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Differences from draft-ietf-http-v11-spec-00.txt
Hypertext Transfer Protocol -- HTTP/1.1
Status of this Memo
This document is an Internet-Draft. Internet-Drafts are working
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and its working groups. Note that other groups may also distribute
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Distribution of this document is unlimited. Please send comments to
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================================================================
NOTE: This specification is for discussion purposes only. It is not
claimed to represent the consensus of the HTTP working group, and
contains a number of proposals that either have not been discussed or
are controversial. The working group is discussing significant
changes in many areas, including logic bags, support for caching,
range retrieval, content negotiation, MIME compatibility,
authentication, timing of the PUT operation.
================================================================
Abstract
The Hypertext Transfer Protocol (HTTP) is an application-level
protocol for distributed, collaborative, hypermedia information
systems. It is a generic, stateless, object-oriented protocol which
can be used for many tasks, such as name servers and distributed
object management systems, through extension of its request methods
(commands). A feature of HTTP is the typing and negotiation of data
representation, allowing systems to be built independently of the
data being transferred.
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".
Table of Contents
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
9.2 Successful 2xx
9.3 Redirection 3xx
9.4 Client Error 4xx
9.5 Server Error 5xx
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
1. Introduction
1.1 Purpose
The Hypertext Transfer Protocol (HTTP) is an application-level
protocol for distributed, collaborative, hypermedia information
systems. HTTP has been in use by the World-Wide Web global
information initiative since 1990. The first version of HTTP,
referred to as HTTP/0.9, was a simple protocol for raw data
transfer across the Internet. HTTP/1.0, as defined by RFC xxxx [6],
improved the protocol by allowing messages to be in the format of
MIME-like entities, containing metainformation about the data
transferred and modifiers on the request/response semantics.
However, HTTP/1.0 does not sufficiently take into consideration the
effect of hierarchical proxies and caching, the desire for
persistent connections and virtual hosts, and a number of other
details that slipped through the cracks of existing
implementations. In addition, the proliferation of incompletely-
implemented applications calling themselves "HTTP/1.0" has
necessitated a protocol version change in order for two
communicating applications to determine each other's true
capabilities.
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.
1.2 Requirements
This specification uses the same words as RFC 1123 [8] for defining
the significance of each particular requirement. These words are:
must
This word or the adjective "required" means that the item is an
absolute requirement of the specification.
should
This word or the adjective "recommended" means that there may
exist valid reasons in particular circumstances to ignore this
item, but the full implications should be understood and the
case carefully weighed before choosing a different course.
may
This word or the adjective "optional" means that this item is
truly optional. One vendor may choose to include the item
because a particular marketplace requires it or because it
enhances the product, for example; another vendor may omit the
same item.
An implementation is not compliant if it fails to satisfy one or
more of the must requirements for the protocols it implements. An
implementation that satisfies all the must and all the should
requirements for its protocols is said to be "unconditionally
compliant"; one that satisfies all the must requirements but not
all the should requirements for its protocols is said to be
"conditionally compliant".
1.3 Terminology
This specification uses a number of terms to refer to the roles
played by participants in, and objects of, the HTTP communication.
connection
A transport layer virtual circuit established between two
application programs for the purpose of communication.
message
The basic unit of HTTP communication, consisting of a structured
sequence of octets matching the syntax defined in Section 4 and
transmitted via the connection.
request
An HTTP request message (as defined in Section 5).
response
An HTTP response message (as defined in Section 6).
resource
A network data object or service which can be identified by a
URI (Section 3.2).
entity
A particular representation or rendition of a data resource, or
reply from a service resource, that may be enclosed within a
request or response message. An entity consists of
metainformation in the form of entity headers and content in the
form of an entity body.
client
An application program that establishes connections for the
purpose of sending requests.
user agent
The client which initiates a request. These are often browsers,
editors, spiders (web-traversing robots), or other end user
tools.
server
An application program that accepts connections in order to
service requests by sending back responses.
origin server
The server on which a given resource resides or is to be created.
proxy
An intermediary program which acts as both a server and a client
for the purpose of making requests on behalf of other clients.
Requests are serviced internally or by passing them, with
possible translation, on to other servers. A proxy must
interpret and, if necessary, rewrite a request message before
forwarding it. Proxies are often used as client-side portals
through network firewalls and as helper applications for
handling requests via protocols not implemented by the user
agent.
gateway
A server which acts as an intermediary for some other server.
Unlike a proxy, a gateway receives requests as if it were the
origin server for the requested resource; the requesting client
may not be aware that it is communicating with a gateway.
Gateways are often used as server-side portals through network
firewalls and as protocol translators for access to resources
stored on non-HTTP systems.
tunnel
A tunnel is an intermediary program which is acting as a blind
relay between two connections. Once active, a tunnel is not
considered a party to the HTTP communication, though the tunnel
may have been initiated by an HTTP request. The tunnel ceases to
exist when both ends of the relayed connections are closed.
Tunnels are used when a portal is necessary and the intermediary
cannot, or should not, interpret the relayed communication.
cache
A program's local store of response messages and the subsystem
that controls its message storage, retrieval, and deletion. A
cache stores cachable responses in order to reduce the response
time and network bandwidth consumption on future, equivalent
requests. Any client or server may include a cache, though a
cache cannot be used by a server while it is acting as a tunnel.
Any given program may be capable of being both a client and a
server; our use of these terms refers only to the role being
performed by the program for a particular connection, rather than
to the program's capabilities in general. Likewise, any server may
act as an origin server, proxy, gateway, or tunnel, switching
behavior based on the nature of each request.
1.4 Overall Operation
The HTTP protocol is based on a request/response paradigm. A client
establishes a connection with a server and sends a request to the
server in the form of a request method, URI, and protocol version,
followed by a MIME-like message containing request modifiers,
client information, and possible body content. The server responds
with a status line, including the message's protocol version and a
success or error code, followed by a MIME-like message containing
server information, entity metainformation, and possible body
content.
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.
2. Notational Conventions and Generic Grammar
2.1 Augmented BNF
All of the mechanisms specified in this document are described in
both prose and an augmented Backus-Naur Form (BNF) similar to that
used by RFC 822 [9]. Implementors will need to be familiar with the
notation in order to understand this specification. The augmented
BNF includes the following constructs:
name = definition
The name of a rule is simply the name itself (without any
enclosing "<" 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"
Quotation marks surround literal text. Unless stated otherwise,
the text is case-insensitive.
rule1 | rule2
Elements separated by a bar ("I") are alternatives, e.g.,
"yes | no" will accept yes or no.
(rule1 rule2)
Elements enclosed in parentheses are treated as a single
element. Thus, "(elem (foo | bar) elem)" allows the token
sequences "elem foo elem" and "elem bar elem".
*rule
The character "*" 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]
Square brackets enclose optional elements; "[foo bar]" is
equivalent to "*1(foo bar)".
N rule
Specific repetition: "<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
A construct "#" 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
A semi-colon, set off some distance to the right of rule text,
starts a comment that continues to the end of line. This is a
simple way of including useful notes in parallel with the
specifications.
implied *LWS
The grammar described by this specification is word-based.
Except where noted otherwise, linear whitespace (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.
2.2 Basic Rules
The following rules are used throughout this specification to
describe basic parsing constructs. The US-ASCII coded character set
is defined by [21].
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
3. Protocol Parameters
3.1 HTTP Version
HTTP uses a "<major>.<minor>" numbering scheme to indicate versions
of the protocol. The protocol versioning policy is intended to
allow the sender to indicate the format of a message and its
capacity for understanding further HTTP communication, rather than
the features obtained via that communication. No change is made to
the version number for the addition of message components which do
not affect communication behavior or which only add to extensible
field values. The <minor> number is incremented when the changes
made to the protocol add features which do not change the general
message parsing algorithm, but which may add to the message
semantics and imply additional capabilities of the sender. The
<major> number is incremented when the format of a message within
the protocol is changed.
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:
o recognize the format of the Request-Line for HTTP/0.9, 1.0, and
1.1 requests;
o understand any valid request in the format of HTTP/0.9, 1.0, or
1.1;
o respond appropriately with a message in the same major version
used by the client.
HTTP/1.1 clients must:
o recognize the format of the Status-Line for HTTP/1.0 and 1.1
responses;
o understand any valid response in the format of HTTP/0.9, 1.0,
or 1.1.
Proxy and gateway applications must be careful in forwarding
requests that are received in a format different than that of the
application's native HTTP version. Since the protocol version
indicates the protocol capability of the sender, a proxy/gateway
must never send a message with a version indicator which is greater
than its native version; if a higher version request is received,
the proxy/gateway must either downgrade the request version,
respond with an error, or switch to tunnel behavior. Requests with
a version lower than that of the application's native format may be
upgraded before being forwarded; the proxy/gateway's response to
that request must follow the server requirements listed above.
3.2 Uniform Resource Identifiers
URIs have been known by many names: WWW addresses, Universal
Document Identifiers, Universal Resource Identifiers [3], and
finally the combination of Uniform Resource Locators (URL) [4] and
Names (URN) [20]. As far as HTTP is concerned, Uniform Resource
Identifiers are simply formatted strings which identify--via name,
location, or any other characteristic--a network resource.
3.2.1 General Syntax
URIs in HTTP can be represented in absolute form or relative to
some known base URI [11], depending upon the context of their use.
The two forms are differentiated by the fact that absolute URIs
always begin with a scheme name followed by a colon.
URI = ( absoluteURI | relativeURI ) [ "#" fragment ]
absoluteURI = scheme ":" *( uchar | reserved )
relativeURI = net_path | abs_path | rel_path
net_path = "//" net_loc [ abs_path ]
abs_path = "/" rel_path
rel_path = [ path ] [ ";" params ] [ "?" query ]
path = fsegment *( "/" segment )
fsegment = 1*pchar
segment = *pchar
params = param *( ";" param )
param = *( pchar | "/" )
scheme = 1*( ALPHA | DIGIT | "+" | "-" | "." )
net_loc = *( pchar | ";" | "?" )
query = *( uchar | reserved )
fragment = *( uchar | reserved )
pchar = uchar | ":" | "@" | "&" | "="
uchar = unreserved | escape
unreserved = ALPHA | DIGIT | safe | extra | national
escape = "%" HEX HEX
reserved = ";" | "/" | "?" | ":" | "@" | "&" | "="
extra = "!" | "*" | "'" | "(" | ")" | ","
safe = "$" | "-" | "_" | "." | "+"
unsafe = CTL | SP | <"> | "#" | "%" | "<" | ">"
national = <any OCTET excluding ALPHA, DIGIT,
reserved, extra, safe, and unsafe>
For definitive information on URL syntax and semantics, see RFC
1738 [4] and RFC 1808 [11]. The BNF above includes national
characters not allowed in valid URLs as specified by RFC 1738,
since HTTP servers are not restricted in the set of unreserved
characters allowed to represent the rel_path part of addresses, and
HTTP proxies may receive requests for URIs not defined by RFC 1738.
3.2.2 http URL
The "http" scheme is used to locate network resources via the HTTP
protocol. This section defines the scheme-specific syntax and
semantics for http URLs.
http_URL = "http:" "//" host [ ":" port ] [ abs_path ]
host = <A legal Internet host domain name
or IP address (in dotted-decimal form),
as defined by Section 2.1 of RFC 1123>
port = *DIGIT
If the port is empty or not given, port 80 is assumed. The
semantics are that the identified resource is located at the server
listening for TCP connections on that port of that host, and the
Request-URI for the resource is abs_path. If the abs_path is not
present in the URL, it must be given as "/" when used as a
Request-URI for a resource (Section 5.1.2).
Note: Although the HTTP protocol is independent of the
transport layer protocol, the http URL only identifies
resources by their TCP location, and thus non-TCP resources
must be identified by some other URI scheme.
The canonical form for "http" URLs is obtained by converting any
UPALPHA characters in host to their LOALPHA equivalent (hostnames
are case-insensitive), eliding the [ ":" port ] if the port is 80,
and replacing an empty abs_path with "/".
3.3 Date/Time Formats
3.3.1 Full Date
HTTP applications have historically allowed three different formats
for the representation of date/time stamps:
Sun, 06 Nov 1994 08:49:37 GMT ; RFC 822, updated by RFC 1123
Sunday, 06-Nov-94 08:49:37 GMT ; RFC 850, obsoleted by RFC 1036
Sun Nov 6 08:49:37 1994 ; ANSI C's asctime() format
The first format is preferred as an Internet standard and
represents a fixed-length subset of that defined by RFC 1123 [8]
(an update to RFC 822 [9]). The second format is in common use, but
is based on the obsolete RFC 850 [12] date format and lacks a
four-digit year. HTTP/1.1 clients and servers that parse the date
value must accept all three formats, though they must only generate
the RFC 1123 format for representing date/time stamps in HTTP
message fields.
Note: Recipients of date values are encouraged to be robust
in accepting date values that may have been generated by
non-HTTP applications, as is sometimes the case when
retrieving or posting messages via proxies/gateways to SMTP
or NNTP.
