MAY"> MUST"> MUST NOT"> OPTIONAL"> RECOMMENDED"> REQUIRED"> SHALL"> SHALL NOT"> SHOULD"> SHOULD NOT"> "> "> "> "> "> "> "> "> "> "> "> "> "> "> "> "> "> "> "> "> "> "> "> "> "> "> "> "> "> "> "> "> "> "> "> "> "> "> "> "> "> "> "> "> "> "> "> "> "> "> "> "> "> "> "> "> "> "> "> "> "> ]> Day Software

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Alcatel-Lucent Bell Labs

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Hewlett-Packard Company

HP Labs, Large Scale Systems Group 1501 Page Mill Road, MS 1177 Palo Alto CA 94304 USA JeffMogul@acm.org

Microsoft Corporation

1 Microsoft Way Redmond WA 98052 USA henrikn@microsoft.com

Adobe Systems, Incorporated

345 Park Ave San Jose CA 95110 USA LMM@acm.org http://larry.masinter.net/

Microsoft Corporation

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World Wide Web Consortium

MIT Computer Science and Artificial Intelligence Laboratory The Stata Center, Building 32 32 Vassar Street Cambridge MA 02139 USA timbl@w3.org http://www.w3.org/People/Berners-Lee/

World Wide Web Consortium

W3C / ERCIM 2004, rte des Lucioles Sophia-Antipolis AM 06902 France ylafon@w3.org http://www.raubacapeu.net/people/yves/

greenbytes GmbH

Hafenweg 16 MuensterNW48155 Germany +49 251 2807760 +49 251 2807761 julian.reschke@greenbytes.de http://greenbytes.de/tech/webdav/

HTTPbis Working Group 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. 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 and related documents (including fancy diffs) can be found at . The changes in this draft are summarized in .

This document defines HTTP/1.1 request and response semantics. Each HTTP message, as defined in &messaging;, 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. 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 .

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 . 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".

This specification uses the ABNF syntax defined in ¬ation; (which extends the syntax defined in with a list rule). shows the collected ABNF, with the list rule expanded. The following core rules are included by reference, as defined in : 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).

The core rules below are defined in &basic-rules;:

quoted-string = <quoted-string, defined in &basic-rules;> token = <token, defined in &basic-rules;> OWS = <OWS, defined in &basic-rules;> RWS = <RWS, defined in &basic-rules;> obs-text = <obs-text, defined in &basic-rules;>

The ABNF rules below are defined in other parts:

absolute-URI = <absolute-URI, defined in &uri;> comment = <comment, defined in &header-fields;> Host = <Host, defined in &uri;> HTTP-date = <HTTP-date, defined in &full-date;> partial-URI = <partial-URI, defined in &uri;> product = <product, defined in &product-tokens;> TE = <TE, defined in &header-te;> URI-reference = <URI-reference, defined in &uri;>

Accept = <Accept, defined in &header-accept;> Accept-Charset = <Accept-Charset, defined in &header-accept-charset;> Accept-Encoding = <Accept-Encoding, defined in &header-accept-encoding;> Accept-Language = <Accept-Language, defined in &header-accept-language;>

ETag = <ETag, defined in &header-etag;> If-Match = <If-Match, defined in &header-if-match;> If-Modified-Since = <If-Modified-Since, defined in &header-if-modified-since;> If-None-Match = <If-None-Match, defined in &header-if-none-match;> If-Unmodified-Since = <If-Unmodified-Since, defined in &header-if-unmodified-since;>

Accept-Ranges = <Accept-Ranges, defined in &header-accept-ranges;> If-Range = <If-Range, defined in &header-if-range;> Range = <Range, defined in &header-range;>

Age = <Age, defined in &header-age;> Vary = <Vary, defined in &header-vary;>

Authorization = <Authorization, defined in &header-authorization;> Proxy-Authenticate = <Proxy-Authenticate, defined in &header-proxy-authenticate;> Proxy-Authorization = <Proxy-Authorization, defined in &header-proxy-authorization;> WWW-Authenticate = <WWW-Authenticate, defined in &header-www-authenticate;>

The Method token indicates the method to be performed on the target resource (&effective-request-uri;). The method is case-sensitive.

