source: draft-ietf-httpbis/21/draft-ietf-httpbis-p1-messaging-21.xml @ 2132

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<rfc obsoletes="2145,2616" updates="2817" category="std" ipr="pre5378Trust200902" docName="draft-ietf-httpbis-p1-messaging-21">


<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="October" year="2012" day="4"/>
  <workgroup>HTTPbis Working Group</workgroup>

<abstract>
<t>
   The Hypertext Transfer Protocol (HTTP) is an application-level protocol for
   distributed, collaborative, hypertext information systems. HTTP has been in
   use by the World Wide Web global information initiative since 1990.
   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 general 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.20"/>.
  </t>
</note>
</front>
<middle>
<section title="Introduction" anchor="introduction">
<t>
   The Hypertext Transfer Protocol (HTTP) is an application-level
   request/response protocol that uses extensible semantics and MIME-like
   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 and moves to historic status
   RFC 2616, its predecessor
   RFC 2068,
   RFC 2145 (on HTTP versioning),
   and RFC 2817 (on using CONNECT
   for TLS upgrades).
</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 HTTP 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 the list rule extension defined in
   <xref target="abnf.extension"/>.  <xref target="collected.abnf"/> shows
   the collected ABNF with the list rule expanded.
</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 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.  We use
   the term "user agent" to refer to the program that initiates a request,
   such as a WWW browser, editor, or spider (web-traversing robot), and
   the term "origin server" to refer to the program that can originate
   authoritative responses to a request.  For general requirements, we use
   the term "sender" to refer to whichever component sent a given message
   and the term "recipient" to refer to any component that receives the
   message.
</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 on the URI "http://www.example.com/hello.txt":
</t>
<figure><preamble>
client request:
</preamble><artwork type="message/http; msgtype=&#34;request&#34;"><![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=&#34;response&#34;"><![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: 14
  Vary: Accept-Encoding
  Content-Type: text/plain
  
  Hello World!
  ]]></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 we cannot assume the
   user agent can make interactive suggestions to a user or provide adequate
   warning for security or privacy options.  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 can me met via advance configuration choices,
   run-time options, or simply not proceeding with the unsafe action.
</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.
</t>
<t>
<iref primary="true" item="upstream"/><iref primary="true" item="downstream"/>
<iref primary="true" item="inbound"/><iref primary="true" item="outbound"/>
   We use the terms "upstream" and "downstream"
   to describe various requirements in relation to the directional flow of a
   message: all messages flow from upstream to downstream.
   Likewise, we use the terms inbound and outbound to refer to
   directions in relation to the request path:
   "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.
</t>
<t>
<iref primary="true" item="transforming proxy"/>
<iref primary="true" item="non-transforming proxy"/>
   An HTTP-to-HTTP proxy is called a "transforming proxy" if it is designed
   or configured to modify request or response 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 an intranet-to-Internet privacy filter.  Such
   transformations are presumed to be desired by the client (or client
   organization) that selected the proxy and are beyond the scope of
   this specification.  However, when a proxy is not intended to transform
   a given message, we use the term "non-transforming proxy" to target
   requirements that preserve HTTP message semantics. See Section 7.3.4 of <xref target="Part2"/> and
   Section 7.5 of <xref target="Part6"/> for status and warning codes related to 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 a receiving agent that acts
   as a layer above some other server(s) and translates the received
   requests to the underlying server's protocol.  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>
   A gateway behaves as an origin server on its outbound connection and
   as a user agent on its inbound connection.
   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 MUST
   conform to HTTP user agent requirements on the gateway's inbound
   connection and MUST implement the <xref target="header.connection" format="none">Connection</xref>
   (<xref target="header.connection"/>) and <xref target="header.via" format="none">Via</xref>
   (<xref target="header.via"/>) header fields for both connections.
</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><iref primary="true" item="interception proxy"/>
<iref primary="true" item="transparent proxy"/>
<iref primary="true" item="captive portal"/>
   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 often introduce security flaws or
   interoperability problems by violating HTTP semantics.  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.
   They are indistinguishable from a man-in-the-middle attack.
</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, servers 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 which 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 and proxies deployed across the World Wide Web and
   inside large organizations. These systems include national hierarchies
   of proxy caches to save transoceanic bandwidth, systems that
   broadcast or multicast cache entries, organizations that distribute
   subsets of cached data via optical media, 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. Note that
   SHOULD-level requirements are relevant here, unless one of the documented
   exceptions is applicable.
</t>
<t>
   Conformance applies to both the syntax and semantics of HTTP 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
   ABNF rules for those protocol elements that are applicable to the sender's
   role. If a received protocol element is processed, the recipient MUST be
   able to parse any value that would match the ABNF rules for that protocol
   element, excluding only those rules not applicable to the recipient's role.
</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 "&lt;major&gt;.&lt;minor&gt;" 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 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 defined such that, when they are
   understood by a recipient, they might override or enhance the
   interpretation of previously defined header fields.  When an
   implementation receives an unrecognized header field, the recipient
   MUST ignore that header field for local processing regardless of
   the message's HTTP version.  An unrecognized header field received
   by a proxy MUST be forwarded downstream unless the header field's
   field-name is listed in the message's <xref target="header.connection" format="none">Connection</xref> header field
   (see <xref target="header.connection"/>).
   These requirements allow HTTP's functionality to be enhanced without
   requiring prior update of deployed intermediaries.
</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 MUST NOT 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>
   An HTTP 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.  An HTTP client MUST NOT send a
   version to which it is not conformant.
</t>
<t>
   An HTTP 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 or header fields (e.g., Server) that
   the server improperly handles higher request versions.
</t>
<t>
   An HTTP server SHOULD send a response version equal to the highest
   version to which the server is conformant and
   whose major version is less than or equal to the one received in the
   request.  An HTTP server MUST NOT send a version to which it is not
   conformant.  A server MAY send a 505 (HTTP Version Not
   Supported) response if it cannot send a response using the
   major version used in the client's request.
</t>
<t>
   An HTTP server MAY send an HTTP/1.0 response to an HTTP/1.0 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
   is specifically avoiding any such changes to the protocol.
</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>
   This specification adopts the definitions of "URI-reference",
   "absolute-URI", "relative-part", "port", "host",
   "path-abempty", "path-absolute", "query", and "authority" from the
   URI generic syntax.
   In addition, we define a partial-URI rule for protocol elements
   that allow a relative URI but not a fragment.
</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="authority"/><iref primary="true" item="Grammar" subitem="path-absolute"/><iref primary="true" item="Grammar" subitem="port"/><iref primary="true" item="Grammar" subitem="query"/><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>
  authority     = <authority, defined in [RFC3986], Section 3.2>
  path-abempty  = <path-abempty, defined in [RFC3986], Section 3.3>
  path-absolute = <path-absolute, defined in [RFC3986], Section 3.3>
  port          = <port, defined in [RFC3986], Section 3.2.3>
  query         = <query, defined in [RFC3986], Section 3.4>
  uri-host      = <host, defined in [RFC3986], Section 3.2.2>
  
  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 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 ]
]]></artwork></figure>
<t>
   The HTTP origin server is identified by the generic syntax's 
   <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 remainder of the URI, consisting of both the hierarchical path
   component and optional query component, serves as an identifier for
   a potential resource within that origin server's name space.
</t>
<t>
   If the host identifier is provided as an IP literal or IPv4 address,
   then the origin server is any listener on the indicated TCP port at
   that IP address. If host is a registered name, then that name is
   considered an indirect identifier and the recipient might use a name
   resolution service, such as DNS, to find the address of a listener
   for that host.
   The host MUST NOT be empty; if an "http" URI is received with an
   empty host, then it MUST be rejected as invalid. 
   If the port subcomponent is empty or not given, then TCP port 80 is
   assumed (the default reserved port for WWW services).
</t>
<t>
   Regardless of the form of host identifier, access to that host is not
   implied by the mere presence of its name or address. The host might or might
   not exist and, even when it does exist, might or might not be running an
   HTTP server or listening to the indicated port. The "http" URI scheme
   makes use of the delegated nature of Internet names and addresses to
   establish a naming authority (whatever entity has the ability to place
   an HTTP server at that Internet name or address) and allows that
   authority to determine which names are valid and how they might be used.
</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 7 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 used for mapping the namespace 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.
   Senders MUST NOT include a userinfo subcomponent (and its "@"
   delimiter) when transmitting an "http" URI in a message.  Recipients
   of HTTP messages that contain a URI reference SHOULD parse for the
   existence of userinfo and treat its presence as an error, likely
   indicating that the deprecated subcomponent is 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 a default TCP port
   of 443 is assumed if the port subcomponent is empty or not given,
   and the TCP connection MUST be secured, end-to-end, through the
   use of strong encryption 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 ]
]]></artwork></figure>
<t>
   Unlike the "http" scheme, responses to "https" identified requests
   are never "public" and thus MUST NOT be reused for shared caching.
   They can, however, be reused in a private cache if the message is
   cacheable by default in HTTP or specifically indicated as such by
   the Cache-Control header field (Section 7.2 of <xref target="Part6"/>).
</t>
<t>
   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 <xref target="RFC3986"/>, Section 6, 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 elide the port subcomponent. Likewise, 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 (see <xref target="RFC3986"/>, Section 2.1): the normal form is to not encode them.
</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>
   Recipients 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>

<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"/>).
   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>
<t>
   A sender MUST NOT send whitespace between the start-line and
   the first header field. 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="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>
<t>
   A server MUST be able to parse any received message that begins
   with a request-line and matches the ABNF rule for HTTP-message.
</t>
<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 methods defined by this specification can be found in
   Section 5 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>
   No whitespace is allowed inside the method, request-target, and
   protocol version.  Hence, recipients typically parse the request-line
   into its component parts by splitting on the SP characters.
</t>
<t>
   Unfortunately, some user agents fail to properly encode hypertext
   references that have embedded whitespace, sending the characters
   directly instead of properly percent-encoding the disallowed characters.
   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.  Recipients 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.
   A server that receives a method longer than any that it implements
   SHOULD respond with either a 405 (Method Not Allowed), if it is an origin
   server, or a 501 (Not Implemented) status code.
   A server MUST be prepared to receive URIs of unbounded length and
   respond with the 414 (URI Too Long) status code if the received
   request-target would be longer than the server wishes to handle
   (see Section 7.5.12 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 up to 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>
   A client MUST be able to parse any received message that begins
   with a status-line and matches the ABNF rule for HTTP-message.
</t>
<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 7 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 HTTP header field consists of a case-insensitive field name
   followed by a colon (":"), optional whitespace, and the field value.
</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-content"/><iref primary="true" item="Grammar" subitem="obs-fold"/><artwork type="abnf2616"><![CDATA[
  header-field   = field-name ":" OWS field-value BWS
  field-name     = token
  field-value    = *( field-content / obs-fold )
  field-content  = *( HTAB / SP / VCHAR / obs-text )
  obs-fold       = CRLF ( SP / HTAB )
                 ; obsolete line folding
                 ; see Section 3.2.2
]]></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 8.1.1.2 of <xref target="Part2"/> as containing the origination
   timestamp for the message in which it appears.
</t>
<t>
   HTTP header fields are fully extensible: there is no limit on the
   introduction of new field names, each presumably defining new semantics,
   or 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 the standards process.
   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.
</t>
<t>
   New HTTP header fields SHOULD be registered with IANA in the
   Message Header Field Registry, as described in Section 9.3 of <xref target="Part2"/>.
   Unrecognized header fields MUST be forwarded by a proxy 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.
   Unrecognized header fields SHOULD be ignored by other recipients.
</t>
<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 wait until the entire header section is received before interpreting
   a request message, since later header fields might include conditionals,
   authentication credentials, or deliberately misleading duplicate
   header fields that would impact request processing.
</t>
<t>
   Multiple header fields with the same field name MUST NOT be
   sent in a message unless the entire field value for that
   header field is defined as a comma-separated list [i.e., #(values)].
   Multiple header fields with the same field name can be combined 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: The "Set-Cookie" header field as implemented in
   practice can occur multiple times, but does not use the list syntax, and
   thus cannot be combined into a single line (<xref target="RFC6265"/>). (See Appendix A.2.3 of <xref target="Kri2001"/>
   for details.) Also note that the Set-Cookie2 header field specified in
   <xref target="RFC2965"/> does not share this problem. 
  </t>
</list></t>

