source: draft-ietf-httpbis/12/draft-ietf-httpbis-p2-semantics-12.xml @ 1051

<?xml version="1.0" encoding="UTF-8"?>
<!--
    This XML document is the output of clean-for-DTD.xslt; a tool that strips
    extensions to RFC2629(bis) from documents for processing with xml2rfc.
-->
<?xml-stylesheet type='text/xsl' href='../myxml2rfc.xslt'?>
<?rfc toc="yes" ?>
<?rfc symrefs="yes" ?>
<?rfc sortrefs="yes" ?>
<?rfc compact="yes"?>
<?rfc subcompact="no" ?>
<?rfc linkmailto="no" ?>
<?rfc editing="no" ?>
<?rfc comments="yes"?>
<?rfc inline="yes"?>
<?rfc rfcedstyle="yes"?>
<!DOCTYPE rfc
  PUBLIC "" "rfc2629.dtd">
<rfc obsoletes="2616" updates="2817" category="std" ipr="pre5378Trust200902" docName="draft-ietf-httpbis-p2-semantics-12">
<front>

  <title abbrev="HTTP/1.1, Part 2">HTTP/1.1, part 2: Message Semantics</title>

  <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
    <organization abbrev="Day Software">Day Software</organization>
    <address>
      <postal>
        <street>23 Corporate Plaza DR, Suite 280</street>
        <city>Newport Beach</city>
        <region>CA</region>
        <code>92660</code>
        <country>USA</country>
      </postal>
      <phone>+1-949-706-5300</phone>
      <facsimile>+1-949-706-5305</facsimile>
      <email>fielding@gbiv.com</email>
      <uri>http://roy.gbiv.com/</uri>
    </address>
  </author>

  <author initials="J." surname="Gettys" fullname="Jim Gettys">
    <organization abbrev="Alcatel-Lucent">Alcatel-Lucent Bell Labs</organization>
    <address>
      <postal>
        <street>21 Oak Knoll Road</street>
        <city>Carlisle</city>
        <region>MA</region>
        <code>01741</code>
        <country>USA</country>
      </postal>
      <email>jg@freedesktop.org</email>
      <uri>http://gettys.wordpress.com/</uri>
    </address>
  </author>
  
  <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
    <organization abbrev="HP">Hewlett-Packard Company</organization>
    <address>
      <postal>
        <street>HP Labs, Large Scale Systems Group</street>
        <street>1501 Page Mill Road, MS 1177</street>
        <city>Palo Alto</city>
        <region>CA</region>
        <code>94304</code>
        <country>USA</country>
      </postal>
      <email>JeffMogul@acm.org</email>
    </address>
  </author>

  <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
    <organization abbrev="Microsoft">Microsoft Corporation</organization>
    <address>
      <postal>
        <street>1 Microsoft Way</street>
        <city>Redmond</city>
        <region>WA</region>
        <code>98052</code>
        <country>USA</country>
      </postal>
      <email>henrikn@microsoft.com</email>
    </address>
  </author>

  <author initials="L." surname="Masinter" fullname="Larry Masinter">
    <organization abbrev="Adobe Systems">Adobe Systems, Incorporated</organization>
    <address>
      <postal>
        <street>345 Park Ave</street>
        <city>San Jose</city>
        <region>CA</region>
        <code>95110</code>
        <country>USA</country>
      </postal>
      <email>LMM@acm.org</email>
      <uri>http://larry.masinter.net/</uri>
    </address>
  </author>
  
  <author initials="P." surname="Leach" fullname="Paul J. Leach">
    <organization abbrev="Microsoft">Microsoft Corporation</organization>
    <address>
      <postal>
        <street>1 Microsoft Way</street>
        <city>Redmond</city>
        <region>WA</region>
        <code>98052</code>
      </postal>
      <email>paulle@microsoft.com</email>
    </address>
  </author>
   
  <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
    <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
    <address>
      <postal>
        <street>MIT Computer Science and Artificial Intelligence Laboratory</street>
        <street>The Stata Center, Building 32</street>
        <street>32 Vassar Street</street>
        <city>Cambridge</city>
        <region>MA</region>
        <code>02139</code>
        <country>USA</country>
      </postal>
      <email>timbl@w3.org</email>
      <uri>http://www.w3.org/People/Berners-Lee/</uri>
    </address>
  </author>

  <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
    <organization abbrev="W3C">World Wide Web Consortium</organization>
    <address>
      <postal>
        <street>W3C / ERCIM</street>
        <street>2004, rte des Lucioles</street>
        <city>Sophia-Antipolis</city>
        <region>AM</region>
        <code>06902</code>
        <country>France</country>
      </postal>
      <email>ylafon@w3.org</email>
      <uri>http://www.raubacapeu.net/people/yves/</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>
      <phone>+49 251 2807760</phone>
      <facsimile>+49 251 2807761</facsimile>
      <email>julian.reschke@greenbytes.de</email>
      <uri>http://greenbytes.de/tech/webdav/</uri>
    </address>
  </author>

  <date month="October" year="2010" day="25"/>
  <workgroup>HTTPbis Working Group</workgroup>

<abstract>
<t>
   The Hypertext Transfer Protocol (HTTP) is an application-level
   protocol for distributed, collaborative, hypermedia information
   systems. HTTP has been in use by the World Wide Web global information
   initiative since 1990. This document is Part 2 of the seven-part specification
   that defines the protocol referred to as "HTTP/1.1" and, taken together,
   obsoletes RFC 2616.  Part 2 defines the semantics of HTTP messages
   as expressed by request methods, request-header fields, response status codes,
   and response-header fields.
</t>
</abstract>

<note title="Editorial Note (To be removed by RFC Editor)">
  <t>
    Discussion of this draft should take place on the HTTPBIS working group
    mailing list (ietf-http-wg@w3.org). 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.11"/>.
  </t>
</note>
</front>
<middle>
<section title="Introduction" anchor="introduction">
<t>
   This document defines HTTP/1.1 request and response semantics.  Each HTTP
   message, as defined in <xref target="Part1"/>, is in the form of either a request or
   a response.  An HTTP server listens on a connection for HTTP requests and
   responds to each request, in the order received on that connection, with
   one or more HTTP response messages.  This document defines the commonly
   agreed upon semantics of the HTTP uniform interface, the intentions defined
   by each request method, and the various response messages that might be
   expected as a result of applying that method to the target resource.
</t>
<t>
   This document is currently disorganized in order to minimize the changes
   between drafts and enable reviewers to see the smaller errata changes.
   A future draft will reorganize the sections to better reflect the content.
   In particular, the sections will be ordered according to the typical
   processing of an HTTP request message (after message parsing): resource
   mapping, general header fields, methods, request modifiers, response
   status, and resource metadata.  The current mess reflects how widely
   dispersed these topics and associated requirements had become in
   <xref target="RFC2616"/>.
</t>

<section title="Requirements" 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>
   An implementation is not compliant if it fails to satisfy one or more
   of the "MUST" or "REQUIRED" level requirements for the protocols it
   implements. An implementation that satisfies all the "MUST" or "REQUIRED"
   level and all the "SHOULD" level requirements for its protocols is said
   to be "unconditionally compliant"; one that satisfies all the "MUST"
   level requirements but not all the "SHOULD" level requirements for its
   protocols is said to be "conditionally compliant".
</t>
</section>

<section title="Syntax Notation" anchor="notation">
  
  
  
  
  
<t>
  This specification uses the ABNF syntax defined in Section 1.2 of <xref target="Part1"/> (which
  extends the syntax defined in <xref target="RFC5234"/> with a list rule).
  <xref target="collected.abnf"/> shows the collected ABNF, with the list
  rule expanded.
</t>
<t>
  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), LF (line feed),
  OCTET (any 8-bit sequence of data), SP (space),
  VCHAR (any visible USASCII character),
  and WSP (whitespace).
</t>

<section title="Core Rules" anchor="core.rules">
  
  
  
  
  
<t>
  The core rules below are defined in Section 1.2.2 of <xref target="Part1"/>:
</t>
<figure><artwork type="abnf2616"><![CDATA[
  quoted-string = <quoted-string, defined in [Part1], Section 1.2.2>
  token         = <token, defined in [Part1], Section 1.2.2>
  OWS           = <OWS, defined in [Part1], Section 1.2.2>
  RWS           = <RWS, defined in [Part1], Section 1.2.2>
  obs-text      = <obs-text, defined in [Part1], Section 1.2.2>
]]></artwork></figure>
</section>

<section title="ABNF Rules defined in other Parts of the Specification" anchor="abnf.dependencies">
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
<t>
  The ABNF rules below are defined in other parts: 
</t>
<figure><artwork type="abnf2616"><![CDATA[
  absolute-URI  = <absolute-URI, defined in [Part1], Section 2.6>
  comment       = <comment, defined in [Part1], Section 3.2>
  Host          = <Host, defined in [Part1], Section 2.6>
  HTTP-date     = <HTTP-date, defined in [Part1], Section 6.1>
  partial-URI   = <partial-URI, defined in [Part1], Section 2.6>
  product       = <product, defined in [Part1], Section 6.3>
  TE            = <TE, defined in [Part1], Section 9.5>
  URI-reference = <URI-reference, defined in [Part1], Section 2.6>
]]></artwork></figure>
<figure><artwork type="abnf2616"><![CDATA[
  Accept        = <Accept, defined in [Part3], Section 6.1>
  Accept-Charset =
             <Accept-Charset, defined in [Part3], Section 6.2>
  Accept-Encoding =
             <Accept-Encoding, defined in [Part3], Section 6.3>
  Accept-Language =
             <Accept-Language, defined in [Part3], Section 6.4>
]]></artwork></figure>
<figure><artwork type="abnf2616"><![CDATA[
  ETag          = <ETag, defined in [Part4], Section 6.1>
  If-Match      = <If-Match, defined in [Part4], Section 6.2>
  If-Modified-Since =
             <If-Modified-Since, defined in [Part4], Section 6.3>
  If-None-Match = <If-None-Match, defined in [Part4], Section 6.4>
  If-Unmodified-Since =
             <If-Unmodified-Since, defined in [Part4], Section 6.5>
]]></artwork></figure>
<figure><artwork type="abnf2616"><![CDATA[
  Accept-Ranges = <Accept-Ranges, defined in [Part5], Section 5.1>
  If-Range      = <If-Range, defined in [Part5], Section 5.3>
  Range         = <Range, defined in [Part5], Section 5.4>
]]></artwork></figure>
<figure><artwork type="abnf2616"><![CDATA[
  Age           = <Age, defined in [Part6], Section 3.1>
  Vary          = <Vary, defined in [Part6], Section 3.5>
]]></artwork></figure>
<figure><artwork type="abnf2616"><![CDATA[
  Authorization = <Authorization, defined in [Part7], Section 4.1>
  Proxy-Authenticate =
             <Proxy-Authenticate, defined in [Part7], Section 4.2>
  Proxy-Authorization =
             <Proxy-Authorization, defined in [Part7], Section 4.3>
  WWW-Authenticate = 
             <WWW-Authenticate, defined in [Part7], Section 4.4>
]]></artwork></figure>
</section>
</section>
</section>

<section title="Method" anchor="method">
  
  
<t>
   The Method token indicates the method to be performed on the target
   resource (Section 4.3 of <xref target="Part1"/>). The method is case-sensitive.
</t>
<figure><iref primary="true" item="Grammar" subitem="Method"/><iref primary="true" item="Grammar" subitem="extension-method"/><artwork type="abnf2616"><![CDATA[
  Method         = %x4F.50.54.49.4F.4E.53   ; "OPTIONS", Section 7.2
                 / %x47.45.54               ; "GET", Section 7.3
                 / %x48.45.41.44            ; "HEAD", Section 7.4
                 / %x50.4F.53.54            ; "POST", Section 7.5
                 / %x50.55.54               ; "PUT", Section 7.6
                 / %x44.45.4C.45.54.45      ; "DELETE", Section 7.7
                 / %x54.52.41.43.45         ; "TRACE", Section 7.8
                 / %x43.4F.4E.4E.45.43.54   ; "CONNECT", Section 7.9
                 / extension-method
  extension-method = token
]]></artwork></figure>
<t>
   The list of methods allowed by a resource can be specified in an
   Allow header field (<xref target="header.allow"/>). The status code of the response
   always notifies the client whether a method is currently allowed on a
   resource, since the set of allowed methods can change dynamically. An
   origin server SHOULD respond with the status code 405 (Method Not Allowed)
   if the method is known by the origin server but not allowed for the
   resource, and 501 (Not Implemented) if the method is
   unrecognized or not implemented by the origin server. The methods GET
   and HEAD MUST be supported by all general-purpose servers. All other
   methods are OPTIONAL; however, if the above methods are implemented,
   they MUST be implemented with the same semantics as those specified
   in <xref target="method.definitions"/>.
</t>

<section title="Method Registry" anchor="method.registry">
<t>
  The HTTP Method Registry defines the name space for the Method token in the
  Request line of an HTTP request.
</t>
<t>
  Registrations MUST include the following fields:
  <list style="symbols">
    <t>Method Name (see <xref target="method"/>)</t>
    <t>Safe ("yes" or "no", see <xref target="safe.methods"/>)</t>
    <t>Pointer to specification text</t>
  </list>
</t>
<t>
  Values to be added to this name space are subject to IETF review
  (<xref target="RFC5226"/>, Section 4.1).
</t>
<t>
  The registry itself is maintained at <eref target="http://www.iana.org/assignments/http-methods"/>.
</t>

<section title="Considerations for New Methods" anchor="considerations.for.new.methods">
<t>
   When it is necessary to express new semantics for a HTTP request that
   aren't specific to a single application or media type, and currently defined
   methods are inadequate, it may be appropriate to register a new method.
</t>
<t>
   HTTP methods are generic; that is, they are potentially applicable to any
   resource, not just one particular media type, "type" of resource, or
   application. As such, it is preferred that new HTTP methods be registered
   in a document that isn't specific to a single application, so that this is
   clear.
</t>
<t>
   Due to the parsing rules defined in Section 3.3 of <xref target="Part1"/>, definitions of HTTP
   methods cannot prohibit the presence of a message-body on either the request
   or the response message (with responses to HEAD requests being the single
   exception). Definitions of new methods cannot change this rule, but they can
   specify that only zero-length bodies (as opposed to absent bodies) are allowed.
</t>
<t>
   New method definitions need to indicate whether they are safe (<xref target="safe.methods"/>) and whether they are idempotent (<xref target="idempotent.methods"/>). They also need to state whether they can be
   cached (<xref target="Part6"/>); in particular what conditions a cache may store the
   response, and under what conditions such a stored response may be used to
   satisfy a subsequent request.
</t>
</section>