Method = "OPTIONS" ; "OPTIONS", / "GET" ; "GET", / "HEAD" ; "HEAD", / "POST" ; "POST", / "PUT" ; "PUT", / "DELETE" ; "DELETE", / "TRACE" ; "TRACE", / "CONNECT" ; "CONNECT", / extension-method extension-method = token

The list of methods allowed by a resource can be specified in an Allow header field (). 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 .

The HTTP Method Registry defines the name space for the Method token in the Request line of an HTTP request. Registrations &MUST; include the following fields: Method Name (see ) Safe ("yes" or "no", see ) Pointer to specification text Values to be added to this name space are subject to IETF review (). The registry itself is maintained at .

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. 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. Due to the parsing rules defined in &message-body;, 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. New method definitions need to indicate whether they are safe () and whether they are idempotent (). They also need to state whether they can be cached (&caching;); 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.

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.

request-header = Accept ; &header-accept; / Accept-Charset ; &header-accept-charset; / Accept-Encoding ; &header-accept-encoding; / Accept-Language ; &header-accept-language; / Authorization ; &header-authorization; / Expect ; / From ; / Host ; &header-host; / If-Match ; &header-if-match; / If-Modified-Since ; &header-if-modified-since; / If-None-Match ; &header-if-none-match; / If-Range ; &header-if-range; / If-Unmodified-Since ; &header-if-unmodified-since; / Max-Forwards ; / Proxy-Authorization ; &header-proxy-authorization; / Range ; &header-range; / Referer ; / TE ; &header-te; / User-Agent ;

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.

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 , &p4-status-codes;, &p5-status-codes;, and &p7-status-codes;. The Reason-Phrase is intended to give a short textual description of the Status-Code. The Status-Code is intended for use by automata and the Reason-Phrase is intended for the human user. The client is not required to examine or display the Reason-Phrase. 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.

Status-Code = "100" ; : Continue / "101" ; : Switching Protocols / "200" ; : OK / "201" ; : Created / "202" ; : Accepted / "203" ; : Non-Authoritative Information / "204" ; : No Content / "205" ; : Reset Content / "206" ; &status-206;: Partial Content / "300" ; : Multiple Choices / "301" ; : Moved Permanently / "302" ; : Found / "303" ; : See Other / "304" ; &status-304;: Not Modified / "305" ; : Use Proxy / "307" ; : Temporary Redirect / "400" ; : Bad Request / "401" ; &status-401;: Unauthorized / "402" ; : Payment Required / "403" ; : Forbidden / "404" ; : Not Found / "405" ; : Method Not Allowed / "406" ; : Not Acceptable / "407" ; &status-407;: Proxy Authentication Required / "408" ; : Request Time-out / "409" ; : Conflict / "410" ; : Gone / "411" ; : Length Required / "412" ; &status-412;: Precondition Failed / "413" ; : Request Entity Too Large / "414" ; : URI Too Long / "415" ; : Unsupported Media Type / "416" ; &status-416;: Requested range not satisfiable / "417" ; : Expectation Failed / "500" ; : Internal Server Error / "501" ; : Not Implemented / "502" ; : Bad Gateway / "503" ; : Service Unavailable / "504" ; : Gateway Time-out / "505" ; : HTTP Version not supported / extension-code extension-code = 3DIGIT Reason-Phrase = *( WSP / VCHAR / obs-text )

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.

The HTTP Status Code Registry defines the name space for the Status-Code token in the Status-Line of an HTTP response. Values to be added to this name space are subject to IETF review (). The registry itself is maintained at .

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. 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. 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). New HTTP status codes are required to fall under one of the categories defined in . 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). Likewise, their definitions can specify that caches are allowed to use heuristics to determine their freshness (see &caching;; by default, it is not allowed), and can define how to determine the resource which they carry a representation for (see ; by default, it is anonymous).

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 (&effective-request-uri;).

response-header = Accept-Ranges ; &header-accept-ranges; / Age ; &header-age; / Allow ; / ETag ; &header-etag; / Location ; / Proxy-Authenticate ; &header-proxy-authenticate; / Retry-After ; / Server ; / Vary ; &header-vary; / WWW-Authenticate ; &header-www-authenticate;

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.

