One document matched: draft-ietf-http-v10-spec-00.txt
Hypertext Transfer Protocol -- HTTP/1.0
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Abstract
The Hypertext Transfer Protocol (HTTP) is an application-level
protocol with the lightness and speed necessary 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 reflects preferred usage
of the protocol referred to as "HTTP/1.0", and is compatible with
the most commonly used HTTP server and client programs implemented
prior to November 1994.
Table of Contents
1. Introduction
1.1 Purpose
1.2 Overall Operation
1.3 Terminology
2. Notational Conventions and Generic Grammar
2.1 Augmented BNF
2.2 Basic Rules
3. Protocol Parameters
3.1 HTTP Version
3.2 Universal Resource Identifiers
3.3 Date/Time Formats
3.3.1 Full Date
3.3.2 Delta Seconds
4. HTTP Message
4.1 Message Types
4.2 Message Headers
4.3 General Message Header Fields
4.3.1 Date
4.3.2 Forwarded
4.3.3 Message-ID
4.3.4 MIME-Version
5. Request
5.1 Request-Line
5.2 Method
5.2.1 GET
5.2.2 HEAD
5.2.3 POST
5.2.4 PUT
5.2.5 DELETE
5.2.6 LINK
5.2.7 UNLINK
5.3 Request-URI
5.4 Request Header Fields
5.4.1 Accept
5.4.2 Accept-Charset
5.4.3 Accept-Encoding
5.4.4 Accept-Language
5.4.5 Authorization
5.4.6 From
5.4.7 If-Modified-Since
5.4.8 Pragma
5.4.9 Referer
5.4.10 User-Agent
6. Response
6.1 Status-Line
6.2 Status Codes and Reason Phrases
6.2.1 Successful 2xx
6.2.2 Redirection 3xx
6.2.3 Client Error 4xx
6.2.4 Server Errors 5xx
6.3 Response Header Fields
6.3.1 Public
6.3.2 Retry-After
6.3.3 Server
6.3.4 WWW-Authenticate
7. Entity
7.1 Entity Header Fields
7.1.1 Allow
7.1.2 Content-Encoding
7.1.3 Content-Language
7.1.4 Content-Length
7.1.5 Content-Transfer-Encoding
7.1.6 Content-Type
7.1.7 Derived-From
7.1.8 Expires
7.1.9 Last-Modified
7.1.10 Link
7.1.11 Location
7.1.12 Title
7.1.13 URI
7.1.14 Version
7.2 Entity Body
7.2.1 Type
7.2.2 Length
8. Content Parameters
8.1 Media Types
8.1.1 Canonicalization and Text Defaults
8.1.2 Multipart Types
8.2 Language Tags
8.3 Character Sets
8.4 Encoding Mechanisms
8.5 Transfer Encodings
9. Content Negotiation
10. Access Authentication
10.1 Basic Authentication Scheme
11. Security Considerations
11.1 Authentication of Clients
11.2 Idempotent Methods
11.3 Abuse of Server Log Information
12. Acknowledgments
13. References
14. Authors' Addresses
Appendix A. Internet Media Type message/http
Appendix B. Minimum Compliance
B.1 Servers
Appendix C. Tolerant Applications
C.1 Request-Line, Status-Line, and Header Fields
Appendix D. Relationship to MIME
D.1 Conversion to Canonical Form
D.1.1 Representation of Line Breaks
D.1.2 Default Character Set
D.2 Default Content-Transfer-Encoding
D.3 Introduction of Content-Encoding
Appendix E. Example of Version Control
1. Introduction
1.1 Purpose
The Hypertext Transfer Protocol (HTTP) is an application-level
protocol with the lightness and speed necessary for distributed,
collaborative, hypermedia information systems. HTTP has been in use
by the World-Wide Web global information initiative since 1990.
This specification reflects preferred usage of the protocol
referred to as "HTTP/1.0". This specification does not necessarily
reflect the "current practice" of any single HTTP server or client
implementation. It does, however, seek to remain compatible with
existing implementations wherever possible, and should be
considered the reference for future implementations of HTTP/1.0.
