One document matched: draft-fielding-http-p2-semantics-00.xml
<?xml version="1.0" encoding="utf-8"?>
<!DOCTYPE rfc [
<!ENTITY MAY "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>MAY</bcp14>">
<!ENTITY MUST "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>MUST</bcp14>">
<!ENTITY MUST-NOT "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>MUST NOT</bcp14>">
<!ENTITY OPTIONAL "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>OPTIONAL</bcp14>">
<!ENTITY RECOMMENDED "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>RECOMMENDED</bcp14>">
<!ENTITY REQUIRED "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>REQUIRED</bcp14>">
<!ENTITY SHALL "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>SHALL</bcp14>">
<!ENTITY SHALL-NOT "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>SHALL NOT</bcp14>">
<!ENTITY SHOULD "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>SHOULD</bcp14>">
<!ENTITY SHOULD-NOT "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>SHOULD NOT</bcp14>">
<!ENTITY messaging "[Part 1]">
<!ENTITY payload "[Part 3]">
<!ENTITY conditional "[Part 4]">
<!ENTITY range "[Part 5]">
<!ENTITY caching "[Part 6]">
<!ENTITY auth "[Part 7]">
<!ENTITY content-negotiation "[Part 3]">
<!ENTITY diff2045entity "[Part 3]">
<!ENTITY uri "[Part 1]">
<!ENTITY http-url "[Part 1]">
<!ENTITY http-version "[Part 1]">
<!ENTITY use100 "[Part 1]">
<!ENTITY qvalue "[Part 3]">
<!ENTITY header-accept "[Part 3]">
<!ENTITY header-accept-charset "[Part 3]">
<!ENTITY header-accept-encoding "[Part 3]">
<!ENTITY header-accept-language "[Part 3]">
<!ENTITY header-accept-ranges "[Part 3]">
<!ENTITY header-age "[Part 6]">
<!ENTITY header-authorization "[Part 7]">
<!ENTITY header-cache-control "[Part 6]">
<!ENTITY header-content-location "[Part 3]">
<!ENTITY header-content-range "[Part 5]">
<!ENTITY header-etag "[Part 4]">
<!ENTITY header-expires "[Part 6]">
<!ENTITY header-host "[Part 1]">
<!ENTITY header-if-match "[Part 4]">
<!ENTITY header-if-modified-since "[Part 4]">
<!ENTITY header-if-none-match "[Part 4]">
<!ENTITY header-if-range "[Part 5]">
<!ENTITY header-if-unmodified-since "[Part 4]">
<!ENTITY header-pragma "[Part 6]">
<!ENTITY header-proxy-authenticate "[Part 7]">
<!ENTITY header-proxy-authorization "[Part 7]">
<!ENTITY header-range "[Part 5]">
<!ENTITY header-upgrade "[Part 1]">
<!ENTITY header-te "[Part 1]">
<!ENTITY header-vary "[Part 6]">
<!ENTITY header-via "[Part 1]">
<!ENTITY header-warning "[Part 6]">
<!ENTITY header-www-authenticate "[Part 7]">
<!ENTITY message-body "[Part 1]">
]>
<?rfc toc="yes" ?>
<?rfc symrefs="yes" ?>
<?rfc sortrefs="yes" ?>
<?rfc compact="yes"?>
<?rfc subcompact="no" ?>
<?rfc linkmailto="no" ?>
<?rfc editing="no" ?>
<?rfc-ext allow-markup-in-artwork="yes" ?>
<?rfc-ext include-references-in-index="yes" ?>
<rfc obsoletes="2068, 2616, 2617" category="std"
ipr="full3978" docName="draft-fielding-http-p2-semantics-00"
xmlns:x='http://purl.org/net/xml2rfc/ext' xmlns:ed="http://greenbytes.de/2002/rfcedit">
<front>
<title abbrev="HTTP/1.1">HTTP/1.1, part 2: Message Semantics</title>
<author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
<organization abbrev="Day Software">Day Software</organization>
<address>
<postal>
<street>23 Corporate Plaza DR, Suite 280</street>
<city>Newport Beach</city>
<region>CA</region>
<code>92660</code>
<country>USA</country>
</postal>
<phone>+1-949-706-5300</phone>
<facsimile>+1-949-706-5305</facsimile>
<email>fielding@gbiv.com</email>
<uri>http://roy.gbiv.com/</uri>
</address>
</author>
<author initials="J." surname="Gettys" fullname="James Gettys">
<organization abbrev="HP">Hewlett-Packard Company</organization>
<address>
<postal>
<street>HP Labs, Cambridge Research Laboratory</street>
<street>One Cambridge Center</street>
<city>Cambridge</city>
<region>MA</region>
<code>02138</code>
<country>USA</country>
</postal>
<email>Jim.Gettys@hp.com</email>
</address>
</author>
<author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
<organization abbrev="HP">Hewlett-Packard Company</organization>
<address>
<postal>
<street>HP Labs, Large Scale Systems Group</street>
<street>1501 Page Mill Road, MS 1177</street>
<city>Palo Alto</city>
<region>CA</region>
<code>94304</code>
<country>USA</country>
</postal>
<email>JeffMogul@acm.org</email>
</address>
</author>
<author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
<organization abbrev="Microsoft">Microsoft Corporation</organization>
<address>
<postal>
<street>1 Microsoft Way</street>
<city>Redmond</city>
<region>WA</region>
<code>98052</code>
<country>USA</country>
</postal>
<email>henrikn@microsoft.com</email>
</address>
</author>
<author initials="L." surname="Masinter" fullname="Larry Masinter">
<organization abbrev="Adobe Systems">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>LMM@acm.org</email>
<uri>http://larry.masinter.net/</uri>
</address>
</author>
<author initials="P." surname="Leach" fullname="Paul J. Leach">
<organization abbrev="Microsoft">Microsoft Corporation</organization>
<address>
<postal>
<street>1 Microsoft Way</street>
<city>Redmond</city>
<region>WA</region>
<code>98052</code>
</postal>
<email>paulle@microsoft.com</email>
</address>
</author>
<author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
<organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
<address>
<postal>
<street>MIT Laboratory for Computer Science</street>
<street>545 Technology Square</street>
<city>Cambridge</city>
<region>MA</region>
<code>02139</code>
<country>USA</country>
</postal>
<facsimile>+1 (617) 258 8682</facsimile>
<email>timbl@w3.org</email>
</address>
</author>
<date month="November" year="2007"/>
<abstract>
<t>
The Hypertext Transfer Protocol (HTTP) is an application-level
protocol for distributed, collaborative, hypermedia information
systems. HTTP has been in use by the World Wide Web global information
initiative since 1990. This document is Part 2 of the eight-part specification
that defines the protocol referred to as "HTTP/1.1" and, taken together,
updates RFC 2616 and RFC 2617. Part 2 defines the semantics of HTTP messages
as expressed by request methods, request-header fields, response status codes,
and response-header fields.
</t>
</abstract>
</front>
<middle>
<section title="Introduction" anchor="introduction">
<t>
This document will define aspects of HTTP related to request and response
semantics. Right now it only includes the extracted relevant sections of
RFC 2616 with only minor edits.
</t>
<t>
The HTTP protocol is a request/response protocol. A client sends a
request to the server in the form of a request method, URI, and
protocol version, followed by a MIME-like message containing request
modifiers, client information, and possible body content over a
connection with a server. The server responds with a status line,
including the message's protocol version and a success or error code,
followed by a MIME-like message containing server information, entity
metainformation, and possible entity-body content. The relationship
between HTTP and MIME is described in &diff2045entity;.
</t>
</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 white space. By
convention, the products are listed in order of their significance
for identifying the application.
</t>
<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="product"/><iref primary="true" item="Grammar" subitem="product-version"/>
product = token ["/" product-version]
product-version = token
</artwork></figure>
<t>
Examples:
</t>
<figure><artwork type="example">
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 character &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="Method" anchor="method">
<t>
The Method token indicates the method to be performed on the
resource identified by the Request-URI. The method is case-sensitive.
