One document matched: draft-ietf-httpbis-p1-messaging-26.xml
<?xml version="1.0" encoding="UTF-8"?>
<!--
This XML document is the output of clean-for-DTD.xslt; a tool that strips
extensions to RFC2629(bis) from documents for processing with xml2rfc.
-->
<?xml-stylesheet type='text/xsl' href='../myxml2rfc.xslt'?>
<?rfc toc="yes" ?>
<?rfc symrefs="yes" ?>
<?rfc sortrefs="yes" ?>
<?rfc compact="yes"?>
<?rfc subcompact="no" ?>
<?rfc linkmailto="no" ?>
<?rfc editing="no" ?>
<?rfc comments="yes"?>
<?rfc inline="yes"?>
<?rfc rfcedstyle="yes"?>
<!DOCTYPE rfc
PUBLIC "" "rfc2629.dtd">
<rfc obsoletes="2145,2616" updates="2817,2818" category="std" ipr="pre5378Trust200902" docName="draft-ietf-httpbis-p1-messaging-26">
<front>
<title abbrev="HTTP/1.1 Message Syntax and Routing">Hypertext Transfer Protocol (HTTP/1.1): Message Syntax and Routing</title>
<author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
<organization abbrev="Adobe">Adobe Systems Incorporated</organization>
<address>
<postal>
<street>345 Park Ave</street>
<city>San Jose</city>
<region>CA</region>
<code>95110</code>
<country>USA</country>
</postal>
<email>fielding@gbiv.com</email>
<uri>http://roy.gbiv.com/</uri>
</address>
</author>
<author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
<organization abbrev="greenbytes">greenbytes GmbH</organization>
<address>
<postal>
<street>Hafenweg 16</street>
<city>Muenster</city><region>NW</region><code>48155</code>
<country>Germany</country>
</postal>
<email>julian.reschke@greenbytes.de</email>
<uri>http://greenbytes.de/tech/webdav/</uri>
</address>
</author>
<date month="February" year="2014" day="6"/>
<area>Applications</area>
<workgroup>HTTPbis Working Group</workgroup>
<abstract>
<t>
The Hypertext Transfer Protocol (HTTP) is a stateless application-level
protocol for distributed, collaborative, hypertext information systems.
This document provides an overview of HTTP architecture and its associated
terminology, defines the "http" and "https" Uniform Resource Identifier
(URI) schemes, defines the HTTP/1.1 message syntax and parsing
requirements, and describes related security concerns for implementations.
</t>
</abstract>
<note title="Editorial Note (To be removed by RFC Editor)">
<t>
Discussion of this draft takes place on the HTTPBIS working group
mailing list (ietf-http-wg@w3.org), which is archived at
<eref target="http://lists.w3.org/Archives/Public/ietf-http-wg/"/>.
</t>
<t>
The current issues list is at
<eref target="http://tools.ietf.org/wg/httpbis/trac/report/3"/> and related
documents (including fancy diffs) can be found at
<eref target="http://tools.ietf.org/wg/httpbis/"/>.
</t>
<t>
The changes in this draft are summarized in <xref target="changes.since.25"/>.
</t>
</note>
</front>
<middle>
<section title="Introduction" anchor="introduction">
<t>
The Hypertext Transfer Protocol (HTTP) is a stateless application-level
request/response protocol that uses extensible semantics and
self-descriptive message payloads for flexible interaction with
network-based hypertext information systems. This document is the first in
a series of documents that collectively form the HTTP/1.1 specification:
<list style="empty">
<t>RFC xxx1: Message Syntax and Routing</t>
<t>RFC xxx2: Semantics and Content</t>
<t>RFC xxx3: Conditional Requests</t>
<t>RFC xxx4: Range Requests</t>
<t>RFC xxx5: Caching</t>
<t>RFC xxx6: Authentication</t>
</list>
</t>
<t>
This HTTP/1.1 specification obsoletes
RFC 2616 and
RFC 2145 (on HTTP versioning).
This specification also updates the use of CONNECT to establish a tunnel,
previously defined in RFC 2817,
and defines the "https" URI scheme that was described informally in
RFC 2818.
</t>
<t>
HTTP is a generic interface protocol for information systems. It is
designed to hide the details of how a service is implemented by presenting
a uniform interface to clients that is independent of the types of
resources provided. Likewise, servers do not need to be aware of each
client's purpose: an HTTP request can be considered in isolation rather
than being associated with a specific type of client or a predetermined
sequence of application steps. The result is a protocol that can be used
effectively in many different contexts and for which implementations can
evolve independently over time.
</t>
<t>
HTTP is also designed for use as an intermediation protocol for translating
communication to and from non-HTTP information systems.
HTTP proxies and gateways can provide access to alternative information
services by translating their diverse protocols into a hypertext
format that can be viewed and manipulated by clients in the same way
as HTTP services.
</t>
<t>
One consequence of this flexibility is that the protocol cannot be
defined in terms of what occurs behind the interface. Instead, we
are limited to defining the syntax of communication, the intent
of received communication, and the expected behavior of recipients.
If the communication is considered in isolation, then successful
actions ought to be reflected in corresponding changes to the
observable interface provided by servers. However, since multiple
clients might act in parallel and perhaps at cross-purposes, we
cannot require that such changes be observable beyond the scope
of a single response.
</t>
<t>
This document describes the architectural elements that are used or
referred to in HTTP, defines the "http" and "https" URI schemes,
describes overall network operation and connection management,
and defines HTTP message framing and forwarding requirements.
Our goal is to define all of the mechanisms necessary for HTTP message
handling that are independent of message semantics, thereby defining the
complete set of requirements for message parsers and
message-forwarding intermediaries.
</t>
<section title="Requirement Notation" anchor="intro.requirements">
<t>
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in <xref target="RFC2119"/>.
</t>
<t>
Conformance criteria and considerations regarding error handling
are defined in <xref target="conformance"/>.
</t>
</section>
<section title="Syntax Notation" anchor="notation">
<iref primary="true" item="Grammar" subitem="ALPHA"/>
<iref primary="true" item="Grammar" subitem="CR"/>
<iref primary="true" item="Grammar" subitem="CRLF"/>
<iref primary="true" item="Grammar" subitem="CTL"/>
<iref primary="true" item="Grammar" subitem="DIGIT"/>
<iref primary="true" item="Grammar" subitem="DQUOTE"/>
<iref primary="true" item="Grammar" subitem="HEXDIG"/>
<iref primary="true" item="Grammar" subitem="HTAB"/>
<iref primary="true" item="Grammar" subitem="LF"/>
<iref primary="true" item="Grammar" subitem="OCTET"/>
<iref primary="true" item="Grammar" subitem="SP"/>
<iref primary="true" item="Grammar" subitem="VCHAR"/>
<t>
This specification uses the Augmented Backus-Naur Form (ABNF) notation of
<xref target="RFC5234"/> with a list extension, defined in
<xref target="abnf.extension"/>, that allows for compact definition of
comma-separated lists using a '#' operator (similar to how the '*' operator
indicates repetition).
<xref target="collected.abnf"/> shows the collected grammar with all list
operators expanded to standard ABNF notation.
</t>
<t anchor="core.rules">
The following core rules are included by
reference, as defined in <xref target="RFC5234"/>, Appendix B.1:
ALPHA (letters), CR (carriage return), CRLF (CR LF), CTL (controls),
DIGIT (decimal 0-9), DQUOTE (double quote),
HEXDIG (hexadecimal 0-9/A-F/a-f), HTAB (horizontal tab), LF (line feed),
OCTET (any 8-bit sequence of data), SP (space), and
VCHAR (any visible <xref target="USASCII"/> character).
</t>
<t>
As a convention, ABNF rule names prefixed with "obs-" denote
"obsolete" grammar rules that appear for historical reasons.
</t>
</section>
</section>
<section title="Architecture" anchor="architecture">
<t>
HTTP was created for the World Wide Web (WWW) architecture
and has evolved over time to support the scalability needs of a worldwide
hypertext system. Much of that architecture is reflected in the terminology
and syntax productions used to define HTTP.
</t>
<section title="Client/Server Messaging" anchor="operation">
<iref primary="true" item="client"/>
<iref primary="true" item="server"/>
<iref primary="true" item="connection"/>
<t>
HTTP is a stateless request/response protocol that operates by exchanging
messages (<xref target="http.message"/>) across a reliable
transport or session-layer
"connection" (<xref target="connection.management"/>).
An HTTP "client" is a program that establishes a connection
to a server for the purpose of sending one or more HTTP requests.
An HTTP "server" is a program that accepts connections
in order to service HTTP requests by sending HTTP responses.
</t>
<iref primary="true" item="user agent"/>
<iref primary="true" item="origin server"/>
<iref primary="true" item="browser"/>
<iref primary="true" item="spider"/>
<iref primary="true" item="sender"/>
<iref primary="true" item="recipient"/>
<t>
The terms client and server refer only to the roles that
these programs perform for a particular connection. The same program
might act as a client on some connections and a server on others.
The term "user agent" refers to any of the various
client programs that initiate a request, including (but not limited to)
browsers, spiders (web-based robots), command-line tools, custom
applications, and mobile apps.
The term "origin server" refers to the program that can
originate authoritative responses for a given target resource.
The terms "sender" and "recipient" refer to
any implementation that sends or receives a given message, respectively.
</t>
<t>
HTTP relies upon the Uniform Resource Identifier (URI)
standard <xref target="RFC3986"/> to indicate the target resource
(<xref target="target-resource"/>) and relationships between resources.
Messages are passed in a format similar to that used by Internet mail
<xref target="RFC5322"/> and the Multipurpose Internet Mail Extensions
(MIME) <xref target="RFC2045"/> (see Appendix A of <xref target="Part2"/> for the differences
between HTTP and MIME messages).
</t>
<t>
Most HTTP communication consists of a retrieval request (GET) for
a representation of some resource identified by a URI. In the
simplest case, this might be accomplished via a single bidirectional
connection (===) between the user agent (UA) and the origin server (O).
</t>
<figure><artwork type="drawing"><![CDATA[
request >
UA ======================================= O
< response
]]></artwork></figure>
<iref primary="true" item="message"/>
<iref primary="true" item="request"/>
<iref primary="true" item="response"/>
<t>
A client sends an HTTP request to a server in the form of a request
message, beginning with a request-line that includes a method, URI, and
protocol version (<xref target="request.line"/>),
followed by header fields containing
request modifiers, client information, and representation metadata
(<xref target="header.fields"/>),
an empty line to indicate the end of the header section, and finally
a message body containing the payload body (if any,
<xref target="message.body"/>).
</t>
<t>
A server responds to a client's request by sending one or more HTTP
response
messages, each beginning with a status line that
includes the protocol version, a success or error code, and textual
reason phrase (<xref target="status.line"/>),
possibly followed by header fields containing server
information, resource metadata, and representation metadata
(<xref target="header.fields"/>),
an empty line to indicate the end of the header section, and finally
a message body containing the payload body (if any,
<xref target="message.body"/>).
</t>
<t>
A connection might be used for multiple request/response exchanges,
as defined in <xref target="persistent.connections"/>.
</t>
<t>
The following example illustrates a typical message exchange for a
GET request (Section 4.3.1 of <xref target="Part2"/>) on the URI "http://www.example.com/hello.txt":
</t>
<figure><preamble>
Client request:
</preamble><artwork type="message/http; msgtype="request""><![CDATA[
GET /hello.txt HTTP/1.1
User-Agent: curl/7.16.3 libcurl/7.16.3 OpenSSL/0.9.7l zlib/1.2.3
Host: www.example.com
Accept-Language: en, mi
]]></artwork></figure>
<figure><preamble>
Server response:
</preamble><artwork type="message/http; msgtype="response""><![CDATA[
HTTP/1.1 200 OK
Date: Mon, 27 Jul 2009 12:28:53 GMT
Server: Apache
Last-Modified: Wed, 22 Jul 2009 19:15:56 GMT
ETag: "34aa387-d-1568eb00"
Accept-Ranges: bytes
Content-Length: 51
Vary: Accept-Encoding
Content-Type: text/plain
Hello World! My payload includes a trailing CRLF.
]]></artwork>
</figure>
</section>
<section title="Implementation Diversity" anchor="implementation-diversity">
<t>
When considering the design of HTTP, it is easy to fall into a trap of
thinking that all user agents are general-purpose browsers and all origin
servers are large public websites. That is not the case in practice.
Common HTTP user agents include household appliances, stereos, scales,
firmware update scripts, command-line programs, mobile apps,
and communication devices in a multitude of shapes and sizes. Likewise,
common HTTP origin servers include home automation units, configurable
networking components, office machines, autonomous robots, news feeds,
traffic cameras, ad selectors, and video delivery platforms.
</t>
<t>
The term "user agent" does not imply that there is a human user directly
interacting with the software agent at the time of a request. In many
cases, a user agent is installed or configured to run in the background
and save its results for later inspection (or save only a subset of those
results that might be interesting or erroneous). Spiders, for example, are
typically given a start URI and configured to follow certain behavior while
crawling the Web as a hypertext graph.
</t>
<t>
The implementation diversity of HTTP means that not all user agents can
make interactive suggestions to their user or provide adequate warning for
security or privacy concerns. In the few cases where this
specification requires reporting of errors to the user, it is acceptable
for such reporting to only be observable in an error console or log file.
Likewise, requirements that an automated action be confirmed by the user
before proceeding might be met via advance configuration choices,
run-time options, or simple avoidance of the unsafe action; confirmation
does not imply any specific user interface or interruption of normal
processing if the user has already made that choice.
</t>
</section>
<section title="Intermediaries" anchor="intermediaries">
<iref primary="true" item="intermediary"/>
<t>
HTTP enables the use of intermediaries to satisfy requests through
a chain of connections. There are three common forms of HTTP
intermediary: proxy, gateway, and tunnel. In some cases,
a single intermediary might act as an origin server, proxy, gateway,
or tunnel, switching behavior based on the nature of each request.
</t>
<figure><artwork type="drawing"><![CDATA[
> > > >
UA =========== A =========== B =========== C =========== O
< < < <
]]></artwork></figure>
<t>
The figure above shows three intermediaries (A, B, and C) between the
user agent and origin server. A request or response message that
travels the whole chain will pass through four separate connections.
Some HTTP communication options
might apply only to the connection with the nearest, non-tunnel
neighbor, only to the end-points of the chain, or to all connections
along the chain. Although the diagram is linear, each participant might
be engaged in multiple, simultaneous communications. For example, B
might be receiving requests from many clients other than A, and/or
forwarding requests to servers other than C, at the same time that it
is handling A's request. Likewise, later requests might be sent through a
different path of connections, often based on dynamic configuration for
load balancing.
</t>
<t>
<iref primary="true" item="upstream"/><iref primary="true" item="downstream"/>
<iref primary="true" item="inbound"/><iref primary="true" item="outbound"/>
The terms "upstream" and "downstream" are
used to describe directional requirements in relation to the message flow:
all messages flow from upstream to downstream.
The terms inbound and outbound are used to describe directional
requirements in relation to the request route:
"inbound" means toward the origin server and
"outbound" means toward the user agent.
</t>
<t><iref primary="true" item="proxy"/>
A "proxy" is a message forwarding agent that is selected by the
client, usually via local configuration rules, to receive requests
for some type(s) of absolute URI and attempt to satisfy those
requests via translation through the HTTP interface. Some translations
are minimal, such as for proxy requests for "http" URIs, whereas
other requests might require translation to and from entirely different
application-level protocols. Proxies are often used to group an
organization's HTTP requests through a common intermediary for the
sake of security, annotation services, or shared caching. Some proxies
are designed to apply transformations to selected messages or payloads
while they are being forwarded, as described in
<xref target="message.transformations"/>.
</t>
<t><iref primary="true" item="gateway"/><iref primary="true" item="reverse proxy"/>
<iref primary="true" item="accelerator"/>
A "gateway" (a.k.a., "reverse proxy") is an
intermediary that acts as an origin server for the outbound connection, but
translates received requests and forwards them inbound to another server or
servers. Gateways are often used to encapsulate legacy or untrusted
information services, to improve server performance through
"accelerator" caching, and to enable partitioning or load
balancing of HTTP services across multiple machines.
</t>
<t>
All HTTP requirements applicable to an origin server
also apply to the outbound communication of a gateway.
A gateway communicates with inbound servers using any protocol that
it desires, including private extensions to HTTP that are outside
the scope of this specification. However, an HTTP-to-HTTP gateway
that wishes to interoperate with third-party HTTP servers ought to conform
to user agent requirements on the gateway's inbound connection.
</t>
<t><iref primary="true" item="tunnel"/>
A "tunnel" acts as a blind relay between two connections
without changing the messages. Once active, a tunnel is not
considered a party to the HTTP communication, though the tunnel might
have been initiated by an HTTP request. A tunnel ceases to exist when
both ends of the relayed connection are closed. Tunnels are used to
extend a virtual connection through an intermediary, such as when
Transport Layer Security (TLS, <xref target="RFC5246"/>) is used to
establish confidential communication through a shared firewall proxy.
</t>
<t>
The above categories for intermediary only consider those acting as
participants in the HTTP communication. There are also intermediaries
that can act on lower layers of the network protocol stack, filtering or
redirecting HTTP traffic without the knowledge or permission of message
senders. Network intermediaries are indistinguishable (at a protocol level)
from a man-in-the-middle attack, often introducing security flaws or
interoperability problems due to mistakenly violating HTTP semantics.
</t>
<t><iref primary="true" item="interception proxy"/>
<iref primary="true" item="transparent proxy"/>
<iref primary="true" item="captive portal"/>
For example, an
"interception proxy" <xref target="RFC3040"/> (also commonly
known as a "transparent proxy" <xref target="RFC1919"/> or
"captive portal")
differs from an HTTP proxy because it is not selected by the client.
Instead, an interception proxy filters or redirects outgoing TCP port 80
packets (and occasionally other common port traffic).
Interception proxies are commonly found on public network access points,
as a means of enforcing account subscription prior to allowing use of
non-local Internet services, and within corporate firewalls to enforce
network usage policies.
</t>
<t>
HTTP is defined as a stateless protocol, meaning that each request message
can be understood in isolation. Many implementations depend on HTTP's
stateless design in order to reuse proxied connections or dynamically
load-balance requests across multiple servers. Hence, a server MUST NOT
assume that two requests on the same connection are from the same user
agent unless the connection is secured and specific to that agent.
Some non-standard HTTP extensions (e.g., <xref target="RFC4559"/>) have
been known to violate this requirement, resulting in security and
interoperability problems.
</t>
</section>
<section title="Caches" anchor="caches">
<iref primary="true" item="cache"/>
<t>
A "cache" is a local store of previous response messages and the
subsystem that controls its message storage, retrieval, and deletion.
A cache stores cacheable responses in order to reduce the response
time and network bandwidth consumption on future, equivalent
requests. Any client or server MAY employ a cache, though a cache
cannot be used by a server while it is acting as a tunnel.
</t>
<t>
The effect of a cache is that the request/response chain is shortened
if one of the participants along the chain has a cached response
applicable to that request. The following illustrates the resulting
chain if B has a cached copy of an earlier response from O (via C)
for a request that has not been cached by UA or A.
</t>
<figure><artwork type="drawing"><![CDATA[
> >
UA =========== A =========== B - - - - - - C - - - - - - O
< <
]]></artwork></figure>
<t><iref primary="true" item="cacheable"/>
A response is "cacheable" if a cache is allowed to store a copy of
the response message for use in answering subsequent requests.
Even when a response is cacheable, there might be additional
constraints placed by the client or by the origin server on when
that cached response can be used for a particular request. HTTP
requirements for cache behavior and cacheable responses are
defined in Section 2 of <xref target="Part6"/>.
</t>
<t>
There are a wide variety of architectures and configurations
of caches deployed across the World Wide Web and
inside large organizations. These include national hierarchies
of proxy caches to save transoceanic bandwidth, collaborative systems that
broadcast or multicast cache entries, archives of pre-fetched cache
entries for use in off-line or high-latency environments, and so on.
</t>
</section>
<section title="Conformance and Error Handling" anchor="conformance">
<t>
This specification targets conformance criteria according to the role of
a participant in HTTP communication. Hence, HTTP requirements are placed
on senders, recipients, clients, servers, user agents, intermediaries,
origin servers, proxies, gateways, or caches, depending on what behavior
is being constrained by the requirement. Additional (social) requirements
are placed on implementations, resource owners, and protocol element
registrations when they apply beyond the scope of a single communication.
</t>
<t>
The verb "generate" is used instead of "send" where a requirement
differentiates between creating a protocol element and merely forwarding a
received element downstream.
</t>
<t>
An implementation is considered conformant if it complies with all of the
requirements associated with the roles it partakes in HTTP.
</t>
<t>
Conformance includes both the syntax and semantics of protocol
elements. A sender MUST NOT generate protocol elements that convey a
meaning that is known by that sender to be false. A sender MUST NOT
generate protocol elements that do not match the grammar defined by the
corresponding ABNF rules. Within a given message, a sender MUST NOT
generate protocol elements or syntax alternatives that are only allowed to
be generated by participants in other roles (i.e., a role that the sender
does not have for that message).
</t>
<t>
When a received protocol element is parsed, the recipient MUST be able to
parse any value of reasonable length that is applicable to the recipient's
role and matches the grammar defined by the corresponding ABNF rules.
Note, however, that some received protocol elements might not be parsed.
For example, an intermediary forwarding a message might parse a
header-field into generic field-name and field-value components, but then
forward the header field without further parsing inside the field-value.
</t>
<t>
HTTP does not have specific length limitations for many of its protocol
elements because the lengths that might be appropriate will vary widely,
depending on the deployment context and purpose of the implementation.
Hence, interoperability between senders and recipients depends on shared
expectations regarding what is a reasonable length for each protocol
element. Furthermore, what is commonly understood to be a reasonable length
for some protocol elements has changed over the course of the past two
decades of HTTP use, and is expected to continue changing in the future.
</t>
<t>
At a minimum, a recipient MUST be able to parse and process protocol
element lengths that are at least as long as the values that it generates
for those same protocol elements in other messages. For example, an origin
server that publishes very long URI references to its own resources needs
to be able to parse and process those same references when received as a
request target.
</t>
<t>
A recipient MUST interpret a received protocol element according to the
semantics defined for it by this specification, including extensions to
this specification, unless the recipient has determined (through experience
or configuration) that the sender incorrectly implements what is implied by
those semantics.
For example, an origin server might disregard the contents of a received
Accept-Encoding header field if inspection of the
User-Agent header field indicates a specific implementation
version that is known to fail on receipt of certain content codings.
</t>
<t>
Unless noted otherwise, a recipient MAY attempt to recover a usable
protocol element from an invalid construct. HTTP does not define
specific error handling mechanisms except when they have a direct impact
on security, since different applications of the protocol require
different error handling strategies. For example, a Web browser might
wish to transparently recover from a response where the
Location header field doesn't parse according to the ABNF,
whereas a systems control client might consider any form of error recovery
to be dangerous.
</t>
</section>
<section title="Protocol Versioning" anchor="http.version">
<t>
HTTP uses a "<major>.<minor>" numbering scheme to indicate
versions of the protocol. This specification defines version "1.1".
The protocol version as a whole indicates the sender's conformance
with the set of requirements laid out in that version's corresponding
specification of HTTP.
</t>
<t>
The version of an HTTP message is indicated by an HTTP-version field
in the first line of the message. HTTP-version is case-sensitive.
</t>
<figure><iref primary="true" item="Grammar" subitem="HTTP-version"/><iref primary="true" item="Grammar" subitem="HTTP-name"/><artwork type="abnf2616"><![CDATA[
HTTP-version = HTTP-name "/" DIGIT "." DIGIT
HTTP-name = %x48.54.54.50 ; "HTTP", case-sensitive
]]></artwork></figure>
<t>
The HTTP version number consists of two decimal digits separated by a "."
(period or decimal point). The first digit ("major version") indicates the
HTTP messaging syntax, whereas the second digit ("minor version") indicates
the highest minor version within that major version to which the sender is
conformant and able to understand for future communication. The minor
version advertises the sender's communication capabilities even when the
sender is only using a backwards-compatible subset of the protocol,
thereby letting the recipient know that more advanced features can
be used in response (by servers) or in future requests (by clients).
</t>
<t>
When an HTTP/1.1 message is sent to an HTTP/1.0 recipient
<xref target="RFC1945"/> or a recipient whose version is unknown,
the HTTP/1.1 message is constructed such that it can be interpreted
as a valid HTTP/1.0 message if all of the newer features are ignored.
This specification places recipient-version requirements on some
new features so that a conformant sender will only use compatible
features until it has determined, through configuration or the
receipt of a message, that the recipient supports HTTP/1.1.
</t>
<t>
The interpretation of a header field does not change between minor
versions of the same major HTTP version, though the default
behavior of a recipient in the absence of such a field can change.
Unless specified otherwise, header fields defined in HTTP/1.1 are
defined for all versions of HTTP/1.x. In particular, the <xref target="header.host" format="none">Host</xref>
and <xref target="header.connection" format="none">Connection</xref> header fields ought to be implemented by all
HTTP/1.x implementations whether or not they advertise conformance with
HTTP/1.1.
