HTTP Working Group R. Fielding, UC Irvine INTERNET-DRAFT H. Frystyk, MIT/LCS <draft-ietf-http-v11-spec-01.html> T. Berners-Lee, MIT/LCS Expires May 22, 1996 January 19, 1996
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NOTE: This specification is for discussion purposes only. It is not claimed to represent the consensus of the HTTP working group, and contains a number of proposals that either have not been discussed or are controversial. The working group is discussing significant changes in many areas, including logic bags, support for caching, range retrieval, content negotiation, MIME compatibility, authentication, timing of the PUT operation.
HTTP has been in use by the World-Wide Web global information initiative since 1990. This specification defines the protocol referred to as "HTTP/1.1".
1. Introduction 1.1 Purpose 1.2 Requirements 1.3 Terminology 1.4 Overall Operation 2. Notational Conventions and Generic Grammar 2.1 Augmented BNF 2.2 Basic Rules 3. Protocol Parameters 3.1 HTTP Version 3.2 Uniform Resource Identifiers 3.2.1 General Syntax 3.2.2 http URL 3.3 Date/Time Formats 3.3.1 Full Date 3.3.2 Delta Seconds 3.4 Character Sets 3.5 Content Codings 3.6 Transfer Codings 3.7 Media Types 3.7.1 Canonicalization and Text Defaults 3.7.2 Multipart Types 3.8 Product Tokens 3.9 Quality Values 3.10 Language Tags 3.11 Logic Bags 4. HTTP Message 4.1 Message Types 4.2 Message Headers 4.3 General Header Fields 5. Request 5.1 Request-Line 5.1.1 Method 5.1.2 Request-URI 5.2 Request Header Fields 6. Response 6.1 Status-Line 6.1.1 Status Code and Reason Phrase 6.2 Response Header Fields 7. Entity 7.1 Entity Header Fields 7.2 Entity Body 7.2.1 Type 7.2.2 Length 8. Method Definitions 8.1 OPTIONS 8.2 GET 8.3 HEAD 8.4 POST 8.5 PUT 8.6 PATCH 8.7 COPY 8.8 MOVE 8.9 DELETE 8.10 LINK 8.11 UNLINK 8.12 TRACE 8.13 WRAPPED 9. Status Code Definitions 9.1 Informational 1xx 100 Continue 101 Switching Protocols 9.2 Successful 2xx 200 OK 201 Created 202 Accepted 203 Non-Authoritative Information 204 No Content 205 Reset Content 206 Partial Content 9.3 Redirection 3xx 300 Multiple Choices 301 Moved Permanently 302 Moved Temporarily 303 See Other 304 Not Modified 305 Use Proxy 9.4 Client Error 4xx 400 Bad Request 401 Unauthorized 402 Payment Required 403 Forbidden 404 Not Found 405 Method Not Allowed 406 None Acceptable 407 Proxy Authentication Required 408 Request Timeout 409 Conflict 410 Gone 411 Length Required 412 Unless True 9.5 Server Error 5xx 500 Internal Server Error 501 Not Implemented 502 Bad Gateway 503 Service Unavailable 504 Gateway Timeout 10. Header Field Definitions 10.1 Accept 10.2 Accept-Charset 10.3 Accept-Encoding 10.4 Accept-Language 10.5 Allow 10.6 Authorization 10.7 Base 10.8 Cache-Control 10.9 Connection 10.9.1 Persistent Connections 10.10 Content-Encoding 10.11 Content-Language 10.12 Content-Length 10.13 Content-MD5 10.14 Content-Range 10.15 Content-Type 10.16 Content-Version 10.17 Date 10.18 Derived-From 10.19 Expires 10.20 Forwarded 10.21 From 10.22 Host 10.23 If-Modified-Since 10.24 Keep-Alive 10.25 Last-Modified 10.26 Link 10.27 Location 10.28 MIME-Version 10.29 Pragma 10.30 Proxy-Authenticate 10.31 Proxy-Authorization 10.32 Public 10.33 Range 10.34 Referer 10.35 Refresh 10.36 Retry-After 10.37 Server 10.38 Title 10.39 Transfer Encoding 10.40 Unless 10.41 Upgrade 10.42 URI 10.43 User-Agent 10.44 WWW-Authenticate 11. Access Authentication 11.1 Basic Authentication Scheme 11.2 Digest Authentication Scheme 12. Content Negotiation 12.1 Preemptive Negotiation 13. Caching 14. Security Considerations 14.1 Authentication of Clients 14.2 Safe Methods 14.3 Abuse of Server Log Information 14.4 Transfer of Sensitive Information 15. Acknowledgments 16. References 17. Authors' Addresses Appendix A. Internet Media Type message/http Appendix B. Tolerant Applications Appendix C. Relationship to MIME C.1 Conversion to Canonical Form C.1.1 Representation of Line Breaks C.1.2 Default Character Set C.2 Conversion of Date Formats C.3 Introduction of Content-Encoding C.4 No Content-Transfer-Encoding C.5 Introduction of Transfer-Encoding Appendix D. Changes from HTTP/1.0
This specification defines the protocol referred to as "HTTP/1.1". This protocol is backwards-compatible with HTTP/1.0, but includes more stringent requirements in order to ensure reliable implementation of its features.
Practical information systems require more functionality than simple retrieval, including search, front-end update, and annotation. HTTP allows an open-ended set of methods to be used to indicate the purpose of a request. It builds on the discipline of reference provided by the Uniform Resource Identifier (URI) [3], as a location (URL) [4] or name (URN) [20], for indicating the resource on which a method is to be applied. Messages are passed in a format similar to that used by Internet Mail [9] and the Multipurpose Internet Mail Extensions (MIME) [7].
HTTP is also used as a generic protocol for communication between user agents and proxies/gateways to other Internet protocols, such as SMTP [16], NNTP [13], FTP [18], Gopher [2], and WAIS [10], allowing basic hypermedia access to resources available from diverse applications and simplifying the implementation of user agents.
Most HTTP communication is initiated by a user agent and consists of a request to be applied to a resource on some origin server. In the simplest case, this may be accomplished via a single connection (v) between the user agent (UA) and the origin server (O).
request chain ------------------------> UA -------------------v------------------- O <----------------------- response chainA more complicated situation occurs when one or more intermediaries are present in the request/response chain. There are three common forms of intermediary: proxy, gateway, and tunnel. A proxy is a forwarding agent, receiving requests for a URI in its absolute form, rewriting all or parts of the message, and forwarding the reformatted request toward the server identified by the URI. A gateway is a receiving agent, acting as a layer above some other server(s) and, if necessary, translating the requests to the underlying server's protocol. A tunnel acts as a relay point between two connections without changing the messages; tunnels are used when the communication needs to pass through an intermediary (such as a firewall) even when the intermediary cannot understand the contents of the messages.
request chain --------------------------------------> UA -----v----- A -----v----- B -----v----- C -----v----- O <------------------------------------- response chainThe figure above shows three intermediaries (A, B, and C) between the user agent and origin server. A request or response message that travels the whole chain must pass through four separate connections. This distinction is important because some HTTP communication options may apply only to the connection with the nearest, non-tunnel neighbor, only to the end-points of the chain, or to all connections along the chain. Although the diagram is linear, each participant may be engaged in multiple, simultaneous communications. For example, B may be receiving requests from many clients other than A, and/or forwarding requests to servers other than C, at the same time that it is handling A's request.
Any party to the communication which is not acting as a tunnel may employ an internal cache for handling requests. The effect of a cache is that the request/response chain is shortened if one of the participants along the chain has a cached response applicable to that request. The following illustrates the resulting chain if B has a cached copy of an earlier response from O (via C) for a request which has not been cached by UA or A.
request chain ----------> UA -----v----- A -----v----- B - - - - - - C - - - - - - O <--------- response chainNot all responses are cachable, and some requests may contain modifiers which place special requirements on cache behavior. HTTP requirements for cache behavior and cachable responses are defined in Section 13.
On the Internet, HTTP communication generally takes place over TCP/IP connections. The default port is TCP 80 [19], but other ports can be used. This does not preclude HTTP from being implemented on top of any other protocol on the Internet, or on other networks. HTTP only presumes a reliable transport; any protocol that provides such guarantees can be used, and the mapping of the HTTP/1.1 request and response structures onto the transport data units of the protocol in question is outside the scope of this specification.
For most implementations, each connection is established by the client prior to the request and closed by the server after sending the response. However, this is not a feature of the protocol and is not required by this specification. Both clients and servers must be capable of handling cases where either party closes the connection prematurely, due to user action, automated time-out, or program failure. In any case, the closing of the connection by either or both parties always terminates the current request, regardless of its status.
name = definition
"<"
and ">"
) and is
separated from its definition by the equal character "="
. Whitespace is only significant in
that indentation of continuation lines is used to indicate a rule definition that spans more
than one line. Certain basic rules are in uppercase, such as SP
,
LWS
, HT
, CRLF
, DIGIT
,
ALPHA
, etc. Angle brackets are used within definitions whenever their presence will
facilitate discerning the use of rule names.
"literal"
rule1 | rule2
"I"
) are alternatives,
e.g., "yes | no
" will accept yes
or no
.
(rule1 rule2)
(elem (foo | bar) elem)
" allows the token sequences
"elem foo elem
" and "elem bar elem
".
*rule
"*"
preceding an element indicates repetition.
The full form is "<n>*<m>element
" indicating at
least <n>
and at most <m>
occurrences of element
. Default values are 0
and infinity so that "*(element)
" allows any number,
including zero; "1*element
" requires at least one;
and "1*2element
" allows one or two.
[rule]
[foo bar]
"
is equivalent to "*1(foo bar)
".
rule
<n>(element)
" is equivalent to
"<n>*<n>(element)
"; that is, exactly
<n>
occurrences of (element)
.
Thus 2DIGIT
is a 2-digit number, and 3ALPHA
is a string of three alphabetic characters.
#rule
"#"
is defined, similar to "*"
,
for defining lists of elements. The full form is
"<n>#<m>element"
indicating at least
<n>
and at most <m>
elements,
each separated by one or more commas (","
) and optional
linear whitespace (LWS). This makes the usual form of lists very easy;
a rule such as "( *LWS element *( *LWS "," *LWS element ))"
can be shown as "1#element"
. Wherever this construct is used,
null elements are allowed, but do not contribute to the count of elements
present. That is, "(element), , (element)"
is permitted, but
counts as only two elements. Therefore, where at least one element is
required, at least one non-null element must be present. Default values
are 0
and infinity so that "#(element)"
allows any number, including zero; "1#element"
requires
at least one; and "1#2element
" allows one or two.
; comment
implied *LWS
LWS
) can be included
between any two adjacent words (token
or
quoted-string
), and between adjacent tokens and delimiters
(tspecials
), without changing the interpretation of a field.
At least one delimiter (tspecials
) must exist between any
two tokens, since they would otherwise be interpreted as a single token.
However, applications should attempt to follow "common form" when
generating HTTP constructs, since there exist some implementations that
fail to accept anything beyond the common forms.
OCTET = <any 8-bit sequence of data> CHAR = <any US-ASCII character (octets 0 - 127)> UPALPHA = <any US-ASCII uppercase letter "A".."Z"> LOALPHA = <any US-ASCII lowercase letter "a".."z"> ALPHA = UPALPHA | LOALPHA DIGIT = <any US-ASCII digit "0".."9"> CTL = <any US-ASCII control character (octets 0 - 31) and DEL (127)> CR = <US-ASCII CR, carriage return (13)> LF = <US-ASCII LF, linefeed (10)> SP = <US-ASCII SP, space (32)> HT = <US-ASCII HT, horizontal-tab (9)> <"> = <US-ASCII double-quote mark (34)>HTTP/1.1 defines the octet sequence
CR LF
as the end-of-line marker for all protocol elements
except the Entity-Body
(see Appendix B for tolerant applications). The end-of-line marker
within an Entity-Body
is defined by its associated media type, as described in Section 3.7.
CRLF = CR LFHTTP/1.1 headers can be folded onto multiple lines if the continuation line begins with a space or horizontal tab. All linear whitespace, including folding, has the same semantics as
SP
.
LWS = [CRLF] 1*( SP | HT )The
TEXT
rule is only used for descriptive field contents and values that are not intended to be
interpreted by the message parser. Words of *TEXT
may contain octets from character sets other
than US-ASCII only when encoded according to the rules of RFC 1522 [14].
TEXT = <any OCTET except CTLs, but including LWS>Recipients of header field
TEXT
containing octets outside the US-ASCII character set range
may assume that they represent ISO-8859-1 characters if there is no other encoding indicated
by an RFC 1522 mechanism.
Hexadecimal numeric characters are used in several protocol elements.
HEX = "A" | "B" | "C" | "D" | "E" | "F" | "a" | "b" | "c" | "d" | "e" | "f" | DIGITMany HTTP/1.1 header field values consist of words separated by
LWS
or special characters.
These special characters must be in a quoted string to be used within a parameter value.
word = token | quoted-string
token = 1*<any CHAR except CTLs or tspecials>
tspecials = "(" | ")" | "<" | ">" | "@" | "," | ";" | ":" | "\" | <"> | "/" | "[" | "]" | "?" | "=" | "{" | "}" | SP | HTComments can be included in some HTTP header fields by surrounding the comment text with parentheses. Comments are only allowed in fields containing "
comment
" as part of their field
value definition. In all other fields, parentheses are considered part of the field value.
comment = "(" *( ctext | comment ) ")" ctext = <any TEXT excluding "(" and ")">A string of text is parsed as a single word if it is quoted using double-quote marks.
quoted-string = ( <"> *(qdtext) <"> )
qdtext = <any CHAR except <"> and CTLs, but including LWS>The backslash character ("\") may be used as a single-character quoting mechanism only within quoted-string and comment constructs.
quoted-pair = "\" CHARBraces are used to delimit an attribute-value bag, which may consist of a set, list, or recursively defined tokens and quoted strings. The bag semantics are defined by its context and the bag name, which may be a Uniform Resource Identifier (Section 3.2) in some fields.
bag = "{" bagname 1*LWS *bagitem "}" bagname = token | URI bagitem = bag | token | quoted-string
Thpversion of an HTTP message is indicated by anp
Applications sending
HTTP/1.1 servers must:
HTTP/1.1 clients must:
Transfer codings are analogous to the Content-Transfer-Encoding values of MIME [7], which
were designed to enable safe transport of binary data over a 7-bit transport service. However,
"safe transport" has a different focus for an 8bit-clean transfer protocol. In HTTP, the only
unsafe characteristic of message bodies is the difficulty in determining the exact body length
(Section 7.2.2), or the desire to encrypt data over a shared transport.
All HTTP/1.1 applications must be able to receive and decode the "chunked" transfer coding.
The chunked encoding modifies the body of a message in order to transfer it as a series of
chunks, each with its own size indicator, followed by an optional footer containing
entity-header fields. This allows dynamically-produced content to be transferred along with the
information necessary for the recipient to verify that it has received the full message.
If a given
All
HTTP redefines the canonical form of text media to allow multiple octet sequences to indicate
a text line break. In addition to the preferred form of CRLF, HTTP applications must accept a
bare CR or LF alone as representing a single line break in text media. Furthermore, if the text
media is represented in a character set which does not use octets 13 and 10 for CR and LF
respectively, as is the case for some multi-byte character sets, HTTP allows the use of whatever
octet sequence(s) is defined by that character set to represent the equivalent of CRLF, bare CR,
and bare LF. It is assumed that any recipient capable of using such a character set will know
the appropriate octet sequence for representing line breaks within that character set.
HTTP also redefines the default character set for text media in an entity body. If a textual media
type defines a charset parameter with a registered default value of "US-ASCII", HTTP changes
the default to be "ISO-8859-1". Since the ISO-8859-1 [22] character set is a superset of
US-ASCII [21], this does not affect the interpretation of entity bodies which only contain octets
within the US-ASCII character set (0 - 127). The presence of a charset parameter value in a
It is recommended that the character set of an entity body be labelled as the lowest common
denominator of the character codes used within a document, with the exception that no label is
preferred over the labels US-ASCII or ISO-8859-1.
In HTTP, multipart body-parts may contain header fields which are significant to the meaning
of that part. A URI entity-header field (Section 10.42) should be included in the body-part for
each enclosed entity that can be identified by a URI.
In general, an HTTP user agent should follow the same or similar behavior as a MIME user
agent would upon receipt of a multipart type. The following subtypes have been defined:
The syntax and registry of HTTP language tags is the same as that defined by RFC 1766 [1].
In summary, a language tag is composed of 1 or more parts: A primary language tag and a
possibly empty series of subtags:
In the context of the Accept-Language header (Section 10.4), a language tag is not to be
interpreted as a single token, as per RFC 1766, but as a hierarchy. A server should consider that
it has a match when a language tag received in an Accept-Language header matches the initial
portion of the language tag of a document. An exact match should be preferred. This
interpretation allows a browser to send, for example:
Except for "ne", any comparison to a field not defined by the resource evaluates to false.
Multiple
The methods GET and HEAD must be supported by all general-purpose servers. Servers which
provide Last-Modified dates for resources must also support the conditional GET method. All
other methods are optional; however, if the above methods are implemented, they must be
implemented with the same semantics as those specified in Section 8.
If a proxy receives a request without any path in the
The Request-URI is transmitted as an encoded string, where some characters may be escaped
using the "% hex hex" encoding defined by RFC 1738 [4]. The origin server must decode the
Request-URI in order to properly interpret the request.