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 &payload;. A representation body is only present in a message when a message-body is present, as described in &message-body;. 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.

It is sometimes necessary to determine an identifier for the resource associated with a representation. An HTTP request representation, when present, is always associated with an anonymous (i.e., unidentified) resource. In the common case, an HTTP response is a representation of the target resource (see &effective-request-uri;). 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): 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. 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 &combining-responses;). 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. 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). Otherwise, the response is a representation of an anonymous (i.e., unidentified) resource. The comparison function is going to have to be defined somewhere, because we already need to compare URIs for things like cache invalidation.

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.

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. 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. 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.

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.

yes 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. Responses to this method are not cacheable. 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. 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). If the request-target is not an asterisk, the OPTIONS request applies only to the options that are available when communicating with that resource. 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". The Max-Forwards request-header field &MAY; be used to target a specific proxy in the request chain (see ). If no Max-Forwards field is present in the request, then the forwarded request &MUST-NOT; include a Max-Forwards field.

yes The GET method means retrieve whatever information (in the form of a representation) currently corresponds to the target resource. 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. 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. 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 &header-range;. 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. The response to a GET request is cacheable and &MAY; be used to satisfy subsequent GET and HEAD requests (see &caching;). See for security considerations when used for forms.

yes 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. The response to a HEAD request is cacheable and &MAY; be used to satisfy a subsequent HEAD request; see &caching;. 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.

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: Annotation of existing resources; Posting a message to a bulletin board, newsgroup, mailing list, or similar group of articles; Providing a block of data, such as the result of submitting a form, to a data-handling process; Extending a database through an append operation. The actual function performed by the POST method is determined by the server and is usually dependent on the effective request URI. 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. 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 ). Responses to POST requests are only cacheable when they include explicit freshness information (see &p6-explicit;). A cached POST response with a Content-Location header field (see &header-content-location;) whose value is the effective Request URI &MAY; be used to satisfy subsequent GET and HEAD requests. 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.

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. 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. 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. 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. 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. 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. HTTP/1.1 does not define how a PUT method affects the state of an origin server. 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.

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. 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. 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.

yes 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 ). A TRACE request &MUST-NOT; include a message-body. TRACE allows the client to see what is being received at the other end of the request chain and use that data for testing or diagnostic information. The value of the Via header field (&header-via;) is of particular interest, since it acts as a trace of the request chain. Use of the Max-Forwards header field allows the client to limit the length of the request chain, which is useful for testing a chain of proxies forwarding messages in an infinite loop. If the request is valid, the response &SHOULD; have a Content-Type of "message/http" (see &media-type-message-http;) and contain a message-body that encloses a copy of the entire request message. Responses to the TRACE method are not cacheable.

This specification reserves the method name CONNECT for use with a proxy that can dynamically switch to being a tunnel (e.g., SSL tunneling ).

Each Status-Code is described below, including any metadata required in the response.

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. 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. 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).)

The client &SHOULD; continue with its request. This interim response is used to inform the client that the initial part of the request has been received and has not yet been rejected by the server. The client &SHOULD; continue by sending the remainder of the request or, if the request has already been completed, ignore this response. The server &MUST; send a final response after the request has been completed. See &use100; for detailed discussion of the use and handling of this status code.

The server understands and is willing to comply with the client's request, via the Upgrade message header field (&header-upgrade;), for a change in the application protocol being used on this connection. The server will switch protocols to those defined by the response's Upgrade header field immediately after the empty line which terminates the 101 response. 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.

This class of status code indicates that the client's request was successfully received, understood, and accepted.

The request has succeeded. The payload returned with the response is dependent on the method used in the request, for example: a representation of the target resource is sent in the response; the same representation as GET, except without the message-body; a representation describing or containing the result of the action; a representation containing the request message as received by the end server. Caches &MAY; use a heuristic (see &p6-heuristic;) to determine freshness for 200 responses.

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. 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 &header-etag;).

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. 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.