</section>
</section>

<section title="Request Header Fields" anchor="request.header.fields">
  
<t>
   The request-header fields allow the client to pass additional
   information about the request, and about the client itself, to the
   server. These fields act as request modifiers, with semantics
   equivalent to the parameters on a programming language method
   invocation.
</t>
<figure><iref primary="true" item="Grammar" subitem="request-header"/><artwork type="abnf2616"><![CDATA[
  request-header = Accept                   ; [Part3], Section 6.1
                 / Accept-Charset           ; [Part3], Section 6.2
                 / Accept-Encoding          ; [Part3], Section 6.3
                 / Accept-Language          ; [Part3], Section 6.4
                 / Authorization            ; [Part7], Section 4.1
                 / Expect                   ; Section 9.2
                 / From                     ; Section 9.3
                 / Host                     ; [Part1], Section 9.4
                 / If-Match                 ; [Part4], Section 6.2
                 / If-Modified-Since        ; [Part4], Section 6.3
                 / If-None-Match            ; [Part4], Section 6.4
                 / If-Range                 ; [Part5], Section 5.3
                 / If-Unmodified-Since      ; [Part4], Section 6.5
                 / Max-Forwards             ; Section 9.5
                 / Proxy-Authorization      ; [Part7], Section 4.3
                 / Range                    ; [Part5], Section 5.4
                 / Referer                  ; Section 9.6
                 / TE                       ; [Part1], Section 9.5
                 / User-Agent               ; Section 9.9
]]></artwork></figure>
<t>
   Request-header field names can be extended reliably only in
   combination with a change in the protocol version. However, new or
   experimental header fields MAY be given the semantics of request-header
   fields if all parties in the communication recognize them to
   be request-header fields.
</t>
</section>

<section title="Status Code and Reason Phrase" anchor="status.code.and.reason.phrase">
  
  
  
<t>
   The Status-Code element is a 3-digit integer result code of the
   attempt to understand and satisfy the request. The status codes listed
   below are defined in <xref target="status.codes"/>, Section 3 of <xref target="Part4"/>,
   Section 3 of <xref target="Part5"/>, and Section 3 of <xref target="Part7"/>.
</t>
<t>
   The Reason-Phrase is intended to give a short
   textual description of the Status-Code. The Status-Code is intended
   for use by automata and the Reason-Phrase is intended for the human
   user. The client is not required to examine or display the Reason-Phrase.
</t>
<t>  
   The individual values of the numeric status codes defined for
   HTTP/1.1, and an example set of corresponding Reason-Phrase values, are
   presented below. The reason phrases listed here are only
   recommendations -- they MAY be replaced by local equivalents without
   affecting the protocol.
</t>
<figure><iref primary="true" item="Grammar" subitem="Status-Code"/><iref primary="true" item="Grammar" subitem="extension-code"/><iref primary="true" item="Grammar" subitem="Reason-Phrase"/><artwork type="abnf2616"><![CDATA[
  Status-Code =
       "100"  ; Section 8.1.1: Continue
     / "101"  ; Section 8.1.2: Switching Protocols
     / "200"  ; Section 8.2.1: OK
     / "201"  ; Section 8.2.2: Created
     / "202"  ; Section 8.2.3: Accepted
     / "203"  ; Section 8.2.4: Non-Authoritative Information
     / "204"  ; Section 8.2.5: No Content
     / "205"  ; Section 8.2.6: Reset Content
     / "206"  ; [Part5], Section 3.1: Partial Content
     / "300"  ; Section 8.3.1: Multiple Choices
     / "301"  ; Section 8.3.2: Moved Permanently
     / "302"  ; Section 8.3.3: Found
     / "303"  ; Section 8.3.4: See Other
     / "304"  ; [Part4], Section 3.1: Not Modified
     / "305"  ; Section 8.3.6: Use Proxy
     / "307"  ; Section 8.3.8: Temporary Redirect
     / "400"  ; Section 8.4.1: Bad Request
     / "401"  ; [Part7], Section 3.1: Unauthorized
     / "402"  ; Section 8.4.3: Payment Required
     / "403"  ; Section 8.4.4: Forbidden
     / "404"  ; Section 8.4.5: Not Found
     / "405"  ; Section 8.4.6: Method Not Allowed
     / "406"  ; Section 8.4.7: Not Acceptable
     / "407"  ; [Part7], Section 3.2: Proxy Authentication Required
     / "408"  ; Section 8.4.9: Request Time-out
     / "409"  ; Section 8.4.10: Conflict
     / "410"  ; Section 8.4.11: Gone
     / "411"  ; Section 8.4.12: Length Required
     / "412"  ; [Part4], Section 3.2: Precondition Failed
     / "413"  ; Section 8.4.14: Request Entity Too Large
     / "414"  ; Section 8.4.15: URI Too Long
     / "415"  ; Section 8.4.16: Unsupported Media Type
     / "416"  ; [Part5], Section 3.2: Requested range not satisfiable
     / "417"  ; Section 8.4.18: Expectation Failed
     / "500"  ; Section 8.5.1: Internal Server Error
     / "501"  ; Section 8.5.2: Not Implemented
     / "502"  ; Section 8.5.3: Bad Gateway
     / "503"  ; Section 8.5.4: Service Unavailable
     / "504"  ; Section 8.5.5: Gateway Time-out
     / "505"  ; Section 8.5.6: HTTP Version not supported
     / extension-code

  extension-code = 3DIGIT
  Reason-Phrase  = *( WSP / VCHAR / obs-text )
]]></artwork></figure>
<t>
   HTTP status codes are extensible. HTTP applications are not required
   to understand the meaning of all registered status codes, though such
   understanding is obviously desirable. However, applications MUST
   understand the class of any status code, as indicated by the first
   digit, and treat any unrecognized response as being equivalent to the
   x00 status code of that class, with the exception that an
   unrecognized response MUST NOT be cached. For example, if an
   unrecognized status code of 431 is received by the client, it can
   safely assume that there was something wrong with its request and
   treat the response as if it had received a 400 status code. In such
   cases, user agents SHOULD present to the user the representation enclosed
   with the response, since that representation is likely to include human-readable
   information which will explain the unusual status.
</t>

<section title="Status Code Registry" anchor="status.code.registry">
<t>
  The HTTP Status Code Registry defines the name space for the Status-Code
  token in the Status-Line of an HTTP response.
</t>
<t>
  Values to be added to this name space are subject to IETF review
  (<xref target="RFC5226"/>, Section 4.1).
</t>
<t>
  The registry itself is maintained at <eref target="http://www.iana.org/assignments/http-status-codes"/>.
</t>

<section title="Considerations for New Status Codes" anchor="considerations.for.new.status.codes">
<t>
   When it is necessary to express new semantics for a HTTP response that
   aren't specific to a single application or media type, and currently defined
   status codes are inadequate, a new status code can be registered.
</t>
<t>
   HTTP status codes are generic; that is, they are potentially applicable to
   any resource, not just one particular media type, "type" of resource, or
   application. As such, it is preferred that new HTTP status codes be
   registered in a document that isn't specific to a single application, so
   that this is clear.
</t>
<t>
   Definitions of new HTTP status codes typically explain the request
   conditions that produce a response containing the status code (e.g.,
   combinations of request headers and/or method(s)), along with any 
   interactions with response headers (e.g., those that are required, those
   that modify the semantics of the response).
</t>
<t>
   New HTTP status codes are required to fall under one of the categories
   defined in <xref target="status.codes"/>. To allow existing parsers to
   properly handle them, new status codes cannot disallow a response body,
   although they can mandate a zero-length response body. They can require the
   presence of one or more particular HTTP response header(s).
</t>
<t>
   Likewise, their definitions can specify that caches are allowed to use
   heuristics to determine their freshness (see <xref target="Part6"/>; by default, it is
   not allowed), and can define how to determine the resource which they
   carry a representation for (see <xref target="identifying.response.associated.with.representation"/>; by default,
   it is anonymous).
</t>
</section>

</section>

</section>

<section title="Response Header Fields" anchor="response.header.fields">
  
<t>
   The response-header fields allow the server to pass additional
   information about the response which cannot be placed in the Status-Line.
   These header fields give information about the server and about
   further access to the target resource (Section 4.3 of <xref target="Part1"/>).
</t>
<figure><iref primary="true" item="Grammar" subitem="response-header"/><artwork type="abnf2616"><![CDATA[
  response-header = Accept-Ranges           ; [Part5], Section 5.1
                  / Age                     ; [Part6], Section 3.1
                  / Allow                   ; Section 9.1
                  / ETag                    ; [Part4], Section 6.1
                  / Location                ; Section 9.4
                  / Proxy-Authenticate      ; [Part7], Section 4.2
                  / Retry-After             ; Section 9.7
                  / Server                  ; Section 9.8
                  / Vary                    ; [Part6], Section 3.5
                  / WWW-Authenticate        ; [Part7], Section 4.4
]]></artwork></figure>
<t>
   Response-header field names can be extended reliably only in
   combination with a change in the protocol version. However, new or
   experimental header fields MAY be given the semantics of response-header
   fields if all parties in the communication recognize them to
   be response-header fields.
</t>
</section>

<section title="Representation" anchor="representation">
<t>
   Request and Response messages MAY transfer a representation if not otherwise
   restricted by the request method or response status code. A representation
   consists of metadata (representation header fields) and data (representation
   body).  When a complete or partial representation is enclosed in an HTTP message,
   it is referred to as the payload of the message. HTTP representations
   are defined in <xref target="Part3"/>.
</t>
<t>
   A representation body is only present in a message when a message-body is
   present, as described in Section 3.3 of <xref target="Part1"/>. The representation body is obtained
   from the message-body by decoding any Transfer-Encoding that might
   have been applied to ensure safe and proper transfer of the message.
</t>

<section title="Identifying the Resource Associated with a Representation" anchor="identifying.response.associated.with.representation">
<t>
   It is sometimes necessary to determine an identifier for the resource
   associated with a representation.
</t>
<t>
   An HTTP request representation, when present, is always associated with an
   anonymous (i.e., unidentified) resource.
</t>
<t>
   In the common case, an HTTP response is a representation of the target
   resource (see Section 4.3 of <xref target="Part1"/>). However, this is not always the
   case. To determine the URI of the resource a response is associated with,
   the following rules are used (with the first applicable one being selected):
</t>
<t><list style="numbers">
   <t>If the response status code is 200 or 203 and the request method was GET,
   the response payload is a representation of the target resource.</t>
   <t>If the response status code is 204, 206, or 304 and the request method was GET
   or HEAD, the response payload is a partial representation of the target
   (see Section 2.8 of <xref target="Part6"/>).</t>
   <t>If the response has a Content-Location header field, and that URI is the same
   as the effective request URI, the response payload is a representation of the
   target resource.</t>
   <t>If the response has a Content-Location header field, and that URI is not the
   same as the effective request URI, then the response asserts that its
   payload is a representation of the resource identified by the
   Content-Location URI. However, such an assertion cannot be trusted unless
   it can be verified by other means (not defined by HTTP).</t>
   <t>Otherwise, the response is a representation of an anonymous (i.e.,
   unidentified) resource.</t>
</list></t>
<t>
  <cref anchor="TODO-req-uri">
   The comparison function is going to have to be defined somewhere,
   because we already need to compare URIs for things like cache invalidation.</cref>
</t>
</section>

</section>


<section title="Method Definitions" anchor="method.definitions">
<t>
   The set of common methods for HTTP/1.1 is defined below. Although
   this set can be expanded, additional methods cannot be assumed to
   share the same semantics for separately extended clients and servers.
</t>

<section title="Safe and Idempotent Methods" anchor="safe.and.idempotent">

<section title="Safe Methods" anchor="safe.methods">
<iref item="Safe Methods" primary="true"/>
<t>
   Implementors need to be aware that the software represents the user in
   their interactions over the Internet, and need to allow
   the user to be aware of any actions they take which might have an
   unexpected significance to themselves or others.
</t>
<t>
   In particular, the convention has been established that the GET, HEAD,
   OPTIONS, and TRACE methods SHOULD NOT have the significance of taking an action
   other than retrieval. These methods ought to be considered "safe".
   This allows user agents to represent other methods, such as POST, PUT
   and DELETE, in a special way, so that the user is made aware of the
   fact that a possibly unsafe action is being requested.
</t>
<t>
   Naturally, it is not possible to ensure that the server does not
   generate side-effects as a result of performing a GET request; in
   fact, some dynamic resources consider that a feature. The important
   distinction here is that the user did not request the side-effects,
   so therefore cannot be held accountable for them.
</t>
</section>

<section title="Idempotent Methods" anchor="idempotent.methods">
<iref item="Idempotent Methods" primary="true"/>
<t>
   Methods can also have the property of "idempotence" in that, aside
   from error or expiration issues, the intended effect of multiple
   identical requests is the same as for a single request.
   The methods PUT, DELETE, and all safe methods are idempotent.
   It is important to note that idempotence refers only to changes
   requested by the client: a server is free to change its state due
   to multiple requests for the purpose of tracking those requests,
   versioning of results, etc.
</t>
</section>
</section>

<section title="OPTIONS" anchor="OPTIONS">
  
  <iref primary="true" item="OPTIONS method"/>
  <iref primary="true" item="Methods" subitem="OPTIONS"/>
<t>
   The OPTIONS method represents a request for information about the
   communication options available on the request/response chain
   identified by the effective request URI. This method allows the client to
   determine the options and/or requirements associated with a resource,
   or the capabilities of a server, without implying a resource action
   or initiating a resource retrieval.
</t>
<t>
   Responses to this method are not cacheable.
</t>
<t>
   If the OPTIONS request includes a message-body (as indicated by the
   presence of Content-Length or Transfer-Encoding), then the media type
   MUST be indicated by a Content-Type field. Although this
   specification does not define any use for such a body, future
   extensions to HTTP might use the OPTIONS body to make more detailed
   queries on the server.
</t>
<t>
   If the request-target is an asterisk ("*"), the OPTIONS request is
   intended to apply to the server in general rather than to a specific
   resource. Since a server's communication options typically depend on
   the resource, the "*" request is only useful as a "ping" or "no-op"
   type of method; it does nothing beyond allowing the client to test
   the capabilities of the server. For example, this can be used to test
   a proxy for HTTP/1.1 compliance (or lack thereof).
</t>
<t>
   If the request-target is not an asterisk, the OPTIONS request applies
   only to the options that are available when communicating with that
   resource.
</t>
<t>
   A 200 response SHOULD include any header fields that indicate
   optional features implemented by the server and applicable to that
   resource (e.g., Allow), possibly including extensions not defined by
   this specification. The response body, if any, SHOULD also include
   information about the communication options. The format for such a
   body is not defined by this specification, but might be defined by
   future extensions to HTTP. Content negotiation MAY be used to select
   the appropriate response format. If no response body is included, the
   response MUST include a Content-Length field with a field-value of
   "0".
</t>
<t>
   The Max-Forwards request-header field MAY be used to target a
   specific proxy in the request chain (see <xref target="header.max-forwards"/>).
   If no Max-Forwards field is present in the request, then the forwarded
   request MUST NOT include a Max-Forwards field.
</t>
</section>