The first digit of the
For response messages, whether or not an entity body is included with a message is dependent
on both the request method and the response code. All responses to the HEAD request method
must not include a body, even though the presence of entity header fields may lead one to
believe they do. All 1xx (informational), 204 (no content), and 304 (not modified) responses
must not include a body. All other responses must include an entity body or a
Any HTTP/1.1 message containing an entity body should include a
If a request contains an entity body and
Messages must not include both a
When a
The semantics of all methods may be affected by the presence of an
Unless the server's response is an error, the response must not include entity information other
than what can be considered as communication options (e.g.,
If the
If the
The semantics of the
The semantics of the
The response to a
The response to a
There is no "conditional
HTTP/1.1 allows for a two-phase process to occur in accepting and processing a
Upon receipt of a
For compatibility with HTTP/1.0 applications, all
The client can suggest one or more URIs for the new resource by including a URI header field
in the request. However, the server should treat those URIs as advisory and may store the entity
under a different URI, additional URIs, or without any URI.
The client may apply relationships between the new resource and other existing resources by
including Link header fields, as described in Section 10.26. The server may use the Link
information to perform other operations as a result of the new resource being added. For
example, lists and indexes might be updated. However, no mandatory operation is imposed on
the origin server. The origin server may also generate its own or additional links to other
resources.
A successful
If a resource has been created on the origin server, the response should be 201 (created) and
contain an entity (preferably of type "text/html") which describes the status of the request and
refers to the new resource.
Responses to this method are not cachable. However, the 303 (see other) response can be used
to direct the user agent to retrieve a cachable resource.
If the request passes through a cache and the
The fundamental difference between the
A single resource may be identified by many different URIs. For example, an article may have
a URI for identifying "the current version" which is separate from the URI identifying each
particular version. In this case, a
HTTP/1.1 allows for a two-phase process to occur in accepting and processing a
Upon receipt of a
For compatibility with HTTP/1.0 applications, all
The client can create or modify relationships between the enclosed entity and other existing
resources by including Link header fields, as described in Section 10.26. As with POST, the
server may use the Link information to perform other operations as a result of the request.
However, no mandatory operation is imposed on the origin server. The origin server may
generate its own or additional links to other resources.
The actual method for determining how the resource is placed, and what happens to its
predecessor, is defined entirely by the origin server. If version control is implemented by the
origin server, then
If the request passes through a cache and the
HTTP/1.1 allows for a two-phase process to occur in accepting and processing a
Upon receipt of a
For compatibility with HTTP/1.0 applications, all
The client can create or modify relationships between the new resource and other existing
resources by including Link header fields, as described in Section 10.26. As with POST, the
server may use the Link information to perform other operations as a result of the request.
However, no mandatory operation is imposed on the origin server. The origin server may
generate its own or additional links to other resources.
The actual method for determining how the patched resource is placed, and what happens to its
predecessor, is defined entirely by the origin server. If version control is implemented by the
origin server, then
If the request passes through a cache and the
A successful response should be 200 (ok) if the response includes an entity describing the
status, 202 (accepted) if the action has not yet been enacted, or 204 (no content) if the response
is OK but does not include an entity.
If the request passes through a cache and the
If the request passes through a cache and the
If the request passes through a cache and the
If successful, the response should contain the entire, unedited request message in the entity
body, with a Content-Type of "message/http", "application/http", or "text/plain". Responses to
this method are not cachable.
Responses to this method are not cachable. Applications should not use this method for making
requests that would normally be public and cachable.
The request entity must include at least one encapsulated message, with the media type
identifying the protocol of that message. For example, if the wrapped request is another HTTP
request message, then the media type must be either "message/http" (for a single message) or
"application/http" (for a request stream containing one or more requests), with any codings
identied by the
HTTP/1.1 allows for a two-phase process to occur in accepting and processing a
Upon receipt of a
For compatibility with HTTP/1.0 applications, all
The protocol should only be switched 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 may be advantageous when delivering resources that use such features.
The 202 response is intentionally non-committal. Its purpose is to allow a server to accept a
request for some other process (perhaps a batch-oriented process that is only run once per day)
without requiring that the user agent's connection to the server persist until the process is
completed. The entity returned with this response should include an indication of the request's
current status and either a pointer to a status monitor or some estimate of when the user can
expect the request to be fulfilled.
The 204 response must not include an entity body, and thus is always ternminated by the first
empty line after the header fields.
If the new URI is a single location, its URL must be given by the
If the 301 status code is received in response to a request other than
If the new URI is a single location, its URL must be given by the
If the 302 status code is received in response to a request other than
If the new URI is a single location, its URL must be given by the Location field in the response.
If more than one URI exists for the resource, the primary URL should be given in the Location
field and the other URIs given in one or more URI-header fields. Unless it was a HEAD request,
the Entity-Body of the response should contain a short hypertext note with a hyperlink to the new
URI(s).
A cache should update its cached entity to reflect any new field values given in the 304
response. If the new field values indicate that the cached entity differs from the current resource
(as would be indicated by a change in
The 304 response must not include an entity body, and thus is always ternminated by the first
empty line after the header fields.
Conflicts are most likely to occur in response to a
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.
The field may be folded onto several lines and more than one occurrence of the field is allowed,
with the semantics being the same as if all the entries had been in one field value.
The example
If no Accept header is present, then it is assumed that the client accepts all media types with
quality factor 1. This is equivalent to the client sending the following accept header field:
A more elaborate example is
Media ranges can be overridden by more specific media ranges or specific media types. If more
than one media range applies to a given type, the most specific reference has precedence. For
example,
If the server cannot fulfill the request with one or more of the languages given, or if the
languages only represent a subset of a multi-linguistic Entity-Body, it is acceptable to serve the
request in an unspecified language. This is equivalent to assigning a quality value of "q=0.001"
to any unlisted language.
If no
The
A proxy must not modify the
The
Responses to requests containing an
The "cachable" directive indicates that the entire response message is cachable unless required
otherwise by HTTP restrictions on the request method and response code. In other words, this
directive indicates that the server believes the response to be cachable. This directive applies
only to responses and must not be used with any other cache directive.
When the "max-age" directive is present in a request message, an application must forward
the request toward the origin server if it has no cached copy, or refresh its cached copy if it is
older than the age value given (in seconds) prior to returning a response. A cached copy's age
is determined by the cached message's Date header field, or the equivalent as stored by the
cache manager.
In most cases, a cached copy can be refreshed by forwarding a conditional GET request toward
the origin server with the stored message's
When the "max-age" directive is present in a cached response message, an application must
refresh the message if it is older than the age value given (in seconds) at the time of a new
request for that resource. The behavior should be equivalent to what would occur if the request
had included the max-age directive. If both the new request and the cached message have
max-age specified, then the lesser of the two values must be used. A max-age value of zero (0)
forces a cache to perform a refresh (If-Modified-Since) on every request. The max-age directive
on a response implies that the server believes it to be cachable.
The "private" directive indicates that parts of the response message are intended for a single
user and must not be cached except within a private (non-shared) cache controlled by the user
agent. If no list of field names is given, then the entire message is private; otherwise, only the
information within the header fields identified by the list of names is private and the remainder
of the message is believed to be cachable by any application. This allows an origin server to
state that the specified parts of the message are intended for only one user and are not a valid
response for requests by other agents. The "private" directive is only applicable to responses
and must not be generated by clients.
The "no-cache" directive on a response message indicates that parts of the message must
never be cached. If no list of field names is given, then the entire message must not be cached;
otherwise, only the information within the header fields identified by the list of names must not
be cached and the remainder of the message is believed to be cachable. This allows an origin
server to state that the specified parts of the message are intended for only one recipient and
must not be stored unless the user explicitly requests it through a separate action.
The max-age, private, and no-cache directives may be used in combination to define the
cachability of each part of the message. In all cases, no-cache takes precedence over private,
which in turn takes precedence over max-age.
Cache directives must be passed through by a proxy or gateway application, regardless of their
significance to that application, since the directives may be applicable to all recipients along
the request/response chain. It is not possible to specify a cache-directive for a specific cache.
Whether or not the listed field-name(s) occur as header fields in the message is optional. If no
corresponding header field is present, then the field name is treated as a keyword. Keywords
are useful for indicating a desired option without assigning parameters to that option. This
allows for a minimal syntax to provide connection-based options without pre-restricting the
syntax or number of those options. HTTP/1.1 only defines the "keep-alive" keyword.
The semantics of Connection are defined by HTTP/1.1 in order to provide a safe transition to
connection-based features. Connection header fields received in an HTTP/1.0 message, as
would be the case if an older proxy mistakenly forwards the field, cannot be trusted and must
be discarded except under experimental conditions.
As an example, a client would send
The
The persistent connection ends when either side closes the connection or after the receipt of a
response which lacks the "keep-alive" keyword. The server may close the connection
immediately after responding to a request without a "keep-alive" keyword. A client can tell if
the connection will be closed by looking for a "keep-alive" in the response.
If multiple encodings have been applied to a resource, the content codings must be listed in the
order in which they were applied. Additional information about the encoding parameters may
be provided by other Entity-Header fields not defined by this specification.
Multiple languages may be listed for content that is intended for multiple audiences. For
example, a rendition of the "Treaty of Waitangi," presented simultaneously in the original
Maori and English versions, would call for
Content-Language may be applied to any media type -- it should not be limited to textual
documents.
Any
In theory, the date should represent the moment just before the entity is generated. In practice,
the date can be generated at any time during the message origination without affecting its
semantic value.
The Expires field cannot be used to force a user agent to refresh its display or reload a resource;
its semantics apply only to caching mechanisms, and such mechanisms need only check a
resource's expiration status when a new request for that resource is initiated.
User agents often have history mechanisms, such as "Back" buttons and history lists, which can
be used to redisplay an entity retrieved earlier in a session. By default, the
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.
HTTP/1.1 defines semantics for the optional "timeout" and "max" parameters on responses;
other parameters may be added and the field may also be used on request messages. The
"timeout" parameter allows the server to indicate, for diagnostic purposes only, the amount of
time in seconds it is currently allowing between when the response was generated and when
the next request is received from the client (i.e., the request timeout limit). Similarly, the "max"
parameter allows the server to indicate the maximum additional requests that it will allow on
the current persistent connection.
For example, the server may respond to a request for a persistent connection with
An origin server must not send a Last-Modified date which is later than the server's time of
message origination. In such cases, where the resource's last modification would indicate some
time in the future, the server must replace that date with the message origination date.
Examples of usage include:
Pragma directives must be passed through by a proxy or gateway application, regardless of
their significance to that application, since the directives may be applicable to all recipients
along the request/response chain. It is not possible to specify a pragma for a specific recipient;
however, any pragma directive not relevant to a recipient should be ignored by that recipient.
If the
User agents may use this information to notify the user of additional formats and to guide the
process of reactive content negotiation (Section 12).
A user agent that wishes to authenticate itself with a server--usually, but not necessarily, after
receiving a 401 or 411 response--may do so by including an
If the server does not wish to accept the credentials sent with a request, it should return a 401
(unauthorized) response. The response must include a
The HTTP protocol does not restrict applications to this simple challenge-response mechanism
for access authentication. Additional mechanisms may be used, such as encryption at the
transport level or via message encapsulation, and with additional header fields specifying
authentication information. However, these additional mechanisms are not defined by this
specification.
Proxies must be completely transparent regarding user agent authentication. That is, they must
forward the
HTTP/1.1 allows a client pass authentication information to and from a proxy via the
Upon receipt of an unauthorized request for a URI within the protection space, the server
should respond with a challenge like the following:
To receive authorization, the client sends the user-ID and password, separated by a single colon
(":") character, within a base64 [7] encoded string in the
Servers that make use of content negotiated resources must include URI response headers
which accurately describe the available variants, and include the relevant parameters necessary
for the client (user agent or proxy) to evaluate those variants.
The first step in the negotiation algorithm is for the server to determine whether or not there are
any content variants for the requested resource. Content variants may be in the form of multiple
preexisting entities or a set of dynamic conversion filters. These variants make up the set of
entities which may be sent in response to a request for the given Request-URI. In most cases,
there will only be one available form of the resource, and thus a single "variant".
For each variant form of the resource, the server identifies a set of quality values
(Section 3.9)
which act as weights for measuring the desirability of that resource as a response to the current
request. The calculated weights are all real numbers in the range 0 through 1, where 0 is the
minimum and 1 the maximum value. The maximum acceptable bytes for each media range and
the size of the resource variant are also factors in the equation.
The following parameters are included in the calculation:
If no variants remain with a value of Q greater than zero (0), the server should respond with a
406 (none acceptable) response message. If multiple variants remain with an equally high Q
value, the server may either choose one from those available and respond with 200 (ok) or
respond with 300 (multiple choices) and include an entity describing the choices. In the latter
case, the entity should either be of type "text/html', such that the user can choose from among
the choices by following an exact link, or of some type that would allow the user agent to
perform the selection automatically.
The 300 (multiple choices) response can be given even if the server does not perform any
winnowing of the representation choices via the content negotiation algorithm described
above. Furthermore, it may include choices that were not considered as part of the negotiation
algorithm and resources that may be located at other servers.
The algorithm presented above assumes that the user agent has correctly implemented the
protocol and is accurately communicating its intentions in the form of Accept-related header
fields. The server may alter its response if it knows that the particular version of user agent
software making the request has incorrectly or inadequately implemented these fields.
In particular, the convention has been established that the
Naturally, it is not possible to ensure that the server does not generate side-effects as a result of
performing a
Revealing the specific software version of the server may allow the server machine to become
more vulnerable to attacks against software that is known to contain security holes.
Implementors should make the
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
The
The information sent in the
We suggest, though do not require, that a convenient toggle interface be provided for the user
to enable or disable the sending of
The HTTP protocol has evolved considerably over the past four years. It has benefited from a
large and active developer community--the many people who have participated on the
www-talk mailing list--and it is that community which has been most responsible for the
success of HTTP and of the World-Wide Web in general. Marc Andreessen, Robert Cailliau,
Daniel W. Connolly, Bob Denny, John Franks, Jean-Francois Groff, Phillip M. Hallam-Baker,
Håkon W. Lie, Ari Luotonen, Rob McCool, Lou Montulli, Dave Raggett, Tony Sanders, and
Marc VanHeyningen deserve special recognition for their efforts in defining early aspects of
the protocol.
This document has benefited greatly from the comments of all those participating in the
HTTP-WG. In addition to those already mentioned, the following individuals have contributed
to this specification:
Henrik Frystyk Nielsen
Tim Berners-Lee
Clients should be tolerant in parsing the
The line terminator for
This appendix describes specific areas where HTTP differs from MIME. Proxies/gateways to
MIME-compliant protocols must be aware of these differences and provide the appropriate
conversions where necessary.
Where it is possible, a proxy/gateway from HTTP to a MIME-compliant protocol should
translate all line breaks within text/* media types to the MIME canonical form of
An HTTP client may include a
HTTP-Version
field Cn the first line of the
message. If the px$tocol version is not"3pecified, dhe recipient must eósume that the message iw°
in the simplg0HTTPc0ŒÀ fÏ2Ð`
HTTP-Verrùon = "HTTP"%"/ú%1*DIGIT "." 1*DIGIT
Note that the major and minor numbers should be treated as separate integers and that each may
be incremented higher than a single digit. Thus, HTTP/2.4 is a lower version than HTTP/2.13,
which in turn is lower than HTTP/12.3. Leading zeros should be ignored by recipients and
never generated by senders.
Full-Request
or Full-Response
messages, as defined by this specification,
must include an HTTP-Version
of "HTTP/
1.1". Use of this version number indicates that the
sending application is at least conditionally compliant with this specification.
Proxy and gateway applications must be careful in forwarding requests that are received in a
format different than that of the application's native HTTP version. Since the protocol version
indicates the protocol capability of the sender, a proxy/gateway must never send a message
with a version indicator which is greater than its native version; if a higher version request is
received, the proxy/gateway must either downgrade the request version, respond with an error,
or switch to tunnel behavior. Requests with a version lower than that of the application's native
format may be upgraded before being forwarded; the proxy/gateway's response to that request
must follow the server requirements listed above.
3.2 Uniform Resource Identifiers
URIs have been known by many names: WWW addresses, Universal Document Identifiers,
Universal Resource Identifiers [3], and finally the combination of Uniform Resource Locators
(URL) [4] and Names (URN) [20]. As far as HTTP is concerned, Uniform Resource Identifiers
are simply formatted strings which identify--via name, location, or any other characteristic--a
network resource.
3.2.1 General Syntax
URIs in HTTP can be represented in absolute form or relative to some known base URI [11],
depending upon the context of their use. The two forms are differentiated by the fact that
absolute URIs always begin with a scheme name followed by a colon.
URI = ( absoluteURI | relativeURI ) [ "#" fragment ]
absoluteURI = scheme ":" *( uchar | reserved )
relativeURI = net_path | abs_path | rel_path
net_path = "//" net_loc [ abs_path ]
abs_path = "/" rel_path
rel_path = [ path ] [ ";" params ] [ "?" query ]
path = fsegment *( "/" segment )
fsegment = 1*pchar
segment = *pchar
params = param *( ";" param )
param = *( pchar | "/" )
scheme = 1*( ALPHA | DIGIT | "+" | "-" | "." )
net_loc = *( pchar | ";" | "?" )
query = *( uchar | reserved )
fragment = *( uchar | reserved )
pchar = uchar | ":" | "@" | "&" | "="
uchar = unreserved | escape
unreserved = ALPHA | DIGIT | safe | extra | national
escape = "%" HEX HEX
reserved = ";" | "/" | "?" | ":" | "@" | "&" | "="
extra = "!" | "*" | "'" | "(" | ")" | ","
safe = "$" | "-" | "_" | "." | "+"
unsafe = CTL | SP | <"> | "#" | "%" | "<" | ">"
national = <any OCTET excluding ALPHA, DIGIT,
reserved, extra, safe, and unsafe>
For definitive information on URL syntax and semantics, see RFC 1738 [4] and
RFC 1808 [11]. The BNF above includes national
characters not allowed in valid URLs as
specified by RFC 1738, since HTTP servers are not restricted in the set of unreserved
characters
allowed to represent the rel_path
part of addresses, and HTTP proxies may receive requests for
URIs not defined by RFC 1738.