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). Caches &MAY; use a heuristic (see &p6-heuristic;) to determine freshness for 203 responses.

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. 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. The 204 response &MUST-NOT; include a message-body, and thus is always terminated by the first empty line after the header fields.

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.

Part5 The server has fulfilled the partial GET request for the resource and the enclosed payload is a partial representation as defined in &status-206;. Caches &MAY; use a heuristic (see &p6-heuristic;) to determine freshness for 206 responses.

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 . A client &SHOULD; detect infinite redirection loops, since such loops generate network traffic for each redirection. Note: An earlier version of this specification recommended a maximum of five redirections (). Content developers need to be aware that some clients might implement such a fixed limitation.

The target resource has more than one representation, each with its own specific location, and agent-driven negotiation information (&content-negotiation;) is being provided so that the user (or user agent) can select a preferred representation by redirecting its request to that location. 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. 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. Caches &MAY; use a heuristic (see &p6-heuristic;) to determine freshness for 300 responses.

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. Caches &MAY; use a heuristic (see &p6-heuristic;) to determine freshness for 301 responses. 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). If the 301 status code is received in response to a request method that is known to be "safe", as defined in , 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. 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.

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. 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). If the 302 status code is received in response to a request method that is known to be "safe", as defined in , 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. Note: HTTP/1.0 () and the first version of HTTP/1.1 () 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 () has added the status codes 303 and 307 for servers that wish to make unambiguously clear which kind of reaction is expected of the client.

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. 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. 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). 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.

Part4 The response to the request has not been modified since the conditions indicated by the client's conditional GET request, as defined in &status-304;.

The 305 status code was defined in a previous version of this specification (see ), and is now deprecated.

The 306 status code was used in a previous version of the specification, is no longer used, and the code is reserved.

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. 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. If the 307 status code is received in response to a request method that is known to be "safe", as defined in , 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.

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. 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.

The request could not be understood by the server due to malformed syntax. The client &SHOULD-NOT; repeat the request without modifications.

Part7 The request requires user authentication (see &status-401;).

This code is reserved for future use.

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.

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.

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.

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. 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. 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. 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.

This code is similar to 401 (Unauthorized), but indicates that the client must first authenticate itself with the proxy (see &status-407;).

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.

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. 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.

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. 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. Caches &MAY; use a heuristic (see &p6-heuristic;) to determine freshness for 410 responses.

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.

Part4 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 &status-412;.

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. 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.

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.

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.

Part5 The request included a Range request-header field (&header-range;) and none of the range-specifier values in this field overlap the current extent of the selected resource. See &status-416;.

The expectation given in an Expect request-header field (see ) 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.

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.

The server encountered an unexpected condition which prevented it from fulfilling the request.

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.

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.

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. 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.

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. Note to implementors: some deployed proxies are known to return 400 or 500 when DNS lookups time out.

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 &http-version;, 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.

This section defines the syntax and semantics of HTTP/1.1 header fields related to request and response semantics.

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.

Allow = "Allow" ":" OWS Allow-v Allow-v = #Method

Example of use:

Allow: GET, HEAD, PUT

The actual set of allowed methods is defined by the origin server at the time of each request. 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.

The "Expect" request-header field is used to indicate that particular server behaviors are required by the client.

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 ) ]

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. 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. Comparison of expectation values is case-insensitive for unquoted tokens (including the 100-continue token), and is case-sensitive for quoted-string expectation-extensions. 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. Many older HTTP/1.0 and HTTP/1.1 applications do not understand the Expect header field. See &use100; for the use of the 100 (Continue) status code.

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 :

From = "From" ":" OWS From-v From-v = mailbox mailbox = <mailbox, defined in >

An example is:

From: webmaster@example.org

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. 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. 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.

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. 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. The field value consists of a single URI-reference. When it has the form of a relative reference (), the final value is computed by resolving it against the effective request URI ().

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

Examples are: Location: http://www.example.org/pub/WWW/People.html#tim

Location: /index.html

There are circumstances in which a fragment identifier in a Location URI would not be appropriate: With a 201 Created response, because in this usage the Location header field specifies the URI for the entire created resource. With 305 Use Proxy. 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. Note: The Content-Location header field (&header-content-location;) differs from Location in that the Content-Location identifies the most specific resource corresponding to the enclosed representation. It is therefore possible for a response to contain header fields for both Location and Content-Location.