<section title="GET" anchor="GET">
  
  <iref primary="true" item="GET method"/>
  <iref primary="true" item="Methods" subitem="GET"/>
<t>
   The GET method means retrieve whatever information (in the form of a
   representation) currently corresponds to the target resource.
</t>
<t>   
   If the target resource is a data-producing process, it is the
   produced data which shall be returned as the representation in the response and not
   the source text of the process, unless that text happens to be the output of
   the process.
</t>
<t>
   The semantics of the GET method change to a "conditional GET" if the
   request message includes an If-Modified-Since, If-Unmodified-Since,
   If-Match, If-None-Match, or If-Range header field. A conditional GET
   method requests that the representation be transferred only under the
   circumstances described by the conditional header field(s). The
   conditional GET method is intended to reduce unnecessary network
   usage by allowing cached representations to be refreshed without requiring
   multiple requests or transferring data already held by the client.
</t>
<t>
   The semantics of the GET method change to a "partial GET" if the
   request message includes a Range header field. A partial GET requests
   that only part of the representation be transferred, as described in Section 5.4 of <xref target="Part5"/>.
   The partial GET method is intended to reduce unnecessary
   network usage by allowing partially-retrieved representations to be
   completed without transferring data already held by the client.
</t>
<t>
   The response to a GET request is cacheable and MAY be used to satisfy
   subsequent GET and HEAD requests (see <xref target="Part6"/>).
</t>
<t>
   See <xref target="encoding.sensitive.information.in.uris"/> for security considerations when used for forms.
</t>
</section>

<section title="HEAD" anchor="HEAD">
  
  <iref primary="true" item="HEAD method"/>
  <iref primary="true" item="Methods" subitem="HEAD"/>
<t>
   The HEAD method is identical to GET except that the server MUST NOT
   return a message-body in the response. The metadata contained
   in the HTTP header fields in response to a HEAD request SHOULD be identical
   to the information sent in response to a GET request. This method can
   be used for obtaining metadata about the representation implied by the
   request without transferring the representation body. This method is
   often used for testing hypertext links for validity, accessibility,
   and recent modification.
</t>
<t>
   The response to a HEAD request is cacheable and MAY be used to satisfy
   a subsequent HEAD request; see <xref target="Part6"/>. It also MAY be used to update a previously cached
   representation from that resource; if the new field values
   indicate that the cached representation differs from the current representation (as
   would be indicated by a change in Content-Length, Content-MD5, ETag
   or Last-Modified), then the cache MUST treat the cache entry as
   stale.
</t>
</section>

<section title="POST" anchor="POST">
  <iref primary="true" item="POST method"/>
  <iref primary="true" item="Methods" subitem="POST"/>
<t>
   The POST method is used to request that the origin server accept the
   representation enclosed in the request as data to be processed by the 
   target resource. POST is designed to allow a uniform method to cover the
   following functions:
  <list style="symbols">
    <t>
      Annotation of existing resources;
    </t>
    <t>
        Posting a message to a bulletin board, newsgroup, mailing list,
        or similar group of articles;
    </t>
    <t>
        Providing a block of data, such as the result of submitting a
        form, to a data-handling process;
    </t>
    <t>
        Extending a database through an append operation.
    </t>
  </list>
</t>
<t>
   The actual function performed by the POST method is determined by the
   server and is usually dependent on the effective request URI.
</t>
<t>
   The action performed by the POST method might not result in a
   resource that can be identified by a URI. In this case, either 200
   (OK) or 204 (No Content) is the appropriate response status code,
   depending on whether or not the response includes a representation that
   describes the result.
</t>
<t>
   If a resource has been created on the origin server, the response
   SHOULD be 201 (Created) and contain a representation which describes the
   status of the request and refers to the new resource, and a Location
   header field (see <xref target="header.location"/>).
</t>
<t>
   Responses to POST requests are only cacheable when they
   include explicit freshness information (see Section 2.3.1 of <xref target="Part6"/>). A
   cached POST response with a Content-Location header field 
   (see Section 6.7 of <xref target="Part3"/>) whose value is the effective 
   Request URI MAY be used to satisfy subsequent GET and HEAD requests.
</t>
<t>
   Note that POST caching is not widely implemented. 
   However, the 303 (See Other) response can be used to direct the 
   user agent to retrieve a cacheable resource.
</t>
</section>

<section title="PUT" anchor="PUT">
  <iref primary="true" item="PUT method"/>
  <iref primary="true" item="Methods" subitem="PUT"/>
<t>
   The PUT method requests that the enclosed representation be stored at the
   effective request URI. If the effective request URI refers to an already
   existing resource, the enclosed representation SHOULD be considered a
   modified version of the one residing on the origin server. Otherwise, if the
   effective request URI does not point to an existing resource, and that URI is
   capable of being defined as a new resource by the requesting user
   agent, the origin server can create the resource with that URI.
</t>
<t>   
   If a new resource is created at the effective request URI, the origin
   server MUST inform the user agent
   via the 201 (Created) response. If an existing resource is modified,
   either the 200 (OK) or 204 (No Content) response codes SHOULD be sent
   to indicate successful completion of the request.
</t>
<t>   
   If the target resource could not be created or modified, an appropriate
   error response SHOULD be given that reflects the nature of the problem.
   The recipient of the representation MUST NOT ignore any Content-*
   header fields (headers starting with the prefix "Content-") that it does
   not understand or implement
   and MUST return a 501 (Not Implemented) response in such cases.
</t>
<t>
   If the request passes through a cache that has one or more stored
   responses for the effective request URI, those stored responses
   SHOULD be marked as stale if the response to the PUT request
   has a success status code. Responses to the PUT method are 
   not cacheable.
</t>
<t>
   The fundamental difference between the POST and PUT requests is
   reflected in the different meaning of the effective request URI. The URI in a
   POST request identifies the resource that will handle the enclosed
   representation. That resource might be a data-accepting process, a gateway to
   some other protocol, or a document that accepts annotations.
   In contrast, the URI in a PUT request identifies the resource for
   which enclosed representation is a new or replacement value; the
   user agent knows what URI is intended and the server MUST NOT attempt
   to apply the request to some other resource.
   If the server desires that the request be applied to a different URI,
   it MUST send a 301 (Moved Permanently) response; the user agent MAY
   then make its own decision regarding whether or not to redirect the
   request.
</t>
<t>
   A single resource MAY be identified by many different URIs. For
   example, an article might have a URI for identifying "the current
   version" which is separate from the URI identifying each particular
   version. In this case, a PUT request on a general URI might result in
   several other URIs being defined by the origin server.
</t>
<t>
   HTTP/1.1 does not define how a PUT method affects the state of an
   origin server.
</t>
<t>
   Header fields in a PUT request that are recognized as representation
   metadata SHOULD be applied to the resource created or modified by
   the PUT.  Unrecognized header fields SHOULD be ignored.
</t>
</section>

<section title="DELETE" anchor="DELETE">
  <iref primary="true" item="DELETE method"/>
  <iref primary="true" item="Methods" subitem="DELETE"/>
<t>
   The DELETE method requests that the origin server delete the target
   resource. This method MAY be overridden by
   human intervention (or other means) on the origin server. The client cannot
   be guaranteed that the operation has been carried out, even if the
   status code returned from the origin server indicates that the action
   has been completed successfully. However, the server SHOULD NOT 
   indicate success unless, at the time the response is given, it
   intends to delete the resource or move it to an inaccessible
   location.
</t>
<t>
   A successful response SHOULD be 200 (OK) if the response includes an
   representation describing the status, 202 (Accepted) if the action has not
   yet been enacted, or 204 (No Content) if the action has been enacted
   but the response does not include a representation.
</t>
<t>
   If the request passes through a cache and the effective request URI
   identifies one or more currently cached representations, those entries SHOULD be
   treated as stale. Responses to the DELETE method are not cacheable.
</t>
</section>

<section title="TRACE" anchor="TRACE">
  
  <iref primary="true" item="TRACE method"/>
  <iref primary="true" item="Methods" subitem="TRACE"/>
<t>
   The TRACE method is used to invoke a remote, application-layer loop-back
   of the request message. The final recipient of the request
   SHOULD reflect the message received back to the client as the
   message-body of a 200 (OK) response. The final recipient is either the
   origin server or the first proxy or gateway to receive a Max-Forwards
   value of zero (0) in the request (see <xref target="header.max-forwards"/>).
   A TRACE request MUST NOT include a message-body.
</t>
<t>
   TRACE allows the client to see what is being received at the other
   end of the request chain and use that data for testing or diagnostic
   information. The value of the Via header field (Section 9.9 of <xref target="Part1"/>) is of
   particular interest, since it acts as a trace of the request chain.
   Use of the Max-Forwards header field allows the client to limit the
   length of the request chain, which is useful for testing a chain of
   proxies forwarding messages in an infinite loop.
</t>
<t>
   If the request is valid, the response SHOULD have a Content-Type of
   "message/http" (see Section 10.3.1 of <xref target="Part1"/>) and contain a message-body
   that encloses a copy of the entire request message.
   Responses to the TRACE method are not cacheable.
</t>
</section>

<section title="CONNECT" anchor="CONNECT">
  <iref primary="true" item="CONNECT method"/>
  <iref primary="true" item="Methods" subitem="CONNECT"/>
<t>
   This specification reserves the method name CONNECT for use with a
   proxy that can dynamically switch to being a tunnel (e.g., SSL
   tunneling <xref target="RFC2817"/>).
</t>
</section>
</section>


<section title="Status Code Definitions" anchor="status.codes">
<t>
   Each Status-Code is described below, including any metadata required
   in the response.
</t>

<section title="Informational 1xx" anchor="status.1xx">
<t>
   This class of status code indicates a provisional response,
   consisting only of the Status-Line and optional header fields, and is
   terminated by an empty line. There are no required header fields for this
   class of status code. Since HTTP/1.0 did not define any 1xx status
   codes, servers MUST NOT send a 1xx response to an HTTP/1.0 client
   except under experimental conditions.
</t>
<t>
   A client MUST be prepared to accept one or more 1xx status responses
   prior to a regular response, even if the client does not expect a 100
   (Continue) status message. Unexpected 1xx status responses MAY be
   ignored by a user agent.
</t>
<t>
   Proxies MUST forward 1xx responses, unless the connection between the
   proxy and its client has been closed, or unless the proxy itself
   requested the generation of the 1xx response. (For example, if a
   proxy adds a "Expect: 100-continue" field when it forwards a request,
   then it need not forward the corresponding 100 (Continue)
   response(s).)
</t>

<section title="100 Continue" anchor="status.100">
  <iref primary="true" item="100 Continue (status code)"/>
  <iref primary="true" item="Status Codes" subitem="100 Continue"/>
<t>
   The client SHOULD continue with its request. This interim response is
   used to inform the client that the initial part of the request has
   been received and has not yet been rejected by the server. The client
   SHOULD continue by sending the remainder of the request or, if the
   request has already been completed, ignore this response. The server
   MUST send a final response after the request has been completed. See
   Section 7.2.3 of <xref target="Part1"/> for detailed discussion of the use and handling of this
   status code.
</t>
</section>

<section title="101 Switching Protocols" anchor="status.101">
  <iref primary="true" item="101 Switching Protocols (status code)"/>
  <iref primary="true" item="Status Codes" subitem="101 Switching Protocols"/>
<t>
   The server understands and is willing to comply with the client's
   request, via the Upgrade message header field (Section 9.8 of <xref target="Part1"/>), for a
   change in the application protocol being used on this connection. The
   server will switch protocols to those defined by the response's
   Upgrade header field immediately after the empty line which
   terminates the 101 response.
</t>
<t>
   The protocol SHOULD be switched only when it is advantageous to do
   so. For example, switching to a newer version of HTTP is advantageous
   over older versions, and switching to a real-time, synchronous
   protocol might be advantageous when delivering resources that use
   such features.
</t>
</section>
</section>

<section title="Successful 2xx" anchor="status.2xx">
<t>
   This class of status code indicates that the client's request was
   successfully received, understood, and accepted.
</t>

<section title="200 OK" anchor="status.200">
  <iref primary="true" item="200 OK (status code)"/>
  <iref primary="true" item="Status Codes" subitem="200 OK"/>
<t>
   The request has succeeded. The payload returned with the response
   is dependent on the method used in the request, for example:
  <list style="hanging">
    <t hangText="GET">
          a representation of the target resource is sent in the response;
    </t>
    <t hangText="HEAD">
          the same representation as GET, except without the message-body;
    </t>
    <t hangText="POST">
      a representation describing or containing the result of the action;
    </t>
    <t hangText="TRACE">
      a representation containing the request message as received by the
      end server.
    </t>
  </list>
</t>
<t>
   Caches MAY use a heuristic (see Section 2.3.1.1 of <xref target="Part6"/>) to determine 
   freshness for 200 responses.
</t>
</section>

<section title="201 Created" anchor="status.201">
  <iref primary="true" item="201 Created (status code)"/>
  <iref primary="true" item="Status Codes" subitem="201 Created"/>
<t>
   The request has been fulfilled and has resulted in a new resource being
   created. The newly created resource can be referenced by the URI(s)
   returned in the payload of the response, with the most specific URI
   for the resource given by a Location header field. The response
   SHOULD include a payload containing a list of resource
   characteristics and location(s) from which the user or user agent can
   choose the one most appropriate. The payload format is specified by
   the media type given in the Content-Type header field. The origin
   server MUST create the resource before returning the 201 status code.
   If the action cannot be carried out immediately, the server SHOULD
   respond with 202 (Accepted) response instead.
</t>
<t>
   A 201 response MAY contain an ETag response header field indicating
   the current value of the entity-tag for the representation of the resource
   just created (see Section 6.1 of <xref target="Part4"/>).
</t>
</section>

<section title="202 Accepted" anchor="status.202">
  <iref primary="true" item="202 Accepted (status code)"/>
  <iref primary="true" item="Status Codes" subitem="202 Accepted"/>
<t>
   The request has been accepted for processing, but the processing has
   not been completed.  The request might or might not eventually be
   acted upon, as it might be disallowed when processing actually takes
   place. There is no facility for re-sending a status code from an
   asynchronous operation such as this.
</t>
<t>
   The 202 response is intentionally non-committal. Its purpose is to
   allow a server to accept a request for some other process (perhaps a
   batch-oriented process that is only run once per day) without
   requiring that the user agent's connection to the server persist
   until the process is completed. The representation returned with this
   response SHOULD include an indication of the request's current status
   and either a pointer to a status monitor or some estimate of when the
   user can expect the request to be fulfilled.
</t>
</section>

<section title="203 Non-Authoritative Information" anchor="status.203">
  <iref primary="true" item="203 Non-Authoritative Information (status code)"/>
  <iref primary="true" item="Status Codes" subitem="203 Non-Authoritative Information"/>
<t>
   The returned metadata in the header fields is not the
   definitive set as available from the origin server, but is gathered
   from a local or a third-party copy. The set presented MAY be a subset
   or superset of the original version. For example, including local
   annotation information about the resource might result in a superset
   of the metadata known by the origin server. Use of this
   response code is not required and is only appropriate when the
   response would otherwise be 200 (OK).
</t>
<t>
   Caches MAY use a heuristic (see Section 2.3.1.1 of <xref target="Part6"/>) to determine 
   freshness for 203 responses.
</t>

</section>

<section title="204 No Content" anchor="status.204">
  <iref primary="true" item="204 No Content (status code)"/>
  <iref primary="true" item="Status Codes" subitem="204 No Content"/>
<t>
   The server has successfully fulfilled the request, but there is no
   additional content to return in the response payload body.  The
   resource metadata and representation metadata in the response message's
   header fields refer to the target resource
   and its current representation, respectively, after the requested action.
   For example, if a 204 status code is received in response to a PUT
   and the response contains an ETag header field, then the value of
   that field is the current entity-tag for the representation that
   was successfully PUT.
</t>
<t>
   If the client is a user agent, it SHOULD NOT change its document view
   from that which caused the request to be sent. This response is
   primarily intended to allow input for actions to take place without
   causing a change to the user agent's active document view, although
   any new or updated metadata SHOULD be applied to the document
   currently in the user agent's active view.
</t>
<t>
   The 204 response MUST NOT include a message-body, and thus is always
   terminated by the first empty line after the header fields.
</t>
</section>

