<t>
Closed issues:
<list style="symbols">
<t>
<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/378"/>:
"is 'q=' case-sensitive?"
</t>
</list>
</t>
<t>
Other changes:
<list style="symbols">
<t>
Conformance criteria and considerations regarding error handling are
now defined in Part 1.
</t>
<t>
Properly explain what HTTP semantics are and why.
Rewrite introductory description of methods.
Rewrite definition of "safe" to be more operable and weaken the original
same-origin restrictions to be more consistent with modern UAs.
Rewrite definition of "idempotent", add definition of "cacheable".
</t>
<t>
Conneg terminology change: "server-driven" => "proactive" (UA sends Accept* fields),
"agent-driven" => "reactive" (UA waits for 300/Alternatives)
</t>
<t>
Move description of "100-continue" from Part 1 over here.
</t>
<t>
Move definition of "Vary" header field from Part 6 over here.
</t>
<t>
Rewrite definition of "representation".
</t>
</list>
</t>
</section>
</section>
</back>
</rfc>| PAFTECH AB 2003-2026 | 2026-04-23 14:17:50 |