</t>
<t>
New header fields can be introduced without changing the protocol version
if their defined semantics allow them to be safely ignored by recipients
that do not recognize them. Header field extensibility is discussed in
<xref target="field.extensibility"/>.
</t>
<t>
Intermediaries that process HTTP messages (i.e., all intermediaries
other than those acting as tunnels) MUST send their own HTTP-version
in forwarded messages. In other words, they are not allowed to blindly
forward the first line of an HTTP message without ensuring that the
protocol version in that message matches a version to which that
intermediary is conformant for both the receiving and
sending of messages. Forwarding an HTTP message without rewriting
the HTTP-version might result in communication errors when downstream
recipients use the message sender's version to determine what features
are safe to use for later communication with that sender.
</t>
<t>
A client SHOULD send a request version equal to the highest
version to which the client is conformant and
whose major version is no higher than the highest version supported
by the server, if this is known. A client MUST NOT send a
version to which it is not conformant.
</t>
<t>
A client MAY send a lower request version if it is known that
the server incorrectly implements the HTTP specification, but only
after the client has attempted at least one normal request and determined
from the response status code or header fields (e.g., Server) that
the server improperly handles higher request versions.
</t>
<t>
A server SHOULD send a response version equal to the highest version to
which the server is conformant that has a major version less than or equal
to the one received in the request.
A server MUST NOT send a version to which it is not conformant.
A server can send a 505 (HTTP Version Not Supported)
response if it wishes, for any reason, to refuse service of the client's
major protocol version.
</t>
<t>
A server MAY send an HTTP/1.0 response to a request
if it is known or suspected that the client incorrectly implements the
HTTP specification and is incapable of correctly processing later
version responses, such as when a client fails to parse the version
number correctly or when an intermediary is known to blindly forward
the HTTP-version even when it doesn't conform to the given minor
version of the protocol. Such protocol downgrades SHOULD NOT be
performed unless triggered by specific client attributes, such as when
one or more of the request header fields (e.g., User-Agent)
uniquely match the values sent by a client known to be in error.
</t>
<t>
The intention of HTTP's versioning design is that the major number
will only be incremented if an incompatible message syntax is
introduced, and that the minor number will only be incremented when
changes made to the protocol have the effect of adding to the message
semantics or implying additional capabilities of the sender. However,
the minor version was not incremented for the changes introduced between
<xref target="RFC2068"/> and <xref target="RFC2616"/>, and this revision
has specifically avoided any such changes to the protocol.
</t>
<t>
When an HTTP message is received with a major version number that the
recipient implements, but a higher minor version number than what the
recipient implements, the recipient SHOULD process the message as if it
were in the highest minor version within that major version to which the
recipient is conformant. A recipient can assume that a message with a
higher minor version, when sent to a recipient that has not yet indicated
support for that higher version, is sufficiently backwards-compatible to be
safely processed by any implementation of the same major version.
</t>
</section>
<section title="Uniform Resource Identifiers" anchor="uri">
<iref primary="true" item="resource"/>
<t>
Uniform Resource Identifiers (URIs) <xref target="RFC3986"/> are used
throughout HTTP as the means for identifying resources (Section 2 of <xref target="Part2"/>).
URI references are used to target requests, indicate redirects, and define
relationships.
</t>
<t>
The definitions of "URI-reference",
"absolute-URI", "relative-part", "scheme", "authority", "port", "host",
"path-abempty", "segment", "query", and "fragment" are adopted from the
URI generic syntax.
An "absolute-path" rule is defined for protocol elements that can contain a
non-empty path component. (This rule differs slightly from RFC 3986's
path-abempty rule, which allows for an empty path to be used in references,
and path-absolute rule, which does not allow paths that begin with "//".)
A "partial-URI" rule is defined for protocol elements
that can contain a relative URI but not a fragment component.
</t>
<figure><iref primary="true" item="Grammar" subitem="URI-reference"><!--exported production--></iref><iref primary="true" item="Grammar" subitem="absolute-URI"/><iref primary="true" item="Grammar" subitem="scheme"/><iref primary="true" item="Grammar" subitem="authority"/><iref primary="true" item="Grammar" subitem="absolute-path"/><iref primary="true" item="Grammar" subitem="port"/><iref primary="true" item="Grammar" subitem="query"/><iref primary="true" item="Grammar" subitem="fragment"/><iref primary="true" item="Grammar" subitem="segment"/><iref primary="true" item="Grammar" subitem="uri-host"/><iref primary="true" item="Grammar" subitem="partial-URI"><!--exported production--></iref><artwork type="abnf2616"><![CDATA[
URI-reference = <URI-reference, defined in [RFC3986], Section 4.1>
absolute-URI = <absolute-URI, defined in [RFC3986], Section 4.3>
relative-part = <relative-part, defined in [RFC3986], Section 4.2>
scheme = <scheme, defined in [RFC3986], Section 3.1>
authority = <authority, defined in [RFC3986], Section 3.2>
uri-host = <host, defined in [RFC3986], Section 3.2.2>
port = <port, defined in [RFC3986], Section 3.2.3>
path-abempty = <path-abempty, defined in [RFC3986], Section 3.3>
segment = <segment, defined in [RFC3986], Section 3.3>
query = <query, defined in [RFC3986], Section 3.4>
fragment = <fragment, defined in [RFC3986], Section 3.5>
absolute-path = 1*( "/" segment )
partial-URI = relative-part [ "?" query ]
]]></artwork></figure>
<t>
Each protocol element in HTTP that allows a URI reference will indicate
in its ABNF production whether the element allows any form of reference
(URI-reference), only a URI in absolute form (absolute-URI), only the
path and optional query components, or some combination of the above.
Unless otherwise indicated, URI references are parsed
relative to the effective request URI
(<xref target="effective.request.uri"/>).
</t>
<section title="http URI scheme" anchor="http.uri">
<iref item="http URI scheme" primary="true"/>
<iref item="URI scheme" subitem="http" primary="true"/>
<t>
The "http" URI scheme is hereby defined for the purpose of minting
identifiers according to their association with the hierarchical
namespace governed by a potential HTTP origin server listening for
TCP (<xref target="RFC0793"/>) connections on a given port.
</t>
<figure><iref primary="true" item="Grammar" subitem="http-URI"><!--terminal production--></iref><artwork type="abnf2616"><![CDATA[
http-URI = "http:" "//" authority path-abempty [ "?" query ]
[ "#" fragment ]
]]></artwork></figure>
<t>
The origin server for an "http" URI is identified by the
<xref target="uri" format="none">authority</xref> component, which includes a host identifier
and optional TCP port (<xref target="RFC3986"/>, Section 3.2.2).
The hierarchical path component and optional query component serve as an
identifier for a potential target resource within that origin server's name
space. The optional fragment component allows for indirect identification
of a secondary resource, independent of the URI scheme, as defined in
Section 3.5 of <xref target="RFC3986"/>.
</t>
<t>
A sender MUST NOT generate an "http" URI with an empty host identifier.
A recipient that processes such a URI reference MUST reject it as invalid.
</t>
<t>
If the host identifier is provided as an IP address, the origin server is
the listener (if any) on the indicated TCP port at that IP address.
If host is a registered name, the registered name is an indirect identifier
for use with a name resolution service, such as DNS, to find an address for
that origin server.
If the port subcomponent is empty or not given, TCP port 80 (the
reserved port for WWW services) is the default.
</t>
<t>
Note that the presence of a URI with a given authority component does not
imply that there is always an HTTP server listening for connections on
that host and port. Anyone can mint a URI. What the authority component
determines is who has the right to respond authoritatively to requests that
target the identified resource. The delegated nature of registered names
and IP addresses creates a federated namespace, based on control over the
indicated host and port, whether or not an HTTP server is present.
See <xref target="establishing.authority"/> for security considerations
related to establishing authority.
</t>
<t>
When an "http" URI is used within a context that calls for access to the
indicated resource, a client MAY attempt access by resolving
the host to an IP address, establishing a TCP connection to that address
on the indicated port, and sending an HTTP request message
(<xref target="http.message"/>) containing the URI's identifying data
(<xref target="message.routing"/>) to the server.
If the server responds to that request with a non-interim HTTP response
message, as described in Section 6 of <xref target="Part2"/>, then that response
is considered an authoritative answer to the client's request.
</t>
<t>
Although HTTP is independent of the transport protocol, the "http"
scheme is specific to TCP-based services because the name delegation
process depends on TCP for establishing authority.
An HTTP service based on some other underlying connection protocol
would presumably be identified using a different URI scheme, just as
the "https" scheme (below) is used for resources that require an
end-to-end secured connection. Other protocols might also be used to
provide access to "http" identified resources — it is only the
authoritative interface that is specific to TCP.
</t>
<t>
The URI generic syntax for authority also includes a deprecated
userinfo subcomponent (<xref target="RFC3986"/>, Section 3.2.1)
for including user authentication information in the URI. Some
implementations make use of the userinfo component for internal
configuration of authentication information, such as within command
invocation options, configuration files, or bookmark lists, even
though such usage might expose a user identifier or password.
A sender MUST NOT generate the userinfo subcomponent (and its "@"
delimiter) when an "http" URI reference is generated within a message as a
request target or header field value.
Before making use of an "http" URI reference received from an untrusted
source, a recipient SHOULD parse for userinfo and treat its presence as
an error; it is likely being used to obscure the authority for the sake of
phishing attacks.
</t>
</section>
<section title="https URI scheme" anchor="https.uri">
<iref item="https URI scheme"/>
<iref item="URI scheme" subitem="https"/>
<t>
The "https" URI scheme is hereby defined for the purpose of minting
identifiers according to their association with the hierarchical
namespace governed by a potential HTTP origin server listening to a
given TCP port for TLS-secured connections (<xref target="RFC5246"/>).
</t>
<t>
All of the requirements listed above for the "http" scheme are also
requirements for the "https" scheme, except that TCP port 443 is the
default if the port subcomponent is empty or not given,
and the user agent MUST ensure that its connection to the origin
server is secured through the use of strong encryption, end-to-end,
prior to sending the first HTTP request.
</t>
<figure><iref primary="true" item="Grammar" subitem="https-URI"><!--terminal production--></iref><artwork type="abnf2616"><![CDATA[
https-URI = "https:" "//" authority path-abempty [ "?" query ]
[ "#" fragment ]
]]></artwork></figure>
<t>
Note that the "https" URI scheme depends on both TLS and TCP for
establishing authority.
Resources made available via the "https" scheme have no shared
identity with the "http" scheme even if their resource identifiers
indicate the same authority (the same host listening to the same
TCP port). They are distinct name spaces and are considered to be
distinct origin servers. However, an extension to HTTP that is
defined to apply to entire host domains, such as the Cookie protocol
<xref target="RFC6265"/>, can allow information
set by one service to impact communication with other services
within a matching group of host domains.
</t>
<t>
The process for authoritative access to an "https" identified
resource is defined in <xref target="RFC2818"/>.
</t>
</section>
<section title="http and https URI Normalization and Comparison" anchor="uri.comparison">
<t>
Since the "http" and "https" schemes conform to the URI generic syntax,
such URIs are normalized and compared according to the algorithm defined
in Section 6 of <xref target="RFC3986"/>, using the defaults
described above for each scheme.
</t>
<t>
If the port is equal to the default port for a scheme, the normal form is
to omit the port subcomponent. When not being used in absolute form as the
request target of an OPTIONS request, an empty path component is equivalent
to an absolute path of "/", so the normal form is to provide a path of "/"
instead. The scheme and host are case-insensitive and normally provided in
lowercase; all other components are compared in a case-sensitive manner.
Characters other than those in the "reserved" set are equivalent to their
percent-encoded octets: the normal form is to not encode them
(see Sections 2.1 and
2.2 of
<xref target="RFC3986"/>).
</t>
<t>
For example, the following three URIs are equivalent:
</t>
<figure><artwork type="example"><![CDATA[
http://example.com:80/~smith/home.html
http://EXAMPLE.com/%7Esmith/home.html
http://EXAMPLE.com:/%7esmith/home.html
]]></artwork></figure>
</section>
</section>
</section>
<section title="Message Format" anchor="http.message">
<iref item="header section"/>
<iref item="headers"/>
<iref item="header field"/>
<t>
All HTTP/1.1 messages consist of a start-line followed by a sequence of
octets in a format similar to the Internet Message Format
<xref target="RFC5322"/>: zero or more header fields (collectively
referred to as the "headers" or the "header section"), an empty line
indicating the end of the header section, and an optional message body.
</t>
<figure><iref primary="true" item="Grammar" subitem="HTTP-message"><!--terminal production--></iref><artwork type="abnf2616"><![CDATA[
HTTP-message = start-line
*( header-field CRLF )
CRLF
[ message-body ]
]]></artwork></figure>
<t>
The normal procedure for parsing an HTTP message is to read the
start-line into a structure, read each header field into a hash
table by field name until the empty line, and then use the parsed
data to determine if a message body is expected. If a message body
has been indicated, then it is read as a stream until an amount
of octets equal to the message body length is read or the connection
is closed.
</t>
<t>
A recipient MUST parse an HTTP message as a sequence of octets in an
encoding that is a superset of US-ASCII <xref target="USASCII"/>.
Parsing an HTTP message as a stream of Unicode characters, without regard
for the specific encoding, creates security vulnerabilities due to the
varying ways that string processing libraries handle invalid multibyte
character sequences that contain the octet LF (%x0A). String-based
parsers can only be safely used within protocol elements after the element
has been extracted from the message, such as within a header field-value
after message parsing has delineated the individual fields.
</t>
<t>
An HTTP message can be parsed as a stream for incremental processing or
forwarding downstream. However, recipients cannot rely on incremental
delivery of partial messages, since some implementations will buffer or
delay message forwarding for the sake of network efficiency, security
checks, or payload transformations.
</t>
<t>
A sender MUST NOT send whitespace between the start-line and
the first header field.
A recipient that receives whitespace between the start-line and
the first header field MUST either reject the message as invalid or
consume each whitespace-preceded line without further processing of it
(i.e., ignore the entire line, along with any subsequent lines preceded
by whitespace, until a properly formed header field is received or the
header section is terminated).
</t>
<t>
The presence of such whitespace in a request
might be an attempt to trick a server into ignoring that field or
processing the line after it as a new request, either of which might
result in a security vulnerability if other implementations within
the request chain interpret the same message differently.
Likewise, the presence of such whitespace in a response might be
ignored by some clients or cause others to cease parsing.
</t>
<section title="Start Line" anchor="start.line">
<t>
An HTTP message can either be a request from client to server or a
response from server to client. Syntactically, the two types of message
differ only in the start-line, which is either a request-line (for requests)
or a status-line (for responses), and in the algorithm for determining
the length of the message body (<xref target="message.body"/>).
</t>
<t>
In theory, a client could receive requests and a server could receive
responses, distinguishing them by their different start-line formats,
but in practice servers are implemented to only expect a request
(a response is interpreted as an unknown or invalid request method)
and clients are implemented to only expect a response.
</t>
<figure><iref primary="true" item="Grammar" subitem="start-line"/><artwork type="abnf2616"><![CDATA[
start-line = request-line / status-line
]]></artwork></figure>
<section title="Request Line" anchor="request.line">
<t>
A request-line begins with a method token, followed by a single
space (SP), the request-target, another single space (SP), the
protocol version, and ending with CRLF.
</t>
<figure><iref primary="true" item="Grammar" subitem="request-line"/><artwork type="abnf2616"><![CDATA[
request-line = method SP request-target SP HTTP-version CRLF
]]></artwork></figure>
<iref primary="true" item="method"/>
<t anchor="method">
The method token indicates the request method to be performed on the
target resource. The request method is case-sensitive.
</t>
<figure><iref primary="true" item="Grammar" subitem="method"/><artwork type="abnf2616"><![CDATA[
method = token
]]></artwork></figure>
<t>
The request methods defined by this specification can be found in
Section 4 of <xref target="Part2"/>, along with information regarding the HTTP method registry
and considerations for defining new methods.
</t>
<iref item="request-target"/>
<t>
The request-target identifies the target resource upon which to apply
the request, as defined in <xref target="request-target"/>.
</t>
<t>
Recipients typically parse the request-line into its component parts by
splitting on whitespace (see <xref target="message.robustness"/>), since
no whitespace is allowed in the three components.
Unfortunately, some user agents fail to properly encode or exclude
whitespace found in hypertext references, resulting in those disallowed
characters being sent in a request-target.
</t>
<t>
Recipients of an invalid request-line SHOULD respond with either a
400 (Bad Request) error or a 301 (Moved Permanently)
redirect with the request-target properly encoded. A recipient SHOULD NOT
attempt to autocorrect and then process the request without a redirect,
since the invalid request-line might be deliberately crafted to bypass
security filters along the request chain.
</t>
<t>
HTTP does not place a pre-defined limit on the length of a request-line,
as described in <xref target="conformance"/>.
A server that receives a method longer than any that it implements
SHOULD respond with a 501 (Not Implemented) status code.
A server that receives a request-target longer than any URI it wishes to
parse MUST respond with a
414 (URI Too Long) status code (see Section 6.5.12 of <xref target="Part2"/>).
</t>
<t>
Various ad-hoc limitations on request-line length are found in practice.
It is RECOMMENDED that all HTTP senders and recipients support, at a
minimum, request-line lengths of 8000 octets.
</t>
</section>
<section title="Status Line" anchor="status.line">
<t>
The first line of a response message is the status-line, consisting
of the protocol version, a space (SP), the status code, another space,
a possibly-empty textual phrase describing the status code, and
ending with CRLF.
</t>
<figure><iref primary="true" item="Grammar" subitem="status-line"/><artwork type="abnf2616"><![CDATA[
status-line = HTTP-version SP status-code SP reason-phrase CRLF
]]></artwork></figure>
<t>
The status-code element is a 3-digit integer code describing the
result of the server's attempt to understand and satisfy the client's
corresponding request. The rest of the response message is to be
interpreted in light of the semantics defined for that status code.
See Section 6 of <xref target="Part2"/> for information about the semantics of status codes,
including the classes of status code (indicated by the first digit),
the status codes defined by this specification, considerations for the
definition of new status codes, and the IANA registry.
</t>
<figure><iref primary="true" item="Grammar" subitem="status-code"/><artwork type="abnf2616"><![CDATA[
status-code = 3DIGIT
]]></artwork></figure>
<t>
The reason-phrase element exists for the sole purpose of providing a
textual description associated with the numeric status code, mostly
out of deference to earlier Internet application protocols that were more
frequently used with interactive text clients. A client SHOULD ignore
the reason-phrase content.
</t>
<figure><iref primary="true" item="Grammar" subitem="reason-phrase"/><artwork type="abnf2616"><![CDATA[
reason-phrase = *( HTAB / SP / VCHAR / obs-text )
]]></artwork></figure>
</section>
</section>
<section title="Header Fields" anchor="header.fields">
<t>
Each header field consists of a case-insensitive field name
followed by a colon (":"), optional leading whitespace, the field value,
and optional trailing whitespace.
</t>
<figure><iref primary="true" item="Grammar" subitem="header-field"/><iref primary="true" item="Grammar" subitem="field-name"/><iref primary="true" item="Grammar" subitem="field-value"/><iref primary="true" item="Grammar" subitem="field-vchar"/><iref primary="true" item="Grammar" subitem="field-content"/><iref primary="true" item="Grammar" subitem="obs-fold"/><artwork type="abnf2616"><![CDATA[
header-field = field-name ":" OWS field-value OWS
field-name = token
field-value = *( field-content / obs-fold )
field-content = field-vchar [ 1*( SP / HTAB ) field-vchar ]
field-vchar = VCHAR / obs-text
obs-fold = CRLF 1*( SP / HTAB )
; obsolete line folding
; see Section 3.2.4
]]></artwork></figure>
<t>
The field-name token labels the corresponding field-value as having the
semantics defined by that header field. For example, the Date
header field is defined in Section 7.1.1.2 of <xref target="Part2"/> as containing the origination
timestamp for the message in which it appears.
</t>
<section title="Field Extensibility" anchor="field.extensibility">
<t>
Header fields are fully extensible: there is no limit on the
introduction of new field names, each presumably defining new semantics,
nor on the number of header fields used in a given message. Existing
fields are defined in each part of this specification and in many other
specifications outside this document set.
</t>
<t>
New header fields can be defined such that, when they are understood by a
recipient, they might override or enhance the interpretation of previously
defined header fields, define preconditions on request evaluation, or
refine the meaning of responses.
</t>
<t>
A proxy MUST forward unrecognized header fields unless the
field-name is listed in the <xref target="header.connection" format="none">Connection</xref> header field
(<xref target="header.connection"/>) or the proxy is specifically
configured to block, or otherwise transform, such fields.
Other recipients SHOULD ignore unrecognized header fields.
These requirements allow HTTP's functionality to be enhanced without
requiring prior update of deployed intermediaries.
</t>
<t>
All defined header fields ought to be registered with IANA in the
Message Header Field Registry, as described in Section 8.3 of <xref target="Part2"/>.
</t>
</section>
<section title="Field Order" anchor="field.order">
<t>
The order in which header fields with differing field names are
received is not significant. However, it is good practice to send
header fields that contain control data first, such as <xref target="header.host" format="none">Host</xref>
on requests and Date on responses, so that implementations
can decide when not to handle a message as early as possible.
A server MUST NOT apply a request to the target resource until the entire
request header section is received, since later header fields might include
conditionals, authentication credentials, or deliberately misleading
duplicate header fields that would impact request processing.
</t>
<t>
A sender MUST NOT generate multiple header fields with the same field
name in a message unless either the entire field value for that
header field is defined as a comma-separated list [i.e., #(values)]
or the header field is a well-known exception (as noted below).
</t>
<t>
A recipient MAY combine multiple header fields with the same field name
into one "field-name: field-value" pair, without changing the semantics of
the message, by appending each subsequent field value to the combined
field value in order, separated by a comma. The order in which
header fields with the same field name are received is therefore
significant to the interpretation of the combined field value;
a proxy MUST NOT change the order of these field values when
forwarding a message.
</t>
<t><list>
<t>
Note: In practice, the "Set-Cookie" header field (<xref target="RFC6265"/>)
often appears multiple times in a response message and does not use the
list syntax, violating the above requirements on multiple header fields
with the same name. Since it cannot be combined into a single field-value,
recipients ought to handle "Set-Cookie" as a special case while processing
header fields. (See Appendix A.2.3 of <xref target="Kri2001"/> for details.)
</t>
</list></t>
</section>
<section title="Whitespace" anchor="whitespace">
<t anchor="rule.LWS">
This specification uses three rules to denote the use of linear
whitespace: OWS (optional whitespace), RWS (required whitespace), and
BWS ("bad" whitespace).
</t>
<t anchor="rule.OWS">
The OWS rule is used where zero or more linear whitespace octets might
appear. For protocol elements where optional whitespace is preferred to
improve readability, a sender SHOULD generate the optional whitespace
as a single SP; otherwise, a sender SHOULD NOT generate optional
whitespace except as needed to white-out invalid or unwanted protocol
elements during in-place message filtering.
</t>
<t anchor="rule.RWS">
The RWS rule is used when at least one linear whitespace octet is required
to separate field tokens. A sender SHOULD generate RWS as a single SP.
</t>
<t anchor="rule.BWS">
The BWS rule is used where the grammar allows optional whitespace only for
historical reasons. A sender MUST NOT generate BWS in messages.
A recipient MUST parse for such bad whitespace and remove it before
interpreting the protocol element.
</t>
<t anchor="rule.whitespace">
</t>
<figure><iref primary="true" item="Grammar" subitem="OWS"/><iref primary="true" item="Grammar" subitem="RWS"/><iref primary="true" item="Grammar" subitem="BWS"/><artwork type="abnf2616"><![CDATA[
OWS = *( SP / HTAB )
; optional whitespace
RWS = 1*( SP / HTAB )
; required whitespace
BWS = OWS
; "bad" whitespace
]]></artwork></figure>
</section>
<section title="Field Parsing" anchor="field.parsing">
<t>
Messages are parsed using a generic algorithm, independent of the
individual header field names. The contents within a given field value are
not parsed until a later stage of message interpretation (usually after the
message's entire header section has been processed).
Consequently, this specification does not use ABNF rules to define each
"Field-Name: Field Value" pair, as was done in previous editions.
Instead, this specification uses ABNF rules which are named according to
each registered field name, wherein the rule defines the valid grammar for
that field's corresponding field values (i.e., after the field-value
has been extracted from the header section by a generic field parser).
</t>
<t>
No whitespace is allowed between the header field-name and colon.
In the past, differences in the handling of such whitespace have led to
security vulnerabilities in request routing and response handling.
A server MUST reject any received request message that contains
whitespace between a header field-name and colon with a response code of
400 (Bad Request). A proxy MUST remove any such whitespace
from a response message before forwarding the message downstream.
</t>
<t>
A field value might be preceded and/or followed by optional whitespace
(OWS); a single SP preceding the field-value is preferred for consistent
readability by humans.