All HTTP date/time stamps must be represented in Universal Time
(UT), also known as Greenwich Mean Time (GMT), without exception.
This is indicated in the first two formats by the inclusion of
"GMT" as the three-letter abbreviation for time zone, and should be
assumed when reading the asctime format.
HTTP-date = rfc1123-date | rfc850-date | asctime-date
rfc1123-date = wkday "," SP date1 SP time SP "GMT"
rfc850-date = weekday "," SP date2 SP time SP "GMT"
asctime-date = wkday SP date3 SP time SP 4DIGIT
date1 = 2DIGIT SP month SP 4DIGIT
; day month year (e.g., 02 Jun 1982)
date2 = 2DIGIT "-" month "-" 2DIGIT
; day-month-year (e.g., 02-Jun-82)
date3 = month SP ( 2DIGIT | ( SP 1DIGIT ))
; month day (e.g., Jun 2)
time = 2DIGIT ":" 2DIGIT ":" 2DIGIT
; 00:00:00 - 23:59:59
wkday = "Mon" | "Tue" | "Wed"
| "Thu" | "Fri" | "Sat" | "Sun"
weekday = "Monday" | "Tuesday" | "Wednesday"
| "Thursday" | "Friday" | "Saturday" | "Sunday"
month = "Jan" | "Feb" | "Mar" | "Apr"
| "May" | "Jun" | "Jul" | "Aug"
| "Sep" | "Oct" | "Nov" | "Dec"
Note: HTTP requirements for the date/time stamp format apply
only to their usage within the protocol stream. Clients and
servers are not required to use these formats for user
presentation, request logging, etc.
3.3.2 Delta Seconds
Some HTTP header fields allow a time value to be specified as an
integer number of seconds, represented in decimal, after the time
that the message was received. This format should only be used to
represent short time periods or periods that cannot start until
receipt of the message.
delta-seconds = 1*DIGIT
3.4 Character Sets
HTTP uses the same definition of the term "character set" as that
described for MIME:
The term "character set" is used in this document to
refer to a method used with one or more tables to convert
a sequence of octets into a sequence of characters. Note
that unconditional conversion in the other direction is
not required, in that not all characters may be available
in a given character set and a character set may provide
more than one sequence of octets to represent a
particular character. This definition is intended to
allow various kinds of character encodings, from simple
single-table mappings such as US-ASCII to complex table
switching methods such as those that use ISO 2022's
techniques. However, the definition associated with a
MIME character set name must fully specify the mapping to
be performed from octets to characters. In particular,
use of external profiling information to determine the
exact mapping is not permitted.
HTTP character sets are identified by case-insensitive tokens. The
complete set of tokens are defined by the IANA Character Set
registry [19]. However, because that registry does not define a
single, consistent token for each character set, we define here the
preferred names for those character sets most likely to be used
with HTTP entities. These character sets include those registered
by RFC 1521 [7] -- the US-ASCII [21] and ISO-8859 [22] character
sets -- and other names specifically recommended for use within MIME
charset parameters.
charset = "US-ASCII"
| "ISO-8859-1" | "ISO-8859-2" | "ISO-8859-3"
| "ISO-8859-4" | "ISO-8859-5" | "ISO-8859-6"
| "ISO-8859-7" | "ISO-8859-8" | "ISO-8859-9"
| "ISO-2022-JP" | "ISO-2022-JP-2" | "ISO-2022-KR"
| "UNICODE-1-1" | "UNICODE-1-1-UTF-7" | "UNICODE-1-1-UTF-8"
| token
Although HTTP allows an arbitrary token to be used as a charset
value, any token that has a predefined value within the IANA
Character Set registry [19] must represent the character set
defined by that registry. Applications should limit their use of
character sets to those defined by the IANA registry.
Note: This use of the term "character set" is more commonly
referred to as a "character encoding." However, since HTTP
and MIME share the same registry, it is important that the
terminology also be shared.
3.5 Content Codings
Content coding values are used to indicate an encoding
transformation that has been or can be applied to a resource.
Content codings are primarily used to allow a document to be
compressed or encrypted without losing the identity of its
underlying media type. Typically, the resource is stored in this
encoding and only decoded before rendering or analogous usage.
content-coding = "gzip" | "compress" | token
Note: For historical reasons, HTTP applications should
consider "x-gzip" and "x-compress" to be equivalent to "gzip"
and "compress", respectively.
All 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:
gzip
An encoding format produced by the file compression program
"gzip" (GNU zip) developed by Jean-loup Gailly. This format is
typically a Lempel-Ziv coding (LZ77) with a 32 bit CRC. Gzip is
available from the GNU project at
<URL:ftp://prep.ai.mit.edu/pub/gnu/>.
compress
The encoding format produced by the file compression program
"compress". This format is an adaptive Lempel-Ziv-Welch coding
(LZW).
Note: Use of program names for the identification of
encoding formats is not desirable and should be discouraged
for future encodings. Their use here is representative of
historical practice, not good design.
3.6 Transfer Codings
Transfer coding values are used to indicate an encoding
transformation that has been, can be, or may need to be applied to
an Entity-Body in order to ensure safe transport through the
network. This differs from a content coding in that the transfer
coding is a property of the message, not of the original resource.
transfer-coding = "chunked" | token
All transfer-coding values are case-insensitive. HTTP/1.1 uses
transfer coding values in the Transfer-Encoding header field
(Section 10.39).
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.
3.7 Media Types
HTTP uses Internet Media Types [17] in the Content-Type
(Section 10.15) and Accept (Section 10.1) header fields in order to
provide open and extensible data typing and type negotiation. For
mail applications, where there is no type negotiation between
sender and recipient, it is reasonable to put strict limits on the
set of allowed media types. With HTTP, where the sender and
recipient can communicate directly, applications are allowed more
freedom in the use of non-registered types. The following grammar
for media types is a superset of that for MIME because it does not
restrict itself to the official IANA and x-token types.
media-type = type "/" subtype *( ";" parameter )
type = token
subtype = token
Parameters may follow the type/subtype in the form of
attribute/value pairs.
parameter = attribute "=" value
attribute = token
value = token | quoted-string
The type, subtype, and parameter attribute names are
case-insensitive. Parameter values may or may not be
case-sensitive, depending on the semantics of the parameter name.
LWS should not be generated between the type and subtype, nor
between an attribute and its value.
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.
3.7.1 Canonicalization and Text Defaults
Media types are registered in a canonical form. In general, entity
bodies transferred via HTTP must be represented in the appropriate
canonical form prior to transmission. If the body has been encoded
via a Content-Encoding and/or Transfer-Encoding, the data must be
in canonical form prior to that encoding. However, HTTP modifies
the canonical form requirements for media of primary type "text"
and for "application" types consisting of text-like records.
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.
3.7.2 Multipart Types
MIME provides for a number of "multipart" types -- encapsulations of
one or more entities within a single message's Entity-Body. All
multipart types share a common syntax, as defined in Section 7.2.1
of RFC 1521 [7], and must include a boundary parameter as part of
the media type value. The message body is itself a protocol element
and must therefore use only CRLF to represent line breaks between
body-parts. Unlike in MIME, the epilogue of any multipart message
must be empty; HTTP applications must not transmit the epilogue
even if the original resource contains an epilogue.
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:
multipart/mixed
The mixed subtype is used when there are no additional semantics
implied beyond the fact that one or more entities are
encaspsulated. HTTP servers should not use this type to send
groups of entities if it is possible for those entities to be
individually retrieved and cached.
multipart/alternative
The alternative subtype implies that each of the parts is an
alternative format for the same information; the user agent
should present only the part most preferred by the user. HTTP
servers should use some form of content negotiation (Section 12)
instead of this type.
multipart/digest
The digest subtype implies that each of the parts is a message
(normally of type "message/rfc822") and thus the whole entity is
a collected sequence of message traffic. This type does not have
any special significance for HTTP.
multipart/form-data
The form-data subtype is defined by RFC 1867 [15] for use in
submitting the data that comes about from filling-in a form.
multipart/parallel
The parallel subtype implies that the parts should be presented
simultaneously by the user agent. This media type would be
appropriate for situations where simultaneous presentation is an
important aspect of the information, such as for audio-annotated
slides.
Note: This document does not define what is meant by
"simultaneous presentation". That is, HTTP does not provide
any means of synchronization between the parts in messages
of type "multipart/parallel".
Other multipart subtypes may be registered by IANA [19] according
to the procedures defined in RFC 1590 [17]. If an application
receives an unrecognized multipart subtype, the application must
treat it as being equivalent to "multipart/mixed".
3.8 Product Tokens
Product tokens are used to allow communicating applications to
identify themselves via a simple product token, with an optional
slash and version designator. Most fields using product tokens also
allow subproducts which form a significant part of the application
to be listed, separated by whitespace. By convention, the products
are listed in order of their significance for identifying the
application.
product = token ["/" product-version]
product-version = token
Examples:
User-Agent: CERN-LineMode/2.15 libwww/2.17b3
Server: Apache/0.8.4
Product tokens should be short and to the point -- use of them for
advertizing or other non-essential information is explicitly
forbidden. Although any token character may appear in a
product-version, this token should only be used for a version
identifier (i.e., successive versions of the same product should
only differ in the product-version portion of the product value).
3.9 Quality Values
HTTP content negotiation (Section 12) uses short "floating point"
numbers to indicate the relative importance ("weight") of various
negotiable parameters. The weights are normalized to a real number
in the range 0 through 1, where 0 is the minimum and 1 the maximum
value. In order to discourage misuse of this feature, HTTP/1.1
applications must not generate more than three digits after the
decimal point. User configuration of these values should also be
limited in this fashion.
qvalue = ( "0" [ "." 0*3DIGIT ] )
| ( "." 0*3DIGIT )
| ( "1" [ "." 0*3("0") ] )
"Quality values" is a slight misnomer, since these values actually
measure relative degradation in perceived quality. Thus, a value of
"0.8" represents a 20% degradation from the optimum rather than a
statement of 80% quality.
3.10 Language Tags
A language tag identifies a natural language spoken, written, or
otherwise conveyed by human beings for communication of information
to other human beings. Computer languages are explicitly excluded.
HTTP uses language tags within the Accept-Language,
Content-Language, and URI-header fields.
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.
3.11 Logic Bags
A logic bag is a binary logic expression tree represented in prefix
notation using the generic bag syntax. Logic bags are used by HTTP
in the Unless (Section 10.40) header field as expressions to be
tested against the requested resource's header field
metainformation.
logic-bag = "{" expression "}"
expression = ( log-op 1*logic-bag )
| ( rel-op 1*field-tuple )
| ( "def" 1*field-name )
log-op = "and" | "or" | "xor" | "not"
rel-op = "eq" | "ne" | "lt" | "le" | "ge" | "gt" | "in"
field-tuple = "{" field-name ( bag | token | quoted-string ) "}"
The recursive structure of a logic bag allows a complex expression
tree to be formed by joining together subexpressions with logical
operators. Expressions with relational operators are used to
compare the requested resource's corresponding metainformation
(header field values) to those inside the expression field-tuples.
For example,
{or {ne {Content-MD5 "Q2hlY2sgSW50ZWdyaXR5IQ=="}}
{ne {Content-Length 10036}}
{ne {Content-Version "12.4.8"}}
{gt {Last-Modified "Mon, 04 Dec 1995 01:23:45 GMT"}}}
The expression is evaluated recursively by depth-first traversal
and bottom-up evaluation of the subexpressions until a true or
false value can be determined. Multiple operands to an operator
imply a conjunctive ("and") expression; e.g.,
{eq {A "a"} {B "b"} {C "c"}}
is equivalent to
{and {eq {A "a"}} {eq {B "b"}} {eq {C "c"}}}
Each expression is evaluated as defined by the operator:
and True if all of the operands evaluate true.
or True if any of the operands evaluate true.
xor True if one and only one operand evaluates true.
not True if all of the operands evaluate false.
eq True if all field-tuple values exactly match the resource's
corresponding field values.
ne True if all field-tuple values do not match the resource's
corresponding field values.
lt True if, for each field-tuple, the resource's corresponding
field value is less than the one given in the expression.
le True if, for each field-tuple, the resource's corresponding
field value is less than or equal to the one given in the
expression.
ge True if, for each field-tuple, the resource's corresponding
field value is greater than or equal to the one given in the
expression.
gt True if, for each field-tuple, the resource's corresponding
field value is greater than the one given in the expression.
in True if, for each field-tuple, the resource's corresponding
field value contains the component value given in the
expression.
def True if, for each field-name operand, the resource defines a
value for that field.
A field-tuple consists of a field-name (assumed to be an HTTP
header field name, though not constrained to those defined by this
specification) and the field-value component which is to be
compared against the resource's field value. The actual method of
comparison (e.g., byte equivalence, substring matching, numeric
order, substructure containment, etc.) is defined by the logical
definition of the operator and the type of field-value allowed for
that field-name. Server implementors must use an appropriate
comparison function for each type of field-value given in this
specification. The default functions for unrecognized fields are
numeric comparison (for values consisting of 1*DIGIT) and lexical
comparison (for all others).