Practical information systems require more functionality than
simple retrieval, including search, front-end update, and
annotation. HTTP/1.0 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 Universal Resource Identifier
(URI) [3], as a location (URL) [5] or name (URN), 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 [8] and
the Multipurpose Internet Mail Extensions (MIME) [6].
HTTP/1.0 is also used for communication between user agents and
various gateways, allowing hypermedia access to existing Internet
protocols like SMTP [14], NNTP [12], FTP [16], Gopher [2], and
WAIS [9]. HTTP/1.0 is designed to allow such gateways, via proxy
servers, without any loss of the data conveyed by those earlier
protocols.
1.2 Overall Operation
The HTTP protocol is based on a request/response paradigm. A
requesting program (termed a client) establishes a connection with
a receiving program (termed 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 its protocol version and a success or
error code), followed by a MIME-like message containing server
information, entity metainformation, and possible body content. It
should be noted that a given program may be capable of being both a
client and a server; our use of those terms refers only to the role
being performed by the program during a particular connection,
rather than to the program's purpose in general.
On the Internet, the communication generally takes place over a
TCP/IP connection. The default port is TCP 80 [17], but other ports
can be used. This does not preclude the HTTP/1.0 protocol from
being implemented on top of any other protocol on the Internet, or
on other networks. The mapping of the HTTP/1.0 request and response
structures onto the transport data units of the protocol in
question is outside the scope of this specification.
For most implementations, the connection is established by the
client prior to each 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.
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 virtual circuit established between two parties for the
purpose of communication.
message
A structured sequence of octets transmitted via the connection
as the basic component of communication.
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.
entity
A particular representation or rendition of a 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
A program that establishes connections for the purpose of
sending requests.
user agent
The client program which is closest to the user and which
initiates requests at their behest.
server
A 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 forwarding requests. Proxies are often used
to act as a portal through a network firewall. A proxy server
accepts requests from other clients and services them either
internally or by passing them (with possible translation) on to
other servers. A caching proxy is a proxy server with a local
cache of server responses -- some requested resources can be
serviced from the cache rather than from the origin server. Some
proxy servers also act as origin servers.
gateway
A proxy which services HTTP requests by translation into
protocols other than HTTP. The reply sent from the remote server
to the gateway is likewise translated into HTTP before being
forwarded to the user agent.
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 [8]. 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, HTAB, 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, zero or more linear whitespace
(LWS) can be included between any two words (token or
quoted-string) without changing the interpretation of a field.
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 character set is
defined by [18].
OCTET = <any 8-bit character>
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)>
HTAB = <US-ASCII HT, horizontal-tab (9)>
<"> = <US-ASCII double-quote mark>
HTTP/1.0 defines the octet sequence CR LF as the end-of-line marker
for all protocol elements except the Entity-Body (see Appendix C
for tolerant applications). The end-of-line marker for an
Entity-Body is defined by its associated media type, as described
in Section 8.1.
CRLF = CR LF
HTTP/1.0 headers can be folded onto multiple lines if the
continuation lines begin with linear whitespace characters. All
linear whitespace (including folding) has the same semantics as SP.
LWS = [CRLF] 1*( SP | HTAB )
Many HTTP/1.0 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 | HTAB
A string of text is parsed as a single word if it is quoted using
double-quote marks or angle brackets.
quoted-string = ( <"> *(qdtext) <"> )
| ( "<" *(qatext) ">" )
qdtext = <any CHAR except <"> and CTLs,
but including LWS>
qatext = <any CHAR except "<", ">", and CTLs,
but including LWS>
The text rule is only used for descriptive field contents. Words of
*text may contain characters from character sets other than
US-ASCII only when encoded according to the rules of RFC 1522 [13].
text = <any OCTET except CTLs,
but including LWS>
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.
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 zeroes should be ignored by
recipients and never generated by senders.
This document defines both the 0.9 and 1.0 versions of the HTTP
protocol. Applications sending Full-Request or Full-Response
messages, as defined by this specification, must include an
HTTP-Version of "HTTP/1.0".
HTTP servers are required to be able to recognize the format of the
Request-Line for all lower-version requests, understand requests
with a format within one major number of their native version (i.e.