</t>
<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Method"/><iref primary="true" item="Grammar" subitem="extension-method"/>
Method = "OPTIONS" ; <xref target="OPTIONS"/>
| "GET" ; <xref target="GET"/>
| "HEAD" ; <xref target="HEAD"/>
| "POST" ; <xref target="POST"/>
| "PUT" ; <xref target="PUT"/>
| "DELETE" ; <xref target="DELETE"/>
| "TRACE" ; <xref target="TRACE"/>
| "CONNECT" ; <xref target="CONNECT"/>
| extension-method
extension-method = token
</artwork></figure>
<t>
The list of methods allowed by a resource can be specified in an
Allow header field (<xref target="header.allow"/>). The return code of the response
always notifies the client whether a method is currently allowed on a
resource, since the set of allowed methods can change dynamically. An
origin server &SHOULD; return the status code 405 (Method Not Allowed)
if the method is known by the origin server but not allowed for the
requested resource, and 501 (Not Implemented) if the method is
unrecognized or not implemented by the origin server. The methods GET
and HEAD &MUST; be supported by all general-purpose servers. All other
methods are &OPTIONAL;; however, if the above methods are implemented,
they &MUST; be implemented with the same semantics as those specified
in <xref target="method.definitions"/>.
</t>
</section>
<section title="Request Header Fields" anchor="request.header.fields">
<t>
The request-header fields allow the client to pass additional
information about the request, and about the client itself, to the
server. These fields act as request modifiers, with semantics
equivalent to the parameters on a programming language method
invocation.
</t>
<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="request-header"/>
request-header = Accept ; &header-accept;
| Accept-Charset ; &header-accept-charset;
| Accept-Encoding ; &header-accept-encoding;
| Accept-Language ; &header-accept-language;
| Authorization ; &header-authorization;
| Expect ; <xref target="header.expect"/>
| From ; <xref target="header.from"/>
| Host ; &header-host;
| If-Match ; &header-if-match;
| If-Modified-Since ; &header-if-modified-since;
| If-None-Match ; &header-if-none-match;
| If-Range ; &header-if-range;
| If-Unmodified-Since ; &header-if-unmodified-since;
| Max-Forwards ; <xref target="header.max-forwards"/>
| Proxy-Authorization ; &header-proxy-authorization;
| Range ; &header-range;
| Referer ; <xref target="header.referer"/>
| TE ; &header-te;
| User-Agent ; <xref target="header.user-agent"/>
</artwork></figure>
<t>
Request-header field names can be extended reliably only in
combination with a change in the protocol version. However, new or
experimental header fields &MAY; be given the semantics of request-header
fields if all parties in the communication recognize them to
be request-header fields. Unrecognized header fields are treated as
entity-header fields.
</t>
</section>
<section title="Status Code and Reason Phrase" anchor="status.code.and.reason.phrase">
<t>
The Status-Code element is a 3-digit integer result code of the
attempt to understand and satisfy the request. These codes are fully
defined in <xref target="status.codes"/>. The Reason-Phrase is intended to give a short
textual description of the Status-Code. The Status-Code is intended
for use by automata and the Reason-Phrase is intended for the human
user. The client is not required to examine or display the Reason-Phrase.
</t>
<t>
The individual values of the numeric status codes defined for
HTTP/1.1, and an example set of corresponding Reason-Phrase's, are
presented below. The reason phrases listed here are only
recommendations -- they &MAY; be replaced by local equivalents without
affecting the protocol.
</t>
<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Status-Code"/><iref primary="true" item="Grammar" subitem="extension-code"/><iref primary="true" item="Grammar" subitem="Reason-Phrase"/>
Status-Code =
"100" ; <xref target="status.100"/>: Continue
| "101" ; <xref target="status.101"/>: Switching Protocols
| "200" ; <xref target="status.200"/>: OK
| "201" ; <xref target="status.201"/>: Created
| "202" ; <xref target="status.202"/>: Accepted
| "203" ; <xref target="status.203"/>: Non-Authoritative Information
| "204" ; <xref target="status.204"/>: No Content
| "205" ; <xref target="status.205"/>: Reset Content
| "206" ; <xref target="status.206"/>: Partial Content
| "300" ; <xref target="status.300"/>: Multiple Choices
| "301" ; <xref target="status.301"/>: Moved Permanently
| "302" ; <xref target="status.302"/>: Found
| "303" ; <xref target="status.303"/>: See Other
| "304" ; <xref target="status.304"/>: Not Modified
| "305" ; <xref target="status.305"/>: Use Proxy
| "307" ; <xref target="status.307"/>: Temporary Redirect
| "400" ; <xref target="status.400"/>: Bad Request
| "401" ; <xref target="status.401"/>: Unauthorized
| "402" ; <xref target="status.402"/>: Payment Required
| "403" ; <xref target="status.403"/>: Forbidden
| "404" ; <xref target="status.404"/>: Not Found
| "405" ; <xref target="status.405"/>: Method Not Allowed
| "406" ; <xref target="status.406"/>: Not Acceptable
| "407" ; <xref target="status.407"/>: Proxy Authentication Required
| "408" ; <xref target="status.408"/>: Request Time-out
| "409" ; <xref target="status.409"/>: Conflict
| "410" ; <xref target="status.410"/>: Gone
| "411" ; <xref target="status.411"/>: Length Required
| "412" ; <xref target="status.412"/>: Precondition Failed
| "413" ; <xref target="status.413"/>: Request Entity Too Large
| "414" ; <xref target="status.414"/>: Request-URI Too Large
| "415" ; <xref target="status.415"/>: Unsupported Media Type
| "416" ; <xref target="status.416"/>: Requested range not satisfiable
| "417" ; <xref target="status.417"/>: Expectation Failed
| "500" ; <xref target="status.500"/>: Internal Server Error
| "501" ; <xref target="status.501"/>: Not Implemented
| "502" ; <xref target="status.502"/>: Bad Gateway
| "503" ; <xref target="status.503"/>: Service Unavailable
| "504" ; <xref target="status.504"/>: Gateway Time-out
| "505" ; <xref target="status.505"/>: HTTP Version not supported
| extension-code
extension-code = 3DIGIT
Reason-Phrase = *<TEXT, excluding CR, LF>
</artwork></figure>
<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 entity returned
with the response, since that entity is likely to include human-readable
information which will explain the unusual status.
</t>
</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 resource identified by the Request-URI.
</t>
<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="response-header"/>
response-header = Accept-Ranges ; &header-accept-ranges;
| Age ; &header-age;
| ETag ; &header-etag;
| Location ; <xref target="header.location"/>
| Proxy-Authenticate ; &header-proxy-authenticate;
| Retry-After ; <xref target="header.retry-after"/>
| Server ; <xref target="header.server"/>
| Vary ; &header-vary;
| WWW-Authenticate ; &header-www-authenticate;
</artwork></figure>
<t>
Response-header field names can be extended reliably only in
combination with a change in the protocol version. However, new or
experimental header fields &MAY; be given the semantics of response-header
fields if all parties in the communication recognize them to
be response-header fields. Unrecognized header fields are treated as
entity-header fields.
</t>
</section>
<section title="Entity" anchor="entity">
<t>
Request and Response messages &MAY; transfer an entity if not otherwise
restricted by the request method or response status code. An entity
consists of entity-header fields and an entity-body, although some
responses will only include the entity-headers. HTTP entity-body and
entity-header fields are defined in &payload;.
</t>
<t>
An entity-body is only present in a message when a message-body is
present, as described in &message-body;. The entity-body is obtained
from the message-body by decoding any Transfer-Encoding that might
have been applied to ensure safe and proper transfer of the message.
</t>
</section>
<section title="Method Definitions" anchor="method.definitions">
<t>
The set of common methods for HTTP/1.1 is defined below. Although
this set can be expanded, additional methods cannot be assumed to
share the same semantics for separately extended clients and servers.
The Host request-header field (&header-host;) &MUST; accompany all
HTTP/1.1 requests.
</t>
<section title="Safe and Idempotent Methods" anchor="safe.and.idempotent">
<section title="Safe Methods" anchor="safe.methods">
<t>
Implementors should be aware that the software represents the user in
their interactions over the Internet, and should be careful to allow
the user to be aware of any actions they might take which may have an
unexpected significance to themselves or others.
</t>
<t>
In particular, the convention has been established that the GET and
HEAD methods &SHOULD-NOT; have the significance of taking an action
other than retrieval. These methods ought to be considered "safe".
This allows user agents to represent other methods, such as POST, PUT
and DELETE, in a special way, so that the user is made aware of the
fact that a possibly unsafe action is being requested.
</t>
<t>
Naturally, it is not possible to ensure that the server does not
generate side-effects as a result of performing a GET request; in
fact, some dynamic resources consider that a feature. The important
distinction here is that the user did not request the side-effects,
so therefore cannot be held accountable for them.
</t>
</section>
<section title="Idempotent Methods" anchor="idempotent.methods">
<t>
Methods can also have the property of "idempotence" in that (aside
from error or expiration issues) the side-effects of N > 0 identical
requests is the same as for a single request. The methods GET, HEAD,
PUT and DELETE share this property. Also, the methods OPTIONS and
TRACE &SHOULD-NOT; have side effects, and so are inherently idempotent.