Except for "ne", any comparison to a field not defined by the
resource evaluates to false.
4. HTTP Message
4.1 Message Types
HTTP messages consist of requests from client to server and
responses from server to client.
HTTP-message = Simple-Request ; HTTP/0.9 messages
| Simple-Response
| Full-Request ; HTTP/1.1 messages
| Full-Response
Full-Request and Full-Response use the generic message format of
RFC 822 [9] for transferring entities. Both messages may include
optional header fields (also known as "headers") and an entity
body. The entity body is separated from the headers by a null line
(i.e., a line with nothing preceding the CRLF).
Full-Request = Request-Line ; Section 5.1
*( General-Header ; Section 4.3
| Request-Header ; Section 5.2
| Entity-Header ) ; Section 7.1
CRLF
[ Entity-Body ] ; Section 7.2
Full-Response = Status-Line ; Section 6.1
*( General-Header ; Section 4.3
| Response-Header ; Section 6.2
| Entity-Header ) ; Section 7.1
CRLF
[ Entity-Body ] ; Section 7.2
Simple-Request and Simple-Response do not allow the use of any
header information and are limited to a single request method (GET).
Simple-Request = "GET" SP Request-URI CRLF
Simple-Response = [ Entity-Body ]
Use of the Simple-Request format is discouraged because it prevents
the client from using content negotiation and the server from
identifying the media type of the returned entity.
4.2 Message Headers
HTTP header fields, which include General-Header (Section 4.3),
Request-Header (Section 5.2), Response-Header (Section 6.2), and
Entity-Header (Section 7.1) fields, follow the same generic format
as that given in Section 3.1 of RFC 822 [9]. Each header field
consists of a name followed by a colon (":") and the field value.
Field names are case-insensitive. The field value may be preceded
by any amount of LWS, though a single SP is preferred. Header
fields can be extended over multiple lines by preceding each extra
line with at least one SP or HT.
HTTP-header = field-name ":" [ field-value ] CRLF
field-name = token
field-value = *( field-content | LWS )
field-content = <the OCTETs making up the field-value
and consisting of either *TEXT or combinations
of token, tspecials, and quoted-string>
The order in which header fields are received is not significant.
However, it is "good practice" to send General-Header fields first,
followed by Request-Header or Response-Header fields prior to the
Entity-Header fields.
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.
4.3 General Header Fields
There are a few header fields which have general applicability for
both request and response messages, but which do not apply to the
entity being transferred. These headers apply only to the message
being transmitted.
General-Header = Cache-Control ; Section 10.8
| Connection ; Section 10.9
| Date ; Section 10.17
| Forwarded ; Section 10.20
| Keep-Alive ; Section 10.24
| MIME-Version ; Section 10.28
| Pragma ; Section 10.29
| Upgrade ; Section 10.41
General header field names can be extended reliably only in
combination with a change in the protocol version. However, new or
experimental header fields may be given the semantics of general
header fields if all parties in the communication recognize them to
be general header fields. Unrecognized header fields are treated as
Entity-Header fields.
5. Request
A request message from a client to a server includes, within the
first line of that message, the method to be applied to the
resource, the identifier of the resource, and the protocol version
in use. For backwards compatibility with the more limited HTTP/0.9
protocol, there are two valid formats for an HTTP request:
Request = Simple-Request | Full-Request
Simple-Request = "GET" SP Request-URI CRLF
Full-Request = Request-Line ; Section 5.1
*( General-Header ; Section 4.3
| Request-Header ; Section 5.2
| Entity-Header ) ; Section 7.1
CRLF
[ Entity-Body ] ; Section 7.2
If an HTTP/1.1 server receives a Simple-Request, it must respond
with an HTTP/0.9 Simple-Response. An HTTP/1.1 client must never
generate a Simple-Request.
5.1 Request-Line
The Request-Line begins with a method token, followed by the
Request-URI and the protocol version, and ending with CRLF. The
elements are separated by SP characters. No CR or LF are allowed
except in the final CRLF sequence.
Request-Line = Method SP Request-URI SP HTTP-Version CRLF
Note that the difference between a Simple-Request and the
Request-Line of a Full-Request is the presence of the HTTP-Version
field and the availability of methods other than GET.
5.1.1 Method
The Method token indicates the method to be performed on the
resource identified by the Request-URI. The method is
case-sensitive.
Method = "OPTIONS" ; Section 8.1
| "GET" ; Section 8.2
| "HEAD" ; Section 8.3
| "POST" ; Section 8.4
| "PUT" ; Section 8.5
| "PATCH" ; Section 8.6
| "COPY" ; Section 8.7
| "MOVE" ; Section 8.8
| "DELETE" ; Section 8.9
| "LINK" ; Section 8.10
| "UNLINK" ; Section 8.11
| "TRACE" ; Section 8.12
| "WRAPPED" ; Section 8.13
| extension-method
extension-method = token
The list of methods acceptable by a specific resource can be
specified in an Allow header field (Section 10.5). However, the
client is always notified through the return code of the response
whether a method is currently allowed on a specific resource, as
this can change dynamically. Servers should return the status code
405 (method not allowed) if the method is known by the server but
not allowed for the requested resource, and 501 (not implemented)
if the method is unrecognized or not implemented by the server. The
list of methods known by a server can be listed in a Public
response header field (Section 10.32).
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.
5.1.2 Request-URI
The Request-URI is a Uniform Resource Identifier (Section 3.2) and
identifies the resource upon which to apply the request.
Request-URI = "*" | absoluteURI | abs_path
The three options for Request-URI are dependent on the nature of
the request. The asterisk "*" means that the request does not apply
to a particular resource, but to the server itself, and is only
allowed when the Method used does not necessarily apply to a
resource. One example would be
OPTIONS * HTTP/1.1
The absoluteURI form is only allowed when the request is being made
to a proxy. The proxy is requested to forward the request and
return the response. If the request is GET or HEAD and a prior
response is cached, the proxy may use the cached message if it
passes any restrictions in the Cache-Control and Expires header
fields. Note that the proxy may forward the request on to another
proxy or directly to the server specified by the absoluteURI. In
order to avoid request loops, a proxy must be able to recognize all
of its server names, including any aliases, local variations, and
the numeric IP address. An example Request-Line would be:
GET http://www.w3.org/pub/WWW/TheProject.html HTTP/1.1
The most common form of Request-URI is that used to identify a
resource on an origin server or gateway. In this case, only the
absolute path of the URI is transmitted (see Section 3.2.1,
abs_path). For example, a client wishing to retrieve the resource
above directly from the origin server would create a TCP connection
to port 80 of the host "www.w3.org" and send the line:
GET /pub/WWW/TheProject.html HTTP/1.1
followed by the remainder of the Full-Request. Note that the
absolute path cannot be empty; if none is present in the original
URI, it must be given as "/" (the server root).
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.
5.2 Request Header Fields
The request header fields allow the client to pass additional
information about the request, and about the client itself, to the
server. These fields act as request modifiers, with semantics
equivalent to the parameters on a programming language method
(procedure) invocation.
Request-Header = Accept ; Section 10.1
| Accept-Charset ; Section 10.2
| Accept-Encoding ; Section 10.3
| Accept-Language ; Section 10.4
| Authorization ; Section 10.6
| From ; Section 10.21
| Host ; Section 10.22
| If-Modified-Since ; Section 10.23
| Proxy-Authorization ; Section 10.31
| Range ; Section 10.33
| Referer ; Section 10.34
| Unless ; Section 10.40
| User-Agent ; Section 10.43
Request-Header field names can be extended reliably only in
combination with a change in the protocol version. However, new or
experimental header fields may be given the semantics of request
header fields if all parties in the communication recognize them to
be request header fields. Unrecognized header fields are treated as
Entity-Header fields.
6. Response
After receiving and interpreting a request message, a server
responds in the form of an HTTP response message.
Response = Simple-Response | Full-Response
Simple-Response = [ Entity-Body ]
Full-Response = Status-Line ; Section 6.1
*( General-Header ; Section 4.3
| Response-Header ; Section 6.2
| Entity-Header ) ; Section 7.1
CRLF
[ Entity-Body ] ; Section 7.2
A Simple-Response should only be sent in response to an HTTP/0.9
Simple-Request or if the server only supports the more limited
HTTP/0.9 protocol. If a client sends an HTTP/1.1 Full-Request and
receives a response that does not begin with a Status-Line, it
should assume that the response is a Simple-Response and parse it
accordingly. Note that the Simple-Response consists only of the
entity body and is terminated by the server closing the connection.
6.1 Status-Line
The first line of a Full-Response message is the Status-Line,
consisting of the protocol version followed by a numeric status
code and its associated textual phrase, with each element separated
by SP characters. No CR or LF is allowed except in the final CRLF
sequence.
Status-Line = HTTP-Version SP Status-Code SP Reason-Phrase CRLF
Since a status line always begins with the protocol version and
status code
"HTTP/" 1*DIGIT "." 1*DIGIT SP 3DIGIT SP
(e.g., "HTTP/1.1 200 "), the presence of that expression is
sufficient to differentiate a Full-Response from a Simple-Response.
Although the Simple-Response format may allow such an expression to
occur at the beginning of an entity body, and thus cause a
misinterpretation of the message if it was given in response to a
Full-Request, most HTTP/0.9 servers are limited to responses of
type "text/html" and therefore would never generate such a response.
6.1.1 Status Code and Reason Phrase
The Status-Code element is a 3-digit integer result code of the
attempt to understand and satisfy the request. The Reason-Phrase is
intended to give a short textual description of the Status-Code.
The Status-Code is intended for use by automata and the
Reason-Phrase is intended for the human user. The client is not
required to examine or display the Reason-Phrase.
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:
o 1xx: Informational - Request received, continuing process
o 2xx: Success - The action was successfully received,
understood, and accepted
o 3xx: Redirection - Further action must be taken in order to
complete the request
o 4xx: Client Error - The request contains bad syntax or cannot
be fulfilled
o 5xx: Server Error - The server failed to fulfill an apparently
valid request
The individual values of the numeric status codes defined for
HTTP/1.1, and an example set of corresponding Reason-Phrase's, are
presented below. The reason phrases listed here are only
recommended -- they may be replaced by local equivalents without
affecting the protocol. These codes are fully defined in Section 9.
Status-Code = "100" ; Continue
| "101" ; Switching Protocols
| "200" ; OK
| "201" ; Created
| "202" ; Accepted
| "203" ; Non-Authoritative Information
| "204" ; No Content
| "205" ; Reset Content
| "206" ; Partial Content
| "300" ; Multiple Choices
| "301" ; Moved Permanently
| "302" ; Moved Temporarily
| "303" ; See Other
| "304" ; Not Modified
| "305" ; Use Proxy
| "400" ; Bad Request
| "401" ; Unauthorized
| "402" ; Payment Required
| "403" ; Forbidden
| "404" ; Not Found
| "405" ; Method Not Allowed
| "406" ; None Acceptable
| "407" ; Proxy Authentication Required
| "408" ; Request Timeout
| "409" ; Conflict
| "410" ; Gone
| "411" ; Length Required
| "412" ; Unless True
| "500" ; Internal Server Error
| "501" ; Not Implemented
| "502" ; Bad Gateway
| "503" ; Service Unavailable
| "504" ; Gateway Timeout
| extension-code
extension-code = 3DIGIT
Reason-Phrase = *<TEXT, excluding CR, LF>
HTTP status codes are extensible. HTTP applications are not
required to understand the meaning of all registered status codes,
though such understanding is obviously desirable. However,
applications must understand the class of any status code, as
indicated by the first digit, and treat any unrecognized response
as being equivalent to the x00 status code of that class, with the
exception that an unrecognized response must not be cached. For
example, if an unrecognized status code of 431 is received by the
client, it can safely assume that there was something wrong with
its request and treat the response as if it had received a 400
status code. In such cases, user agents should present to the user
the entity returned with the response, since that entity is likely
to include human-readable information which will explain the
unusual status.
6.2 Response Header Fields
The response header fields allow the server to pass additional
information about the response which cannot be placed in the
Status-Line. These header fields are not intended to give
information about an Entity-Body returned in the response, but
about access to the resource or the server itself.
Response-Header= Location ; Section 10.27
| Proxy-Authenticate ; Section 10.30
| Public ; Section 10.32
| Retry-After ; Section 10.36
| Server ; Section 10.37
| WWW-Authenticate ; Section 10.44
Response-Header field names can be extended reliably only in
combination with a change in the protocol version. However, new or
experimental header fields may be given the semantics of response
header fields if all parties in the communication recognize them to
be response header fields. Unrecognized header fields are treated
as Entity-Header fields.
7. Entity
Full-Request and Full-Response messages may transfer an entity
within some requests and responses. An entity consists of
Entity-Header fields and (usually) an Entity-Body. In this section,
both sender and recipient refer to either the client or the server,
depending on who sends and who receives the entity.
7.1 Entity Header Fields
Entity-Header fields define optional metainformation about the
Entity-Body or, if no body is present, about the resource
identified by the request.