<section title="205 Reset Content" anchor="status.205">
  <iref primary="true" item="205 Reset Content (status code)"/>
  <iref primary="true" item="Status Codes" subitem="205 Reset Content"/>
<t>
   The server has fulfilled the request and the user agent SHOULD reset
   the document view which caused the request to be sent. This response
   is primarily intended to allow input for actions to take place via
   user input, followed by a clearing of the form in which the input is
   given so that the user can easily initiate another input action. The
   response MUST NOT include a message-body.
</t>
</section>

<section title="206 Partial Content" anchor="status.206">
  <iref primary="true" item="206 Partial Content (status code)"/>
  <iref primary="true" item="Status Codes" subitem="206 Partial Content"/>
  
<t>
   The server has fulfilled the partial GET request for the resource
   and the enclosed payload is a partial representation as defined in Section 3.1 of <xref target="Part5"/>.
</t>
<t>
   Caches MAY use a heuristic (see Section 2.3.1.1 of <xref target="Part6"/>) to determine 
   freshness for 206 responses.
</t>
</section>
</section>

<section title="Redirection 3xx" anchor="status.3xx">
<t>
   This class of status code indicates that further action needs to be
   taken by the user agent in order to fulfill the request.  The action
   required MAY be carried out by the user agent without interaction
   with the user if and only if the method used in the second request is
   known to be "safe", as defined in <xref target="safe.methods"/>.
   A client SHOULD detect infinite redirection loops, since such loops
   generate network traffic for each redirection.
</t>
<t><list>
  <t>
    Note: An earlier version of this specification recommended a
    maximum of five redirections (<xref target="RFC2068"/>, Section 10.3).
    Content developers need to be aware that some clients might
    implement such a fixed limitation.
  </t>
</list></t>

<section title="300 Multiple Choices" anchor="status.300">
  <iref primary="true" item="300 Multiple Choices (status code)"/>
  <iref primary="true" item="Status Codes" subitem="300 Multiple Choices"/>
<t>
   The target resource has more than one
   representation, each with its own specific location, and agent-driven
   negotiation information (Section 5 of <xref target="Part3"/>) is being provided so that
   the user (or user agent) can select a preferred representation by
   redirecting its request to that location.
</t>
<t>
   Unless it was a HEAD request, the response SHOULD include a representation
   containing a list of representation metadata and location(s) from
   which the user or user agent can choose the one most appropriate. The
   data format is specified by the media type given in the Content-Type
   header field. Depending upon the format and the capabilities of
   the user agent, selection of the most appropriate choice MAY be
   performed automatically. However, this specification does not define
   any standard for such automatic selection.
</t>
<t>
   If the server has a preferred choice of representation, it SHOULD
   include the specific URI for that representation in the Location
   field; user agents MAY use the Location field value for automatic
   redirection. 
</t>
<t>
   Caches MAY use a heuristic (see Section 2.3.1.1 of <xref target="Part6"/>) to determine 
   freshness for 300 responses.
</t>

</section>

<section title="301 Moved Permanently" anchor="status.301">
  <iref primary="true" item="301 Moved Permanently (status code)"/>
  <iref primary="true" item="Status Codes" subitem="301 Moved Permanently"/>
<t>
   The target resource has been assigned a new permanent URI and any
   future references to this resource SHOULD use one of the returned
   URIs.  Clients with link editing capabilities ought to automatically
   re-link references to the effective request URI to one or more of the new
   references returned by the server, where possible.
</t>
<t>
   Caches MAY use a heuristic (see Section 2.3.1.1 of <xref target="Part6"/>) to determine 
   freshness for 301 responses.
</t>
<t>
   The new permanent URI SHOULD be given by the Location field in the
   response. Unless the request method was HEAD, the representation of the
   response SHOULD contain a short hypertext note with a hyperlink to
   the new URI(s).
</t>
<t>
   If the 301 status code is received in response to a request method
   that is known to be "safe", as defined in <xref target="safe.methods"/>,
   then the request MAY be automatically redirected by the user agent without
   confirmation.  Otherwise, the user agent MUST NOT automatically redirect the
   request unless it can be confirmed by the user, since this might
   change the conditions under which the request was issued.
</t>
<t><list>
  <t>
    Note: When automatically redirecting a POST request after
    receiving a 301 status code, some existing HTTP/1.0 user agents
    will erroneously change it into a GET request.
  </t>
</list></t>
</section>

<section title="302 Found" anchor="status.302">
  <iref primary="true" item="302 Found (status code)"/>
  <iref primary="true" item="Status Codes" subitem="302 Found"/>
<t>
   The target resource resides temporarily under a different URI.
   Since the redirection might be altered on occasion, the client SHOULD
   continue to use the effective request URI for future requests.
</t>
<t>
   The temporary URI SHOULD be given by the Location field in the
   response. Unless the request method was HEAD, the representation of the
   response SHOULD contain a short hypertext note with a hyperlink to
   the new URI(s).
</t>
<t>
   If the 302 status code is received in response to a request method
   that is known to be "safe", as defined in <xref target="safe.methods"/>,
   then the request MAY be automatically redirected by the user agent without
   confirmation.  Otherwise, the user agent MUST NOT automatically redirect the
   request unless it can be confirmed by the user, since this might
   change the conditions under which the request was issued.
</t>
<t><list>
  <t>
    Note: HTTP/1.0 (<xref target="RFC1945"/>, Section 9.3)
    and the first version of HTTP/1.1 (<xref target="RFC2068"/>, Section 10.3.3)
    specify that the client is not allowed to change the method on the
    redirected request.  However, most existing user agent implementations
    treat 302 as if it were a 303 response, performing a GET on the Location
    field-value regardless of the original request method. Therefore, a 
    previous version of this specification
    (<xref target="RFC2616"/>, Section 10.3.3) has added the 
    status codes
    <xref target="status.303" format="none">303</xref> and
    <xref target="status.307" format="none">307</xref> for servers that wish
    to make unambiguously clear which kind of reaction is expected of the
    client.
  </t>
</list></t>
</section>

<section title="303 See Other" anchor="status.303">
  <iref primary="true" item="303 See Other (status code)"/>
  <iref primary="true" item="Status Codes" subitem="303 See Other"/>
<t>
   The server directs the user agent to a different resource, indicated
   by a URI in the Location header field, that provides an indirect
   response to the original request.  The user agent MAY perform a GET
   request on the URI in the Location field in order to obtain a
   representation corresponding to the response, be redirected again,
   or end with an error status.  The Location URI is not a substitute
   reference for the effective request URI.
</t>
<t>
   The 303 status code is generally applicable to any HTTP method.  It is
   primarily used to allow the output of a POST action to redirect
   the user agent to a selected resource, since doing so provides the
   information corresponding to the POST response in a form that
   can be separately identified, bookmarked, and cached independent
   of the original request.
</t>
<t>
   A 303 response to a GET request indicates that the requested
   resource does not have a representation of its own that can be
   transferred by the server over HTTP.  The Location URI indicates a
   resource that is descriptive of the target resource, such that the
   follow-on representation might be useful to recipients without
   implying that it adequately represents the target resource.
   Note that answers to the questions of what can be represented, what
   representations are adequate, and what might be a useful description
   are outside the scope of HTTP and thus entirely determined by the
   URI owner(s).
</t>
<t>
   Except for responses to a HEAD request, the representation of a 303 
   response SHOULD contain a short hypertext note with a hyperlink 
   to the Location URI.
</t>
</section>

<section title="304 Not Modified" anchor="status.304">
  <iref primary="true" item="304 Not Modified (status code)"/>
  <iref primary="true" item="Status Codes" subitem="304 Not Modified"/>
  
<t>
   The response to the request has not been modified since the conditions
   indicated by the client's conditional GET request, as defined in Section 3.1 of <xref target="Part4"/>.
</t>
</section>

<section title="305 Use Proxy" anchor="status.305">
  <iref primary="true" item="305 Use Proxy (status code)"/>
  <iref primary="true" item="Status Codes" subitem="305 Use Proxy"/>
<t>
   The 305 status code was defined in a previous version of this specification
   (see <xref target="changes.from.rfc.2616"/>), and is now deprecated.
</t>
</section>

<section title="306 (Unused)" anchor="status.306">
  <iref primary="true" item="306 (Unused) (status code)"/>
  <iref primary="true" item="Status Codes" subitem="306 (Unused)"/>
<t>
   The 306 status code was used in a previous version of the
   specification, is no longer used, and the code is reserved.
</t>
</section>

<section title="307 Temporary Redirect" anchor="status.307">
  <iref primary="true" item="307 Temporary Redirect (status code)"/>
  <iref primary="true" item="Status Codes" subitem="307 Temporary Redirect"/>
<t>
   The target resource resides temporarily under a different URI.
   Since the redirection can change over time, the client SHOULD
   continue to use the effective request URI for future requests.
</t>
<t>
   The temporary URI SHOULD be given by the Location field in the
   response. Unless the request method was HEAD, the representation of the
   response SHOULD contain a short hypertext note with a hyperlink to
   the new URI(s), since many pre-HTTP/1.1 user agents do not
   understand the 307 status code. Therefore, the note SHOULD contain the
   information necessary for a user to repeat the original request on
   the new URI.
</t>
<t>
   If the 307 status code is received in response to a request method
   that is known to be "safe", as defined in <xref target="safe.methods"/>,
   then the request MAY be automatically redirected by the user agent without
   confirmation.  Otherwise, the user agent MUST NOT automatically redirect the
   request unless it can be confirmed by the user, since this might
   change the conditions under which the request was issued.
</t>
</section>
</section>

<section title="Client Error 4xx" anchor="status.4xx">
<t>
   The 4xx class of status code is intended for cases in which the
   client seems to have erred. Except when responding to a HEAD request,
   the server SHOULD include a representation containing an explanation of the
   error situation, and whether it is a temporary or permanent
   condition. These status codes are applicable to any request method.
   User agents SHOULD display any included representation to the user.
</t>
<t>
   If the client is sending data, a server implementation using TCP
   SHOULD be careful to ensure that the client acknowledges receipt of
   the packet(s) containing the response, before the server closes the
   input connection. If the client continues sending data to the server
   after the close, the server's TCP stack will send a reset packet to
   the client, which might erase the client's unacknowledged input buffers
   before they can be read and interpreted by the HTTP application.
</t>

<section title="400 Bad Request" anchor="status.400">
  <iref primary="true" item="400 Bad Request (status code)"/>
  <iref primary="true" item="Status Codes" subitem="400 Bad Request"/>
<t>
   The request could not be understood by the server due to malformed
   syntax. The client SHOULD NOT repeat the request without
   modifications.
</t>
</section>

<section title="401 Unauthorized" anchor="status.401">
  <iref primary="true" item="401 Unauthorized (status code)"/>
  <iref primary="true" item="Status Codes" subitem="401 Unauthorized"/>
  
<t>
   The request requires user authentication (see Section 3.1 of <xref target="Part7"/>).
</t>
</section>

<section title="402 Payment Required" anchor="status.402">
  <iref primary="true" item="402 Payment Required (status code)"/>
  <iref primary="true" item="Status Codes" subitem="402 Payment Required"/>
<t>
   This code is reserved for future use.
</t>
</section>

<section title="403 Forbidden" anchor="status.403">
  <iref primary="true" item="403 Forbidden (status code)"/>
  <iref primary="true" item="Status Codes" subitem="403 Forbidden"/>
<t>
   The server understood the request, but is refusing to fulfill it.
   Authorization will not help and the request SHOULD NOT  be repeated.
   If the request method was not HEAD and the server wishes to make
   public why the request has not been fulfilled, it SHOULD describe the
   reason for the refusal in the representation.  If the server does not wish to
   make this information available to the client, the status code 404
   (Not Found) can be used instead.
</t>
</section>

<section title="404 Not Found" anchor="status.404">
  <iref primary="true" item="404 Not Found (status code)"/>
  <iref primary="true" item="Status Codes" subitem="404 Not Found"/>
<t>
   The server has not found anything matching the effective request URI. No
   indication is given of whether the condition is temporary or
   permanent. The 410 (Gone) status code SHOULD be used if the server
   knows, through some internally configurable mechanism, that an old
   resource is permanently unavailable and has no forwarding address.
   This status code is commonly used when the server does not wish to
   reveal exactly why the request has been refused, or when no other
   response is applicable.
</t>
</section>

<section title="405 Method Not Allowed" anchor="status.405">
  <iref primary="true" item="405 Method Not Allowed (status code)"/>
  <iref primary="true" item="Status Codes" subitem="405 Method Not Allowed"/>
<t>
   The method specified in the Request-Line is not allowed for the target
   resource. The response MUST include an
   Allow header field containing a list of valid methods for the requested
   resource.
</t>
</section>

<section title="406 Not Acceptable" anchor="status.406">
  <iref primary="true" item="406 Not Acceptable (status code)"/>
  <iref primary="true" item="Status Codes" subitem="406 Not Acceptable"/>
<t>
   The resource identified by the request is only capable of generating
   response representations which have content characteristics not acceptable
   according to the accept header fields sent in the request.
</t>
<t>
   Unless it was a HEAD request, the response SHOULD include a representation
   containing a list of available representation characteristics and location(s)
   from which the user or user agent can choose the one most
   appropriate. The data format is specified by the media type given
   in the Content-Type header field. Depending upon the format and the
   capabilities of the user agent, selection of the most appropriate
   choice MAY be performed automatically. However, this specification
   does not define any standard for such automatic selection.
</t>
<t><list>
  <t>
    Note: HTTP/1.1 servers are allowed to return responses which are
    not acceptable according to the accept header fields sent in the
    request. In some cases, this might even be preferable to sending a
    406 response. User agents are encouraged to inspect the header fields of
    an incoming response to determine if it is acceptable.
  </t>
</list></t>
<t>
   If the response could be unacceptable, a user agent SHOULD
   temporarily stop receipt of more data and query the user for a
   decision on further actions.
</t>
</section>

<section title="407 Proxy Authentication Required" anchor="status.407">
  <iref primary="true" item="407 Proxy Authentication Required (status code)"/>
  <iref primary="true" item="Status Codes" subitem="407 Proxy Authentication Required"/>
<t>
   This code is similar to 401 (Unauthorized), but indicates that the
   client must first authenticate itself with the proxy (see Section 3.2 of <xref target="Part7"/>).
</t>
</section>

<section title="408 Request Timeout" anchor="status.408">
  <iref primary="true" item="408 Request Timeout (status code)"/>
  <iref primary="true" item="Status Codes" subitem="408 Request Timeout"/>
<t>
   The client did not produce a request within the time that the server
   was prepared to wait. The client MAY repeat the request without
   modifications at any later time.
</t>
</section>