</t>
<t>
However, it is possible that a sequence of several requests is non-idempotent,
even if all of the methods executed in that sequence are
idempotent. (A sequence is idempotent if a single execution of the
entire sequence always yields a result that is not changed by a
reexecution of all, or part, of that sequence.) For example, a
sequence is non-idempotent if its result depends on a value that is
later modified in the same sequence.
</t>
<t>
A sequence that never has side effects is idempotent, by definition
(provided that no concurrent operations are being executed on the
same set of resources).
</t>
</section>
</section>
<section title="OPTIONS" anchor="OPTIONS">
<iref primary="true" item="OPTIONS method" x:for-anchor=""/>
<iref primary="true" item="Methods" subitem="OPTIONS" x:for-anchor=""/>
<t>
The OPTIONS method represents a request for information about the
communication options available on the request/response chain
identified by the Request-URI. This method allows the 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 this method are not cacheable.
</t>
<t>
If the OPTIONS request includes an entity-body (as indicated by the
presence of Content-Length or Transfer-Encoding), then the media type
&MUST; be indicated by a Content-Type 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. A server that does not support such an
extension &MAY; discard the request body.
</t>
<t>
If the Request-URI 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 compliance (or lack thereof).
</t>
<t>
If the Request-URI is not an asterisk, the OPTIONS request applies
only to the options that are available when communicating with that
resource.
</t>
<t>
A 200 response &SHOULD; include any header fields that indicate
optional features implemented by the server and applicable to that
resource (e.g., Allow), possibly including extensions not defined by
this specification. The response body, if any, &SHOULD; also include
information about the communication options. The format for such a
body is not defined by this specification, but might be defined by
future extensions to HTTP. Content negotiation &MAY; be used to select
the appropriate response format. If no response body is included, the
response &MUST; include a Content-Length field with a field-value of
"0".
</t>
<t>
The Max-Forwards request-header field &MAY; be used to target a
specific proxy in the request chain. When a proxy receives an OPTIONS
request on an absoluteURI for which request forwarding is permitted,
the proxy &MUST; check for a Max-Forwards field. If the Max-Forwards
field-value is zero ("0"), the proxy &MUST-NOT; forward the message;
instead, the proxy &SHOULD; respond with its own communication options.
If the Max-Forwards field-value is an integer greater than zero, the
proxy &MUST; decrement the field-value when it forwards the request. 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="GET" anchor="GET">
<iref primary="true" item="GET method" x:for-anchor=""/>
<iref primary="true" item="Methods" subitem="GET" x:for-anchor=""/>
<t>
The GET method means retrieve whatever information (in the form of an
entity) is identified by the Request-URI. If the Request-URI refers
to a data-producing process, it is the produced data which shall be
returned as the entity 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. A conditional GET
method requests that the entity be transferred only under the
circumstances described by the conditional header field(s). The
conditional GET method is intended to reduce unnecessary network
usage by allowing cached entities 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. A partial GET requests
that only part of the entity be transferred, as described in &header-range;.
The partial GET method is intended to reduce unnecessary
network usage by allowing partially-retrieved entities to be
completed without transferring data already held by the client.
</t>
<t>
The response to a GET request is cacheable if and only if it meets
the requirements for HTTP caching described in &caching;.
</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" x:for-anchor=""/>
<iref primary="true" item="Methods" subitem="HEAD" x:for-anchor=""/>
<t>
The HEAD method is identical to GET except that the server &MUST-NOT;
return a message-body in the response. The metainformation contained
in the HTTP headers 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 metainformation about the entity implied by the
request without transferring the entity-body itself. This method is
often used for testing hypertext links for validity, accessibility,
and recent modification.
</t>
<t>
The response to a HEAD request &MAY; be cacheable in the sense that the
information contained in the response &MAY; be used to update a
previously cached entity from that resource. If the new field values
indicate that the cached entity differs from the current entity (as
would be indicated by a change in Content-Length, Content-MD5, ETag
or Last-Modified), then the cache &MUST; treat the cache entry as
stale.
</t>
</section>
<section title="POST" anchor="POST">
<iref primary="true" item="POST method" x:for-anchor=""/>
<iref primary="true" item="Methods" subitem="POST" x:for-anchor=""/>
<t>
The POST method is used to request that the origin server accept the
entity enclosed in the request as data to be processed by the resource
identified by the Request-URI in the Request-Line. 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 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 200
(OK) or 204 (No Content) is the appropriate response status,
depending on whether or not the response includes an entity that
describes the result.
</t>
<t>
If a resource has been created on the origin server, the response
&SHOULD; be 201 (Created) and contain an entity which describes the
status of the request and refers to the new resource, and a Location
header (see <xref target="header.location"/>).
</t>
<t>
Responses to this method are not cacheable, unless the response
includes appropriate Cache-Control or Expires header fields. However,
the 303 (See Other) response can be used to direct the user agent to
retrieve a cacheable resource.
</t>
<t>
POST requests &MUST; obey the message transmission requirements set out
in [message.transmission.requirements].
</t>
<t>
See <xref target="encoding.sensitive.information.in.uris"/> for security considerations.
</t>
</section>
<section title="PUT" anchor="PUT">
<iref primary="true" item="PUT method" x:for-anchor=""/>
<iref primary="true" item="Methods" subitem="PUT" x:for-anchor=""/>
<t>
The PUT method requests that the enclosed entity be stored under the
supplied Request-URI. If the Request-URI refers to an already
existing resource, the enclosed entity &SHOULD; be considered as a
modified version of the one residing on the origin server. If the
Request-URI does not point to an existing resource, and that URI is
capable of being defined as a new resource by the requesting user
agent, the origin server can create the resource with that URI. If a
new resource is created, the origin server &MUST; inform the user agent
via the 201 (Created) response. If an existing resource is modified,
either the 200 (OK) or 204 (No Content) response codes &SHOULD; be sent
to indicate successful completion of the request. If the resource
could not be created or modified with the Request-URI, an appropriate
error response &SHOULD; be given that reflects the nature of the
problem. The recipient of the entity &MUST-NOT; ignore any Content-*
(e.g. Content-Range) headers that it does not understand or implement
and &MUST; return a 501 (Not Implemented) response in such cases.
</t>
<t>
If the request passes through a cache and the Request-URI identifies
one or more currently cached entities, those entries &SHOULD; be
treated as stale. Responses to this method are not cacheable.
</t>
<t>
The fundamental difference between the POST and PUT requests is
reflected in the different meaning of the Request-URI. The URI in a
POST request identifies the resource that will handle the enclosed
entity. That resource might be a data-accepting process, a gateway to
some other protocol, or a separate entity that accepts annotations.
In contrast, the URI in a PUT request identifies the entity enclosed
with the request -- the user agent knows what URI is intended and the
server &MUST-NOT; attempt to apply the request to some other resource.
If the server desires that the request be applied to a different URI,
it &MUST; send a 301 (Moved Permanently) response; the user agent &MAY;
then make its own decision regarding whether or not to redirect the
request.
</t>
<t>
A single resource &MAY; be identified by many different URIs. For
example, an article might have a URI for identifying "the current
version" which is separate from the URI identifying each particular
version. In this case, a PUT request on a general URI might result in
several other URIs being defined by the origin server.
</t>
<t>
HTTP/1.1 does not define how a PUT method affects the state of an
origin server.
</t>
<t>
PUT requests &MUST; obey the message transmission requirements set out
in [message.transmission.requirements].
</t>
<t>
Unless otherwise specified for a particular entity-header, the
entity-headers in the PUT request &SHOULD; be applied to the resource
created or modified by the PUT.
</t>
</section>
<section title="DELETE" anchor="DELETE">
<iref primary="true" item="DELETE method" x:for-anchor=""/>
<iref primary="true" item="Methods" subitem="DELETE" x:for-anchor=""/>
<t>
The DELETE method requests that the origin server delete the resource
identified by the Request-URI. 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 200 (OK) if the response includes an
entity describing the status, 202 (Accepted) if the action has not
yet been enacted, or 204 (No Content) if the action has been enacted
but the response does not include an entity.
</t>
<t>
If the request passes through a cache and the Request-URI identifies
one or more currently cached entities, those entries &SHOULD; be
treated as stale. Responses to this method are not cacheable.