Entity-Header = Allow ; Section 10.5
| Content-Encoding ; Section 10.10
| Content-Language ; Section 10.11
| Content-Length ; Section 10.12
| Content-MD5 ; Section 10.13
| Content-Range ; Section 10.14
| Content-Type ; Section 10.15
| Content-Version ; Section 10.16
| Derived-From ; Section 10.18
| Expires ; Section 10.19
| Last-Modified ; Section 10.25
| Link ; Section 10.26
| Title ; Section 10.38
| Transfer-Encoding ; Section 10.39
| URI-header ; Section 10.42
| extension-header
extension-header=HTTP-header
The extension-header mechanism allows additional Entity-Header
fields to be defined without changing the protocol, but these
fields cannot be assumed to be recognizable by the recipient.
Unrecognized header fields should be ignored by the recipient and
forwarded by proxies.
7.2 Entity Body
The entity body (if any) sent with an HTTP request or response is
in a format and encoding defined by the Entity-Header fields.
Entity-Body = *OCTET
An entity body is included with a request message only when the
request method calls for one. The presence of an entity body in a
request is signaled by the inclusion of a Content-Length and/or
Content-Type header field in the request message headers.
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).
7.2.1 Type
When an entity body is included with a message, the data type of
that body is determined via the header fields Content-Type,
Content-Encoding, and Transfer-Encoding. These define a
three-layer, ordered encoding model:
entity-body :=
Transfer-Encoding( Content-Encoding( Content-Type( data ) ) )
The default for both encodings is none (i.e., the identity
function). Content-Type specifies the media type of the underlying
data. Content-Encoding may be used to indicate any additional
content codings applied to the type, usually for the purpose of
data compression, that are a property of the resource requested.
Transfer-Encoding may be used to indicate any additional transfer
codings applied by an application to ensure safe and proper
transfer of the message. Note that Transfer-Encoding is a property
of the message, not of the resource.
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".
7.2.2 Length
When an entity body is included with a message, the length of that
body may be determined in one of several ways. If a Content-Length
header field is present, its value in bytes represents the length
of the entity body. Otherwise, the body length is determined by the
Transfer-Encoding (if the "chunked" transfer coding has been
applied), by the Content-Type (for multipart types with an explicit
end-of-body delimiter), or by the server closing the connection.
Note: Any response message which must not include an entity
body (such as the 1xx, 204, and 304 responses and any
response to a HEAD request) is always terminated by the
first empty line after the header fields, regardless of the
entity header fields present in the message.
Closing the connection cannot be used to indicate the end of a
request body, since it leaves no possibility for the server to send
back a response. For compatibility with HTTP/1.0 applications,
HTTP/1.1 requests containing an entity body must include a valid
Content-Length header field unless the server is known to be
HTTP/1.1 compliant. HTTP/1.1 servers must accept the "chunked"
transfer coding (Section 3.6) and multipart media types
(Section 3.7.2), thus allowing either mechanism to be used for a
request when Content-Length is unknown.
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.
8. Method Definitions
The set of common methods for HTTP/1.1 is defined below. Although
this set can be expanded, additional methods cannot be assumed to
share the same semantics for separately extended clients and
servers.
The semantics of all methods may be affected by the presence of an
Unless request header field, as described in Section 10.40.
8.1 OPTIONS
The OPTIONS method represents a request for information about the
communication options available on the request/response chain
identified by the Request-URI. This method allows the client to
determine the options and/or requirements associated with a
resource, or the capabilities of a server, without implying a
resource action or initiating a resource retrieval.
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.
8.2 GET
The GET method means retrieve whatever information (in the form of
an entity) is identified by the Request-URI. If the Request-URI
refers to a data-producing process, it is the produced data which
shall be returned as the entity in the response and not the source
text of the process, unless that text happens to be the output of
the process.
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.
8.3 HEAD
The HEAD method is identical to GET except that the server must not
return any Entity-Body in the response. The metainformation
contained in the HTTP headers in response to a HEAD request should
be identical to the information sent in response to a GET request.
This method can be used for obtaining metainformation about the
resource identified by the Request-URI without transferring the
Entity-Body itself. This method is often used for testing hypertext
links for validity, accessibility, and recent modification.
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.
8.4 POST
The POST method is used to request that the destination server
accept the entity enclosed in the request as a new subordinate of
the resource identified by the Request-URI in the Request-Line.
POST is designed to allow a uniform method to cover the following
functions:
o Annotation of existing resources;
o Posting a message to a bulletin board, newsgroup, mailing list,
or similar group of articles;
o Providing a block of data, such as the result of submitting a
form [5], to a data-handling process;
o Extending a database through an append operation.
The actual function performed by the POST method is determined by
the server and is usually dependent on the 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.
8.5 PUT
The PUT method requests that the enclosed entity be stored under
the supplied Request-URI. If the Request-URI refers to an already
existing resource, the enclosed entity should be considered as a
modified version of the one residing on the origin server. If the
Request-URI does not point to an existing resource, and that URI is
capable of being defined as a new resource by the requesting user
agent, the origin server can create the resource with that URI. If
a new resource is created, the origin server must inform the user
agent via the 201 (created) response. If an existing resource is
modified, either the 200 (ok) or 204 (no content) response codes
should be sent to indicate successful completion of the request. If
the resource could not be created or modified with the Request-URI,
an appropriate error response should be given that reflects the
nature of the problem.
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.
8.6 PATCH
The PATCH method is similar to PUT except that the entity contains
a list of differences between the original version of the resource
identified by the Request-URI and the desired content of the
resource after the PATCH action has been applied. The list of
differences is in a format defined by the media type of the entity
(e.g., "application/diff") and must include sufficient information
to allow the server to recreate the changes necessary to convert
the original version of the resource to the desired version.
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.
8.7 COPY
The COPY method requests that the resource identified by the
Request-URI be copied to the location(s) given in the URI header
field of the request. Responses to this method are not cachable.
8.8 MOVE
The MOVE method requests that the resource identified by the
Request-URI be moved to the location(s) given in the URI header
field of the request. This method is equivalent to a COPY
immediately followed by a DELETE, but enables both to occur within
a single transaction.
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.
8.9 DELETE
The DELETE method requests that the origin server delete the
resource identified by the Request-URI. This method may be
overridden by human intervention (or other means) on the origin
server. The client cannot be guaranteed that the operation has been
carried out, even if the status code returned from the origin
server indicates that the action has been completed successfully.
However, the server should not indicate success unless, at the time
the response is given, it intends to delete the resource or move it
to an inaccessible location.
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.
8.10 LINK
The LINK method establishes one or more Link relationships between
the existing resource identified by the Request-URI and other
existing resources. The difference between LINK and other methods
allowing links to be established between resources is that the LINK
method does not allow any Entity-Body to be sent in the request and
does not directly result in the creation of new resources.
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.
8.11 UNLINK
The UNLINK method removes one or more Link relationships from the
existing resource identified by the Request-URI. These
relationships may have been established using the LINK method or by
any other method supporting the Link header. The removal of a link
to a resource does not imply that the resource ceases to exist or
becomes inaccessible for future references.
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.
8.12 TRACE
The TRACE method requests that the server identified by the
Request-URI reflect whatever is received back to the client as the
entity body of the response. In this way, the client can see what
is being received at the other end of the request chain, and may
use this data for testing or diagnostic information.
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.
8.13 WRAPPED
The WRAPPED method allows a client to send one or more encapsulated
requests to the server identified by the Request-URI. This method
is intended to allow the request(s) to be wrapped together,
possibly encrypted in order to improve the security and/or privacy
of the request, and delivered for unwrapping by the destination
server. Upon receipt of the WRAPPED request, the destination server
must unwrap the message and feed it to the appropriate protocol
handler as if it were an incoming request stream.
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.
9. Status Code Definitions
Each Status-Code is described below, including a description of
which method(s) it can follow and any metainformation required in
the response.
9.1 Informational 1xx
This class of status code indicates a provisional response,
consisting only of the Status-Line and optional headers, and is
terminated by an empty line. Since HTTP/1.0 did not define any 1xx
status codes, servers should not send a 1xx response to an HTTP/1.0
client except under experimental conditions.
100 Continue
The client may continue with its request. This interim response is
used to inform the client that the initial part of the request has
been received and has not yet been rejected by the server. The
client should continue by sending the remainder of the request or,
if the request has already been completed, ignore this response.
The server must send a final response after the request has been
completed.
101 Switching Protocols
The server understands and is willing to comply with the client's
request, via the Upgrade message header field (Section 10.41), for
a change in the application protocol being used on this connection.
The server will switch protocols to those defined by the response's
Upgrade header field immediately after the empty line which
terminates the 101 response.
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.
9.2 Successful 2xx
This class of status code indicates that the client's request was
successfully received, understood, and accepted.
200 OK
The request has succeeded. The information returned with the
response is dependent on the method used in the request, as follows:
GET an entity corresponding to the requested resource is sent
in the response;
HEAD the response must only contain the header information and
no Entity-Body;
POST an entity describing or containing the result of the action;
TRACE an entity containing the request message as received by the
end server;
otherwise, an entity describing the result of the action;
If the entity corresponds to a resource, the response may include a
Location header field giving the actual location of that specific
resource for later reference.
201 Created
The request has been fulfilled and resulted in a new resource being
created. The newly created resource can be referenced by the URI(s)
returned in the URI-header field and/or the entity of the response,
with the most specific URL for the resource given by a Location
header field. The origin server should create the resource before
using this Status-Code. If the action cannot be carried out
immediately, the server must include in the response body a
description of when the resource will be available; otherwise, the
server should respond with 202 (accepted).
202 Accepted
The request has been accepted for processing, but the processing
has not been completed. The request may or may not eventually be
acted upon, as it may be disallowed when processing actually takes
place. There is no facility for re-sending a status code from an
asynchronous operation such as this.
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.
203 Non-Authoritative Information
The returned metainformation in the Entity-Header is not the
definitive set as available from the origin server, but is gathered
from a local or a third-party copy. The set presented may be a
subset or superset of the original version. For example, including
local annotation information about the resource may result in a
superset of the metainformation known by the origin server. Use of
this response code is not required and is only appropriate when the
response would otherwise be 200 (ok).
204 No Content
The server has fulfilled the request but there is no new
information to send back. If the client is a user agent, it should
not change its document view from that which caused the request to
be generated. This response is primarily intended to allow input
for actions to take place without causing a change to the user
agent's active document view. The response may include new
metainformation in the form of entity headers, which should apply
to the document currently in the user agent's active view.
The 204 response must not include an entity body, and thus is
always ternminated by the first empty line after the header fields.
205 Reset Content
The server has fulfilled the request and the user agent should
reset the document view which caused the request to be generated.
This response is primarily intended to allow input for actions to
take place via user input, followed by a clearing of the form in
which the input is given so that the user can easily initiate
another input action. The response must include a Content-Length
with a value of zero (0) and no entity body.
206 Partial Content
The server has fulfilled the partial GET request for the resource.
The request must have included a Range header field (Section 10.33)
indicating the desired range. The response must include a
Content-Range header field (Section 10.14) indicating the range
included with this response. All entity header fields in the
response must describe the actual entity transmitted rather than
what would have been transmitted in a full response. In particular,
the Content-Length header field in the response must match the
actual number of OCTETs transmitted in the entity body. It is
assumed that the client already has the complete entity's header
field data.
9.3 Redirection 3xx
This class of status code indicates that further action needs to be
taken by the user agent in order to fulfill the request. The action
required may be carried out by the user agent without interaction
with the user if and only if the method used in the second request
is GET or HEAD. A user agent should never automatically redirect a
request more than 5 times, since such redirections usually indicate
an infinite loop.
300 Multiple Choices
The requested resource is available at one or more locations and a
preferred location could not be determined via preemptive content
negotiation (Section 12). Unless it was a HEAD request, the
response should include an entity containing a list of resource
characteristics and locations from which the user or user agent can
choose the one most appropriate. The entity format is specified by
the media type given in the Content-Type header field. Depending
upon the format and the capabilities of the user agent, selection
of the most appropriate choice may be performed automatically. If
the server has a preferred choice, it should include the URL in a
Location field; user agents not capable of complex selection may
use this field value for automatic redirection. This response is
cachable unless indicated otherwise.
301 Moved Permanently
The requested resource has been assigned a new permanent URI and
any future references to this resource should be done using one of
the returned URIs. Clients with link editing capabilities should
automatically relink references to the Request-URI to one or more
of the new references returned by the server, where possible. This
response is cachable unless indicated otherwise.
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.
302 Moved Temporarily
The requested resource resides temporarily under a different URI.
Since the redirection may be altered on occasion, the client should
continue to use the Request-URI for future requests. This response
is only cachable if indicated by a Cache-Control or Expires header
field.
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.
303 See Other
The response to the request can be found under a different URI and
should be retrieved using a GET method on that resource. This
method exists primarily to allow the output of a POST-activated
script to redirect the user agent to a selected resource. The new
resource is not a replacement reference for the original
Request-URI. The 303 response is not cachable, but the response to
the second request may be cachable.
