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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<URL:http://www.ics.uci.edu/pub/ietf/http/>. General discussions about HTTP
and the applications which use HTTP should take place on the <www-talk@w3.org> mailing
list.
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 chain
A 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 chain
The figure above shows three intermediaries (A, B, and C) between the user agent and origin
server. A request or response message that travels the whole chain 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 chain
Not 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 LF
HTTP/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" | DIGIT
Many 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 | HT
Comments can be included in some HTTP header fields by surrounding the comment text with
parentheses. Comments are only allowed in fields containing "comment" as part of their field
value definition. 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 = "\" CHAR
Braces 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
The version of an HTTP message is indicated by an HTTP-Version field in the first line of the
message. If the protocol version is not specified, the recipient must assume that the message is
in the simple HTTP/0.9 format [6].
HTTP-Version = "HTTP" "/" 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.
Applications sending 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.
HTTP/1.1 servers must:
HTTP/1.1 clients must:
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.
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 "/".
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.
delta-seconds = 1*DIGIT
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.
content-coding = "gzip" | "compress" | token
Note: For historical reasons, HTTP applications should consider "x-gzip" andAll
"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.
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).
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.
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.
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.
If a given 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].
All 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.
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.
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.
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.
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
Content-Type header field overrides the default.
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.
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.
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:
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".
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).
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.
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:
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.
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:
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.
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:
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).
Except for "ne", any comparison to a field not defined by the resource evaluates to false.
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.
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.
Multiple 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.
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.
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.
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.
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).
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.
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).
If a proxy receives a request without any path in the 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".
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.
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.
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.
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.
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.
The first digit of the 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:
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.
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.
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.
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.
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.
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 Content-Length
header field defined with a value of zero (0).
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.
Any HTTP/1.1 message containing an entity body should include a 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".
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.
If a request contains an entity body and 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.
Messages must not include both a Content-Length header field and the "chunked" transfer
coding. If both are received, the Content-Length must be ignored.
When a 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.
The semantics of all methods may be affected by the presence of an Unless request header field,
as described in Section 10.40.
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.
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., 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.
If the 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.
If the 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.
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.
The semantics of the 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.
The semantics of the GET method change to a "partial GET" if the request message includes a
Range header field. A partial GET requests that only part of the 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.
The response to a GET request may be cachable if and only if it meets the requirements for
HTTP caching described in Section 13.
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.
The response to a 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.
There is no "conditional 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.
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:
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.
HTTP/1.1 allows for a two-phase process to occur in accepting and processing a 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.
Upon receipt of a 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.
For compatibility with HTTP/1.0 applications, all 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.
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 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.
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 Request-URI identifies a currently cached entity,
that entity must be removed from the cache. Responses to this method are not cachable.
The fundamental difference between the 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.
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 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.
HTTP/1.1 allows for a two-phase process to occur in accepting and processing a 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.
Upon receipt of a 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.
For compatibility with HTTP/1.0 applications, all 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.
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 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.
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.
If the request passes through a cache and the Request-URI identifies a currently cached entity,
that entity must be removed from the cache. Responses to this method are not cachable.
HTTP/1.1 allows for a two-phase process to occur in accepting and processing a 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.
Upon receipt of a 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.
For compatibility with HTTP/1.0 applications, all 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.
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 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.
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.
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.
If the request passes through a cache and the Request-URI identifies a currently cached entity,
that entity must be removed from the cache. Responses to this method are not cachable.
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 Request-URI identifies a currently cached entity,
that entity must be removed from the cache. Responses to this method are not cachable.
If the request passes through a cache and the Request-URI identifies a currently cached entity,
that entity must be removed from the cache. Responses to this method are not cachable.
If the request passes through a cache and the Request-URI identifies a currently cached entity,
that entity must be removed from the cache. Responses to this method are not cachable.
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.
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 Content-Encoding and Transfer-Encoding header fields.
HTTP/1.1 allows for a two-phase process to occur in accepting and processing a 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.
Upon receipt of a 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.
For compatibility with HTTP/1.0 applications, all 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.
Status-Code is described below, including a description of which method(s) it can follow
and any metainformation required in the response.
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.
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.
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.