</t>
</section>
<section title="TRACE" anchor="TRACE">
<iref primary="true" item="TRACE method" x:for-anchor=""/>
<iref primary="true" item="Methods" subitem="TRACE" x:for-anchor=""/>
<t>
The TRACE method is used to invoke a remote, application-layer loop-back
of the request message. The final recipient of the request
&SHOULD; reflect the message received back to the client as the
entity-body of a 200 (OK) response. The final recipient is either the
origin server or the first proxy or gateway to receive a Max-Forwards
value of zero (0) in the request (see <xref target="header.max-forwards"/>). A TRACE request
&MUST-NOT; include an entity.
</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 (&header-via;) is of
particular interest, since it acts as a trace of the request chain.
Use of the Max-Forwards 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; contain the entire
request message in the entity-body, with a Content-Type of
"message/http". Responses to this method &MUST-NOT; be cached.
</t>
</section>
<section title="CONNECT" anchor="CONNECT">
<iref primary="true" item="CONNECT method" x:for-anchor=""/>
<iref primary="true" item="Methods" subitem="CONNECT" x:for-anchor=""/>
<t>
This specification reserves the method name CONNECT for use with a
proxy that can dynamically switch to being a tunnel (e.g. SSL
tunneling <xref target="Luo1998"/>).
</t>
</section>
</section>
<section title="Status Code Definitions" anchor="status.codes">
<t>
Each Status-Code is described below, including a description of which
method(s) it can follow and any metainformation required in the
response.
</t>
<section title="Informational 1xx" anchor="status.1xx">
<t>
This class of status code indicates a provisional response,
consisting only of the Status-Line and optional headers, and is
terminated by an empty line. There are no required headers 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 100
(Continue) 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 a "Expect: 100-continue" field when it forwards a request,
then it need not forward the corresponding 100 (Continue)
response(s).)
</t>
<section title="100 Continue" anchor="status.100">
<iref primary="true" item="100 Continue (status code)" x:for-anchor=""/>
<iref primary="true" item="Status Codes" subitem="100 Continue" x:for-anchor=""/>
<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
&use100; 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)" x:for-anchor=""/>
<iref primary="true" item="Status Codes" subitem="101 Switching Protocols" x:for-anchor=""/>
<t>
The server understands and is willing to comply with the client's
request, via the Upgrade message header field (&header-upgrade;), 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">
<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)" x:for-anchor=""/>
<iref primary="true" item="Status Codes" subitem="200 OK" x:for-anchor=""/>
<t>
The request has succeeded. The information returned with the response
is dependent on the method used in the request, for example:
<list style="hanging">
<t hangText="GET">
an entity corresponding to the requested resource is sent in
the response;
</t>
<t hangText="HEAD">
the entity-header fields corresponding to the requested
resource are sent in the response without any message-body;
</t>
<t hangText="POST">
an entity describing or containing the result of the action;
</t>
<t hangText="TRACE">
an entity containing the request message as received by the
end server.
</t>
</list>
</t>
</section>
<section title="201 Created" anchor="status.201">
<iref primary="true" item="201 Created (status code)" x:for-anchor=""/>
<iref primary="true" item="Status Codes" subitem="201 Created" x:for-anchor=""/>
<t>
The request has been fulfilled and resulted in a new resource being
created. The newly created resource can be referenced by the URI(s)
returned in the entity of the response, with the most specific URI
for the resource given by a Location header field. The response
&SHOULD; include an entity containing a list of resource
characteristics and location(s) from which the user or user agent can
choose the one most appropriate. The entity format is specified by
the media type given in the Content-Type header field. The origin
server &MUST; create the resource before returning the 201 status code.
If the action cannot be carried out immediately, the server &SHOULD;
respond with 202 (Accepted) response instead.
</t>
<t>
A 201 response &MAY; contain an ETag response header field indicating
the current value of the entity tag for the requested variant just
created, see &header-etag;.
</t>
</section>
<section title="202 Accepted" anchor="status.202">
<iref primary="true" item="202 Accepted (status code)" x:for-anchor=""/>
<iref primary="true" item="Status Codes" subitem="202 Accepted" x:for-anchor=""/>
<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 entity 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)" x:for-anchor=""/>
<iref primary="true" item="Status Codes" subitem="203 Non-Authoritative Information" x:for-anchor=""/>
<t>
The returned metainformation in the entity-header is not the
definitive set as available from the origin server, but is gathered
from a local or a third-party copy. The set presented &MAY; be a subset
or superset of the original version. For example, including local
annotation information about the resource might result in a superset
of the metainformation known by the origin server. Use of this
response code is not required and is only appropriate when the
response would otherwise be 200 (OK).
</t>
</section>
<section title="204 No Content" anchor="status.204">
<iref primary="true" item="204 No Content (status code)" x:for-anchor=""/>
<iref primary="true" item="Status Codes" subitem="204 No Content" x:for-anchor=""/>
<t>
The server has fulfilled the request but does not need to return an
entity-body, and might want to return updated metainformation. The
response &MAY; include new or updated metainformation in the form of
entity-headers, which if present &SHOULD; be associated with the
requested variant.
</t>
<t>
If the client is a user agent, it &SHOULD-NOT; change its document view
from that which caused the request to be sent. This response is
primarily intended to allow input for actions to take place without
causing a change to the user agent's active document view, although
any new or updated metainformation &SHOULD; be applied to the document
currently in the user agent's active view.
</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)" x:for-anchor=""/>
<iref primary="true" item="Status Codes" subitem="205 Reset Content" x:for-anchor=""/>
<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. The
response &MUST-NOT; include an entity.
</t>
</section>
<section title="206 Partial Content" anchor="status.206">
<iref primary="true" item="206 Partial Content (status code)" x:for-anchor=""/>
<iref primary="true" item="Status Codes" subitem="206 Partial Content" x:for-anchor=""/>
<t>
The server has fulfilled the partial GET request for the resource
and the enclosed entity is a partial representation as defined in ⦥.
</t>
</section>
</section>
<section title="Redirection 3xx" anchor="status.3xx">
<t>
This class of status code indicates that further action needs to be
taken by the user agent in order to fulfill the request. The action
required &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
GET or HEAD. A client &SHOULD; detect infinite redirection loops, since
such loops generate network traffic for each redirection.
<list><t>
<x:h>Note:</x:h> previous versions of this specification recommended a
maximum of five redirections. Content developers should be aware
that there might be clients that 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)" x:for-anchor=""/>
<iref primary="true" item="Status Codes" subitem="300 Multiple Choices" x:for-anchor=""/>
<t>
The requested resource corresponds to any one of a set of
representations, each with its own specific location, and agent-driven
negotiation information (&content-negotiation;) is being provided so that
the user (or user agent) can select a preferred representation and
redirect its request to that location.
</t>
<t>
Unless it was a HEAD request, the response &SHOULD; include an entity
containing a list of resource characteristics and location(s) from
which the user or user agent can choose the one most appropriate. The
entity format is specified by the media type given in the Content-Type
header field. 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 Location
field; user agents &MAY; use the Location field value for automatic
redirection. This response is cacheable unless indicated otherwise.
</t>
</section>
<section title="301 Moved Permanently" anchor="status.301">
<iref primary="true" item="301 Moved Permanently (status code)" x:for-anchor=""/>
<iref primary="true" item="Status Codes" subitem="301 Moved Permanently" x:for-anchor=""/>
<t>
The requested 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 Request-URI to one or more of the new
references returned by the server, where possible. This response is
cacheable unless indicated otherwise.
</t>
<t>
The new permanent URI &SHOULD; be given by the Location field in the
response. Unless the request method was HEAD, the entity of the
response &SHOULD; contain a short hypertext note with a hyperlink to
the new URI(s).
</t>
<t>
If the 301 status code is received in response to a request method
that is known to be "safe", as defined in <xref target="safe.methods"/>,
then the request MAY be automatically redirected by the user agent without
confirmation. Otherwise, the user agent &MUST-NOT; automatically redirect the
request unless it can be confirmed by the user, since this might
change the conditions under which the request was issued.
<list><t>
<x:h>Note:</x:h> When automatically redirecting a POST request after
receiving a 301 status code, some existing HTTP/1.0 user agents
will erroneously change it into a GET request.
</t></list>
</t>
</section>
<section title="302 Found" anchor="status.302">
<iref primary="true" item="302 Found (status code)" x:for-anchor=""/>
<iref primary="true" item="Status Codes" subitem="302 Found" x:for-anchor=""/>
<t>
The requested resource resides temporarily under a different URI.
Since the redirection might be altered on occasion, the client &SHOULD;
continue to use the Request-URI for future requests. This response
is only cacheable if indicated by a Cache-Control or Expires header
field.