<major1> and <major>), and respond appropriately with a message
within the same <major> protocol number (even if the response is
simply an error message). HTTP clients are required to be able to
recognize the format of the Status-Line for all lower-version
responses and understand responses with a format within one major
number of their request version. The following hypothetical example
illustrates the required behavior.
o A valid HTTP/3.5 request is received and the server's native
protocol version is
o Less than 3.0: it should attempt to understand the request
and respond (possibly with an error) in its native format;
o Major number of 3: It should understand the request and
respond in its native format;
o Major number of 4: It should understand the request and
respond with a version 3 message;
o Major number higher than 4: It should attempt to understand
the request and respond (possibly with an error) with a
version 3 message;
o User agent receives a response to an HTTP/3.5 request, and the
response version is
o Less than 2.0: It should attempt to understand the response
and unobtrusively warn the user of the version mismatch;
o 2.0--3.4: It should understand the response and be aware
that its request may not have been fully understood by the
server;
o 3.5 or higher 3: It should understand the response and can
assume that the server understood all aspects of the request
if the response does not indicate an error;
o 4.0 or higher: It should attempt to understand the response
and unobtrusively warn the user of the version mismatch.
Proxies must be careful in forwarding requests that are received in
a format different than that of the proxy's native version. Since
the protocol version indicates the protocol capability of the
sender, a proxy 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 must either downgrade the request
version or respond with an error. Requests with a version lower
than that of the proxy's native format may be upgraded by the proxy
before being forwarded; the proxy's response to that request must
follow the normal server requirements.
3.2 Universal Resource Identifiers
This section is To-Be-Specified. It will contain a brief
description of URIs as defined by RFC 1630, including mention of
the allowed characters and the hex encoding, and provide a full
definition of the http URL scheme.
URI = <As defined in RFC 1630>
All URI protocol elements must be encoded using the escaping scheme
described in RFC 1630 [3].
3.3 Date/Time Formats
3.3.1 Full Date
HTTP/1.0 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 [7]
(an update to RFC 822 [8]). The second format is in common use, but
is based on the obsolete RFC 850 [11] date format and lacks a four-
digit year. HTTP/1.0 clients and servers must accept all three
formats, though they should never generate the third (asctime)
format. Future clients and servers must only generate the RFC 1123
format for representing date/time stamps in HTTP/1.0 requests and
responses.
All HTTP/1.0 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"
Comments and/or extra LWS are not permitted inside an HTTP-date
value generated by a conformant application. However, recipients of
date values should 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 gateways to SMTP or NNTP).
Note: HTTP/1.0 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
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/1.0 messages
| Full-Response
Full-Request and Full-Response use the generic message format of
RFC 822 [8] for transferring entities. Both messages may include
optional header fields (a.k.a. "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 5.4
| 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 6.3
| 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 5.4), Response-Header (Section 6.3), and
Entity-Header (Section 7.1) fields, follow the same generic format
as that given in Section 3.1 of RFC 822 [8]. Each header field
consists of a name followed by a colon (":") and the field value.
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 LWS.
HTTP-header = field-name ":" [ field-value ] CRLF
field-name = 1*<any CHAR, excluding CTLs, SP, and ":">
field-value = *( field-content | comment | 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 considered "good practice" to send General-Header
fields first, followed by Request-Header or Response-Header fields
prior to the Entity-Header fields. Comments can be included in HTTP
header fields by surrounding the comment text with parentheses.
comment = "(" *( ctext | comment ) ")"
ctext = <any text excluding "(" and ")">
Note: Use of comments within HTTP headers is generally
discouraged, since they are rarely seen by human eyes and
hence only increase network traffic. However, they may be
useful for messages posted or retrieved via NNTP and SMTP
gateways.
4.3 General Message 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
communicating parties or the entity being transferred. Although
none of the General-Header fields are required, they are all
strongly recommended where their use is appropriate, and should be
understood by all future HTTP/1.0 clients and servers. These
headers apply only to the message being transmitted.
General-Header = Date
| Forwarded
| Message-ID
| MIME-Version
| extension-header
Although additional general header fields may be implemented via
the extension mechanism, applications which do not recognize those
fields should treat them as Entity-Header fields.