3.2.2 http URL
The "http" scheme is used to locate network resources via the HTTP protocol. This section
defines the scheme-specific syntax and semantics for http URLs.
http_URL = "http:" "//" host [ ":" port ] [ abs_path ]
host = <A legal Internet host domain name
or IP address (in dotted-decimal form),
as defined by Section 2.1 of RFC 1123>
port = *DIGIT
If the port
is empty or not given, port 80 is assumed. The semantics are that the identified
resource is located at the server listening for TCP connections on that port
of that host
, and the
Request-URI
for the resource is abs_path
. If the abs_path
is not present in the URL, it must be
given as "/" when used as a Request-URI
for a resource (Section 5.1.2).
Note: Although the HTTP protocol is independent of the transport layer protocol, the
http URL only identifies resources by their TCP location, and thus non-TCP resources
must be identified by some other URI scheme.
The canonical form for "http" URLs is obtained by converting any UPALPHA
characters in host
to their LOALPHA
equivalent (hostnames are case-insensitive), eliding the [ ":" port ]
if the port
is 80, and replacing an empty abs_path
with "/".
3.3 Date/Time Formats
3.3.1 Full Date
HTTP applications have historically allowed three different formats for the representation of
date/time stamps:
Sun, 06 Nov 1994 08:49:37 GMT ; RFC 822, updated by RFC 1123
Sunday, 06-Nov-94 08:49:37 GMT ; RFC 850, obsoleted by RFC 1036
Sun Nov 6 08:49:37 1994 ; ANSI C's asctime() format
The first format is preferred as an Internet standard and represents a fixed-length subset of that
defined by RFC 1123 [8] (an update to RFC 822 [9]). The second format is in common use, but
is based on the obsolete RFC 850 [12] date format and lacks a four-digit year. HTTP/1.1 clients
and servers that parse the date value must accept all three formats, though they must only
generate the RFC 1123 format for representing date/time stamps in HTTP message fields.
Note: Recipients of date values are encouraged to be robust in accepting date values
that may have been generated by non-HTTP applications, as is sometimes the case
when retrieving or posting messages via proxies/gateways to SMTP or NNTP.
All HTTP date/time stamps must be represented in Universal Time (UT), also known as
Greenwich Mean Time (GMT), without exception. This is indicated in the first two formats by
the inclusion of "GMT" as the three-letter abbreviation for time zone, and should be assumed
when reading the asctime format.
HTTP-date = rfc1123-date | rfc850-date | asctime-date
rfc1123-date = wkday "," SP date1 SP time SP "GMT"
rfc850-date = weekday "," SP date2 SP time SP "GMT"
asctime-date = wkday SP date3 SP time SP 4DIGIT
date1 = 2DIGIT SP month SP 4DIGIT
; day month year (e.g., 02 Jun 1982)
date2 = 2DIGIT "-" month "-" 2DIGIT
; day-month-year (e.g., 02-Jun-82)
date3 = month SP ( 2DIGIT | ( SP 1DIGIT ))
; month day (e.g., Jun 2)
time = 2DIGIT ":" 2DIGIT ":" 2DIGIT
; 00:00:00 - 23:59:59
wkday = "Mon" | "Tue" | "Wed"
| "Thu" | "Fri" | "Sat" | "Sun"
weekday = "Monday" | "Tuesday" | "Wednesday"
| "Thursday" | "Friday" | "Saturday" | "Sunday"
month = "Jan" | "Feb" | "Mar" | "Apr"
| "May" | "Jun" | "Jul" | "Aug"
| "Sep" | "Oct" | "Nov" | "Dec"
Note: HTTP requirements for the date/time stamp format apply only to their usage
within the protocol stream. Clients and servers are not required to use these formats
for user presentation, request logging, etc.
3.3.2 Delta Seconds
Some HTTP header fields allow a time value to be specified as an integer number of seconds,
represented in decimal, after the time that the message was received. This format should only
be used to represent short time periods or periods that cannot start until receipt of the message.
delta-seconds = 1*DIGIT
3.4 Character Sets
HTTP uses the same definition of the term "character set" as that described for MIME:
The term "character set" is used in this document to refer to a method used with
one or more tables to convert a sequence of octets into a sequence of characters.
Note that unconditional conversion in the other direction is not required, in that
not all characters may be available in a given character set and a character set may
provide more than one sequence of octets to represent a particular character. This
definition is intended to allow various kinds of character encodings, from simple
single-table mappings such as US-ASCII to complex table switching methods
such as those that use ISO 2022's techniques. However, the definition associated
with a MIME character set name must fully specify the mapping to be performed
from octets to characters. In particular, use of external profiling information to
determine the exact mapping is not permitted.
HTTP character sets are identified by case-insensitive tokens. The complete set of tokens are
defined by the IANA Character Set registry [19]. However, because that registry does not
define a single, consistent token for each character set, we define here the preferred names for
those character sets most likely to be used with HTTP entities. These character sets include
those registered by RFC 1521 [7] -- the US-ASCII [21] and ISO-8859 [22] character sets --
and other names specifically recommended for use within MIME charset parameters.
charset = "US-ASCII"
| "ISO-8859-1" | "ISO-8859-2" | "ISO-8859-3"
| "ISO-8859-4" | "ISO-8859-5" | "ISO-8859-6"
| "ISO-8859-7" | "ISO-8859-8" | "ISO-8859-9"
| "ISO-2022-JP" | "ISO-2022-JP-2" | "ISO-2022-KR"
| "UNICODE-1-1" | "UNICODE-1-1-UTF-7" | "UNICODE-1-1-UTF-8"
| token
Although HTTP allows an arbitrary token to be used as a charset value, any token that has a
predefined value within the IANA Character Set registry [19] must represent the character set
defined by that registry. Applications should limit their use of character sets to those defined by
the IANA registry.
Note: This use of the term "character set" is more commonly referred to as a
"character encoding." However, since HTTP and MIME share the same registry, it is
important that the terminology also be shared.
3.5 Content Codings
Content coding values are used to indicate an encoding transformation that has been or can be
applied to a resource. Content codings are primarily used to allow a document to be compressed
or encrypted without losing the identity of its underlying media type. Typically, the resource is
stored in this encoding and only decoded before rendering or analogous usage.
content-coding = "gzip" | "compress" | token
Note: For historical reasons, HTTP applications should consider "x-gzip" and
All
"x-compress" to be equivalent to "gzip" and "compress", respectively.
content-coding
values are case-insensitive. HTTP/1.1 uses content-coding
values in the
Accept-Encoding
(Section 10.3) and Content-Encoding
(Section 10.10) header fields. Although
the value describes the content-coding, what is more important is that it indicates what
decoding mechanism will be required to remove the encoding. Note that a single program may
be capable of decoding multiple content-coding formats. Two values are defined by this
specification:
Note: Use of program names for the identification of encoding formats is not
desirable and should be discouraged for future encodings. Their use here is
representative of historical practice, not good design.
3.6 Transfer Codings
Transfer coding values are used to indicate an encoding transformation that has been, can be,
or may need to be applied to an Entity-Body in order to ensure safe transport through the
network. This differs from a content coding in that the transfer coding is a property of the
message, not of the original resource.
transfer-coding = "chunked" | token
All transfer-coding values are case-insensitive. HTTP/1.1 uses transfer coding values in the
Transfer-Encoding header field (Section 10.39).
Chunked-Body = *chunk
"0" CRLF
footer
CRLF
chunk = chunk-size CRLF
chunk-data CRLF
chunk-size = hex-no-zero *HEX
chunk-data = chunk-size(OCTET)
footer = *<Entity-Header, excluding Content-Length
and Transfer-Encoding>
hex-no-zero = <HEX excluding "0">
Note that the chunks are ended by a zero-sized chunk, followed by the footer and terminated
by an empty line. An example process for decoding a Chunked-Body
is presented in
Appendix C.5.
3.7 Media Types
HTTP uses Internet Media Types [17] in the Content-Type (Section 10.15) and Accept
(Section 10.1) header fields in order to provide open and extensible data typing and type
negotiation. For mail applications, where there is no type negotiation between sender and
recipient, it is reasonable to put strict limits on the set of allowed media types. With HTTP,
where the sender and recipient can communicate directly, applications are allowed more
freedom in the use of non-registered types. The following grammar for media types is a
superset of that for MIME because it does not restrict itself to the official IANA and x-token
types.
media-type = type "/" subtype *( ";" parameter )
type = token
subtype = token
Parameters may follow the type/subtype in the form of attribute/value pairs.
parameter = attribute "=" value
attribute = token
value = token | quoted-string
The type, subtype, and parameter attribute names are case-insensitive. Parameter values may
or may not be case-sensitive, depending on the semantics of the parameter name. LWS
should
not be generated between the type and subtype, nor between an attribute and its value.
media-type
value has been registered by the IANA, any use of that value must be
indicative of the registered data format. Although HTTP allows the use of non-registered media
types, such usage must not conflict with the IANA registry. Data providers are strongly
encouraged to register their media types with IANA via the procedures outlined in
RFC 1590 [17].
media-type
's registered by IANA must be preferred over extension tokens. However, HTTP
does not limit applications to the use of officially registered media types, nor does it encourage
the use of an "x-
" prefix for unofficial types outside of explicitly short experimental use
between consenting applications.
3.7.1 Canonicalization and Text Defaults
Media types are registered in a canonical form. In general, entity bodies transferred via HTTP
must be represented in the appropriate canonical form prior to transmission. If the body has
been encoded via a Content-Encoding
and/or Transfer-Encoding
, the data must be in canonical
form prior to that encoding. However, HTTP modifies the canonical form requirements for
media of primary type "text" and for "application" types consisting of text-like records.
Note: This interpretation of line breaks applies only to the contents of an Entity-Body
and only after any Transfer-Encoding and/or Content-Encoding has been removed.
All other HTTP constructs use CRLF exclusively to indicate a line break. Content and
transfer codings define their own line break requirements.
A recipient of an HTTP text entity should translate the received entity line breaks to the local
line break conventions before saving the entity external to the application and its cache;
whether this translation takes place immediately upon receipt of the entity, or only when
prompted by the user, is entirely up to the individual application.
Content-Type
header field overrides the default.
3.7.2 Multipart Types
MIME provides for a number of "multipart" types -- encapsulations of one or more entities
within a single message's Entity-Body
. All multipart types share a common syntax, as defined in
Section 7.2.1 of RFC 1521 [7], and must include a boundary parameter as part of the media
type value. The message body is itself a protocol element and must therefore use only CRLF
to
represent line breaks between body-parts. Unlike in MIME, the epilogue of any multipart
message must be empty; HTTP applications must not transmit the epilogue even if the original
resource contains an epilogue.
Note: This document does not define what is meant by "simultaneous presentation".
That is, HTTP does not provide any means of synchronization between the parts in
messages of type "multipart/parallel".
Other multipart subtypes may be registered by IANA [19] according to the procedures defined
in RFC 1590 [17]. If an application receives an unrecognized
multipart subtype, the application must treat it as being equivalent to "multipart/mixed".
3.8 Product Tokens
Product tokens are used to allow communicating applications to identify themselves via a
simple product token, with an optional slash and version designator. Most fields using product
tokens also allow subproducts which form a significant part of the application to be listed,
separated by whitespace. By convention, the products are listed in order of their significance
for identifying the application.
product = token ["/" product-version]
product-version = token
Examples:
User-Agent: CERN-LineMode/2.15 libwww/2.17b3
Server: Apache/0.8.4
Product tokens should be short and to the point -- use of them for advertizing or other
non-essential information is explicitly forbidden. Although any token character may appear in
a product-version
, this token should only be used for a version identifier (i.e., successive versions
of the same product should only differ in the product-version
portion of the product
value).
3.9 Quality Values
HTTP content negotiation (Section 12)
uses short "floating point" numbers to indicate the
relative importance ("weight") of various negotiable parameters. The weights are normalized
to a real number in the range 0 through 1, where 0 is the minimum and 1 the maximum value.
In order to discourage misuse of this feature, HTTP/1.1 applications must not generate more
than three digits after the decimal point. User configuration of these values should also be
limited in this fashion.
qvalue = ( "0" [ "." 0*3DIGIT ] )
| ( "." 0*3DIGIT )
| ( "1" [ "." 0*3("0") ] )
"Quality values" is a slight misnomer, since these values actually measure relative degradation
in perceived quality. Thus, a value of "0.8" represents a 20% degradation from the optimum
rather than a statement of 80% quality.
3.10 Language Tags
A language tag identifies a natural language spoken, written, or otherwise conveyed by human
beings for communication of information to other human beings. Computer languages are
explicitly excluded. HTTP uses language tags within the Accept-Language, Content-Language,
and URI-header fields.
language-tag = primary-tag *( "-" subtag )
primary-tag = 1*8ALPHA
subtag = 1*8ALPHA
Whitespace is not allowed within the tag and all tags are case-insensitive. The namespace of
language tags is administered by the IANA. Example tags include:
en, en-US, en-cockney, i-cherokee, x-pig-latin
where any two-letter primary-tag is an ISO 639 language abbreviation and any two-letter initial
subtag is an ISO 3166 country code.
Accept-Language: en-US, en; ql=0.95
when the intent is to access, in order of preference, documents in US-English ("en-US"), 'plain'
or 'international' English ("en"), and any other variant of English (initial "en-").
Note: Using the language tag as a hierarchy does not imply that all languages with
a common prefix will be understood by those fluent in one or more of those languages;
it simply allows the user to request this commonality when it is true for that user.
3.11 Logic Bags
A logic bag is a binary logic expression tree represented in prefix notation using the generic bag
syntax. Logic bags are used by HTTP in the Unless
(Section 10.40) header field as expressions
to be tested against the requested resource's header field metainformation.
logic-bag = "{" expression "}"
expression = ( log-op 1*logic-bag )
| ( rel-op 1*field-tuple )
| ( "def" 1*field-name )
log-op = "and" | "or" | "xor" | "not"
rel-op = "eq" | "ne" | "lt" | "le" | "ge" | "gt" | "in"
field-tuple = "{" field-name ( bag | token | quoted-string ) "}"
The recursive structure of a logic bag allows a complex expression tree to be formed by joining
together subexpressions with logical operators. Expressions with relational operators are used
to compare the requested resource's corresponding metainformation (header field values) to
those inside the expression field-tuples. For example,
{or {ne {Content-MD5 "Q2hlY2sgSW50ZWdyaXR5IQ=="}}
{ne {Content-Length 10036}}
{ne {Content-Version "12.4.8"}}
{gt {Last-Modified "Mon, 04 Dec 1995 01:23:45 GMT"}}}
The expression is evaluated recursively by depth-first traversal and bottom-up evaluation of the
subexpressions until a true or false value can be determined. Multiple operands to an operator
imply a conjunctive ("and") expression; e.g.,
{eq {A "a"} {B "b"} {C "c"}}
is equivalent to
{and {eq {A "a"}} {eq {B "b"}} {eq {C "c"}}}
Each expression is evaluated as defined by the operator:
A field-tuple consists of a field-name (assumed to be an HTTP header field name, though not
constrained to those defined by this specification) and the field-value component which is to be
compared against the resource's field value. The actual method of comparison (e.g., byte
equivalence, substring matching, numeric order, substructure containment, etc.) is defined by
the logical definition of the operator and the type of field-value allowed for that field-name.
Server implementors must use an appropriate comparison function for each type of field-value
given in this specification. The default functions for unrecognized fields are numeric
comparison (for values consisting of field-tuple
values exactly match the resource's corresponding field values.
field-tuple
values do not match the resource's corresponding field values.
1*DIGIT
) and lexical comparison (for all others).
4. HTTP Message
4.1 Message Types
HTTP messages consist of requests from client to server and responses from server to client.
HTTP-message = Simple-Request ; HTTP/0.9 messages
| Simple-Response
| Full-Request ; HTTP/1.1 messages
| Full-Response
Full-Request
and Full-Response
use the generic
message format of RFC 822 [9] for transferring
entities. Both messages may include optional header fields (also known as "headers") and an
entity body. The entity body is separated from the headers by a null line (i.e., a line with nothing
preceding the CRLF
).
Full-Request = Request-Line ; Section 5.1
*( General-Header ; Section 4.3
| Request-Header ; Section 5.2
| Entity-Header ) ; Section 7.1
CRLF
[ Entity-Body ] ; Section 7.2
Full-Response = Status-Line ; Section 6.1
*( General-Header ; Section 4.3
| Response-Header ; Section 6.2
| Entity-Header ) ; Section 7.1
CRLF
[ Entity-Body ] ; Section 7.2
Simple-Request
and Simple-Response
do not allow the use of any header information and are
limited to a single request method (GET
).
Simple-Request = "GET" SP Request-URI CRLF
Simple-Response = [ Entity-Body ]
Use of the Simple-Request
format is discouraged because it prevents the client from using
content negotiation and the server from identifying the media type of the returned entity.
4.2 Message Headers
HTTP header fields, which include General-Header
(Section 4.3), Request-Header
(Section 5.2),
Response-Header
(Section 6.2), and Entity-Header
(Section 7.1) fields, follow the same generic
format as that given in Section 3.1 of RFC 822 [9]. Each header field consists of a name
followed by a colon (":"
) and the field value. Field names are case-insensitive. The field value
may be preceded by any amount of LWS
, though a single SP
is preferred. Header fields can be
extended over multiple lines by preceding each extra line with at least one SP
or HT
.
HTTP-header = field-name ":" [ field-value ] CRLF
field-name = token
field-value = *( field-content | LWS )
field-content = <the OCTETs making up the field-value
and consisting of either *TEXT or combinations
of token, tspecials, and quoted-string>
The order in which header fields are received is not significant. However, it is "good practice"
to send General-Header
fields first, followed by Request-Header
or Response-Header
fields prior
to the Entity-Header
fields.