</t>
<t>
The temporary URI &SHOULD; be given by the Location field in the
response. Unless the request method was HEAD, the entity of the
response &SHOULD; contain a short hypertext note with a hyperlink to
the new URI(s).
</t>
<t>
If the 302 status code is received in response to a request method
that is known to be "safe", as defined in <xref target="safe.methods"/>,
then the request MAY be automatically redirected by the user agent without
confirmation. Otherwise, the user agent &MUST-NOT; automatically redirect the
request unless it can be confirmed by the user, since this might
change the conditions under which the request was issued.
<list><t>
<x:h>Note:</x:h> RFC 1945 and RFC 2068 specify that the client is not allowed
to change the method on the redirected request. However, most
existing user agent implementations treat 302 as if it were a 303
response, performing a GET on the Location field-value regardless
of the original request method. The status codes 303 and 307 have
been added for servers that wish to make unambiguously clear which
kind of reaction is expected of the client.
</t></list>
</t>
</section>
<section title="303 See Other" anchor="status.303">
<iref primary="true" item="303 See Other (status code)" x:for-anchor=""/>
<iref primary="true" item="Status Codes" subitem="303 See Other" x:for-anchor=""/>
<t>
The response to the request can be found under a different URI and
&SHOULD; be retrieved using a GET method on that resource. This method
exists primarily to allow the output of a POST-activated script to
redirect the user agent to a selected resource. The new URI is not a
substitute reference for the originally requested resource. The 303
response &MUST-NOT; be cached, but the response to the second
(redirected) request might be cacheable.
</t>
<t>
The different URI &SHOULD; be given by the Location field in the
response. Unless the request method was HEAD, the entity of the
response &SHOULD; contain a short hypertext note with a hyperlink to
the new URI(s).
<list><t>
<x:h>Note:</x:h> Many pre-HTTP/1.1 user agents do not understand the 303
status. When interoperability with such clients is a concern, the
302 status code may be used instead, since most user agents react
to a 302 response as described here for 303.
</t></list>
</t>
</section>
<section title="304 Not Modified" anchor="status.304">
<iref primary="true" item="304 Not Modified (status code)" x:for-anchor=""/>
<iref primary="true" item="Status Codes" subitem="304 Not Modified" x:for-anchor=""/>
<t>
If the client has performed a conditional GET request and access is
allowed, but the document has not been modified, the server &SHOULD;
respond with this status code. The 304 response &MUST-NOT; contain a
message-body, and thus is always terminated by the first empty line
after the header fields.
</t>
<t>
The response &MUST; include the following header fields:
<list style="symbols">
<t>Date, unless its omission is required by [clockless.origin.server.operation]</t>
</list>
</t>
<t>
If a clockless origin server obeys these rules, and proxies and
clients add their own Date to any response received without one (as
already specified by [RFC 2068], section <xref target="RFC2068" x:sec="14.19" x:fmt="number"/>), caches will operate
correctly.
<list style="symbols">
<t>ETag and/or Content-Location, if the header would have been sent
in a 200 response to the same request</t>
<t>Expires, Cache-Control, and/or Vary, if the field-value might
differ from that sent in any previous response for the same
variant</t>
</list>
</t>
<t>
If the conditional GET used a strong cache validator (see &caching;),
the response &SHOULD-NOT; include other entity-headers.
Otherwise (i.e., the conditional GET used a weak validator), the
response &MUST-NOT; include other entity-headers; this prevents
inconsistencies between cached entity-bodies and updated headers.
</t>
<t>
If a 304 response indicates an entity not currently cached, then the
cache &MUST; disregard the response and repeat the request without the
conditional.
</t>
<t>
If a cache uses a received 304 response to update a cache entry, the
cache &MUST; update the entry to reflect any new field values given in
the response.
</t>
</section>
<section title="305 Use Proxy" anchor="status.305">
<iref primary="true" item="305 Use Proxy (status code)" x:for-anchor=""/>
<iref primary="true" item="Status Codes" subitem="305 Use Proxy" x:for-anchor=""/>
<t>
The requested resource &MUST; be accessed through the proxy given by
the Location field. The Location field gives the URI of the proxy.
The recipient is expected to repeat this single request via the
proxy. 305 responses &MUST; only be generated by origin servers.
<list><t>
<x:h>Note:</x:h> RFC 2068 was not clear that 305 was intended to redirect a
single request, and to be generated by origin servers only. Not
observing these limitations has significant security consequences.
</t></list>
</t>
</section>
<section title="306 (Unused)" anchor="status.306">
<iref primary="true" item="306 (Unused) (status code)" x:for-anchor=""/>
<iref primary="true" item="Status Codes" subitem="306 (Unused)" x:for-anchor=""/>
<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)" x:for-anchor=""/>
<iref primary="true" item="Status Codes" subitem="307 Temporary Redirect" x:for-anchor=""/>
<t>
The requested resource resides temporarily under a different URI.
Since the redirection &MAY; be altered on occasion, the client &SHOULD;
continue to use the Request-URI for future requests. This response
is only cacheable if indicated by a Cache-Control or Expires header
field.
</t>
<t>
The temporary URI &SHOULD; be given by the Location field in the
response. Unless the request method was HEAD, the entity of the
response &SHOULD; contain a short hypertext note with a hyperlink to
the new URI(s) , since many pre-HTTP/1.1 user agents do not
understand the 307 status. Therefore, the note &SHOULD; contain the
information necessary for a user to repeat the original request on
the new URI.
</t>
<t>
If the 307 status code is received in response to a request method
that is known to be "safe", as defined in <xref target="safe.methods"/>,
then the request MAY be automatically redirected by the user agent without
confirmation. Otherwise, the user agent &MUST-NOT; automatically redirect the
request unless it can be confirmed by the user, since this might
change the conditions under which the request was issued.
</t>
</section>
</section>
<section title="Client Error 4xx" anchor="status.4xx">
<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 an entity 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 entity to the user.
</t>
<t>
If the client is sending data, a server implementation using TCP
&SHOULD; be careful to ensure that the client acknowledges receipt of
the packet(s) containing the response, before the server closes the
input connection. If the client continues sending data to the server
after the close, the server's TCP stack will send a reset packet to
the client, which may erase the client's unacknowledged input buffers
before they can be read and interpreted by the HTTP application.
</t>
<section title="400 Bad Request" anchor="status.400">
<iref primary="true" item="400 Bad Request (status code)" x:for-anchor=""/>
<iref primary="true" item="Status Codes" subitem="400 Bad Request" x:for-anchor=""/>
<t>
The request could not be understood by the server due to malformed
syntax. The client &SHOULD-NOT; repeat the request without
modifications.
</t>
</section>
<section title="401 Unauthorized" anchor="status.401">
<iref primary="true" item="401 Unauthorized (status code)" x:for-anchor=""/>
<iref primary="true" item="Status Codes" subitem="401 Unauthorized" x:for-anchor=""/>
<t>
The request requires user authentication. The response &MUST; include a
WWW-Authenticate header field (&header-www-authenticate;) containing a challenge
applicable to the requested resource. The client &MAY; repeat the
request with a suitable Authorization header field (&header-authorization;). If
the request already included Authorization credentials, then the 401
response indicates that authorization has been refused for those
credentials. If the 401 response contains the same challenge as the
prior response, and the user agent has already attempted
authentication at least once, then the user &SHOULD; be presented the
entity that was given in the response, since that entity might
include relevant diagnostic information. HTTP access authentication
is explained in "HTTP Authentication: Basic and Digest Access
Authentication" <xref target="RFC2617"/>.
</t>
</section>
<section title="402 Payment Required" anchor="status.402">
<iref primary="true" item="402 Payment Required (status code)" x:for-anchor=""/>
<iref primary="true" item="Status Codes" subitem="402 Payment Required" x:for-anchor=""/>
<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)" x:for-anchor=""/>
<iref primary="true" item="Status Codes" subitem="403 Forbidden" x:for-anchor=""/>
<t>
The server understood the request, but is refusing to fulfill it.
Authorization will not help and the request &SHOULD-NOT; be repeated.
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 entity. If the server does not wish to
make this information available to the client, the status code 404
(Not Found) can be used instead.
</t>
</section>
<section title="404 Not Found" anchor="status.404">
<iref primary="true" item="404 Not Found (status code)" x:for-anchor=""/>
<iref primary="true" item="Status Codes" subitem="404 Not Found" x:for-anchor=""/>
<t>
The server has not found anything matching the Request-URI. No
indication is given of whether the condition is temporary or
permanent. The 410 (Gone) 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)" x:for-anchor=""/>
<iref primary="true" item="Status Codes" subitem="405 Method Not Allowed" x:for-anchor=""/>
<t>
The method specified in the Request-Line is not allowed for the
resource identified by the Request-URI. The response &MUST; include an
Allow header 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)" x:for-anchor=""/>
<iref primary="true" item="Status Codes" subitem="406 Not Acceptable" x:for-anchor=""/>
<t>
The resource identified by the request is only capable of generating
response entities which have content characteristics not acceptable
according to the accept headers sent in the request.