<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. OWS SHOULD either not be produced or be produced as a single
   SP. Multiple OWS octets that occur within field-content SHOULD either
   be replaced with a single SP or transformed to all SP octets (each
   octet other than SP replaced with SP) before interpreting the field value
   or forwarding the message downstream.
</t>
<t anchor="rule.RWS">
   RWS is used when at least one linear whitespace octet is required to
   separate field tokens. RWS SHOULD be produced as a single SP.
   Multiple RWS octets that occur within field-content SHOULD either
   be replaced with a single SP or transformed to all SP octets before
   interpreting the field value or forwarding the message downstream.
</t>
<t anchor="rule.BWS">
   BWS is used where the grammar allows optional whitespace, for historical
   reasons, but senders SHOULD NOT produce it in messages;
   recipients MUST accept such bad optional whitespace and remove it before
   interpreting the field value or forwarding the message downstream.
</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>
   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.
   Any received request message that contains whitespace between a header
   field-name and colon MUST be rejected 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 MAY be preceded by optional whitespace (OWS); a single SP is
   preferred. 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
   is ignored and SHOULD be removed before further processing (as this does
   not change the meaning of the 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"/>).
   HTTP senders MUST NOT produce messages that include line folding
   (i.e., that contain any field-value that matches the obs-fold rule) unless
   the message is intended for packaging within the message/http media type.
   HTTP recipients SHOULD accept line folding and replace any embedded
   obs-fold whitespace with either a single SP or a matching number of SP
   octets (to avoid buffer copying) prior to interpreting the field value or
   forwarding the message downstream.
</t>
<t>
   Historically, HTTP has allowed field content with text in the ISO-8859-1
   <xref target="ISO-8859-1"/> character encoding and supported other
   character sets only through use of <xref target="RFC2047"/> encoding.
   In practice, most HTTP header field values use only a subset of the
   US-ASCII character encoding <xref target="USASCII"/>. Newly defined
   header fields SHOULD limit their field values to US-ASCII octets.
   Recipients SHOULD treat other (obs-text) octets in field content as
   opaque data.
</t>
</section>

<section title="Field Length" anchor="field.length">
<t>
   HTTP does not place a pre-defined limit on the length of header fields,
   either in isolation or as a set. A server MUST be prepared to receive
   request header fields of unbounded length and respond with a 4xx
   (Client Error) status code if the received header field(s) would be
   longer than the server wishes to handle.
</t>
<t>
   A client that receives response header fields that are longer than it wishes
   to handle can only treat it as a server error.
</t>
<t>
   Various ad-hoc limitations on header field length are found in practice. It
   is RECOMMENDED that all HTTP senders and recipients support messages whose
   combined header fields have 4000 or more octets.
</t>
</section>

<section title="Field value components" anchor="field.components">
<t anchor="rule.token.separators">
  
  
  
  
   Many HTTP header field values consist of words (token or quoted-string)
   separated by whitespace or special characters. These special characters
   MUST be in a quoted string to be used within a parameter value (as defined
   in <xref target="transfer.codings"/>).
</t>
<figure><iref primary="true" item="Grammar" subitem="word"/><iref primary="true" item="Grammar" subitem="token"/><iref primary="true" item="Grammar" subitem="tchar"/><iref primary="true" item="Grammar" subitem="special"><!--unused production--></iref><artwork type="abnf2616"><![CDATA[
  word           = token / quoted-string

  token          = 1*tchar

  tchar          = "!" / "#" / "$" / "%" / "&" / "'" / "*"
                 / "+" / "-" / "." / "^" / "_" / "`" / "|" / "~" 
                 / DIGIT / ALPHA
                 ; any VCHAR, except special

  special        = "(" / ")" / "<" / ">" / "@" / ","
                 / ";" / ":" / "\" / DQUOTE / "/" / "[" 
                 / "]" / "?" / "=" / "{" / "}"
]]></artwork></figure>
<t anchor="rule.quoted-string">
  
  
  
   A string of text is parsed as a single word 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         = OWS / %x21 / %x23-5B / %x5D-7E / obs-text
  obs-text       = %x80-FF
]]></artwork></figure>
<t anchor="rule.quoted-pair">
  
   The backslash octet ("\") can be used as a single-octet
   quoting mechanism within quoted-string constructs:
</t>
<figure><iref primary="true" item="Grammar" subitem="quoted-pair"/><artwork type="abnf2616"><![CDATA[
  quoted-pair    = "\" ( HTAB / SP / VCHAR / obs-text ) 
]]></artwork></figure>
<t>
   Recipients that process the value of the quoted-string MUST handle a
   quoted-pair as if it were replaced by the octet following the backslash. 
</t>
<t>
   Senders SHOULD NOT escape octets in quoted-strings that do not require
   escaping (i.e., other than DQUOTE and the backslash octet).
</t>
<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-cpair / comment ) ")"
  ctext          = OWS / %x21-27 / %x2A-5B / %x5D-7E / obs-text
]]></artwork></figure>
<t anchor="rule.quoted-cpair">
  
   The backslash octet ("\") can be used as a single-octet
   quoting mechanism within comment constructs:
</t>
<figure><iref primary="true" item="Grammar" subitem="quoted-cpair"/><artwork type="abnf2616"><![CDATA[
  quoted-cpair   = "\" ( HTAB / SP / VCHAR / obs-text ) 
]]></artwork></figure>
<t>
   Senders SHOULD NOT escape octets in comments that do not require escaping
   (i.e., other than the backslash octet "\" and the parentheses "(" and ")").
</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
   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 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 5.3.2 of <xref target="Part2"/>).
   2xx (Successful) responses to CONNECT switch to tunnel
   mode instead of having a message body (Section 5.3.6 of <xref target="Part2"/>).
   All 1xx (Informational), 204 (No Content), and
   304 (Not Modified) responses MUST NOT include a message body.
   All other responses do include a message body, although the body
   MAY be of zero length.
</t>

<section title="Transfer-Encoding" anchor="header.transfer-encoding">
  <iref primary="true" item="Transfer-Encoding header field"/>
  
<t>
   When one or more transfer codings are applied to a payload body in order
   to form the message body, a Transfer-Encoding header field MUST be sent
   in the message and MUST contain the list of corresponding
   transfer-coding names in the same order that they were applied.
   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 target resource.
</t>
<t>
   The "chunked" transfer-coding (<xref target="chunked.encoding"/>)
   MUST be implemented by all HTTP/1.1 recipients because it plays a
   crucial role in delimiting messages when the payload body size is not
   known in advance.
   When the "chunked" transfer-coding is used, it MUST be the last
   transfer-coding applied to form the message body and MUST NOT
   be applied more than once in a message body.
   If any transfer-coding is applied to a request payload body,
   the final transfer-coding applied MUST be "chunked".
   If any transfer-coding is applied to a response payload body, then either
   the final transfer-coding applied MUST be "chunked" or
   the message MUST be terminated 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>
   If more than one Transfer-Encoding header field is present in a message,
   the multiple field-values MUST be combined into one field-value,
   according to the algorithm defined in <xref target="header.fields"/>,
   before determining the message body length.
</t>
<t>
   Unlike Content-Encoding (Section 3.1.2.1 of <xref target="Part2"/>),
   Transfer-Encoding is a property of the message, not of the payload, and thus
   MAY be added or removed by any implementation along the request/response
   chain. Additional information about the encoding parameters MAY 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>
   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) and then
   close the connection.
</t>
</section>

<section title="Content-Length" anchor="header.content-length">
  <iref primary="true" item="Content-Length header field"/>
  
<t>
   When a message is allowed to contain a message body, does not have a
   <xref target="header.transfer-encoding" format="none">Transfer-Encoding</xref> header field, and has a payload body
   length that is known to the sender before the message header section has
   been sent, the sender SHOULD send a Content-Length header field to
   indicate the length of the payload body as a decimal number of octets.
</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 server MAY send a Content-Length header field in a response to a HEAD
   request (Section 5.3.2 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 SHOULD NOT send a Content-Length header field in any
   2xx (Successful) response to a CONNECT request (Section 5.3.6 of <xref target="Part2"/>).
</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 an HTTP payload,
   recipients SHOULD anticipate potentially large decimal numerals and
   prevent parsing errors due to integer conversion overflows
   (<xref target="attack.protocol.element.size.overflows"/>).
</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.
</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">
<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 Transfer-Encoding 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 or response
     smuggling (bypass of security-related checks on message routing or content)
     and thus ought to be handled as an error.  The provided Content-Length MUST
     be removed, prior to forwarding the message downstream, or replaced with
     the real message body length after the transfer-coding is decoded.
    </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 MUST be treated
     as an error to prevent request or response smuggling.
     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 discard the received response, send a 502 (Bad Gateway)
     status code as its downstream response, and then close the connection.
     If this is a response message received by a user-agent, it MUST be
     treated as an error by discarding the message and closing the connection.
    </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
     message body length in octets.  If the actual number of octets sent in
     the message is less than the indicated Content-Length, the recipient
     MUST consider the message to be incomplete and treat the connection
     as no longer usable.
     If the actual number of octets sent in the message is more than the indicated
     Content-Length, the recipient MUST only process the message body up to the
     field value's number of octets; the remainder of the message MUST either
     be discarded or treated as the next message in a pipeline.  For the sake of
     robustness, a user-agent MAY attempt to detect and correct such an error
     in message framing if it is parsing the response to the last request on
     a connection and the connection has been closed by the server.
    </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 use 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" encoding, since some
   existing services respond to "chunked" with a 411 (Length Required)
   status code even though they understand the chunked encoding.  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 client that sends a request containing a message body MUST include 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>
</section>
</section>