HTTP-header
fields with the same field-name
may be present in a message if and only
if the entire field-value
for that header field is defined as a comma-separated list [i.e., #(values)
].
It must be possible to combine the multiple header fields into one "field-name: field-value" pair,
without changing the semantics of the message, by appending each subsequent field-value to
the first, each separated by a comma.
4.3 General Header Fields
There are a few header fields which have general applicability for both request and response
messages, but which do not apply to the entity being transferred. These headers apply only to
the message being transmitted.
General-Header = Cache-Control ; Section 10.8
| Connection ; Section 10.9
| Date ; Section 10.17
| Forwarded ; Section 10.20
| Keep-Alive ; Section 10.24
| MIME-Version ; Section 10.28
| Pragma ; Section 10.29
| Upgrade ; Section 10.41
General 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
general header fields if all parties in the communication recognize them to be general header
fields. Unrecognized header fields are treated as Entity-Header
fields.
5. Request
A request message from a client to a server includes, within the first line of that message, the
method to be applied to the resource, the identifier of the resource, and the protocol version in
use. For backwards compatibility with the more limited HTTP/0.9 protocol, there are two valid
formats for an HTTP request:
Request = Simple-Request | Full-Request
Simple-Request = "GET" SP Request-URI CRLF
Full-Request = Request-Line ; Section 5.1
*( General-Header ; Section 4.3
| Request-Header ; Section 5.2
| Entity-Header ) ; Section 7.1
CRLF
[ Entity-Body ] ; Section 7.2
If an HTTP/1.1 server receives a Simple-Request
, it must respond with an HTTP/0.9
Simple-Response
. An HTTP/1.1 client must never generate a Simple-Request
.
5.1 Request-Line
The Request-Line
begins with a method token, followed by the Request-URI
and the protocol
version, and ending with CRLF
. The elements are separated by SP
characters. No CR
or LF
are
allowed except in the final CRLF
sequence.
Request-Line = Method SP Request-URI SP HTTP-Version CRLF
Note that the difference between a Simple-Request
and the Request-Line
of a Full-Request
is the
presence of the HTTP-Version
field and the availability of methods other than GET
.
5.1.1 Method
The Method
token indicates the method to be performed on the resource identified by the
Request-URI
. The method is case-sensitive.
Method = "OPTIONS" ; Section 8.1
| "GET" ; Section 8.2
| "HEAD" ; Section 8.3
| "POST" ; Section 8.4
| "PUT" ; Section 8.5
| "PATCH" ; Section 8.6
| "COPY" ; Section 8.7
| "MOVE" ; Section 8.8
| "DELETE" ; Section 8.9
| "LINK" ; Section 8.10
| "UNLINK" ; Section 8.11
| "TRACE" ; Section 8.12
| "WRAPPED" ; Section 8.13
| extension-method
extension-method = token
The list of methods acceptable by a specific resource can be specified in an Allow
header field
(Section 10.5). However, the client is always notified through the return code of the response
whether a method is currently allowed on a specific resource, as this can change dynamically.
Servers should return the status code 405 (method not allowed) if the method is known by the
server but not allowed for the requested resource, and 501 (not implemented) if the method is
unrecognized or not implemented by the server. The list of methods known by a server can be
listed in a Public response header field (Section 10.32).
5.1.2 Request-URI
The Request-URI
is a Uniform Resource Identifier (Section 3.2) and identifies the resource upon
which to apply the request.
Request-URI = "*" | absoluteURI | abs_path
The three options for Request-URI are dependent on the nature of the request. The asterisk "*"
means that the request does not apply to a particular resource, but to the server itself, and is
only allowed when the Method used does not necessarily apply to a resource. One example
would be
OPTIONS * HTTP/1.1
The absoluteURI
form is only allowed when the request is being made to a proxy. The proxy is
requested to forward the request and return the response. If the request is GET
or HEAD
and a
prior response is cached, the proxy may use the cached message if it passes any restrictions in
the Cache-Control and Expires
header fields. Note that the proxy may forward the request on to
another proxy or directly to the server specified by the absoluteURI
. In order to avoid request
loops, a proxy must be able to recognize all of its server names, including any aliases, local
variations, and the numeric IP address. An example Request-Line
would be:
GET http://www.w3.org/pub/WWW/TheProject.html HTTP/1.1
The most common form of Request-URI
is that used to identify a resource on an origin server
or gateway. In this case, only the absolute path of the URI is transmitted (see Section 3.2.1,
abs_path
). For example, a client wishing to retrieve the resource above directly from the origin
server would create a TCP connection to port 80 of the host "www.w3.org" and send the line:
GET /pub/WWW/TheProject.html HTTP/1.1
followed by the remainder of the Full-Request
. Note that the absolute path cannot be empty; if
none is present in the original URI, it must be given as "/" (the server root).
Request-URI
and the method used is capable
of supporting the asterisk form of request, then the last proxy on the request chain must forward
the request with "*" as the final Request-URI
. For example, the request
OPTIONS http://www.ics.uci.edu:8001 HTTP/1.1
would be forwarded by the proxy as
OPTIONS * HTTP/1.1
after connecting to port 8001 of host "www.ics.uci.edu".
5.2 Request Header Fields
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 (procedure) invocation.
Request-Header = Accept ; Section 10.1
| Accept-Charset ; Section 10.2
| Accept-Encoding ; Section 10.3
| Accept-Language ; Section 10.4
| Authorization ; Section 10.6
| From ; Section 10.21
| Host ; Section 10.22
| If-Modified-Since ; Section 10.23
| Proxy-Authorization ; Section 10.31
| Range ; Section 10.33
| Referer ; Section 10.34
| Unless ; Section 10.40
| User-Agent ; Section 10.43
Request-Header
field names can be extended reliably only in combination with a change in the
protocol version. However, new or experimental header fields may be given the semantics of
request header fields if all parties in the communication recognize them to be request header
fields. Unrecognized header fields are treated as Entity-Header
fields.
6. Response
After receiving and interpreting a request message, a server responds in the form of an HTTP
response message.
Response = Simple-Response | Full-Response
Simple-Response = [ Entity-Body ]
Full-Response = Status-Line ; Section 6.1
*( General-Header ; Section 4.3
| Response-Header ; Section 6.2
| Entity-Header ) ; Section 7.1
CRLF
[ Entity-Body ] ; Section 7.2
A Simple-Response
should only be sent in response to an HTTP/0.9 Simple-Request
or if the
server only supports the more limited HTTP/0.9 protocol. If a client sends an HTTP/1.1
Full-Request
and receives a response that does not begin with a
Status-Line
, it should assume that
the response is a Simple-Response
and parse it accordingly. Note that the Simple-Response
consists only of the entity body and is terminated by the server closing the connection.
6.1 Status-Line
The first line of a Full-Response
message is the
Status-Line
, consisting of the protocol version
followed by a numeric status code and its associated textual phrase, with each element
separated by SP
characters. No CR
or LF
is allowed except in the final CRLF
sequence.
Status-Line = HTTP-Version SP Status-Code SP Reason-Phrase CRLF
Since a status line always begins with the protocol version and status code
"HTTP/" 1*DIGIT "." 1*DIGIT SP 3DIGIT SP
(e.g., "HTTP/1.1 200 "
), the presence of that expression is sufficient to differentiate a
Full-Response
from a Simple-Response
.
Although the Simple-Response
format may allow such
an expression to occur at the beginning of an entity body, and thus cause a misinterpretation of
the message if it was given in response to a Full-Request
, most HTTP/0.9 servers are limited to
responses of type "text/html" and therefore would never generate such a response.
6.1.1 Status Code and Reason Phrase
The Status-Code
element is a 3-digit integer result code of the attempt to understand and satisfy
the request. 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
.
Status-Code
defines the class of response. The last two digits do not have
any categorization role. There are 5 values for the first digit:
The individual values of the numeric status codes defined for HTTP/1.1, and an example set of
corresponding Reason-Phrase
's, are presented below. The reason phrases listed here are only
recommended -- they may be replaced by local equivalents without affecting the protocol.
These codes are fully defined in Section 9.
Status-Code = "100" ; Continue
| "101" ; Switching Protocols
| "200" ; OK
| "201" ; Created
| "202" ; Accepted
| "203" ; Non-Authoritative Information
| "204" ; No Content
| "205" ; Reset Content
| "206" ; Partial Content
| "300" ; Multiple Choices
| "301" ; Moved Permanently
| "302" ; Moved Temporarily
| "303" ; See Other
| "304" ; Not Modified
| "305" ; Use Proxy
| "400" ; Bad Request
| "401" ; Unauthorized
| "402" ; Payment Required
| "403" ; Forbidden
| "404" ; Not Found
| "405" ; Method Not Allowed
| "406" ; None Acceptable
| "407" ; Proxy Authentication Required
| "408" ; Request Timeout
| "409" ; Conflict
| "410" ; Gone
| "411" ; Length Required
| "412" ; Unless True
| "500" ; Internal Server Error
| "501" ; Not Implemented
| "502" ; Bad Gateway
| "503" ; Service Unavailable
| "504" ; Gateway Timeout
| extension-code
extension-code = 3DIGIT
Reason-Phrase = *<TEXT, excluding CR, LF>
HTTP status codes are extensible. HTTP applications are not required to understand the
meaning of all registered status codes, though such understanding is obviously desirable.
However, applications must understand the class of any status code, as indicated by the first
digit, and treat any unrecognized response as being equivalent to the x00 status code of that
class, with the exception that an unrecognized response must not be cached. For example, if an
unrecognized status code of 431 is received by the client, it can safely assume that there was
something wrong with its request and treat the response as if it had received a 400 status code.
In such cases, user agents should present to the user the entity returned with the response, since
that entity is likely to include human-readable information which will explain the unusual
status.
6.2 Response Header Fields
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 are not intended to give
information about an Entity-Body
returned in the response, but about access to the resource or
the server itself.
Response-Header = Location ; Section 10.27
| Proxy-Authenticate ; Section 10.30
| Public ; Section 10.32
| Retry-After ; Section 10.36
| Server ; Section 10.37
| WWW-Authenticate ; Section 10.44
Response-Header
field names can be extended reliably only in combination with a change in the
protocol version. However, new or experimental header fields may be given the semantics of
response header fields if all parties in the communication recognize them to be response header
fields. Unrecognized header fields are treated as Entity-Header
fields.
7. Entity
Full-Request
and Full-Response
messages may transfer an entity within some requests and
responses. An entity consists of Entity-Header
fields
and (usually) an Entity-Body
. In this section,
both sender and recipient refer to either the client or the server, depending on who sends and
who receives the entity.
7.1 Entity Header Fields
Entity-Header
fields define optional metainformation about the Entity-Body
or, if no body is
present, about the resource identified by the request.
Entity-Header = Allow ; Section 10.5
| Content-Encoding ; Section 10.10
| Content-Language ; Section 10.11
| Content-Length ; Section 10.12
| Content-MD5 ; Section 10.13
| Content-Range ; Section 10.14
| Content-Type ; Section 10.15
| Content-Version ; Section 10.16
| Derived-From ; Section 10.18
| Expires ; Section 10.19
| Last-Modified ; Section 10.25
| Link ; Section 10.26
| Title ; Section 10.38
| Transfer-Encoding ; Section 10.39
| URI-header ; Section 10.42
| extension-header
extension-header = HTTP-header
The extension-header
mechanism allows additional Entity-Header
fields to be defined without
changing the protocol, but these fields cannot be assumed to be recognizable by the recipient.
Unrecognized header fields should be ignored by the recipient and forwarded by proxies.
7.2 Entity Body
The entity body (if any) sent with an HTTP request or response is in a format and encoding
defined by the Entity-Header
fields.
Entity-Body = *OCTET
An entity body is included with a request message only when the request method calls for one.
The presence of an entity body in a request is signaled by the inclusion of a Content-Length
and/or Content-Type
header field in the request message headers.
Content-Length
header field defined with a value of zero (0).
7.2.1 Type
When an entity body is included with a message, the data type of that body is determined via
the header fields Content-Type
, Content-Encoding
, and Transfer-Encoding. These define a
three-layer, ordered encoding model:
entity-body :=
Transfer-Encoding( Content-Encoding( Content-Type( data ) ) )
The default for both encodings is none (i.e., the identity function). Content-Type
specifies the
media type of the underlying data. Content-Encoding
may be used to indicate any additional
content codings applied to the type, usually for the purpose of data compression, that are a
property of the resource requested. Transfer-Encoding
may be used to indicate any additional
transfer codings applied by an application to ensure safe and proper transfer of the message.
Note that Transfer-Encoding
is a property of the message, not of the resource.
Content-Type
header field
defining the media type of that body. If and only if
the media type is not given by a Content-Type
header, as is the case for Simple-Response
messages, the recipient may attempt to guess the
media type via inspection of its content and/or the name extension(s) of the URL used to
identify the resource. If the media type remains unknown, the recipient should treat it as type
"application/octet-stream
".
7.2.2 Length
When an entity body is included with a message, the length of that body may be determined in
one of several ways. If a Content-Length
header field is present, its value in bytes represents the
length of the entity body. Otherwise, the body length is determined by the Transfer-Encoding
(if
the "chunked" transfer coding has been applied), by the Content-Type
(for multipart types with
an explicit end-of-body delimiter), or by the server closing the connection.
Note: Any response message which must not include an entity body (such as the 1xx,
204, and 304 responses and any response to a HEAD request) is always terminated
by the first empty line after the header fields, regardless of the entity header fields
present in the message.
Closing the connection cannot be used to indicate the end of a request body, since it leaves no
possibility for the server to send back a response. For compatibility with HTTP/1.0
applications, HTTP/1.1 requests containing an entity body must include a valid Content-Length
header field unless the server is known to be HTTP/1.1 compliant. HTTP/1.1 servers must
accept the "chunked" transfer coding (Section 3.6)
and multipart media types (Section 3.7.2),
thus allowing either mechanism to be used for a request when Content-Length
is unknown.
Content-Length
is not specified, the server should
respond with 400 (bad request) if it cannot determine the length of the request message's
content, or with 411 (length required) if it wishes to insist on receiving a valid Content-Length
.
Content-Length
header field and the "chunked" transfer
coding. If both are received, the Content-Length
must be ignored.
Content-Length
is given in a message where an entity body is allowed, its field value
must exactly match the number of OCTETs
in the entity body. HTTP/1.1 user agents must notify
the user when an invalid length is received and detected.
8. Method Definitions
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.
Unless
request header field,
as described in Section 10.40.
8.1 OPTIONS
The OPTIONS
method represents a request for information about the communication options
available on the request/response chain identified by the Request-URI
. This method allows the
client to determine the options and/or requirements associated with a resource, or the
capabilities of a server, without implying a resource action or initiating a resource retrieval.
Allow
is appropriate, but
Content-Type
is not) and must include a Content-Length
with a value of zero (0). Responses to
this method are not cachable.
Request-URI
is an asterisk ("*"), the OPTIONS
request is intended to apply to the server
as a whole. A 200 response should include any header fields which indicate optional features
implemented by the server (e.g., Public
), including any extensions not defined by this
specification, in addition to any applicable general or response header fields. As described in
Section 5.1.2, an "OPTIONS *
" request
can be applied through a proxy by specifying the
destination server in the Request-URI
without any path information.
Request-URI
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 which indicate optional features implemented by the server and applicable to that
resource (e.g., Allow
), including any extensions not defined by this specification, in addition to
any applicable general or response header fields. If the OPTIONS
request passes through a
proxy, the proxy must edit the response to exclude those options known to be unavailable
through that proxy.
8.2 GET
The GET
method means retrieve whatever information (in the form of an entity) is identified by
the Request-URI
. If the Request-URI
refers to a data-producing process, it is the produced data
which shall be returned as the entity in the response and not the source text of the process,
unless that text happens to be the output of the process.
GET
method change to a "conditional GET
" if the request message
includes an If-Modified-Since
header field.
A conditional GET
method requests that the identified
resource be transferred only if it has been modified since the date given by the If-Modified-Since
header, as described in Section 10.23.
The conditional GET
method is intended to reduce
unnecessary network usage by allowing cached entities to be refreshed without requiring
multiple requests or transferring data already held by the client.
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 identified resource be
transferred, as described in Section 10.33.
The partial GET
method is intended to reduce
unnecessary network usage by allowing partially-retrieved entities to be completed without
transferring data already held by the client.
GET
request may be cachable if and only if it meets the requirements for
HTTP caching described in Section 13.
8.3 HEAD
The HEAD
method is identical to GET
except that
the server must not return any Entity-Body
in
the response. The metainformation contained in the HTTP headers in response to a HEAD
request should be identical to the information sent in response to a GET
request. This method
can be used for obtaining metainformation about the resource identified by the Request-URI
without transferring the Entity-Body
itself. This method is often used for testing hypertext links
for validity, accessibility, and recent modification.
HEAD
request may be cachable in the sense that the information contained in
the response may be used to update a previously cached entity from that resource. If the new
field values indicate that the cached entity differs from the current resource (as would be
indicated by a change in Content-Length
, Content-MD5
,
or Content-Version
), then the cache must discard the cached entity.
HEAD
" or "partial HEAD
" request analogous to those associated with
the GET
method. If an If-Modified-Since
and/or
Range
header field is included with a HEAD
request, they should be ignored.
8.4 POST
The POST
method is used to request that the destination server accept the entity enclosed in the
request as a new subordinate of the resource identified by the Request-URI
in the Request-Line
.
POST is designed to allow a uniform method to cover the following functions:
The actual function performed by the POST method is determined by the server and is usually
dependent on the Request-URI
. The posted entity is subordinate to that URI in the same way
that a file is subordinate to a directory containing it, a news article is subordinate to a
newsgroup to which it is posted, or a record is subordinate to a database.