<section title="409 Conflict" anchor="status.409">
  <iref primary="true" item="409 Conflict (status code)"/>
  <iref primary="true" item="Status Codes" subitem="409 Conflict"/>
<t>
   The request could not be completed due to a conflict with the current
   state of the resource. This code is only allowed in situations where
   it is expected that the user might be able to resolve the conflict
   and resubmit the request. The response body SHOULD include enough
   information for the user to recognize the source of the conflict.
   Ideally, the response representation would include enough information for the
   user or user agent to fix the problem; however, that might not be
   possible and is not required.
</t>
<t>
   Conflicts are most likely to occur in response to a PUT request. For
   example, if versioning were being used and the representation being PUT
   included changes to a resource which conflict with those made by an
   earlier (third-party) request, the server might use the 409 response
   to indicate that it can't complete the request. In this case, the
   response representation would likely contain a list of the differences
   between the two versions in a format defined by the response
   Content-Type.
</t>
</section>

<section title="410 Gone" anchor="status.410">
  <iref primary="true" item="410 Gone (status code)"/>
  <iref primary="true" item="Status Codes" subitem="410 Gone"/>
<t>
   The target resource is no longer available at the server and no
   forwarding address is known. This condition is expected to be
   considered permanent. Clients with link editing capabilities SHOULD
   delete references to the effective request URI after user approval. If the
   server does not know, or has no facility to determine, whether or not
   the condition is permanent, the status code 404 (Not Found) SHOULD be
   used instead.
</t>
<t>
   The 410 response is primarily intended to assist the task of web
   maintenance by notifying the recipient that the resource is
   intentionally unavailable and that the server owners desire that
   remote links to that resource be removed. Such an event is common for
   limited-time, promotional services and for resources belonging to
   individuals no longer working at the server's site. It is not
   necessary to mark all permanently unavailable resources as "gone" or
   to keep the mark for any length of time -- that is left to the
   discretion of the server owner.
</t>
<t>
   Caches MAY use a heuristic (see Section 2.3.1.1 of <xref target="Part6"/>) to determine freshness 
   for 410 responses.
</t>

</section>

<section title="411 Length Required" anchor="status.411">
  <iref primary="true" item="411 Length Required (status code)"/>
  <iref primary="true" item="Status Codes" subitem="411 Length Required"/>
<t>
   The server refuses to accept the request without a defined Content-Length.
   The client MAY repeat the request if it adds a valid
   Content-Length header field containing the length of the message-body
   in the request message.
</t>
</section>

<section title="412 Precondition Failed" anchor="status.412">
  <iref primary="true" item="412 Precondition Failed (status code)"/>
  <iref primary="true" item="Status Codes" subitem="412 Precondition Failed"/>
  
<t>
   The precondition given in one or more of the request-header fields
   evaluated to false when it was tested on the server, as defined in
   Section 3.2 of <xref target="Part4"/>.
</t>
</section>

<section title="413 Request Entity Too Large" anchor="status.413">
  <iref primary="true" item="413 Request Entity Too Large (status code)"/>
  <iref primary="true" item="Status Codes" subitem="413 Request Entity Too Large"/>
<t>
   The server is refusing to process a request because the request
   representation is larger than the server is willing or able to process. The
   server MAY close the connection to prevent the client from continuing
   the request.
</t>
<t>
   If the condition is temporary, the server SHOULD include a Retry-After
   header field to indicate that it is temporary and after what
   time the client MAY try again.
</t>
</section>

<section title="414 URI Too Long" anchor="status.414">
  <iref primary="true" item="414 URI Too Long (status code)"/>
  <iref primary="true" item="Status Codes" subitem="414 URI Too Long"/>
<t>
   The server is refusing to service the request because the effective request URI
   is longer than the server is willing to interpret. This rare
   condition is only likely to occur when a client has improperly
   converted a POST request to a GET request with long query
   information, when the client has descended into a URI "black hole" of
   redirection (e.g., a redirected URI prefix that points to a suffix of
   itself), or when the server is under attack by a client attempting to
   exploit security holes present in some servers using fixed-length
   buffers for reading or manipulating the effective request URI.
</t>
</section>

<section title="415 Unsupported Media Type" anchor="status.415">
  <iref primary="true" item="415 Unsupported Media Type (status code)"/>
  <iref primary="true" item="Status Codes" subitem="415 Unsupported Media Type"/>
<t>
   The server is refusing to service the request because the representation of
   the request is in a format not supported by the target resource
   for the requested method.
</t>
</section>

<section title="416 Requested Range Not Satisfiable" anchor="status.416">
  <iref primary="true" item="416 Requested Range Not Satisfiable (status code)"/>
  <iref primary="true" item="Status Codes" subitem="416 Requested Range Not Satisfiable"/>
  
<t>
   The request included a Range request-header field (Section 5.4 of <xref target="Part5"/>) and none of
   the range-specifier values in this field overlap the current extent
   of the selected resource. See Section 3.2 of <xref target="Part5"/>.
</t>
</section>

<section title="417 Expectation Failed" anchor="status.417">
  <iref primary="true" item="417 Expectation Failed (status code)"/>
  <iref primary="true" item="Status Codes" subitem="417 Expectation Failed"/>
<t>
   The expectation given in an Expect request-header field (see <xref target="header.expect"/>)
   could not be met by this server, or, if the server is a proxy,
   the server has unambiguous evidence that the request could not be met
   by the next-hop server.
</t>
</section>
</section>

<section title="Server Error 5xx" anchor="status.5xx">
<t>
   Response status codes beginning with the digit "5" indicate cases in
   which the server is aware that it has erred or is incapable of
   performing the request. Except when responding to a HEAD request, the
   server SHOULD include a representation containing an explanation of the
   error situation, and whether it is a temporary or permanent
   condition. User agents SHOULD display any included representation to the
   user. These response codes are applicable to any request method.
</t>

<section title="500 Internal Server Error" anchor="status.500">
  <iref primary="true" item="500 Internal Server Error (status code)"/>
  <iref primary="true" item="Status Codes" subitem="500 Internal Server Error"/>
<t>
   The server encountered an unexpected condition which prevented it
   from fulfilling the request.
</t>
</section>

<section title="501 Not Implemented" anchor="status.501">
  <iref primary="true" item="501 Not Implemented (status code)"/>
  <iref primary="true" item="Status Codes" subitem="501 Not Implemented"/>
<t>
   The server does not support the functionality required to fulfill the
   request. This is the appropriate response when the server does not
   recognize the request method and is not capable of supporting it for
   any resource.
</t>
</section>

<section title="502 Bad Gateway" anchor="status.502">
  <iref primary="true" item="502 Bad Gateway (status code)"/>
  <iref primary="true" item="Status Codes" subitem="502 Bad Gateway"/>
<t>
   The server, while acting as a gateway or proxy, received an invalid
   response from the upstream server it accessed in attempting to
   fulfill the request.
</t>
</section>

<section title="503 Service Unavailable" anchor="status.503">
  <iref primary="true" item="503 Service Unavailable (status code)"/>
  <iref primary="true" item="Status Codes" subitem="503 Service Unavailable"/>
<t>
   The server is currently unable to handle the request due to a
   temporary overloading or maintenance of the server. The implication
   is that this is a temporary condition which will be alleviated after
   some delay. If known, the length of the delay MAY be indicated in a
   Retry-After header field. If no Retry-After is given, the client SHOULD
   handle the response as it would for a 500 response.
</t>
<t><list>
  <t>
    Note: The existence of the 503 status code does not imply that a
    server must use it when becoming overloaded. Some servers might wish
    to simply refuse the connection.
  </t>
</list></t>
</section>

<section title="504 Gateway Timeout" anchor="status.504">
  <iref primary="true" item="504 Gateway Timeout (status code)"/>
  <iref primary="true" item="Status Codes" subitem="504 Gateway Timeout"/>
<t>
   The server, while acting as a gateway or proxy, did not receive a
   timely response from the upstream server specified by the URI (e.g.,
   HTTP, FTP, LDAP) or some other auxiliary server (e.g., DNS) it needed
   to access in attempting to complete the request.
</t>
<t><list>
  <t>
    Note to implementors: some deployed proxies are known to
    return 400 or 500 when DNS lookups time out.
  </t>
</list></t>
</section>

<section title="505 HTTP Version Not Supported" anchor="status.505">
  <iref primary="true" item="505 HTTP Version Not Supported (status code)"/>
  <iref primary="true" item="Status Codes" subitem="505 HTTP Version Not Supported"/>
<t>
   The server does not support, or refuses to support, the protocol
   version that was used in the request message. The server is
   indicating that it is unable or unwilling to complete the request
   using the same major version as the client, as described in Section 2.5 of <xref target="Part1"/>,
   other than with this error message. The response SHOULD contain
   a representation describing why that version is not supported and what other
   protocols are supported by that server.
</t>

</section>
</section>
</section>


<section title="Header Field Definitions" anchor="header.fields">
<t>
   This section defines the syntax and semantics of HTTP/1.1 header fields
   related to request and response semantics.
</t>

<section title="Allow" anchor="header.allow">
  <iref primary="true" item="Allow header"/>
  <iref primary="true" item="Headers" subitem="Allow"/>
  
  
<t>
   The "Allow" response-header field lists the set of methods advertised as
   supported by the target resource. The purpose of
   this field is strictly to inform the recipient of valid methods
   associated with the resource.
</t>
<figure><iref primary="true" item="Grammar" subitem="Allow"/><iref primary="true" item="Grammar" subitem="Allow-v"/><artwork type="abnf2616"><![CDATA[
  Allow   = "Allow" ":" OWS Allow-v
  Allow-v = #Method
]]></artwork></figure>
<t>
      Example of use:
</t>
<figure><artwork type="example"><![CDATA[
  Allow: GET, HEAD, PUT
]]></artwork></figure>
<t>
      The actual set of allowed methods is defined
      by the origin server at the time of each request.
</t>
<t>
      A proxy MUST NOT modify the Allow header field even if it does not
      understand all the methods specified, since the user agent might
      have other means of communicating with the origin server.
</t>
</section>

<section title="Expect" anchor="header.expect">
  <iref primary="true" item="Expect header"/>
  <iref primary="true" item="Headers" subitem="Expect"/>
  
  
  
  
  
<t>
   The "Expect" request-header field is used to indicate that particular
   server behaviors are required by the client.
</t>
<figure><iref primary="true" item="Grammar" subitem="Expect"/><iref primary="true" item="Grammar" subitem="Expect-v"/><iref primary="true" item="Grammar" subitem="expectation"/><iref primary="true" item="Grammar" subitem="expectation-extension"/><iref primary="true" item="Grammar" subitem="expect-params"/><artwork type="abnf2616"><![CDATA[
  Expect       = "Expect" ":" OWS Expect-v
  Expect-v     = 1#expectation
  
  expectation  = "100-continue" / expectation-extension
  expectation-extension = token [ "=" ( token / quoted-string )
                           *expect-params ]
  expect-params = ";" token [ "=" ( token / quoted-string ) ]
]]></artwork></figure>
<t>
   A server that does not understand or is unable to comply with any of
   the expectation values in the Expect field of a request MUST respond
   with appropriate error status code. The server MUST respond with a 417
   (Expectation Failed) status code if any of the expectations cannot be met
   or, if there are other problems with the request, some other 4xx
   status code.
</t>
<t>
   This header field is defined with extensible syntax to allow for
   future extensions. If a server receives a request containing an
   Expect field that includes an expectation-extension that it does not
   support, it MUST respond with a 417 (Expectation Failed) status code.
</t>
<t>
   Comparison of expectation values is case-insensitive for unquoted
   tokens (including the 100-continue token), and is case-sensitive for
   quoted-string expectation-extensions.
</t>
<t>
   The Expect mechanism is hop-by-hop: that is, an HTTP/1.1 proxy MUST
   return a 417 (Expectation Failed) status code if it receives a request
   with an expectation that it cannot meet. However, the Expect
   request-header field itself is end-to-end; it MUST be forwarded if the
   request is forwarded.
</t>
<t>
   Many older HTTP/1.0 and HTTP/1.1 applications do not understand the
   Expect header field.
</t>
<t>
   See Section 7.2.3 of <xref target="Part1"/> for the use of the 100 (Continue) status code.
</t>
</section>

<section title="From" anchor="header.from">
  <iref primary="true" item="From header"/>
  <iref primary="true" item="Headers" subitem="From"/>
  
  
  
<t>
   The "From" request-header field, if given, SHOULD contain an Internet
   e-mail address for the human user who controls the requesting user
   agent. The address SHOULD be machine-usable, as defined by "mailbox"
   in Section 3.4 of <xref target="RFC5322"/>:
</t>
<figure><iref primary="true" item="Grammar" subitem="From"/><iref primary="true" item="Grammar" subitem="From-v"/><artwork type="abnf2616"><![CDATA[
  From    = "From" ":" OWS From-v
  From-v  = mailbox
  
  mailbox = <mailbox, defined in [RFC5322], Section 3.4>
]]></artwork></figure>
<t>
   An example is:
</t>
<figure><artwork type="example"><![CDATA[
  From: webmaster@example.org
]]></artwork></figure>
<t>
   This header field MAY be used for logging purposes and as a means for
   identifying the source of invalid or unwanted requests. It SHOULD NOT 
   be used as an insecure form of access protection. The interpretation
   of this field is that the request is being performed on behalf of the
   person given, who accepts responsibility for the method performed. In
   particular, robot agents SHOULD include this header field so that the
   person responsible for running the robot can be contacted if problems
   occur on the receiving end.
</t>
<t>
   The Internet e-mail address in this field MAY be separate from the
   Internet host which issued the request. For example, when a request
   is passed through a proxy the original issuer's address SHOULD be
   used.
</t>
<t>
   The client SHOULD NOT  send the From header field without the user's
   approval, as it might conflict with the user's privacy interests or
   their site's security policy. It is strongly recommended that the
   user be able to disable, enable, and modify the value of this field
   at any time prior to a request.
</t>
</section>

<section title="Location" anchor="header.location">
  <iref primary="true" item="Location header"/>
  <iref primary="true" item="Headers" subitem="Location"/>
  
  
<t>
   The "Location" response-header field is used to identify a newly created
   resource, or to redirect the recipient to a different location for
   completion of the request.
</t>
<t>
   For 201 (Created) responses, the Location is the URI of the new resource
   which was created by the request. For 3xx responses, the location SHOULD
   indicate the server's preferred URI for automatic redirection to the
   resource.
</t>
<t>
   The field value consists of a single URI-reference. When it has the form
   of a relative reference (<xref target="RFC3986"/>, Section 4.2),
   the final value is computed by resolving it against the effective request
   URI (<xref target="RFC3986"/>, Section 5).
</t>
<figure><iref primary="true" item="Grammar" subitem="Location"/><iref primary="true" item="Grammar" subitem="Location-v"/><artwork type="abnf2616"><![CDATA[
  Location       = "Location" ":" OWS Location-v
  Location-v     = URI-reference
]]></artwork></figure>
<figure>
<preamble>Examples are:</preamble><!--DO NOT DARE changing the vertical WSP below, it's necessary this way for xml2rfc-->
<artwork type="example"><![CDATA[
  Location: http://www.example.org/pub/WWW/People.html#tim
]]></artwork></figure><figure><artwork type="example"><![CDATA[  Location: /index.html
]]></artwork></figure>
<t>
   There are circumstances in which a fragment identifier in a Location URI
   would not be appropriate:
   <list style="symbols">
      <t>With a 201 Created response, because in this usage the Location header
      field specifies the URI for the entire created resource.</t>
      <t>With 305 Use Proxy.</t>
   </list>
</t>
<t><list>
  <t>
    Note: This specification does not define precedence rules
    for the case where the original URI, as navigated to by the user
    agent, and the Location header field value both contain fragment
    identifiers.
  </t>
</list></t>
<t><list>
  <t>
    Note: The Content-Location header field (Section 6.7 of <xref target="Part3"/>) differs
    from Location in that the Content-Location identifies the most specific
    resource corresponding to the enclosed representation.
    It is therefore possible for a response to contain header fields for
    both Location and Content-Location.
  </t>
</list></t>
</section>