</t>
<t>
Unless it was a HEAD request, the response &SHOULD; include an entity
containing a list of available entity characteristics and location(s)
from which the user or user agent can choose the one most
appropriate. The entity format is specified by the media type given
in the Content-Type header field. 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.
<list><t>
<x:h>Note:</x:h> HTTP/1.1 servers are allowed to return responses which are
not acceptable according to the accept headers sent in the
request. In some cases, this may even be preferable to sending a
406 response. User agents are encouraged to inspect the headers 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="407 Proxy Authentication Required" anchor="status.407">
<iref primary="true" item="407 Proxy Authentication Required (status code)" x:for-anchor=""/>
<iref primary="true" item="Status Codes" subitem="407 Proxy Authentication Required" x:for-anchor=""/>
<t>
This code is similar to 401 (Unauthorized), but indicates that the
client must first authenticate itself with the proxy. The proxy &MUST;
return a Proxy-Authenticate header field (&header-proxy-authenticate;) containing a
challenge applicable to the proxy for the requested resource. The
client &MAY; repeat the request with a suitable Proxy-Authorization
header field (&header-proxy-authorization;). HTTP access authentication is explained
in "HTTP Authentication: Basic and Digest Access Authentication"
<xref target="RFC2617"/>.
</t>
</section>
<section title="408 Request Timeout" anchor="status.408">
<iref primary="true" item="408 Request Timeout (status code)" x:for-anchor=""/>
<iref primary="true" item="Status Codes" subitem="408 Request Timeout" x:for-anchor=""/>
<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)" x:for-anchor=""/>
<iref primary="true" item="Status Codes" subitem="409 Conflict" x:for-anchor=""/>
<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 response body &SHOULD; include enough
information for the user to recognize the source of the conflict.
Ideally, the response entity 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 entity 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 entity would likely contain a list of the differences
between the two versions in a format defined by the response
Content-Type.
</t>
</section>
<section title="410 Gone" anchor="status.410">
<iref primary="true" item="410 Gone (status code)" x:for-anchor=""/>
<iref primary="true" item="Status Codes" subitem="410 Gone" x:for-anchor=""/>
<t>
The requested 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 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 404 (Not Found) &SHOULD; be
used instead. This response is cacheable unless indicated otherwise.
</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>
</section>
<section title="411 Length Required" anchor="status.411">
<iref primary="true" item="411 Length Required (status code)" x:for-anchor=""/>
<iref primary="true" item="Status Codes" subitem="411 Length Required" x:for-anchor=""/>
<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="412 Precondition Failed" anchor="status.412">
<iref primary="true" item="412 Precondition Failed (status code)" x:for-anchor=""/>
<iref primary="true" item="Status Codes" subitem="412 Precondition Failed" x:for-anchor=""/>
<t>
The precondition given in one or more of the request-header fields
evaluated to false when it was tested on the server. This response
code allows the client to place preconditions on the current resource
metainformation (header field data) and thus prevent the requested
method from being applied to a resource other than the one intended.
</t>
</section>
<section title="413 Request Entity Too Large" anchor="status.413">
<iref primary="true" item="413 Request Entity Too Large (status code)" x:for-anchor=""/>
<iref primary="true" item="Status Codes" subitem="413 Request Entity Too Large" x:for-anchor=""/>
<t>
The server is refusing to process a request because the request
entity 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 Retry-After
header field to indicate that it is temporary and after what
time the client &MAY; try again.
</t>
</section>
<section title="414 Request-URI Too Long" anchor="status.414">
<iref primary="true" item="414 Request-URI Too Long (status code)" x:for-anchor=""/>
<iref primary="true" item="Status Codes" subitem="414 Request-URI Too Long" x:for-anchor=""/>
<t>
The server is refusing to service the request because the 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-URI.
</t>
</section>
<section title="415 Unsupported Media Type" anchor="status.415">
<iref primary="true" item="415 Unsupported Media Type (status code)" x:for-anchor=""/>
<iref primary="true" item="Status Codes" subitem="415 Unsupported Media Type" x:for-anchor=""/>
<t>
The server is refusing to service the request because the entity of
the request is in a format not supported by the requested resource
for the requested method.
</t>
</section>
<section title="416 Requested Range Not Satisfiable" anchor="status.416">
<iref primary="true" item="416 Requested Range Not Satisfiable (status code)" x:for-anchor=""/>
<iref primary="true" item="Status Codes" subitem="416 Requested Range Not Satisfiable" x:for-anchor=""/>
<t>
The request included a Range request-header field (&header-range;) and none of
the range-specifier values in this field overlap the current extent
of the selected resource.
</t>
</section>
<section title="417 Expectation Failed" anchor="status.417">
<iref primary="true" item="417 Expectation Failed (status code)" x:for-anchor=""/>
<iref primary="true" item="Status Codes" subitem="417 Expectation Failed" x:for-anchor=""/>
<t>
The expectation given in an Expect request-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>
<section title="Server Error 5xx" anchor="status.5xx">
<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 an entity containing an explanation of the
error situation, and whether it is a temporary or permanent
condition. User agents &SHOULD; display any included entity 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)" x:for-anchor=""/>
<iref primary="true" item="Status Codes" subitem="500 Internal Server Error" x:for-anchor=""/>
<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)" x:for-anchor=""/>
<iref primary="true" item="Status Codes" subitem="501 Not Implemented" x:for-anchor=""/>
<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)" x:for-anchor=""/>
<iref primary="true" item="Status Codes" subitem="502 Bad Gateway" x:for-anchor=""/>
<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)" x:for-anchor=""/>
<iref primary="true" item="Status Codes" subitem="503 Service Unavailable" x:for-anchor=""/>
<t>
The server is currently unable to handle the request due to a
temporary overloading or maintenance of the server. 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
Retry-After header. If no Retry-After is given, the client &SHOULD;
handle the response as it would for a 500 response.
<list><t>
<x:h>Note:</x:h> The existence of the 503 status code does not imply that a
server must use it when becoming overloaded. Some servers may 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)" x:for-anchor=""/>
<iref primary="true" item="Status Codes" subitem="504 Gateway Timeout" x:for-anchor=""/>
<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.
<list><t>
<x:h>Note:</x:h> Note to implementors: some deployed proxies are known to
return 400 or 500 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)" x:for-anchor=""/>
<iref primary="true" item="Status Codes" subitem="505 HTTP Version Not Supported" x:for-anchor=""/>
<t>
The server does not support, or refuses to support, the HTTP 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 &http-version;,
other than with this error message. The response &SHOULD; contain
an entity describing why that version is not supported and what other
protocols are supported by that server.
</t>
</section>
</section>
</section>
<section title="Header Field Definitions" anchor="header.fields">
<t>
This section defines the syntax and semantics of all standard
HTTP/1.1 header fields. For entity-header fields, both sender and
recipient refer to either the client or the server, depending on who
sends and who receives the entity.
</t>
<section title="Allow" anchor="header.allow">
<iref primary="true" item="Allow header" x:for-anchor=""/>
<iref primary="true" item="Headers" subitem="Allow" x:for-anchor=""/>
<t>
The Allow entity-header field lists the set of methods supported
by the resource identified by the Request-URI. The purpose of this
field is strictly to inform the recipient of valid methods
associated with the resource. An Allow header field &MUST; be
present in a 405 (Method Not Allowed) response.
</t>
<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Allow"/>
Allow = "Allow" ":" #Method
</artwork></figure>
<t>
Example of use:
</t>
<figure><artwork type="example">
Allow: GET, HEAD, PUT
</artwork></figure>
<t>
This field cannot prevent a client from trying other methods.
However, the indications given by the Allow header field value
&SHOULD; be followed. The actual set of allowed methods is defined
by the origin server at the time of each request.
</t>
<t>
The Allow header field &MAY; be provided with a PUT request to
recommend the methods to be supported by the new or modified
resource. The server is not required to support these methods and
&SHOULD; include an Allow header in the response giving the actual
supported methods.
</t>
<t>
A proxy &MUST-NOT; modify the Allow header field even if it does not
understand all the methods specified, since the user agent might
have other means of communicating with the origin server.