POST
request.
If the media type of the posted entity is not "application/x-www-form-urlencoded" [5], an
HTTP/1.1 client must pause between sending the message header fields (including the empty
line signifying the end of the headers) and sending the message body; the duration of the pause
is five (5) seconds or until a response is received from the server, whichever is shorter. If no
response is received during the pause period, or if the initial response is 100 (continue), the
client may continue sending the POST
request. If the response indicates an error, the client must
discontinue the request and close the connection with the server after reading the response.
POST
request, the server must examine the header fields and determine
whether or not the client should continue its request. If any of the header fields indicate the
request is insufficient or unacceptable to the server (i.e., will result in a 4xx or 5xx response),
or if the server can determine the response without reading the entity body (e.g., a 301 or 302
response due to an old Request-URI
), the server must send that response immediately upon its
determination. If, on the other hand, the request appears (at least initially) to be acceptable and
the client has indicated HTTP/1.1 compliance, the server must transmit an interim 100 response
message after receiving the empty line terminating the request headers and continue processing
the request. After processing has finished, a final response message must be sent to indicate the
actual result of the request. A 100 response should not be sent in response to an HTTP/1.0
request except under experimental conditions, since an HTTP/1.0 client may mistake the 100
response for the final response.
POST
requests must include a valid
Content-Length
header field unless the server is known to be HTTP/1.1 compliant. When
sending a POST
request to an HTTP/1.1 server, a client must use at least one of: a valid
Content-Length
, a multipart Content-Type
, or the
"chunked" Transfer-Encoding
. The server should
respond with a 400 (bad request) message if it cannot determine the length of the request
message's content, or with 411 (length required) if it wishes to insist on receiving a valid
Content-Length
.
POST
does not require that the entity be created as a resource on the origin server
or made accessible for future reference. That is, the action performed by the POST
method
might not result in a resource that can be identified by a URI. In this case, either 200 (ok) or
204 (no content) is the appropriate response status, depending on whether or not the response
includes an entity that describes the result.
8.5 PUT
The PUT method requests that the enclosed entity be stored under the supplied Request-URI. If
the Request-URI refers to an already existing resource, the enclosed entity should be considered
as a modified version of the one residing on the origin server. If the Request-URI does not point
to an existing resource, and that URI is capable of being defined as a new resource by the
requesting user agent, the origin server can create the resource with that URI. If a new resource
is created, the origin server must inform the user agent via the 201 (created) response. If an
existing resource is modified, either the 200 (ok) or 204 (no content) response codes should be
sent to indicate successful completion of the request. If the resource could not be created or
modified with the Request-URI, an appropriate error response should be given that reflects the
nature of the problem.
Request-URI
identifies a currently cached entity,
that entity must be removed from the cache. Responses to this method are not cachable.
POST
and PUT
requests is reflected in the different
meaning of the Request-URI. The URI in a POST
request identifies the resource that will handle
the enclosed entity as an appendage. That resource may be a data-accepting process, a gateway
to some other protocol, or a separate entity that accepts annotations. In contrast, the URI in a
PUT
request identifies the entity enclosed with the request -- the user agent knows what URI
is intended and the server must not attempt to apply the request to some other resource. If the
server desires that the request be applied to a different URI, it must send a 301 (moved
permanently) response; the user agent may then make its own decision regarding whether or
not to redirect the request.
PUT
request on a general URI may result in several other URIs
being defined by the origin server. The user agent should be informed of these URIs via one or
more URI header fields in the response.
PUT
request.
An HTTP/1.1 client must pause between sending the message header fields (including the
empty line signifying the end of the headers) and sending the message body; the duration of the
pause is five (5) seconds or until a response is received from the server, whichever is shorter.
If no response is received during the pause period, or if the initial response is 100 (continue),
the client may continue sending the PUT
request. If the response indicates an error, the client
must discontinue the request and close the connection with the server after reading the
response.
PUT
request, the server must examine the header fields and determine
whether or not the client should continue its request. If any of the header fields indicate the
request is insufficient or unacceptable to the server (i.e., will result in a 4xx or 5xx response),
or if the server can determine the response without reading the entity body (e.g., a 301 or 302
response due to an old Request-URI
), the server must send that response immediately upon its
determination. If, on the other hand, the request appears (at least initially) to be acceptable and
the client has indicated HTTP/1.1 compliance, the server must transmit an interim 100 response
message after receiving the empty line terminating the request headers and continue processing
the request. After processing has finished, a final response message must be sent to indicate the
actual result of the request. A 100 response should not be sent in response to an HTTP/1.0
request except under experimental conditions, since an HTTP/1.0 client may mistake the 100
response for the final response.
PUT
requests must include a valid
Content-Length
header field unless the server is known to be HTTP/1.1 compliant. When
sending a PUT
request to an HTTP/1.1 server, a client must use at least one of: a valid
Content-Length
, a multipart Content-Type
,
or the "chunked" Transfer-Encoding
. The server should
respond with a 400 (bad request) message if it cannot determine the length of the request
message's content, or with 411 (length required) if it wishes to insist on receiving a valid
Content-Length
.
Link
relationships should be defined by the server to help identify and control
revisions to a resource. If the entity being PUT
was derived from an existing resource which
included a Content-Version
header field,
the new entity must include a Derived-From
header field
corresponding to the value of the original Content-Version
header field. Multiple Derived-From
values may be included if the entity was derived from multiple resources with Content-Version
information. Applications are encouraged to use these fields for constructing versioning
relationships and resolving version conflicts.
8.6 PATCH
The PATCH
method is similar to PUT
except that
the entity contains a list of differences between
the original version of the resource identified by the Request-URI
and the desired content of the
resource after the PATCH
action has been applied. The list of differences is in a format defined
by the media type of the entity (e.g., "application/diff") and must include sufficient information
to allow the server to recreate the changes necessary to convert the original version of the
resource to the desired version.
Request-URI
identifies a currently cached entity,
that entity must be removed from the cache. Responses to this method are not cachable.
PATCH
request. An HTTP/1.1 client must pause between sending the message header fields (including
the empty line signifying the end of the headers) and sending the message body; the duration
of the pause is five (5) seconds or until a response is received from the server, whichever is
shorter. If no response is received during the pause period, or if the initial response is 100
(continue), the client may continue sending the PATCH
request. If the response indicates an
error, the client must discontinue the request and close the connection with the server after
reading the response.
PATCH
request, the server must examine the header fields and determine
whether or not the client should continue its request. If any of the header fields indicate the
request is insufficient or unacceptable to the server (i.e., will result in a 4xx or 5xx response),
or if the server can determine the response without reading the entity body (e.g., a 301 or 302
response due to an old Request-URI
), the server must send that response immediately upon its
determination. If, on the other hand, the request appears (at least initially) to be acceptable and
the client has indicated HTTP/1.1 compliance, the server must transmit an interim 100 response
message after receiving the empty line terminating the request headers and continue processing
the request. After processing has finished, a final response message must be sent to indicate the
actual result of the request. A 100 response should not be sent in response to an HTTP/1.0
request except under experimental conditions, since an HTTP/1.0 client may mistake the 100
response for the final response.
PATCH
requests must include a valid
Content-Length
header field unless the server is known to be HTTP/1.1 compliant. When
sending a PATCH
request to an HTTP/1.1 server, a client must use at least one of: a valid
Content-Length
, a multipart Content-Type
,
or the "chunked" Transfer-Encoding
. The server should
respond with a 400 (bad request) message if it cannot determine the length of the request
message's content, or with 411 (length required) if it wishes to insist on receiving a valid
Content-Length
.
Link
relationships should be defined by the server to help identify and control
revisions to a resource. If the original version of the resource being patched included a
Content-Version
header field, the request entity must include a Derived-From
header field
corresponding to the value of the original Content-Version
header field. Applications are
encouraged to use these fields for constructing versioning relationships and resolving version
conflicts.
8.7 COPY
The COPY
method requests that the resource identified by the Request-URI
be copied to the
location(s) given in the URI header field of the request. Responses to this method are not
cachable.
8.8 MOVE
The MOVE
method requests that the resource identified by the Request-URI
be moved to the
location(s) given in the URI header field of the request. This method is equivalent to a COPY
immediately followed by a DELETE
, but enables both to occur within a single transaction.
Request-URI
identifies a currently cached entity,
that entity must be removed from the cache. Responses to this method are not cachable.
8.9 DELETE
The DELETE method requests that the origin server delete the resource identified by the
Request-URI. This method may be overridden by human intervention (or other means) on the
origin server. The client cannot be guaranteed that the operation has been carried out, even if
the status code returned from the origin server indicates that the action has been completed
successfully. However, the server should not indicate success unless, at the time the response
is given, it intends to delete the resource or move it to an inaccessible location.
Request-URI
identifies a currently cached entity,
that entity must be removed from the cache. Responses to this method are not cachable.
8.10 LINK
The LINK method establishes one or more Link relationships between the existing resource
identified by the Request-URI and other existing resources. The difference between LINK and
other methods allowing links to be established between resources is that the LINK method does
not allow any Entity-Body to be sent in the request and does not directly result in the creation of
new resources.
Request-URI
identifies a currently cached entity,
that entity must be removed from the cache. Responses to this method are not cachable.
8.11 UNLINK
The UNLINK method removes one or more Link relationships from the existing resource
identified by the Request-URI. These relationships may have been established using the LINK
method or by any other method supporting the Link header. The removal of a link to a resource
does not imply that the resource ceases to exist or becomes inaccessible for future references.
Request-URI
identifies a currently cached entity,
that entity must be removed from the cache. Responses to this method are not cachable.
8.12 TRACE
The TRACE method requests that the server identified by the Request-URI
reflect whatever is
received back to the client as the entity body of the response. In this way, the client can see what
is being received at the other end of the request chain, and may use this data for testing or
diagnostic information.
8.13 WRAPPED
The WRAPPED method allows a client to send one or more encapsulated requests to the server
identified by the Request-URI. This method is intended to allow the request(s) to be wrapped
together, possibly encrypted in order to improve the security and/or privacy of the request, and
delivered for unwrapping by the destination server. Upon receipt of the WRAPPED request,
the destination server must unwrap the message and feed it to the appropriate protocol handler
as if it were an incoming request stream.
Content-Encoding
and Transfer-Encoding
header fields.
WRAPPED
request. An HTTP/1.1 client must pause between sending the message header fields (including
the empty line signifying the end of the headers) and sending the message body; the duration
of the pause is five (5) seconds or until a response is received from the server, whichever is
shorter. If no response is received during the pause period, or if the initial response is 100
(continue), the client may continue sending the WRAPPED
request. If the response indicates an
error, the client must discontinue the request and close the connection with the server after
reading the response.
WRAPPED
request, the server must examine the header fields and determine
whether or not the client should continue its request. If any of the header fields indicate the
request is insufficient or unacceptable to the server (i.e., will result in a 4xx or 5xx response),
or if the server can determine the response without reading the entity body (e.g., a 301 or 302
response due to an old Request-URI
), the server must send that response immediately upon its
determination. If, on the other hand, the request appears (at least initially) to be acceptable and
the client has indicated HTTP/1.1 compliance, the server must transmit an interim 100 response
message after receiving the empty line terminating the request headers and continue processing
the request. After processing has finished, a final response message must be sent to indicate the
actual result of the request. A 100 response should not be sent in response to an HTTP/1.0
request except under experimental conditions, since an HTTP/1.0 client may mistake the 100
response for the final response.
WRAPPED
requests must include a valid
Content-Length
header field unless the server is known to be HTTP/1.1 compliant. When
sending a WRAPPED
request to an HTTP/1.1 server, a client must use at least one of: a valid
Content-Length
, a multipart Content-Type
,
or the "chunked" Transfer-Encoding
. The server should
respond with a 400 (bad request) message if it cannot determine the length of the request
message's content, or with 411 (length required) if it wishes to insist on receiving a valid
Content-Length
.
9. Status Code Definitions
Each Status-Code
is described below, including a description of which method
(s) it can follow
and any metainformation required in the response.
9.1 Informational 1xx
This class of status code indicates a provisional response, consisting only of the Status-Line
and
optional headers, and is terminated by an empty line. Since HTTP/1.0 did not define any 1xx
status codes, servers should not send a 1xx response to an HTTP/1.0 client except under
experimental conditions.
100 Continue
The client may 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.
101 Switching Protocols
The server understands and is willing to comply with the client's request, via the Upgrade
message header field (Section 10.41), 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.
9.2 Successful 2xx
This class of status code indicates that the client's request was successfully received,
understood, and accepted.
200 OK
The request has succeeded. The information returned with the response is dependent on the
method used in the request, as follows:
If the entity corresponds to a resource, the response may include a Location header field giving
the actual location of that specific resource for later reference.
GET
HEAD
Entity-Body
;
POST
TRACE
201 Created
The request has been fulfilled and resulted in a new resource being created. The newly created
resource can be referenced by the URI(s) returned in the URI-header
field and/or the entity of
the response, with the most specific URL for the resource given by a Location
header field. The
origin server should create the resource before using this Status-Code
. If the action cannot be
carried out immediately, the server must include in the response body a description of when the
resource will be available; otherwise, the server should respond with 202 (accepted).
202 Accepted
The request has been accepted for processing, but the processing has not been completed. The
request may or may not eventually be acted upon, as it may be disallowed when processing
actually takes place. There is no facility for re-sending a status code from an asynchronous
operation such as this.
203 Non-Authoritative Information
The returned metainformation in the Entity-Header is not the definitive set as available from the
origin server, but is gathered from a local or a third-party copy. The set presented may be a
subset or superset of the original version. For example, including local annotation information
about the resource may result in a superset of the metainformation known by the origin server.
Use of this response code is not required and is only appropriate when the response would
otherwise be 200 (ok).
204 No Content
The server has fulfilled the request but there is no new information to send back. If the client is
a user agent, it should not change its document view from that which caused the request to be
generated. 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. The response may include new
metainformation in the form of entity headers, which should apply to the document currently
in the user agent's active view.
205 Reset Content
The server has fulfilled the request and the user agent should reset the document view which
caused the request to be generated. 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 include a
Content-Length
with a value of zero (0) and no entity body.
206 Partial Content
The server has fulfilled the partial GET
request for the resource. The request must have included
a Range
header field (Section 10.33)
indicating the desired range. The response must include a Content-Range
header field
(Section 10.14) indicating the range included with this response. All
entity header fields in the response must describe the actual entity transmitted rather than what
would have been transmitted in a full response. In particular, the Content-Length
header field in
the response must match the actual number of OCTETs
transmitted in the entity body. It is
assumed that the client already has the complete entity's header field data.
9.3 Redirection 3xx
This class of status code indicates that further action needs to be taken by the user agent in order
to fulfill the request. The action required may be carried out by the user agent without
interaction with the user if and only if the method used in the second request is GET
or HEAD
.
A user agent should never automatically redirect a request more than 5 times, since such
redirections usually indicate an infinite loop.
300 Multiple Choices
The requested resource is available at one or more locations and a preferred location could not
be determined via preemptive content negotiation (Section 12).
Unless it was a HEAD request,
the response should include an entity containing a list of resource characteristics and locations
from which the user or user agent can choose the one most appropriate. The entity format is
specified by the media type given in the Content-Type header field. Depending upon the format
and the capabilities of the user agent, selection of the most appropriate choice may be
performed automatically. If the server has a preferred choice, it should include the URL in a
Location field; user agents not capable of complex selection may use this field value for
automatic redirection. This response is cachable unless indicated otherwise.
301 Moved Permanently
The requested resource has been assigned a new permanent URI and any future references to
this resource should be done using one of the returned URIs. Clients with link editing
capabilities should automatically relink references to the Request-URI
to one or more of the new
references returned by the server, where possible. This response is cachable unless indicated
otherwise.
Location
field in the response.
If more than one URI exists for the resource, the primary URL should be given in the Location
field and the other URIs given in one or more URI-header fields. Unless it was a HEAD
request,
the Entity-Body
of the response should contain a short hypertext note with a hyperlink to the new
URI(s).
GET
or HEAD
, 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.
302 Moved Temporarily
The requested resource resides temporarily under a different URI. Since the redirection may be
altered on occasion, the client should continue to use the Request-URI
for future requests. This
response is only cachable if indicated by a Cache-Control
or Expires
header field.
Location
field in the response.
If more than one URI exists for the resource, the primary URL should be given in the Location
field and the other URIs given in one or more URI-header fields. Unless it was a HEAD
request,
the Entity-Body
of the response should contain a short hypertext note with a hyperlink to the new
URI(s).
GET
or HEAD
,
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.
303 See Other
The response to the request can be found under a different URI and should be retrieved using
a GET method on that resource. This method exists primarily to allow the output of a
POST-activated script to redirect the user agent to a selected resource. The new resource is not
a replacement reference for the original Request-URI. The 303 response is not cachable, but the
response to the second request may be cachable.
304 Not Modified
If the client has performed a conditional GET request and access is allowed, but the document
has not been modified since the date and time specified in the If-Modified-Since
field, the server
must respond with this status code and not send an Entity-Body
to the client. Header fields
contained in the response should only include information which is relevant to cache managers
or which may have changed independently of the entity's Last-Modified
date. Examples of
relevant header fields include: Date
, Server
, Content-Length
,
Content-MD5
, Content-Version
,
Cache-Control
and Expires
.
Content-Length
,
Content-MD5
, or Content-Version
), then the
cache must disregard the 304 response and repeat the request without an If-Modified-Since
field.
305 Use Proxy
The requested resource must be accessed through the proxy given by the Location field in the
response. In other words, this is a proxy redirect.
9.4 Client Error 4xx
The 4xx class of status code is intended for cases in which the client seems to have erred. If the
client has not completed the request when a 4xx code is received, it should immediately cease
sending data to the server. Except when responding to a HEAD request, the server should
include an entity containing an explanation of the error situation, and whether it is a temporary
or permanent condition. These status codes are applicable to any request method.