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).
304 Not Modified
If the client has performed a conditional GET request and access is
allowed, but the document has not been modified since the date and
time specified in the If-Modified-Since field, the server must
respond with this status code and not send an Entity-Body to the
client. Header fields contained in the response should only include
information which is relevant to cache managers or which may have
changed independently of the entity's Last-Modified date. Examples
of relevant header fields include: Date, Server, Content-Length,
Content-MD5, Content-Version, Cache-Control and Expires.
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.
305 Use Proxy
The requested resource must be accessed through the proxy given by
the Location field in the response. In other words, this is a proxy
redirect.
9.4 Client Error 4xx
The 4xx class of status code is intended for cases in which the
client seems to have erred. If the client has not completed the
request when a 4xx code is received, it should immediately cease
sending data to the server. Except when responding to a HEAD
request, the server should include an entity containing an
explanation of the error situation, and whether it is a temporary
or permanent condition. These status codes are applicable to any
request method.
Note: If the client is sending data, server implementations
on TCP should be careful to ensure that the client
acknowledges receipt of the packet(s) containing the
response prior to closing the input connection. If the
client continues sending data to the server after the close,
the server's controller will send a reset packet to the
client, which may erase the client's unacknowledged input
buffers before they can be read and interpreted by the HTTP
application.
400 Bad Request
The request could not be understood by the server due to malformed
syntax. The client should not repeat the request without
modifications.
401 Unauthorized
The request requires user authentication. The response must include
a WWW-Authenticate header field (Section 10.44) containing a
challenge applicable to the requested resource. The client may
repeat the request with a suitable Authorization header field
(Section 10.6). If the request already included Authorization
credentials, then the 401 response indicates that authorization has
been refused for those credentials. If the 401 response contains
the same challenge as the prior response, and the user agent has
already attempted authentication at least once, then the user
should be presented the entity that was given in the response,
since that entity may include relevant diagnostic information. HTTP
access authentication is explained in Section 11.
402 Payment Required
This code is reserved for future use.
403 Forbidden
The server understood the request, but is refusing to fulfill it.
Authorization will not help and the request should not be repeated.
If the request method was not HEAD and the server wishes to make
public why the request has not been fulfilled, it should describe
the reason for the refusal in the entity body. This status code is
commonly used when the server does not wish to reveal exactly why
the request has been refused, or when no other response is
applicable.
404 Not Found
The server has not found anything matching the Request-URI. No
indication is given of whether the condition is temporary or
permanent. If the server does not wish to make this information
available to the client, the status code 403 (forbidden) can be
used instead. The 410 (gone) status code should be used if the
server knows, through some internally configurable mechanism, that
an old resource is permanently unavailable and has no forwarding
address.
405 Method Not Allowed
The method specified in the Request-Line is not allowed for the
resource identified by the Request-URI. The response must include
an Allow header containing a list of valid methods for the
requested resource.
406 None Acceptable
The server has found a resource matching the Request-URI, but not
one that satisfies the conditions identified by the Accept and
Accept-Encoding request headers. Unless it was a HEAD request, the
response should include an entity containing a list of resource
characteristics and locations from which the user or user agent can
choose the one most appropriate. The entity format is specified by
the media type given in the Content-Type header field. Depending
upon the format and the capabilities of the user agent, selection
of the most appropriate choice may be performed automatically.
407 Proxy Authentication Required
This code is similar to 401 (unauthorized), but indicates that the
client must first authenticate itself with the proxy. The proxy
must return a Proxy-Authenticate header field (Section 10.30)
containing a challenge applicable to the proxy for the requested
resource. The client may repeat the request with a suitable
Proxy-Authorization header field (Section 10.31). HTTP access
authentication is explained in Section 11.
408 Request Timeout
The client did not produce a request within the time that the
server was prepared to wait. The client may repeat the request
without modifications at any later time.
409 Conflict
The request could not be completed due to a conflict with the
current state of the resource. This code is only allowed in
situations where it is expected that the user may be able to
resolve the conflict and resubmit the request. The response body
should include enough information for the user to recognize the
source of the conflict. Ideally, the response entity would include
enough information for the user or user-agent to fix the problem;
however, that may not be possible and is not required.
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.
410 Gone
The requested resource is no longer available at the server and no
forwarding address is known. This condition should be considered
permanent. Clients with link editing capabilities should delete
references to the Request-URI after user approval. If the server
does not know, or has no facility to determine, whether or not the
condition is permanent, the status code 404 (not found) should be
used instead. This response is cachable unless indicated otherwise.
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.
411 Length Required
The server refuses to accept the request without a defined
Content-Length. The client may repeat the request if it adds a
valid Content-Length header field containing the length of the
entity body in the request message.
412 Unless True
The condition given in the Unless request-header field
(Section 10.40) evaluated to true when it was tested on the server
and the request did not include a Range header field (which would
indicate a partial GET) or an If-Modified-Since header field (which
would indicate a conditional GET). This response code allows the
client to place arbitrary preconditions on the current resource
metainformation (header field data) and thus prevent the requested
method from being applied to a resource other than the one intended.
9.5 Server Error 5xx
Response status codes beginning with the digit "5" indicate cases
in which the server is aware that it has erred or is incapable of
performing the request. If the client has not completed the request
when a 5xx code is received, it should immediately cease sending
data to the server. Except when responding to a HEAD request, the
server should include an entity containing an explanation of the
error situation, and whether it is a temporary or permanent
condition. These response codes are applicable to any request
method and there are no required header fields.
500 Internal Server Error
The server encountered an unexpected condition which prevented it
from fulfilling the request.
501 Not Implemented
The server does not support the functionality required to fulfill
the request. This is the appropriate response when the server does
not recognize the request method and is not capable of supporting
it for any resource.
502 Bad Gateway
The server, while acting as a gateway or proxy, received an invalid
response from the upstream server it accessed in attempting to
fulfill the request.
503 Service Unavailable
The server is currently unable to handle the request due to a
temporary overloading or maintenance of the server. The implication
is that this is a temporary condition which will be alleviated
after some delay. If known, the length of the delay may be
indicated in a Retry-After header. If no Retry-After is given, the
client should handle the response as it would for a 500 response.
Note: The existence of the 503 status code does not imply
that a server must use it when becoming overloaded. Some
servers may wish to simply refuse the connection.
504 Gateway Timeout
The server, while acting as a gateway or proxy, did not receive a
timely response from the upstream server it accessed in attempting
to complete the request.
10. Header Field Definitions
This section defines the syntax and semantics of all standard
HTTP/1.1 header fields. For Entity-Header fields, both sender and
recipient refer to either the client or the server, depending on
who sends and who receives the entity.
10.1 Accept
The Accept response-header field can be used to indicate a list of
media ranges which are acceptable as a response to the request. The
asterisk "*" character is used to group media types into ranges,
with "*/*" indicating all media types and "type/*" indicating all
subtypes of that type. The set of ranges given by the client should
represent what types are acceptable given the context of the
request. The Accept field should only be used when the request is
specifically limited to a set of desired types, as in the case of a
request for an in-line image, or to indicate qualitative
preferences for specific media types.
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.
10.2 Accept-Charset
The Accept-Charset request-header field can be used to indicate
what character sets are acceptable for the response. This field
allows clients capable of understanding more comprehensive or
special-purpose character sets to signal that capability to a
server which is capable of representing documents in those
character sets. The US-ASCII character set can be assumed to be
acceptable to all user agents.
Accept-Charset = "Accept-Charset" ":" 1#charset
Character set values are described in Section 3.4. An example is
Accept-Charset: iso-8859-1, unicode-1-1
If no Accept-Charset field is given, the default is that any
character set is acceptable. If the Accept-Charset field is given
and the requested resource is not available in one of the listed
character sets, then the server should respond with the 406 (none
acceptable) status code.
10.3 Accept-Encoding
The Accept-Encoding request-header field is similar to Accept, but
restricts the content-coding values (Section 3.5) which are
acceptable in the response.
Accept-Encoding = "Accept-Encoding" ":"
#( content-coding )
An example of its use is
Accept-Encoding: compress, gzip
If no Accept-Encoding field is present in a request, the server may
assume that the client will accept any content coding. If an
Accept-Encoding field is present, but contains an empty field
value, then the user agent is refusing to accept any content coding.
10.4 Accept-Language
The Accept-Language request-header field is similar to Accept, but
restricts the set of natural languages that are preferred as a
response to the request.
Accept-Language = "Accept-Language" ":"
1#( language-tag [ ";" "q" "=" qvalue ] )
The language-tag is described in Section 3.10. Each language may be
given an associated quality value which represents an estimate of
the user's comprehension of that language. The quality value
defaults to "q=1" (100% comprehension) for listed languages. This
value may be used in the server's content negotiation algorithm
(Section 12). For example,
Accept-Language: da, en-gb;q=0.8, de;q=0.55
would mean: "I prefer Danish, but will accept British English (with
80% comprehension) or German (with a 55% comprehension)."
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.
10.5 Allow
The Allow entity-header field lists the set of methods supported by
the resource identified by the Request-URI. The purpose of this
field is strictly to inform the recipient of valid methods
associated with the resource. An Allow header field must be present
in a 405 (method not allowed) response. The Allow header field is
not permitted in a request using the POST method, and thus should
be ignored if it is received as part of a POST entity.
Allow = "Allow" ":" 1#method
Example of use:
Allow: GET, HEAD, PUT
This field cannot prevent a client from trying other methods.
However, the indications given by the Allow header field value
should be followed. The actual set of allowed methods is defined by
the origin server at the time of each request.
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.
10.6 Authorization
A user agent that wishes to authenticate itself with a
server--usually, but not necessarily, after receiving a 401
response--may do so by including an Authorization request-header
field with the request. The Authorization field value consists of
credentials containing the authentication information of the user
agent for the realm of the resource being requested.
Authorization = "Authorization" ":" credentials
HTTP access authentication is described in Section 11. If a request
is authenticated and a realm specified, the same credentials should
be valid for all other requests within this realm.
Responses to requests containing an Authorization field are not
cachable.
10.7 Base
The Base entity-header field may be used to specify the base URI
for resolving relative URLs, as described in RFC 1808 [11].
10.8 Cache-Control
The Cache-Control general-header field is used to specify
directives that must be obeyed by all caching mechanisms along the
request/response chain. The directives specify behavior intended to
prevent caches from adversely interfering with the request or
response. Cache directives are unidirectional in that the presence
of a directive in a request does not imply that the same directive
should be given in the response.
Cache-Control = "Cache-Control" ":" 1#cache-directive
cache-directive = "cachable"
| "max-age" "=" delta-seconds
| "private" [ "=" <"> 1#field-name <"> ]
| "no-cache" [ "=" <"> 1#field-name <"> ]
The Cache-Control header field may be used to modify the optional
behavior of caching mechanisms, and the default cachability of a
response message; it cannot be used to modify the required behavior
of caching mechanisms. HTTP requirements for caching and cachable
messages are described in Section 13.
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.
10.9 Connection
The Connection general-header field is used to indicate a list of
keywords and header field names containing information which is
only applicable to the current connection between the sender and
the nearest non-tunnel recipient on the request/response chain.
This information must not be forwarded or cached. Unlike the
default behavior, the recipient cannot safely ignore the semantics
of the listed field-names if they are not understood, since
forwarding them may imply that understanding.
Connection = "Connection" ":" 1#field-name
Proxies and gateways must discard the named header fields, and the
Connection header itself, before forwarding the message. Proxies
and gateways may add their own Connection information to forwarded
messages if such options are desired for the forwarding connection.
These restrictions do not apply to a tunnel, since the tunnel is
acting as a relay between two connections and does not affect the
connection options.
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.
10.9.1 Persistent Connections
The "keep-alive" keyword in a Connection header field allows the
sender to indicate its desire for a persistent connection (i.e., a
connection that lasts beyond the current request/response
transaction). Persistent connections allow the client to perform
multiple requests without the overhead of connection tear-down and
set-up between each request.
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.
10.10 Content-Encoding
The Content-Encoding entity-header field is used as a modifier to
the media-type. When present, its value indicates what additional
content codings have been applied to the resource, and thus what
decoding mechanisms must be applied in order to obtain the
media-type referenced by the Content-Type header field.
Content-Encoding is primarily used to allow a document to be
compressed without losing the identity of its underlying media type.
Content-Encoding = "Content-Encoding" ":" 1#content-coding
Content codings are defined in Section 3.5. An example of its use is
Content-Encoding: gzip
The Content-Encoding is a characteristic of the resource identified
by the Request-URI. Typically, the resource is stored with this
encoding and is only decoded before rendering or analogous usage.
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.
10.11 Content-Language
The Content-Language entity-header field describes the natural
language(s) of the intended audience for the enclosed entity. Note
that this may not be equivalent to all the languages used within
the entity.