<section title="Max-Forwards" anchor="header.max-forwards">
  <iref primary="true" item="Max-Forwards header"/>
  <iref primary="true" item="Headers" subitem="Max-Forwards"/>
  
  
<t>
   The "Max-Forwards" request-header field provides a mechanism with the
   TRACE (<xref target="TRACE"/>) and OPTIONS (<xref target="OPTIONS"/>)
   methods to limit the number of times that the request is forwarded by
   proxies or gateways. This can be useful when the client is attempting to
   trace a request which appears to be failing or looping in mid-chain.
</t>
<figure><iref primary="true" item="Grammar" subitem="Max-Forwards"/><iref primary="true" item="Grammar" subitem="Max-Forwards-v"/><artwork type="abnf2616"><![CDATA[
  Max-Forwards   = "Max-Forwards" ":" OWS Max-Forwards-v
  Max-Forwards-v = 1*DIGIT
]]></artwork></figure>
<t>
   The Max-Forwards value is a decimal integer indicating the remaining
   number of times this request message can be forwarded.
</t>
<t>
   Each proxy or gateway recipient of a TRACE or OPTIONS request
   containing a Max-Forwards header field MUST check and update its
   value prior to forwarding the request. If the received value is zero
   (0), the recipient MUST NOT forward the request; instead, it MUST
   respond as the final recipient. If the received Max-Forwards value is
   greater than zero, then the forwarded message MUST contain an updated
   Max-Forwards field with a value decremented by one (1).
</t>
<t>
   The Max-Forwards header field MAY be ignored for all other methods
   defined by this specification and for any extension methods for which
   it is not explicitly referred to as part of that method definition.
</t>
</section>

<section title="Referer" anchor="header.referer">
  <iref primary="true" item="Referer header"/>
  <iref primary="true" item="Headers" subitem="Referer"/>
  
  
<t>
   The "Referer" [sic] request-header field allows the client to specify the
   URI of the resource from which the effective request URI was obtained (the
   "referrer", although the header field is misspelled.).
</t>
<t>
   The Referer header field allows servers to generate lists of back-links to
   resources for interest, logging, optimized caching, etc. It also allows
   obsolete or mistyped links to be traced for maintenance. Some servers use
   Referer as a means of controlling where they allow links from (so-called
   "deep linking"), but legitimate requests do not always
   contain a Referer header field.
</t>
<t>
   If the effective request URI was obtained from a source that does not have its own
   URI (e.g., input from the user keyboard), the Referer field MUST either be
   sent with the value "about:blank", or not be sent at all. Note that this
   requirement does not apply to sources with non-HTTP URIs (e.g., FTP).
</t>
<figure><iref primary="true" item="Grammar" subitem="Referer"/><iref primary="true" item="Grammar" subitem="Referer-v"/><artwork type="abnf2616"><![CDATA[
  Referer        = "Referer" ":" OWS Referer-v
  Referer-v      = absolute-URI / partial-URI
]]></artwork></figure>
<t>
   Example:
</t>
<figure><artwork type="example"><![CDATA[
  Referer: http://www.example.org/hypertext/Overview.html
]]></artwork></figure>
<t>
   If the field value is a relative URI, it SHOULD be interpreted
   relative to the effective request URI. The URI MUST NOT include a fragment. See
   <xref target="encoding.sensitive.information.in.uris"/> for security considerations.
</t>
</section>

<section title="Retry-After" anchor="header.retry-after">
  <iref primary="true" item="Retry-After header"/>
  <iref primary="true" item="Headers" subitem="Retry-After"/>
  
  
<t>
   The response-header "Retry-After" field can be used with a 503 (Service
   Unavailable) response to indicate how long the service is expected to
   be unavailable to the requesting client. This field MAY also be used
   with any 3xx (Redirection) response to indicate the minimum time the
   user-agent is asked wait before issuing the redirected request.
</t>
<t>
   The value of this field can be either an HTTP-date or an integer number
   of seconds (in decimal) after the time of the response.
</t>
<figure><iref primary="true" item="Grammar" subitem="Retry-After"/><iref primary="true" item="Grammar" subitem="Retry-After-v"/><artwork type="abnf2616"><![CDATA[
  Retry-After   = "Retry-After" ":" OWS Retry-After-v
  Retry-After-v = HTTP-date / delta-seconds
]]></artwork></figure>
<t anchor="rule.delta-seconds">
  
   Time spans are non-negative decimal integers, representing time in
   seconds.
</t>
<figure><iref primary="true" item="Grammar" subitem="delta-seconds"/><artwork type="abnf2616"><![CDATA[
  delta-seconds  = 1*DIGIT
]]></artwork></figure>
<t>
   Two examples of its use are
</t>
<figure><artwork type="example"><![CDATA[
  Retry-After: Fri, 31 Dec 1999 23:59:59 GMT
  Retry-After: 120
]]></artwork></figure>
<t>
   In the latter example, the delay is 2 minutes.
</t>
</section>

<section title="Server" anchor="header.server">
  <iref primary="true" item="Server header"/>
  <iref primary="true" item="Headers" subitem="Server"/>
  
  
<t>
   The "Server" response-header field contains information about the
   software used by the origin server to handle the request.
</t>
<t>
   The field can contain multiple product tokens (Section 6.3 of <xref target="Part1"/>) and
   comments (Section 3.2 of <xref target="Part1"/>) identifying the server and any significant
   subproducts. The product tokens are listed in order of their significance
   for identifying the application.
</t>
<figure><iref primary="true" item="Grammar" subitem="Server"/><iref primary="true" item="Grammar" subitem="Server-v"/><artwork type="abnf2616"><![CDATA[
  Server         = "Server" ":" OWS Server-v
  Server-v       = product
                   *( RWS ( product / comment ) )
]]></artwork></figure>
<t>
   Example:
</t>
<figure><artwork type="example"><![CDATA[
  Server: CERN/3.0 libwww/2.17
]]></artwork></figure>
<t>
   If the response is being forwarded through a proxy, the proxy
   application MUST NOT modify the Server response-header field. Instead, it
   MUST include a Via field (as described in Section 9.9 of <xref target="Part1"/>).
</t>
<t><list>
  <t>
    Note: Revealing the specific software version of the server might
    allow the server machine to become more vulnerable to attacks
    against software that is known to contain security holes. Server
    implementors are encouraged to make this field a configurable
    option.
  </t>
</list></t>
</section>

<section title="User-Agent" anchor="header.user-agent">
  <iref primary="true" item="User-Agent header"/>
  <iref primary="true" item="Headers" subitem="User-Agent"/>
  
  
<t>
   The "User-Agent" request-header field contains information about the user
   agent originating the request. User agents SHOULD include this field with
   requests.
</t>
<t>
   Typically, it is used for statistical purposes, the tracing of protocol
   violations, and tailoring responses to avoid particular user agent
   limitations.
</t>
<t>
   The field can contain multiple product tokens (Section 6.3 of <xref target="Part1"/>)
   and comments (Section 3.2 of <xref target="Part1"/>) identifying the agent and its
   significant subproducts. By convention, the product tokens are listed in
   order of their significance for identifying the application.
</t>
<t>
   Because this field is usually sent on every request a user agent makes,
   implementations are encouraged not to include needlessly fine-grained
   detail, and to limit (or even prohibit) the addition of subproducts by third
   parties. Overly long and detailed User-Agent field values make requests
   larger and can also be used to identify ("fingerprint") the user against
   their wishes.
</t>
<t>
   Likewise, implementations are encouraged not to use the product tokens of
   other implementations in order to declare compatibility with them, as this
   circumvents the purpose of the field. Finally, they are encouraged not to
   use comments to identify products; doing so makes the field value more
   difficult to parse.
</t>
<figure><iref primary="true" item="Grammar" subitem="User-Agent"/><iref primary="true" item="Grammar" subitem="User-Agent-v"/><artwork type="abnf2616"><![CDATA[
  User-Agent     = "User-Agent" ":" OWS User-Agent-v
  User-Agent-v   = product
                   *( RWS ( product / comment ) )
]]></artwork></figure>
<t>
   Example:
</t>
<figure><artwork type="example"><![CDATA[
  User-Agent: CERN-LineMode/2.15 libwww/2.17b3
]]></artwork></figure>
</section>

</section>

<section title="IANA Considerations" anchor="IANA.considerations">

<section title="Method Registry" anchor="method.registration">
<t>
  The registration procedure for HTTP Methods is defined by 
  <xref target="method.registry"/> of this document.
</t>
<t>
   The HTTP Method Registry shall be created at <eref target="http://www.iana.org/assignments/http-methods"/>
   and be populated with the registrations below:
</t>

<!--AUTOGENERATED FROM extract-method-defs.xslt, do not edit manually-->
<texttable align="left" suppress-title="true" anchor="iana.method.registration.table">
   <ttcol>Method</ttcol>
   <ttcol>Safe</ttcol>
   <ttcol>Reference</ttcol>
   <c>CONNECT</c>
   <c>no</c>
   <c>
      <xref target="CONNECT"/>
   </c>
   <c>DELETE</c>
   <c>no</c>
   <c>
      <xref target="DELETE"/>
   </c>
   <c>GET</c>
   <c>yes</c>
   <c>
      <xref target="GET"/>
   </c>
   <c>HEAD</c>
   <c>yes</c>
   <c>
      <xref target="HEAD"/>
   </c>
   <c>OPTIONS</c>
   <c>yes</c>
   <c>
      <xref target="OPTIONS"/>
   </c>
   <c>POST</c>
   <c>no</c>
   <c>
      <xref target="POST"/>
   </c>
   <c>PUT</c>
   <c>no</c>
   <c>
      <xref target="PUT"/>
   </c>
   <c>TRACE</c>
   <c>yes</c>
   <c>
      <xref target="TRACE"/>
   </c>
</texttable>
<!--(END)-->

</section>

<section title="Status Code Registry" anchor="status.code.registration">
<t>
   The registration procedure for HTTP Status Codes -- previously defined
   in Section 7.1 of <xref target="RFC2817"/> -- is now defined
   by <xref target="status.code.registry"/> of this document.
</t>
<t>
   The HTTP Status Code Registry located at <eref target="http://www.iana.org/assignments/http-status-codes"/>
   shall be updated with the registrations below:
</t>

<!--AUTOGENERATED FROM extract-status-code-defs.xslt, do not edit manually-->
<texttable align="left" suppress-title="true" anchor="iana.status.code.registration.table">
   <ttcol>Value</ttcol>
   <ttcol>Description</ttcol>
   <ttcol>Reference</ttcol>
   <c>100</c>
   <c>Continue</c>
   <c>
      <xref target="status.100"/>
   </c>
   <c>101</c>
   <c>Switching Protocols</c>
   <c>
      <xref target="status.101"/>
   </c>
   <c>200</c>
   <c>OK</c>
   <c>
      <xref target="status.200"/>
   </c>
   <c>201</c>
   <c>Created</c>
   <c>
      <xref target="status.201"/>
   </c>
   <c>202</c>
   <c>Accepted</c>
   <c>
      <xref target="status.202"/>
   </c>
   <c>203</c>
   <c>Non-Authoritative Information</c>
   <c>
      <xref target="status.203"/>
   </c>
   <c>204</c>
   <c>No Content</c>
   <c>
      <xref target="status.204"/>
   </c>
   <c>205</c>
   <c>Reset Content</c>
   <c>
      <xref target="status.205"/>
   </c>
   <c>300</c>
   <c>Multiple Choices</c>
   <c>
      <xref target="status.300"/>
   </c>
   <c>301</c>
   <c>Moved Permanently</c>
   <c>
      <xref target="status.301"/>
   </c>
   <c>302</c>
   <c>Found</c>
   <c>
      <xref target="status.302"/>
   </c>
   <c>303</c>
   <c>See Other</c>
   <c>
      <xref target="status.303"/>
   </c>
   <c>305</c>
   <c>Use Proxy</c>
   <c>
      <xref target="status.305"/>
   </c>
   <c>306</c>
   <c>(Unused)</c>
   <c>
      <xref target="status.306"/>
   </c>
   <c>307</c>
   <c>Temporary Redirect</c>
   <c>
      <xref target="status.307"/>
   </c>
   <c>400</c>
   <c>Bad Request</c>
   <c>
      <xref target="status.400"/>
   </c>
   <c>402</c>
   <c>Payment Required</c>
   <c>
      <xref target="status.402"/>
   </c>
   <c>403</c>
   <c>Forbidden</c>
   <c>
      <xref target="status.403"/>
   </c>
   <c>404</c>
   <c>Not Found</c>
   <c>
      <xref target="status.404"/>
   </c>
   <c>405</c>
   <c>Method Not Allowed</c>
   <c>
      <xref target="status.405"/>
   </c>
   <c>406</c>
   <c>Not Acceptable</c>
   <c>
      <xref target="status.406"/>
   </c>
   <c>407</c>
   <c>Proxy Authentication Required</c>
   <c>
      <xref target="status.407"/>
   </c>
   <c>408</c>
   <c>Request Timeout</c>
   <c>
      <xref target="status.408"/>
   </c>
   <c>409</c>
   <c>Conflict</c>
   <c>
      <xref target="status.409"/>
   </c>
   <c>410</c>
   <c>Gone</c>
   <c>
      <xref target="status.410"/>
   </c>
   <c>411</c>
   <c>Length Required</c>
   <c>
      <xref target="status.411"/>
   </c>
   <c>413</c>
   <c>Request Entity Too Large</c>
   <c>
      <xref target="status.413"/>
   </c>
   <c>414</c>
   <c>URI Too Long</c>
   <c>
      <xref target="status.414"/>
   </c>
   <c>415</c>
   <c>Unsupported Media Type</c>
   <c>
      <xref target="status.415"/>
   </c>
   <c>417</c>
   <c>Expectation Failed</c>
   <c>
      <xref target="status.417"/>
   </c>
   <c>500</c>
   <c>Internal Server Error</c>
   <c>
      <xref target="status.500"/>
   </c>
   <c>501</c>
   <c>Not Implemented</c>
   <c>
      <xref target="status.501"/>
   </c>
   <c>502</c>
   <c>Bad Gateway</c>
   <c>
      <xref target="status.502"/>
   </c>
   <c>503</c>
   <c>Service Unavailable</c>
   <c>
      <xref target="status.503"/>
   </c>
   <c>504</c>
   <c>Gateway Timeout</c>
   <c>
      <xref target="status.504"/>
   </c>
   <c>505</c>
   <c>HTTP Version Not Supported</c>
   <c>
      <xref target="status.505"/>
   </c>
</texttable>
<!--(END)-->