<section anchor="incomplete.messages" title="Handling Incomplete Messages">
<t>
   Request messages that are prematurely terminated, possibly due to a
   canceled connection or a server-imposed time-out exception, MUST
   result in closure of the connection; sending an error response
   prior to closing the connection is OPTIONAL.
</t>
<t>
   Response messages that are prematurely terminated, usually by closure
   of the connection prior to receiving the expected number of octets or by
   failure to decode a transfer-encoded message body, MUST be recorded
   as incomplete.  A response that terminates in the middle of the header
   block (before the empty line is received) cannot be assumed to convey the
   full semantics of the response and MUST be treated as an error.
</t>
<t>
   A message body that uses the chunked transfer encoding 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 encoding 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 block was received
   intact.
</t>
<t>
   A user agent MUST NOT render an incomplete response message body as if
   it were complete (i.e., some indication needs to be given to the user that an
   error occurred).  Cache requirements for incomplete responses are defined
   in Section 3 of <xref target="Part6"/>.
</t>
<t>
   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.  Pipelining
   multiple requests on a connection is described in <xref target="pipelining"/>.
</t>
</section>

<section title="Message Parsing Robustness" anchor="message.robustness">
<t>
   Older HTTP/1.0 client implementations might send an extra CRLF
   after a POST request as a lame 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 client 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
   client MUST include the terminating CRLF octets as part of the
   message body length. 
</t>
<t>
   In the interest of robustness, servers SHOULD ignore at least one
   empty line received where a request-line is expected. In other words, if
   the server is reading the protocol stream at the beginning of a
   message and receives a CRLF first, it SHOULD ignore the CRLF.
   Likewise, although the line terminator for the start-line and header
   fields is the sequence CRLF, we recommend that recipients recognize a
   single LF as a line terminator and ignore any CR.
</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 MUST respond with an HTTP/1.1 400 (Bad Request) response.  
</t>
</section>
</section>

<section title="Transfer Codings" anchor="transfer.codings">
  
  
<t>
   Transfer-coding values 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 attribute/value pairs.
</t>
<figure><iref primary="true" item="Grammar" subitem="transfer-parameter"/><iref primary="true" item="Grammar" subitem="attribute"/><iref primary="true" item="Grammar" subitem="value"/><iref primary="true" item="Grammar" subitem="date2"/><iref primary="true" item="Grammar" subitem="date3"/><artwork type="abnf2616"><![CDATA[
  transfer-parameter = attribute BWS "=" BWS value
  attribute          = token
  value              = word
]]></artwork></figure>
<t>
   All transfer-coding values are case-insensitive and SHOULD 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 item="chunked (Coding Format)"/>
  
  
  
  
  
  
  
  
  
  
  
<t>
   The chunked encoding modifies the body of a message in order to
   transfer it as a series of chunks, each with its own size indicator,
   followed by an OPTIONAL trailer containing header fields. This
   allows dynamically produced content to be transferred along with the
   information necessary for the recipient to verify that it has
   received the full 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="true" item="Grammar" subitem="chunk-ext"/><iref primary="true" item="Grammar" subitem="chunk-ext-name"/><iref primary="true" item="Grammar" subitem="chunk-ext-val"/><iref primary="true" item="Grammar" subitem="chunk-data"/><iref primary="true" item="Grammar" subitem="trailer-part"/><iref primary="true" item="Grammar" subitem="quoted-str-nf"/><iref primary="true" item="Grammar" subitem="qdtext-nf"/><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-ext      = *( ";" chunk-ext-name [ "=" chunk-ext-val ] )
  chunk-ext-name = token
  chunk-ext-val  = token / quoted-str-nf
  chunk-data     = 1*OCTET ; a sequence of chunk-size octets
  trailer-part   = *( header-field CRLF )
  
  quoted-str-nf  = DQUOTE *( qdtext-nf / quoted-pair ) DQUOTE
                 ; like quoted-string, but disallowing line folding
  qdtext-nf      = HTAB / SP / %x21 / %x23-5B / %x5D-7E / obs-text
]]></artwork></figure>
<t>
   Chunk extensions within the chucked encoding are deprecated.
   Senders SHOULD NOT send chunk-ext.
   Definition of new chunk extensions is discouraged. 
</t>
<t>
   The chunk-size field is a string of hex digits indicating the size of
   the chunk-data in octets. The chunked encoding is ended by any chunk whose size is
   zero, followed by the trailer, which is terminated by an empty line.
</t>

<section title="Trailer" anchor="header.trailer">
  <iref primary="true" item="Trailer header field"/>
  
<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 MUST NOT contain fields that need to be known before a
   recipient processes the body, such as <xref target="header.transfer-encoding" format="none">Transfer-Encoding</xref>,
   <xref target="header.content-length" format="none">Content-Length</xref>, and <xref target="header.trailer" format="none">Trailer</xref>.
</t>
<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 send 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"/><artwork type="abnf2616"><![CDATA[
  Trailer = 1#field-name
]]></artwork></figure>
<t>
   If no <xref target="header.trailer" format="none">Trailer</xref> header field is present, the sender of a
   chunked message body SHOULD send an empty trailer.
</t>
<t>
   A server MUST send an empty trailer with the chunked transfer-coding
   unless at least one of the following is true:
  <list style="numbers">
    <t>the request included a <xref target="header.te" format="none">TE</xref> header field that indicates
    "trailers" is acceptable in the transfer-coding of the response, as
    described in <xref target="header.te"/>; or,</t>
     
    <t>the trailer fields consist entirely of optional metadata and the
    recipient could use the message (in a manner acceptable to the server where
    the field originated) without receiving that metadata. In other words,
    the server that generated the header field is willing to accept the
    possibility that the trailer fields might be silently discarded along
    the path to the client.</t>
  </list>
</t>
<t>
   The above requirement prevents the need for an infinite buffer when a
   message is being received by an HTTP/1.1 (or later) proxy and forwarded to
   an HTTP/1.0 recipient.
</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 and CRLF
  }
  read header-field
  while (header-field not empty) {
     append header-field to existing header fields
     read header-field
  }
  Content-Length := length
  Remove "chunked" from Transfer-Encoding
  Remove Trailer from existing header fields
]]></artwork></figure>
<t>
   All recipients MUST be able to receive and decode the
   "chunked" transfer-coding and MUST ignore chunk-ext extensions
   they do not understand.
</t>
</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" format is produced by the common UNIX file compression
   program "compress". This format is an adaptive Lempel-Ziv-Welch
   coding (LZW). Recipients 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" format is defined as the "deflate" compression mechanism
   (described in <xref target="RFC1951"/>) used inside the "zlib"
   data format (<xref target="RFC1950"/>).
</t>
<t><list>
  <t>
    Note: Some incorrect 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" format is produced by the file compression program
   "gzip" (GNU zip), as described in <xref target="RFC1952"/>. This format is a
   Lempel-Ziv coding (LZ77) with a 32 bit CRC.
   Recipients 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".
   Clients 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.encoding"/>, on behalf of itself and
   any downstream clients. For chained requests, this implies that either:
   (a) all downstream clients are willing to accept trailer fields in the
   forwarded response; or,
   (b) the client 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 a client 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 6.3.1 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>

<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 identifier 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 response cache and the request semantics can be
   satisfied by a cache (<xref target="Part6"/>), then the request is
   usually directed to the cache 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="true" item="Grammar" subitem="origin-form"/><iref primary="true" item="Grammar" subitem="absolute-form"/><iref primary="true" item="Grammar" subitem="authority-form"/><iref primary="true" item="Grammar" subitem="asterisk-form"/><artwork type="abnf2616"><![CDATA[
  request-target = origin-form
                 / absolute-form
                 / authority-form
                 / asterisk-form

  origin-form    = path-absolute [ "?" query ]
  absolute-form  = absolute-URI
  authority-form = authority
  asterisk-form  = "*"
]]></artwork></figure>
<t anchor="origin-form"><iref item="origin-form (of request-target)"/>
   The most common form of request-target is the origin-form.
   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, then 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"/>, containing the target URI's
   authority component (excluding any userinfo).
</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=&#34;request&#34;"><![CDATA[
  GET /where?q=now HTTP/1.1
  Host: www.example.org
  ]]></artwork></figure>
<t>
   followed by the remainder of the request message.
</t>
<t anchor="absolute-form"><iref item="absolute-form (of request-target)"/>
   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.
   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=&#34;request&#34;"><![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, HTTP/1.1 servers MUST accept the absolute-form
   in requests, even though HTTP/1.1 clients will only send them in requests
   to proxies.
</t>
<t anchor="authority-form"><iref item="authority-form (of request-target)"/>
   The authority-form of request-target is only used for CONNECT requests
   (Section 5.3.6 of <xref target="Part2"/>).  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) as the request-target.
   For example,
</t>
<figure><artwork type="message/http; msgtype=&#34;request&#34;"><![CDATA[
  CONNECT www.example.com:80 HTTP/1.1
  ]]></artwork></figure>
<t anchor="asterisk-form"><iref item="asterisk-form (of request-target)"/>
   The asterisk-form of request-target is only used for a server-wide
   OPTIONS request (Section 5.3.7 of <xref target="Part2"/>).  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=&#34;request&#34;"><![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=&#34;request&#34;"><![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=&#34;request&#34;"><![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 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.  Since the Host
   field-value is critical information for handling a request, it
   SHOULD be sent as the first header field following the request-line.
</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
   the Host field-value MUST be identical to that authority component
   after excluding any userinfo (<xref target="http.uri"/>).
   If the authority component is missing or undefined for the target URI,
   then the Host header field MUST be sent with an empty field-value.
</t>
<t>
   For example, a GET request to the origin server for
   &lt;http://www.example.org/pub/WWW/&gt; would begin with:
</t>
<figure><artwork type="message/http; msgtype=&#34;request&#34;"><![CDATA[
  GET /pub/WWW/ HTTP/1.1
  Host: www.example.org
  ]]></artwork></figure>
<t>
   The Host header field MUST be sent 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.  If the proxy forwards the request,
   it 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>
   A server that receives an HTTP request message MUST reconstruct
   the user agent's original target URI, based on the pieces of information
   learned from the request-target, <xref target="header.host" format="none">Host</xref> header field, and
   connection context, in order to identify the intended target resource and
   properly service the request. The URI derived from this reconstruction
   process is referred to as the "effective request URI".
</t>
<t>
   For a user agent, the effective request URI is the target URI.
</t>
<t>
   If the request-target is in absolute-form, then the effective request URI
   is the same as the request-target.  Otherwise, the effective request URI
   is constructed as follows.
</t>
<t>
   If the request is received over a TLS-secured TCP connection,
   then the effective request URI's scheme is "https"; otherwise, the
   scheme is "http".
</t>
<t>
   If the request-target is in authority-form, then the effective
   request URI's authority component is the same as the request-target.
   Otherwise, if a <xref target="header.host" format="none">Host</xref> header field is supplied with a
   non-empty field-value, then the authority component is the same as the
   Host field-value. Otherwise, the authority component is the concatenation of
   the default host name configured for the server, a colon (":"), and the
   connection's incoming TCP port number in decimal form.
</t>
<t>
   If the request-target is in authority-form or asterisk-form, then the
   effective request URI's combined path and query component is empty.
   Otherwise, the combined path and query 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 absolute-URI form by concatenating the scheme,
   "://", authority, and combined path and query component.
</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>
   An origin server that does not allow resources to differ by requested
   host MAY ignore the <xref target="header.host" format="none">Host</xref> field-value and instead replace it
   with a configured server name when constructing the effective request URI.
</t>
<t>
   Recipients of an HTTP/1.0 request that lacks a <xref target="header.host" format="none">Host</xref> header
   field MAY attempt 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>
</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>
   Intermediaries that forward a message MUST implement the
   <xref target="header.connection" format="none">Connection</xref> header field, as specified in
   <xref target="header.connection"/>, to exclude fields that are only
   intended for the incoming connection.
</t>
<t>
   In order to avoid request loops, a proxy that forwards requests to other
   proxies MUST be able to recognize and exclude all of its own server
   names, including any aliases, local variations, or literal IP addresses.
</t>
</section>