GET
HEAD
Entity-Body;
POST
TRACE
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).
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.
Content-Length with a value of zero (0) and no entity body.
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.
GET or HEAD.
A user agent should never automatically redirect a request more than 5 times, since such
redirections usually indicate an infinite loop.
Request-URI to one or more of the new
references returned by the server, where possible. This response is cachable unless indicated
otherwise.
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).
If the 301 status code is received in response to a request other than 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.
Request-URI for future requests. This
response is only cachable if indicated by a Cache-Control or Expires header field.
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).
If the 302 status code is received in response to a request other than 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.
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).
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.
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 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.
The 304 response must not include an entity body, and thus is always ternminated by the first empty line after the header fields.
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.
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.
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.
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.
Conflicts are most likely to occur in response to a PUT or
PATCH request. If versioning is being
used and the entity being PUT or PATCHed 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.
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.
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.
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.
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.
Entity-Header fields, both sender and recipient
refer to either the client or the server, depending on who sends and who receives the entity.
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.
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).
The example
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."
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:
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.
A more elaborate example is
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."
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,
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.
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.
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.
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)."
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 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.
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.
The 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.
A proxy must not modify the 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.
The 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.
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.
Responses to requests containing an Authorization field are not cachable.
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.
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 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.
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.
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.
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.
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.
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.
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.
As an example, a client would send
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).
The 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.
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.
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.
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.
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.
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: 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".
Content-Language may be applied to any media type -- it should not be limited to textual documents.
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.
Any 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.
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.
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.
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.
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.
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.
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.
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.
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 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.
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.
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.
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.
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.
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).
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:
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.
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.
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
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.
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.
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.
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.
Examples of usage include:
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.
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].
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.
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.
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.
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.
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.
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.
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 theRefererfield is sent. For example, a browser client could have a toggle switch for browsing openly/anonymously, which would respectively enable/disable the sending ofRefererandFrominformation.
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.
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.
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].
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.
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.
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.
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.
If the 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.
User agents may use this information to notify the user of additional formats and to guide the process of reactive content negotiation (Section 12).
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
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.
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.
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 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.
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 WWW-Authenticate header field
containing the (possibly new) challenge applicable to the requested resource and an entity
explaining the refusal.
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 WWW-Authenticate and Authorization headers untouched, and must not cache the
response to a request containing Authorization.
HTTP/1.1 allows a client pass authentication information to and from a proxy via the
Proxy-Authenticate and Proxy-Authorization headers.
Request-URI. There are no optional authentication parameters.
Upon receipt of an unauthorized request for a URI within the protection space, the server should respond with a challenge like the following:
WWW-Authenticate: Basic realm="WallyWorld"
where "WallyWorld" is the string assigned by the server to identify the protection space of the
Request-URI.
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 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.
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:
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.
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.
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.
In particular, the convention has been established that the 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.
Naturally, it is not possible to ensure that the server does not generate side-effects as a result of
performing a GET request; in fact, some dynamic resources consider that a feature. The
important distinction here is that the user did not request the side-effects, so therefore cannot
be held accountable for them.
Server, Forwarded, Referer and
From.
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 Server header field a configurable option.
Proxies which serve as a portal through a network firewall should take special precautions
regarding the transfer of header information that identifies the hosts behind the firewall. In
particular, they should remove, or replace with sanitized versions, any Forwarded fields
generated behind the firewall.
The 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.
The information sent in the From field might conflict with the user's privacy interests or their
site's security policy, and hence it should not be transmitted without the user being able to
disable, enable, and modify the contents of the field. The user must be able to set the contents
of this field within a user preference or application defaults configuration.
We suggest, though do not require, that a convenient toggle interface be provided for the user
to enable or disable the sending of From and Referer information.
The 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:
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
Henrik Frystyk Nielsen
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
Tim Berners-Lee
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
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
Clients should be tolerant in parsing the 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.
The line terminator for 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.
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.
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.
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 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.
;charset="iso-8859-1"
should be added by the proxy/gateway if the entity contains any octets greater than 127.
Date header field present in a
message conforms to one of the HTTP/1.1 formats and rewrite the date if necessary.
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.
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.
An HTTP client may include a 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.
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