Note: If the client is sending data, server implementations on TCP should be careful
to ensure that the client acknowledges receipt of the packet(s) containing the response
prior to closing the input connection. If the client continues sending data to the server
after the close, the server's controller will send a reset packet to the client, which may
erase the client's unacknowledged input buffers before they can be read and
interpreted by the HTTP application.
400 Bad Request
The request could not be understood by the server due to malformed syntax. The client should
not repeat the request without modifications.
401 Unauthorized
The request requires user authentication. The response must include a WWW-Authenticate
header field (Section 10.44) containing a
challenge
applicable to the requested resource. The
client may repeat the request with a suitable Authorization
header field (Section 10.6). If the
request already included Authorization credentials, then the 401 response indicates that
authorization has been refused for those credentials. If the 401 response contains the same
challenge as the prior response, and the user agent has already attempted authentication at least
once, then the user should be presented the entity that was given in the response, since that
entity may include relevant diagnostic information. HTTP access authentication is explained
in Section 11.
402 Payment Required
This code is reserved for future use.
403 Forbidden
The server understood the request, but is refusing to fulfill it. Authorization will not help and
the request should not be repeated. If the request method was not HEAD
and the server wishes
to make public why the request has not been fulfilled, it should describe the reason for the
refusal in the entity body. 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.
404 Not Found
The server has not found anything matching the Request-URI
. No indication is given of whether
the condition is temporary or permanent. If the server does not wish to make this information
available to the client, the status code 403 (forbidden) can be used instead. 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.
405 Method Not Allowed
The method specified in the Request-Line is not allowed for the resource identified by the
Request-URI. The response must include an Allow header containing a list of valid methods for
the requested resource.
406 None Acceptable
The server has found a resource matching the Request-URI, but not one that satisfies the
conditions identified by the Accept and Accept-Encoding request headers. Unless it was a HEAD
request, the response should include an entity containing a list of resource characteristics and
locations from which the user or user agent can choose the one most appropriate. The entity
format is specified by the media type given in the Content-Type header field. Depending upon
the format and the capabilities of the user agent, selection of the most appropriate choice may
be performed automatically.
407 Proxy Authentication Required
This code is similar to 401 (unauthorized), but indicates that the client must first authenticate
itself with the proxy. The proxy must return a Proxy-Authenticate header field
(Section 10.30)
containing a challenge applicable to the proxy for the requested resource. The client may repeat
the request with a suitable Proxy-Authorization header field
(Section 10.31). HTTP access
authentication is explained in Section 11.
408 Request Timeout
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.
409 Conflict
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 may be able to resolve the
conflict and resubmit the request. The response body should include enough information for
the user to recognize the source of the conflict. Ideally, the response entity would include
enough information for the user or user-agent to fix the problem; however, that may not be
possible and is not required.
PUT
or
PATCH
request. If versioning is being
used and the entity being PUT
or PATCH
ed includes changes to a resource which conflict with
those made by an earlier (third-party) request, the server may use the 409 response to indicate
that it can't complete the request. In this case, the response entity should contain a list of the
differences between the two versions in a format defined by the response Content-Type
.
410 Gone
The requested resource is no longer available at the server and no forwarding address is known.
This condition should be considered permanent. Clients with link editing capabilities should
delete references to the Request-URI after user approval. If the server does not know, or has no
facility to determine, whether or not the condition is permanent, the status code 404 (not found)
should be used instead. This response is cachable unless indicated otherwise.
411 Length Required
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 entity
body in the request message.
412 Unless True
The condition given in the Unless
request-header field
(Section 10.40) evaluated to true when
it was tested on the server and the request did not include a Range
header field (which would
indicate a partial GET
) or an If-Modified-Since
header field
(which would indicate a conditional
GET
). This response code allows the client to place arbitrary preconditions on the current
resource metainformation (header field data) and thus prevent the requested method from being
applied to a resource other than the one intended.
9.5 Server Error 5xx
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. If the client has not completed the
request when a 5xx code is received, it should immediately cease sending data to the server.
Except when responding to a HEAD request, the server should include an entity containing an
explanation of the error situation, and whether it is a temporary or permanent condition. These
response codes are applicable to any request method and there are no required header fields.
500 Internal Server Error
The server encountered an unexpected condition which prevented it from fulfilling the request.
501 Not Implemented
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.
502 Bad Gateway
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.
503 Service Unavailable
The server is currently unable to handle the request due to a temporary overloading or
maintenance of the server. The implication is that this is a temporary condition which will be
alleviated after some delay. If known, the length of the delay may be indicated in a Retry-After
header. If no Retry-After is given, the client should handle the response as it would for a 500
response.
Note: The existence of the 503 status code does not imply that a server must use it
when becoming overloaded. Some servers may wish to simply refuse the connection.
504 Gateway Timeout
The server, while acting as a gateway or proxy, did not receive a timely response from the
upstream server it accessed in attempting to complete the request.
10. Header Field Definitions
This section defines the syntax and semantics of all standard HTTP/1.1 header fields. For
Entity-Header
fields, both sender and recipient
refer to either the client or the server, depending on who sends and who receives the entity.
10.1 Accept
The Accept response-header field can be used to indicate a list of media ranges which are
acceptable as a response to the request. The asterisk "*" character is used to group media types
into ranges, with "*/*" indicating all media types and "type/*" indicating all subtypes of that
type. The set of ranges given by the client should represent what types are acceptable given the
context of the request. The Accept field should only be used when the request is specifically
limited to a set of desired types, as in the case of a request for an in-line image, or to indicate
qualitative preferences for specific media types.
Accept = "Accept" ":" #(
media-range
[ ";" "q" "=" qvalue ]
[ ";" "mxb" "=" 1*DIGIT ] )
media-range = ( "*/*"
| ( type "/" "*" )
| ( type "/" subtype )
) *( ";" parameter )
The parameter q is used to indicate the quality factor, which represents the user's preference for
that range of media types. The parameter mxb gives the maximum acceptable size of the
Entity-Body, in decimal number of octets, for that range of media types.
Section 12 describes the
content negotiation algorithm which makes use of these values. The default values are: q=1 and
mxb=undefined (i.e., infinity).
Accept: audio/*; q=0.2, audio/basic
should be interpreted as "I prefer audio/basic, but send me any audio type if it is the best
available after an 80% mark-down in quality."
Accept: */*; q=1
or
Accept: */*
If a single Accept
header is provided and it contains no field value, then the server must interpret
it as a request to not perform any preemptive content negotiation
(Section 12) and instead
return a 406 (none acceptable) response if there are variants available for the Request-URI
.
Accept: text/plain; q=0.5, text/html,
text/x-dvi; q=0.8; mxb=100000, text/x-c
Verbally, this would be interpreted as "text/html and text/x-c are the preferred media types, but
if they do not exist, then send the text/x-dvi entity if it is less than 100000 bytes, otherwise send
the text/plain entity."
Accept: text/*, text/html, text/html;version=2.0, */*
have the following precedence:
1) text/html;version=2.0
2) text/html
3) text/*
4) */*
The quality value associated with a given type is determined by finding the media range with
the highest precedence which matches that type. For example,
Accept: text/*;q=0.3, text/html;q=0.7, text/html;version=2.0,
*/*;q=0.5
would cause the following values to be associated:
text/html;version=2.0 = 1
text/html = 0.7
text/plain = 0.3
image/jpeg = 0.5
text/html;level=3 = 0.7
It must be emphasized that the Accept field should only be used when it is necessary to restrict
the response media types to a subset of those possible or when the user has been permitted to
specify qualitative values for ranges of media types. If no quality factors have been set by the
user, and the context of the request is such that the user agent is capable of saving the entity to
a file if the received media type is unknown, then the only appropriate value for Accept is "*/*",
or an empty value if the user desires reactive negotiation.
Note: A user agent may be provided with a default set of quality values for certain
media ranges. However, unless the user agent is a closed system which cannot
interact with other rendering agents, this default set should be configurable by the
user.
10.2 Accept-Charset
The Accept-Charset
request-header field can be used to indicate what character sets are
acceptable for the response. This field allows clients capable of understanding more
comprehensive or special-purpose character sets to signal that capability to a server which is
capable of representing documents in those character sets. The US-ASCII character set can be
assumed to be acceptable to all user agents.
Accept-Charset = "Accept-Charset" ":" 1#charset
Character set values are described in Section 3.4. An example is
Accept-Charset: iso-8859-1, unicode-1-1
If no Accept-Charset
field is given, the default is that any character set is acceptable. If the
Accept-Charset
field is given and the requested resource is not available in one of the listed
character sets, then the server should respond with the 406 (none acceptable) status code.
10.3 Accept-Encoding
The Accept-Encoding request-header field is similar to Accept, but restricts the content-coding
values (Section 3.5) which are acceptable in the response.
Accept-Encoding = "Accept-Encoding" ":"
#( content-coding )
An example of its use is
Accept-Encoding: compress, gzip
If no Accept-Encoding field is present in a request, the server may assume that the client will
accept any content coding. If an Accept-Encoding
field is present, but contains an empty field
value, then the user agent is refusing to accept any content coding.
10.4 Accept-Language
The Accept-Language request-header field is similar to Accept, but restricts the set of natural
languages that are preferred as a response to the request.
Accept-Language = "Accept-Language" ":"
1#( language-tag [ ";" "q" "=" qvalue ] )
The language-tag is described in Section 3.10. Each language may be given an associated
quality value which represents an estimate of the user's comprehension of that language. The
quality value defaults to "q=1" (100% comprehension) for listed languages. This value may be
used in the server's content negotiation algorithm (Section 12). For example,
Accept-Language: da, en-gb;q=0.8, de;q=0.55
would mean: "I prefer Danish, but will accept British English (with 80% comprehension) or
German (with a 55% comprehension)."
Accept-Language
header is present in the request, the server should assume that all
languages are equally acceptable.
Note: As intelligibility is highly dependent on the individual user, it is recommended
that client applications make the choice of linguistic preference available to the user.
If the choice is not made available, then the Accept-Language header field must not
be given in the request.
10.5 Allow
The Allow
entity-header field lists the set of methods supported by the resource identified by the
Request-URI
. The purpose of this field is strictly to inform the recipient of valid methods
associated with the resource. An Allow
header field must be present in a 405 (method not
allowed) response. The Allow
header field is not permitted in a request using the POST method,
and thus should be ignored if it is received as part of a POST entity.
Allow = "Allow" ":" 1#method
Example of use:
Allow: GET, HEAD, PUT
This field cannot prevent a client from trying other methods. However, the indications given by
the Allow
header field value should be followed. The actual set of allowed methods is defined
by the origin server at the time of each request.
Allow
header field may be provided with a PUT request to recommend the methods to be
supported by the new or modified resource. The server is not required to support these methods
and should include an Allow
header in the response giving the actual supported methods.
Allow
header field even if it does not understand all the methods
specified, since the user agent may have other means of communicating with the origin server.
Allow
header field does not indicate what methods are implemented at the server level.
Servers may use the Public response header field (Section 10.32) to describe what methods are
implemented on the server as a whole.
10.6 Authorization
A user agent that wishes to authenticate itself with a server--usually, but not necessarily, after
receiving a 401 response--may do so by including an Authorization
request-header field with
the request. The Authorization
field value consists of credentials
containing the authentication
information of the user agent for the realm of the resource being requested.
Authorization = "Authorization" ":" credentials
HTTP access authentication is described in Section 11.
If a request is authenticated and a realm
specified, the same credentials
should be valid for all other requests within this realm
.
Authorization
field are not cachable.
10.7 Base
The Base entity-header field may be used to specify the base URI for resolving relative URLs,
as described in RFC 1808 [11].
10.8 Cache-Control
The Cache-Control general-header field is used to specify directives that must be obeyed by all
caching mechanisms along the request/response chain. The directives specify behavior
intended to prevent caches from adversely interfering with the request or response. Cache
directives are unidirectional in that the presence of a directive in a request does not imply that
the same directive should be given in the response.
Cache-Control = "Cache-Control" ":" 1#cache-directive
cache-directive = "cachable"
| "max-age" "=" delta-seconds
| "private" [ "=" <"> 1#field-name <"> ]
| "no-cache" [ "=" <"> 1#field-name <"> ]
The Cache-Control
header field may be used to modify the optional behavior of caching
mechanisms, and the default cachability of a response message; it cannot be used to modify the
required behavior of caching mechanisms. HTTP requirements for caching and cachable
messages are described in Section 13.
Last-Modified
value in the If-Modified-Since field. The
Unless
header field may be used to add further restrictions to the modification test on the server.
If a 304 (not modified) response is received, the cache should replace the cached message's
Date with that of the 304 response and send this refreshed message as the response. Any other
response should be forwarded directly to the requestor and, depending on the response code
and the discretion of the cache manager, may replace the message in the cache.
Note: This usage of the word "private" implies only that the message must not be
cached publically; it does not ensure the privacy of the message content.
The "no-cache" directive on a request message requires any cache to forward the request
toward the origin server even if it has a cached copy of what is being requested. This allows a
client to insist upon receiving an authoritative response to its request. It also allows a client to
refresh a cached copy which is known to be corrupted or stale. This is equivalent to the
"no-cache" pragma-directive in Section 10.29. The list of field names is not used with requests
and must not be generated by clients. The no-cache directive overrides any max-age directive.
10.9 Connection
The Connection general-header field is used to indicate a list of keywords and header field
names containing information which is only applicable to the current connection between the
sender and the nearest non-tunnel recipient on the request/response chain. This information
must not be forwarded or cached. Unlike the default behavior, the recipient cannot safely ignore
the semantics of the listed field-names if they are not understood, since forwarding them may
imply that understanding.
Connection = "Connection" ":" 1#field-name
Proxies and gateways must discard the named header fields, and the Connection header itself,
before forwarding the message. Proxies and gateways may add their own Connection
information to forwarded messages if such options are desired for the forwarding connection.
These restrictions do not apply to a tunnel, since the tunnel is acting as a relay between two
connections and does not affect the connection options.
10.9.1 Persistent Connections
The "keep-alive" keyword in a Connection
header field allows the sender to indicate its desire
for a persistent connection (i.e., a connection that lasts beyond the current request/response
transaction). Persistent connections allow the client to perform multiple requests without the
overhead of connection tear-down and set-up between each request.
Connection: Keep-Alive
to indicate that it desires to keep the connection open for multiple requests. The server may then
respond with a message containing
Connection: Keep-Alive
to indicate that the connection will be kept open for the next request. The Connection
header
field with a keep-alive keyword must be sent on all requests and responses that wish to continue
the persistence. The client sends requests as normal and the server responds as normal, except
that all messages containing an entity body must have a length that can be determined without
closing the connection (i.e., each message containg an entity body must have a valid
Content-Length
, be a multipart media type, or be encoded using the "chunked" transfer coding,
as described in Section 7.2.2).
Keep-Alive
header field (Section 10.24)
may be used to include diagnostic information and
other optional parameters. For example, the server may responds with
Connection: Keep-Alive
Keep-Alive: timeout=10, max=5
to indicate that the server has selected (perhaps dynamically) a maximum of 5 requests, but will
timeout if the next request is not received within 10 seconds. Note, however, that this additional
information is optional and the Keep-Alive
header field does not need to be present. If it is
present, the semantics of the Connection header field prevents it from being accidentally
forwarded to downstream connections.
10.10 Content-Encoding
The Content-Encoding
entity-header field is used as a modifier to the media-type
. When present,
its value indicates what additional content codings have been applied to the resource, and thus
what decoding mechanisms must be applied in order to obtain the media-type
referenced by the
Content-Type
header field. Content-Encoding
is primarily used to allow a document to be
compressed without losing the identity of its underlying media type.
Content-Encoding = "Content-Encoding" ":" 1#content-coding
Content codings are defined in Section 3.5. An example of its use is
Content-Encoding: gzip
The Content-Encoding is a characteristic of the resource identified by the Request-URI
.
Typically, the resource is stored with this encoding and is only decoded before rendering or
analogous usage.
10.11 Content-Language
The Content-Language entity-header field describes the natural language(s) of the intended
audience for the enclosed entity. Note that this may not be equivalent to all the languages used
within the entity.
Content-Language = "Content-Language" ":" 1#language-tag
Language tags are defined in Section 3.10.
The primary purpose of Content-Language is to allow
a selective consumer to identify and differentiate resources according to the consumer's own
preferred language. Thus, if the body content is intended only for a Danish-literate audience,
the appropriate field is
Content-Language: dk
If no Content-Language is specified, the default is that the content is intended for all language
audiences. This may mean that the sender does not consider it to be specific to any natural
language, or that the sender does not know for which language it is intended.
Content-Language: mi, en
However, just because multiple languages are present within an entity does not mean that it is
intended for multiple linguistic audiences. An example would be a beginner's language primer,
such as "A First Lesson in Latin," which is clearly intended to be used by an English-literate
audience. In this case, the Content-Language should only include "en".
10.12 Content-Length
The Content-Length
entity-header field indicates the size of the
Entity-Body
, in decimal number
of octets, sent to the recipient or, in the case of the HEAD
method, the size of the Entity-Body
that
would have been sent had the request been a GET
.
Content-Length = "Content-Length" ":" 1*DIGIT
An example is
Content-Length: 3495
Applications should use this field to indicate the size of the Entity-Body
to be transferred,
regardless of the media type of the entity. A valid Content-Length
field value is required on all
HTTP/1.1 request messages containing an entity body.
Content-Length
greater than or equal to zero is a valid value.
Section 7.2.2 describes how
to determine the length of an Entity-Body
if a Content-Length
is not given.
Note: The meaning of this field is significantly different from the corresponding
definition in MIME, where it is an optional field used within the
"message/external-body" content-type. In HTTP, it should be used whenever the
entity's length can be determined prior to being transferred.