The "Max-Forwards" request-header field provides a mechanism with the TRACE () and 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.

Max-Forwards = "Max-Forwards" ":" OWS Max-Forwards-v Max-Forwards-v = 1*DIGIT

The Max-Forwards value is a decimal integer indicating the remaining number of times this request message can be forwarded. 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). 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.

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.). 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. 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).

Referer = "Referer" ":" OWS Referer-v Referer-v = absolute-URI / partial-URI

Example:

Referer: http://www.example.org/hypertext/Overview.html

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 for security considerations.

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. 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.

Retry-After = "Retry-After" ":" OWS Retry-After-v Retry-After-v = HTTP-date / delta-seconds

Time spans are non-negative decimal integers, representing time in seconds.

delta-seconds = 1*DIGIT

Two examples of its use are

Retry-After: Fri, 31 Dec 1999 23:59:59 GMT Retry-After: 120

In the latter example, the delay is 2 minutes.

The "Server" response-header field contains information about the software used by the origin server to handle the request. The field can contain multiple product tokens (&product-tokens;) and comments (&header-fields;) identifying the server and any significant subproducts. The product tokens are listed in order of their significance for identifying the application.

Server = "Server" ":" OWS Server-v Server-v = product *( RWS ( product / comment ) )

Example:

Server: CERN/3.0 libwww/2.17

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 &header-via;). 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.

The "User-Agent" request-header field contains information about the user agent originating the request. User agents &SHOULD; include this field with requests. Typically, it is used for statistical purposes, the tracing of protocol violations, and tailoring responses to avoid particular user agent limitations. The field can contain multiple product tokens (&product-tokens;) and comments (&header-fields;) identifying the agent and its significant subproducts. By convention, the product tokens are listed in order of their significance for identifying the application. 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. 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.

User-Agent = "User-Agent" ":" OWS User-Agent-v User-Agent-v = product *( RWS ( product / comment ) )

Example:

User-Agent: CERN-LineMode/2.15 libwww/2.17b3

The registration procedure for HTTP Methods is defined by of this document. The HTTP Method Registry shall be created at and be populated with the registrations below: Method Safe Reference CONNECT no DELETE no GET yes HEAD yes OPTIONS yes POST no PUT no TRACE yes

The registration procedure for HTTP Status Codes -- previously defined in -- is now defined by of this document. The HTTP Status Code Registry located at shall be updated with the registrations below: Value Description Reference 100 Continue 101 Switching Protocols 200 OK 201 Created 202 Accepted 203 Non-Authoritative Information 204 No Content 205 Reset Content 300 Multiple Choices 301 Moved Permanently 302 Found 303 See Other 305 Use Proxy 306 (Unused) 307 Temporary Redirect 400 Bad Request 402 Payment Required 403 Forbidden 404 Not Found 405 Method Not Allowed 406 Not Acceptable 407 Proxy Authentication Required 408 Request Timeout 409 Conflict 410 Gone 411 Length Required 413 Request Entity Too Large 414 URI Too Long 415 Unsupported Media Type 417 Expectation Failed 500 Internal Server Error 501 Not Implemented 502 Bad Gateway 503 Service Unavailable 504 Gateway Timeout 505 HTTP Version Not Supported

The Message Header Field Registry located at shall be updated with the permanent registrations below (see ): Header Field Name Protocol Status Reference Allow http standard Expect http standard From http standard Location http standard Max-Forwards http standard Referer http standard Retry-After http standard Server http standard User-Agent http standard The change controller is: "IETF (iesg@ietf.org) - Internet Engineering Task Force".

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.

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. 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. 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. 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. 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. 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. The User-Agent () or 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. Furthermore, the User-Agent header field may contain enough entropy to be used, possibly in conjunction with other material, to uniquely identify the user. Some methods, like 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.

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. Clients &SHOULD-NOT; include a Referer header field in a (non-secure) HTTP request if the referring page was transferred with a secure protocol. 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.