</t>
</section>
<section title="Expect" anchor="header.expect">
<iref primary="true" item="Expect header" x:for-anchor=""/>
<iref primary="true" item="Headers" subitem="Expect" x:for-anchor=""/>
<t>
The Expect request-header field is used to indicate that particular
server behaviors are required by the client.
</t>
<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Expect"/><iref primary="true" item="Grammar" subitem="expectation"/><iref primary="true" item="Grammar" subitem="expectation-extension"/><iref primary="true" item="Grammar" subitem="expect-params"/>
Expect = "Expect" ":" 1#expectation
expectation = "100-continue" | expectation-extension
expectation-extension = token [ "=" ( token | quoted-string )
*expect-params ]
expect-params = ";" token [ "=" ( token | quoted-string ) ]
</artwork></figure>
<t>
A server that does not understand or is unable to comply with any of
the expectation values in the Expect field of a request &MUST; respond
with appropriate error status. The server &MUST; respond with a 417
(Expectation Failed) status if any of the expectations cannot be met
or, if there are other problems with the request, some other 4xx
status.
</t>
<t>
This header field is defined with extensible syntax to allow for
future extensions. If a server receives a request containing an
Expect field that includes an expectation-extension that it does not
support, it &MUST; respond with a 417 (Expectation Failed) status.
</t>
<t>
Comparison of expectation values is case-insensitive for unquoted
tokens (including the 100-continue token), and is case-sensitive for
quoted-string expectation-extensions.
</t>
<t>
The Expect mechanism is hop-by-hop: that is, an HTTP/1.1 proxy &MUST;
return a 417 (Expectation Failed) status if it receives a request
with an expectation that it cannot meet. However, the Expect
request-header 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.
</t>
<t>
See &use100; for the use of the 100 (continue) status.
</t>
</section>
<section title="From" anchor="header.from">
<iref primary="true" item="From header" x:for-anchor=""/>
<iref primary="true" item="Headers" subitem="From" x:for-anchor=""/>
<t>
The From request-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 RFC 822 <xref target="RFC822"/> as updated by RFC 1123 <xref target="RFC1123"/>:
</t>
<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="From"/>
From = "From" ":" mailbox
</artwork></figure>
<t>
An example is:
</t>
<figure><artwork type="example">
From: webmaster@w3.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 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="Location" anchor="header.location">
<iref primary="true" item="Location header" x:for-anchor=""/>
<iref primary="true" item="Headers" subitem="Location" x:for-anchor=""/>
<t>
The Location response-header field is used to redirect the recipient
to a location other than the Request-URI for completion of the
request or identification of a new resource. For 201 (Created)
responses, the Location is that of the new resource which was created
by the request. For 3xx responses, the location &SHOULD; indicate the
server's preferred URI for automatic redirection to the resource. The
field value consists of a single absolute URI.
</t>
<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Location"/>
Location = "Location" ":" absoluteURI [ "#" fragment ]
</artwork></figure>
<t>
An example is:
</t>
<figure><artwork type="example">
Location: http://www.w3.org/pub/WWW/People.html
</artwork></figure>
<t>
<list><t>
<x:h>Note:</x:h> The Content-Location header field (&header-content-location;) differs
from Location in that the Content-Location identifies the original
location of the entity enclosed in the request. It is therefore
possible for a response to contain header fields for both Location
and Content-Location.
</t></list>
</t>
</section>
<section title="Max-Forwards" anchor="header.max-forwards">
<iref primary="true" item="Max-Forwards header" x:for-anchor=""/>
<iref primary="true" item="Headers" subitem="Max-Forwards" x:for-anchor=""/>
<t>
The Max-Forwards request-header field provides a mechanism with the
TRACE (<xref target="TRACE"/>) and OPTIONS (<xref target="OPTIONS"/>) methods to limit the
number of proxies or gateways that can forward the request to the
next inbound server. This can be useful when the client is attempting
to trace a request chain which appears to be failing or looping in
mid-chain.
</t>
<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Max-Forwards"/>
Max-Forwards = "Max-Forwards" ":" 1*DIGIT
</artwork></figure>
<t>
The Max-Forwards value is a decimal integer indicating the remaining
number of times this request message may be forwarded.
</t>
<t>
Each proxy or gateway 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 methods
defined by this specification and for any extension methods for which
it is not explicitly referred to as part of that method definition.
</t>
</section>
<section title="Referer" anchor="header.referer">
<iref primary="true" item="Referer header" x:for-anchor=""/>
<iref primary="true" item="Headers" subitem="Referer" x:for-anchor=""/>
<t>
The Referer[sic] request-header field allows the client to specify,
for the server's benefit, the address (URI) of the resource from
which the Request-URI was obtained (the "referrer", although the
header field is misspelled.) The Referer request-header allows a
server 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. The Referer field &MUST-NOT; be
sent if the Request-URI was obtained from a source that does not have
its own URI, such as input from the user keyboard.
</t>
<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Referer"/>
Referer = "Referer" ":" ( absoluteURI | relativeURI )
</artwork></figure>
<t>
Example:
</t>
<figure><artwork type="example">
Referer: http://www.w3.org/hypertext/DataSources/Overview.html
</artwork></figure>
<t>
If the field value is a relative URI, it &SHOULD; be interpreted
relative to the Request-URI. The URI &MUST-NOT; include a fragment. See
<xref target="encoding.sensitive.information.in.uris"/> for security considerations.
</t>
</section>
<section title="Retry-After" anchor="header.retry-after">
<iref primary="true" item="Retry-After header" x:for-anchor=""/>
<iref primary="true" item="Headers" subitem="Retry-After" x:for-anchor=""/>
<t>
The Retry-After response-header field can be used with a 503 (Service
Unavailable) response to indicate how long the service is expected to
be unavailable to the requesting client. This field &MAY; also be used
with any 3xx (Redirection) response to indicate the minimum time the
user-agent is asked wait before issuing the redirected request. 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><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Retry-After"/>
Retry-After = "Retry-After" ":" ( HTTP-date | delta-seconds )
</artwork></figure>
<t>
Two examples of its use are
</t>
<figure><artwork type="example">
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 title="Server" anchor="header.server">
<iref primary="true" item="Server header" x:for-anchor=""/>
<iref primary="true" item="Headers" subitem="Server" x:for-anchor=""/>
<t>
The Server response-header field contains information about the
software used by the origin server to handle the request. The field
can contain multiple product tokens (<xref target="product.tokens"/>) and comments
identifying the server and any significant subproducts. The product
tokens are listed in order of their significance for identifying the
application.
</t>
<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Server"/>
Server = "Server" ":" 1*( product | comment )
</artwork></figure>
<t>
Example:
</t>
<figure><artwork type="example">
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 Server response-header. Instead, it
&MUST; include a Via field (as described in &header-via;).
<list><t>
<x:h>Note:</x:h> 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
implementors are encouraged to make this field a configurable
option.
</t></list>
</t>
</section>
<section title="User-Agent" anchor="header.user-agent">
<iref primary="true" item="User-Agent header" x:for-anchor=""/>
<iref primary="true" item="Headers" subitem="User-Agent" x:for-anchor=""/>
<t>
The User-Agent request-header field contains information about the
user agent originating the request. This is for statistical purposes,
the tracing of protocol violations, and automated recognition of user
agents for the sake of tailoring responses to avoid particular user
agent limitations. User agents &SHOULD; include this field with
requests. The field can contain multiple product tokens (<xref target="product.tokens"/>)
and comments identifying the agent and any subproducts which form a
significant part of the user agent. By convention, the product tokens
are listed in order of their significance for identifying the
application.
</t>
<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="User-Agent"/>
User-Agent = "User-Agent" ":" 1*( product | comment )
</artwork></figure>
<t>
Example:
</t>
<figure><artwork type="example">
User-Agent: CERN-LineMode/2.15 libwww/2.17b3
</artwork></figure>
</section>
</section>
<section title="IANA Considerations" anchor="IANA.considerations">
<t>
TBD.
</t>
</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: Server, Via, Referer and From.
</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. Implementors &SHOULD; make the
Server 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 Referer header 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 might indicate a private document's URI whose
publication would be inappropriate.
</t>
<t>
The information sent in the From 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 From and
Referer information.
</t>
<t>
The User-Agent (<xref target="header.user-agent"/>) or Server (<xref target="header.server"/>) header
fields can sometimes be used to determine that a specific client or
server have 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>
</section>
<section title="Encoding Sensitive Information in URI's" 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
Referer 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 Referer header field in a (non-secure)
HTTP request if the referring page was transferred with a secure
protocol.