<section title="Via" anchor="header.via">
  <iref primary="true" item="Via header field"/>
  
  
  
  
<t>
   The "Via" header field MUST be sent by a proxy or gateway
   in forwarded messages to
   indicate the intermediate protocols and recipients between the user
   agent and the server on requests, and between the origin server and
   the client on responses. It is analogous to the "Received" field
   used by email systems (Section 3.6.7 of <xref target="RFC5322"/>).
   Via is used in HTTP for tracking message forwards,
   avoiding request loops, and identifying the protocol capabilities of
   all 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
  received-by       = ( uri-host [ ":" port ] ) / pseudonym
  pseudonym         = token
]]></artwork></figure>
<t>
   The received-protocol indicates the protocol version of the message
   received by the server or client along each segment of the
   request/response chain. The received-protocol version is appended to
   the Via field value when the message is forwarded so that information
   about the protocol capabilities of upstream applications remains
   visible to all recipients.
</t>
<t>
   The protocol-name is excluded if and only if it would be "HTTP". The
   received-by field 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,
   it MAY be replaced by a pseudonym. If the port is not given, it MAY
   be assumed to be the default port of the received-protocol.
</t>
<t>
   Multiple Via field values represent each proxy or gateway that has
   forwarded the message. Each recipient MUST append its information
   such that the end result is ordered according to the sequence of
   forwarding applications.
</t>
<t>
   Comments MAY be used 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 MAY be removed by any recipient 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 (Apache/1.1)
]]></artwork></figure>
<t>
   A proxy or gateway 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, the
   received-by host of any host behind the firewall SHOULD be replaced
   by an appropriate pseudonym for that host.
</t>
<t>
   A proxy or gateway 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>
   Senders SHOULD NOT combine multiple entries unless they are all
   under the same organizational control and the hosts have already been
   replaced by pseudonyms. Senders MUST NOT combine entries which
   have different received-protocol values.
</t>
</section>

<section title="Message Transforming" anchor="message.transforming">
<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 it is a fully qualified domain name.
</t>
<t>
   A non-transforming proxy MUST NOT modify the "path-absolute" 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 non-transforming proxy MUST preserve the message payload (Section 3.3 of <xref target="Part2"/>),
   though it MAY change the message body through application or removal
   of a transfer-coding (<xref target="transfer.codings"/>).
</t>
<t>
   A non-transforming proxy SHOULD NOT modify header fields that provide
   information about the end points of the communication chain, the resource
   state, or the selected representation.
</t>
<t>
   A non-transforming proxy MUST NOT modify any of the following fields in a
   request or response, and it MUST NOT add any of these fields if not
   already present:
  <list style="symbols">
    <t>Allow (Section 8.4.1 of <xref target="Part2"/>)</t>
    <t>Content-Location (Section 3.1.4.2 of <xref target="Part2"/>)</t>
    <t>Content-MD5 (Section 14.15 of <xref target="RFC2616"/>)</t>
    <t>ETag (Section 2.3 of <xref target="Part4"/>)</t>
    <t>Last-Modified (Section 2.2 of <xref target="Part4"/>)</t>
    <t>Server (Section 8.4.2 of <xref target="Part2"/>)</t>
  </list>
</t>
<t>
   A non-transforming proxy MUST NOT modify an Expires
   header field (Section 7.3 of <xref target="Part6"/>) if already present in a response, but
   it MAY add an Expires header field with a field-value
   identical to that of the Date header field.
</t>
<t>
   A proxy MUST NOT modify or add any of the following fields in a
   message that contains the no-transform cache-control directive:
  <list style="symbols">
    <t>Content-Encoding (Section 3.1.2.2 of <xref target="Part2"/>)</t>
    <t>Content-Range (Section 5.2 of <xref target="Part5"/>)</t>
    <t>Content-Type (Section 3.1.1.5 of <xref target="Part2"/>)</t>
  </list>
</t>
<t>
   A transforming proxy MAY modify or add these fields to a message
   that does not include no-transform, but if it does so, it MUST add a
   Warning 214 (Transformation applied) if one does not already appear
   in the message (see Section 7.5 of <xref target="Part6"/>).
</t>
<t><list>
  <t>
    Warning: Unnecessary modification of header fields might
    cause authentication failures if stronger authentication
    mechanisms are introduced in later versions of HTTP. Such
    authentication mechanisms MAY rely on the values of header fields
    not listed here.
  </t>
</list></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 7.2 of <xref target="Part2"/>) precede a final response
   to the same request.
</t>
<t>
   A client that uses persistent connections and sends more than one request
   per connection MUST maintain a list of outstanding requests in the
   order sent on that connection and MUST associate each received response
   message to the highest ordered request that has not yet received a final
   (non-1xx) response.
</t>
</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 is used to supply control information for or about
   the current connection, the sender SHOULD 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 include field-names in the Connection header
   field-value for fields that are defined as expressing constraints
   for all recipients in the request or response chain, such as the
   Cache-Control header field (Section 7.2 of <xref target="Part6"/>).
</t>
<t>
   The connection options do not have to 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 that
   connection option.  Recipients that trigger certain connection
   behavior based on the presence of connection options MUST do so
   based on the presence of the connection-option rather than only the
   presence of the optional header field.  In other words, if the
   connection option is received as a header field but not indicated
   within the Connection field-value, then the recipient MUST ignore
   the connection-specific header field because it has likely been
   forwarded by an intermediary that is only partially conformant.
</t>
<t>
   When defining new connection options, specifications ought to
   carefully consider existing deployed header fields and ensure
   that the new connection option does not share the same name as
   an unrelated header field that might already be deployed.
   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 connection SHOULD be closed after the current request/response
   is complete (<xref target="persistent.tear-down"/>).
</t>
<t>
   A client that does not support persistent connections MUST
   send the "close" connection option in every request message.
</t>
<t>
   A server that does not support persistent connections MUST
   send the "close" connection option in every response message that
   does not have a 1xx (Informational) status code.
</t>
</section>

<section title="Persistent Connections" anchor="persistent.connections">
  
<t>
   HTTP was originally designed to use a separate connection for each
   request/response pair. As the Web evolved and embedded requests became
   common for inline images, the connection establishment overhead was
   a significant drain on performance and a concern for Internet congestion.
   Message framing (via <xref target="header.content-length" format="none">Content-Length</xref>) and optional
   long-lived connections (via Keep-Alive) were added to HTTP/1.0 in order
   to improve performance for some requests. However, these extensions were
   insufficient for dynamically generated responses and difficult to use
   with intermediaries.
</t>
<t>
   HTTP/1.1 defaults to the use of "<xref target="persistent.connections" format="none">persistent connections</xref>",
   which allow 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 close after the current request/response.
   Persistent connections have a number of advantages:
  <list style="symbols">
      <t>
        By opening and closing fewer connections, CPU time is saved
        in routers and hosts (clients, servers, proxies, gateways,
        tunnels, or caches), and memory used for protocol control
        blocks can be saved in hosts.
      </t>
      <t>
        Most requests and responses can be pipelined on a connection.
        Pipelining allows a client to make multiple requests without
        waiting for each response, allowing a single connection to
        be used much more efficiently and with less overall latency.
      </t>
      <t>
        For TCP connections, network congestion is reduced by eliminating the
        packets associated with the three way handshake and graceful close
        procedures, and by allowing sufficient time to determine the
        congestion state of the network.
      </t>
      <t>
        Latency on subsequent requests is reduced since there is no time
        spent in the connection opening handshake.
      </t>
      <t>
        HTTP can evolve more gracefully, since most errors can be reported
        without the penalty of closing the connection. Clients using
        future versions of HTTP might optimistically try a new feature,
        but if communicating with an older server, retry with old
        semantics after an error is reported.
      </t>
    </list>
</t>
<t>
   HTTP implementations SHOULD implement persistent connections.
</t>
   
<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>
<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 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>
</section>

<section title="Reuse" anchor="persistent.reuse">
<t>
   In order to remain persistent, all messages on a connection MUST
   have a self-defined message length (i.e., one not defined by closure
   of the connection), as described in <xref target="message.body"/>.
</t>
<t>
   A server MAY assume that an HTTP/1.1 client intends to maintain a
   persistent connection until a <xref target="header.connection" format="none">close</xref> connection option
   is received in a request.
</t>
<t>
   A client MAY reuse 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>
   Clients and servers SHOULD NOT assume that a persistent connection is
   maintained for HTTP versions less than 1.1 unless it is explicitly
   signaled.
   See <xref target="compatibility.with.http.1.0.persistent.connections"/>
   for more information on backward compatibility with HTTP/1.0 clients.
</t>

<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 MUST send its responses to those requests in the
   same order that the requests were received.
</t>
<t>
   Clients which assume persistent connections and pipeline immediately
   after connection establishment SHOULD be prepared to retry their
   connection if the first pipelined attempt fails. If a client does
   such a retry, it MUST NOT pipeline before it knows the connection is
   persistent. Clients MUST also be prepared to resend their requests if
   the server closes the connection before sending all of the
   corresponding responses.
</t>
<t>
   Clients SHOULD NOT pipeline requests using non-idempotent request methods
   or non-idempotent sequences of request methods (see Section 5.2.2 of <xref target="Part2"/>).
   Otherwise, a premature termination of the transport connection could lead
   to indeterminate results. A client wishing to send a non-idempotent
   request SHOULD wait to send that request until it has received the
   response status line for the previous request.
</t>
</section>

<section title="Retrying Requests" anchor="persistent.retrying.requests">
<t>
   Senders can close the transport connection at any time. Therefore, 
   clients, servers, and proxies MUST be able to recover
   from asynchronous close events. Client software MAY reopen the
   transport connection and retransmit the aborted sequence of requests
   without user interaction so long as the request sequence is
   idempotent (see Section 5.2.2 of <xref target="Part2"/>). Non-idempotent request methods or sequences
   MUST NOT be automatically retried, although user agents MAY offer a
   human operator the choice of retrying the request(s). Confirmation by
   user-agent software with semantic understanding of the application
   MAY substitute for user confirmation. The automatic retry SHOULD NOT 
   be repeated if the second sequence of requests fails.
</t>
</section>
</section>
   