4.3.1 Date
The Date header 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 default 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
receiver if and only if the message will be cached by that receiver
or gatewayed via a protocol which requires a Date.
Only one Date header field is allowed per message. In theory, the
date should represent the moment just before the status/request-
line is generated (i.e. the time at which the originator made the
determination of what the request/response should be). 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.
4.3.2 Forwarded
The Forwarded header is to be used by 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 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 that has forwarded the message. It is strongly
recommended that proxies 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.
4.3.3 Message-ID
The Message-ID field in HTTP is identical to that used by Internet
Mail and USENET messages, as defined in [11]. That is, it gives the
message a single, unique identifier which can be used for
identifying the message (not its contents) for "much longer" than
the expected lifetime of that message.
Message-ID = "Message-ID" ":" "<" addr-spec ">"
addr-spec = <as defined in RFC 822 [8]>
Although it is not required, the addr-spec format typically used
within a Message-ID consists of a string that is unique at the
originator's machine, followed by the required "@" character and
the fully-qualified domain name of that machine. An example is
Message-ID: <9411151630.4256@info.cern.ch>
which is composed using the time, date and process-ID on the host
info.cern.ch. However, this is only one of many possible methods
for generating a unique Message-ID and recipients of a message
should consider the entire value opaque.
The Message-ID field is normally not generated by HTTP applications
and is never required. It should only be generated by a gateway
application when the message is being posted to some other protocol
that desires a Message-ID. HTTP responses should only include a
Message-ID header field when the entity being transferred already
has one assigned to it (as in the case of resources that were
originally posted via Internet Mail or USENET).
4.3.4 MIME-Version
HTTP is not a MIME-conformant protocol. However, HTTP/1.0 messages
may include a single MIME-Version header field to indicate what
version of the MIME protocol was used to construct the message. Use
of the MIME-Version header field should indicate that the message
is in full compliance with the MIME protocol (as defined in [6]).
Unfortunately, current versions of HTTP/1.0 clients and servers use
this field indiscriminately, and thus receivers must not take it
for granted that the message is indeed in full compliance with
MIME. Gateways are responsible for ensuring this compliance (where
possible) when exporting HTTP messages to strict MIME environments.
Future HTTP/1.0 applications must only use MIME-Version when the
message is intended to be MIME-conformant.
MIME-Version = "MIME-Version" ":" 1*DIGIT "." 1*DIGIT
MIME version "1.0" is the default for use in HTTP/1.0. However,
HTTP/1.0 message parsing and semantics are defined by this document
and not the MIME specification.
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 requested, 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 5.4
| Entity-Header ) ; Section 7.1
CRLF
[ Entity-Body ] ; Section 7.2
If an HTTP/1.0 server receives a Simple-Request, it must respond
with an HTTP/0.9 Simple-Response. An HTTP/1.0 client capable of
receiving a Full-Response should 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.
5.2 Method
The Method token indicates the method to be performed on the
resource identified by the Request-URI. The method is case-
sensitive and extensible.
Method = "GET" | "HEAD" | "PUT" | "POST"
| "DELETE" | "LINK" | "UNLINK"
| extension-method
extension-method = token
The list of methods acceptable by a specific resource can be
specified in an "Allow" Entity-Header (Section 7.1.1). 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 unknown or not implemented by the server.
The set of common methods for HTTP/1.0 is described below. Although
this set can be easily expanded, additional methods cannot be
assumed to share the same semantics for separately extended clients
and servers. In order to maintain compatibility, the semantic
definition for extension methods should be registered with the
IANA [17].
5.2.1 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 changes 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. 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.
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 the If-Modified-
Since date, the server shall return a "304 Not Modified"
response.
The conditional GET method is intended to reduce network usage by
allowing cached entities to be refreshed without requiring multiple
requests or transferring unnecessary data.
5.2.2 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.
There is no "conditional HEAD" requests analogous to the
conditional GET. If an If-Modified-Since header field is included
with a HEAD request, it should be ignored.
5.2.3 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 (usually a form) 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 considered to be 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.