Content-Language = "Content-Language" ":" 1#language-tag
Language tags are defined in Section 3.10. The primary purpose of
Content-Language is to allow a selective consumer to identify and
differentiate resources according to the consumer's own preferred
language. Thus, if the body content is intended only for a
Danish-literate audience, the appropriate field is
Content-Language: dk
If no Content-Language is specified, the default is that the
content is intended for all language audiences. This may mean that
the sender does not consider it to be specific to any natural
language, or that the sender does not know for which language it is
intended.
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.
10.12 Content-Length
The Content-Length entity-header field indicates the size of the
Entity-Body, in decimal number of octets, sent to the recipient or,
in the case of the HEAD method, the size of the Entity-Body that
would have been sent had the request been a GET.
Content-Length = "Content-Length" ":" 1*DIGIT
An example is
Content-Length: 3495
Applications should use this field to indicate the size of the
Entity-Body to be transferred, regardless of the media type of the
entity. A valid Content-Length field value is required on all
HTTP/1.1 request messages containing an entity body.
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.
10.13 Content-MD5
TBS
10.14 Content-Range
TBS
10.15 Content-Type
The Content-Type entity-header field indicates the media type of
the Entity-Body sent to the recipient or, in the case of the HEAD
method, the media type that would have been sent had the request
been a GET.
Content-Type = "Content-Type" ":" media-type
Media types are defined in Section 3.7. An example of the field is
Content-Type: text/html; charset=ISO-8859-4
Further discussion of methods for identifying the media type of an
entity is provided in Section 7.2.1.
10.16 Content-Version
The Content-Version entity-header field defines the version tag
associated with a rendition of an evolving entity. Together with
the Derived-From field described in Section 10.18, it allows a
group of people to work simultaneously on the creation of a work as
an iterative process. The field should be used to allow evolution
of a particular work along a single path. It should not be used to
indicate derived works or renditions in different representations.
It may also me used as an opaque value for comparing a cached
entity's version with that of the current resource.
Content-Version= "Content-Version" ":" quoted-string
Examples of the Content-Version field include:
Content-Version: "2.1.2"
Content-Version: "Fred 19950116-12:26:48"
Content-Version: "2.5a4-omega7"
The value of the Content-Version field should be considered opaque
to all parties but the origin server. A user agent may suggest a
value for the version of an entity transferred via a PUT request;
however, only the origin server can reliably assign that value.
10.17 Date
The Date general-header field represents the date and time at which
the message was originated, having the same semantics as orig-date
in RFC 822. The field value is an HTTP-date, as described in
Section 3.3.
Date = "Date" ":" HTTP-date
An example is
Date: Tue, 15 Nov 1994 08:12:31 GMT
If a message is received via direct connection with the user agent
(in the case of requests) or the origin server (in the case of
responses), then the date can be assumed to be the current date at
the receiving end. However, since the date--as it is believed by the
origin--is important for evaluating cached responses, origin servers
should always include a Date header. Clients should only send a
Date header field in messages that include an entity body, as in
the case of the PUT and POST requests, and even then it is
optional. A received message which does not have a Date header
field should be assigned one by the recipient if the message will
be cached by that recipient or gatewayed via a protocol which
requires a Date.
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.
10.18 Derived-From
The Derived-From entity-header field can be used to indicate the
version tag of the resource from which the enclosed entity was
derived before modifications were made by the sender. This field is
used to help manage the process of merging successive changes to a
resource, particularly when such changes are being made in parallel
and from multiple sources.
Derived-From = "Derived-From" ":" quoted-string
An example use of the field is:
Derived-From: "2.1.1"
The Derived-From field is required for PUT and PATCH requests if
the entity being sent was previously retrieved from the same URI
and a Content-Version header was included with the entity when it
was last retrieved.
10.19 Expires
The Expires entity-header field gives the date/time after which the
entity should be considered stale. This allows information
providers to suggest the volatility of the resource, or a date
after which the information may no longer be valid. Applications
must not cache this entity beyond the date given. The presence of
an Expires field does not imply that the original resource will
change or cease to exist at, before, or after that time. However,
information providers that know or even suspect that a resource
will change by a certain date should include an Expires header with
that date. The format is an absolute date and time as defined by
HTTP-date in Section 3.3.
Expires = "Expires" ":" HTTP-date
An example of its use is
Expires: Thu, 01 Dec 1994 16:00:00 GMT
If the date given is equal to or earlier than the value of the Date
header, the recipient must not cache the enclosed entity. If a
resource is dynamic by nature, as is the case with many
data-producing processes, entities from that resource should be
given an appropriate Expires value which reflects that dynamism.
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.
10.20 Forwarded
The Forwarded general-header field is to be used by gateways and
proxies to indicate the intermediate steps between the user agent
and the server on requests, and between the origin server and the
client on responses. It is analogous to the "Received" field of RFC
822 [9] and is intended to be used for tracing transport problems
and avoiding request loops.
Forwarded = "Forwarded" ":" #( "by" URI [ "(" product ")" ]
[ "for" FQDN ] )
FQDN = <Fully-Qualified Domain Name>
For example, a message could be sent from a client on
ptsun00.cern.ch to a server at www.ics.uci.edu port 80, via an
intermediate HTTP proxy at info.cern.ch port 8000. The request
received by the server at www.ics.uci.edu would then have the
following Forwarded header field:
Forwarded: by http://info.cern.ch:8000/ for ptsun00.cern.ch
Multiple Forwarded header fields are allowed and should represent
each proxy/gateway that has forwarded the message. It is strongly
recommended that proxies/gateways used as a portal through a
network firewall do not, by default, send out information about the
internal hosts within the firewall region. This information should
only be propagated if explicitly enabled. If not enabled, the for
token and FQDN should not be included in the field value, and any
Forwarded headers already present in the message (those added
behind the firewall) should be removed.
10.21 From
The From request-header field, if given, should contain an Internet
e-mail address for the human user who controls the requesting user
agent. The address should be machine-usable, as defined by mailbox
in RFC 822 [9] (as updated by RFC 1123 [8]):
From = "From" ":" mailbox
An example is:
From: webmaster@w3.org
This header field may be used for logging purposes and as a means
for identifying the source of invalid or unwanted requests. It
should not be used as an insecure form of access protection. The
interpretation of this field is that the request is being performed
on behalf of the person given, who accepts responsibility for the
method performed. In particular, robot agents should include this
header so that the person responsible for running the robot can be
contacted if problems occur on the receiving end.
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.
10.22 Host
The Host request-header field allows the client to specify, for the
server's benefit, the Internet host given by the original Uniform
Resource Identifier (Section 3.2) of the resource being requested,
as it was obtained from the user or the referring resource. This
allows a server to differentiate between internally-ambiguous URLs
(such as the root "/" URL of a server harboring multiple virtual
hostnames). This field is required on all HTTP/1.1 requests which
do not already include the host in the Request-URI.
Host = "Host" ":" host ; Section 3.2.2
Example:
Host: www.w3.org
The contents of the Host header field should exactly match the host
information used to contact the origin server or gateway in
question. It must not include the trailing ":port" information
which may also be found in the net_loc portion of a URL
(Section 3.2).
10.23 If-Modified-Since
The If-Modified-Since request-header field is used with the GET
method to make it conditional: if the requested resource has not
been modified since the time specified in this field, a copy of the
resource will not be returned from the server; instead, a 304 (not
modified) response will be returned without any Entity-Body.
If-Modified-Since = "If-Modified-Since" ":" HTTP-date
An example of the field is:
If-Modified-Since: Sat, 29 Oct 1994 19:43:31 GMT
A conditional GET method requests that the identified resource be
transferred only if it has been modified since the date given by
the If-Modified-Since header. The algorithm for determining this
includes the following cases:
a) If the request would normally result in anything other than
a 200 (ok) status, or if the passed 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.
b) If the resource has been modified since the
If-Modified-Since date, the response is exactly the same as
for a normal GET.
c) If the resource has not been modified since a valid
If-Modified-Since date, the server must return a 304 (not
modified) response.
The purpose of this feature is to allow efficient updates of cached
information with a minimum amount of transaction overhead.
10.24 Keep-Alive
The Keep-Alive general-header field may be used to include
diagnostic information and other optional parameters associated
with the "keep-alive" keyword of the Connection header field
(Section 10.9). This Keep-Alive field must only be used when the
"keep-alive" keyword is present (Section 10.9.1).
Keep-Alive = "Keep-Alive" ":" 1#kaparam
kaparam = ( "timeout" "=" delta-seconds )
| ( "max" "=" 1*DIGIT )
| ( attribute [ "=" value ] )
The Keep-Alive header field and the additional information it
provides are optional and do not need to be present to indicate a
persistent connection has been established. The semantics of the
Connection header field prevent the Keep-Alive field from being
accidentally forwarded to downstream connections.
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.
10.25 Last-Modified
The Last-Modified entity-header field indicates the date and time
at which the sender believes the resource was last modified. The
exact semantics of this field are defined in terms of how the
recipient should interpret it: if the recipient has a copy of this
resource which is older than the date given by the Last-Modified
field, that copy should be considered stale.
Last-Modified = "Last-Modified" ":" HTTP-date
An example of its use is
Last-Modified: Tue, 15 Nov 1994 12:45:26 GMT
The exact meaning of this header field depends on the
implementation of the sender and the nature of the original
resource. For files, it may be just the file system last-modified
time. For entities with dynamically included parts, it may be the
most recent of the set of last-modify times for its component
parts. For database gateways, it may be the last-update timestamp
of the record. For virtual objects, it may be the last time the
internal state changed.
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.
10.26 Link
The Link entity-header field provides a means for describing a
relationship between the entity and some other resource. An entity
may include multiple Link values. Links at the metainformation
level typically indicate relationships like hierarchical structure
and navigation paths. The Link field is semantically equivalent to
the <LINK> element in HTML [5].
Link = "Link" ":" #("<" URI ">"
[ ";" "rel" "=" relationship ]
[ ";" "rev" "=" relationship ]
[ ";" "title" "=" quoted-string ] )
relationship = sgml-name
| ( <"> sgml-name *( SP sgml-name) <"> )
sgml-name = ALPHA *( ALPHA | DIGIT | "." | "-" )
Relationship values are case-insensitive and may be extended within
the constraints of the sgml-name syntax. The title parameter may be
used to label the destination of a link such that it can be used as
identification within a human-readable menu.
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.
10.27 Location
The Location response-header field defines the exact location of
the resource that was identified by the Request-URI. For 2xx
responses, if the Request-URI corresponds to a negotiable set of
variants and the response includes one of those variants, then the
response must also include a Location header field containing the
exact location of the chosen variant. For 3xx responses, the
location should indicate the server's preferred URL for automatic
redirection to the resource. The field value consists of a single
absolute URL.
Location = "Location" ":" absoluteURI
An example is
Location: http://www.w3.org/pub/WWW/People.html
If no base URL is provided by or within the entity, the value of
the Location field should be used as the base for resolving
relative URLs [11].
10.28 MIME-Version
HTTP is not a MIME-compliant protocol (see Appendix C). However,
HTTP/1.1 messages may include a single MIME-Version general-header
field to indicate what version of the MIME protocol was used to
construct the message. Use of the MIME-Version header field
indicates that the message is in full compliance with the MIME
protocol (as defined in [7]). Proxies/gateways are responsible for
ensuring full compliance (where possible) when exporting HTTP
messages to strict MIME environments.
MIME-Version = "MIME-Version" ":" 1*DIGIT "." 1*DIGIT
MIME version "1.0" is the default for use in HTTP/1.1. However,
HTTP/1.1 message parsing and semantics are defined by this document
and not the MIME specification.
10.29 Pragma
The Pragma general-header field is used to include
implementation-specific directives that may apply to any recipient
along the request/response chain. All pragma directives specify
optional behavior from the viewpoint of the protocol; however, some
systems may require that behavior be consistent with the directives.
Pragma = "Pragma" ":" 1#pragma-directive
pragma-directive = "no-cache" | extension-pragma
extension-pragma = token [ "=" word ]
When the "no-cache" directive is present in a request message, an
application should forward the request toward the origin server
even if it has a cached copy of what is being requested. This
pragma directive has the same semantics as the "no-cache"
cache-directive (see Section 10.8) and is defined here for
backwards compatibility with HTTP/1.0. Clients should include both
header fields when a "no-cache" request is sent to a server not
known to be HTTP/1.1 compliant.
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.
10.30 Proxy-Authenticate
The Proxy-Authenticate response-header field must be included as
part of a 407 (proxy authentication required) response. The field
value consists of a challenge that indicates the authentication
scheme and parameters applicable to the proxy for this Request-URI.
Proxy-Authentication = "Proxy-Authentication" ":" challenge
The HTTP access authentication process is described in Section 11.
Unlike WWW-Authenticate, the Proxy-Authenticate header field
applies only to the current connection and must not be passed on to
downstream clients.
10.31 Proxy-Authorization
The Proxy-Authorization request-header field allows the client to
identify itself (or its user) to a proxy which requires
authentication. The Proxy-Authorization field value consists of
credentials containing the authentication information of the user
agent for the proxy and/or realm of the resource being requested.