<section title="Concurrency" anchor="persistent.concurrency">
<t>
   Clients SHOULD limit the number of simultaneous
   connections that they maintain 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 servers might reject traffic that they deem abusive, including an
   excessive number of connections from a 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 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>
   When a client or server wishes to time-out it SHOULD issue a graceful
   close on the transport connection. Clients and servers SHOULD both
   constantly watch for the other side of the transport close, and
   respond to it as appropriate. If a client or server does not detect
   the other side's close promptly it could cause unnecessary resource
   drain on the network.
</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>
   Servers SHOULD maintain persistent connections 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 status code while it is transmitting
   the request. If the client sees an error status code, it SHOULD
   immediately cease transmitting the body and close 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 lingering close of the connection after it sends the final
   response to the request that contained <xref target="header.connection" format="none">close</xref>.
   The server SHOULD include 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 lingering close of the connection 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
   assume that they will not 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, a server can perform a lingering close on a
   connection by closing only the write side of the read/write connection
   (a half-close) and continuing to read from the connection until the
   connection is closed by the client or 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. It is then safe for the
   server to fully close 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>

<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 before sending the final response.
   A server MUST send an Upgrade header field in 101 (Switching
   Protocols) responses to indicate which protocol(s) are being
   switched to, and MUST send it in 426 (Upgrade Required)
   responses to indicate acceptable protocols.
   A server MAY send an Upgrade header field in any other response to
   indicate that they might be willing to upgrade to one of the
   specified protocols for a future request.
</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>
   For example,
</t>
<figure><artwork type="example"><![CDATA[
  Upgrade: HTTP/2.0, SHTTP/1.3, IRC/6.9, RTA/x11
]]></artwork></figure>
<t>
   Upgrade eases the difficult transition between incompatible protocols by
   allowing the client to initiate a request in the more commonly
   supported protocol while indicating to the server that it would like
   to use a "better" protocol if available (where "better" is determined
   by the server, possibly according to the nature of the request method
   or target resource).
</t>
<t>
   Upgrade cannot be used to insist on a protocol change; its acceptance and
   use by the server is optional. The capabilities and nature of the
   application-level communication after the protocol change is entirely
   dependent upon the new protocol chosen, although the first action
   after changing the protocol MUST be a response to the initial HTTP
   request that contained the Upgrade header field.
</t>
<t>
   For example, if the Upgrade header field is received in a GET request
   and the server decides to switch protocols, then it MUST first respond
   with a 101 (Switching Protocols) message in HTTP/1.1 and
   then immediately follow 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>
<t>
   When Upgrade is sent, a sender MUST also send a 
   <xref target="header.connection" format="none">Connection</xref> header field (<xref target="header.connection"/>)
   that contains the "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>
   The Upgrade header field only applies to switching application-level
   protocols on the existing connection; it cannot be used
   to switch to a protocol on a different connection. For that purpose, it is
   more appropriate to use a 3xx (Redirection) response
   (Section 7.4 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 can be registered with IANA using the
   registration procedure defined in <xref target="upgrade.token.registry"/>.
</t>
</section>
</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
   <xref target="RFC3864"/> maintained by IANA at
   <eref target="http://www.iana.org/assignments/message-headers/message-header-index.html"/>.
</t>
<t>
   This document defines the following HTTP header fields, so their
   associated registry entries shall be updated according to the permanent
   registrations below:
</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="RFC4395"/> at
   <eref target="http://www.iana.org/assignments/uri-schemes.html"/>.
</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 Registrations" anchor="internet.media.type.http">
<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 (see <xref target="RFC4288"/>).
</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:">
      none
    </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:">
      none
    </t>
    <t hangText="Interoperability considerations:">
      none
    </t>
    <t hangText="Published specification:">
      This specification (see <xref target="internet.media.type.message.http"/>).
    </t>
    <t hangText="Applications that use this media type:">
    </t>
    <t hangText="Additional information:">
      <list style="hanging">
        <t hangText="Magic number(s):">none</t>
        <t hangText="File extension(s):">none</t>
        <t hangText="Macintosh file type code(s):">none</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:">
      none
    </t>
    <t hangText="Author/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:">
      none
    </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:">
      none
    </t>
    <t hangText="Interoperability considerations:">
      none
    </t>
    <t hangText="Published specification:">
      This specification (see <xref target="internet.media.type.application.http"/>).
    </t>
    <t hangText="Applications that use this media type:">
    </t>
    <t hangText="Additional information:">
      <list style="hanging">
        <t hangText="Magic number(s):">none</t>
        <t hangText="File extension(s):">none</t>
        <t hangText="Macintosh file type code(s):">none</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:">
      none
    </t>
    <t hangText="Author/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.
</t>
<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 section.
   Use of program names for the identification of encoding formats
   is not desirable and is discouraged for future encodings.
</t>
<t>
   The registry itself is maintained at
   <eref target="http://www.iana.org/assignments/http-parameters"/>.
</t>
</section>

<section title="Transfer Coding Registrations" 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" program method</c>
   <c>
      <xref target="compress.coding"/>
   </c>
   <c>deflate</c>
   <c>"deflate" compression mechanism (<xref target="RFC1951"/>) used inside
   the "zlib" data format (<xref target="RFC1950"/>)
   </c>
   <c>
      <xref target="deflate.coding"/>
   </c>
   <c>gzip</c>
   <c>Same as GNU zip <xref target="RFC1952"/></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. 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 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 title="Security Considerations" anchor="security.considerations">
<t>
   This section is meant to inform application developers, information
   providers, and users of the security limitations in HTTP/1.1 as
   described by this document. The discussion does not include
   definitive solutions to the problems revealed, though it does make
   some suggestions for reducing security risks.
</t>

<section title="Personal Information" anchor="personal.information">
<t>
   HTTP clients are often privy to large amounts of personal information,
   including both information provided by the user to interact with resources
   (e.g., the user's name, location, mail address, passwords, encryption
   keys, etc.) and information about the user's browsing activity over
   time (e.g., history, bookmarks, etc.). HTTP implementations need to
   prevent unintentional leakage of this information.
</t>
</section>

<section title="Abuse of Server Log Information" anchor="abuse.of.server.log.information">
<t>
   A server is in the position to save personal data about a user's
   requests 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 should not
   be published even if the key is pseudonymous.
</t>
<t>
   To minimize the risk of theft or accidental publication, log information
   should 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 title="Attacks Based On File and Path Names" anchor="attack.pathname">
<t>
   Origin servers SHOULD be careful to restrict
   the documents returned by HTTP requests to be only those that were
   intended by the server administrators. If an HTTP server translates
   HTTP URIs directly into file system calls, the server MUST take
   special care not to serve files that were not intended to be
   delivered to HTTP clients. For example, UNIX, Microsoft Windows, and
   other operating systems use ".." as a path component to indicate a
   directory level above the current one. On such a system, an HTTP
   server MUST disallow any such construct in the request-target if it
   would otherwise allow access to a resource outside those intended to
   be accessible via the HTTP server. Similarly, files intended for
   reference only internally to the server (such as access control
   files, configuration files, and script code) MUST be protected from
   inappropriate retrieval, since they might contain sensitive
   information.
</t>
</section>

<section title="DNS-related Attacks" anchor="dns.related.attacks">
<t>
   HTTP clients rely heavily on the Domain Name Service (DNS), and are thus
   generally prone to security attacks based on the deliberate misassociation
   of IP addresses and DNS names not protected by DNSSec. Clients need to be
   cautious in assuming the validity of an IP number/DNS name association unless
   the response is protected by DNSSec (<xref target="RFC4033"/>).
</t>
</section>

<section title="Intermediaries and Caching" anchor="attack.intermediaries">
<t>
   By their very nature, HTTP intermediaries are men-in-the-middle, and
   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 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.
</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="Protocol Element Size Overflows" anchor="attack.protocol.element.size.overflows">
<t>
   Because HTTP uses mostly textual, character-delimited fields, attackers can
   overflow buffers in implementations, and/or perform a Denial of Service
   against implementations that accept fields with unlimited lengths.
</t>
<t>
   To promote interoperability, this specification makes specific
   recommendations for minimum size limits on request-line
   (<xref target="request.line"/>)
   and blocks of 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>
   This specification also provides a way for servers to reject messages that
   have request-targets that are too long (Section 7.5.12 of <xref target="Part2"/>) or request entities
   that are too large (Section 7.5 of <xref target="Part2"/>).
</t>
<t>
   Recipients SHOULD carefully limit the extent to which they read other
   fields, including (but not limited to) request methods, response status
   phrases, header field-names, and body chunks, so as to avoid denial of
   service attacks without impeding interoperability.
</t>
</section>
</section>

<section title="Acknowledgments" anchor="acks">
<t>
   This edition of HTTP 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,
   Paul J. Leach, and Mark Nottingham.
   See Section 16 of <xref target="RFC2616"/> for additional
   acknowledgements from prior revisions.
</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,
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,
Anil Sharma,
Anne van Kesteren,
Anthony Bryan,
Asbjorn Ulsberg,
Balachander Krishnamurthy,
Barry Leiba,
Ben Laurie,
Benjamin Niven-Jenkins,
Bil Corry,
Bill Burke,
Bjoern Hoehrmann,
Bob Scheifler,
Boris Zbarsky,
Brett Slatkin,
Brian Kell,
Brian McBarron,
Brian Pane,
Brian Smith,
Bryce Nesbitt,
Cameron Heavon-Jones,
Carl Kugler,
Carsten Bormann,
Charles Fry,
Chris Newman,
Cyrus Daboo,
Dale Robert Anderson,
Dan Wing,
Dan Winship,
Daniel Stenberg,
Dave Cridland,
Dave Crocker,
Dave Kristol,
David Booth,
David Singer,
David W. Morris,
Diwakar Shetty,
Dmitry Kurochkin,
Drummond Reed,
Duane Wessels,
Edward Lee,
Eliot Lear,
Eran Hammer-Lahav,
Eric D. Williams,
Eric J. Bowman,
Eric Lawrence,
Eric Rescorla,
Erik Aronesty,
Evan Prodromou,
Florian Weimer,
Frank Ellermann,
Fred Bohle,
Gabriel Montenegro,
Geoffrey Sneddon,
Gervase Markham,
Grahame Grieve,
Greg Wilkins,
Harald Tveit Alvestrand,
Harry Halpin,
Helge Hess,
Henrik Nordstrom,
Henry S. Thompson,
Henry Story,
Herbert van de Sompel,
Howard Melman,
Hugo Haas,
Ian Fette,
Ian Hickson,
Ido Safruti,
Ingo Struck,
J. Ross Nicoll,
James H. Manger,
James Lacey,
James M. Snell,
Jamie Lokier,
Jan Algermissen,
Jeff Hodges (who came up with the term 'effective Request-URI'),
Jeff Walden,
Jim Luther,
Joe D. Williams,
Joe Gregorio,
Joe Orton,
John C. Klensin,
John C. Mallery,
John Cowan,
John Kemp,
John Panzer,
John Schneider,
John Stracke,
John Sullivan,
Jonas Sicking,
Jonathan Billington,
Jonathan Moore,
Jonathan Rees,
Jonathan Silvera,
Jordi Ros,
Joris Dobbelsteen,
Josh Cohen,
Julien Pierre,
Jungshik Shin,
Justin Chapweske,
Justin Erenkrantz,
Justin James,
Kalvinder Singh,
Karl Dubost,
Keith Hoffman,
Keith Moore,
Koen Holtman,
Konstantin Voronkov,
Kris Zyp,
Lisa Dusseault,
Maciej Stachowiak,
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,
Max Clark,
Michael Burrows,
Michael Hausenblas,
Mike Amundsen,
Mike Belshe,
Mike Kelly,
Mike Schinkel,
Miles Sabin,
Murray S. Kucherawy,
Mykyta Yevstifeyev,
Nathan Rixham,
Nicholas Shanks,
Nico Williams,
Nicolas Alvarez,
Nicolas Mailhot,
Noah Slater,
Pablo Castro,
Pat Hayes,
Patrick R. McManus,
Paul E. Jones,
Paul Hoffman,
Paul Marquess,
Peter Lepeska,
Peter Saint-Andre,
Peter Watkins,
Phil Archer,
Philippe Mougin,
Phillip Hallam-Baker,
Poul-Henning Kamp,
Preethi Natarajan,
Rajeev Bector,
Ray Polk,
Reto Bachmann-Gmuer,
Richard Cyganiak,
Robert Brewer,
Robert Collins,
Robert O'Callahan,
Robert Olofsson,
Robert Sayre,
Robert Siemer,
Robert de Wilde,
Roberto Javier Godoy,
Roberto Peon,
Ronny Widjaja,
S. Mike Dierken,
Salvatore Loreto,
Sam Johnston,
Sam Ruby,
Scott Lawrence (who maintained the original issues list),
Sean B. Palmer,
Shane McCarron,
Stefan Eissing,
Stefan Tilkov,
Stefanos Harhalakis,
Stephane Bortzmeyer,
Stephen Farrell,
Stephen Ludin,
Stuart Williams,
Subbu Allamaraju,
Sylvain Hellegouarch,
Tapan Divekar,
Tatsuya Hayashi,
Ted Hardie,
Thomas Broyer,
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,
Yutaka Oiwa,
Yves Lafon (long-time member of the editor team),
Zed A. Shaw, and 
Zhong Yu.
</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="October" year="2012"/>
  </front>
  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p2-semantics-21"/>
  