10.13 Content-MD5
TBS
10.14 Content-Range
TBS
10.15 Content-Type
The Content-Type
entity-header field indicates the media type of the Entity-Body
sent to the
recipient or, in the case of the HEAD
method, the media type that would have been sent had the
request been a GET
.
Content-Type = "Content-Type" ":" media-type
Media types are defined in Section 3.7. An example of the field is
Content-Type: text/html; charset=ISO-8859-4
Further discussion of methods for identifying the media type of an entity is provided in
Section 7.2.1.
10.16 Content-Version
The Content-Version entity-header field defines the version tag associated with a rendition of an
evolving entity. Together with the Derived-From field described in
Section 10.18, it allows a
group of people to work simultaneously on the creation of a work as an iterative process. The
field should be used to allow evolution of a particular work along a single path. It should not
be used to indicate derived works or renditions in different representations. It may also me used
as an opaque value for comparing a cached entity's version with that of the current resource.
Content-Version = "Content-Version" ":" quoted-string
Examples of the Content-Version field include:
Content-Version: "2.1.2"
Content-Version: "Fred 19950116-12:26:48"
Content-Version: "2.5a4-omega7"
The value of the Content-Version
field should be considered opaque to all parties but the origin
server. A user agent may suggest a value for the version of an entity transferred via a PUT
request; however, only the origin server can reliably assign that value.
10.17 Date
The Date
general-header field represents the date and time at which the message was originated,
having the same semantics as orig-date
in RFC 822. The field value is an HTTP-date
, as
described in Section 3.3.
Date = "Date" ":" HTTP-date
An example is
Date: Tue, 15 Nov 1994 08:12:31 GMT
If a message is received via direct connection with the user agent (in the case of requests) or
the origin server (in the case of responses), then the date can be assumed to be the current date
at the receiving end. However, since the date--as it is believed by the origin--is important for
evaluating cached responses, origin servers should always include a Date
header. Clients should
only send a Date
header field in messages that include an entity body, as in the case of the PUT
and POST requests, and even then it is optional. A received message which does not have a
Date
header field should be assigned one by the recipient if the message will be cached by that
recipient or gatewayed via a protocol which requires a Date
.
Note: An earlier version of this document incorrectly specified that this field should
contain the creation date of the enclosed
Entity-Body
. This has been changed to reflect
actual (and proper) usage.
10.18 Derived-From
The Derived-From entity-header field can be used to indicate the version tag of the resource from
which the enclosed entity was derived before modifications were made by the sender. This field
is used to help manage the process of merging successive changes to a resource, particularly
when such changes are being made in parallel and from multiple sources.
Derived-From = "Derived-From" ":" quoted-string
An example use of the field is:
Derived-From: "2.1.1"
The Derived-From field is required for PUT
and PATCH
requests if the entity being sent was
previously retrieved from the same URI and a Content-Version header was included with the
entity when it was last retrieved.
10.19 Expires
The Expires
entity-header field gives the date/time after which the entity should be considered
stale. This allows information providers to suggest the volatility of the resource, or a date after
which the information may no longer be valid. Applications must not cache this entity beyond
the date given. The presence of an Expires field does not imply that the original resource will
change or cease to exist at, before, or after that time. However, information providers that know
or even suspect that a resource will change by a certain date should include an Expires header
with that date. The format is an absolute date and time as defined by
HTTP-date
in Section 3.3.
Expires = "Expires" ":" HTTP-date
An example of its use is
Expires: Thu, 01 Dec 1994 16:00:00 GMT
If the date given is equal to or earlier than the value of the Date
header, the recipient must not
cache the enclosed entity. If a resource is dynamic by nature, as is the case with many
data-producing processes, entities from that resource should be given an appropriate Expires
value which reflects that dynamism.
Expires
field does not
apply to history mechanisms. If the entity is still in storage, a history mechanism should display
it even if the entity has expired, unless the user has specifically configured the agent to refresh
expired history documents.
Note: Applications are encouraged to be tolerant of bad or misinformed
implementations of the Expires header. A value of zero (0) or an invalid date format
should be considered equivalent to an "expires immediately." Although these values
are not legitimate for HTTP/1.1, a robust implementation is always desirable.
10.20 Forwarded
The Forwarded general-header field is to be used by gateways and proxies to indicate the
intermediate steps between the user agent and the server on requests, and between the origin
server and the client on responses. It is analogous to the "Received" field of RFC 822 [9] and
is intended to be used for tracing transport problems and avoiding request loops.
Forwarded = "Forwarded" ":" #( "by" URI [ "(" product ")" ]
[ "for" FQDN ] )
FQDN = <Fully-Qualified Domain Name>
For example, a message could be sent from a client on ptsun00.cern.ch to a server at
www.ics.uci.edu port 80, via an intermediate HTTP proxy at info.cern.ch port 8000. The
request received by the server at www.ics.uci.edu would then have the following Forwarded
header field:
Forwarded: by http://info.cern.ch:8000/ for ptsun00.cern.ch
Multiple Forwarded header fields are allowed and should represent each proxy/gateway that has
forwarded the message. It is strongly recommended that proxies/gateways used as a portal
through a network firewall do not, by default, send out information about the internal hosts
within the firewall region. This information should only be propagated if explicitly enabled. If
not enabled, the for token and FQDN should not be included in the field value, and any Forwarded
headers already present in the message (those added behind the firewall) should be removed.
10.21 From
The From
request-header field, if given, should contain an Internet e-mail address for the human
user who controls the requesting user agent. The address should be machine-usable, as defined
by mailbox
in RFC 822 [9] (as updated by RFC 1123 [8]):
From = "From" ":" mailbox
An example is:
From: webmaster@w3.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 so that the person responsible for running the robot can be contacted if
problems occur on the receiving end.
Note: The client should not send the
From
header field without the user's approval, as
it may 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.
10.22 Host
The Host
request-header field allows the client to specify, for the server's benefit, the Internet
host given by the original Uniform Resource Identifier (Section 3.2) of the resource being
requested, as it was obtained from the user or the referring resource. This allows a server to
differentiate between internally-ambiguous URLs (such as the root "/" URL of a server
harboring multiple virtual hostnames). This field is required on all HTTP/1.1 requests which
do not already include the host in the Request-URI
.
Host = "Host" ":" host ; Section 3.2.2
Example:
Host: www.w3.org
The contents of the Host header field should exactly match the host information used to contact
the origin server or gateway in question. It must not include the trailing ":port" information
which may also be found in the net_loc
portion of a URL (Section 3.2).
10.23 If-Modified-Since
The If-Modified-Since
request-header field is used with the GET
method to make it conditional:
if the requested resource has not been modified since the time specified in this field, a copy of
the resource will not be returned from the server; instead, a 304 (not modified) response will
be returned without any Entity-Body
.
If-Modified-Since = "If-Modified-Since" ":" HTTP-date
An example of the field is:
If-Modified-Since: Sat, 29 Oct 1994 19:43:31 GMT
A conditional GET
method requests that the identified resource be transferred only if it has been
modified since the date given by the If-Modified-Since
header. The algorithm for determining this
includes the following cases:
The purpose of this feature is to allow efficient updates of cached information with a minimum
amount of transaction overhead.
If-Modified-Since
date is invalid, the response is exactly the same as for a
normal GET
. A date which is later than the server's current time is invalid.
If-Modified-Since
date, the response is
exactly the same as for a normal GET
.
If-Modified-Since
date, the server
must return a 304 (not modified) response.
10.24 Keep-Alive
The Keep-Alive
general-header field may be used to include diagnostic information and other
optional parameters associated with the "keep-alive" keyword of the Connection
header field
(Section 10.9). This Keep-Alive
field must only be used when the "keep-alive" keyword is
present (Section 10.9.1).
Keep-Alive = "Keep-Alive" ":" 1#kaparam
kaparam = ( "timeout" "=" delta-seconds )
| ( "max" "=" 1*DIGIT )
| ( attribute [ "=" value ] )
The Keep-Alive
header field and the additional information it provides are optional and do not
need to be present to indicate a persistent connection has been established. The semantics of
the Connection
header field prevent the Keep-Alive
field from being accidentally forwarded to
downstream connections.
Connection: Keep-Alive
Keep-Alive: timeout=10, max=5
to indicate that the server has selected (perhaps dynamically) a maximum of 5 requests, but will
timeout the connection if the next request is not received within 10 seconds. Although these
parameters have no affect on the operational requirements of the connection, they are
sometimes useful for testing functionality and monitoring server behavior.
10.25 Last-Modified
The Last-Modified
entity-header field indicates the date and time at which the sender believes
the resource was last modified. The exact semantics of this field are defined in terms of how the
recipient should interpret it: if the recipient has a copy of this resource which is older than the
date given by the Last-Modified
field, that copy should be considered stale.
Last-Modified = "Last-Modified" ":" HTTP-date
An example of its use is
Last-Modified: Tue, 15 Nov 1994 12:45:26 GMT
The exact meaning of this header field depends on the implementation of the sender and the
nature of the original resource. For files, it may be just the file system last-modified time. For
entities with dynamically included parts, it may be the most recent of the set of last-modify
times for its component parts. For database gateways, it may be the last-update timestamp of
the record. For virtual objects, it may be the last time the internal state changed.
10.26 Link
The Link entity-header field provides a means for describing a relationship between the entity
and some other resource. An entity may include multiple Link values. Links at the
metainformation level typically indicate relationships like hierarchical structure and navigation
paths. The Link field is semantically equivalent to the <LINK> element in HTML [5].
Link = "Link" ":" #("<" URI ">"
[ ";" "rel" "=" relationship ]
[ ";" "rev" "=" relationship ]
[ ";" "title" "=" quoted-string ] )
relationship = sgml-name
| ( <"> sgml-name *( SP sgml-name) <"> )
sgml-name = ALPHA *( ALPHA | DIGIT | "." | "-" )
Relationship values are case-insensitive and may be extended within the constraints of the
sgml-name syntax. The title parameter may be used to label the destination of a link such that it
can be used as identification within a human-readable menu.
Link: <http://www.cern.ch/TheBook/chapter2>; rel="Previous"
Link: <mailto:timbl@w3.org>; rev="Made"; title="Tim Berners-Lee"
The first example indicates that chapter2 is previous to the entity in a logical navigation path.
The second indicates that the person responsible for making the resource available is identified
by the given e-mail address.
10.27 Location
The Location response-header field defines the exact location of the resource that was identified
by the Request-URI
. For 2xx responses, if the Request-URI
corresponds to a negotiable set of
variants and the response includes one of those variants, then the response must also include a
Location
header field containing the exact location of the chosen variant. For 3xx responses, the
location should indicate the server's preferred URL for automatic redirection to the resource.
The field value consists of a single absolute URL.
Location = "Location" ":" absoluteURI
An example is
Location: http://www.w3.org/pub/WWW/People.html
If no base URL is provided by or within the entity, the value of the Location
field should be used
as the base for resolving relative URLs [11].
10.28 MIME-Version
HTTP is not a MIME-compliant protocol (see Appendix C). However, HTTP/1.1 messages
may include a single MIME-Version
general-header field to indicate what version of the MIME
protocol was used to construct the message. Use of the MIME-Version
header field indicates that
the message is in full compliance with the MIME protocol (as defined in [7]). Proxies/gateways
are responsible for ensuring full compliance (where possible) when exporting HTTP messages
to strict MIME environments.
MIME-Version = "MIME-Version" ":" 1*DIGIT "." 1*DIGIT
MIME version "1.0
" is the default for use in HTTP/1.1. However, HTTP/1.1 message parsing
and semantics are defined by this document and not the MIME specification.
10.29 Pragma
The Pragma general-header field is used to include implementation-specific directives that may
apply to any recipient along the request/response chain. All pragma directives specify optional
behavior from the viewpoint of the protocol; however, some systems may require that behavior
be consistent with the directives.
Pragma = "Pragma" ":" 1#pragma-directive
pragma-directive = "no-cache" | extension-pragma
extension-pragma = token [ "=" word ]
When the "no-cache
" directive is present in a request message, an application should forward
the request toward the origin server even if it has a cached copy of what is being requested. This
pragma directive has the same semantics as the "no-cache" cache-directive
(see Section 10.8)
and is defined here for backwards compatibility with HTTP/1.0. Clients should include both
header fields when a "no-cache" request is sent to a server not known to be HTTP/1.1
compliant.
10.30 Proxy-Authenticate
The Proxy-Authenticate response-header field must be included as part of a 407 (proxy
authentication required) response. The field value consists of a challenge that indicates the
authentication scheme and parameters applicable to the proxy for this Request-URI.
Proxy-Authentication = "Proxy-Authentication" ":" challenge
The HTTP access authentication process is described in Section 11. Unlike WWW-Authenticate,
the Proxy-Authenticate header field applies only to the current connection and must not be passed
on to downstream clients.
10.31 Proxy-Authorization
The Proxy-Authorization request-header field allows the client to identify itself (or its user) to a
proxy which requires authentication. The Proxy-Authorization field value consists of credentials
containing the authentication information of the user agent for the proxy and/or realm of the
resource being requested.
Proxy-Authorization = "Proxy-Authorization" ":" credentials
The HTTP access authentication process is described in Section 11. Unlike Authorization, the
Proxy-Authorization applies only to the current connection and must not be passed on to upstream
servers. If a request is authenticated and a realm specified, the same credentials should be valid
for all other requests within this realm.
10.32 Public
The Public response-header field lists the set of non-standard methods supported by the server.
The purpose of this field is strictly to inform the recipient of the capabilities of the server
regarding unusual methods. The methods listed may or may not be applicable to the
Request-URI; the Allow header field (Section 10.5) should be used to indicate methods allowed
for a particular URI. This does not prevent a client from trying other methods. The field value
should not include the methods predefined for HTTP/1.1 in Section 5.1.1.
Public = "Public" ":" 1#method
Example of use:
Public: OPTIONS, MGET, MHEAD
This header field applies only to the server directly connected to the client (i.e., the nearest
neighbor in a chain of connections). If the response passes through a proxy, the proxy must
either remove the Public header field or replace it with one applicable to its own capabilities.
10.33 Range
TBS
10.34 Referer
The Referer
request-header field allows the client to specify, for the server's benefit, the address
(URI) of the resource from which the Request-URI
was obtained. This allows a server to
generate lists of back-links to resources for interest, logging, optimized caching, etc. It also
allows obsolete or mistyped links to be traced for maintenance. The Referer
field must not be
sent if the Request-URI
was obtained from a source that does not have its own URI, such as input
from the user keyboard.
Referer = "Referer" ":" ( absoluteURI | relativeURI )
Example:
Referer: http://www.w3.org/hypertext/DataSources/Overview.html
If a partial URI is given, it should be interpreted relative to the Request-URI
. The URI must not
include a fragment.
Note: Because the source of a link may be private information or may 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.
10.35 Refresh
TBS
10.36 Retry-After
The Retry-After response-header field can be used with a 503 (service unavailable) response to
indicate how long the service is expected to be unavailable to the requesting client. 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" ":" ( HTTP-date | delta-seconds )
Two examples of its use are
Retry-After: Wed, 14 Dec 1994 18:22:54 GMT
Retry-After: 120
In the latter example, the delay is 2 minutes.
10.37 Server
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 (Section 3.8) and
comments identifying the server and any significant subproducts. By convention, the product
tokens are listed in order of their significance for identifying the application.
Server = "Server" ":" 1*( product | comment )
Example:
Server: CERN/3.0 libwww/2.17
If the response is being forwarded through a proxy, the proxy application must not add its data
to the product list. Instead, it should include a Forwarded
field
(as described in Section 10.20).
Note: Revealing the specific software version of the server may 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.
10.38 Title
The Title entity-header field indicates the title of the entity
Title = "Title" ":" *TEXT
An example of the field is
Title: Hypertext Transfer Protocol -- HTTP/1.1
This field is isomorphic with the <TITLE> element in HTML [5].
10.39 Transfer Encoding
The Transfer-Encoding general-header field indicates what (if any) type of transformation has
been applied to the message body in order to safely transfer it between the sender and the
recipient. This differs from the Content-Encoding in that the transfer coding is a property of the
message, not of the original resource.
Transfer-Encoding = "Transfer-Encoding" ":" 1#transfer-coding
Transfer codings are defined in Section 3.6. An example is:
Transfer-Encoding: chunked
Many older HTTP/1.0 applications do not understand the Transfer-Encoding header.
10.40 Unless
The Unless request-header field performs a similar function as If-Modified-Since, but the
comparison is based on any Entity-Header field value of the resource and is not restricted to the
GET
method.
Unless = "Unless" ":" 1#logic-bag
For example,
Unless: {or {ne {Content-MD5 "Q2hlY2sgSW50ZWdyaXR5IQ=="}}
{ne {Content-Length 10036}}
{ne {Content-Version "12.4.8"}}
{gt {Last-Modified "Mon, 04 Dec 1995 01:23:45 GMT"}}}
Multiple Unless
headers, or multiple bags separated by commas, can be combined by OR'ing
them together:
Unless: {eq {A "a"}}
Unless: {eq {B "b"}}
is equivalent to
Unless: {eq {A "a"}},{eq {B "b"}}
which in turn is equivalent to
Unless: {or {eq {A "a"}} {eq {B "b"}}}
When a request containing an Unless
header field is received, the server must evaluate the
expression defined by the listed logic-bags (Section 3.11).
If the expression evaluates to false,
then no change is made to the semantics of the request. If it evaluates true and the request is not
a conditional GET
(If-Modified-Since
,
Section 10.23) or a partial GET
(Range
, Section 10.33),
then the server must abort the request and respond with the 412 (unless true) status code. If the
request is a conditional GET
, then the server must disregard the If-Modified-Since
value and
respond as it would for a normal GET
.
Similarly, if the request is a partial GET
, then the server
must disregard the Range
value and respond as it would for a normal GET
.