The field value does not include any leading or trailing white space: OWS
occurring before the first non-whitespace octet of the field value or after
the last non-whitespace octet of the field value ought to be excluded by
parsers when extracting the field value from a header field.
</t>
<t>
Historically, HTTP header field values could be extended over multiple
lines by preceding each extra line with at least one space or horizontal
tab (obs-fold). This specification deprecates such line folding except
within the message/http media type
(<xref target="internet.media.type.message.http"/>).
A sender MUST NOT generate a message that includes line folding
(i.e., that has any field-value that contains a match to the
<xref target="header.fields" format="none">obs-fold</xref> rule) unless the message is intended for packaging
within the message/http media type.
</t>
<t>
A server that receives an <xref target="header.fields" format="none">obs-fold</xref> in a request message that
is not within a message/http container MUST either reject the message by
sending a 400 (Bad Request), preferably with a
representation explaining that obsolete line folding is unacceptable, or
replace each received <xref target="header.fields" format="none">obs-fold</xref> with one or more
<xref target="core.rules" format="none">SP</xref> octets prior to interpreting the field value or
forwarding the message downstream.
</t>
<t>
A proxy or gateway that receives an <xref target="header.fields" format="none">obs-fold</xref> in a response
message that is not within a message/http container MUST either discard
the message and replace it with a 502 (Bad Gateway)
response, preferably with a representation explaining that unacceptable
line folding was received, or replace each received <xref target="header.fields" format="none">obs-fold</xref>
with one or more <xref target="core.rules" format="none">SP</xref> octets prior to interpreting the field
value or forwarding the message downstream.
</t>
<t>
A user agent that receives an <xref target="header.fields" format="none">obs-fold</xref> in a response message
that is not within a message/http container MUST replace each received
<xref target="header.fields" format="none">obs-fold</xref> with one or more <xref target="core.rules" format="none">SP</xref> octets prior to
interpreting the field value.
</t>
<t>
Historically, HTTP has allowed field content with text in the ISO-8859-1
<xref target="ISO-8859-1"/> charset, supporting other charsets only
through use of <xref target="RFC2047"/> encoding.
In practice, most HTTP header field values use only a subset of the
US-ASCII charset <xref target="USASCII"/>. Newly defined
header fields SHOULD limit their field values to US-ASCII octets.
A recipient SHOULD treat other octets in field content (obs-text) as
opaque data.
</t>
</section>
<section title="Field Limits" anchor="field.limits">
<t>
HTTP does not place a pre-defined limit on the length of each header field
or on the length of the header section as a whole, as described in
<xref target="conformance"/>. Various ad-hoc limitations on individual
header field length are found in practice, often depending on the specific
field semantics.
</t>
<t>
A server that receives a request header field, or set of fields, larger
than it wishes to process MUST respond with an appropriate
4xx (Client Error) status code. Ignoring such header fields
would increase the server's vulnerability to request smuggling attacks
(<xref target="request.smuggling"/>).
</t>
<t>
A client MAY discard or truncate received header fields that are larger
than the client wishes to process if the field semantics are such that the
dropped value(s) can be safely ignored without changing the
message framing or response semantics.
</t>
</section>
<section title="Field value components" anchor="field.components">
<t anchor="rule.token.separators">
<iref item="Delimiters"/>
Most HTTP header field values are defined using common syntax components
(token, quoted-string, and comment) separated by whitespace or specific
delimiting characters. Delimiters are chosen from the set of US-ASCII
visual characters not allowed in a <xref target="rule.token.separators" format="none">token</xref>
(DQUOTE and "(),/:;<=>?@[\]{}").
</t>
<figure><iref primary="true" item="Grammar" subitem="token"/><iref primary="true" item="Grammar" subitem="tchar"/><artwork type="abnf2616"><![CDATA[
token = 1*tchar
tchar = "!" / "#" / "$" / "%" / "&" / "'" / "*"
/ "+" / "-" / "." / "^" / "_" / "`" / "|" / "~"
/ DIGIT / ALPHA
; any VCHAR, except delimiters
]]></artwork></figure>
<t anchor="rule.quoted-string">
A string of text is parsed as a single value if it is quoted using
double-quote marks.
</t>
<figure><iref primary="true" item="Grammar" subitem="quoted-string"/><iref primary="true" item="Grammar" subitem="qdtext"/><iref primary="true" item="Grammar" subitem="obs-text"/><artwork type="abnf2616"><![CDATA[
quoted-string = DQUOTE *( qdtext / quoted-pair ) DQUOTE
qdtext = HTAB / SP /%x21 / %x23-5B / %x5D-7E / obs-text
obs-text = %x80-FF
]]></artwork></figure>
<t anchor="rule.comment">
Comments can be included in some HTTP header fields by surrounding
the comment text with parentheses. Comments are only allowed in
fields containing "comment" as part of their field value definition.
</t>
<figure><iref primary="true" item="Grammar" subitem="comment"/><iref primary="true" item="Grammar" subitem="ctext"/><artwork type="abnf2616"><![CDATA[
comment = "(" *( ctext / quoted-pair / comment ) ")"
ctext = HTAB / SP / %x21-27 / %x2A-5B / %x5D-7E / obs-text
]]></artwork></figure>
<t anchor="rule.quoted-pair">
The backslash octet ("\") can be used as a single-octet
quoting mechanism within quoted-string and comment constructs.
Recipients that process the value of a quoted-string MUST handle a
quoted-pair as if it were replaced by the octet following the backslash.
</t>
<figure><iref primary="true" item="Grammar" subitem="quoted-pair"/><artwork type="abnf2616"><![CDATA[
quoted-pair = "\" ( HTAB / SP / VCHAR / obs-text )
]]></artwork></figure>
<t>
A sender SHOULD NOT generate a quoted-pair in a quoted-string except
where necessary to quote DQUOTE and backslash octets occurring within that
string.
A sender SHOULD NOT generate a quoted-pair in a comment except
where necessary to quote parentheses ["(" and ")"] and backslash octets
occurring within that comment.
</t>
</section>
</section>
<section title="Message Body" anchor="message.body">
<t>
The message body (if any) of an HTTP message is used to carry the
payload body of that request or response. The message body is
identical to the payload body unless a transfer coding has been
applied, as described in <xref target="header.transfer-encoding"/>.
</t>
<figure><iref primary="true" item="Grammar" subitem="message-body"/><artwork type="abnf2616"><![CDATA[
message-body = *OCTET
]]></artwork></figure>
<t>
The rules for when a message body is allowed in a message differ for
requests and responses.
</t>
<t>
The presence of a message body in a request is signaled by a
<xref target="header.content-length" format="none">Content-Length</xref> or <xref target="header.transfer-encoding" format="none">Transfer-Encoding</xref> header
field. Request message framing is independent of method semantics,
even if the method does not define any use for a message body.
</t>
<t>
The presence of a message body in a response depends on both
the request method to which it is responding and the response
status code (<xref target="status.line"/>).
Responses to the HEAD request method (Section 4.3.2 of <xref target="Part2"/>) never include a message body
because the associated response header fields (e.g.,
<xref target="header.transfer-encoding" format="none">Transfer-Encoding</xref>, <xref target="header.content-length" format="none">Content-Length</xref>, etc.),
if present, indicate only what their values would have been if the request
method had been GET (Section 4.3.1 of <xref target="Part2"/>).
2xx (Successful) responses to a CONNECT request method
(Section 4.3.6 of <xref target="Part2"/>) switch to tunnel mode instead of having a message body.
All 1xx (Informational), 204 (No Content), and
304 (Not Modified) responses do not include a message body.
All other responses do include a message body, although the body
might be of zero length.
</t>
<section title="Transfer-Encoding" anchor="header.transfer-encoding">
<iref primary="true" item="Transfer-Encoding header field"/>
<iref item="chunked (Coding Format)"/>
<t>
The Transfer-Encoding header field lists the transfer coding names
corresponding to the sequence of transfer codings that have been
(or will be) applied to the payload body in order to form the message body.
Transfer codings are defined in <xref target="transfer.codings"/>.
</t>
<figure><iref primary="true" item="Grammar" subitem="Transfer-Encoding"/><artwork type="abnf2616"><![CDATA[
Transfer-Encoding = 1#transfer-coding
]]></artwork></figure>
<t>
Transfer-Encoding is analogous to the Content-Transfer-Encoding field of
MIME, which was designed to enable safe transport of binary data over a
7-bit transport service (<xref target="RFC2045"/>, Section 6).
However, safe transport has a different focus for an 8bit-clean transfer
protocol. In HTTP's case, Transfer-Encoding is primarily intended to
accurately delimit a dynamically generated payload and to distinguish
payload encodings that are only applied for transport efficiency or
security from those that are characteristics of the selected resource.
</t>
<t>
A recipient MUST be able to parse the chunked transfer coding
(<xref target="chunked.encoding"/>) because it plays a crucial role in
framing messages when the payload body size is not known in advance.
A sender MUST NOT apply chunked more than once to a message body
(i.e., chunking an already chunked message is not allowed).
If any transfer coding other than chunked is applied to a request payload
body, the sender MUST apply chunked as the final transfer coding to
ensure that the message is properly framed.
If any transfer coding other than chunked is applied to a response payload
body, the sender MUST either apply chunked as the final transfer coding
or terminate the message by closing the connection.
</t>
<figure><preamble>
For example,
</preamble><artwork type="example"><![CDATA[
Transfer-Encoding: gzip, chunked
]]></artwork><postamble>
indicates that the payload body has been compressed using the gzip
coding and then chunked using the chunked coding while forming the
message body.
</postamble></figure>
<t>
Unlike Content-Encoding (Section 3.1.2.1 of <xref target="Part2"/>),
Transfer-Encoding is a property of the message, not of the representation, and
any recipient along the request/response chain MAY decode the received
transfer coding(s) or apply additional transfer coding(s) to the message
body, assuming that corresponding changes are made to the Transfer-Encoding
field-value. Additional information about the encoding parameters can be
provided by other header fields not defined by this specification.
</t>
<t>
Transfer-Encoding MAY be sent in a response to a HEAD request or in a
304 (Not Modified) response (Section 4.1 of <xref target="Part4"/>) to a GET request,
neither of which includes a message body,
to indicate that the origin server would have applied a transfer coding
to the message body if the request had been an unconditional GET.
This indication is not required, however, because any recipient on
the response chain (including the origin server) can remove transfer
codings when they are not needed.
</t>
<t>
A server MUST NOT send a Transfer-Encoding header field in any response
with a status code of
1xx (Informational) or 204 (No Content).
A server MUST NOT send a Transfer-Encoding header field in any
2xx (Successful) response to a CONNECT request (Section 4.3.6 of <xref target="Part2"/>).
</t>
<t>
Transfer-Encoding was added in HTTP/1.1. It is generally assumed that
implementations advertising only HTTP/1.0 support will not understand
how to process a transfer-encoded payload.
A client MUST NOT send a request containing Transfer-Encoding unless it
knows the server will handle HTTP/1.1 (or later) requests; such knowledge
might be in the form of specific user configuration or by remembering the
version of a prior received response.
A server MUST NOT send a response containing Transfer-Encoding unless
the corresponding request indicates HTTP/1.1 (or later).
</t>
<t>
A server that receives a request message with a transfer coding it does
not understand SHOULD respond with 501 (Not Implemented).
</t>
</section>
<section title="Content-Length" anchor="header.content-length">
<iref primary="true" item="Content-Length header field"/>
<t>
When a message does not have a <xref target="header.transfer-encoding" format="none">Transfer-Encoding</xref> header
field, a Content-Length header field can provide the anticipated size,
as a decimal number of octets, for a potential payload body.
For messages that do include a payload body, the Content-Length field-value
provides the framing information necessary for determining where the body
(and message) ends. For messages that do not include a payload body, the
Content-Length indicates the size of the selected representation
(Section 3 of <xref target="Part2"/>).
</t>
<figure><iref primary="true" item="Grammar" subitem="Content-Length"/><artwork type="abnf2616"><![CDATA[
Content-Length = 1*DIGIT
]]></artwork></figure>
<t>
An example is
</t>
<figure><artwork type="example"><![CDATA[
Content-Length: 3495
]]></artwork></figure>
<t>
A sender MUST NOT send a Content-Length header field in any message that
contains a <xref target="header.transfer-encoding" format="none">Transfer-Encoding</xref> header field.
</t>
<t>
A user agent SHOULD send a Content-Length in a request message when no
<xref target="header.transfer-encoding" format="none">Transfer-Encoding</xref> is sent and the request method defines
a meaning for an enclosed payload body. For example, a Content-Length
header field is normally sent in a POST request even when the value is
0 (indicating an empty payload body). A user agent SHOULD NOT send a
Content-Length header field when the request message does not contain a
payload body and the method semantics do not anticipate such a body.
</t>
<t>
A server MAY send a Content-Length header field in a response to a HEAD
request (Section 4.3.2 of <xref target="Part2"/>); a server MUST NOT send Content-Length in such a
response unless its field-value equals the decimal number of octets that
would have been sent in the payload body of a response if the same
request had used the GET method.
</t>
<t>
A server MAY send a Content-Length header field in a
304 (Not Modified) response to a conditional GET request
(Section 4.1 of <xref target="Part4"/>); a server MUST NOT send Content-Length in such a
response unless its field-value equals the decimal number of octets that
would have been sent in the payload body of a 200 (OK)
response to the same request.
</t>
<t>
A server MUST NOT send a Content-Length header field in any response
with a status code of
1xx (Informational) or 204 (No Content).
A server MUST NOT send a Content-Length header field in any
2xx (Successful) response to a CONNECT request (Section 4.3.6 of <xref target="Part2"/>).
</t>
<t>
Aside from the cases defined above, in the absence of Transfer-Encoding,
an origin server SHOULD send a Content-Length header field when the
payload body size is known prior to sending the complete header section.
This will allow downstream recipients to measure transfer progress,
know when a received message is complete, and potentially reuse the
connection for additional requests.
</t>
<t>
Any Content-Length field value greater than or equal to zero is valid.
Since there is no predefined limit to the length of a payload, a
recipient MUST anticipate potentially large decimal numerals and
prevent parsing errors due to integer conversion overflows
(<xref target="attack.protocol.element.length"/>).
</t>
<t>
If a message is received that has multiple Content-Length header fields
with field-values consisting of the same decimal value, or a single
Content-Length header field with a field value containing a list of
identical decimal values (e.g., "Content-Length: 42, 42"), indicating that
duplicate Content-Length header fields have been generated or combined by an
upstream message processor, then the recipient MUST either reject the
message as invalid or replace the duplicated field-values with a single
valid Content-Length field containing that decimal value prior to
determining the message body length or forwarding the message.
</t>
<t><list>
<t>
Note: HTTP's use of Content-Length for message framing differs
significantly from the same field's use in MIME, where it is an optional
field used only within the "message/external-body" media-type.
</t>
</list></t>
</section>
<section title="Message Body Length" anchor="message.body.length">
<iref item="chunked (Coding Format)"/>
<t>
The length of a message body is determined by one of the following
(in order of precedence):
</t>
<t>
<list style="numbers">
<t>
Any response to a HEAD request and any response with a
1xx (Informational), 204 (No Content), or
304 (Not Modified) status code is always
terminated by the first empty line after the header fields, regardless of
the header fields present in the message, and thus cannot contain a
message body.
</t>
<t>
Any 2xx (Successful) response to a CONNECT request implies that the
connection will become a tunnel immediately after the empty line that
concludes the header fields. A client MUST ignore any
<xref target="header.content-length" format="none">Content-Length</xref> or <xref target="header.transfer-encoding" format="none">Transfer-Encoding</xref> header
fields received in such a message.
</t>
<t>
If a <xref target="header.transfer-encoding" format="none">Transfer-Encoding</xref> header field is present
and the chunked transfer coding (<xref target="chunked.encoding"/>)
is the final encoding, the message body length is determined by reading
and decoding the chunked data until the transfer coding indicates the
data is complete.
<vspace blankLines="1"/>
If a <xref target="header.transfer-encoding" format="none">Transfer-Encoding</xref> header field is present in a
response and the chunked transfer coding is not the final encoding, the
message body length is determined by reading the connection until it is
closed by the server.
If a <xref target="header.transfer-encoding" format="none">Transfer-Encoding</xref> header field is present in a request and the
chunked transfer coding is not the final encoding, the message body
length cannot be determined reliably; the server MUST respond with
the 400 (Bad Request) status code and then close the connection.
<vspace blankLines="1"/>
If a message is received with both a <xref target="header.transfer-encoding" format="none">Transfer-Encoding</xref>
and a <xref target="header.content-length" format="none">Content-Length</xref> header field, the Transfer-Encoding
overrides the Content-Length. Such a message might indicate an attempt to
perform request smuggling (<xref target="request.smuggling"/>) or
response splitting (<xref target="response.splitting"/>) and ought to be
handled as an error. A sender MUST remove the received Content-Length
field prior to forwarding such a message downstream.
</t>
<t>
If a message is received without <xref target="header.transfer-encoding" format="none">Transfer-Encoding</xref> and with
either multiple <xref target="header.content-length" format="none">Content-Length</xref> header fields having
differing field-values or a single Content-Length header field having an
invalid value, then the message framing is invalid and
the recipient MUST treat it as an unrecoverable error.
If this is a request message, the server MUST respond with
a 400 (Bad Request) status code and then close the connection.
If this is a response message received by a proxy,
the proxy MUST close the connection to the server, discard the received
response, and send a 502 (Bad Gateway) response to the
client.
If this is a response message received by a user agent,
the user agent MUST close the connection to the server and discard the
received response.
</t>
<t>
If a valid <xref target="header.content-length" format="none">Content-Length</xref> header field is present without
<xref target="header.transfer-encoding" format="none">Transfer-Encoding</xref>, its decimal value defines the
expected message body length in octets.
If the sender closes the connection or the recipient times out before the
indicated number of octets are received, the recipient MUST consider
the message to be incomplete and close the connection.
</t>
<t>
If this is a request message and none of the above are true, then the
message body length is zero (no message body is present).
</t>
<t>
Otherwise, this is a response message without a declared message body
length, so the message body length is determined by the number of octets
received prior to the server closing the connection.
</t>
</list>
</t>
<t>
Since there is no way to distinguish a successfully completed,
close-delimited message from a partially-received message interrupted
by network failure, a server SHOULD generate encoding or
length-delimited messages whenever possible. The close-delimiting
feature exists primarily for backwards compatibility with HTTP/1.0.
</t>
<t>
A server MAY reject a request that contains a message body but
not a <xref target="header.content-length" format="none">Content-Length</xref> by responding with
411 (Length Required).
</t>
<t>
Unless a transfer coding other than chunked has been applied,
a client that sends a request containing a message body SHOULD
use a valid <xref target="header.content-length" format="none">Content-Length</xref> header field if the message body
length is known in advance, rather than the chunked transfer coding, since some
existing services respond to chunked with a 411 (Length Required)
status code even though they understand the chunked transfer coding. This
is typically because such services are implemented via a gateway that
requires a content-length in advance of being called and the server
is unable or unwilling to buffer the entire request before processing.
</t>
<t>
A user agent that sends a request containing a message body MUST send a
valid <xref target="header.content-length" format="none">Content-Length</xref> header field if it does not know the
server will handle HTTP/1.1 (or later) requests; such knowledge can be in
the form of specific user configuration or by remembering the version of a
prior received response.
</t>
<t>
If the final response to the last request on a connection has been
completely received and there remains additional data to read, a user agent
MAY discard the remaining data or attempt to determine if that data
belongs as part of the prior response body, which might be the case if the
prior message's Content-Length value is incorrect. A client MUST NOT
process, cache, or forward such extra data as a separate response, since
such behavior would be vulnerable to cache poisoning.
</t>
</section>
</section>
<section anchor="incomplete.messages" title="Handling Incomplete Messages">
<t>
A server that receives an incomplete request message, usually due to a
canceled request or a triggered time-out exception, MAY send an error
response prior to closing the connection.
</t>
<t>
A client that receives an incomplete response message, which can occur
when a connection is closed prematurely or when decoding a supposedly
chunked transfer coding fails, MUST record the message as incomplete.
Cache requirements for incomplete responses are defined in
Section 3 of <xref target="Part6"/>.
</t>
<t>
If a response terminates in the middle of the header section (before the
empty line is received) and the status code might rely on header fields to
convey the full meaning of the response, then the client cannot assume
that meaning has been conveyed; the client might need to repeat the
request in order to determine what action to take next.
</t>
<t>
A message body that uses the chunked transfer coding is
incomplete if the zero-sized chunk that terminates the encoding has not
been received. A message that uses a valid <xref target="header.content-length" format="none">Content-Length</xref> is
incomplete if the size of the message body received (in octets) is less than
the value given by Content-Length. A response that has neither chunked
transfer coding nor Content-Length is terminated by closure of the
connection, and thus is considered complete regardless of the number of
message body octets received, provided that the header section was received
intact.
</t>
</section>
<section title="Message Parsing Robustness" anchor="message.robustness">
<t>
Older HTTP/1.0 user agent implementations might send an extra CRLF
after a POST request as a workaround for some early server
applications that failed to read message body content that was
not terminated by a line-ending. An HTTP/1.1 user agent MUST NOT
preface or follow a request with an extra CRLF. If terminating
the request message body with a line-ending is desired, then the
user agent MUST count the terminating CRLF octets as part of the
message body length.
</t>
<t>
In the interest of robustness, a server that is expecting to receive and
parse a request-line SHOULD ignore at least one empty line (CRLF)
received prior to the request-line.
</t>
<t>
Although the line terminator for the start-line and header
fields is the sequence CRLF, a recipient MAY recognize a
single LF as a line terminator and ignore any preceding CR.
</t>
<t>
Although the request-line and status-line grammar rules require that each
of the component elements be separated by a single SP octet, recipients
MAY instead parse on whitespace-delimited word boundaries and, aside
from the CRLF terminator, treat any form of whitespace as the SP separator
while ignoring preceding or trailing whitespace;
such whitespace includes one or more of the following octets:
SP, HTAB, VT (%x0B), FF (%x0C), or bare CR.
However, lenient parsing can result in security vulnerabilities if there
are multiple recipients of the message and each has its own unique
interpretation of robustness (see <xref target="request.smuggling"/>).
</t>
<t>
When a server listening only for HTTP request messages, or processing
what appears from the start-line to be an HTTP request message,
receives a sequence of octets that does not match the HTTP-message
grammar aside from the robustness exceptions listed above, the
server SHOULD respond with a 400 (Bad Request) response.
</t>
</section>
</section>
<section title="Transfer Codings" anchor="transfer.codings">
<t>
Transfer coding names are used to indicate an encoding
transformation that has been, can be, or might need to be applied to a
payload body in order to ensure "safe transport" through the network.
This differs from a content coding in that the transfer coding is a
property of the message rather than a property of the representation
that is being transferred.
</t>
<figure><iref primary="true" item="Grammar" subitem="transfer-coding"/><iref primary="true" item="Grammar" subitem="transfer-extension"/><artwork type="abnf2616"><![CDATA[
transfer-coding = "chunked" ; Section 4.1
/ "compress" ; Section 4.2.1
/ "deflate" ; Section 4.2.2
/ "gzip" ; Section 4.2.3
/ transfer-extension
transfer-extension = token *( OWS ";" OWS transfer-parameter )
]]></artwork></figure>
<t anchor="rule.parameter">
Parameters are in the form of a name or name=value pair.
</t>
<figure><iref primary="true" item="Grammar" subitem="transfer-parameter"/><artwork type="abnf2616"><![CDATA[
transfer-parameter = token BWS "=" BWS ( token / quoted-string )
]]></artwork></figure>
<t>
All transfer-coding names are case-insensitive and ought to be registered
within the HTTP Transfer Coding registry, as defined in
<xref target="transfer.coding.registry"/>.
They are used in the <xref target="header.te" format="none">TE</xref> (<xref target="header.te"/>) and
<xref target="header.transfer-encoding" format="none">Transfer-Encoding</xref> (<xref target="header.transfer-encoding"/>)
header fields.
</t>
<section title="Chunked Transfer Coding" anchor="chunked.encoding">
<iref primary="true" item="chunked (Coding Format)"/>
<t>
The chunked transfer coding wraps the payload body in order to transfer it
as a series of chunks, each with its own size indicator, followed by an
OPTIONAL trailer containing header fields. Chunked enables content
streams of unknown size to be transferred as a sequence of length-delimited
buffers, which enables the sender to retain connection persistence and the
recipient to know when it has received the entire message.
</t>
<figure><iref primary="true" item="Grammar" subitem="chunked-body"><!--terminal production--></iref><iref primary="true" item="Grammar" subitem="chunk"/><iref primary="true" item="Grammar" subitem="chunk-size"/><iref primary="true" item="Grammar" subitem="last-chunk"/><iref primary="false" item="Grammar" subitem="trailer-part"/><iref primary="false" item="Grammar" subitem="chunk-ext"/><iref primary="true" item="Grammar" subitem="chunk-data"/><artwork type="abnf2616"><![CDATA[
chunked-body = *chunk
last-chunk
trailer-part
CRLF
chunk = chunk-size [ chunk-ext ] CRLF
chunk-data CRLF
chunk-size = 1*HEXDIG
last-chunk = 1*("0") [ chunk-ext ] CRLF
chunk-data = 1*OCTET ; a sequence of chunk-size octets
]]></artwork></figure>
<t>
The chunk-size field is a string of hex digits indicating the size of
the chunk-data in octets. The chunked transfer coding is complete when a
chunk with a chunk-size of zero is received, possibly followed by a
trailer, and finally terminated by an empty line.