The client can suggest a URI for identifying the new resource by
including a URI-header field in the request. However, the server
should treat that URI as advisory only and may store the entity
under a different URI 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 7.1.10. 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 the allocated URI, all
applicable Link header fields, and an entity (preferably of type
"text/html") which describes the status of the request and refers
to the new resource.
5.2.4 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 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, the "200 OK" response 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.
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 requestor of a
PUT knows what URI is intended and the receiver must not attempt to
apply the request to some other resource. If the receiver desires
that the request be applied to a different URI, it must send a
"301 Moved Permanently" response; the requestor may then make its
own decision regarding whether or not to redirect the request.
The client can create or modify relationships between the enclosed
entity and other existing resources by including Link header
fields, as described in Section 7.1.10. 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, the
Version and Derived-From header fields should be used to help
identify and control revisions to a resource.
5.2.5 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).
5.2.6 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 result in the creation of new resources.
5.2.7 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.
5.3 Request-URI
The Request-URI is a Universal Resource Identifier (Section 3.2)
and identifies the resource upon which to apply the request.
Request-URI = URI
Unless the server is being used as a proxy, a partial URI shall be
given with the assumptions of the scheme (http) and hostname:port
(the server's address) being obvious. That is, if the full URI
looks like
http://info.cern.ch/hypertext/WWW/TheProject.html
then the corresponding partial URI in the Simple-Request or
Full-Request is
/hypertext/WWW/TheProject.html
If the client is sending the request through a proxy, the absolute
form of the URI (including scheme and server address) must be used.
A proxy must be able to recognize all of its server names,
including any aliases, local variations, and the numeric IP address.
5.4 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. All header fields are optional and conform to the generic
HTTP-header syntax.
Request-Header = Accept
| Accept-Charset
| Accept-Encoding
| Accept-Language
| Authorization
| From
| If-Modified-Since
| Pragma
| Referer
| User-Agent
| extension-header
Although additional request header fields may be implemented via
the extension mechanism, applications which do not recognize those
fields should treat them as Entity-Header fields.
5.4.1 Accept
The Accept 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), to indicate qualitative preferences
for specific media types, or to indicate acceptance of unusual
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" ":" 1#(
media-range
[ ";" "q" "=" ( "0" | "1" | float ) ]
[ ";" "mxb" "=" 1*DIGIT ] )
media-range = ( "*/*"
| ( type "/" "*" )
| ( type "/" subtype )
) *( ";" parameter )
float = < ANSI-C floating point text representation,
where (0.0 < float < 1.0) >
The parameter q is used to indicate the quality factor, which
represents the user's preference for that range of media types, and
the parameter mxb gives the maximum acceptable size of the Entity-
Body (in decimal number of octets) for that range of media types.
Section 9 describes the content negotiation algorithm which makes
use of these values. If at least one Accept header is present, a
quality factor of 0 is equivalent to not sending an Accept header
field containing that media-type or set of media-types. The default
values are: q=1 and mxb=undefined (i.e. infinity).
The example
Accept: audio/*; q=0.2, audio/basic
should verbally be interpreted as "if you have audio/basic, send
it; otherwise send me any audio type."
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: */*
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
Entity-Body in text/x-dvi if the entity is less than 100000 bytes,
otherwise send text/plain".
Note: In earlier versions of this document, the mxs
parameter defined the maximum acceptable delay in seconds
before the response would arrive. This has been removed as
the server has no means of obtaining a useful reference
value. However, this does not prevent the client from
internally measuring the response time and optimizing the
Accept header field accordingly.
It must be emphasized that this field should only be used when it
is necessary to restrict the response media types to a subset of
those possible, to indicate the acceptance of unusual media types,
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 "*/*" and the list of unusual types. Whether or not a particular
media type is deemed "unusual" should be a configurable aspect of
the user agent.
5.4.2 Accept-Charset
The Accept-Charset header field can be used to indicate a list of
preferred character sets other than the default US-ASCII and
ISO-8859-1. 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.