10.41 Upgrade
The Upgrade
general-header allows the client to specify what additional communication
protocols it supports and would like to use if the server finds it appropriate to switch protocols.
The server must use the Upgrade
header field within a 101 (switching protocols) response to
indicate which protocol(s) are being switched.
Upgrade = "Upgrade" ":" 1#product
For example,
Upgrade: HTTP/2.0, SHTTP/1.3, IRC/6.9, RTA/x11
The purpose of the Upgrade header is to allow easier migration across protocols in order to
better match the application needs with protocol capabilities.
10.42 URI
The URI entity-header field is used to inform the recipient of other Uniform Resource
Identifiers (Section 3.2) by which the resource can be identified, and of all negotiable variants
corresponding to the Request-URI
.
URI-header = "URI" ":" 1#( uri-mirror | uri-name | uri-variant )
uri-mirror = "{" "mirror" <"> URI <"> "}"
uri-name = "{" "name" <"> URI <"> "}"
uri-variant = "{" "variant" <"> URI <"> qvalue
[ "{" "type" <"> media-type <"> "}" ]
[ "{" "language" <"> 1#language-tag <"> "}" ]
[ "{" "encoding" <"> 1#content-coding <"> "}" ]
[ "{" "length" 1*DIGIT "}" ]
[ "{" "user-agent" "}" ]
"}"
Any URI specified in this field can be absolute or relative to the Request-URI. The "mirror" form
of URI refers to a location which is a mirror copy of the Request-URI
. The "name" form refers
to a location-independent name corresponding to the Request-URI
. The "variant" form refers to
one of the set of negotiable variants that may be retrieved via a request on the Request-URI
.
Request-URI
maps to a set of variants, then the dimensions of that variance must be given
in any response containing one of those variants. If the Location header field is present in a 2xx
response, its value identifies which one of the variants is included with the response. An
example is:
Location: http://www.w3.org/pub/WWW/TheProject.en.html
URI: {variant "TheProject.fr.html" 1.0
{type "text/html"} {language "fr"}},
{variant "TheProject.en.html" 1.0
{type "text/html"} {language "en"}},
{variant "TheProject.fr.txt" 0.7
{type "text/plain"} {language "fr"}},
{variant "TheProject.en.txt" 0.8
{type "text/plain"} {language "en"}}
which indicates that the negotiable Request-URI
covers a group of four individual resources that
vary in media type and natural language. The type, language, encoding, and length attributes
refer to their Content-* counterparts for each resource. The user-agent attribute indicates that
the associated URI is negotiable based on the User-Agent header field.
10.43 User-Agent
The User-Agent
request-header field contains information about the user agent originating the
request. This is for statistical purposes, the tracing of protocol violations, and automated
recognition of user agents for the sake of tailoring responses to avoid particular user agent
limitations. Although it is not required, user agents should include this field with requests. The
field can contain multiple product tokens (Section 3.8) and comments identifying the agent and
any subproducts which form a significant part of the user agent. By convention, the product
tokens are listed in order of their significance for identifying the application.
User-Agent = "User-Agent" ":" 1*( product | comment )
Example:
User-Agent: CERN-LineMode/2.15 libwww/2.17b3
10.44 WWW-Authenticate
The WWW-Authenticate
response-header field must be included in 401 (unauthorized) response
messages. The field value consists of at least one challenge
that indicates the authentication
scheme(s) and parameters applicable to the Request-URI
.
WWW-Authenticate = "WWW-Authenticate" ":" 1#challenge
The HTTP access authentication process is described in Section 11. User agents must take
special care in parsing the WWW-Authenticate
field value if it contains more than one challenge,
or if more than one WWW-Authenticate
header field is provided, since the contents of a challenge
may itself contain a comma-separated list of authentication parameters.
11. Access Authentication
HTTP provides a simple challenge-response authentication mechanism which may be used by
a server to challenge a client request and by a client to provide authentication information. It
uses an extensible, case-insensitive token to identify the authentication scheme, followed by a
comma-separated list of attribute-value pairs which carry the parameters necessary for
achieving authentication via that scheme.
auth-scheme = token
auth-param = token "=" quoted-string
The 401 (unauthorized) response message is used by an origin server to challenge the
authorization of a user agent. This response must include a WWW-Authenticate
header field
containing at least one challenge
applicable to the requested resource.
challenge = auth-scheme 1*SP realm *( "," auth-param )
realm = "realm" "=" realm-value
realm-value = quoted-string
The realm attribute (case-insensitive) is required for all authentication schemes which issue a
challenge. The realm value (case-sensitive), in combination with the canonical root URL of the
server being accessed, defines the protection space. These realms allow the protected resources
on a server to be partitioned into a set of protection spaces, each with its own authentication
scheme and/or authorization database. The realm value is a string, generally assigned by the
origin server, which may have additional semantics specific to the authentication scheme.
Authorization
header field with the
request. The Authorization
field value consists of credentials
containing the authentication
information of the user agent for the realm of the resource being requested.
credentials = basic-credentials
| auth-scheme *("," auth-param )
The domain over which credentials can be automatically applied by a user agent is determined
by the protection space. If a prior request has been authorized, the same credentials may be
reused for all other requests within that protection space for a period of time determined by the
authentication scheme, parameters, and/or user preference. Unless otherwise defined by the
authentication scheme, a single protection space cannot extend outside the scope of its server.
WWW-Authenticate
header field
containing the (possibly new) challenge
applicable to the requested resource and an entity
explaining the refusal.
WWW-Authenticate
and Authorization
headers untouched, and must not cache the
response to a request containing Authorization
.
Proxy-Authenticate
and Proxy-Authorization
headers.
11.1 Basic Authentication Scheme
The "basic" authentication scheme is based on the model that the user agent must authenticate
itself with a user-ID and a password for each realm. The realm value should be considered an
opaque string which can only be compared for equality with other realms on that server. The
server will service the request only if it can validate the user-ID and password for the protection
space of the Request-URI
. There are no optional authentication parameters.
WWW-Authenticate: Basic realm="WallyWorld"
where "WallyWorld" is the string assigned by the server to identify the protection space of the
Request-URI
.
credentials
.
basic-credentials = "Basic" SP basic-cookie
basic-cookie = <base64 [7] encoding of userid-password,
except not limited to 76 char/line>
userid-password = [ token ] ":" *TEXT
If the user agent wishes to send the user-ID "Aladdin" and password "open sesame", it would
use the following header field:
Authorization: Basic QWxhZGRpbjpvcGVuIHNlc2FtZQ==
The basic authentication scheme is a non-secure method of filtering unauthorized access to
resources on an HTTP server. It is based on the assumption that the connection between the
client and the server can be regarded as a trusted carrier. As this is not generally true on an open
network, the basic authentication scheme should be used accordingly. In spite of this, clients
should implement the scheme in order to communicate with servers that use it.
11.2 Digest Authentication Scheme
The "digest" authentication scheme is [currently described in an expired Internet-Draft, and
this description will have to be improved to reference a new draft or include the old one].
12. Content Negotiation
Content negotiation is an optional feature of the HTTP protocol. It is designed to allow for
selection of a preferred content representation based upon the attributes of the negotiable
variants corresponding to the requested resource. HTTP/1.1 provides for two types of
negotiation: preemptive and reactive.
12.1 Preemptive Negotiation
Preemptive negotiation attempts to "negotiate" the variant parameters by including the user
agent preferences within each request. In this way, the preferred representation of the resource
may be negotiated and obtained within a single request-response round-trip, and without
intervention from the user. However, this also means that the user agent preferences are all the
time, even though relatively few resources are ever negotiable. Preemptive negotiation may not
always be desirable for the user and is sometimes unnecessary for the content provider.
Implementors should provide mechanisms whereby the amount of preemptive content
negotiation, and the parameters of that negotiation, are configurable by the user and server
maintainer.
The mapping function is defined as:
Q(qs,qe,qc,ql, { if mxb=undefined, then (qs*qe*qc*ql*q) }
q,mxb,bs) = { if mxb >= bs, then (qs*qe*qc*ql*q) }
{ if mxb < bs, then 0 }
The variants with a maximal value for the Q function represent the preferred representation(s)
of the entity; those with a Q values less than the maximal value are therefore excluded from
further consideration. If multiple representations exist that only vary by Content-Encoding, then
the smallest representation (lowest bs) is preferred.
13. Caching
[This will be a summary of what is already defined in the Methods, Status Codes,
Cache-Control, Unless, and If-Modified-Since sections.]
14. Security Considerations
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.
14.1 Authentication of Clients
As mentioned in Section 11.1, the Basic authentication scheme is not a secure method of user
authentication, nor does it prevent the Entity-Body
from being transmitted in clear text across the
physical network used as the carrier. HTTP does not prevent additional authentication schemes
and encryption mechanisms from being employed to increase security.
14.2 Safe Methods
The writers of client software should be aware that the software represents the user in their
interactions over the Internet, and should be careful to allow the user to be aware of any actions
they may take which may have an unexpected significance to themselves or others.
GET
and HEAD
methods should never
have the significance of taking an action other than retrieval. These methods should 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.
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.
14.3 Abuse of Server Log Information
A server is in the position to save personal data about a user's requests which may identify their
reading patterns or subjects of interest. This information is clearly confidential in nature and its
handling may be constrained by law in certain countries. People using the HTTP protocol to
provide data are responsible for ensuring that such material is not distributed without the
permission of any individuals that are identifiable by the published results.
14.4 Transfer of Sensitive Information
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
, Forwarded
, Referer
and
From
.
Server
header field a configurable option.
Forwarded
fields
generated behind the firewall.
Referer
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
field may indicate a private document's URI whose publication would be inappropriate.
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.
From
and Referer
information.
15. Acknowledgments
This specification makes heavy use of the augmented BNF and generic constructs defined by
David H. Crocker for RFC 822 [9]. Similarly, it reuses many of the definitions provided by
Nathaniel Borenstein and Ned Freed for MIME [7]. We hope that their inclusion in this
specification will help reduce past confusion over the relationship between HTTP and Internet
mail message formats.
Gary Adams Harald Tveit Alvestrand
Keith Ball Brian Behlendorf
Paul Burchard Maurizio Codogno
Mike Cowlishaw Roman Czyborra
Michael A. Dolan Jim Gettys
Marc Hedlund Koen Holtman
Alex Hopmann Bob Jernigan
Shel Kaphan Rohit Khare
Martijn Koster Alexei Kosut
Dave Kristol Daniel LaLiberte
Paul Leach Albert Lunde
John C. Mallery Jean-Philippe Martin-Flatin
Larry Masinter Mitra
Jeffrey Mogul Gavin Nicol
Bill Perry Jeffrey Perry
Owen Rees Luigi Rizzo
David Robinson Marc Salomon
Rich Salz Jim Seidman
Chuck Shotton Eric W. Sink
Simon E. Spero Richard N. Taylor
Robert S. Thau François Yergeau
Mary Ellen Zurko
16. References
8-bit Single-Byte Coded Graphic Character Sets --
Part 1: Latin alphabet No. 1, ISO 8859-1:1987.
Part 2: Latin alphabet No. 2, ISO 8859-2, 1987.
Part 3: Latin alphabet No. 3, ISO 8859-3, 1988.
Part 4: Latin alphabet No. 4, ISO 8859-4, 1988.
Part 5: Latin/Cyrillic alphabet, ISO 8859-5, 1988.
Part 6: Latin/Arabic alphabet, ISO 8859-6, 1987.
Part 7: Latin/Greek alphabet, ISO 8859-7, 1987.
Part 8: Latin/Hebrew alphabet, ISO 8859-8, 1988.
Part 9: Latin alphabet No. 5, ISO 8859-9, 1990.
17. Authors' Addresses
Roy T. Fielding
Department of Information and Computer Science
University of California
Irvine, CA 92717-3425, U.S.A.
Fax: +1 (714) 824-4056
Email: fielding@ics.uci.edu
W3 Consortium
MIT Laboratory for Computer Science
545 Technology Square
Cambridge, MA 02139, U.S.A.
Fax: +1 (617) 258 8682
Email: frystyk@w3.org
Director, W3 Consortium
MIT Laboratory for Computer Science
545 Technology Square
Cambridge, MA 02139, U.S.A.
Fax: +1 (617) 258 8682
Email: timbl@w3.org
Appendices
These appendices are provided for informational reasons only -- they do not form a part of the
HTTP/1.1 specification.
A. Internet Media Type message/http
In addition to defining the HTTP/1.1 protocol, this document serves as the specification for the
Internet media type "message/http". The following is to be registered with IANA [17].
Media Type name: message
Media subtype name: http
Required parameters: none
Optional parameters: version, msgtype
version: The HTTP-Version number of the enclosed message
(e.g., "1.1"). If not present, the version can be
determined from the first line of the body.
msgtype: The message type -- "request" or "response". If not
present, the type can be determined from the first
line of the body.
Encoding considerations: only "7bit", "8bit", or "binary" are
permitted
Security considerations: none
B. Tolerant Applications
Although this document specifies the requirements for the generation of HTTP/1.1 messages,
not all applications will be correct in their implementation. We therefore recommend that
operational applications be tolerant of deviations whenever those deviations can be interpreted
unambiguously.
Status-Line
and servers tolerant when parsing the
Request-Line
. In particular, they should accept any amount
of SP
or HT
characters between
fields, even though only a single SP
is required.
HTTP-header
fields is the sequence CRLF
. However, we recommend that
applications, when parsing such headers, recognize a single LF
as a line terminator and ignore
the leading CR
.
C. Relationship to MIME
HTTP/1.1 reuses many of the constructs defined for Internet Mail (RFC 822 [9]) and the
Multipurpose Internet Mail Extensions (MIME [7]) to allow entities to be transmitted in an
open variety of representations and with extensible mechanisms. However, HTTP is not a
MIME-compliant application. HTTP's performance requirements differ substantially from
those of Internet mail. Since it is not limited by the restrictions of existing mail protocols and
SMTP gateways, HTTP does not obey some of the constraints imposed by RFC 822 and MIME
for mail transport.
C.1 Conversion to Canonical Form
MIME requires that an entity be converted to canonical form prior to being transferred, as
described in Appendix G of RFC 1521 [7]. Although HTTP does require media types to be
transferred in canonical form, it changes the definition of "canonical form" for text-based
media types as described in Section 3.7.1.
C.1.1 Representation of Line Breaks
MIME requires that the canonical form of any text type represent line breaks as CRLF
and
forbids the use of CR
or LF
outside of line break sequences.
Since HTTP allows CRLF
, bare CR
,
and bare LF
(or the octet sequence(s) to which they would be translated for the given character
set) to indicate a line break within text content, recipients of an HTTP message cannot rely
upon receiving MIME-canonical line breaks in text.
CRLF
.
However, this may be complicated by the presence of a Content-Encoding and by the fact that
HTTP allows the use of some character sets which do not use octets 13 and 10 to represent CR
and LF
, as is the case for some multi-byte character sets. If canonicalization is performed, the
Content-Length header field value must be updated to reflect the new body length.
C.1.2 Default Character Set
MIME requires that all subtypes of the top-level Content-Type "text" have a default character
set of US-ASCII [21]. In contrast, HTTP defines the default character set for "text" to be
ISO-8859-1 [22] (a superset of US-ASCII). Therefore, if a text/* media type given in the
Content-Type header field does not already include an explicit charset parameter, the parameter
;charset="iso-8859-1"
should be added by the proxy/gateway if the entity contains any octets greater than 127.
C.2 Conversion of Date Formats
HTTP/1.1 uses a restricted subset of date formats to simplify the process of date comparison.
Proxies/gateways from other protocols should ensure that any Date
header field present in a
message conforms to one of the HTTP/1.1 formats and rewrite the date if necessary.
C.3 Introduction of Content-Encoding
MIME does not include any concept equivalent to HTTP's Content-Encoding
header field. Since
this acts as a modifier on the media type, proxies/gateways to MIME-compliant protocols must
either change the value of the Content-Type
header field or decode the Entity-Body
before
forwarding the message.
Note: Some experimental applications of Content-Type for Internet mail have used a
media-type parameter of ";conversions=<content-coding>" to perform an
equivalent function as Content-Encoding. However, this parameter is not part of the
MIME specification at the time of this writing.
C.4 No Content-Transfer-Encoding
HTTP does not use the Content-Transfer-Encoding
(CTE) field of MIME. Proxies/gateways from
MIME-compliant protocols must remove any non-identity CTE ("quoted-printable" or
"base64") encoding prior to delivering the response message to an HTTP client.
Proxies/gateways to MIME-compliant protocols are responsible for ensuring that the message
is in the correct format and encoding for safe transport on that protocol, where "safe transport"
is defined by the limitations of the protocol being used. At a minimum, the CTE field of
Content-Transfer-Encoding: binary
should be added by the proxy/gateway if it is unwilling to apply a content transfer encoding.
Content-Transfer-Encoding
as an extension Entity-Header
in a
POST
request when it knows the destination of that request is a proxy/gateway to a
MIME-compliant protocol.
C.5 Introduction of Transfer-Encoding
HTTP/1.1 introduces the Transfer-Encoding header field (Section 10.39).
Proxies/gateways must remove any transfer coding prior to forwarding a message via a MIME-compliant
protocol. The process for decoding the "chunked" transfer coding (Section 3.6) can be
represented in pseudo-code as:
length := 0
read chunk-size and CRLF
while (chunk-size > 0) {
read chunk-data and CRLF
append chunk-data to Entity-Body
length := length + chunk-size
read chunk-size and CRLF
}
read entity-header
while (entity-header not empty) {
append entity-header to existing header fields
read entity-header
}
Content-Length := length
Remove "chunked" from Transfer-Encoding
D. Changes from HTTP/1.0
This section will summarize the differences between versions 1.0 and 1.1 of the Hypertext
Transfer Protocol.
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