</t>
<t>
Authors of services which use the HTTP protocol &SHOULD-NOT; use GET
based forms for the submission of sensitive data, because this will
cause this data to be encoded in the Request-URI. Many existing
servers, proxies, and user agents will log the request URI in some
place where it might be visible to third parties. Servers can use
POST-based form submission instead
</t>
</section>
<section title="Location Headers and Spoofing" anchor="location.spoofing">
<t>
If a single server supports multiple organizations that do not trust
one another, then it &MUST; check the values of Location and Content-Location
headers 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>
</section>
</section>
<section title="Acknowledgments" anchor="ack">
<t>
Based on an XML translation of RFC 2616 by Julian Reschke.
</t>
</section>
</middle>
<back>
<references>
<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>
<postal>
<street>4676 Admiralty Way</street>
<city>Marina del Rey</city>
<region>CA</region>
<code>90292-6695</code>
<country>US</country></postal>
<phone>+1 213 822 1511</phone>
<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="RFC822">
<front>
<title abbrev="Standard for ARPA Internet Text Messages">Standard for the format of ARPA Internet text messages</title>
<author initials="D.H." surname="Crocker" fullname="David H. Crocker">
<organization>University of Delaware, Dept. of Electrical Engineering</organization>
<address>
<postal>
<street/>
<city>Newark</city>
<region>DE</region>
<code>19711</code>
<country>US</country></postal>
<email>DCrocker@UDel-Relay</email></address></author>
<date month="August" day="13" year="1982"/></front>
<seriesInfo name="STD" value="11"/>
<seriesInfo name="RFC" value="822"/>
</reference>
<reference anchor="RFC2068">
<front>
<title abbrev="HTTP/1.1">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>
<postal>
<street/>
<city>Irvine</city>
<region>CA</region>
<code>92717-3425</code>
<country>US</country></postal>
<facsimile>+1 714 824 4056</facsimile>
<email>fielding@ics.uci.edu</email></address></author>
<author initials="J." surname="Gettys" fullname="Jim Gettys">
<organization>MIT Laboratory for Computer Science</organization>
<address>
<postal>
<street>545 Technology Square</street>
<city>Cambridge</city>
<region>MA</region>
<code>02139</code>
<country>US</country></postal>
<facsimile>+1 617 258 8682</facsimile>
<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>
<postal>
<street>250 University Avenue</street>
<city>Palo Alto</city>
<region>CA</region>
<code>94301</code>
<country>US</country></postal>
<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>
<postal>
<street>545 Technology Square</street>
<city>Cambridge</city>
<region>MA</region>
<code>02139</code>
<country>US</country></postal>
<facsimile>+1 617 258 8682</facsimile>
<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>
<postal>
<street>545 Technology Square</street>
<city>Cambridge</city>
<region>MA</region>
<code>02139</code>
<country>US</country></postal>
<facsimile>+1 617 258 8682</facsimile>
<email>timbl@w3.org</email></address></author>
<date month="January" year="1997"/>
<abstract>
<t>The Hypertext Transfer Protocol (HTTP) is an application-level protocol for distributed, collaborative, hypermedia information systems. It is a generic, stateless, object-oriented protocol which can be used for many tasks, such as name servers and distributed object management systems, through extension of its request methods. A feature of HTTP is the typing and negotiation of data representation, allowing systems to be built independently of the data being transferred.</t>
<t>HTTP has been in use by the World-Wide Web global information initiative since 1990. This specification defines the protocol referred to as "HTTP/1.1".</t></abstract></front>
<seriesInfo name="RFC" value="2068"/>
</reference>
<reference anchor="RFC2617">
<front>
<title abbrev="HTTP Authentication">HTTP Authentication: Basic and Digest Access Authentication</title>
<author initials="J." surname="Franks" fullname="John Franks">
<organization>Northwestern University, Department of Mathematics</organization>
<address>
<postal>
<street/>
<city>Evanston</city>
<region>IL</region>
<code>60208-2730</code>
<country>US</country></postal>
<email>john@math.nwu.edu</email></address></author>
<author initials="P.M." surname="Hallam-Baker" fullname="Phillip M. Hallam-Baker">
<organization>Verisign Inc.</organization>
<address>
<postal>
<street>301 Edgewater Place</street>
<street>Suite 210</street>
<city>Wakefield</city>
<region>MA</region>
<code>01880</code>
<country>US</country></postal>
<email>pbaker@verisign.com</email></address></author>
<author initials="J.L." surname="Hostetler" fullname="Jeffery L. Hostetler">
<organization>AbiSource, Inc.</organization>
<address>
<postal>
<street>6 Dunlap Court</street>
<city>Savoy</city>
<region>IL</region>
<code>61874</code>
<country>US</country></postal>
<email>jeff@AbiSource.com</email></address></author>
<author initials="S.D." surname="Lawrence" fullname="Scott D. Lawrence">
<organization>Agranat Systems, Inc.</organization>
<address>
<postal>
<street>5 Clocktower Place</street>
<street>Suite 400</street>
<city>Maynard</city>
<region>MA</region>
<code>01754</code>
<country>US</country></postal>
<email>lawrence@agranat.com</email></address></author>
<author initials="P.J." surname="Leach" fullname="Paul J. Leach">
<organization>Microsoft Corporation</organization>
<address>
<postal>
<street>1 Microsoft Way</street>
<city>Redmond</city>
<region>WA</region>
<code>98052</code>
<country>US</country></postal>
<email>paulle@microsoft.com</email></address></author>
<author initials="A." surname="Luotonen" fullname="Ari Luotonen">
<organization>Netscape Communications Corporation</organization>
<address>
<postal>
<street>501 East Middlefield Road</street>
<city>Mountain View</city>
<region>CA</region>
<code>94043</code>
<country>US</country></postal></address></author>
<author initials="L." surname="Stewart" fullname="Lawrence C. Stewart">
<organization>Open Market, Inc.</organization>
<address>
<postal>
<street>215 First Street</street>
<city>Cambridge</city>
<region>MA</region>
<code>02142</code>
<country>US</country></postal>
<email>stewart@OpenMarket.com</email></address></author>
<date month="June" year="1999"/>
</front>
<seriesInfo name="RFC" value="2617"/>
</reference>
<reference anchor="Luo1998">
<front>
<title>Tunneling TCP based protocols through Web proxy servers</title>
<author initials="A." surname="Luotonen" fullname="A. Luotonen">
<organization/>
</author>
<date/>
</front>
<seriesInfo name="" value="Work in Progress"/>
</reference>
</references>
<section title="Changes from RFC 2068" anchor="changes.from.rfc.2068">
<t>
Clarified which error code should be used for inbound server failures
(e.g. DNS failures). (<xref target="status.504"/>).
</t>
<t>
CREATE had a race that required an Etag be sent when a resource is
first created. (<xref target="status.201"/>).
</t>
<t>
Rewrite of message transmission requirements to make it much harder
for implementors to get it wrong, as the consequences of errors here
can have significant impact on the Internet, and to deal with the
following problems:
<list style="numbers">
<t>Changing "HTTP/1.1 or later" to "HTTP/1.1", in contexts where
this was incorrectly placing a requirement on the behavior of
an implementation of a future version of HTTP/1.x</t>
<t>Made it clear that user-agents should retry requests, not
"clients" in general.</t>
<t>Converted requirements for clients to ignore unexpected 100
(Continue) responses, and for proxies to forward 100 responses,
into a general requirement for 1xx responses.</t>
<t>Modified some TCP-specific language, to make it clearer that
non-TCP transports are possible for HTTP.</t>
<t>Require that the origin server &MUST-NOT; wait for the request
body before it sends a required 100 (Continue) response.</t>
<t>Allow, rather than require, a server to omit 100 (Continue) if
it has already seen some of the request body.</t>
<t>Allow servers to defend against denial-of-service attacks and
broken clients.</t>
</list>
</t>
<t>
This change adds the Expect header and 417 status code.
</t>
<t>
Clean up confusion between 403 and 404 responses. (Section <xref target="status.403" format="counter"/>,
<xref target="status.404" format="counter"/>, and <xref target="status.410" format="counter"/>)
</t>
<t>
The PATCH<iref item="PATCH method" primary="true"/><iref item="Methods" subitem="PATCH" primary="true"/>, LINK<iref item="LINK method" primary="true"/><iref item="Methods" subitem="LINK" primary="true"/>, UNLINK<iref item="UNLINK method" primary="true"/><iref item="Methods" subitem="UNLINK" primary="true"/> methods were defined but not commonly
implemented in previous versions of this specification. See RFC 2068
<xref target="RFC2068"/>.
</t>
</section>
</back>
</rfc>
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