</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="October" year="2012"/>
  </front>
  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p4-conditional-21"/>
  
</reference>

<reference anchor="Part5">
  <front>
    <title>Hypertext Transfer Protocol (HTTP/1.1): Range Requests</title>
    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
      <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
      <address><email>fielding@gbiv.com</email></address>
    </author>
    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
      <organization abbrev="W3C">World Wide Web Consortium</organization>
      <address><email>ylafon@w3.org</email></address>
    </author>
    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
      <organization abbrev="greenbytes">greenbytes GmbH</organization>
      <address><email>julian.reschke@greenbytes.de</email></address>
    </author>
    <date month="October" year="2012"/>
  </front>
  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p5-range-21"/>
  
</reference>

<reference anchor="Part6">
  <front>
    <title>Hypertext Transfer Protocol (HTTP/1.1): Caching</title>
    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
      <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
      <address><email>fielding@gbiv.com</email></address>
    </author>
    <author initials="M." surname="Nottingham" fullname="Mark Nottingham" role="editor">
      <organization>Akamai</organization>
      <address><email>mnot@mnot.net</email></address>
    </author>
    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
      <organization abbrev="greenbytes">greenbytes GmbH</organization>
      <address><email>julian.reschke@greenbytes.de</email></address>
    </author>
    <date month="October" year="2012"/>
  </front>
  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p6-cache-21"/>
  
</reference>

<reference anchor="Part7">
  <front>
    <title>Hypertext Transfer Protocol (HTTP/1.1): Authentication</title>
    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
      <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
      <address><email>fielding@gbiv.com</email></address>
    </author>
    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
      <organization abbrev="greenbytes">greenbytes GmbH</organization>
      <address><email>julian.reschke@greenbytes.de</email></address>
    </author>
    <date month="October" year="2012"/>
  </front>
  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p7-auth-21"/>
  
</reference>

<reference anchor="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="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>

</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="RFC2965">
  <front>
    <title>HTTP State Management Mechanism</title>
    <author initials="D. M." surname="Kristol" fullname="David M. Kristol">
      <organization>Bell Laboratories, Lucent Technologies</organization>
      <address><email>dmk@bell-labs.com</email></address>
    </author>
    <author initials="L." surname="Montulli" fullname="Lou Montulli">
      <organization>Epinions.com, Inc.</organization>
      <address><email>lou@montulli.org</email></address>
    </author>
    <date year="2000" month="October"/>
  </front>
  <seriesInfo name="RFC" value="2965"/>
</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="RFC3864">
  <front>
    <title>Registration Procedures for Message Header Fields</title>
    <author initials="G." surname="Klyne" fullname="G. Klyne">
      <organization>Nine by Nine</organization>
      <address><email>GK-IETF@ninebynine.org</email></address>
    </author>
    <author initials="M." surname="Nottingham" fullname="M. Nottingham">
      <organization>BEA Systems</organization>
      <address><email>mnot@pobox.com</email></address>
    </author>
    <author initials="J." surname="Mogul" fullname="J. Mogul">
      <organization>HP Labs</organization>
      <address><email>JeffMogul@acm.org</email></address>
    </author>
    <date year="2004" month="September"/>
  </front>
  <seriesInfo name="BCP" value="90"/>
  <seriesInfo name="RFC" value="3864"/>
</reference>

<reference anchor="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="RFC4288">
  <front>
    <title>Media Type Specifications and Registration Procedures</title>
    <author initials="N." surname="Freed" fullname="N. Freed">
      <organization>Sun Microsystems</organization>
      <address>
        <email>ned.freed@mrochek.com</email>
      </address>
    </author>
    <author initials="J." surname="Klensin" fullname="J. Klensin">
      <address>
        <email>klensin+ietf@jck.com</email>
      </address>
    </author>
    <date year="2005" month="December"/>
  </front>
  <seriesInfo name="BCP" value="13"/>
  <seriesInfo name="RFC" value="4288"/>
</reference>

<reference anchor="RFC4395">
  <front>
    <title>Guidelines and Registration Procedures for New URI Schemes</title>
    <author initials="T." surname="Hansen" fullname="T. Hansen">
      <organization>AT&amp;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">
         <organization/>
      </author>
      <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='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="Vol. 1, #2"/>
</reference>

</references>


<section title="HTTP Version History" anchor="compatibility">
<t>
   HTTP has been in use by the World-Wide Web global information initiative
   since 1990. The first version of HTTP, later referred to as HTTP/0.9,
   was a simple protocol for hypertext data transfer across the Internet
   with 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 that could include metadata about the data
   transferred and modifiers 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 new features that will 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>
   It is beyond the scope of a protocol specification to mandate
   conformance with previous versions. HTTP/1.1 was deliberately
   designed, however, to make supporting previous versions easy.
   We would expect a general-purpose HTTP/1.1 server to understand
   any valid request in the format of HTTP/1.0 and respond appropriately
   with an HTTP/1.1 message that only uses features understood (or
   safely ignored) by HTTP/1.0 clients.  Likewise, we would expect
   an HTTP/1.1 client 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 wherein a buggy client failed to properly encode
   linear whitespace found in a URI reference and placed in
   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 a 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 need 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"/>). Proxies/gateways MUST remove
   any transfer-coding prior to forwarding a message via a MIME-compliant
   protocol.
</t>
</section>

</section>

<section title="Changes from RFC 2616" anchor="changes.from.rfc.2616">
<t>
  Clarify that the string "HTTP" in the HTTP-version ABNF production is case
  sensitive. Restrict the version numbers to be single digits due to the fact
  that implementations are known to handle multi-digit version numbers
  incorrectly.
  (<xref target="http.version"/>)
</t>
<t>
  Require that invalid whitespace around field-names be rejected.
  Change ABNF productions for header fields to only define 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>  
  The NUL octet is no longer allowed in comment and quoted-string
  text. The quoted-pair rule no longer allows escaping control characters other than HTAB.
  Non-ASCII content in header fields and reason phrase has been obsoleted and
  made opaque (the TEXT rule was removed).
  (<xref target="field.components"/>)
</t>
<t>
  Require recipients to handle bogus "<xref target="header.content-length" format="none">Content-Length</xref>" header
  fields as errors.
  (<xref target="message.body"/>)
</t>
<t>
  Remove reference to non-existent identity transfer-coding value tokens.
  (Sections <xref format="counter" target="message.body"/> and
  <xref format="counter" target="transfer.codings"/>)
</t>
<t>
  Clarification that the chunk length does not include the count of the octets
  in the chunk header and trailer. Furthermore disallowed line folding
  in chunk extensions, and deprecate their use.
  (<xref target="chunked.encoding"/>)
</t>
<t>
  Update use of abs_path production from RFC 1808 to the path-absolute + query
  components of RFC 3986. State that the asterisk form is allowed for the OPTIONS
  request method only.
  (<xref target="request-target"/>)
</t>
<t>
  Clarify exactly when "close" connection options have to be sent; drop
  notion of header fields being "hop-by-hop" without being listed in the
  Connection header field.
  (<xref target="header.connection"/>)
</t>
<t>
  Remove hard limit of two connections per server.
  Remove requirement to retry a sequence of requests as long it was idempotent.
  Remove requirements about when servers are allowed to close connections
  prematurely.
  (<xref target="persistent.connections"/>)
</t>
<t>
  Remove requirement to retry requests under certain circumstances when the
  server prematurely closes the connection.
  (<xref target="persistent.reuse"/>)
</t>
<t>
  Define the semantics of the <xref target="header.upgrade" format="none">Upgrade</xref> header field in responses
  other than 101 (this was incorporated from <xref target="RFC2817"/>).
  (<xref target="header.upgrade"/>)
</t>
<t>
  Registration of Transfer Codings now requires IETF Review
  (<xref target="transfer.coding.registry"/>)
</t>
<t>
  Take over the Upgrade Token Registry, previously defined in
  Section 7.2 of <xref target="RFC2817"/>.
  (<xref target="upgrade.token.registry"/>)
</t>
<t>
  Empty list elements in list productions have been deprecated.
  (<xref target="abnf.extension"/>)
</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 "&lt;n&gt;#&lt;m&gt;element" indicating
  at least &lt;n&gt; and at most &lt;m&gt; elements, each separated by a single
  comma (",") and optional whitespace (OWS).   
</t>
<figure><preamble>
  Thus,
</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 &gt;= 1 and m &gt; 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, recipients SHOULD accept empty
  list elements. In other words, consumers would follow the list productions:
</t>
<figure><artwork type="example"><![CDATA[
  #element => [ ( "," / element ) *( OWS "," [ OWS element ] ) ]
  