Accept-Charset = "Accept-Charset" ":" 1#charset
Character set values are described in Section 8.3. An example is
Accept-Charset: iso-8859-5, unicode-1-1
The value of this field should not include "US-ASCII" or
"ISO-8859-1", since those values are always assumed by default. If
a resource is only available in a character set other than the
defaults, and that character set is not listed in the Accept-
Charset field, it is only acceptable for the server to send the
entity if the character set can be identified by an appropriate
charset parameter on the media type or within the format of the
media type itself.
Note: User agents are not required to be able to render the
characters associated with the ISO-8859-1 character set.
However, they must be able to interpret their meaning to
whatever extent is required to properly handle messages in
that character set..
5.4.3 Accept-Encoding
The Accept-Encoding header field is similar to Accept, but lists
the encoding-mechanisms and transfer-encoding values which are
acceptable in the response.
Accept-Encoding = "Accept-Encoding" ":"
1#( encoding-mechanism | transfer-encoding )
An example of its use is
Accept-Encoding: compress, base64, gzip, quoted-printable
The field value should never include the identity transfer-encoding
values ("7bit", "8bit", and "binary") since they actually represent
"no encoding." If no Accept-Encoding field is present in a request,
it must be assumed that the client does not accept any encoding-
mechanism and only the identity transfer-encodings.
5.4.4 Accept-Language
The Accept-Language header field is similar to Accept, but lists
the set of natural languages that are preferred as a response to
the request.
Accept-Language = "Accept-Language" ":" 1#language-tag
The language-tag is described in Section 8.2. Languages are listed
in the order of their preference to the user. For example,
Accept-Language: dk, en-gb
would mean: "Send me a Danish version if you have it; else a
British English version."
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.
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.
5.4.5 Authorization
A user agent that wishes to authenticate itself with a server
(usually, but not necessarily, after receiving a "401 Unauthorized"
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.
Authorization = "Authorization" ":" credentials
HTTP access authentication is described in Section 10. If a request
is authenticated and a realm specified, the same credentials should
be valid for all other requests within this realm.
5.4.6 From
The From 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 addr-spec in
RFC 822:
From = "From" ":" addr-spec
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 does not have to
correspond to the Internet host which issued the request. (For
example, when a request is passed through a proxy, then the
original issuer's address should be used). The address should, if
possible, be a valid Internet e-mail address, whether or not it is
in fact an Internet e-mail address or the Internet e-mail
representation of an address on some other mail system.
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.
5.4.7 If-Modified-Since
The If-Modified-Since 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
The purpose of this feature is to allow efficient updates of local
cache information with a minimum amount of transaction overhead.
The same functionality can be obtained, though with much greater
overhead, by issuing a HEAD request and following it with a GET
request if the server indicates that the entity has been modified.
5.4.8 Pragma
The Pragma header field is used to specify directives that must be
applied to all servers along the request chain (where relevant).
The directives typically specify behavior that prevents
intermediate proxies from changing the nature of the request.
Although multiple pragma directives can be listed as part of the
request, HTTP/1.0 only defines semantics for the
"no-cache" directive.
Pragma = "Pragma" ":" 1#pragma-directive
pragma-directive = "no-cache" | extension-pragma
extension-pragma = token
When the "no-cache" directive is present, a caching proxy must
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 has become
corrupted or is known to be stale.
Pragmas must be passed through by a proxy even when they have
significance to that proxy. This is necessary in cases when the
request has to go through many proxies, and the pragma may affect
all of them. It is not possible to specify a pragma for a specific
proxy; however, any pragma-directive not relevant to a gateway or
proxy should be ignored.
5.4.9 Referer
The Referer field allows the client to specify, for the server's
benefit, the address (URI) of the document (or element within the
document) from which the Request-URI was obtained. This allows a
server to generate lists of back-links to documents, for interest,
logging, optimized caching, etc. It also allows obsolete or
mistyped links to be traced for maintenance. The format of the
field is:
Referer = "Referer" ":" URI
Example:
Referer: http://info.cern.ch/hypertext/DataSources/Overview.html
If a partial URI is given, it should be interpreted relative to the
Request-URI.
Note: Because the source of a link may be considered private
information or may reveal an otherwise secure 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.