Proxy-Authorization = "Proxy-Authorization" ":" credentials
The HTTP access authentication process is described in Section 11.
Unlike Authorization, the Proxy-Authorization applies only to the
current connection and must not be passed on to upstream servers.
If a request is authenticated and a realm specified, the same
credentials should be valid for all other requests within this
realm.
10.32 Public
The Public response-header field lists the set of non-standard
methods supported by the server. The purpose of this field is
strictly to inform the recipient of the capabilities of the server
regarding unusual methods. The methods listed may or may not be
applicable to the Request-URI; the Allow header field
(Section 10.5) should be used to indicate methods allowed for a
particular URI. This does not prevent a client from trying other
methods. The field value should not include the methods predefined
for HTTP/1.1 in Section 5.1.1.
Public = "Public" ":" 1#method
Example of use:
Public: OPTIONS, MGET, MHEAD
This header field applies only to the server directly connected to
the client (i.e., the nearest neighbor in a chain of connections).
If the response passes through a proxy, the proxy must either
remove the Public header field or replace it with one applicable to
its own capabilities.
10.33 Range
TBS
10.34 Referer
The Referer request-header field allows the client to specify, for
the server's benefit, the address (URI) of the resource from which
the Request-URI was obtained. This allows a server to generate
lists of back-links to resources for interest, logging, optimized
caching, etc. It also allows obsolete or mistyped links to be
traced for maintenance. The Referer field must not be sent if the
Request-URI was obtained from a source that does not have its own
URI, such as input from the user keyboard.
Referer = "Referer" ":" ( absoluteURI | relativeURI )
Example:
Referer: http://www.w3.org/hypertext/DataSources/Overview.html
If a partial URI is given, it should be interpreted relative to the
Request-URI. The URI must not include a fragment.
Note: Because the source of a link may be private
information or may reveal an otherwise private information
source, it is strongly recommended that the user be able to
select whether or not the Referer field is sent. For
example, a browser client could have a toggle switch for
browsing openly/anonymously, which would respectively
enable/disable the sending of Referer and From information.
10.35 Refresh
TBS
10.36 Retry-After
The Retry-After response-header field can be used with a 503
(service unavailable) response to indicate how long the service is
expected to be unavailable to the requesting client. The value of
this field can be either an HTTP-date or an integer number of
seconds (in decimal) after the time of the response.
Retry-After = "Retry-After" ":" ( HTTP-date | delta-seconds )
Two examples of its use are
Retry-After: Wed, 14 Dec 1994 18:22:54 GMT
Retry-After: 120
In the latter example, the delay is 2 minutes.
10.37 Server
The Server response-header field contains information about the
software used by the origin server to handle the request. The field
can contain multiple product tokens (Section 3.8) and comments
identifying the server and any significant subproducts. By
convention, the product tokens are listed in order of their
significance for identifying the application.
Server = "Server" ":" 1*( product | comment )
Example:
Server: CERN/3.0 libwww/2.17
If the response is being forwarded through a proxy, the proxy
application must not add its data to the product list. Instead, it
should include a Forwarded field (as described in Section 10.20).
Note: Revealing the specific software version of the server
may allow the server machine to become more vulnerable to
attacks against software that is known to contain security
holes. Server implementors are encouraged to make this field
a configurable option.
10.38 Title
The Title entity-header field indicates the title of the entity
Title = "Title" ":" *TEXT
An example of the field is
Title: Hypertext Transfer Protocol -- HTTP/1.1
This field is isomorphic with the <TITLE> element in HTML [5].
10.39 Transfer Encoding
The Transfer-Encoding general-header field indicates what (if any)
type of transformation has been applied to the message body in
order to safely transfer it between the sender and the recipient.
This differs from the Content-Encoding in that the transfer coding
is a property of the message, not of the original resource.
Transfer-Encoding = "Transfer-Encoding" ":" 1#transfer-coding
Transfer codings are defined in Section 3.6. An example is:
Transfer-Encoding: chunked
Many older HTTP/1.0 applications do not understand the
Transfer-Encoding header.
10.40 Unless
The Unless request-header field performs a similar function as
If-Modified-Since, but the comparison is based on any Entity-Header
field value of the resource and is not restricted to the GET method.
Unless = "Unless" ":" 1#logic-bag
For example,
Unless: {or {ne {Content-MD5 "Q2hlY2sgSW50ZWdyaXR5IQ=="}}
{ne {Content-Length 10036}}
{ne {Content-Version "12.4.8"}}
{gt {Last-Modified "Mon, 04 Dec 1995 01:23:45 GMT"}}}
Multiple Unless headers, or multiple bags separated by commas, can
be combined by OR'ing them together:
Unless: {eq {A "a"}}
Unless: {eq {B "b"}}
is equivalent to
Unless: {eq {A "a"}},{eq {B "b"}}
which in turn is equivalent to
Unless: {or {eq {A "a"}} {eq {B "b"}}}
When a request containing an Unless header field is received, the
server must evaluate the expression defined by the listed
logic-bags (Section 3.11). If the expression evaluates to false,
then no change is made to the semantics of the request. If it
evaluates true and the request is not a conditional GET
(If-Modified-Since, Section 10.23) or a partial GET (Range,
Section 10.33), then the server must abort the request and respond
with the 412 (unless true) status code. If the request is a
conditional GET, then the server must disregard the
If-Modified-Since value and respond as it would for a normal GET.
Similarly, if the request is a partial GET, then the server must
disregard the Range value and respond as it would for a normal GET.
10.41 Upgrade
The Upgrade general-header allows the client to specify what
additional communication protocols it supports and would like to
use if the server finds it appropriate to switch protocols. The
server must use the Upgrade header field within a 101 (switching
protocols) response to indicate which protocol(s) are being
switched.
Upgrade = "Upgrade" ":" 1#product
For example,
Upgrade: HTTP/2.0, SHTTP/1.3, IRC/6.9, RTA/x11
The purpose of the Upgrade header is to allow easier migration
across protocols in order to better match the application needs
with protocol capabilities.
10.42 URI
The URI entity-header field is used to inform the recipient of
other Uniform Resource Identifiers (Section 3.2) by which the
resource can be identified, and of all negotiable variants
corresponding to the Request-URI.
URI-header = "URI" ":" 1#( uri-mirror | uri-name | uri-variant )
uri-mirror = "{" "mirror" <"> URI <"> "}"
uri-name = "{" "name" <"> URI <"> "}"
uri-variant = "{" "variant" <"> URI <"> qvalue
[ "{" "type" <"> media-type <"> "}" ]
[ "{" "language" <"> 1#language-tag <"> "}" ]
[ "{" "encoding" <"> 1#content-coding <"> "}" ]
[ "{" "length" 1*DIGIT "}" ]
[ "{" "user-agent" "}" ]
"}"
Any URI specified in this field can be absolute or relative to the
Request-URI. The "mirror" form of URI refers to a location which is
a mirror copy of the Request-URI. The "name" form refers to a
location-independent name corresponding to the Request-URI. The
"variant" form refers to one of the set of negotiable variants that
may be retrieved via a request on the Request-URI.
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).
10.43 User-Agent
The User-Agent request-header field contains information about the
user agent originating the request. This is for statistical
purposes, the tracing of protocol violations, and automated
recognition of user agents for the sake of tailoring responses to
avoid particular user agent limitations. Although it is not
required, user agents should include this field with requests. The
field can contain multiple product tokens (Section 3.8) and
comments identifying the agent and any subproducts which form a
significant part of the user agent. By convention, the product
tokens are listed in order of their significance for identifying
the application.
User-Agent = "User-Agent" ":" 1*( product | comment )
Example:
User-Agent: CERN-LineMode/2.15 libwww/2.17b3
10.44 WWW-Authenticate
The WWW-Authenticate response-header field must be included in 401
(unauthorized) response messages. The field value consists of at
least one challenge that indicates the authentication scheme(s) and
parameters applicable to the Request-URI.
WWW-Authenticate = "WWW-Authenticate" ":" 1#challenge
The HTTP access authentication process is described in Section 11.
User agents must take special care in parsing the WWW-Authenticate
field value if it contains more than one challenge, or if more than
one WWW-Authenticate header field is provided, since the contents
of a challenge may itself contain a comma-separated list of
authentication parameters.
11. Access Authentication
HTTP provides a simple challenge-response authentication mechanism
which may be used by a server to challenge a client request and by
a client to provide authentication information. It uses an
extensible, case-insensitive token to identify the authentication
scheme, followed by a comma-separated list of attribute-value pairs
which carry the parameters necessary for achieving authentication
via that scheme.
auth-scheme = token
auth-param = token "=" quoted-string
The 401 (unauthorized) response message is used by an origin server
to challenge the authorization of a user agent. This response must
include a WWW-Authenticate header field containing at least one
challenge applicable to the requested resource.
challenge = auth-scheme 1*SP realm *( "," auth-param )
realm = "realm" "=" realm-value
realm-value = quoted-string
The realm attribute (case-insensitive) is required for all
authentication schemes which issue a challenge. The realm value
(case-sensitive), in combination with the canonical root URL of the
server being accessed, defines the protection space. These realms
allow the protected resources on a server to be partitioned into a
set of protection spaces, each with its own authentication scheme
and/or authorization database. The realm value is a string,
generally assigned by the origin server, which may have additional
semantics specific to the authentication scheme.
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.
11.1 Basic Authentication Scheme
The "basic" authentication scheme is based on the model that the
user agent must authenticate itself with a user-ID and a password
for each realm. The realm value should be considered an opaque
string which can only be compared for equality with other realms on
that server. The server will service the request only if it can
validate the user-ID and password for the protection space of the
Request-URI. There are no optional authentication parameters.
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.
11.2 Digest Authentication Scheme
The "digest" authentication scheme is [currently described in an
expired Internet-Draft, and this description will have to be
improved to reference a new draft or include the old one].
12. Content Negotiation
Content negotiation is an optional feature of the HTTP protocol. It
is designed to allow for selection of a preferred content
representation based upon the attributes of the negotiable variants
corresponding to the requested resource. HTTP/1.1 provides for two
types of negotiation: preemptive and reactive.
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.
12.1 Preemptive Negotiation
Preemptive negotiation attempts to "negotiate" the variant
parameters by including the user agent preferences within each
request. In this way, the preferred representation of the resource
may be negotiated and obtained within a single request-response
round-trip, and without intervention from the user. However, this
also means that the user agent preferences are all the time, even
though relatively few resources are ever negotiable. Preemptive
negotiation may not always be desirable for the user and is
sometimes unnecessary for the content provider. Implementors should
provide mechanisms whereby the amount of preemptive content
negotiation, and the parameters of that negotiation, are
configurable by the user and server maintainer.
The 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:
qs Source quality is measured by the content provider as
representing the amount of degradation from the original
source. For example, a picture originally in JPEG form
would have a lower qs when translated to the XBM format,
and much lower qs when translated to an ASCII-art
representation. Note, however, that this is a function of
the source -- an original piece of ASCII-art may degrade in
quality if it is captured in JPEG form. The qs value should
be assigned to each variant by the content provider; if no
qs value has been assigned, the default is generally
"qs=1". A server may define its own default qs value based
on the resource characteristics, but only if individual
resources can override those defaults.
qe Encoding quality is measured by comparing the variant's
applied content-codings (Section 3.5) to those listed in
the request message's Accept-Encoding field. If the variant
has no assigned Content-Encoding, or if no Accept-Encoding
field is present, the value assigned is "qe=1". If all of
the variant's content encodings are listed in the
Accept-Encoding field, then the value assigned is "qe=1".
If any of the variant's content encodings are not listed in
the provided Accept-Encoding field, then the value assigned
is "qe=0".
qc Charset quality is measured by comparing the variant
media-type's charset parameter value (if any) to those
character sets (Section 3.4) listed in the request
message's Accept-Charset field. If the variant's media-type
has no charset parameter, or the variant's charset is
US-ASCII, or if no Accept-Charset field is present, then
the value assigned is "qc=1". If the variant's charset is
listed in the Accept-Charset field, then the value assigned
is "qc=1". Otherwise, if the variant's charset is not
listed in the provided Accept-Encoding field, then the
value assigned is "qc=0".
ql Language quality is measured by comparing the variant's
assigned language tag(s) (Section 3.10) to those listed in
the request message's Accept-Language field. If no variant
has an assigned Content-Language, or if no Accept-Language
field is present, the value assigned is "ql=1". If at least
one variant has an assigned content language, but the one
currently under consideration does not, then it should be
assigned the value "ql=0.5". If any of the variant's
content languages are listed in the Accept-Language field,
then the value assigned is the maximum of the "q" parameter
values for those language tags (Section 10.4); if there was
no exact match and at least one of the Accept-Language
field values is a complete subtag prefix of the content
language tag(s), then the "q" parameter value of the
largest matching prefix is used. If none of the variant's
content language tags or tag prefixes are listed in the
provided Accept-Language field, then the value assigned is
"ql=0.001".
q Media type quality is measured by comparing the variant's
assigned media type (Section 3.7) to those listed in the
request message's Accept field. If no Accept field is
given, then the value assigned is "q=1". If at least one
listed media range (Section 10.1) matches the variant's
media type, then the "q" parameter value assigned to the
most specific of those matched is used (e.g.,
"text/html;version=3.0" is more specific than "text/html",
which is more specific than "text/*", which in turn is more
specific than "*/*"). If no media range in the provided
Accept field matches the variant's media type, then the
value assigned is "q=0".
mxb The maximum number of bytes in an Entity-Body that the
client will accept is also obtained from the matching of
the variant's assigned media type to those listed in the
request message's Accept field. If no Accept field is
given, or if no media range in the provided Accept field
matches the variant's media type, then the value assigned
is "mxb=undefined" (i.e., infinity). Otherwise, the value
used is that given to the "mxb" parameter in the media
range chosen above for the q value.
bs The actual number of bytes in the Entity-Body for the
variant when it is included in a response message. This
should equal the value of Content-Length.