  1#element => *( "," OWS ) element *( OWS "," [ OWS element ] )
]]></artwork></figure>
<t>
  Note that empty elements do not contribute to the count of elements present,
  though.
</t>
<t>
  For example, given these ABNF productions: 
</t>
<figure><artwork type="example"><![CDATA[
  example-list      = 1#example-list-elmt
  example-list-elmt = token ; see Section 3.2.4 
]]></artwork></figure>
<t>
  Then these 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>
  But these values would be invalid, as at least one non-empty element is
  required:
</t>
<figure><artwork type="example"><![CDATA[
  ""
  ","
  ",   ,"
]]></artwork></figure>
<t>
  <xref target="collected.abnf"/> shows the collected ABNF, with the list rules
  expanded as explained above.
</t>
</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
asterisk-form = "*"
attribute = token
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-str-nf
chunk-size = 1*HEXDIG
chunked-body = *chunk last-chunk trailer-part CRLF
comment = "(" *( ctext / quoted-cpair / comment ) ")"
connection-option = token
ctext = OWS / %x21-27 ; '!'-'''
 / %x2A-5B ; '*'-'['
 / %x5D-7E ; ']'-'~'
 / obs-text

field-content = *( HTAB / SP / VCHAR / obs-text )
field-name = token
field-value = *( field-content / obs-fold )

header-field = field-name ":" OWS field-value BWS
http-URI = "http://" authority path-abempty [ "?" query ]
https-URI = "https://" authority path-abempty [ "?" query ]

last-chunk = 1*"0" [ chunk-ext ] CRLF

message-body = *OCTET
method = token

obs-fold = CRLF ( SP / HTAB )
obs-text = %x80-FF
origin-form = path-absolute [ "?" query ]

partial-URI = relative-part [ "?" query ]
path-abempty = <path-abempty, defined in [RFC3986], Section 3.3>
path-absolute = <path-absolute, 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 = OWS / "!" / %x23-5B ; '#'-'['
 / %x5D-7E ; ']'-'~'
 / obs-text
qdtext-nf = HTAB / SP / "!" / %x23-5B ; '#'-'['
 / %x5D-7E ; ']'-'~'
 / obs-text
query = <query, defined in [RFC3986], Section 3.4>
quoted-cpair = "\" ( HTAB / SP / VCHAR / obs-text )
quoted-pair = "\" ( HTAB / SP / VCHAR / obs-text )
quoted-str-nf = DQUOTE *( qdtext-nf / quoted-pair ) DQUOTE
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

special = "(" / ")" / "<" / ">" / "@" / "," / ";" / ":" / "\" /
 DQUOTE / "/" / "[" / "]" / "?" / "=" / "{" / "}"
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 = attribute BWS "=" BWS value

uri-host = <host, defined in [RFC3986], Section 3.2.2>

value = word

word = token / quoted-string
]]></artwork>
</figure>
</section>


<section title="Change Log (to be removed by RFC Editor before publication)" anchor="change.log">

<section title="Since RFC 2616">
<t>
  Extracted relevant partitions from <xref target="RFC2616"/>.
</t>
</section>

<section title="Since draft-ietf-httpbis-p1-messaging-00">
<t>
  Closed issues:
  <list style="symbols"> 
    <t>
      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/1"/>:
      "HTTP Version should be case sensitive"
      (<eref target="http://purl.org/NET/http-errata#verscase"/>)
    </t>
    <t>
      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/2"/>:
      "'unsafe' characters"
      (<eref target="http://purl.org/NET/http-errata#unsafe-uri"/>)
    </t>
    <t>
      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/3"/>:
      "Chunk Size Definition"
      (<eref target="http://purl.org/NET/http-errata#chunk-size"/>)
    </t>
    <t>
      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/4"/>:
      "Message Length"
      (<eref target="http://purl.org/NET/http-errata#msg-len-chars"/>)
    </t>
    <t>
      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/8"/>:
      "Media Type Registrations"
      (<eref target="http://purl.org/NET/http-errata#media-reg"/>)
    </t>
    <t>
      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/11"/>:
      "URI includes query"
      (<eref target="http://purl.org/NET/http-errata#uriquery"/>)
    </t>
    <t>
      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/15"/>:
      "No close on 1xx responses"
      (<eref target="http://purl.org/NET/http-errata#noclose1xx"/>)
    </t>
    <t>
      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/16"/>:
      "Remove 'identity' token references"
      (<eref target="http://purl.org/NET/http-errata#identity"/>)
    </t>
    <t>
      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/26"/>:
      "Import query BNF"
    </t>
    <t>
      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/31"/>:
      "qdtext BNF"
    </t>
    <t>
      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/35"/>:
      "Normative and Informative references"
    </t>
    <t>
      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/42"/>:
      "RFC2606 Compliance"
    </t>
    <t>
      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/45"/>:
      "RFC977 reference"
    </t>
    <t>
      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/46"/>:
      "RFC1700 references"
    </t>
    <t>
      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/47"/>:
      "inconsistency in date format explanation"
    </t>
    <t>
      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/48"/>:
      "Date reference typo"
    </t>
    <t>
      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/65"/>:
      "Informative references"
    </t>
    <t>
      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/66"/>:
      "ISO-8859-1 Reference"
    </t>
    <t>
      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/86"/>:
      "Normative up-to-date references"
    </t>
  </list>
</t>
<t>
  Other changes:
  <list style="symbols"> 
    <t>
      Update media type registrations to use RFC4288 template.
    </t>
    <t>
      Use names of RFC4234 core rules DQUOTE and HTAB,
      fix broken ABNF for chunk-data
      (work in progress on <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/36"/>)
    </t>
  </list>
</t>
</section>

<section title="Since draft-ietf-httpbis-p1-messaging-01">
<t>
  Closed issues:
  <list style="symbols"> 
    <t>
      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/19"/>:
      "Bodies on GET (and other) requests"
    </t>
    <t>
      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/55"/>:
      "Updating to RFC4288"
    </t>
    <t>
      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/57"/>:
      "Status Code and Reason Phrase"
    </t>
    <t>
      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/82"/>:
      "rel_path not used"
    </t>
  </list>
</t>
<t>
  Ongoing work on ABNF conversion (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/36"/>):
  <list style="symbols"> 
    <t>
      Get rid of duplicate BNF rule names ("host" -&gt; "uri-host", "trailer" -&gt;
      "trailer-part").
    </t>
    <t>
      Avoid underscore character in rule names ("http_URL" -&gt;
      "http-URL", "abs_path" -&gt; "path-absolute").
    </t>
    <t>
      Add rules for terms imported from URI spec ("absoluteURI", "authority",
      "path-absolute", "port", "query", "relativeURI", "host) — these will
      have to be updated when switching over to RFC3986.
    </t>
    <t>
      Synchronize core rules with RFC5234.
    </t>
    <t>
      Get rid of prose rules that span multiple lines.
    </t>
    <t>
      Get rid of unused rules LOALPHA and UPALPHA.
    </t>
    <t>
      Move "Product Tokens" section (back) into Part 1, as "token" is used
      in the definition of the Upgrade header field.
    </t>
    <t>
      Add explicit references to BNF syntax and rules imported from other parts of the specification.
    </t>
    <t>
      Rewrite prose rule "token" in terms of "tchar", rewrite prose rule "TEXT".
    </t>
  </list>
</t>
</section>

<section title="Since draft-ietf-httpbis-p1-messaging-02" anchor="changes.since.02">
<t>
  Closed issues:
  <list style="symbols"> 
    <t>
      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/51"/>:
      "HTTP-date vs. rfc1123-date"
    </t>
    <t>
      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/64"/>:
      "WS in quoted-pair"
    </t>
  </list>
</t>
<t>
  Ongoing work on IANA Message Header Field Registration (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/40"/>):
  <list style="symbols"> 
    <t>
      Reference RFC 3984, and update header field registrations for header
      fields defined in this document.
    </t>
  </list>
</t>
<t>
  Ongoing work on ABNF conversion (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/36"/>):
  <list style="symbols"> 
    <t>
      Replace string literals when the string really is case-sensitive (HTTP-version).
    </t>
  </list>
</t>
</section>

<section title="Since draft-ietf-httpbis-p1-messaging-03" anchor="changes.since.03">
<t>
  Closed issues:
  <list style="symbols"> 
    <t>
      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/28"/>:
      "Connection closing"
    </t>
    <t>
      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/97"/>:
      "Move registrations and registry information to IANA Considerations"
    </t>
    <t>
      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/120"/>:
      "need new URL for PAD1995 reference"
    </t>
    <t>
      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/127"/>:
      "IANA Considerations: update HTTP URI scheme registration"
    </t>
    <t>
      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/128"/>:
      "Cite HTTPS URI scheme definition"
    </t>
    <t>
      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/129"/>:
      "List-type header fields vs Set-Cookie"
    </t>
  </list>
</t>
<t>
  Ongoing work on ABNF conversion (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/36"/>):
  <list style="symbols"> 
    <t>
      Replace string literals when the string really is case-sensitive (HTTP-Date).
    </t>
    <t>
      Replace HEX by HEXDIG for future consistence with RFC 5234's core rules. 
    </t>
  </list>
</t>
</section>

<section title="Since draft-ietf-httpbis-p1-messaging-04" anchor="changes.since.04">
<t>
  Closed issues:
  <list style="symbols"> 
    <t>
      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/34"/>:
      "Out-of-date reference for URIs"
    </t>
    <t>
      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/132"/>:
      "RFC 2822 is updated by RFC 5322"
    </t>
  </list>
</t>
<t>
  Ongoing work on ABNF conversion (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/36"/>):
  <list style="symbols"> 
    <t>
      Use "/" instead of "|" for alternatives.
    </t>
    <t>
      Get rid of RFC822 dependency; use RFC5234 plus extensions instead.
    </t>
    <t>
      Only reference RFC 5234's core rules.
    </t>
    <t>
      Introduce new ABNF rules for "bad" whitespace ("BWS"), optional
      whitespace ("OWS") and required whitespace ("RWS").
    </t>
    <t>
      Rewrite ABNFs to spell out whitespace rules, factor out
      header field value format definitions.
    </t>
  </list>
</t>
</section>

<section title="Since draft-ietf-httpbis-p1-messaging-05" anchor="changes.since.05">
<t>
  Closed issues:
  <list style="symbols"> 
    <t>
      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/30"/>:
      "Header LWS"
    </t>
    <t>
      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/52"/>:
      "Sort 1.3 Terminology"
    </t>
    <t>
      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/63"/>:
      "RFC2047 encoded words"
    </t>
    <t>
      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/74"/>:
      "Character Encodings in TEXT"
    </t>
    <t>
      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/77"/>:
      "Line Folding"
    </t>
    <t>
      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/83"/>:
      "OPTIONS * and proxies"
    </t>
    <t>
      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/94"/>:
      "reason-phrase BNF"
    </t>
    <t>
      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/111"/>:
      "Use of TEXT"
    </t>
    <t>
      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/118"/>:
      "Join "Differences Between HTTP Entities and RFC 2045 Entities"?"
    </t>
    <t>
      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/134"/>:
      "RFC822 reference left in discussion of date formats"
    </t>
  </list>
</t>
<t>
  Final work on ABNF conversion (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/36"/>):
  <list style="symbols"> 
    <t>
      Rewrite definition of list rules, deprecate empty list elements.
    </t>
    <t>
      Add appendix containing collected and expanded ABNF.
    </t>
  </list>
</t>
<t>
  Other changes:
  <list style="symbols"> 
    <t>
      Rewrite introduction; add mostly new Architecture Section.
    </t>
    <t>
      Move definition of quality values from Part 3 into Part 1;
      make TE request header field grammar independent of accept-params (defined in Part 3).
    </t>
  </list>
</t>
</section>