</section>
<section title="Header Field Registration" anchor="header.field.registration">
<t>
   The Message Header Field Registry located at <eref target="http://www.iana.org/assignments/message-headers/message-header-index.html"/> shall be updated
   with the permanent registrations below (see <xref target="RFC3864"/>):
</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>Allow</c>
   <c>http</c>
   <c>standard</c>
   <c>
      <xref target="header.allow"/>
   </c>
   <c>Expect</c>
   <c>http</c>
   <c>standard</c>
   <c>
      <xref target="header.expect"/>
   </c>
   <c>From</c>
   <c>http</c>
   <c>standard</c>
   <c>
      <xref target="header.from"/>
   </c>
   <c>Location</c>
   <c>http</c>
   <c>standard</c>
   <c>
      <xref target="header.location"/>
   </c>
   <c>Max-Forwards</c>
   <c>http</c>
   <c>standard</c>
   <c>
      <xref target="header.max-forwards"/>
   </c>
   <c>Referer</c>
   <c>http</c>
   <c>standard</c>
   <c>
      <xref target="header.referer"/>
   </c>
   <c>Retry-After</c>
   <c>http</c>
   <c>standard</c>
   <c>
      <xref target="header.retry-after"/>
   </c>
   <c>Server</c>
   <c>http</c>
   <c>standard</c>
   <c>
      <xref target="header.server"/>
   </c>
   <c>User-Agent</c>
   <c>http</c>
   <c>standard</c>
   <c>
      <xref target="header.user-agent"/>
   </c>
</texttable>
<!--(END)-->

<t>
   The change controller 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="Transfer of Sensitive Information" anchor="security.sensitive">
<t>
   Like any generic data transfer protocol, HTTP cannot regulate the
   content of the data that is transferred, nor is there any a priori
   method of determining the sensitivity of any particular piece of
   information within the context of any given request. Therefore,
   applications SHOULD supply as much control over this information as
   possible to the provider of that information. Four header fields are
   worth special mention in this context: Server, Via, Referer and From.
</t>
<t>
   Revealing the specific software version of the server might allow the
   server machine to become more vulnerable to attacks against software
   that is known to contain security holes. Implementors SHOULD make the
   Server header field a configurable option.
</t>
<t>
   Proxies which serve as a portal through a network firewall SHOULD
   take special precautions regarding the transfer of header information
   that identifies the hosts behind the firewall. In particular, they
   SHOULD remove, or replace with sanitized versions, any Via fields
   generated behind the firewall.
</t>
<t>
   The Referer header field allows reading patterns to be studied and reverse
   links drawn. Although it can be very useful, its power can be abused
   if user details are not separated from the information contained in
   the Referer. Even when the personal information has been removed, the
   Referer header field might indicate a private document's URI whose
   publication would be inappropriate.
</t>
<t>
   The information sent in the From field might conflict with the user's
   privacy interests or their site's security policy, and hence it
   SHOULD NOT  be transmitted without the user being able to disable,
   enable, and modify the contents of the field. The user MUST be able
   to set the contents of this field within a user preference or
   application defaults configuration.
</t>
<t>
   We suggest, though do not require, that a convenient toggle interface
   be provided for the user to enable or disable the sending of From and
   Referer information.
</t>
<t>
   The User-Agent (<xref target="header.user-agent"/>) or Server (<xref target="header.server"/>) header fields can sometimes be used to determine
   that a specific client or server have a particular security hole which might
   be exploited. Unfortunately, this same information is often used for other
   valuable purposes for which HTTP currently has no better mechanism.
</t>
<t>
   Furthermore, the User-Agent header field may contain enough entropy to be
   used, possibly in conjunction with other material, to uniquely identify the
   user.
</t>
<t>
   Some methods, like TRACE (<xref target="TRACE"/>), expose information
   that was sent in request header fields within the body of their response. 
   Clients SHOULD be careful with sensitive information, like Cookies, 
   Authorization credentials and other header fields that might be used to 
   collect data from the client.
</t> 
</section>

<section title="Encoding Sensitive Information in URIs" anchor="encoding.sensitive.information.in.uris">
<t>
   Because the source of a link might be private information or might
   reveal an otherwise private information source, it is strongly
   recommended that the user be able to select whether or not the
   Referer field is sent. For example, a browser client could have a
   toggle switch for browsing openly/anonymously, which would
   respectively enable/disable the sending of Referer and From
   information.
</t>
<t>
   Clients SHOULD NOT include a Referer header field in a (non-secure)
   HTTP request if the referring page was transferred with a secure
   protocol.
</t>
<t>
   Authors of services SHOULD NOT use GET-based forms for the submission of
   sensitive data because that data will be placed in the request-target. Many
   existing servers, proxies, and user agents log or display the request-target
   in places where it might be visible to third parties. Such services can
   use POST-based form submission instead.
</t>
</section>

<section title="Location Headers and Spoofing" anchor="location.spoofing">
<t>
   If a single server supports multiple organizations that do not trust
   one another, then it MUST check the values of Location and Content-Location
   header fields in responses that are generated under control of
   said organizations to make sure that they do not attempt to
   invalidate resources over which they have no authority.
</t>
</section>

</section>

<section title="Acknowledgments" anchor="ack">
</section>
</middle>
<back>

<references title="Normative References">

<reference anchor="Part1">
  <front>
    <title abbrev="HTTP/1.1">HTTP/1.1, part 1: URIs, Connections, and Message Parsing</title>
    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
      <organization abbrev="Day Software">Day Software</organization>
      <address><email>fielding@gbiv.com</email></address>
    </author>
    <author initials="J." surname="Gettys" fullname="Jim Gettys">
      <organization abbrev="Alcatel-Lucent">Alcatel-Lucent Bell Labs</organization>
      <address><email>jg@freedesktop.org</email></address>
    </author>
    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
      <organization abbrev="HP">Hewlett-Packard Company</organization>
      <address><email>JeffMogul@acm.org</email></address>
    </author>
    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
      <organization abbrev="Microsoft">Microsoft Corporation</organization>
      <address><email>henrikn@microsoft.com</email></address>
    </author>
    <author initials="L." surname="Masinter" fullname="Larry Masinter">
      <organization abbrev="Adobe Systems">Adobe Systems, Incorporated</organization>
      <address><email>LMM@acm.org</email></address>
    </author>
    <author initials="P." surname="Leach" fullname="Paul J. Leach">
      <organization abbrev="Microsoft">Microsoft Corporation</organization>
      <address><email>paulle@microsoft.com</email></address>
    </author>
    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
      <address><email>timbl@w3.org</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="2010"/>
  </front>
  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p1-messaging-12"/>
  
</reference>

<reference anchor="Part3">
  <front>
    <title abbrev="HTTP/1.1">HTTP/1.1, part 3: Message Payload and Content Negotiation</title>
    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
      <organization abbrev="Day Software">Day Software</organization>
      <address><email>fielding@gbiv.com</email></address>
    </author>
    <author initials="J." surname="Gettys" fullname="Jim Gettys">
      <organization abbrev="Alcatel-Lucent">Alcatel-Lucent Bell Labs</organization>
      <address><email>jg@freedesktop.org</email></address>
    </author>
    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
      <organization abbrev="HP">Hewlett-Packard Company</organization>
      <address><email>JeffMogul@acm.org</email></address>
    </author>
    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
      <organization abbrev="Microsoft">Microsoft Corporation</organization>
      <address><email>henrikn@microsoft.com</email></address>
    </author>
    <author initials="L." surname="Masinter" fullname="Larry Masinter">
      <organization abbrev="Adobe Systems">Adobe Systems, Incorporated</organization>
      <address><email>LMM@acm.org</email></address>
    </author>
    <author initials="P." surname="Leach" fullname="Paul J. Leach">
      <organization abbrev="Microsoft">Microsoft Corporation</organization>
      <address><email>paulle@microsoft.com</email></address>
    </author>
    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
      <address><email>timbl@w3.org</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="2010"/>
  </front>
  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p3-payload-12"/>
  
</reference>

<reference anchor="Part4">
  <front>
    <title abbrev="HTTP/1.1">HTTP/1.1, part 4: Conditional Requests</title>
    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
      <organization abbrev="Day Software">Day Software</organization>
      <address><email>fielding@gbiv.com</email></address>
    </author>
    <author initials="J." surname="Gettys" fullname="Jim Gettys">
      <organization abbrev="Alcatel-Lucent">Alcatel-Lucent Bell Labs</organization>
      <address><email>jg@freedesktop.org</email></address>
    </author>
    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
      <organization abbrev="HP">Hewlett-Packard Company</organization>
      <address><email>JeffMogul@acm.org</email></address>
    </author>
    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
      <organization abbrev="Microsoft">Microsoft Corporation</organization>
      <address><email>henrikn@microsoft.com</email></address>
    </author>
    <author initials="L." surname="Masinter" fullname="Larry Masinter">
      <organization abbrev="Adobe Systems">Adobe Systems, Incorporated</organization>
      <address><email>LMM@acm.org</email></address>
    </author>
    <author initials="P." surname="Leach" fullname="Paul J. Leach">
      <organization abbrev="Microsoft">Microsoft Corporation</organization>
      <address><email>paulle@microsoft.com</email></address>
    </author>
    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
      <address><email>timbl@w3.org</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="2010"/>
  </front>
  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p4-conditional-12"/>
  
</reference>

<reference anchor="Part5">
  <front>
    <title abbrev="HTTP/1.1">HTTP/1.1, part 5: Range Requests and Partial Responses</title>
    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
      <organization abbrev="Day Software">Day Software</organization>
      <address><email>fielding@gbiv.com</email></address>
    </author>
    <author initials="J." surname="Gettys" fullname="Jim Gettys">
      <organization abbrev="Alcatel-Lucent">Alcatel-Lucent Bell Labs</organization>
      <address><email>jg@freedesktop.org</email></address>
    </author>
    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
      <organization abbrev="HP">Hewlett-Packard Company</organization>
      <address><email>JeffMogul@acm.org</email></address>
    </author>
    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
      <organization abbrev="Microsoft">Microsoft Corporation</organization>
      <address><email>henrikn@microsoft.com</email></address>
    </author>
    <author initials="L." surname="Masinter" fullname="Larry Masinter">
      <organization abbrev="Adobe Systems">Adobe Systems, Incorporated</organization>
      <address><email>LMM@acm.org</email></address>
    </author>
    <author initials="P." surname="Leach" fullname="Paul J. Leach">
      <organization abbrev="Microsoft">Microsoft Corporation</organization>
      <address><email>paulle@microsoft.com</email></address>
    </author>
    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
      <address><email>timbl@w3.org</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="2010"/>
  </front>
  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p5-range-12"/>
  
</reference>

<reference anchor="Part6">
  <front>
    <title abbrev="HTTP/1.1">HTTP/1.1, part 6: Caching</title>
    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
      <organization abbrev="Day Software">Day Software</organization>
      <address><email>fielding@gbiv.com</email></address>
    </author>
    <author initials="J." surname="Gettys" fullname="Jim Gettys">
      <organization abbrev="Alcatel-Lucent">Alcatel-Lucent Bell Labs</organization>
      <address><email>jg@freedesktop.org</email></address>
    </author>
    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
      <organization abbrev="HP">Hewlett-Packard Company</organization>
      <address><email>JeffMogul@acm.org</email></address>
    </author>
    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
      <organization abbrev="Microsoft">Microsoft Corporation</organization>
      <address><email>henrikn@microsoft.com</email></address>
    </author>
    <author initials="L." surname="Masinter" fullname="Larry Masinter">
      <organization abbrev="Adobe Systems">Adobe Systems, Incorporated</organization>
      <address><email>LMM@acm.org</email></address>
    </author>
    <author initials="P." surname="Leach" fullname="Paul J. Leach">
      <organization abbrev="Microsoft">Microsoft Corporation</organization>
      <address><email>paulle@microsoft.com</email></address>
    </author>
    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
      <address><email>timbl@w3.org</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="M." surname="Nottingham" fullname="Mark Nottingham" role="editor">
      <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="2010"/>
  </front>
  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p6-cache-12"/>
  
</reference>

<reference anchor="Part7">
  <front>
    <title abbrev="HTTP/1.1">HTTP/1.1, part 7: Authentication</title>
    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
      <organization abbrev="Day Software">Day Software</organization>
      <address><email>fielding@gbiv.com</email></address>
    </author>
    <author initials="J." surname="Gettys" fullname="Jim Gettys">
      <organization abbrev="Alcatel-Lucent">Alcatel-Lucent Bell Labs</organization>
      <address><email>jg@freedesktop.org</email></address>
    </author>
    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
      <organization abbrev="HP">Hewlett-Packard Company</organization>
      <address><email>JeffMogul@acm.org</email></address>
    </author>
    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
      <organization abbrev="Microsoft">Microsoft Corporation</organization>
      <address><email>henrikn@microsoft.com</email></address>
    </author>
    <author initials="L." surname="Masinter" fullname="Larry Masinter">
      <organization abbrev="Adobe Systems">Adobe Systems, Incorporated</organization>
      <address><email>LMM@acm.org</email></address>
    </author>
    <author initials="P." surname="Leach" fullname="Paul J. Leach">
      <organization abbrev="Microsoft">Microsoft Corporation</organization>
      <address><email>paulle@microsoft.com</email></address>
    </author>
    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
      <address><email>timbl@w3.org</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="2010"/>
  </front>
  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p7-auth-12"/>
  
</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="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>

</references>

<references title="Informative References">

<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="RFC2068">
  <front>
    <title abbrev="HTTP/1.1">Hypertext Transfer Protocol -- HTTP/1.1</title>
    <author initials="R." surname="Fielding" fullname="Roy T. Fielding">
      <organization>University of California, Irvine, Department of Information and Computer Science</organization>
      <address><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="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="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="RFC5226">
  <front>
    <title>Guidelines for Writing an IANA Considerations Section in RFCs</title>
    <author initials="T." surname="Narten" fullname="T. Narten">
      <organization>IBM</organization>
      <address><email>narten@us.ibm.com</email></address>
    </author>
    <author initials="H." surname="Alvestrand" fullname="H. Alvestrand">
      <organization>Google</organization>
      <address><email>Harald@Alvestrand.no</email></address>
    </author>
    <date year="2008" month="May"/>
  </front>
  <seriesInfo name="BCP" value="26"/>
  <seriesInfo name="RFC" value="5226"/>
</reference>

<reference anchor="RFC5322">
  <front>
    <title>Internet Message Format</title>
    <author initials="P." surname="Resnick" fullname="P. Resnick">
      <organization>Qualcomm Incorporated</organization>
    </author>
    <date year="2008" month="October"/>
  </front> 
  <seriesInfo name="RFC" value="5322"/>
</reference>