</t>
<t>
A recipient MUST be able to parse and decode the chunked transfer coding.
</t>
<section title="Chunk Extensions" anchor="chunked.extension">
<t>
The chunked encoding allows each chunk to include zero or more chunk
extensions, immediately following the <xref target="chunked.encoding" format="none">chunk-size</xref>, for the
sake of supplying per-chunk metadata (such as a signature or hash),
mid-message control information, or randomization of message body size.
</t>
<figure><iref primary="true" item="Grammar" subitem="chunked-body"><!--terminal production--></iref><iref primary="true" item="Grammar" subitem="chunk-ext"/><iref primary="true" item="Grammar" subitem="chunk-ext-name"/><iref primary="true" item="Grammar" subitem="chunk-ext-val"/><artwork type="abnf2616"><![CDATA[
chunk-ext = *( ";" chunk-ext-name [ "=" chunk-ext-val ] )
chunk-ext-name = token
chunk-ext-val = token / quoted-string
]]></artwork></figure>
<t>
The chunked encoding is specific to each connection and is likely to be
removed or recoded by each recipient (including intermediaries) before any
higher-level application would have a chance to inspect the extensions.
Hence, use of chunk extensions is generally limited to specialized HTTP
services such as "long polling" (where client and server can have shared
expectations regarding the use of chunk extensions) or for padding within
an end-to-end secured connection.
</t>
<t>
A recipient MUST ignore unrecognized chunk extensions.
A server ought to limit the total length of chunk extensions received in a
request to an amount reasonable for the services provided, in the same way
that it applies length limitations and timeouts for other parts of a
message, and generate an appropriate 4xx (Client Error)
response if that amount is exceeded.
</t>
</section>
<section title="Chunked Trailer Part" anchor="chunked.trailer.part">
<t>
A trailer allows the sender to include additional fields at the end of a
chunked message in order to supply metadata that might be dynamically
generated while the message body is sent, such as a message integrity
check, digital signature, or post-processing status. The trailer fields are
identical to header fields, except they are sent in a chunked trailer
instead of the message's header section.
</t>
<figure><iref primary="true" item="Grammar" subitem="trailer-part"/><iref primary="false" item="Grammar" subitem="header-field"/><artwork type="abnf2616"><![CDATA[
trailer-part = *( header-field CRLF )
]]></artwork></figure>
<t>
A sender MUST NOT generate a trailer that contains a field necessary for
message framing (e.g., <xref target="header.transfer-encoding" format="none">Transfer-Encoding</xref> and
<xref target="header.content-length" format="none">Content-Length</xref>), routing (e.g., <xref target="header.host" format="none">Host</xref>),
request modifiers (e.g., controls and conditionals in
Section 5 of <xref target="Part2"/>), authentication (e.g., see <xref target="Part7"/>
and <xref target="RFC6265"/>), response control data (e.g., see
Section 7.1 of <xref target="Part2"/>), or determining how to process the payload
(e.g., Content-Encoding, Content-Type,
Content-Range, and <xref target="header.trailer" format="none">Trailer</xref>).
</t>
<t>
When a chunked message containing a non-empty trailer is received, the
recipient MAY process the fields (aside from those forbidden above)
as if they were appended to the message's header section.
A recipient MUST ignore (or consider as an error) any fields that are
forbidden to be sent in a trailer, since processing them as if they were
present in the header section might bypass external security filters.
</t>
<t>
Unless the request includes a <xref target="header.te" format="none">TE</xref> header field indicating
"trailers" is acceptable, as described in <xref target="header.te"/>, a
server SHOULD NOT generate trailer fields that it believes are necessary
for the user agent to receive. Without a TE containing "trailers", the
server ought to assume that the trailer fields might be silently discarded
along the path to the user agent. This requirement allows intermediaries to
forward a de-chunked message to an HTTP/1.0 recipient without buffering the
entire response.
</t>
</section>
<section title="Decoding Chunked" anchor="decoding.chunked">
<t>
A process for decoding the chunked transfer coding
can be represented in pseudo-code as:
</t>
<figure><artwork type="code"><![CDATA[
length := 0
read chunk-size, chunk-ext (if any), and CRLF
while (chunk-size > 0) {
read chunk-data and CRLF
append chunk-data to decoded-body
length := length + chunk-size
read chunk-size, chunk-ext (if any), and CRLF
}
read trailer field
while (trailer field is not empty) {
if (trailer field is allowed to be sent in a trailer) {
append trailer field to existing header fields
}
read trailer-field
}
Content-Length := length
Remove "chunked" from Transfer-Encoding
Remove Trailer from existing header fields
]]></artwork></figure>
</section>
</section>
<section title="Compression Codings" anchor="compression.codings">
<t>
The codings defined below can be used to compress the payload of a
message.
</t>
<section title="Compress Coding" anchor="compress.coding">
<iref item="compress (Coding Format)"/>
<t>
The "compress" coding is an adaptive Lempel-Ziv-Welch (LZW) coding
<xref target="Welch"/> that is commonly produced by the UNIX file
compression program "compress".
A recipient SHOULD consider "x-compress" to be equivalent to "compress".
</t>
</section>
<section title="Deflate Coding" anchor="deflate.coding">
<iref item="deflate (Coding Format)"/>
<t>
The "deflate" coding is a "zlib" data format <xref target="RFC1950"/>
containing a "deflate" compressed data stream <xref target="RFC1951"/>
that uses a combination of the Lempel-Ziv (LZ77) compression algorithm and
Huffman coding.
</t>
<t><list>
<t>
Note: Some non-conformant implementations send the "deflate"
compressed data without the zlib wrapper.
</t>
</list></t>
</section>
<section title="Gzip Coding" anchor="gzip.coding">
<iref item="gzip (Coding Format)"/>
<t>
The "gzip" coding is an LZ77 coding with a 32 bit CRC that is commonly
produced by the gzip file compression program <xref target="RFC1952"/>.
A recipient SHOULD consider "x-gzip" to be equivalent to "gzip".
</t>
</section>
</section>
<section title="TE" anchor="header.te">
<iref primary="true" item="TE header field"/>
<t>
The "TE" header field in a request indicates what transfer codings,
besides chunked, the client is willing to accept in response, and
whether or not the client is willing to accept trailer fields in a
chunked transfer coding.
</t>
<t>
The TE field-value consists of a comma-separated list of transfer coding
names, each allowing for optional parameters (as described in
<xref target="transfer.codings"/>), and/or the keyword "trailers".
A client MUST NOT send the chunked transfer coding name in TE;
chunked is always acceptable for HTTP/1.1 recipients.
</t>
<figure><iref primary="true" item="Grammar" subitem="TE"/><iref primary="true" item="Grammar" subitem="t-codings"/><iref primary="true" item="Grammar" subitem="t-ranking"/><iref primary="true" item="Grammar" subitem="rank"/><artwork type="abnf2616"><![CDATA[
TE = #t-codings
t-codings = "trailers" / ( transfer-coding [ t-ranking ] )
t-ranking = OWS ";" OWS "q=" rank
rank = ( "0" [ "." 0*3DIGIT ] )
/ ( "1" [ "." 0*3("0") ] )
]]></artwork></figure>
<t>
Three examples of TE use are below.
</t>
<figure><artwork type="example"><![CDATA[
TE: deflate
TE:
TE: trailers, deflate;q=0.5
]]></artwork></figure>
<t>
The presence of the keyword "trailers" indicates that the client is willing
to accept trailer fields in a chunked transfer coding, as defined in
<xref target="chunked.trailer.part"/>, on behalf of itself and any downstream
clients. For requests from an intermediary, this implies that either:
(a) all downstream clients are willing to accept trailer fields in the
forwarded response; or,
(b) the intermediary will attempt to buffer the response on behalf of
downstream recipients.
Note that HTTP/1.1 does not define any means to limit the size of a
chunked response such that an intermediary can be assured of buffering the
entire response.
</t>
<t>
When multiple transfer codings are acceptable, the client MAY rank the
codings by preference using a case-insensitive "q" parameter (similar to
the qvalues used in content negotiation fields, Section 5.3.1 of <xref target="Part2"/>). The rank value
is a real number in the range 0 through 1, where 0.001 is the least
preferred and 1 is the most preferred; a value of 0 means "not acceptable".
</t>
<t>
If the TE field-value is empty or if no TE field is present, the only
acceptable transfer coding is chunked. A message with no transfer coding
is always acceptable.
</t>
<t>
Since the TE header field only applies to the immediate connection,
a sender of TE MUST also send a "TE" connection option within the
<xref target="header.connection" format="none">Connection</xref> header field (<xref target="header.connection"/>)
in order to prevent the TE field from being forwarded by intermediaries
that do not support its semantics.
</t>
</section>
<section title="Trailer" anchor="header.trailer">
<iref primary="true" item="Trailer header field"/>
<t>
When a message includes a message body encoded with the chunked
transfer coding and the sender desires to send metadata in the form of
trailer fields at the end of the message, the sender SHOULD generate a
<xref target="header.trailer" format="none">Trailer</xref> header field before the message body to indicate
which fields will be present in the trailers. This allows the recipient
to prepare for receipt of that metadata before it starts processing the body,
which is useful if the message is being streamed and the recipient wishes
to confirm an integrity check on the fly.
</t>
<figure><iref primary="true" item="Grammar" subitem="Trailer"/><iref primary="false" item="Grammar" subitem="field-name"/><artwork type="abnf2616"><![CDATA[
Trailer = 1#field-name
]]></artwork></figure>
</section>
</section>
<section title="Message Routing" anchor="message.routing">
<t>
HTTP request message routing is determined by each client based on the
target resource, the client's proxy configuration, and
establishment or reuse of an inbound connection. The corresponding
response routing follows the same connection chain back to the client.
</t>
<section title="Identifying a Target Resource" anchor="target-resource">
<iref primary="true" item="target resource"/>
<iref primary="true" item="target URI"/>
<t>
HTTP is used in a wide variety of applications, ranging from
general-purpose computers to home appliances. In some cases,
communication options are hard-coded in a client's configuration.
However, most HTTP clients rely on the same resource identification
mechanism and configuration techniques as general-purpose Web browsers.
</t>
<t>
HTTP communication is initiated by a user agent for some purpose.
The purpose is a combination of request semantics, which are defined in
<xref target="Part2"/>, and a target resource upon which to apply those
semantics. A URI reference (<xref target="uri"/>) is typically used as
an identifier for the "target resource", which a user agent
would resolve to its absolute form in order to obtain the
"target URI". The target URI
excludes the reference's fragment component, if any,
since fragment identifiers are reserved for client-side processing
(<xref target="RFC3986"/>, Section 3.5).
</t>
</section>
<section title="Connecting Inbound" anchor="connecting.inbound">
<t>
Once the target URI is determined, a client needs to decide whether
a network request is necessary to accomplish the desired semantics and,
if so, where that request is to be directed.
</t>
<t>
If the client has a cache <xref target="Part6"/> and the request can be
satisfied by it, then the request is
usually directed there first.
</t>
<t>
If the request is not satisfied by a cache, then a typical client will
check its configuration to determine whether a proxy is to be used to
satisfy the request. Proxy configuration is implementation-dependent,
but is often based on URI prefix matching, selective authority matching,
or both, and the proxy itself is usually identified by an "http" or
"https" URI. If a proxy is applicable, the client connects inbound by
establishing (or reusing) a connection to that proxy.
</t>
<t>
If no proxy is applicable, a typical client will invoke a handler routine,
usually specific to the target URI's scheme, to connect directly
to an authority for the target resource. How that is accomplished is
dependent on the target URI scheme and defined by its associated
specification, similar to how this specification defines origin server
access for resolution of the "http" (<xref target="http.uri"/>) and
"https" (<xref target="https.uri"/>) schemes.
</t>
<t>
HTTP requirements regarding connection management are defined in
<xref target="connection.management"/>.
</t>
</section>
<section title="Request Target" anchor="request-target">
<t>
Once an inbound connection is obtained,
the client sends an HTTP request message (<xref target="http.message"/>)
with a request-target derived from the target URI.
There are four distinct formats for the request-target, depending on both
the method being requested and whether the request is to a proxy.
</t>
<figure><iref primary="true" item="Grammar" subitem="request-target"/><iref primary="false" item="Grammar" subitem="origin-form"/><iref primary="false" item="Grammar" subitem="absolute-form"/><iref primary="false" item="Grammar" subitem="authority-form"/><iref primary="false" item="Grammar" subitem="asterisk-form"/><artwork type="abnf2616"><![CDATA[
request-target = origin-form
/ absolute-form
/ authority-form
/ asterisk-form
]]></artwork></figure>
<section title="origin-form" anchor="origin-form">
<iref item="origin-form (of request-target)"/>
<t>
The most common form of request-target is the origin-form.
</t>
<figure><iref primary="true" item="Grammar" subitem="origin-form"/><artwork type="abnf2616"><![CDATA[
origin-form = absolute-path [ "?" query ]
]]></artwork></figure>
<t>
When making a request directly to an origin server, other than a CONNECT
or server-wide OPTIONS request (as detailed below),
a client MUST send only the absolute path and query components of
the target URI as the request-target.
If the target URI's path component is empty, the client MUST send
"/" as the path within the origin-form of request-target.
A <xref target="header.host" format="none">Host</xref> header field is also sent, as defined in
<xref target="header.host"/>.
</t>
<t>
For example, a client wishing to retrieve a representation of the resource
identified as
</t>
<figure><artwork type="example"><![CDATA[
http://www.example.org/where?q=now
]]></artwork></figure>
<t>
directly from the origin server would open (or reuse) a TCP connection
to port 80 of the host "www.example.org" and send the lines:
</t>
<figure><artwork type="message/http; msgtype="request""><![CDATA[
GET /where?q=now HTTP/1.1
Host: www.example.org
]]></artwork></figure>
<t>
followed by the remainder of the request message.
</t>
</section>
<section title="absolute-form" anchor="absolute-form">
<iref item="absolute-form (of request-target)"/>
<t>
When making a request to a proxy, other than a CONNECT or server-wide
OPTIONS request (as detailed below), a client MUST send the target URI
in absolute-form as the request-target.
</t>
<figure><iref primary="true" item="Grammar" subitem="absolute-form"/><artwork type="abnf2616"><![CDATA[
absolute-form = absolute-URI
]]></artwork></figure>
<t>
The proxy is requested to either service that request from a valid cache,
if possible, or make the same request on the client's behalf to either
the next inbound proxy server or directly to the origin server indicated
by the request-target. Requirements on such "forwarding" of messages are
defined in <xref target="message.forwarding"/>.
</t>
<t>
An example absolute-form of request-line would be:
</t>
<figure><artwork type="message/http; msgtype="request""><![CDATA[
GET http://www.example.org/pub/WWW/TheProject.html HTTP/1.1
]]></artwork></figure>
<t>
To allow for transition to the absolute-form for all requests in some
future version of HTTP, a server MUST accept the absolute-form
in requests, even though HTTP/1.1 clients will only send them in requests
to proxies.
</t>
</section>
<section title="authority-form" anchor="authority-form">
<iref item="authority-form (of request-target)"/>
<t>
The authority-form of request-target is only used for
CONNECT requests (Section 4.3.6 of <xref target="Part2"/>).
</t>
<figure><iref primary="true" item="Grammar" subitem="authority-form"/><artwork type="abnf2616"><![CDATA[
authority-form = authority
]]></artwork></figure>
<t>
When making a CONNECT request to establish a
tunnel through one or more proxies, a client MUST send only the target
URI's authority component (excluding any userinfo and its "@" delimiter) as
the request-target. For example,
</t>
<figure><artwork type="message/http; msgtype="request""><![CDATA[
CONNECT www.example.com:80 HTTP/1.1
]]></artwork></figure>
</section>
<section title="asterisk-form" anchor="asterisk-form">
<iref item="asterisk-form (of request-target)"/>
<t>
The asterisk-form of request-target is only used for a server-wide
OPTIONS request (Section 4.3.7 of <xref target="Part2"/>).
</t>
<figure><iref primary="true" item="Grammar" subitem="asterisk-form"/><artwork type="abnf2616"><![CDATA[
asterisk-form = "*"
]]></artwork></figure>
<t>
When a client wishes to request OPTIONS
for the server as a whole, as opposed to a specific named resource of
that server, the client MUST send only "*" (%x2A) as the request-target.
For example,
</t>
<figure><artwork type="message/http; msgtype="request""><![CDATA[
OPTIONS * HTTP/1.1
]]></artwork></figure>
<t>
If a proxy receives an OPTIONS request with an absolute-form of
request-target in which the URI has an empty path and no query component,
then the last proxy on the request chain MUST send a request-target
of "*" when it forwards the request to the indicated origin server.
</t>
<figure><preamble>
For example, the request
</preamble><artwork type="message/http; msgtype="request""><![CDATA[
OPTIONS http://www.example.org:8001 HTTP/1.1
]]></artwork></figure>
<figure><preamble>
would be forwarded by the final proxy as
</preamble><artwork type="message/http; msgtype="request""><![CDATA[
OPTIONS * HTTP/1.1
Host: www.example.org:8001
]]></artwork>
<postamble>
after connecting to port 8001 of host "www.example.org".
</postamble>
</figure>
</section>
</section>
<section title="Host" anchor="header.host">
<iref primary="true" item="Host header field"/>
<t>
The "Host" header field in a request provides the host and port
information from the target URI, enabling the origin
server to distinguish among resources while servicing requests
for multiple host names on a single IP address.
</t>
<figure><iref primary="true" item="Grammar" subitem="Host"/><artwork type="abnf2616"><![CDATA[
Host = uri-host [ ":" port ] ; Section 2.7.1
]]></artwork></figure>
<t>
A client MUST send a Host header field in all HTTP/1.1 request messages.
If the target URI includes an authority component, then a client MUST
send a field-value for Host that is identical to that authority
component, excluding any userinfo subcomponent and its "@" delimiter
(<xref target="http.uri"/>).
If the authority component is missing or undefined for the target URI,
then a client MUST send a Host header field with an empty field-value.
</t>
<t>
Since the Host field-value is critical information for handling a request,
a user agent SHOULD generate Host as the first header field following the
request-line.
</t>
<t>
For example, a GET request to the origin server for
<http://www.example.org/pub/WWW/> would begin with:
</t>
<figure><artwork type="message/http; msgtype="request""><![CDATA[
GET /pub/WWW/ HTTP/1.1
Host: www.example.org
]]></artwork></figure>
<t>
A client MUST send a Host header field in an HTTP/1.1 request even
if the request-target is in the absolute-form, since this
allows the Host information to be forwarded through ancient HTTP/1.0
proxies that might not have implemented Host.
</t>
<t>
When a proxy receives a request with an absolute-form of
request-target, the proxy MUST ignore the received
Host header field (if any) and instead replace it with the host
information of the request-target. A proxy that forwards such a request
MUST generate a new Host field-value based on the received
request-target rather than forward the received Host field-value.
</t>
<t>
Since the Host header field acts as an application-level routing
mechanism, it is a frequent target for malware seeking to poison
a shared cache or redirect a request to an unintended server.
An interception proxy is particularly vulnerable if it relies on
the Host field-value for redirecting requests to internal
servers, or for use as a cache key in a shared cache, without
first verifying that the intercepted connection is targeting a
valid IP address for that host.
</t>
<t>
A server MUST respond with a 400 (Bad Request) status code
to any HTTP/1.1 request message that lacks a Host header field and
to any request message that contains more than one Host header field
or a Host header field with an invalid field-value.
</t>
</section>
<section title="Effective Request URI" anchor="effective.request.uri">
<iref primary="true" item="effective request URI"/>
<t>
Since the request-target often contains only part of the user agent's
target URI, a server reconstructs the intended target as an
"effective request URI" to properly service the request.
This reconstruction involves both the server's local configuration and
information communicated in the <xref target="request-target" format="none">request-target</xref>,
<xref target="header.host" format="none">Host</xref> header field, and connection context.
</t>
<t>
For a user agent, the effective request URI is the target URI.
</t>
<t>
If the <xref target="request-target" format="none">request-target</xref> is in <xref target="absolute-form" format="none">absolute-form</xref>,
the effective request URI is the same as the request-target. Otherwise, the
effective request URI is constructed as follows:
<list style="empty">
<t>
If the server's configuration (or outbound gateway) provides a fixed URI
<xref target="uri" format="none">scheme</xref>, that scheme is used for the effective request URI.
Otherwise, if the request is received over a TLS-secured TCP connection,
the effective request URI's scheme is "https"; if not, the scheme is "http".
</t>
<t>
If the server's configuration (or outbound gateway) provides a fixed URI
<xref target="uri" format="none">authority</xref> component, that authority is used for the
effective request URI. If not, then if the request-target is in
<xref target="authority-form" format="none">authority-form</xref>, the effective request URI's authority
component is the same as the request-target.
If not, then if a <xref target="header.host" format="none">Host</xref> header field is supplied with a
non-empty field-value, the authority component is the same as the
Host field-value. Otherwise, the authority component is assigned
the default name configured for the server and, if the connection's
incoming TCP port number differs from the default port for the effective
request URI's scheme, then a colon (":") and the incoming port number (in
decimal form) are appended to the authority component.
</t>
<t>
If the request-target is in <xref target="authority-form" format="none">authority-form</xref> or
<xref target="asterisk-form" format="none">asterisk-form</xref>, the effective request URI's combined
<xref target="uri" format="none">path</xref> and <xref target="uri" format="none">query</xref> component is empty. Otherwise,
the combined <xref target="uri" format="none">path</xref> and <xref target="uri" format="none">query</xref> component is the
same as the request-target.
</t>
<t>
The components of the effective request URI, once determined as above, can
be combined into <xref target="uri" format="none">absolute-URI</xref> form by concatenating the
scheme, "://", authority, and combined path and query component.
</t>
</list>
</t>
<figure>
<preamble>
Example 1: the following message received over an insecure TCP connection
</preamble>
<artwork type="example"><![CDATA[
GET /pub/WWW/TheProject.html HTTP/1.1
Host: www.example.org:8080
]]></artwork>
</figure>
<figure>
<preamble>
has an effective request URI of
</preamble>
<artwork type="example"><![CDATA[
http://www.example.org:8080/pub/WWW/TheProject.html
]]></artwork>
</figure>
<figure>
<preamble>
Example 2: the following message received over a TLS-secured TCP connection
</preamble>
<artwork type="example"><![CDATA[
OPTIONS * HTTP/1.1
Host: www.example.org
]]></artwork>
</figure>
<figure>
<preamble>
has an effective request URI of
</preamble>
<artwork type="example"><![CDATA[
https://www.example.org
]]></artwork>
</figure>
<t>
Recipients of an HTTP/1.0 request that lacks a <xref target="header.host" format="none">Host</xref> header
field might need to use heuristics (e.g., examination of the URI path for
something unique to a particular host) in order to guess the
effective request URI's authority component.
</t>
<t>
Once the effective request URI has been constructed, an origin server needs
to decide whether or not to provide service for that URI via the connection
in which the request was received. For example, the request might have been
misdirected, deliberately or accidentally, such that the information within
a received <xref target="request-target" format="none">request-target</xref> or <xref target="header.host" format="none">Host</xref> header
field differs from the host or port upon which the connection has been
made. If the connection is from a trusted gateway, that inconsistency might
be expected; otherwise, it might indicate an attempt to bypass security
filters, trick the server into delivering non-public content, or poison a
cache. See <xref target="security.considerations"/> for security
considerations regarding message routing.
</t>
</section>
<section title="Associating a Response to a Request" anchor="associating.response.to.request">
<t>
HTTP does not include a request identifier for associating a given
request message with its corresponding one or more response messages.
Hence, it relies on the order of response arrival to correspond exactly
to the order in which requests are made on the same connection.
More than one response message per request only occurs when one or more
informational responses (1xx, see Section 6.2 of <xref target="Part2"/>) precede a
final response to the same request.
</t>
<t>
A client that has more than one outstanding request on a connection MUST
maintain a list of outstanding requests in the order sent and MUST
associate each received response message on that connection to the highest
ordered request that has not yet received a final (non-1xx)
response.
</t>
</section>
<section title="Message Forwarding" anchor="message.forwarding">
<t>
As described in <xref target="intermediaries"/>, intermediaries can serve
a variety of roles in the processing of HTTP requests and responses.
Some intermediaries are used to improve performance or availability.
Others are used for access control or to filter content.
Since an HTTP stream has characteristics similar to a pipe-and-filter
architecture, there are no inherent limits to the extent an intermediary
can enhance (or interfere) with either direction of the stream.
</t>
<t>
An intermediary not acting as a tunnel MUST implement the
<xref target="header.connection" format="none">Connection</xref> header field, as specified in
<xref target="header.connection"/>, and exclude fields from being forwarded
that are only intended for the incoming connection.