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.

Day Software

fielding@gbiv.com

Alcatel-Lucent Bell Labs

jg@freedesktop.org

Hewlett-Packard Company

JeffMogul@acm.org

Microsoft Corporation

henrikn@microsoft.com

Adobe Systems, Incorporated

LMM@acm.org

Microsoft Corporation

paulle@microsoft.com

World Wide Web Consortium

timbl@w3.org

World Wide Web Consortium

ylafon@w3.org

greenbytes GmbH

julian.reschke@greenbytes.de

Day Software

fielding@gbiv.com

Alcatel-Lucent Bell Labs

jg@freedesktop.org

Hewlett-Packard Company

JeffMogul@acm.org

Microsoft Corporation

henrikn@microsoft.com

Adobe Systems, Incorporated

LMM@acm.org

Microsoft Corporation

paulle@microsoft.com

World Wide Web Consortium

timbl@w3.org

World Wide Web Consortium

ylafon@w3.org

greenbytes GmbH

julian.reschke@greenbytes.de

Day Software

fielding@gbiv.com

Alcatel-Lucent Bell Labs

jg@freedesktop.org

Hewlett-Packard Company

JeffMogul@acm.org

Microsoft Corporation

henrikn@microsoft.com

Adobe Systems, Incorporated

LMM@acm.org

Microsoft Corporation

paulle@microsoft.com

World Wide Web Consortium

timbl@w3.org

World Wide Web Consortium

ylafon@w3.org

greenbytes GmbH

julian.reschke@greenbytes.de

Day Software

fielding@gbiv.com

Alcatel-Lucent Bell Labs

jg@freedesktop.org

Hewlett-Packard Company

JeffMogul@acm.org

Microsoft Corporation

henrikn@microsoft.com

Adobe Systems, Incorporated

LMM@acm.org

Microsoft Corporation

paulle@microsoft.com

World Wide Web Consortium

timbl@w3.org

World Wide Web Consortium

ylafon@w3.org

greenbytes GmbH

julian.reschke@greenbytes.de

Day Software

fielding@gbiv.com

Alcatel-Lucent Bell Labs

jg@freedesktop.org

Hewlett-Packard Company

JeffMogul@acm.org

Microsoft Corporation

henrikn@microsoft.com

Adobe Systems, Incorporated

LMM@acm.org

Microsoft Corporation

paulle@microsoft.com

World Wide Web Consortium

timbl@w3.org

World Wide Web Consortium

ylafon@w3.org

mnot@mnot.net

greenbytes GmbH

julian.reschke@greenbytes.de

Day Software

fielding@gbiv.com

Alcatel-Lucent Bell Labs

jg@freedesktop.org

Hewlett-Packard Company

JeffMogul@acm.org

Microsoft Corporation

henrikn@microsoft.com

Adobe Systems, Incorporated

LMM@acm.org

Microsoft Corporation

paulle@microsoft.com

World Wide Web Consortium

timbl@w3.org

World Wide Web Consortium

ylafon@w3.org

greenbytes GmbH

julian.reschke@greenbytes.de

Harvard University

sob@harvard.edu

World Wide Web Consortium

timbl@w3.org http://www.w3.org/People/Berners-Lee/

Day Software

fielding@gbiv.com http://roy.gbiv.com/

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Brandenburg InternetWorking

dcrocker@bbiw.net

THUS plc.

paul.overell@thus.net

MIT, Laboratory for Computer Science

timbl@w3.org

University of California, Irvine, Department of Information and Computer Science

fielding@ics.uci.edu

W3 Consortium, MIT Laboratory for Computer Science

frystyk@w3.org

University of California, Irvine, Department of Information and Computer Science

fielding@ics.uci.edu

MIT Laboratory for Computer Science

jg@w3.org

Digital Equipment Corporation, Western Research Laboratory

mogul@wrl.dec.com

MIT Laboratory for Computer Science

frystyk@w3.org

MIT Laboratory for Computer Science

timbl@w3.org

University of California, Irvine

fielding@ics.uci.edu

W3C

jg@w3.org

Compaq Computer Corporation

mogul@wrl.dec.com

MIT Laboratory for Computer Science

frystyk@w3.org

Xerox Corporation

masinter@parc.xerox.com

Microsoft Corporation

paulle@microsoft.com

W3C

timbl@w3.org

4K Associates / UC Irvine

rohit@4K-associates.com

Agranat Systems, Inc.