The mapping function is defined as:
Q(qs,qe,qc,ql, { if mxb=undefined, then (qs*qe*qc*ql*q) }
q,mxb,bs) = { if mxb >= bs, then (qs*qe*qc*ql*q) }
{ if mxb < bs, then 0 }
The variants with a maximal value for the Q function represent the
preferred representation(s) of the entity; those with a Q values
less than the maximal value are therefore excluded from further
consideration. If multiple representations exist that only vary by
Content-Encoding, then the smallest representation (lowest bs) is
preferred.
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.
13. Caching
[This will be a summary of what is already defined in the Methods,
Status Codes, Cache-Control, Unless, and If-Modified-Since
sections.]
14. Security Considerations
This section is meant to inform application developers, information
providers, and users of the security limitations in HTTP/1.1 as
described by this document. The discussion does not include
definitive solutions to the problems revealed, though it does make
some suggestions for reducing security risks.
14.1 Authentication of Clients
As mentioned in Section 11.1, the Basic authentication scheme is
not a secure method of user authentication, nor does it prevent the
Entity-Body from being transmitted in clear text across the
physical network used as the carrier. HTTP does not prevent
additional authentication schemes and encryption mechanisms from
being employed to increase security.
14.2 Safe Methods
The writers of client software should be aware that the software
represents the user in their interactions over the Internet, and
should be careful to allow the user to be aware of any actions they
may take which may have an unexpected significance to themselves or
others.
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.
14.3 Abuse of Server Log Information
A server is in the position to save personal data about a user's
requests which may identify their reading patterns or subjects of
interest. This information is clearly confidential in nature and
its handling may be constrained by law in certain countries. People
using the HTTP protocol to provide data are responsible for
ensuring that such material is not distributed without the
permission of any individuals that are identifiable by the
published results.
14.4 Transfer of Sensitive Information
Like any generic data transfer protocol, HTTP cannot regulate the
content of the data that is transferred, nor is there any a priori
method of determining the sensitivity of any particular piece of
information within the context of any given request. Therefore,
applications should supply as much control over this information as
possible to the provider of that information. Four header fields
are worth special mention in this context: Server, Forwarded,
Referer and From.
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.
15. Acknowledgments
This specification makes heavy use of the augmented BNF and generic
constructs defined by David H. Crocker for RFC 822 [9]. Similarly,
it reuses many of the definitions provided by Nathaniel Borenstein
and Ned Freed for MIME [7]. We hope that their inclusion in this
specification will help reduce past confusion over the relationship
between HTTP and Internet mail message formats.
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,
H&kon 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 Franccedillaois Yergeau
Mary Ellen Zurko
16. References
[1] H. Alvestrand. "Tags for the identification of languages." RFC
1766, UNINETT, March 1995.
[2] F. Anklesaria, M. McCahill, P. Lindner, D. Johnson, D. Torrey,
B. Alberti. "The Internet Gopher Protocol: A distributed
document search and retrieval protocol." RFC 1436, University
of Minnesota, March 1993.
[3] T. Berners-Lee. "Universal Resource Identifiers in WWW: A
Unifying Syntax for the Expression of Names and Addresses of
Objects on the Network as used in the World-Wide Web."
RFC 1630, CERN, June 1994.
[4] T. Berners-Lee, L. Masinter, M. McCahill. "Uniform Resource
Locators (URL)." RFC 1738, CERN, Xerox PARC, University of
Minnesota, December 1994.
[5] T. Berners-Lee, D. Connolly. "HyperText Markup Language
Specification - 2.0." RFC 1866, MIT/LCS, November 1995.
[6] T. Berners-Lee, R. Fielding, H. Frystyk. "Hypertext Transfer
Protocol - HTTP/1.0." Work in Progress
(draft-ietf-http-v10-spec-04.txt), MIT/LCS, UC Irvine,
September 1995.
[7] N. Borenstein, N. Freed. "MIME (Multipurpose Internet Mail
Extensions) Part One: Mechanisms for Specifying and Describing
the Format of Internet Message Bodies." RFC 1521, Bellcore,
Innosoft, September 1993.
[8] R. Braden. "Requirements for Internet hosts - application and
support." STD 3, RFC 1123, IETF, October 1989.
[9] D. H. Crocker. "Standard for the Format of ARPA Internet Text
Messages." STD 11, RFC 822, UDEL, August 1982.
[10] F. Davis, B. Kahle, H. Morris, J. Salem, T. Shen, R. Wang,
J. Sui, M. Grinbaum. "WAIS Interface Protocol Prototype
Functional Specification." (v1.5), Thinking Machines
Corporation, April 1990.
[11] R. Fielding. "Relative Uniform Resource Locators." RFC 1808, UC
Irvine, June 1995.
[12] M. Horton, R. Adams. "Standard for interchange of USENET
messages." RFC 1036 (Obsoletes RFC 850), AT&T Bell
Laboratories, Center for Seismic Studies, December 1987.
[13] B. Kantor, P. Lapsley. "Network News Transfer Protocol: A
Proposed Standard for the Stream-Based Transmission of News."
RFC 977, UC San Diego, UC Berkeley, February 1986.
[14] K. Moore. "MIME (Multipurpose Internet Mail Extensions) Part
Two: Message Header Extensions for Non-ASCII Text." RFC 1522,
University of Tennessee, September 1993.
[15] E. Nebel, L. Masinter. "Form-based File Upload in HTML."
RFC 1867, Xerox Corporation, November 1995.
[16] J. Postel. "Simple Mail Transfer Protocol." STD 10, RFC 821,
USC/ISI, August 1982.
[17] J. Postel. "Media Type Registration Procedure." RFC 1590,
USC/ISI, March 1994.
[18] J. Postel, J. K. Reynolds. "File Transfer Protocol (FTP)." STD
9, RFC 959, USC/ISI, October 1985.
[19] J. Reynolds, J. Postel. "Assigned Numbers." STD 2, RFC 1700,
USC/ISI, October 1994.
[20] K. Sollins, L. Masinter. "Functional Requirements for Uniform
Resource Names." RFC 1737, MIT/LCS, Xerox Corporation, December
1994.
[21] US-ASCII. Coded Character Set - 7-Bit American Standard Code
for Information Interchange. Standard ANSI X3.4-1986, ANSI,
1986.
[22] ISO-8859. International Standard -- Information Processing --
8-bit Single-Byte Coded Graphic Character Sets --
Part 1: Latin alphabet No. 1, ISO 8859-1:1987.
Part 2: Latin alphabet No. 2, ISO 8859-2, 1987.
Part 3: Latin alphabet No. 3, ISO 8859-3, 1988.
Part 4: Latin alphabet No. 4, ISO 8859-4, 1988.
Part 5: Latin/Cyrillic alphabet, ISO 8859-5, 1988.
Part 6: Latin/Arabic alphabet, ISO 8859-6, 1987.
Part 7: Latin/Greek alphabet, ISO 8859-7, 1987.
Part 8: Latin/Hebrew alphabet, ISO 8859-8, 1988.
Part 9: Latin alphabet No. 5, ISO 8859-9, 1990.
17. Authors' Addresses
Roy T. Fielding
Department of Information and Computer Science
University of California
Irvine, CA 92717-3425, U.S.A.
Fax: +1 (714) 824-4056
Email: fielding@ics.uci.edu
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
Appendices
These appendices are provided for informational reasons only -- they
do not form a part of the HTTP/1.1 specification.
A. Internet Media Type message/http
In addition to defining the HTTP/1.1 protocol, this document serves
as the specification for the Internet media type "message/http".
The following is to be registered with IANA [17].
Media Type name: message
Media subtype name: http
Required parameters: none
Optional parameters: version, msgtype
version: The HTTP-Version number of the enclosed message
(e.g., "1.1"). If not present, the version can be
determined from the first line of the body.
msgtype: The message type -- "request" or "response". If
not present, the type can be determined from the
first line of the body.
Encoding considerations: only "7bit", "8bit", or "binary" are
permitted
Security considerations: none
B. Tolerant Applications
Although this document specifies the requirements for the
generation of HTTP/1.1 messages, not all applications will be
correct in their implementation. We therefore recommend that
operational applications be tolerant of deviations whenever those
deviations can be interpreted unambiguously.
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.
C. Relationship to MIME
HTTP/1.1 reuses many of the constructs defined for Internet Mail
(RFC 822 [9]) and the Multipurpose Internet Mail Extensions
(MIME [7]) to allow entities to be transmitted in an open variety
of representations and with extensible mechanisms. However, HTTP is
not a MIME-compliant application. HTTP's performance requirements
differ substantially from those of Internet mail. Since it is not
limited by the restrictions of existing mail protocols and SMTP
gateways, HTTP does not obey some of the constraints imposed by
RFC 822 and MIME for mail transport.
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.
C.1 Conversion to Canonical Form
MIME requires that an entity be converted to canonical form prior
to being transferred, as described in Appendix G of RFC 1521 [7].
Although HTTP does require media types to be transferred in
canonical form, it changes the definition of "canonical form" for
text-based media types as described in Section 3.7.1.
C.1.1 Representation of Line Breaks
MIME requires that the canonical form of any text type represent
line breaks as CRLF and forbids the use of CR or LF outside of line
break sequences. Since HTTP allows CRLF, bare CR, and bare LF (or
the octet sequence(s) to which they would be translated for the
given character set) to indicate a line break within text content,
recipients of an HTTP message cannot rely upon receiving
MIME-canonical line breaks in text.
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.
C.1.2 Default Character Set
MIME requires that all subtypes of the top-level Content-Type
"text" have a default character set of US-ASCII [21]. In contrast,
HTTP defines the default character set for "text" to be
ISO-8859-1 [22] (a superset of US-ASCII). Therefore, if a text/*
media type given in the Content-Type header field does not already
include an explicit charset parameter, the parameter
;charset="iso-8859-1"
should be added by the proxy/gateway if the entity contains any
octets greater than 127.
C.2 Conversion of Date Formats
HTTP/1.1 uses a restricted subset of date formats to simplify the
process of date comparison. Proxies/gateways from other protocols
should ensure that any Date header field present in a message
conforms to one of the HTTP/1.1 formats and rewrite the date if
necessary.
C.3 Introduction of Content-Encoding
MIME does not include any concept equivalent to HTTP's
Content-Encoding header field. Since this acts as a modifier on the
media type, proxies/gateways to MIME-compliant protocols must
either change the value of the Content-Type header field or decode
the Entity-Body before forwarding the message.
Note: Some experimental applications of Content-Type for
Internet mail have used a media-type parameter of
";conversions=<content-coding>" to perform an equivalent
function as Content-Encoding. However, this parameter is not
part of the MIME specification at the time of this writing.
C.4 No Content-Transfer-Encoding
HTTP does not use the Content-Transfer-Encoding (CTE) field of
MIME. Proxies/gateways from MIME-compliant protocols must remove
any non-identity CTE ("quoted-printable" or "base64") encoding
prior to delivering the response message to an HTTP client.
Proxies/gateways to MIME-compliant protocols are responsible for
ensuring that the message is in the correct format and encoding for
safe transport on that protocol, where "safe transport" is defined
by the limitations of the protocol being used. At a minimum, the
CTE field of
Content-Transfer-Encoding: binary
should be added by the proxy/gateway if it is unwilling to apply a
content transfer encoding.
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.
C.5 Introduction of Transfer-Encoding
HTTP/1.1 introduces the Transfer-Encoding header field
(Section 10.39). Proxies/gateways must remove any transfer coding
prior to forwarding a message via a MIME-compliant protocol. The
process for decoding the "chunked" transfer coding (Section 3.6)
can be represented in pseudo-code as:
length := 0
read chunk-size and CRLF
while (chunk-size > 0) {
read chunk-data and CRLF
append chunk-data to Entity-Body
length := length + chunk-size
read chunk-size and CRLF
}
read entity-header
while (entity-header not empty) {
append entity-header to existing header fields
read entity-header
}
Content-Length := length
Remove "chunked" from Transfer-Encoding
D. Changes from HTTP/1.0
This section will summarize the differences between versions 1.0
and 1.1 of the Hypertext Transfer Protocol.
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