</t>
<t>
An intermediary MUST NOT forward a message to itself unless it is
protected from an infinite request loop. In general, an intermediary ought
to recognize its own server names, including any aliases, local variations,
or literal IP addresses, and respond to such requests directly.
</t>
<section title="Via" anchor="header.via">
<iref primary="true" item="Via header field"/>
<t>
The "Via" header field indicates the presence of intermediate protocols and
recipients between the user agent and the server (on requests) or between
the origin server and the client (on responses), similar to the
"Received" header field in email
(Section 3.6.7 of <xref target="RFC5322"/>).
Via can be used for tracking message forwards,
avoiding request loops, and identifying the protocol capabilities of
senders along the request/response chain.
</t>
<figure><iref primary="true" item="Grammar" subitem="Via"/><iref primary="true" item="Grammar" subitem="received-protocol"/><iref primary="true" item="Grammar" subitem="protocol-name"/><iref primary="true" item="Grammar" subitem="protocol-version"/><iref primary="true" item="Grammar" subitem="received-by"/><iref primary="true" item="Grammar" subitem="pseudonym"/><artwork type="abnf2616"><![CDATA[
Via = 1#( received-protocol RWS received-by [ RWS comment ] )
received-protocol = [ protocol-name "/" ] protocol-version
; see Section 6.7
received-by = ( uri-host [ ":" port ] ) / pseudonym
pseudonym = token
]]></artwork></figure>
<t>
Multiple Via field values represent each proxy or gateway that has
forwarded the message. Each intermediary appends its own information
about how the message was received, such that the end result is ordered
according to the sequence of forwarding recipients.
</t>
<t>
A proxy MUST send an appropriate Via header field, as described below, in
each message that it forwards.
An HTTP-to-HTTP gateway MUST send an appropriate Via header field in
each inbound request message and MAY send a Via header field in
forwarded response messages.
</t>
<t>
For each intermediary, the received-protocol indicates the protocol and
protocol version used by the upstream sender of the message. Hence, the
Via field value records the advertised protocol capabilities of the
request/response chain such that they remain visible to downstream
recipients; this can be useful for determining what backwards-incompatible
features might be safe to use in response, or within a later request, as
described in <xref target="http.version"/>. For brevity, the protocol-name
is omitted when the received protocol is HTTP.
</t>
<t>
The received-by portion of the field value is normally the host and optional
port number of a recipient server or client that subsequently forwarded the
message.
However, if the real host is considered to be sensitive information, a
sender MAY replace it with a pseudonym. If a port is not provided,
a recipient MAY interpret that as meaning it was received on the default
TCP port, if any, for the received-protocol.
</t>
<t>
A sender MAY generate comments in the Via header field to identify the
software of each recipient, analogous to the User-Agent and
Server header fields. However, all comments in the Via field
are optional and a recipient MAY remove them prior to forwarding the
message.
</t>
<t>
For example, a request message could be sent from an HTTP/1.0 user
agent to an internal proxy code-named "fred", which uses HTTP/1.1 to
forward the request to a public proxy at p.example.net, which completes
the request by forwarding it to the origin server at www.example.com.
The request received by www.example.com would then have the following
Via header field:
</t>
<figure><artwork type="example"><![CDATA[
Via: 1.0 fred, 1.1 p.example.net
]]></artwork></figure>
<t>
An intermediary used as a portal through a network firewall
SHOULD NOT forward the names and ports of hosts within the firewall
region unless it is explicitly enabled to do so. If not enabled, such an
intermediary SHOULD replace each received-by host of any host behind the
firewall by an appropriate pseudonym for that host.
</t>
<t>
An intermediary MAY combine an ordered subsequence of Via header
field entries into a single such entry if the entries have identical
received-protocol values. For example,
</t>
<figure><artwork type="example"><![CDATA[
Via: 1.0 ricky, 1.1 ethel, 1.1 fred, 1.0 lucy
]]></artwork></figure>
<t>
could be collapsed to
</t>
<figure><artwork type="example"><![CDATA[
Via: 1.0 ricky, 1.1 mertz, 1.0 lucy
]]></artwork></figure>
<t>
A sender SHOULD NOT combine multiple entries unless they are all
under the same organizational control and the hosts have already been
replaced by pseudonyms. A sender MUST NOT combine entries that
have different received-protocol values.
</t>
</section>
<section title="Transformations" anchor="message.transformations">
<iref primary="true" item="transforming proxy"/>
<iref primary="true" item="non-transforming proxy"/>
<t>
Some intermediaries include features for transforming messages and their
payloads. A proxy might, for example, convert between image formats in
order to save cache space or to reduce the amount of traffic on a slow
link. However, operational problems might occur when these transformations
are applied to payloads intended for critical applications, such as medical
imaging or scientific data analysis, particularly when integrity checks or
digital signatures are used to ensure that the payload received is
identical to the original.
</t>
<t>
An HTTP-to-HTTP proxy is called a "transforming proxy"
if it is designed or configured to modify messages in a semantically
meaningful way (i.e., modifications, beyond those required by normal
HTTP processing, that change the message in a way that would be
significant to the original sender or potentially significant to
downstream recipients). For example, a transforming proxy might be
acting as a shared annotation server (modifying responses to include
references to a local annotation database), a malware filter, a
format transcoder, or a privacy filter. Such transformations are presumed
to be desired by whichever client (or client organization) selected the
proxy.
</t>
<t>
If a proxy receives a request-target with a host name that is not a
fully qualified domain name, it MAY add its own domain to the host name
it received when forwarding the request. A proxy MUST NOT change the
host name if the request-target contains a fully qualified domain name.
</t>
<t>
A proxy MUST NOT modify the "absolute-path" and "query" parts of the
received request-target when forwarding it to the next inbound server,
except as noted above to replace an empty path with "/" or "*".
</t>
<t>
A proxy MAY modify the message body through application
or removal of a transfer coding (<xref target="transfer.codings"/>).
</t>
<t>
A proxy MUST NOT transform the payload (Section 3.3 of <xref target="Part2"/>) of a message that
contains a no-transform cache-control directive (Section 5.2 of <xref target="Part6"/>).
</t>
<t>
A proxy MAY transform the payload of a message
that does not contain a no-transform cache-control directive.
A proxy that transforms a payload MUST add a Warning
header field with the warn-code of 214 ("Transformation Applied")
if one is not already in the message (see Section 5.5 of <xref target="Part6"/>).
A proxy that transforms the payload of a 200 (OK) response
can further inform downstream recipients that a transformation has been
applied by changing the response status code to
203 (Non-Authoritative Information) (Section 6.3.4 of <xref target="Part2"/>).
</t>
<t>
A proxy SHOULD NOT modify header fields that provide information about
the end points of the communication chain, the resource state, or the
selected representation (other than the payload) unless the field's
definition specifically allows such modification or the modification is
deemed necessary for privacy or security.
</t>
</section>
</section>
</section>
<section title="Connection Management" anchor="connection.management">
<t>
HTTP messaging is independent of the underlying transport or
session-layer connection protocol(s). HTTP only presumes a reliable
transport with in-order delivery of requests and the corresponding
in-order delivery of responses. The mapping of HTTP request and
response structures onto the data units of an underlying transport
protocol is outside the scope of this specification.
</t>
<t>
As described in <xref target="connecting.inbound"/>, the specific
connection protocols to be used for an HTTP interaction are determined by
client configuration and the <xref target="target-resource" format="none">target URI</xref>.
For example, the "http" URI scheme
(<xref target="http.uri"/>) indicates a default connection of TCP
over IP, with a default TCP port of 80, but the client might be
configured to use a proxy via some other connection, port, or protocol.
</t>
<t>
HTTP implementations are expected to engage in connection management,
which includes maintaining the state of current connections,
establishing a new connection or reusing an existing connection,
processing messages received on a connection, detecting connection
failures, and closing each connection.
Most clients maintain multiple connections in parallel, including
more than one connection per server endpoint.
Most servers are designed to maintain thousands of concurrent connections,
while controlling request queues to enable fair use and detect
denial of service attacks.
</t>
<section title="Connection" anchor="header.connection">
<iref primary="true" item="Connection header field"/>
<iref primary="true" item="close"/>
<t>
The "Connection" header field allows the sender to indicate desired
control options for the current connection. In order to avoid confusing
downstream recipients, a proxy or gateway MUST remove or replace any
received connection options before forwarding the message.
</t>
<t>
When a header field aside from Connection is used to supply control
information for or about the current connection, the sender MUST list
the corresponding field-name within the "Connection" header field.
A proxy or gateway MUST parse a received Connection
header field before a message is forwarded and, for each
connection-option in this field, remove any header field(s) from
the message with the same name as the connection-option, and then
remove the Connection header field itself (or replace it with the
intermediary's own connection options for the forwarded message).
</t>
<t>
Hence, the Connection header field provides a declarative way of
distinguishing header fields that are only intended for the
immediate recipient ("hop-by-hop") from those fields that are
intended for all recipients on the chain ("end-to-end"), enabling the
message to be self-descriptive and allowing future connection-specific
extensions to be deployed without fear that they will be blindly
forwarded by older intermediaries.
</t>
<t>
The Connection header field's value has the following grammar:
</t>
<figure><iref primary="true" item="Grammar" subitem="Connection"/><iref primary="true" item="Grammar" subitem="connection-option"/><artwork type="abnf2616"><![CDATA[
Connection = 1#connection-option
connection-option = token
]]></artwork></figure>
<t>
Connection options are case-insensitive.
</t>
<t>
A sender MUST NOT send a connection option corresponding to a header
field that is intended for all recipients of the payload.
For example, Cache-Control is never appropriate as a
connection option (Section 5.2 of <xref target="Part6"/>).
</t>
<t>
The connection options do not always correspond to a header field
present in the message, since a connection-specific header field
might not be needed if there are no parameters associated with a
connection option. In contrast, a connection-specific header field that
is received without a corresponding connection option usually indicates
that the field has been improperly forwarded by an intermediary and
ought to be ignored by the recipient.
</t>
<t>
When defining new connection options, specification authors ought to survey
existing header field names and ensure that the new connection option does
not share the same name as an already deployed header field.
Defining a new connection option essentially reserves that potential
field-name for carrying additional information related to the
connection option, since it would be unwise for senders to use
that field-name for anything else.
</t>
<t>
The "close" connection option is defined for a
sender to signal that this connection will be closed after completion of
the response. For example,
</t>
<figure><artwork type="example"><![CDATA[
Connection: close
]]></artwork></figure>
<t>
in either the request or the response header fields indicates that the
sender is going to close the connection after the current request/response
is complete (<xref target="persistent.tear-down"/>).
</t>
<t>
A client that does not support <xref target="persistent.connections" format="none">persistent connections</xref> MUST
send the "close" connection option in every request message.
</t>
<t>
A server that does not support <xref target="persistent.connections" format="none">persistent connections</xref> MUST
send the "close" connection option in every response message that
does not have a 1xx (Informational) status code.
</t>
</section>
<section title="Establishment" anchor="persistent.establishment">
<t>
It is beyond the scope of this specification to describe how connections
are established via various transport or session-layer protocols.
Each connection applies to only one transport link.
</t>
</section>
<section title="Persistence" anchor="persistent.connections">
<t>
HTTP/1.1 defaults to the use of "persistent connections",
allowing multiple requests and responses to be carried over a single
connection. The "<xref target="header.connection" format="none">close</xref>" connection-option is used to signal
that a connection will not persist after the current request/response.
HTTP implementations SHOULD support persistent connections.
</t>
<t>
A recipient determines whether a connection is persistent or not based on
the most recently received message's protocol version and
<xref target="header.connection" format="none">Connection</xref> header field (if any):
<list style="symbols">
<t>If the <xref target="header.connection" format="none">close</xref> connection option is present, the
connection will not persist after the current response; else,</t>
<t>If the received protocol is HTTP/1.1 (or later), the connection will
persist after the current response; else,</t>
<t>If the received protocol is HTTP/1.0, the "keep-alive"
connection option is present, the recipient is not a proxy, and
the recipient wishes to honor the HTTP/1.0 "keep-alive" mechanism,
the connection will persist after the current response; otherwise,</t>
<t>The connection will close after the current response.</t>
</list>
</t>
<t>
A client MAY send additional requests on a persistent connection until it
sends or receives a <xref target="header.connection" format="none">close</xref> connection option or receives an
HTTP/1.0 response without a "keep-alive" connection option.
</t>
<t>
In order to remain persistent, all messages on a connection need to
have a self-defined message length (i.e., one not defined by closure
of the connection), as described in <xref target="message.body"/>.
A server MUST read the entire request message body or close
the connection after sending its response, since otherwise the
remaining data on a persistent connection would be misinterpreted
as the next request. Likewise,
a client MUST read the entire response message body if it intends
to reuse the same connection for a subsequent request.
</t>
<t>
A proxy server MUST NOT maintain a persistent connection with an
HTTP/1.0 client (see Section 19.7.1 of <xref target="RFC2068"/> for
information and discussion of the problems with the Keep-Alive header field
implemented by many HTTP/1.0 clients).
</t>
<t>
See <xref target="compatibility.with.http.1.0.persistent.connections"/>
for more information on backward compatibility with HTTP/1.0 clients.
</t>
<section title="Retrying Requests" anchor="persistent.retrying.requests">
<t>
Connections can be closed at any time, with or without intention.
Implementations ought to anticipate the need to recover
from asynchronous close events.
</t>
<t>
When an inbound connection is closed prematurely, a client MAY open a new
connection and automatically retransmit an aborted sequence of requests if
all of those requests have idempotent methods (Section 4.2.2 of <xref target="Part2"/>).
A proxy MUST NOT automatically retry non-idempotent requests.
</t>
<t>
A user agent MUST NOT automatically retry a request with a non-idempotent
method unless it has some means to know that the request semantics are
actually idempotent, regardless of the method, or some means to detect that
the original request was never applied. For example, a user agent that
knows (through design or configuration) that a POST request to a given
resource is safe can repeat that request automatically.
Likewise, a user agent designed specifically to operate on a version
control repository might be able to recover from partial failure conditions
by checking the target resource revision(s) after a failed connection,
reverting or fixing any changes that were partially applied, and then
automatically retrying the requests that failed.
</t>
<t>
A client SHOULD NOT automatically retry a failed automatic retry.
</t>
</section>
<section title="Pipelining" anchor="pipelining">
<t>
A client that supports persistent connections MAY "pipeline"
its requests (i.e., send multiple requests without waiting for each
response). A server MAY process a sequence of pipelined requests in
parallel if they all have safe methods (Section 4.2.1 of <xref target="Part2"/>), but MUST send
the corresponding responses in the same order that the requests were
received.
</t>
<t>
A client that pipelines requests SHOULD retry unanswered requests if the
connection closes before it receives all of the corresponding responses.
When retrying pipelined requests after a failed connection (a connection
not explicitly closed by the server in its last complete response), a
client MUST NOT pipeline immediately after connection establishment,
since the first remaining request in the prior pipeline might have caused
an error response that can be lost again if multiple requests are sent on a
prematurely closed connection (see the TCP reset problem described in
<xref target="persistent.tear-down"/>).
</t>
<t>
Idempotent methods (Section 4.2.2 of <xref target="Part2"/>) are significant to pipelining
because they can be automatically retried after a connection failure.
A user agent SHOULD NOT pipeline requests after a non-idempotent method,
until the final response status code for that method has been received,
unless the user agent has a means to detect and recover from partial
failure conditions involving the pipelined sequence.
</t>
<t>
An intermediary that receives pipelined requests MAY pipeline those
requests when forwarding them inbound, since it can rely on the outbound
user agent(s) to determine what requests can be safely pipelined. If the
inbound connection fails before receiving a response, the pipelining
intermediary MAY attempt to retry a sequence of requests that have yet
to receive a response if the requests all have idempotent methods;
otherwise, the pipelining intermediary SHOULD forward any received
responses and then close the corresponding outbound connection(s) so that
the outbound user agent(s) can recover accordingly.
</t>
</section>
</section>
<section title="Concurrency" anchor="persistent.concurrency">
<t>
A client ought to limit the number of simultaneous open
connections that it maintains to a given server.
</t>
<t>
Previous revisions of HTTP gave a specific number of connections as a
ceiling, but this was found to be impractical for many applications. As a
result, this specification does not mandate a particular maximum number of
connections, but instead encourages clients to be conservative when opening
multiple connections.
</t>
<t>
Multiple connections are typically used to avoid the "head-of-line
blocking" problem, wherein a request that takes significant server-side
processing and/or has a large payload blocks subsequent requests on the
same connection. However, each connection consumes server resources.
Furthermore, using multiple connections can cause undesirable side effects
in congested networks.
</t>
<t>
Note that a server might reject traffic that it deems abusive or
characteristic of a denial of service attack, such as an excessive number
of open connections from a single client.
</t>
</section>
<section title="Failures and Time-outs" anchor="persistent.failures">
<t>
Servers will usually have some time-out value beyond which they will
no longer maintain an inactive connection. Proxy servers might make
this a higher value since it is likely that the client will be making
more connections through the same proxy server. The use of persistent
connections places no requirements on the length (or existence) of
this time-out for either the client or the server.
</t>
<t>
A client or server that wishes to time-out SHOULD issue a graceful close
on the connection. Implementations SHOULD constantly monitor open
connections for a received closure signal and respond to it as appropriate,
since prompt closure of both sides of a connection enables allocated system
resources to be reclaimed.
</t>
<t>
A client, server, or proxy MAY close the transport connection at any
time. For example, a client might have started to send a new request
at the same time that the server has decided to close the "idle"
connection. From the server's point of view, the connection is being
closed while it was idle, but from the client's point of view, a
request is in progress.
</t>
<t>
A server SHOULD sustain persistent connections, when possible, and allow
the underlying
transport's flow control mechanisms to resolve temporary overloads, rather
than terminate connections with the expectation that clients will retry.
The latter technique can exacerbate network congestion.
</t>
<t>
A client sending a message body SHOULD monitor
the network connection for an error response while it is transmitting
the request. If the client sees a response that indicates the server does
not wish to receive the message body and is closing the connection, the
client SHOULD immediately cease transmitting the body and close its side
of the connection.
</t>
</section>
<section title="Tear-down" anchor="persistent.tear-down">
<iref primary="false" item="Connection header field"/>
<iref primary="false" item="close"/>
<t>
The <xref target="header.connection" format="none">Connection</xref> header field
(<xref target="header.connection"/>) provides a "<xref target="header.connection" format="none">close</xref>"
connection option that a sender SHOULD send when it wishes to close
the connection after the current request/response pair.
</t>
<t>
A client that sends a <xref target="header.connection" format="none">close</xref> connection option MUST NOT
send further requests on that connection (after the one containing
<xref target="header.connection" format="none">close</xref>) and MUST close the connection after reading the
final response message corresponding to this request.
</t>
<t>
A server that receives a <xref target="header.connection" format="none">close</xref> connection option MUST
initiate a close of the connection (see below) after it sends the
final response to the request that contained <xref target="header.connection" format="none">close</xref>.
The server SHOULD send a <xref target="header.connection" format="none">close</xref> connection option
in its final response on that connection. The server MUST NOT process
any further requests received on that connection.
</t>
<t>
A server that sends a <xref target="header.connection" format="none">close</xref> connection option MUST
initiate a close of the connection (see below) after it sends the
response containing <xref target="header.connection" format="none">close</xref>. The server MUST NOT process
any further requests received on that connection.
</t>
<t>
A client that receives a <xref target="header.connection" format="none">close</xref> connection option MUST
cease sending requests on that connection and close the connection
after reading the response message containing the close; if additional
pipelined requests had been sent on the connection, the client SHOULD NOT
assume that they will be processed by the server.
</t>
<t>
If a server performs an immediate close of a TCP connection, there is a
significant risk that the client will not be able to read the last HTTP
response. If the server receives additional data from the client on a
fully-closed connection, such as another request that was sent by the
client before receiving the server's response, the server's TCP stack will
send a reset packet to the client; unfortunately, the reset packet might
erase the client's unacknowledged input buffers before they can be read
and interpreted by the client's HTTP parser.
</t>
<t>
To avoid the TCP reset problem, servers typically close a connection in
stages. First, the server performs a half-close by closing only the write
side of the read/write connection. The server then continues to read from
the connection until it receives a corresponding close by the client, or
until the server is reasonably certain that its own TCP stack has received
the client's acknowledgement of the packet(s) containing the server's last
response. Finally, the server fully closes the connection.
</t>
<t>
It is unknown whether the reset problem is exclusive to TCP or might also
be found in other transport connection protocols.
</t>
</section>
<section title="Upgrade" anchor="header.upgrade">
<iref primary="true" item="Upgrade header field"/>
<t>
The "Upgrade" header field is intended to provide a simple mechanism
for transitioning from HTTP/1.1 to some other protocol on the same
connection. A client MAY send a list of protocols in the Upgrade
header field of a request to invite the server to switch to one or
more of those protocols, in order of descending preference, before sending
the final response. A server MAY ignore a received Upgrade header field
if it wishes to continue using the current protocol on that connection.
Upgrade cannot be used to insist on a protocol change.
</t>
<figure><iref primary="true" item="Grammar" subitem="Upgrade"/><artwork type="abnf2616"><![CDATA[
Upgrade = 1#protocol
protocol = protocol-name ["/" protocol-version]
protocol-name = token
protocol-version = token
]]></artwork></figure>
<t>
A server that sends a 101 (Switching Protocols) response
MUST send an Upgrade header field to indicate the new protocol(s) to
which the connection is being switched; if multiple protocol layers are
being switched, the sender MUST list the protocols in layer-ascending
order. A server MUST NOT switch to a protocol that was not indicated by
the client in the corresponding request's Upgrade header field.
A server MAY choose to ignore the order of preference indicated by the
client and select the new protocol(s) based on other factors, such as the
nature of the request or the current load on the server.
</t>
<t>
A server that sends a 426 (Upgrade Required) response
MUST send an Upgrade header field to indicate the acceptable protocols,
in order of descending preference.
</t>
<t>
A server MAY send an Upgrade header field in any other response to
advertise that it implements support for upgrading to the listed protocols,
in order of descending preference, when appropriate for a future request.
</t>
<figure><preamble>
The following is a hypothetical example sent by a client:
</preamble><artwork type="message/http; msgtype="request""><![CDATA[
GET /hello.txt HTTP/1.1
Host: www.example.com
Connection: upgrade
Upgrade: HTTP/2.0, SHTTP/1.3, IRC/6.9, RTA/x11
]]></artwork></figure>
<t>
The capabilities and nature of the
application-level communication after the protocol change is entirely
dependent upon the new protocol(s) chosen. However, immediately after
sending the 101 response, the server is expected to continue responding to
the original request as if it had received its equivalent within the new
protocol (i.e., the server still has an outstanding request to satisfy
after the protocol has been changed, and is expected to do so without
requiring the request to be repeated).
</t>
<t>
For example, if the Upgrade header field is received in a GET request
and the server decides to switch protocols, it first responds
with a 101 (Switching Protocols) message in HTTP/1.1 and
then immediately follows that with the new protocol's equivalent of a
response to a GET on the target resource. This allows a connection to be
upgraded to protocols with the same semantics as HTTP without the
latency cost of an additional round-trip. A server MUST NOT switch
protocols unless the received message semantics can be honored by the new
protocol; an OPTIONS request can be honored by any protocol.
</t>
<figure><preamble>
The following is an example response to the above hypothetical request:
</preamble><artwork type="message/http; msgtype="response""><![CDATA[
HTTP/1.1 101 Switching Protocols
Connection: upgrade
Upgrade: HTTP/2.0
[... data stream switches to HTTP/2.0 with an appropriate response
(as defined by new protocol) to the "GET /hello.txt" request ...]
]]></artwork></figure>
<t>
When Upgrade is sent, the sender MUST also send a
<xref target="header.connection" format="none">Connection</xref> header field (<xref target="header.connection"/>)
that contains an "upgrade" connection option, in order to prevent Upgrade
from being accidentally forwarded by intermediaries that might not implement
the listed protocols. A server MUST ignore an Upgrade header field that
is received in an HTTP/1.0 request.
</t>
<t>
A client cannot begin using an upgraded protocol on the connection until
it has completely sent the request message (i.e., the client can't change
the protocol it is sending in the middle of a message).
If a server receives both Upgrade and an Expect header field
with the "100-continue" expectation (Section 5.1.1 of <xref target="Part2"/>), the
server MUST send a 100 (Continue) response before sending
a 101 (Switching Protocols) response.
</t>
<t>
The Upgrade header field only applies to switching protocols on top of the
existing connection; it cannot be used to switch the underlying connection
(transport) protocol, nor to switch the existing communication to a
different connection. For those purposes, it is more appropriate to use a
3xx (Redirection) response (Section 6.4 of <xref target="Part2"/>).
</t>
<t>
This specification only defines the protocol name "HTTP" for use by
the family of Hypertext Transfer Protocols, as defined by the HTTP
version rules of <xref target="http.version"/> and future updates to this
specification. Additional tokens ought to be registered with IANA using the
registration procedure defined in <xref target="upgrade.token.registry"/>.