</references>

<section title="Changes from RFC 2616" anchor="changes.from.rfc.2616">
<t>
  This document takes over the Status Code Registry, previously defined
  in Section 7.1 of <xref target="RFC2817"/>.
  (<xref target="status.code.registry"/>)
</t>
<t>
  Clarify definition of POST.
  (<xref target="POST"/>)
</t>
<t>
  Failed to consider that there are
  many other request methods that are safe to automatically redirect,
  and further that the user agent is able to make that determination
  based on the request method semantics.
  (Sections <xref format="counter" target="status.301"/>,
  <xref format="counter" target="status.302"/> and
  <xref format="counter" target="status.307"/>)
</t>
<t>
  Deprecate 305 Use Proxy status code, because user agents did not implement it.
  It used to indicate that the target resource must be accessed through the
  proxy given by the Location field. The Location field gave the URI of the
  proxy. The recipient was expected to repeat this single request via the proxy.
  (<xref target="status.305"/>)
</t>
<t>
  Reclassify "Allow" as response header field, removing the option to
  specify it in a PUT request.
  Relax the server requirement on the contents of the Allow header field and
  remove requirement on clients to always trust the header field value.
  (<xref target="header.allow"/>)
</t>
<t>
  Correct syntax of Location header field to allow URI references (including
  relative references and fragments), as referred symbol "absoluteURI" wasn't
  what was expected, and add some clarifications as to when use of fragments 
  would not be appropriate.
  (<xref target="header.location"/>)
</t>
<t>
  Allow Referer field value of "about:blank" as alternative to not specifying it. 
  (<xref target="header.referer"/>)
</t>
<t>
  In the description of the Server header field, the Via field
  was described as a SHOULD. The requirement was and is stated
  correctly in the description of the Via header field in Section 9.9 of <xref target="Part1"/>.
  (<xref target="header.server"/>)
</t>
</section>


<section title="Collected ABNF" anchor="collected.abnf">
<figure>
<artwork type="abnf" name="p2-semantics.parsed-abnf"><![CDATA[
Accept = <Accept, defined in [Part3], Section 6.1>
Accept-Charset = <Accept-Charset, defined in [Part3], Section 6.2>
Accept-Encoding = <Accept-Encoding, defined in [Part3], Section 6.3>
Accept-Language = <Accept-Language, defined in [Part3], Section 6.4>
Accept-Ranges = <Accept-Ranges, defined in [Part5], Section 5.1>
Age = <Age, defined in [Part6], Section 3.1>
Allow = "Allow:" OWS Allow-v
Allow-v = [ ( "," / Method ) *( OWS "," [ OWS Method ] ) ]
Authorization = <Authorization, defined in [Part7], Section 4.1>

ETag = <ETag, defined in [Part4], Section 6.1>
Expect = "Expect:" OWS Expect-v
Expect-v = *( "," OWS ) expectation *( OWS "," [ OWS expectation ] )

From = "From:" OWS From-v
From-v = mailbox

HTTP-date = <HTTP-date, defined in [Part1], Section 6.1>
Host = <Host, defined in [Part1], Section 2.6>

If-Match = <If-Match, defined in [Part4], Section 6.2>
If-Modified-Since =
 <If-Modified-Since, defined in [Part4], Section 6.3>
If-None-Match = <If-None-Match, defined in [Part4], Section 6.4>
If-Range = <If-Range, defined in [Part5], Section 5.3>
If-Unmodified-Since =
 <If-Unmodified-Since, defined in [Part4], Section 6.5>

Location = "Location:" OWS Location-v
Location-v = URI-reference

Max-Forwards = "Max-Forwards:" OWS Max-Forwards-v
Max-Forwards-v = 1*DIGIT
Method = %x4F.50.54.49.4F.4E.53 ; OPTIONS
 / %x47.45.54 ; GET
 / %x48.45.41.44 ; HEAD
 / %x50.4F.53.54 ; POST
 / %x50.55.54 ; PUT
 / %x44.45.4C.45.54.45 ; DELETE
 / %x54.52.41.43.45 ; TRACE
 / %x43.4F.4E.4E.45.43.54 ; CONNECT
 / extension-method

OWS = <OWS, defined in [Part1], Section 1.2.2>

Proxy-Authenticate =
 <Proxy-Authenticate, defined in [Part7], Section 4.2>
Proxy-Authorization =
 <Proxy-Authorization, defined in [Part7], Section 4.3>

RWS = <RWS, defined in [Part1], Section 1.2.2>
Range = <Range, defined in [Part5], Section 5.4>
Reason-Phrase = *( WSP / VCHAR / obs-text )
Referer = "Referer:" OWS Referer-v
Referer-v = absolute-URI / partial-URI
Retry-After = "Retry-After:" OWS Retry-After-v
Retry-After-v = HTTP-date / delta-seconds

Server = "Server:" OWS Server-v
Server-v = product *( RWS ( product / comment ) )
Status-Code = "100" / "101" / "200" / "201" / "202" / "203" / "204" /
 "205" / "206" / "300" / "301" / "302" / "303" / "304" / "305" /
 "307" / "400" / "401" / "402" / "403" / "404" / "405" / "406" /
 "407" / "408" / "409" / "410" / "411" / "412" / "413" / "414" /
 "415" / "416" / "417" / "500" / "501" / "502" / "503" / "504" /
 "505" / extension-code

TE = <TE, defined in [Part1], Section 9.5>

URI-reference = <URI-reference, defined in [Part1], Section 2.6>
User-Agent = "User-Agent:" OWS User-Agent-v
User-Agent-v = product *( RWS ( product / comment ) )

Vary = <Vary, defined in [Part6], Section 3.5>

WWW-Authenticate =
 <WWW-Authenticate, defined in [Part7], Section 4.4>

absolute-URI = <absolute-URI, defined in [Part1], Section 2.6>

comment = <comment, defined in [Part1], Section 3.2>

delta-seconds = 1*DIGIT

expect-params = ";" token [ "=" ( token / quoted-string ) ]
expectation = "100-continue" / expectation-extension
expectation-extension = token [ "=" ( token / quoted-string )
 *expect-params ]
extension-code = 3DIGIT
extension-method = token

mailbox = <mailbox, defined in [RFC5322], Section 3.4>

obs-text = <obs-text, defined in [Part1], Section 1.2.2>

partial-URI = <partial-URI, defined in [Part1], Section 2.6>
product = <product, defined in [Part1], Section 6.3>

quoted-string = <quoted-string, defined in [Part1], Section 1.2.2>

request-header = Accept / Accept-Charset / Accept-Encoding /
 Accept-Language / Authorization / Expect / From / Host / If-Match /
 If-Modified-Since / If-None-Match / If-Range / If-Unmodified-Since /
 Max-Forwards / Proxy-Authorization / Range / Referer / TE /
 User-Agent
response-header = Accept-Ranges / Age / Allow / ETag / Location /
 Proxy-Authenticate / Retry-After / Server / Vary / WWW-Authenticate

token = <token, defined in [Part1], Section 1.2.2>
]]></artwork>
</figure>
<figure><preamble>ABNF diagnostics:</preamble><artwork type="inline"><![CDATA[
; Reason-Phrase defined but not used
; Status-Code defined but not used
; request-header defined but not used
; response-header defined but not used
]]></artwork></figure></section>


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

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

<section title="Since draft-ietf-httpbis-p2-semantics-00">
<t>
  Closed issues:
  <list style="symbols"> 
    <t>
      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/5"/>:
      "Via is a MUST"
      (<eref target="http://purl.org/NET/http-errata#via-must"/>)
    </t>
    <t>
      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/6"/>:
      "Fragments allowed in Location"
      (<eref target="http://purl.org/NET/http-errata#location-fragments"/>)
    </t>
    <t>
      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/10"/>:
      "Safe Methods vs Redirection"
      (<eref target="http://purl.org/NET/http-errata#saferedirect"/>)
    </t>
    <t>
      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/17"/>:
      "Revise description of the POST method"
      (<eref target="http://purl.org/NET/http-errata#post"/>)
    </t>
    <t>
      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/35"/>:
      "Normative and Informative references"
    </t>
    <t>
      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/42"/>:
      "RFC2606 Compliance"
    </t>
    <t>
      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/65"/>:
      "Informative references"
    </t>
    <t>
      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/84"/>:
      "Redundant cross-references"
    </t>
  </list>
</t>
<t>
  Other changes:
  <list style="symbols"> 
    <t>
      Move definitions of 304 and 412 condition codes to <xref target="Part4"/>
    </t>
  </list>
</t>
</section>

<section title="Since draft-ietf-httpbis-p2-semantics-01">
<t>
  Closed issues:
  <list style="symbols"> 
    <t>
      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/21"/>:
      "PUT side effects"
    </t>
    <t>
      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/91"/>:
      "Duplicate Host header requirements"
    </t>
  </list>
</t>
<t>
  Ongoing work on ABNF conversion (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/36"/>):
  <list style="symbols"> 
    <t>
      Move "Product Tokens" section (back) into Part 1, as "token" is used
      in the definition of the Upgrade header field.
    </t>
    <t>
      Add explicit references to BNF syntax and rules imported from other parts of the specification.
    </t>
    <t>
      Copy definition of delta-seconds from Part6 instead of referencing it.
    </t>
  </list>
</t>
</section>

<section title="Since draft-ietf-httpbis-p2-semantics-02" anchor="changes.since.02">
<t>
  Closed issues:
  <list style="symbols"> 
    <t>
      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/24"/>:
      "Requiring Allow in 405 responses"
    </t>
    <t>
      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/59"/>:
      "Status Code Registry"
    </t>
    <t>
      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/61"/>:
      "Redirection vs. Location"
    </t>
    <t>
      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/70"/>:
      "Cacheability of 303 response"
    </t>
    <t>
      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/76"/>:
      "305 Use Proxy"
    </t>
    <t>
      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/105"/>:
      "Classification for Allow header"
    </t>
    <t>
      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/112"/>:
      "PUT - 'store under' vs 'store at'"
    </t>
  </list>
</t>
<t>
  Ongoing work on IANA Message Header Field Registration (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/40"/>):
  <list style="symbols"> 
    <t>
      Reference RFC 3984, and update header field registrations for headers defined
      in this document.
    </t>
  </list>
</t>
<t>
  Ongoing work on ABNF conversion (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/36"/>):
  <list style="symbols"> 
    <t>
      Replace string literals when the string really is case-sensitive (method).
    </t>
  </list>
</t>
</section>

<section title="Since draft-ietf-httpbis-p2-semantics-03" anchor="changes.since.03">
<t>
  Closed issues:
  <list style="symbols"> 
    <t>
      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/98"/>:
      "OPTIONS request bodies"
    </t>
    <t>
      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/119"/>:
      "Description of CONNECT should refer to RFC2817"
    </t>
    <t>
      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/125"/>:
      "Location Content-Location reference request/response mixup"
    </t>
  </list>
</t>
<t>
  Ongoing work on Method Registry (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/72"/>):
  <list style="symbols"> 
    <t>
      Added initial proposal for registration process, plus initial
      content (non-HTTP/1.1 methods to be added by a separate specification).
    </t>
  </list>
</t>
</section>

<section title="Since draft-ietf-httpbis-p2-semantics-04" anchor="changes.since.04">
<t>
  Closed issues:
  <list style="symbols"> 
    <t>
      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/103"/>:
      "Content-*"
    </t>
    <t>
      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/132"/>:
      "RFC 2822 is updated by RFC 5322"
    </t>
  </list>
</t>
<t>
  Ongoing work on ABNF conversion (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/36"/>):
  <list style="symbols"> 
    <t>
      Use "/" instead of "|" for alternatives.
    </t>
    <t>
      Introduce new ABNF rules for "bad" whitespace ("BWS"), optional
      whitespace ("OWS") and required whitespace ("RWS").
    </t>
    <t>
      Rewrite ABNFs to spell out whitespace rules, factor out
      header field value format definitions.
    </t>
  </list>
</t>
</section>

<section title="Since draft-ietf-httpbis-p2-semantics-05" anchor="changes.since.05">
<t>
  Closed issues:
  <list style="symbols"> 
    <t>
      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/94"/>:
      "Reason-Phrase BNF"
    </t>
  </list>
</t>
<t>
  Final work on ABNF conversion (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/36"/>):
  <list style="symbols"> 
    <t>
      Add appendix containing collected and expanded ABNF, reorganize ABNF introduction.
    </t>
  </list>
</t>
</section>

<section title="Since draft-ietf-httpbis-p2-semantics-06" anchor="changes.since.06">
<t>
  Closed issues:
  <list style="symbols"> 
    <t>
      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/144"/>:
      "Clarify when Referer is sent"
    </t>
    <t>
      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/164"/>:
      "status codes vs methods"
    </t>
    <t>
      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/170"/>:
      "Do not require "updates" relation for specs that register status codes or method names"
    </t>
  </list>
</t>
</section>

<section title="Since draft-ietf-httpbis-p2-semantics-07" anchor="changes.since.07">
<t>
  Closed issues:
  <list style="symbols"> 
    <t>
      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/27"/>:
      "Idempotency"
    </t>
    <t>
      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/33"/>:
      "TRACE security considerations"
    </t>
    <t>
      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/110"/>:
      "Clarify rules for determining what entities a response carries"
    </t>
    <t>
      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/140"/>:
      "update note citing RFC 1945 and 2068"
    </t>
    <t>
      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/182"/>:
      "update note about redirect limit"
    </t>
    <t>
      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/191"/>:
      "Location header ABNF should use 'URI'"
    </t>
    <t>
      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/192"/>:
      "fragments in Location vs status 303"
    </t>
    <t>
      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/198"/>:
      "move IANA registrations for optional status codes"
    </t>
  </list>
</t>
<t>
  Partly resolved issues:
  <list style="symbols"> 
    <t>
      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/171"/>:
      "Are OPTIONS and TRACE safe?"
    </t>
  </list>
</t>
</section>

<section title="Since draft-ietf-httpbis-p2-semantics-08" anchor="changes.since.08">
<t>
  Closed issues:
  <list style="symbols"> 
    <t>
      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/10"/>:
      "Safe Methods vs Redirection" (we missed the introduction to the 3xx
      status codes when fixing this previously)
    </t>
  </list>
</t>
</section>

<section title="Since draft-ietf-httpbis-p2-semantics-09" anchor="changes.since.09">
<t>
  Closed issues:
  <list style="symbols"> 
    <t>
      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/43"/>:
      "Fragment combination / precedence during redirects"
    </t>
  </list>
</t>
<t>
  Partly resolved issues:
  <list style="symbols"> 
    <t>
      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/185"/>:
      "Location header payload handling"
    </t>
    <t>
      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/196"/>:
      "Term for the requested resource's URI"
    </t>
  </list>
</t>
</section>

<section title="Since draft-ietf-httpbis-p2-semantics-10" anchor="changes.since.10">
<t>
  Closed issues:
  <list style="symbols"> 
    <t>
      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/69"/>:
      "Clarify 'Requested Variant'"
    </t>
    <t>
      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/109"/>:
      "Clarify entity / representation / variant terminology"
    </t>
    <t>
      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/139"/>:
      "Methods and Caching"
    </t>
    <t>
      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/190"/>:
      "OPTIONS vs Max-Forwards"
    </t>
    <t>
      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/199"/>:
      "Status codes and caching"
    </t>
    <t>
      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/220"/>:
      "consider removing the 'changes from 2068' sections"
    </t>
  </list>
</t>
</section>

<section title="Since draft-ietf-httpbis-p2-semantics-11" anchor="changes.since.11">
<t>
  Closed issues:
  <list style="symbols"> 
    <t>
      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/229"/>:
      "Considerations for new status codes"
    </t>
    <t>
      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/230"/>:
      "Considerations for new methods"
    </t>
    <t>
      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/232"/>:
      "User-Agent guidelines" (relating to the 'User-Agent' header field)
    </t>
  </list>
</t>
</section>

</section>

</back>
</rfc>