lawrence@agranat.com

Nine by Nine

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HP Labs

JeffMogul@acm.org

IBM

narten@us.ibm.com

Google

Harald@Alvestrand.no

Qualcomm Incorporated

This document takes over the Status Code Registry, previously defined in . () Clarify definition of POST. () 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 , and ) 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. () 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. () 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. () Allow Referer field value of "about:blank" as alternative to not specifying it. () 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 &header-via;. ()

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>

ABNF diagnostics: ; Reason-Phrase defined but not used ; Status-Code defined but not used ; request-header defined but not used ; response-header defined but not used

Extracted relevant partitions from .

Closed issues: : "Via is a MUST" () : "Fragments allowed in Location" () : "Safe Methods vs Redirection" () : "Revise description of the POST method" () : "Normative and Informative references" : "RFC2606 Compliance" : "Informative references" : "Redundant cross-references" Other changes: Move definitions of 304 and 412 condition codes to

Closed issues: : "PUT side effects" : "Duplicate Host header requirements" Ongoing work on ABNF conversion (): Move "Product Tokens" section (back) into Part 1, as "token" is used in the definition of the Upgrade header field. Add explicit references to BNF syntax and rules imported from other parts of the specification. Copy definition of delta-seconds from Part6 instead of referencing it.

Closed issues: : "Requiring Allow in 405 responses" : "Status Code Registry" : "Redirection vs. Location" : "Cacheability of 303 response" : "305 Use Proxy" : "Classification for Allow header" : "PUT - 'store under' vs 'store at'" Ongoing work on IANA Message Header Field Registration (): Reference RFC 3984, and update header field registrations for headers defined in this document. Ongoing work on ABNF conversion (): Replace string literals when the string really is case-sensitive (method).

Closed issues: : "OPTIONS request bodies" : "Description of CONNECT should refer to RFC2817" : "Location Content-Location reference request/response mixup" Ongoing work on Method Registry (): Added initial proposal for registration process, plus initial content (non-HTTP/1.1 methods to be added by a separate specification).

Closed issues: : "Content-*" : "RFC 2822 is updated by RFC 5322" Ongoing work on ABNF conversion (): Use "/" instead of "|" for alternatives. Introduce new ABNF rules for "bad" whitespace ("BWS"), optional whitespace ("OWS") and required whitespace ("RWS"). Rewrite ABNFs to spell out whitespace rules, factor out header field value format definitions.

Closed issues: : "Reason-Phrase BNF" Final work on ABNF conversion (): Add appendix containing collected and expanded ABNF, reorganize ABNF introduction.

Closed issues: : "Clarify when Referer is sent" : "status codes vs methods" : "Do not require "updates" relation for specs that register status codes or method names"

Closed issues: : "Idempotency" : "TRACE security considerations" : "Clarify rules for determining what entities a response carries" : "update note citing RFC 1945 and 2068" : "update note about redirect limit" : "Location header ABNF should use 'URI'" : "fragments in Location vs status 303" : "move IANA registrations for optional status codes" Partly resolved issues: : "Are OPTIONS and TRACE safe?"

Closed issues: : "Safe Methods vs Redirection" (we missed the introduction to the 3xx status codes when fixing this previously)

Closed issues: : "Fragment combination / precedence during redirects" Partly resolved issues: : "Location header payload handling" : "Term for the requested resource's URI"

Closed issues: : "Clarify 'Requested Variant'" : "Clarify entity / representation / variant terminology" : "Methods and Caching" : "OPTIONS vs Max-Forwards" : "Status codes and caching" : "consider removing the 'changes from 2068' sections"

Closed issues: : "Considerations for new status codes" : "Considerations for new methods" : "User-Agent guidelines" (relating to the 'User-Agent' header field)