</t>
</section>
</section>
<section title="ABNF list extension: #rule" anchor="abnf.extension">
<t>
A #rule extension to the ABNF rules of <xref target="RFC5234"/> is used to
improve readability in the definitions of some header field values.
</t>
<t>
A construct "#" is defined, similar to "*", for defining comma-delimited
lists of elements. The full form is "<n>#<m>element" indicating
at least <n> and at most <m> elements, each separated by a single
comma (",") and optional whitespace (OWS).
</t>
<figure><preamble>
In any production that uses the list construct, a sender MUST NOT
generate empty list elements. In other words, a sender MUST generate
lists that satisfy the following syntax:
</preamble><artwork type="example"><![CDATA[
1#element => element *( OWS "," OWS element )
]]></artwork></figure>
<figure><preamble>
and:
</preamble><artwork type="example"><![CDATA[
#element => [ 1#element ]
]]></artwork></figure>
<figure><preamble>
and for n >= 1 and m > 1:
</preamble><artwork type="example"><![CDATA[
<n>#<m>element => element <n-1>*<m-1>( OWS "," OWS element )
]]></artwork></figure>
<t>
For compatibility with legacy list rules, a recipient MUST parse and ignore
a reasonable number of empty list elements: enough to handle common mistakes
by senders that merge values, but not so much that they could be used as a
denial of service mechanism. In other words, a recipient MUST accept lists
that satisfy the following syntax:
</t>
<figure><artwork type="example"><![CDATA[
#element => [ ( "," / element ) *( OWS "," [ OWS element ] ) ]
1#element => *( "," OWS ) element *( OWS "," [ OWS element ] )
]]></artwork></figure>
<t>
Empty elements do not contribute to the count of elements present.
For example, given these ABNF productions:
</t>
<figure><artwork type="example"><![CDATA[
example-list = 1#example-list-elmt
example-list-elmt = token ; see Section 3.2.6
]]></artwork></figure>
<t>
Then the following are valid values for example-list (not including the
double quotes, which are present for delimitation only):
</t>
<figure><artwork type="example"><![CDATA[
"foo,bar"
"foo ,bar,"
"foo , ,bar,charlie "
]]></artwork></figure>
<t>
In contrast, the following values would be invalid, since at least one
non-empty element is required by the example-list production:
</t>
<figure><artwork type="example"><![CDATA[
""
","
", ,"
]]></artwork></figure>
<t>
<xref target="collected.abnf"/> shows the collected ABNF for recipients
after the list constructs have been expanded.
</t>
</section>
<section title="IANA Considerations" anchor="IANA.considerations">
<section title="Header Field Registration" anchor="header.field.registration">
<t>
HTTP header fields are registered within the Message Header Field Registry
maintained at
<eref target="http://www.iana.org/assignments/message-headers/"/>.
</t>
<t>
This document defines the following HTTP header fields, so their
associated registry entries shall be updated according to the permanent
registrations below (see <xref target="BCP90"/>):
</t>
<!--AUTOGENERATED FROM extract-header-defs.xslt, do not edit manually-->
<texttable align="left" suppress-title="true" anchor="iana.header.registration.table">
<ttcol>Header Field Name</ttcol>
<ttcol>Protocol</ttcol>
<ttcol>Status</ttcol>
<ttcol>Reference</ttcol>
<c>Connection</c>
<c>http</c>
<c>standard</c>
<c>
<xref target="header.connection"/>
</c>
<c>Content-Length</c>
<c>http</c>
<c>standard</c>
<c>
<xref target="header.content-length"/>
</c>
<c>Host</c>
<c>http</c>
<c>standard</c>
<c>
<xref target="header.host"/>
</c>
<c>TE</c>
<c>http</c>
<c>standard</c>
<c>
<xref target="header.te"/>
</c>
<c>Trailer</c>
<c>http</c>
<c>standard</c>
<c>
<xref target="header.trailer"/>
</c>
<c>Transfer-Encoding</c>
<c>http</c>
<c>standard</c>
<c>
<xref target="header.transfer-encoding"/>
</c>
<c>Upgrade</c>
<c>http</c>
<c>standard</c>
<c>
<xref target="header.upgrade"/>
</c>
<c>Via</c>
<c>http</c>
<c>standard</c>
<c>
<xref target="header.via"/>
</c>
</texttable>
<!--(END)-->
<t>
Furthermore, the header field-name "Close" shall be registered as
"reserved", since using that name as an HTTP header field might
conflict with the "close" connection option of the "<xref target="header.connection" format="none">Connection</xref>"
header field (<xref target="header.connection"/>).
</t>
<texttable align="left" suppress-title="true">
<ttcol>Header Field Name</ttcol>
<ttcol>Protocol</ttcol>
<ttcol>Status</ttcol>
<ttcol>Reference</ttcol>
<c>Close</c>
<c>http</c>
<c>reserved</c>
<c>
<xref target="header.field.registration"/>
</c>
</texttable>
<t>
The change controller is: "IETF (iesg@ietf.org) - Internet Engineering Task Force".
</t>
</section>
<section title="URI Scheme Registration" anchor="uri.scheme.registration">
<t>
IANA maintains the registry of URI Schemes <xref target="BCP115"/> at
<eref target="http://www.iana.org/assignments/uri-schemes/"/>.
</t>
<t>
This document defines the following URI schemes, so their
associated registry entries shall be updated according to the permanent
registrations below:
</t>
<texttable align="left" suppress-title="true">
<ttcol>URI Scheme</ttcol>
<ttcol>Description</ttcol>
<ttcol>Reference</ttcol>
<c>http</c>
<c>Hypertext Transfer Protocol</c>
<c><xref target="http.uri"/></c>
<c>https</c>
<c>Hypertext Transfer Protocol Secure</c>
<c><xref target="https.uri"/></c>
</texttable>
</section>
<section title="Internet Media Type Registration" anchor="internet.media.type.http">
<t>
IANA maintains the registry of Internet media types <xref target="BCP13"/> at
<eref target="http://www.iana.org/assignments/media-types"/>.
</t>
<t>
This document serves as the specification for the Internet media types
"message/http" and "application/http". The following is to be registered with
IANA.
</t>
<section title="Internet Media Type message/http" anchor="internet.media.type.message.http">
<iref item="Media Type" subitem="message/http" primary="true"/>
<iref item="message/http Media Type" primary="true"/>
<t>
The message/http type can be used to enclose a single HTTP request or
response message, provided that it obeys the MIME restrictions for all
"message" types regarding line length and encodings.
</t>
<t>
<list style="hanging">
<t hangText="Type name:">
message
</t>
<t hangText="Subtype name:">
http
</t>
<t hangText="Required parameters:">
N/A
</t>
<t hangText="Optional parameters:">
version, msgtype
<list style="hanging">
<t hangText="version:">
The HTTP-version number of the enclosed message
(e.g., "1.1"). If not present, the version can be
determined from the first line of the body.
</t>
<t hangText="msgtype:">
The message type — "request" or "response". If not
present, the type can be determined from the first
line of the body.
</t>
</list>
</t>
<t hangText="Encoding considerations:">
only "7bit", "8bit", or "binary" are permitted
</t>
<t hangText="Security considerations:">
see <xref target="security.considerations"/>
</t>
<t hangText="Interoperability considerations:">
N/A
</t>
<t hangText="Published specification:">
This specification (see <xref target="internet.media.type.message.http"/>).
</t>
<t hangText="Applications that use this media type:">
N/A
</t>
<t hangText="Fragment identifier considerations:">
N/A
</t>
<t hangText="Additional information:">
<list style="hanging">
<t hangText="Magic number(s):">N/A</t>
<t hangText="Deprecated alias names for this type:">N/A</t>
<t hangText="File extension(s):">N/A</t>
<t hangText="Macintosh file type code(s):">N/A</t>
</list>
</t>
<t hangText="Person and email address to contact for further information:">
See Authors Section.
</t>
<t hangText="Intended usage:">
COMMON
</t>
<t hangText="Restrictions on usage:">
N/A
</t>
<t hangText="Author:">
See Authors Section.
</t>
<t hangText="Change controller:">
IESG
</t>
</list>
</t>
</section>
<section title="Internet Media Type application/http" anchor="internet.media.type.application.http">
<iref item="Media Type" subitem="application/http" primary="true"/>
<iref item="application/http Media Type" primary="true"/>
<t>
The application/http type can be used to enclose a pipeline of one or more
HTTP request or response messages (not intermixed).
</t>
<t>
<list style="hanging">
<t hangText="Type name:">
application
</t>
<t hangText="Subtype name:">
http
</t>
<t hangText="Required parameters:">
N/A
</t>
<t hangText="Optional parameters:">
version, msgtype
<list style="hanging">
<t hangText="version:">
The HTTP-version number of the enclosed messages
(e.g., "1.1"). If not present, the version can be
determined from the first line of the body.
</t>
<t hangText="msgtype:">
The message type — "request" or "response". If not
present, the type can be determined from the first
line of the body.
</t>
</list>
</t>
<t hangText="Encoding considerations:">
HTTP messages enclosed by this type
are in "binary" format; use of an appropriate
Content-Transfer-Encoding is required when
transmitted via E-mail.
</t>
<t hangText="Security considerations:">
see <xref target="security.considerations"/>
</t>
<t hangText="Interoperability considerations:">
N/A
</t>
<t hangText="Published specification:">
This specification (see <xref target="internet.media.type.application.http"/>).
</t>
<t hangText="Applications that use this media type:">
N/A
</t>
<t hangText="Fragment identifier considerations:">
N/A
</t>
<t hangText="Additional information:">
<list style="hanging">
<t hangText="Deprecated alias names for this type:">N/A</t>
<t hangText="Magic number(s):">N/A</t>
<t hangText="File extension(s):">N/A</t>
<t hangText="Macintosh file type code(s):">N/A</t>
</list>
</t>
<t hangText="Person and email address to contact for further information:">
See Authors Section.
</t>
<t hangText="Intended usage:">
COMMON
</t>
<t hangText="Restrictions on usage:">
N/A
</t>
<t hangText="Author:">
See Authors Section.
</t>
<t hangText="Change controller:">
IESG
</t>
</list>
</t>
</section>
</section>
<section title="Transfer Coding Registry" anchor="transfer.coding.registry">
<t>
The HTTP Transfer Coding Registry defines the name space for transfer
coding names. It is maintained at <eref target="http://www.iana.org/assignments/http-parameters"/>.
</t>
<section title="Procedure" anchor="transfer.coding.registry.procedure">
<t>
Registrations MUST include the following fields:
<list style="symbols">
<t>Name</t>
<t>Description</t>
<t>Pointer to specification text</t>
</list>
</t>
<t>
Names of transfer codings MUST NOT overlap with names of content codings
(Section 3.1.2.1 of <xref target="Part2"/>) unless the encoding transformation is identical, as
is the case for the compression codings defined in
<xref target="compression.codings"/>.
</t>
<t>
Values to be added to this name space require IETF Review (see
Section 4.1 of <xref target="RFC5226"/>), and MUST
conform to the purpose of transfer coding defined in this specification.
</t>
<t>
Use of program names for the identification of encoding formats
is not desirable and is discouraged for future encodings.
</t>
</section>
<section title="Registration" anchor="transfer.coding.registration">
<t>
The HTTP Transfer Coding Registry shall be updated with the registrations
below:
</t>
<texttable align="left" suppress-title="true" anchor="iana.transfer.coding.registration.table">
<ttcol>Name</ttcol>
<ttcol>Description</ttcol>
<ttcol>Reference</ttcol>
<c>chunked</c>
<c>Transfer in a series of chunks</c>
<c>
<xref target="chunked.encoding"/>
</c>
<c>compress</c>
<c>UNIX "compress" data format <xref target="Welch"/></c>
<c>
<xref target="compress.coding"/>
</c>
<c>deflate</c>
<c>"deflate" compressed data (<xref target="RFC1951"/>) inside
the "zlib" data format (<xref target="RFC1950"/>)
</c>
<c>
<xref target="deflate.coding"/>
</c>
<c>gzip</c>
<c>GZIP file format <xref target="RFC1952"/></c>
<c>
<xref target="gzip.coding"/>
</c>
<c>x-compress</c>
<c>Deprecated (alias for compress)</c>
<c>
<xref target="compress.coding"/>
</c>
<c>x-gzip</c>
<c>Deprecated (alias for gzip)</c>
<c>
<xref target="gzip.coding"/>
</c>
</texttable>
</section>
</section>
<section title="Content Coding Registration" anchor="content.coding.registration">
<t>
IANA maintains the registry of HTTP Content Codings at
<eref target="http://www.iana.org/assignments/http-parameters"/>.
</t>
<t>
The HTTP Content Codings Registry shall be updated with the registrations
below:
</t>
<texttable align="left" suppress-title="true" anchor="iana.content.coding.registration.table">
<ttcol>Name</ttcol>
<ttcol>Description</ttcol>
<ttcol>Reference</ttcol>
<c>compress</c>
<c>UNIX "compress" data format <xref target="Welch"/></c>
<c>
<xref target="compress.coding"/>
</c>
<c>deflate</c>
<c>"deflate" compressed data (<xref target="RFC1951"/>) inside
the "zlib" data format (<xref target="RFC1950"/>)</c>
<c>
<xref target="deflate.coding"/>
</c>
<c>gzip</c>
<c>GZIP file format <xref target="RFC1952"/></c>
<c>
<xref target="gzip.coding"/>
</c>
<c>x-compress</c>
<c>Deprecated (alias for compress)</c>
<c>
<xref target="compress.coding"/>
</c>
<c>x-gzip</c>
<c>Deprecated (alias for gzip)</c>
<c>
<xref target="gzip.coding"/>
</c>
</texttable>
</section>
<section title="Upgrade Token Registry" anchor="upgrade.token.registry">
<t>
The HTTP Upgrade Token Registry defines the name space for protocol-name
tokens used to identify protocols in the <xref target="header.upgrade" format="none">Upgrade</xref> header
field. The registry is maintained at <eref target="http://www.iana.org/assignments/http-upgrade-tokens"/>.
</t>
<section title="Procedure" anchor="upgrade.token.registry.procedure">
<t>
Each registered protocol name is associated with contact information
and an optional set of specifications that details how the connection
will be processed after it has been upgraded.
</t>
<t>
Registrations happen on a "First Come First Served" basis (see
Section 4.1 of <xref target="RFC5226"/>) and are subject to the
following rules:
<list style="numbers">
<t>A protocol-name token, once registered, stays registered forever.</t>
<t>The registration MUST name a responsible party for the
registration.</t>
<t>The registration MUST name a point of contact.</t>
<t>The registration MAY name a set of specifications associated with
that token. Such specifications need not be publicly available.</t>
<t>The registration SHOULD name a set of expected "protocol-version"
tokens associated with that token at the time of registration.</t>
<t>The responsible party MAY change the registration at any time.
The IANA will keep a record of all such changes, and make them
available upon request.</t>
<t>The IESG MAY reassign responsibility for a protocol token.
This will normally only be used in the case when a
responsible party cannot be contacted.</t>
</list>
</t>
<t>
This registration procedure for HTTP Upgrade Tokens replaces that
previously defined in Section 7.2 of <xref target="RFC2817"/>.
</t>
</section>
<section title="Upgrade Token Registration" anchor="upgrade.token.registration">
<t>
The "HTTP" entry in the HTTP Upgrade Token Registry shall be updated with
the registration below:
</t>
<texttable align="left" suppress-title="true">
<ttcol>Value</ttcol>
<ttcol>Description</ttcol>
<ttcol>Expected Version Tokens</ttcol>
<ttcol>Reference</ttcol>
<c>HTTP</c>
<c>Hypertext Transfer Protocol</c>
<c>any DIGIT.DIGIT (e.g, "2.0")</c>
<c><xref target="http.version"/></c>
</texttable>
<t>
The responsible party is: "IETF (iesg@ietf.org) - Internet Engineering Task Force".
</t>
</section>
</section>
</section>
<section title="Security Considerations" anchor="security.considerations">
<t>
This section is meant to inform developers, information providers, and
users of known security considerations relevant to HTTP message syntax,
parsing, and routing. Security considerations about HTTP semantics and
payloads are addressed in <xref target="Part2"/>.
</t>
<section title="Establishing Authority" anchor="establishing.authority">
<iref item="authoritative response" primary="true"/>
<iref item="phishing" primary="true"/>
<t>
HTTP relies on the notion of an authoritative response: a
response that has been determined by (or at the direction of) the authority
identified within the target URI to be the most appropriate response for
that request given the state of the target resource at the time of
response message origination. Providing a response from a non-authoritative
source, such as a shared cache, is often useful to improve performance and
availability, but only to the extent that the source can be trusted or
the distrusted response can be safely used.
</t>
<t>
Unfortunately, establishing authority can be difficult.
For example, phishing is an attack on the user's perception
of authority, where that perception can be misled by presenting similar
branding in hypertext, possibly aided by userinfo obfuscating the authority
component (see <xref target="http.uri"/>).
User agents can reduce the impact of phishing attacks by enabling users to
easily inspect a target URI prior to making an action, by prominently
distinguishing (or rejecting) userinfo when present, and by not sending
stored credentials and cookies when the referring document is from an
unknown or untrusted source.
</t>
<t>
When a registered name is used in the authority component, the "http" URI
scheme (<xref target="http.uri"/>) relies on the user's local name
resolution service to determine where it can find authoritative responses.
This means that any attack on a user's network host table, cached names, or
name resolution libraries becomes an avenue for attack on establishing
authority. Likewise, the user's choice of server for Domain Name Service
(DNS), and the hierarchy of servers from which it obtains resolution
results, could impact the authenticity of address mappings;
DNSSEC (<xref target="RFC4033"/>) is one way to improve authenticity.
</t>
<t>
Furthermore, after an IP address is obtained, establishing authority for
an "http" URI is vulnerable to attacks on Internet Protocol routing.
</t>
<t>
The "https" scheme (<xref target="https.uri"/>) is intended to prevent
(or at least reveal) many of these potential attacks on establishing
authority, provided that the negotiated TLS connection is secured and
the client properly verifies that the communicating server's identity
matches the target URI's authority component
(see <xref target="RFC2818"/>). Correctly implementing such verification
can be difficult (see <xref target="Georgiev"/>).
</t>
</section>
<section title="Risks of Intermediaries" anchor="risks.intermediaries">
<t>
By their very nature, HTTP intermediaries are men-in-the-middle, and thus
represent an opportunity for man-in-the-middle attacks. Compromise of
the systems on which the intermediaries run can result in serious security
and privacy problems. Intermediaries might have access to security-related
information, personal information about individual users and
organizations, and proprietary information belonging to users and
content providers. A compromised intermediary, or an intermediary
implemented or configured without regard to security and privacy
considerations, might be used in the commission of a wide range of
potential attacks.
</t>
<t>
Intermediaries that contain a shared cache are especially vulnerable
to cache poisoning attacks, as described in Section 8 of <xref target="Part6"/>.
</t>
<t>
Implementers need to consider the privacy and security
implications of their design and coding decisions, and of the
configuration options they provide to operators (especially the
default configuration).
</t>
<t>
Users need to be aware that intermediaries are no more trustworthy than
the people who run them; HTTP itself cannot solve this problem.
</t>
</section>
<section title="Attacks via Protocol Element Length" anchor="attack.protocol.element.length">
<t>
Because HTTP uses mostly textual, character-delimited fields, parsers are
often vulnerable to attacks based on sending very long (or very slow)
streams of data, particularly where an implementation is expecting a
protocol element with no predefined length.
</t>
<t>
To promote interoperability, specific recommendations are made for minimum
size limits on request-line (<xref target="request.line"/>)
and header fields (<xref target="header.fields"/>). These are
minimum recommendations, chosen to be supportable even by implementations
with limited resources; it is expected that most implementations will
choose substantially higher limits.
</t>
<t>
A server can reject a message that
has a request-target that is too long (Section 6.5.12 of <xref target="Part2"/>) or a request payload
that is too large (Section 6.5.11 of <xref target="Part2"/>). Additional status codes related to
capacity limits have been defined by extensions to HTTP
<xref target="RFC6585"/>.
</t>
<t>
Recipients ought to carefully limit the extent to which they process other
protocol elements, including (but not limited to) request methods, response
status phrases, header field-names, numeric values, and body chunks.
Failure to limit such processing can result in buffer overflows, arithmetic
overflows, or increased vulnerability to denial of service attacks.
</t>
</section>
<section title="Response Splitting" anchor="response.splitting">
<t>
Response splitting (a.k.a, CRLF injection) is a common technique, used in
various attacks on Web usage, that exploits the line-based nature of HTTP
message framing and the ordered association of requests to responses on
persistent connections <xref target="Klein"/>. This technique can be
particularly damaging when the requests pass through a shared cache.
</t>
<t>
Response splitting exploits a vulnerability in servers (usually within an
application server) where an attacker can send encoded data within some
parameter of the request that is later decoded and echoed within any of the
response header fields of the response. If the decoded data is crafted to
look like the response has ended and a subsequent response has begun, the
response has been split and the content within the apparent second response
is controlled by the attacker. The attacker can then make any other request
on the same persistent connection and trick the recipients (including
intermediaries) into believing that the second half of the split is an
authoritative answer to the second request.
</t>
<t>
For example, a parameter within the request-target might be read by an
application server and reused within a redirect, resulting in the same
parameter being echoed in the Location header field of the
response. If the parameter is decoded by the application and not properly
encoded when placed in the response field, the attacker can send encoded
CRLF octets and other content that will make the application's single
response look like two or more responses.
</t>
<t>
A common defense against response splitting is to filter requests for data
that looks like encoded CR and LF (e.g., "%0D" and "%0A"). However, that
assumes the application server is only performing URI decoding, rather
than more obscure data transformations like charset transcoding, XML entity
translation, base64 decoding, sprintf reformatting, etc. A more effective
mitigation is to prevent anything other than the server's core protocol
libraries from sending a CR or LF within the header section, which means
restricting the output of header fields to APIs that filter for bad octets
and not allowing application servers to write directly to the protocol
stream.
</t>
</section>
<section title="Request Smuggling" anchor="request.smuggling">
<t>
Request smuggling (<xref target="Linhart"/>) is a technique that exploits
differences in protocol parsing among various recipients to hide additional
requests (which might otherwise be blocked or disabled by policy) within an
apparently harmless request. Like response splitting, request smuggling
can lead to a variety of attacks on HTTP usage.
</t>
<t>
This specification has introduced new requirements on request parsing,
particularly with regard to message framing in
<xref target="message.body.length"/>, to reduce the effectiveness of
request smuggling.
</t>
</section>
<section title="Message Integrity" anchor="message.integrity">
<t>
HTTP does not define a specific mechanism for ensuring message integrity,
instead relying on the error-detection ability of underlying transport
protocols and the use of length or chunk-delimited framing to detect
completeness. Additional integrity mechanisms, such as hash functions or
digital signatures applied to the content, can be selectively added to
messages via extensible metadata header fields. Historically, the lack of
a single integrity mechanism has been justified by the informal nature of
most HTTP communication. However, the prevalence of HTTP as an information
access mechanism has resulted in its increasing use within environments
where verification of message integrity is crucial.
</t>
<t>
User agents are encouraged to implement configurable means for detecting
and reporting failures of message integrity such that those means can be
enabled within environments for which integrity is necessary. For example,
a browser being used to view medical history or drug interaction
information needs to indicate to the user when such information is detected
by the protocol to be incomplete, expired, or corrupted during transfer.
Such mechanisms might be selectively enabled via user agent extensions or
the presence of message integrity metadata in a response.
At a minimum, user agents ought to provide some indication that allows a
user to distinguish between a complete and incomplete response message
(<xref target="incomplete.messages"/>) when such verification is desired.
</t>
</section>
<section title="Message Confidentiality" anchor="message.confidentiality">
<t>
HTTP relies on underlying transport protocols to provide message
confidentiality when that is desired. HTTP has been specifically designed
to be independent of the transport protocol, such that it can be used
over many different forms of encrypted connection, with the selection of
such transports being identified by the choice of URI scheme or within
user agent configuration.
</t>
<t>
The "https" scheme can be used to identify resources that require a
confidential connection, as described in <xref target="https.uri"/>.
</t>
</section>
<section title="Privacy of Server Log Information" anchor="privacy.of.server.log.information">
<t>
A server is in the position to save personal data about a user's requests
over time, which might identify their reading patterns or subjects of
interest. In particular, log information gathered at an intermediary
often contains a history of user agent interaction, across a multitude
of sites, that can be traced to individual users.
</t>
<t>
HTTP log information is confidential in nature; its handling is often
constrained by laws and regulations. Log information needs to be securely
stored and appropriate guidelines followed for its analysis.
Anonymization of personal information within individual entries helps,
but is generally not sufficient to prevent real log traces from being
re-identified based on correlation with other access characteristics.
As such, access traces that are keyed to a specific client are unsafe to
publish even if the key is pseudonymous.