<section title="Since draft-ietf-httpbis-p1-messaging-06" anchor="changes.since.06">
<t>
  Closed issues:
  <list style="symbols"> 
    <t>
      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/161"/>:
      "base for numeric protocol elements"
    </t>
    <t>
      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/162"/>:
      "comment ABNF"
    </t>
  </list>
</t>
<t>
  Partly resolved issues:
  <list style="symbols"> 
    <t>
      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/88"/>:
      "205 Bodies" (took out language that implied that there might be
      methods for which a payload body MUST NOT be included)
    </t>
    <t>
      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/163"/>:
      "editorial improvements around HTTP-date"
    </t>
  </list>
</t>
</section>

<section title="Since draft-ietf-httpbis-p1-messaging-07" anchor="changes.since.07">
<t>
  Closed issues:
  <list style="symbols"> 
    <t>
      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/93"/>:
      "Repeating single-value header fields"
    </t>
    <t>
      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/131"/>:
      "increase connection limit"
    </t>
    <t>
      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/157"/>:
      "IP addresses in URLs"
    </t>
    <t>
      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/172"/>:
      "take over HTTP Upgrade Token Registry"
    </t>
    <t>
      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/173"/>:
      "CR and LF in chunk extension values"
    </t>
    <t>
      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/184"/>:
      "HTTP/0.9 support"
    </t>
    <t>
      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/188"/>:
      "pick IANA policy (RFC5226) for Transfer Coding / Content Coding"
    </t>
    <t>
      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/189"/>:
      "move definitions of gzip/deflate/compress to part 1"
    </t>
    <t>
      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/194"/>:
      "disallow control characters in quoted-pair"
    </t>
  </list>
</t>
<t>
  Partly resolved issues:
  <list style="symbols"> 
    <t>
      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/148"/>:
      "update IANA requirements wrt Transfer-Coding values" (add the
      IANA Considerations subsection)
    </t>
  </list>
</t>
</section>

<section title="Since draft-ietf-httpbis-p1-messaging-08" anchor="changes.since.08">
<t>
  Closed issues:
  <list style="symbols"> 
    <t>
      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/201"/>:
      "header parsing, treatment of leading and trailing OWS"
    </t>
  </list>
</t>
<t>
  Partly resolved issues:
  <list style="symbols"> 
    <t>
      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/60"/>:
      "Placement of 13.5.1 and 13.5.2"
    </t>
    <t>
      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/200"/>:
      "use of term "word" when talking about header field structure"
    </t>
  </list>
</t>
</section>

<section title="Since draft-ietf-httpbis-p1-messaging-09" anchor="changes.since.09">
<t>
  Closed issues:
  <list style="symbols"> 
    <t>
      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/73"/>:
      "Clarification of the term 'deflate'"
    </t>
    <t>
      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/83"/>:
      "OPTIONS * and proxies"
    </t>
    <t>
      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/122"/>:
      "MIME-Version not listed in P1, general header fields"
    </t>
    <t>
      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/143"/>:
      "IANA registry for content/transfer encodings"
    </t>
    <t>
      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/165"/>:
      "Case-sensitivity of HTTP-date"
    </t>
    <t>
      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/200"/>:
      "use of term "word" when talking about header field structure"
    </t>
  </list>
</t>
<t>
  Partly resolved issues:
  <list style="symbols"> 
    <t>
      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/196"/>:
      "Term for the requested resource's URI"
    </t>
  </list>
</t>
</section>

<section title="Since draft-ietf-httpbis-p1-messaging-10" anchor="changes.since.10">
<t>
  Closed issues:
  <list style="symbols">
    <t>
      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/28"/>:
      "Connection Closing"
    </t>
    <t>
      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/90"/>:
      "Delimiting messages with multipart/byteranges"
    </t>
    <t>
      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/95"/>:
      "Handling multiple Content-Length header fields"
    </t>
    <t>
      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/109"/>:
      "Clarify entity / representation / variant terminology"
    </t>
    <t>
      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/220"/>:
      "consider removing the 'changes from 2068' sections"
    </t>
  </list>
</t>
<t>
  Partly resolved issues:
  <list style="symbols"> 
    <t>
      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/159"/>:
      "HTTP(s) URI scheme definitions"
    </t>
  </list>
</t>
</section>

<section title="Since draft-ietf-httpbis-p1-messaging-11" anchor="changes.since.11">
<t>
  Closed issues:
  <list style="symbols">
    <t>
      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/193"/>:
      "Trailer requirements"
    </t>
    <t>
      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/204"/>:
      "Text about clock requirement for caches belongs in p6"
    </t>
    <t>
      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/221"/>:
      "effective request URI: handling of missing host in HTTP/1.0"
    </t>
    <t>
      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/248"/>:
      "confusing Date requirements for clients"
    </t>
  </list>
</t>
<t>
  Partly resolved issues:
  <list style="symbols"> 
    <t>
      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/95"/>:
      "Handling multiple Content-Length header fields"
    </t>
  </list>
</t>
</section>

<section title="Since draft-ietf-httpbis-p1-messaging-12" anchor="changes.since.12">
<t>
  Closed issues:
  <list style="symbols">
    <t>
      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/75"/>:
      "RFC2145 Normative"
    </t>
    <t>
      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/159"/>:
      "HTTP(s) URI scheme definitions" (tune the requirements on userinfo)
    </t>
    <t>
      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/210"/>:
      "define 'transparent' proxy"
    </t>
    <t>
      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/224"/>:
      "Header Field Classification"
    </t>
    <t>
      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/233"/>:
      "Is * usable as a request-uri for new methods?"
    </t>
    <t>
      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/240"/>:
      "Migrate Upgrade details from RFC2817"
    </t>
    <t>
      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/276"/>:
      "untangle ABNFs for header fields"
    </t>
    <t>
      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/279"/>:
      "update RFC 2109 reference"
    </t>
  </list>
</t>
</section>

<section title="Since draft-ietf-httpbis-p1-messaging-13" anchor="changes.since.13">
<t>
  Closed issues:
  <list style="symbols">
    <t>
      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/53"/>:
      "Allow is not in 13.5.2"
    </t>
    <t>
      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/95"/>:
      "Handling multiple Content-Length header fields"
    </t>
    <t>
      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/276"/>:
      "untangle ABNFs for header fields"
    </t>
    <t>
      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/286"/>:
      "Content-Length ABNF broken"
    </t>
  </list>
</t>
</section>

<section title="Since draft-ietf-httpbis-p1-messaging-14" anchor="changes.since.14">
<t>
  Closed issues:
  <list style="symbols">
    <t>
      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/273"/>:
      "HTTP-version should be redefined as fixed length pair of DIGIT . DIGIT"
    </t>
    <t>
      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/282"/>:
      "Recommend minimum sizes for protocol elements"
    </t>
    <t>
      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/283"/>:
      "Set expectations around buffering"
    </t>
    <t>
      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/288"/>:
      "Considering messages in isolation"
    </t>
  </list>
</t>
</section>

<section title="Since draft-ietf-httpbis-p1-messaging-15" anchor="changes.since.15">
<t>
  Closed issues:
  <list style="symbols">
    <t>
      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/100"/>:
      "DNS Spoofing / DNS Binding advice"
    </t>
    <t>
      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/254"/>:
      "move RFCs 2145, 2616, 2817 to Historic status"
    </t>
    <t>
      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/270"/>:
      "\-escaping in quoted strings"
    </t>
    <t>
      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/305"/>:
      "'Close' should be reserved in the HTTP header field registry"
    </t>
  </list>
</t>
</section>

<section title="Since draft-ietf-httpbis-p1-messaging-16" anchor="changes.since.16">
<t>
  Closed issues:
  <list style="symbols">
    <t>
      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/186"/>:
      "Document HTTP's error-handling philosophy"
    </t>
    <t>
      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/215"/>:
      "Explain header field registration"
    </t>
    <t>
      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/219"/>:
      "Revise Acknowledgements Sections"
    </t>
    <t>
      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/297"/>:
      "Retrying Requests"
    </t>
    <t>
      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/318"/>:
      "Closing the connection on server error"
    </t>
  </list>
</t>
</section>

<section title="Since draft-ietf-httpbis-p1-messaging-17" anchor="changes.since.17">
<t>
  Closed issues:
  <list style="symbols">
    <t>
      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/158"/>:
      "Proxy-Connection and Keep-Alive"
    </t>
    <t>
      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/166"/>:
      "Clarify 'User Agent'"
    </t>
    <t>
      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/300"/>:
      "Define non-final responses"
    </t>
    <t>
      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/323"/>:
      "intended maturity level vs normative references"
    </t>
    <t>
      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/324"/>:
      "Intermediary rewriting of queries"
    </t>
  </list>
</t>
</section>

<section title="Since draft-ietf-httpbis-p1-messaging-18" anchor="changes.since.18">
<t>
  Closed issues:
  <list style="symbols">
    <t>
      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/250"/>:
      "message-body in CONNECT response"
    </t>
    <t>
      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/302"/>:
      "Misplaced text on connection handling in p2"
    </t>
    <t>
      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/335"/>:
      "wording of line folding rule"
    </t>
    <t>
      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/343"/>:
      "chunk-extensions"
    </t>
    <t>
      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/346"/>:
      "make IANA policy definitions consistent"
    </t>
  </list>
</t>
</section>

<section title="Since draft-ietf-httpbis-p1-messaging-19" anchor="changes.since.19">
<t>
  Closed issues:
  <list style="symbols">
    <t>
      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/346"/>:
      "make IANA policy definitions consistent"
    </t>
    <t>
      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/359"/>:
      "clarify connection header field values are case-insensitive"
    </t>
    <t>
      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/361"/>:
      "ABNF requirements for recipients"
    </t>
    <t>
      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/368"/>:
      "note introduction of new IANA registries as normative changes"
    </t>
    <t>
      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/374"/>:
      "Reference to ISO-8859-1 is informative"
    </t>
  </list>
</t>
</section>

<section title="Since draft-ietf-httpbis-p1-messaging-20" anchor="changes.since.20">
<t>
  Closed issues:
  <list style="symbols"> 
    <t>
      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/378"/>:
      "is 'q=' case-sensitive?"
    </t>
    <t>
      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/383"/>:
      "Semantics of HTTPS"
    </t>
  </list>
</t>
<t>
  Other changes:
  <list style="symbols">
    <t>
      Drop notion of header fields being "hop-by-hop" without being listed in
      the Connection header field.      
    </t>
    <t>
      Section about connection management rewritten; dropping some historic
      information.
    </t>
    <t>
      Move description of "100-continue" into Part 2.
    </t>
    <t>
      Rewrite the persistent connection and Upgrade requirements to be
      actionable by role and consistent with the rest of HTTP.
    </t>
  </list>
</t>
</section>

</section>

</back>
</rfc>