</t>
<t>
To minimize the risk of theft or accidental publication, log information
ought to be purged of personally identifiable information, including
user identifiers, IP addresses, and user-provided query parameters,
as soon as that information is no longer necessary to support operational
needs for security, auditing, or fraud control.
</t>
</section>
</section>
<section title="Acknowledgments" anchor="acks">
<t>
This edition of HTTP/1.1 builds on the many contributions that went into
<xref target="RFC1945" format="none">RFC 1945</xref>,
<xref target="RFC2068" format="none">RFC 2068</xref>,
<xref target="RFC2145" format="none">RFC 2145</xref>, and
<xref target="RFC2616" format="none">RFC 2616</xref>, including
substantial contributions made by the previous authors, editors, and
working group chairs: Tim Berners-Lee, Ari Luotonen, Roy T. Fielding,
Henrik Frystyk Nielsen, Jim Gettys, Jeffrey C. Mogul, Larry Masinter,
and Paul J. Leach. Mark Nottingham oversaw this effort as working group chair.
</t>
<t>
Since 1999, the following contributors have helped improve the HTTP
specification by reporting bugs, asking smart questions, drafting or
reviewing text, and evaluating open issues:
</t>
<t>Adam Barth,
Adam Roach,
Addison Phillips,
Adrian Chadd,
Adrian Cole,
Adrien W. de Croy,
Alan Ford,
Alan Ruttenberg,
Albert Lunde,
Alek Storm,
Alex Rousskov,
Alexandre Morgaut,
Alexey Melnikov,
Alisha Smith,
Amichai Rothman,
Amit Klein,
Amos Jeffries,
Andreas Maier,
Andreas Petersson,
Andrei Popov,
Anil Sharma,
Anne van Kesteren,
Anthony Bryan,
Asbjorn Ulsberg,
Ashok Kumar,
Balachander Krishnamurthy,
Barry Leiba,
Ben Laurie,
Benjamin Carlyle,
Benjamin Niven-Jenkins,
Benoit Claise,
Bil Corry,
Bill Burke,
Bjoern Hoehrmann,
Bob Scheifler,
Boris Zbarsky,
Brett Slatkin,
Brian Kell,
Brian McBarron,
Brian Pane,
Brian Raymor,
Brian Smith,
Bruce Perens,
Bryce Nesbitt,
Cameron Heavon-Jones,
Carl Kugler,
Carsten Bormann,
Charles Fry,
Chris Burdess,
Chris Newman,
Christian Huitema,
Cyrus Daboo,
Dale Robert Anderson,
Dan Wing,
Dan Winship,
Daniel Stenberg,
Darrel Miller,
Dave Cridland,
Dave Crocker,
Dave Kristol,
Dave Thaler,
David Booth,
David Singer,
David W. Morris,
Diwakar Shetty,
Dmitry Kurochkin,
Drummond Reed,
Duane Wessels,
Edward Lee,
Eitan Adler,
Eliot Lear,
Emile Stephan,
Eran Hammer-Lahav,
Eric D. Williams,
Eric J. Bowman,
Eric Lawrence,
Eric Rescorla,
Erik Aronesty,
EungJun Yi,
Evan Prodromou,
Felix Geisendoerfer,
Florian Weimer,
Frank Ellermann,
Fred Akalin,
Fred Bohle,
Frederic Kayser,
Gabor Molnar,
Gabriel Montenegro,
Geoffrey Sneddon,
Gervase Markham,
Gili Tzabari,
Grahame Grieve,
Greg Slepak,
Greg Wilkins,
Grzegorz Calkowski,
Harald Tveit Alvestrand,
Harry Halpin,
Helge Hess,
Henrik Nordstrom,
Henry S. Thompson,
Henry Story,
Herbert van de Sompel,
Herve Ruellan,
Howard Melman,
Hugo Haas,
Ian Fette,
Ian Hickson,
Ido Safruti,
Ilari Liusvaara,
Ilya Grigorik,
Ingo Struck,
J. Ross Nicoll,
James Cloos,
James H. Manger,
James Lacey,
James M. Snell,
Jamie Lokier,
Jan Algermissen,
Jari Arkko,
Jeff Hodges (who came up with the term 'effective Request-URI'),
Jeff Pinner,
Jeff Walden,
Jim Luther,
Jitu Padhye,
Joe D. Williams,
Joe Gregorio,
Joe Orton,
Joel Jaeggli,
John C. Klensin,
John C. Mallery,
John Cowan,
John Kemp,
John Panzer,
John Schneider,
John Stracke,
John Sullivan,
Jonas Sicking,
Jonathan A. Rees,
Jonathan Billington,
Jonathan Moore,
Jonathan Silvera,
Jordi Ros,
Joris Dobbelsteen,
Josh Cohen,
Julien Pierre,
Jungshik Shin,
Justin Chapweske,
Justin Erenkrantz,
Justin James,
Kalvinder Singh,
Karl Dubost,
Kathleen Moriarty,
Keith Hoffman,
Keith Moore,
Ken Murchison,
Koen Holtman,
Konstantin Voronkov,
Kris Zyp,
Leif Hedstrom,
Lionel Morand,
Lisa Dusseault,
Maciej Stachowiak,
Manu Sporny,
Marc Schneider,
Marc Slemko,
Mark Baker,
Mark Pauley,
Mark Watson,
Markus Isomaki,
Markus Lanthaler,
Martin J. Duerst,
Martin Musatov,
Martin Nilsson,
Martin Thomson,
Matt Lynch,
Matthew Cox,
Matthew Kerwin,
Max Clark,
Menachem Dodge,
Meral Shirazipour,
Michael Burrows,
Michael Hausenblas,
Michael Scharf,
Michael Sweet,
Michael Tuexen,
Michael Welzl,
Mike Amundsen,
Mike Belshe,
Mike Bishop,
Mike Kelly,
Mike Schinkel,
Miles Sabin,
Murray S. Kucherawy,
Mykyta Yevstifeyev,
Nathan Rixham,
Nicholas Shanks,
Nico Williams,
Nicolas Alvarez,
Nicolas Mailhot,
Noah Slater,
Osama Mazahir,
Pablo Castro,
Pat Hayes,
Patrick R. McManus,
Paul E. Jones,
Paul Hoffman,
Paul Marquess,
Pete Resnick,
Peter Lepeska,
Peter Occil,
Peter Saint-Andre,
Peter Watkins,
Phil Archer,
Phil Hunt,
Philippe Mougin,
Phillip Hallam-Baker,
Piotr Dobrogost,
Poul-Henning Kamp,
Preethi Natarajan,
Rajeev Bector,
Ray Polk,
Reto Bachmann-Gmuer,
Richard Barnes,
Richard Cyganiak,
Rob Trace,
Robby Simpson,
Robert Brewer,
Robert Collins,
Robert Mattson,
Robert O'Callahan,
Robert Olofsson,
Robert Sayre,
Robert Siemer,
Robert de Wilde,
Roberto Javier Godoy,
Roberto Peon,
Roland Zink,
Ronny Widjaja,
Ryan Hamilton,
S. Mike Dierken,
Salvatore Loreto,
Sam Johnston,
Sam Pullara,
Sam Ruby,
Saurabh Kulkarni,
Scott Lawrence (who maintained the original issues list),
Sean B. Palmer,
Sean Turner,
Sebastien Barnoud,
Shane McCarron,
Shigeki Ohtsu,
Simon Yarde,
Stefan Eissing,
Stefan Tilkov,
Stefanos Harhalakis,
Stephane Bortzmeyer,
Stephen Farrell,
Stephen Kent,
Stephen Ludin,
Stuart Williams,
Subbu Allamaraju,
Subramanian Moonesamy,
Susan Hares,
Sylvain Hellegouarch,
Tapan Divekar,
Tatsuhiro Tsujikawa,
Tatsuya Hayashi,
Ted Hardie,
Ted Lemon,
Thomas Broyer,
Thomas Fossati,
Thomas Maslen,
Thomas Nadeau,
Thomas Nordin,
Thomas Roessler,
Tim Bray,
Tim Morgan,
Tim Olsen,
Tom Zhou,
Travis Snoozy,
Tyler Close,
Vincent Murphy,
Wenbo Zhu,
Werner Baumann,
Wilbur Streett,
Wilfredo Sanchez Vega,
William A. Rowe Jr.,
William Chan,
Willy Tarreau,
Xiaoshu Wang,
Yaron Goland,
Yngve Nysaeter Pettersen,
Yoav Nir,
Yogesh Bang,
Yuchung Cheng,
Yutaka Oiwa,
Yves Lafon (long-time member of the editor team),
Zed A. Shaw, and
Zhong Yu.
</t>
<t>
See Section 16 of <xref target="RFC2616"/> for additional
acknowledgements from prior revisions.
</t>
</section>
</middle>
<back>
<references title="Normative References">
<reference anchor="Part2">
<front>
<title>Hypertext Transfer Protocol (HTTP/1.1): Semantics and Content</title>
<author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
<organization abbrev="Adobe">Adobe Systems Incorporated</organization>
<address><email>fielding@gbiv.com</email></address>
</author>
<author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
<organization abbrev="greenbytes">greenbytes GmbH</organization>
<address><email>julian.reschke@greenbytes.de</email></address>
</author>
<date month="February" year="2014"/>
</front>
<seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p2-semantics-26"/>
</reference>
<reference anchor="Part4">
<front>
<title>Hypertext Transfer Protocol (HTTP/1.1): Conditional Requests</title>
<author fullname="Roy T. Fielding" initials="R." role="editor" surname="Fielding">
<organization abbrev="Adobe">Adobe Systems Incorporated</organization>
<address><email>fielding@gbiv.com</email></address>
</author>
<author fullname="Julian F. Reschke" initials="J. F." role="editor" surname="Reschke">
<organization abbrev="greenbytes">greenbytes GmbH</organization>
<address><email>julian.reschke@greenbytes.de</email></address>
</author>
<date month="February" year="2014"/>
</front>
<seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p4-conditional-26"/>
</reference>
<reference anchor="Part5">
<front>
<title>Hypertext Transfer Protocol (HTTP/1.1): Range Requests</title>
<author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
<organization abbrev="Adobe">Adobe Systems Incorporated</organization>
<address><email>fielding@gbiv.com</email></address>
</author>
<author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
<organization abbrev="W3C">World Wide Web Consortium</organization>
<address><email>ylafon@w3.org</email></address>
</author>
<author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
<organization abbrev="greenbytes">greenbytes GmbH</organization>
<address><email>julian.reschke@greenbytes.de</email></address>
</author>
<date month="February" year="2014"/>
</front>
<seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p5-range-26"/>
</reference>
<reference anchor="Part6">
<front>
<title>Hypertext Transfer Protocol (HTTP/1.1): Caching</title>
<author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
<organization abbrev="Adobe">Adobe Systems Incorporated</organization>
<address><email>fielding@gbiv.com</email></address>
</author>
<author initials="M." surname="Nottingham" fullname="Mark Nottingham" role="editor">
<organization>Akamai</organization>
<address><email>mnot@mnot.net</email></address>
</author>
<author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
<organization abbrev="greenbytes">greenbytes GmbH</organization>
<address><email>julian.reschke@greenbytes.de</email></address>
</author>
<date month="February" year="2014"/>
</front>
<seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p6-cache-26"/>
</reference>
<reference anchor="Part7">
<front>
<title>Hypertext Transfer Protocol (HTTP/1.1): Authentication</title>
<author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
<organization abbrev="Adobe">Adobe Systems Incorporated</organization>
<address><email>fielding@gbiv.com</email></address>
</author>
<author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
<organization abbrev="greenbytes">greenbytes GmbH</organization>
<address><email>julian.reschke@greenbytes.de</email></address>
</author>
<date month="February" year="2014"/>
</front>
<seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p7-auth-26"/>
</reference>
<reference anchor="RFC5234">
<front>
<title abbrev="ABNF for Syntax Specifications">Augmented BNF for Syntax Specifications: ABNF</title>
<author initials="D." surname="Crocker" fullname="Dave Crocker" role="editor">
<organization>Brandenburg InternetWorking</organization>
<address>
<email>dcrocker@bbiw.net</email>
</address>
</author>
<author initials="P." surname="Overell" fullname="Paul Overell">
<organization>THUS plc.</organization>
<address>
<email>paul.overell@thus.net</email>
</address>
</author>
<date month="January" year="2008"/>
</front>
<seriesInfo name="STD" value="68"/>
<seriesInfo name="RFC" value="5234"/>
</reference>
<reference anchor="RFC2119">
<front>
<title>Key words for use in RFCs to Indicate Requirement Levels</title>
<author initials="S." surname="Bradner" fullname="Scott Bradner">
<organization>Harvard University</organization>
<address><email>sob@harvard.edu</email></address>
</author>
<date month="March" year="1997"/>
</front>
<seriesInfo name="BCP" value="14"/>
<seriesInfo name="RFC" value="2119"/>
</reference>
<reference anchor="RFC3986">
<front>
<title abbrev="URI Generic Syntax">Uniform Resource Identifier (URI): Generic Syntax</title>
<author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
<organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
<address>
<email>timbl@w3.org</email>
<uri>http://www.w3.org/People/Berners-Lee/</uri>
</address>
</author>
<author initials="R." surname="Fielding" fullname="Roy T. Fielding">
<organization abbrev="Day Software">Day Software</organization>
<address>
<email>fielding@gbiv.com</email>
<uri>http://roy.gbiv.com/</uri>
</address>
</author>
<author initials="L." surname="Masinter" fullname="Larry Masinter">
<organization abbrev="Adobe Systems">Adobe Systems Incorporated</organization>
<address>
<email>LMM@acm.org</email>
<uri>http://larry.masinter.net/</uri>
</address>
</author>
<date month="January" year="2005"/>
</front>
<seriesInfo name="STD" value="66"/>
<seriesInfo name="RFC" value="3986"/>
</reference>
<reference anchor="RFC0793">
<front>
<title>Transmission Control Protocol</title>
<author initials="J." surname="Postel" fullname="Jon Postel">
<organization>University of Southern California (USC)/Information Sciences Institute</organization>
</author>
<date year="1981" month="September"/>
</front>
<seriesInfo name="STD" value="7"/>
<seriesInfo name="RFC" value="793"/>
</reference>
<reference anchor="USASCII">
<front>
<title>Coded Character Set -- 7-bit American Standard Code for Information Interchange</title>
<author>
<organization>American National Standards Institute</organization>
</author>
<date year="1986"/>
</front>
<seriesInfo name="ANSI" value="X3.4"/>
</reference>
<reference anchor="RFC1950">
<front>
<title>ZLIB Compressed Data Format Specification version 3.3</title>
<author initials="L.P." surname="Deutsch" fullname="L. Peter Deutsch">
<organization>Aladdin Enterprises</organization>
<address><email>ghost@aladdin.com</email></address>
</author>
<author initials="J-L." surname="Gailly" fullname="Jean-Loup Gailly"/>
<date month="May" year="1996"/>
</front>
<seriesInfo name="RFC" value="1950"/>
<!--<annotation>
RFC 1950 is an Informational RFC, thus it might be less stable than
this specification. On the other hand, this downward reference was
present since the publication of <xref target="RFC2068" x:fmt="none">RFC 2068</xref> in 1997,
therefore it is unlikely to cause problems in practice. See also
<xref target="BCP97"/>.
</annotation>-->
</reference>
<reference anchor="RFC1951">
<front>
<title>DEFLATE Compressed Data Format Specification version 1.3</title>
<author initials="P." surname="Deutsch" fullname="L. Peter Deutsch">
<organization>Aladdin Enterprises</organization>
<address><email>ghost@aladdin.com</email></address>
</author>
<date month="May" year="1996"/>
</front>
<seriesInfo name="RFC" value="1951"/>
<!--<annotation>
RFC 1951 is an Informational RFC, thus it might be less stable than
this specification. On the other hand, this downward reference was
present since the publication of <xref target="RFC2068" x:fmt="none">RFC 2068</xref> in 1997,
therefore it is unlikely to cause problems in practice. See also
<xref target="BCP97"/>.
</annotation>-->
</reference>
<reference anchor="RFC1952">
<front>
<title>GZIP file format specification version 4.3</title>
<author initials="P." surname="Deutsch" fullname="L. Peter Deutsch">
<organization>Aladdin Enterprises</organization>
<address><email>ghost@aladdin.com</email></address>
</author>
<author initials="J-L." surname="Gailly" fullname="Jean-Loup Gailly">
<address><email>gzip@prep.ai.mit.edu</email></address>
</author>
<author initials="M." surname="Adler" fullname="Mark Adler">
<address><email>madler@alumni.caltech.edu</email></address>
</author>
<author initials="L.P." surname="Deutsch" fullname="L. Peter Deutsch">
<address><email>ghost@aladdin.com</email></address>
</author>
<author initials="G." surname="Randers-Pehrson" fullname="Glenn Randers-Pehrson">
<address><email>randeg@alumni.rpi.edu</email></address>
</author>
<date month="May" year="1996"/>
</front>
<seriesInfo name="RFC" value="1952"/>
<!--<annotation>
RFC 1952 is an Informational RFC, thus it might be less stable than
this specification. On the other hand, this downward reference was
present since the publication of <xref target="RFC2068" x:fmt="none">RFC 2068</xref> in 1997,
therefore it is unlikely to cause problems in practice. See also
<xref target="BCP97"/>.
</annotation>-->
</reference>
<reference anchor="Welch">
<front>
<title>A Technique for High Performance Data Compression</title>
<author initials="T.A." surname="Welch" fullname="Terry A. Welch"/>
<date month="June" year="1984"/>
</front>
<seriesInfo name="IEEE Computer" value="17(6)"/>
</reference>
</references>
<references title="Informative References">
<reference anchor="ISO-8859-1">
<front>
<title>
Information technology -- 8-bit single-byte coded graphic character sets -- Part 1: Latin alphabet No. 1
</title>
<author>
<organization>International Organization for Standardization</organization>
</author>
<date year="1998"/>
</front>
<seriesInfo name="ISO/IEC" value="8859-1:1998"/>
</reference>
<reference anchor="RFC1919">
<front>
<title>Classical versus Transparent IP Proxies</title>
<author initials="M." surname="Chatel" fullname="Marc Chatel">
<address><email>mchatel@pax.eunet.ch</email></address>
</author>
<date year="1996" month="March"/>
</front>
<seriesInfo name="RFC" value="1919"/>
</reference>
<reference anchor="RFC1945">
<front>
<title abbrev="HTTP/1.0">Hypertext Transfer Protocol -- HTTP/1.0</title>
<author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
<organization>MIT, Laboratory for Computer Science</organization>
<address><email>timbl@w3.org</email></address>
</author>
<author initials="R.T." surname="Fielding" fullname="Roy T. Fielding">
<organization>University of California, Irvine, Department of Information and Computer Science</organization>
<address><email>fielding@ics.uci.edu</email></address>
</author>
<author initials="H.F." surname="Nielsen" fullname="Henrik Frystyk Nielsen">
<organization>W3 Consortium, MIT Laboratory for Computer Science</organization>
<address><email>frystyk@w3.org</email></address>
</author>
<date month="May" year="1996"/>
</front>
<seriesInfo name="RFC" value="1945"/>
</reference>
<reference anchor="RFC2045">
<front>
<title abbrev="Internet Message Bodies">Multipurpose Internet Mail Extensions (MIME) Part One: Format of Internet Message Bodies</title>
<author initials="N." surname="Freed" fullname="Ned Freed">
<organization>Innosoft International, Inc.</organization>
<address><email>ned@innosoft.com</email></address>
</author>
<author initials="N.S." surname="Borenstein" fullname="Nathaniel S. Borenstein">
<organization>First Virtual Holdings</organization>
<address><email>nsb@nsb.fv.com</email></address>
</author>
<date month="November" year="1996"/>
</front>
<seriesInfo name="RFC" value="2045"/>
</reference>
<reference anchor="RFC2047">
<front>
<title abbrev="Message Header Extensions">MIME (Multipurpose Internet Mail Extensions) Part Three: Message Header Extensions for Non-ASCII Text</title>
<author initials="K." surname="Moore" fullname="Keith Moore">
<organization>University of Tennessee</organization>
<address><email>moore@cs.utk.edu</email></address>
</author>
<date month="November" year="1996"/>
</front>
<seriesInfo name="RFC" value="2047"/>
</reference>
<reference anchor="RFC2068">
<front>
<title>Hypertext Transfer Protocol -- HTTP/1.1</title>
<author initials="R." surname="Fielding" fullname="Roy T. Fielding">
<organization>University of California, Irvine, Department of Information and Computer Science</organization>
<address><email>fielding@ics.uci.edu</email></address>
</author>
<author initials="J." surname="Gettys" fullname="Jim Gettys">
<organization>MIT Laboratory for Computer Science</organization>
<address><email>jg@w3.org</email></address>
</author>
<author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
<organization>Digital Equipment Corporation, Western Research Laboratory</organization>
<address><email>mogul@wrl.dec.com</email></address>
</author>
<author initials="H." surname="Nielsen" fullname="Henrik Frystyk Nielsen">
<organization>MIT Laboratory for Computer Science</organization>
<address><email>frystyk@w3.org</email></address>
</author>
<author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
<organization>MIT Laboratory for Computer Science</organization>
<address><email>timbl@w3.org</email></address>
</author>
<date month="January" year="1997"/>
</front>
<seriesInfo name="RFC" value="2068"/>
</reference>
<reference anchor="RFC2145">
<front>
<title abbrev="HTTP Version Numbers">Use and Interpretation of HTTP Version Numbers</title>
<author initials="J.C." surname="Mogul" fullname="Jeffrey C. Mogul">
<organization>Western Research Laboratory</organization>
<address><email>mogul@wrl.dec.com</email></address>
</author>
<author initials="R.T." surname="Fielding" fullname="Roy T. Fielding">
<organization>Department of Information and Computer Science</organization>
<address><email>fielding@ics.uci.edu</email></address>
</author>
<author initials="J." surname="Gettys" fullname="Jim Gettys">
<organization>MIT Laboratory for Computer Science</organization>
<address><email>jg@w3.org</email></address>
</author>
<author initials="H.F." surname="Nielsen" fullname="Henrik Frystyk Nielsen">
<organization>W3 Consortium</organization>
<address><email>frystyk@w3.org</email></address>
</author>
<date month="May" year="1997"/>
</front>
<seriesInfo name="RFC" value="2145"/>
</reference>
<reference anchor="RFC2616">
<front>
<title>Hypertext Transfer Protocol -- HTTP/1.1</title>
<author initials="R." surname="Fielding" fullname="R. Fielding">
<organization>University of California, Irvine</organization>
<address><email>fielding@ics.uci.edu</email></address>
</author>
<author initials="J." surname="Gettys" fullname="J. Gettys">
<organization>W3C</organization>
<address><email>jg@w3.org</email></address>
</author>
<author initials="J." surname="Mogul" fullname="J. Mogul">
<organization>Compaq Computer Corporation</organization>
<address><email>mogul@wrl.dec.com</email></address>
</author>
<author initials="H." surname="Frystyk" fullname="H. Frystyk">
<organization>MIT Laboratory for Computer Science</organization>
<address><email>frystyk@w3.org</email></address>
</author>
<author initials="L." surname="Masinter" fullname="L. Masinter">
<organization>Xerox Corporation</organization>
<address><email>masinter@parc.xerox.com</email></address>
</author>
<author initials="P." surname="Leach" fullname="P. Leach">
<organization>Microsoft Corporation</organization>
<address><email>paulle@microsoft.com</email></address>
</author>
<author initials="T." surname="Berners-Lee" fullname="T. Berners-Lee">
<organization>W3C</organization>
<address><email>timbl@w3.org</email></address>
</author>
<date month="June" year="1999"/>
</front>
<seriesInfo name="RFC" value="2616"/>
</reference>
<reference anchor="RFC2817">
<front>
<title>Upgrading to TLS Within HTTP/1.1</title>
<author initials="R." surname="Khare" fullname="R. Khare">
<organization>4K Associates / UC Irvine</organization>
<address><email>rohit@4K-associates.com</email></address>
</author>
<author initials="S." surname="Lawrence" fullname="S. Lawrence">
<organization>Agranat Systems, Inc.</organization>
<address><email>lawrence@agranat.com</email></address>
</author>
<date year="2000" month="May"/>
</front>
<seriesInfo name="RFC" value="2817"/>
</reference>
<reference anchor="RFC2818">
<front>
<title>HTTP Over TLS</title>
<author initials="E." surname="Rescorla" fullname="Eric Rescorla">
<organization>RTFM, Inc.</organization>
<address><email>ekr@rtfm.com</email></address>
</author>
<date year="2000" month="May"/>
</front>
<seriesInfo name="RFC" value="2818"/>
</reference>
<reference anchor="RFC3040">
<front>
<title>Internet Web Replication and Caching Taxonomy</title>
<author initials="I." surname="Cooper" fullname="I. Cooper">
<organization>Equinix, Inc.</organization>
</author>
<author initials="I." surname="Melve" fullname="I. Melve">
<organization>UNINETT</organization>
</author>
<author initials="G." surname="Tomlinson" fullname="G. Tomlinson">
<organization>CacheFlow Inc.</organization>
</author>
<date year="2001" month="January"/>
</front>
<seriesInfo name="RFC" value="3040"/>
</reference>
<reference anchor="BCP90">
<front>
<title>Registration Procedures for Message Header Fields</title>
<author initials="G." surname="Klyne" fullname="G. Klyne">
<organization>Nine by Nine</organization>
<address><email>GK-IETF@ninebynine.org</email></address>
</author>
<author initials="M." surname="Nottingham" fullname="M. Nottingham">
<organization>BEA Systems</organization>
<address><email>mnot@pobox.com</email></address>
</author>
<author initials="J." surname="Mogul" fullname="J. Mogul">
<organization>HP Labs</organization>
<address><email>JeffMogul@acm.org</email></address>
</author>
<date year="2004" month="September"/>
</front>
<seriesInfo name="BCP" value="90"/>
<seriesInfo name="RFC" value="3864"/>
</reference>
<reference anchor="RFC4033">
<front>
<title>DNS Security Introduction and Requirements</title>
<author initials="R." surname="Arends" fullname="R. Arends"/>
<author initials="R." surname="Austein" fullname="R. Austein"/>
<author initials="M." surname="Larson" fullname="M. Larson"/>
<author initials="D." surname="Massey" fullname="D. Massey"/>
<author initials="S." surname="Rose" fullname="S. Rose"/>
<date year="2005" month="March"/>
</front>
<seriesInfo name="RFC" value="4033"/>
</reference>
<reference anchor="BCP13">
<front>
<title>Media Type Specifications and Registration Procedures</title>
<author initials="N." surname="Freed" fullname="Ned Freed">
<organization>Oracle</organization>
<address>
<email>ned+ietf@mrochek.com</email>
</address>
</author>
<author initials="J." surname="Klensin" fullname="John C. Klensin">
<address>
<email>john+ietf@jck.com</email>
</address>
</author>
<author initials="T." surname="Hansen" fullname="Tony Hansen">
<organization>AT&T Laboratories</organization>
<address>
<email>tony+mtsuffix@maillennium.att.com</email>
</address>
</author>
<date year="2013" month="January"/>
</front>
<seriesInfo name="BCP" value="13"/>
<seriesInfo name="RFC" value="6838"/>
</reference>
<reference anchor="BCP115">
<front>
<title>Guidelines and Registration Procedures for New URI Schemes</title>
<author initials="T." surname="Hansen" fullname="T. Hansen">
<organization>AT&T Laboratories</organization>
<address>
<email>tony+urireg@maillennium.att.com</email>
</address>
</author>
<author initials="T." surname="Hardie" fullname="T. Hardie">
<organization>Qualcomm, Inc.</organization>
<address>
<email>hardie@qualcomm.com</email>
</address>
</author>
<author initials="L." surname="Masinter" fullname="L. Masinter">
<organization>Adobe Systems</organization>
<address>
<email>LMM@acm.org</email>
</address>
</author>
<date year="2006" month="February"/>
</front>
<seriesInfo name="BCP" value="115"/>
<seriesInfo name="RFC" value="4395"/>
</reference>
<reference anchor="RFC4559">
<front>
<title>SPNEGO-based Kerberos and NTLM HTTP Authentication in Microsoft Windows</title>
<author initials="K." surname="Jaganathan" fullname="K. Jaganathan"/>
<author initials="L." surname="Zhu" fullname="L. Zhu"/>
<author initials="J." surname="Brezak" fullname="J. Brezak"/>
<date year="2006" month="June"/>
</front>
<seriesInfo name="RFC" value="4559"/>
</reference>
<reference anchor="RFC5226">
<front>
<title>Guidelines for Writing an IANA Considerations Section in RFCs</title>
<author initials="T." surname="Narten" fullname="T. Narten">
<organization>IBM</organization>
<address><email>narten@us.ibm.com</email></address>
</author>
<author initials="H." surname="Alvestrand" fullname="H. Alvestrand">
<organization>Google</organization>
<address><email>Harald@Alvestrand.no</email></address>
</author>
<date year="2008" month="May"/>
</front>
<seriesInfo name="BCP" value="26"/>
<seriesInfo name="RFC" value="5226"/>
</reference>
<reference anchor="RFC5246">
<front>
<title>The Transport Layer Security (TLS) Protocol Version 1.2</title>
<author initials="T." surname="Dierks" fullname="T. Dierks"/>
<author initials="E." surname="Rescorla" fullname="E. Rescorla">
<organization>RTFM, Inc.</organization>
</author>
<date year="2008" month="August"/>
</front>
<seriesInfo name="RFC" value="5246"/>
</reference>
<reference anchor="RFC5322">
<front>
<title>Internet Message Format</title>
<author initials="P." surname="Resnick" fullname="P. Resnick">
<organization>Qualcomm Incorporated</organization>
</author>
<date year="2008" month="October"/>
</front>
<seriesInfo name="RFC" value="5322"/>
</reference>
<reference anchor="RFC6265">
<front>
<title>HTTP State Management Mechanism</title>
<author initials="A." surname="Barth" fullname="Adam Barth">
<organization abbrev="U.C. Berkeley">
University of California, Berkeley
</organization>
<address><email>abarth@eecs.berkeley.edu</email></address>
</author>
<date year="2011" month="April"/>
</front>
<seriesInfo name="RFC" value="6265"/>
</reference>
<reference anchor="RFC6585">
<front>
<title>Additional HTTP Status Codes</title>
<author initials="M." surname="Nottingham" fullname="M. Nottingham">
<organization>Rackspace</organization>
</author>
<author initials="R." surname="Fielding" fullname="R. Fielding">
<organization>Adobe</organization>
</author>
<date year="2012" month="April"/>
</front>
<seriesInfo name="RFC" value="6585"/>
</reference>
<!--<reference anchor='BCP97'>
<front>
<title>Handling Normative References to Standards-Track Documents</title>
<author initials='J.' surname='Klensin' fullname='J. Klensin'>
<address>
<email>klensin+ietf@jck.com</email>
</address>
</author>
<author initials='S.' surname='Hartman' fullname='S. Hartman'>
<organization>MIT</organization>
<address>
<email>hartmans-ietf@mit.edu</email>
</address>
</author>
<date year='2007' month='June' />
</front>
<seriesInfo name='BCP' value='97' />
<seriesInfo name='RFC' value='4897' />
</reference>-->
<reference anchor="Kri2001" target="http://arxiv.org/abs/cs.SE/0105018">
<front>
<title>HTTP Cookies: Standards, Privacy, and Politics</title>
<author initials="D." surname="Kristol" fullname="David M. Kristol"/>
<date year="2001" month="November"/>
</front>
<seriesInfo name="ACM Transactions on Internet Technology" value="1(2)"/>
</reference>
<reference anchor="Klein" target="http://packetstormsecurity.com/papers/general/whitepaper_httpresponse.pdf">
<front>
<title>Divide and Conquer - HTTP Response Splitting, Web Cache Poisoning Attacks, and Related Topics</title>
<author initials="A." surname="Klein" fullname="Amit Klein">
<organization>Sanctum, Inc.</organization>
</author>
<date year="2004" month="March"/>
</front>
</reference>
<reference anchor="Georgiev" target="http://doi.acm.org/10.1145/2382196.2382204">
<front>
<title>The Most Dangerous Code in the World: Validating SSL Certificates in Non-browser Software</title>
<author initials="M." surname="Georgiev" fullname="Martin Georgiev"/>
<author initials="S." surname="Iyengar" fullname="Subodh Iyengar"/>
<author initials="S." surname="Jana" fullname="Suman Jana"/>
<author initials="R." surname="Anubhai" fullname="Rishita Anubhai"/>
<author initials="D." surname="Boneh" fullname="Dan Boneh"/>
<author initials="V." surname="Shmatikov" fullname="Vitaly Shmatikov"/>
<date year="2012" month="October"/>
</front>
<!--Converted from rfc2629.xslt x:prose extension--><seriesInfo name="In" value="Proceedings of the 2012 ACM Conference on Computer and Communications Security (CCS '12), pp. 38-49"/>
</reference>
<reference anchor="Linhart" target="http://www.watchfire.com/news/whitepapers.aspx">
<front>
<title>HTTP Request Smuggling</title>
<author initials="C." surname="Linhart" fullname="Chaim Linhart"/>
<author initials="A." surname="Klein" fullname="Amit Klein"/>
<author initials="R." surname="Heled" fullname="Ronen Heled"/>
<author initials="S." surname="Orrin" fullname="Steve Orrin"/>
<date year="2005" month="June"/>
</front>
</reference>
</references>
<section title="HTTP Version History" anchor="compatibility">
<t>
HTTP has been in use since 1990. The first version, later referred to as
HTTP/0.9, was a simple protocol for hypertext data transfer across the
Internet, using only a single request method (GET) and no metadata.
HTTP/1.0, as defined by <xref target="RFC1945"/>, added a range of request
methods and MIME-like messaging, allowing for metadata to be transferred
and modifiers placed on the request/response semantics. However,
HTTP/1.0 did not sufficiently take into consideration the effects of
hierarchical proxies, caching, the need for persistent connections, or
name-based virtual hosts. The proliferation of incompletely-implemented
applications calling themselves "HTTP/1.0" further necessitated a
protocol version change in order for two communicating applications
to determine each other's true capabilities.
</t>
<t>
HTTP/1.1 remains compatible with HTTP/1.0 by including more stringent
requirements that enable reliable implementations, adding only
those features that can either be safely ignored by an HTTP/1.0
recipient or only sent when communicating with a party advertising
conformance with HTTP/1.1.
</t>
<t>
HTTP/1.1 has been designed to make supporting previous versions easy.
A general-purpose HTTP/1.1 server ought to be able to understand any valid
request in the format of HTTP/1.0, responding appropriately with an
HTTP/1.1 message that only uses features understood (or safely ignored) by
HTTP/1.0 clients. Likewise, an HTTP/1.1 client can be expected to
understand any valid HTTP/1.0 response.
</t>
<t>
Since HTTP/0.9 did not support header fields in a request, there is no
mechanism for it to support name-based virtual hosts (selection of resource
by inspection of the <xref target="header.host" format="none">Host</xref> header field).
Any server that implements name-based virtual hosts ought to disable
support for HTTP/0.9. Most requests that appear to be HTTP/0.9 are, in
fact, badly constructed HTTP/1.x requests caused by a client failing to
properly encode the request-target.
</t>
<section title="Changes from HTTP/1.0" anchor="changes.from.1.0">
<t>
This section summarizes major differences between versions HTTP/1.0
and HTTP/1.1.
</t>
<section title="Multi-homed Web Servers" anchor="changes.to.simplify.multi-homed.web.servers.and.conserve.ip.addresses">
<t>
The requirements that clients and servers support the <xref target="header.host" format="none">Host</xref>
header field (<xref target="header.host"/>), report an error if it is
missing from an HTTP/1.1 request, and accept absolute URIs (<xref target="request-target"/>)
are among the most important changes defined by HTTP/1.1.
</t>
<t>
Older HTTP/1.0 clients assumed a one-to-one relationship of IP
addresses and servers; there was no other established mechanism for
distinguishing the intended server of a request than the IP address
to which that request was directed. The <xref target="header.host" format="none">Host</xref> header field was
introduced during the development of HTTP/1.1 and, though it was
quickly implemented by most HTTP/1.0 browsers, additional requirements
were placed on all HTTP/1.1 requests in order to ensure complete
adoption. At the time of this writing, most HTTP-based services
are dependent upon the Host header field for targeting requests.
</t>
</section>
<section title="Keep-Alive Connections" anchor="compatibility.with.http.1.0.persistent.connections">
<t>
In HTTP/1.0, each connection is established by the client prior to the
request and closed by the server after sending the response. However, some
implementations implement the explicitly negotiated ("Keep-Alive") version
of persistent connections described in Section 19.7.1 of <xref target="RFC2068"/>.
</t>
<t>
Some clients and servers might wish to be compatible with these previous
approaches to persistent connections, by explicitly negotiating for them
with a "Connection: keep-alive" request header field. However, some
experimental implementations of HTTP/1.0 persistent connections are faulty;
for example, if an HTTP/1.0 proxy server doesn't understand
<xref target="header.connection" format="none">Connection</xref>, it will erroneously forward that header field
to the next inbound server, which would result in a hung connection.
</t>
<t>
One attempted solution was the introduction of a Proxy-Connection header
field, targeted specifically at proxies. In practice, this was also
unworkable, because proxies are often deployed in multiple layers, bringing
about the same problem discussed above.
</t>
<t>
As a result, clients are encouraged not to send the Proxy-Connection header
field in any requests.
</t>
<t>
Clients are also encouraged to consider the use of Connection: keep-alive
in requests carefully; while they can enable persistent connections with
HTTP/1.0 servers, clients using them will need to monitor the
connection for "hung" requests (which indicate that the client ought stop
sending the header field), and this mechanism ought not be used by clients
at all when a proxy is being used.
</t>
</section>
<section title="Introduction of Transfer-Encoding" anchor="introduction.of.transfer-encoding">
<t>
HTTP/1.1 introduces the <xref target="header.transfer-encoding" format="none">Transfer-Encoding</xref> header field
(<xref target="header.transfer-encoding"/>).
Transfer codings need to be decoded prior to forwarding an HTTP message
over a MIME-compliant protocol.
</t>
</section>
</section>
<section title="Changes from RFC 2616" anchor="changes.from.rfc.2616">
<t>
HTTP's approach to error handling has been explained.
(<xref target="conformance"/>)
</t>
<t>
The HTTP-version ABNF production has been clarified to be case-sensitive.
Additionally, version numbers has been restricted to single digits, due
to the fact that implementations are known to handle multi-digit version
numbers incorrectly.
(<xref target="http.version"/>)
</t>
<t>
Userinfo (i.e., username and password) are now disallowed in HTTP and
HTTPS URIs, because of security issues related to their transmission on the
wire.
(<xref target="http.uri"/>)
</t>
<t>
The HTTPS URI scheme is now defined by this specification; previously,
it was done in Section 2.4 of <xref target="RFC2818"/>.
Furthermore, it implies end-to-end security.
(<xref target="https.uri"/>)
</t>
<t>
HTTP messages can be (and often are) buffered by implementations; despite
it sometimes being available as a stream, HTTP is fundamentally a
message-oriented protocol.
Minimum supported sizes for various protocol elements have been
suggested, to improve interoperability.
(<xref target="http.message"/>)
</t>
<t>
Invalid whitespace around field-names is now required to be rejected,
because accepting it represents a security vulnerability.
The ABNF productions defining header fields now only list the field value.
(<xref target="header.fields"/>)
</t>
<t>
Rules about implicit linear whitespace between certain grammar productions
have been removed; now whitespace is only allowed where specifically
defined in the ABNF.
(<xref target="whitespace"/>)
</t>
<t>
Header fields that span multiple lines ("line folding") are deprecated.
(<xref target="field.parsing"/>)
</t>
<t>
The NUL octet is no longer allowed in comment and quoted-string text, and
handling of backslash-escaping in them has been clarified.
The quoted-pair rule no longer allows escaping control characters other than
HTAB.
Non-ASCII content in header fields and the reason phrase has been obsoleted
and made opaque (the TEXT rule was removed).
(<xref target="field.components"/>)
</t>
<t>
Bogus "<xref target="header.content-length" format="none">Content-Length</xref>" header fields are now required to be
handled as errors by recipients.
(<xref target="header.content-length"/>)
</t>
<t>
The algorithm for determining the message body length has been clarified
to indicate all of the special cases (e.g., driven by methods or status
codes) that affect it, and that new protocol elements cannot define such
special cases.
CONNECT is a new, special case in determining message body length.
"multipart/byteranges" is no longer a way of determining message body length
detection.
(<xref target="message.body.length"/>)
</t>
<t>
The "identity" transfer coding token has been removed.
(Sections <xref format="counter" target="message.body"/> and
<xref format="counter" target="transfer.codings"/>)
</t>
<t>
Chunk length does not include the count of the octets in the
chunk header and trailer.
Line folding in chunk extensions is disallowed.
(<xref target="chunked.encoding"/>)
</t>
<t>
The meaning of the "deflate" content coding has been clarified.
(<xref target="deflate.coding"/>)
</t>
<t>
The segment + query components of RFC 3986 have been used to define the
request-target, instead of abs_path from RFC 1808.
The asterisk-form of the request-target is only allowed with the OPTIONS
method.
(<xref target="request-target"/>)
</t>
<t>
The term "Effective Request URI" has been introduced.
(<xref target="effective.request.uri"/>)
</t>
<t>
Gateways do not need to generate <xref target="header.via" format="none">Via</xref> header fields anymore.
(<xref target="header.via"/>)
</t>
<t>
Exactly when "close" connection options have to be sent has been clarified.
Also, "hop-by-hop" header fields are required to appear in the Connection header
field; just because they're defined as hop-by-hop in this specification
doesn't exempt them.
(<xref target="header.connection"/>)
</t>
<t>
The limit of two connections per server has been removed.
An idempotent sequence of requests is no longer required to be retried.
The requirement to retry requests under certain circumstances when the
server prematurely closes the connection has been removed.
Also, some extraneous requirements about when servers are allowed to close
connections prematurely have been removed.
(<xref target="persistent.connections"/>)
</t>
<t>
The semantics of the <xref target="header.upgrade" format="none">Upgrade</xref> header field is now defined in
responses other than 101 (this was incorporated from <xref target="RFC2817"/>). Furthermore, the ordering in the field value is now
significant.
(<xref target="header.upgrade"/>)
</t>
<t>
Empty list elements in list productions (e.g., a list header field containing
", ,") have been deprecated.
(<xref target="abnf.extension"/>)
</t>
<t>
Registration of Transfer Codings now requires IETF Review
(<xref target="transfer.coding.registry"/>)
</t>
<t>
This specification now defines the Upgrade Token Registry, previously
defined in Section 7.2 of <xref target="RFC2817"/>.
(<xref target="upgrade.token.registry"/>)
</t>
<t>
The expectation to support HTTP/0.9 requests has been removed.
(<xref target="compatibility"/>)
</t>
<t>
Issues with the Keep-Alive and Proxy-Connection header fields in requests
are pointed out, with use of the latter being discouraged altogether.
(<xref target="compatibility.with.http.1.0.persistent.connections"/>)
</t>
</section>
</section>
<section title="Collected ABNF" anchor="collected.abnf">
<figure>
<artwork type="abnf" name="p1-messaging.parsed-abnf"><![CDATA[
BWS = OWS
Connection = *( "," OWS ) connection-option *( OWS "," [ OWS
connection-option ] )
Content-Length = 1*DIGIT
HTTP-message = start-line *( header-field CRLF ) CRLF [ message-body
]
HTTP-name = %x48.54.54.50 ; HTTP
HTTP-version = HTTP-name "/" DIGIT "." DIGIT
Host = uri-host [ ":" port ]
OWS = *( SP / HTAB )
RWS = 1*( SP / HTAB )
TE = [ ( "," / t-codings ) *( OWS "," [ OWS t-codings ] ) ]
Trailer = *( "," OWS ) field-name *( OWS "," [ OWS field-name ] )
Transfer-Encoding = *( "," OWS ) transfer-coding *( OWS "," [ OWS
transfer-coding ] )
URI-reference = <URI-reference, defined in [RFC3986], Section 4.1>
Upgrade = *( "," OWS ) protocol *( OWS "," [ OWS protocol ] )
Via = *( "," OWS ) ( received-protocol RWS received-by [ RWS comment
] ) *( OWS "," [ OWS ( received-protocol RWS received-by [ RWS
comment ] ) ] )
absolute-URI = <absolute-URI, defined in [RFC3986], Section 4.3>
absolute-form = absolute-URI
absolute-path = 1*( "/" segment )
asterisk-form = "*"
authority = <authority, defined in [RFC3986], Section 3.2>
authority-form = authority
chunk = chunk-size [ chunk-ext ] CRLF chunk-data CRLF
chunk-data = 1*OCTET
chunk-ext = *( ";" chunk-ext-name [ "=" chunk-ext-val ] )
chunk-ext-name = token
chunk-ext-val = token / quoted-string
chunk-size = 1*HEXDIG
chunked-body = *chunk last-chunk trailer-part CRLF
comment = "(" *( ctext / quoted-pair / comment ) ")"
connection-option = token
ctext = HTAB / SP / %x21-27 ; '!'-'''
/ %x2A-5B ; '*'-'['
/ %x5D-7E ; ']'-'~'
/ obs-text
field-content = field-vchar [ 1*( SP / HTAB ) field-vchar ]
field-name = token
field-value = *( field-content / obs-fold )
field-vchar = VCHAR / obs-text
fragment = <fragment, defined in [RFC3986], Section 3.5>
header-field = field-name ":" OWS field-value OWS
http-URI = "http://" authority path-abempty [ "?" query ] [ "#"
fragment ]
https-URI = "https://" authority path-abempty [ "?" query ] [ "#"
fragment ]
last-chunk = 1*"0" [ chunk-ext ] CRLF
message-body = *OCTET
method = token
obs-fold = CRLF 1*( SP / HTAB )
obs-text = %x80-FF
origin-form = absolute-path [ "?" query ]
partial-URI = relative-part [ "?" query ]
path-abempty = <path-abempty, defined in [RFC3986], Section 3.3>
port = <port, defined in [RFC3986], Section 3.2.3>
protocol = protocol-name [ "/" protocol-version ]
protocol-name = token
protocol-version = token
pseudonym = token
qdtext = HTAB / SP / "!" / %x23-5B ; '#'-'['
/ %x5D-7E ; ']'-'~'
/ obs-text
query = <query, defined in [RFC3986], Section 3.4>
quoted-pair = "\" ( HTAB / SP / VCHAR / obs-text )
quoted-string = DQUOTE *( qdtext / quoted-pair ) DQUOTE
rank = ( "0" [ "." *3DIGIT ] ) / ( "1" [ "." *3"0" ] )
reason-phrase = *( HTAB / SP / VCHAR / obs-text )
received-by = ( uri-host [ ":" port ] ) / pseudonym
received-protocol = [ protocol-name "/" ] protocol-version
relative-part = <relative-part, defined in [RFC3986], Section 4.2>
request-line = method SP request-target SP HTTP-version CRLF
request-target = origin-form / absolute-form / authority-form /
asterisk-form
scheme = <scheme, defined in [RFC3986], Section 3.1>
segment = <segment, defined in [RFC3986], Section 3.3>
start-line = request-line / status-line
status-code = 3DIGIT
status-line = HTTP-version SP status-code SP reason-phrase CRLF
t-codings = "trailers" / ( transfer-coding [ t-ranking ] )
t-ranking = OWS ";" OWS "q=" rank
tchar = "!" / "#" / "$" / "%" / "&" / "'" / "*" / "+" / "-" / "." /
"^" / "_" / "`" / "|" / "~" / DIGIT / ALPHA
token = 1*tchar
trailer-part = *( header-field CRLF )
transfer-coding = "chunked" / "compress" / "deflate" / "gzip" /
transfer-extension
transfer-extension = token *( OWS ";" OWS transfer-parameter )
transfer-parameter = token BWS "=" BWS ( token / quoted-string )
uri-host = <host, defined in [RFC3986], Section 3.2.2>
]]></artwork>
</figure>
</section>
<section title="Change Log (to be removed by RFC Editor before publication)" anchor="change.log">
<section title="Since RFC 2616">
<t>
Changes up to the IETF Last Call draft are summarized
in <eref target="http://trac.tools.ietf.org/html/draft-ietf-httpbis-p1-messaging-24#appendix-C"/>.
</t>
</section>
<section title="Since draft-ietf-httpbis-p1-messaging-24" anchor="changes.since.24">
<t>
Closed issues:
<list style="symbols">
<t>
<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/502"/>:
"APPSDIR review of draft-ietf-httpbis-p1-messaging-24"
</t>
<t>
<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/507"/>:
"integer value parsing"
</t>
<t>
<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/517"/>:
"move IANA registrations to correct draft"
</t>
</list>
</t>
</section>
<section title="Since draft-ietf-httpbis-p1-messaging-25" anchor="changes.since.25">
<t>
Closed issues:
<list style="symbols">
<t>
<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/526"/>:
"check media type registration templates"
</t>
<t>
<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/528"/>:
"Redundant rule quoted-str-nf"
</t>
<t>
<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/531"/>:
"IESG ballot on draft-ietf-httpbis-p1-messaging-25"
</t>
<t>
<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/538"/>:
"add 'stateless' to Abstract"
</t>
<t>
<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/540"/>:
"clarify ABNF layering"
</t>
<t>
<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/541"/>:
"use of 'word' ABNF production"
</t>
<t>
<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/542"/>:
"improve introduction of list rule"
</t>
<t>
<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/544"/>:
"moving 2616/2068/2145 to historic"
</t>
<t>
<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/549"/>:
"augment security considerations with pointers to current research"
</t>
<t>
<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/551"/>:
"intermediaries handling trailers"
</t>
<t>
<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/552"/>:
"allow privacy proxies to be conformant"
</t>
</list>
</t>
</section>
</section>
</back>
</rfc>| PAFTECH AB 2003-2026 | 2026-04-23 14:02:10 |