5.4.10 User-Agent
The User-Agent 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
always include this field with requests. The field can contain
multiple tokens specifying the product name, with an optional slash
and version designator, and other products which form a significant
part of the user agent. By convention, the products are listed in
order of their significance for identifying the application.
User-Agent = "User-Agent" ":" 1*( product )
product = token ["/" product-version]
product-version = token
Example:
User-Agent: CERN-LineMode/2.15 libwww/2.17b3
Product tokens should be short and to the point -- use of this field
for advertizing or other non-essential information is explicitly
deprecated and will be considered as non-conformance to the
protocol. 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).
The User-Agent field may include additional information within
comments that are not part of the value of the field.
Note: Some current proxy applications append their product
information to the list in the User-Agent field. This is no
longer recommended, since it makes machine interpretation of
these fields ambiguous. Instead, proxies should use the
Forwarded header described in Section 4.3.2.
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 6.3
| 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/1.0 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's
"HTTP/" 1*DIGIT "." 1*DIGIT
(e.g. "HTTP/1.0"), the presence of that expression is considered
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), the likelihood of such an occurrence is negligible.
6.2 Status Codes and Reason Phrases
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 - Not used, but reserved for future use
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/1.0, 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.
Status-Code = "200" ; OK
| "201" ; Created
| "202" ; Accepted
| "203" ; Provisional Information
| "204" ; No Content
| "300" ; Multiple Choices
| "301" ; Moved Permanently
| "302" ; Moved Temporarily
| "303" ; Method
| "304" ; Not Modified
| "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
| "500" ; Internal Server Error
| "501" ; Not Implemented
| "502" ; Bad Gateway
| "503" ; Service Unavailable
| "504" ; Gateway Timeout
| extension-code
extension-code = 3DIGIT
Reason-Phrase = token *( SP token )
HTTP status codes are extensible and should be registered with the
IANA. HTTP applications are not required to understand the meaning
of all registered status codes, though such understanding is
obviously desirable. However, applications are required to
understand the class of any status code (as indicated by the first
digit) and to treat the response as being equivalent to the x00
status code of that class. For example, if an unknown status code
of 421 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 are
encouraged to present the entity returned with the response to the
user, since that entity is likely to include human-readable
information which will explain the unusual status.
Each Status-Code is described below, including a description of
which method(s) it can follow and any metainformation required in
the response.
6.2.1 Successful 2xx
This class of status codes indicates that the client's request was
successfully received, understood, and accepted.
200 OK
o Following: any method
o Required headers: none
The request has been fulfilled and an entity corresponding to the
requested resource is being sent in the response. If the HEAD
method was used, the response should only contain the Entity-Header
information and no Entity-Body.
201 Created
o Following: any method that may request a new resource
be created
o Required headers: URI-header
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 of the response. The origin server
is encouraged, but not obliged, to actually create the resource
before using this Status-Code. If the action cannot be carried out
immediately, or within a clearly defined timeframe, the server
should respond with "202 Accepted" instead.
Of the methods defined by this specification, only PUT and POST can
create a resource.
202 Accepted
o Following: any method
o Required headers: none
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 Accepted" 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 enacted.
203 Provisional Information
o Following: GET, HEAD
o Required headers: none
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.
204 No Content
o Following: any method
o Required headers: none
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. This response is primarily intended
to allow input for scripts or other actions to take place without
causing a change to the user agent's current document view.
6.2.2 Redirection 3xx
This class of status code indicates that further action needs to be
taken by the client in order to fulfill the request. The action
required can sometimes be carried out by the client without
interaction with the user, but it is strongly recommended that this
only takes place if the method used in the request is idempotent
(GET or HEAD).
300 Multiple Choices
o Following: any method
o Required headers: none
The requested resource is available at one or more locations and a
preferred location could not be determined via content negotiation.
Unless it was a HEAD request, the response must include an entity
containing a formatted list of resource characteristics and
locations from which the 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.
301 Moved Permanently
o Following: any method
o Required headers: URI-header, Location
The requested resource has been assigned a new permanent URI and
any future references to this resource must be done using the
returned URI. Clients with link editing capabilities are encouraged
to automatically relink references to the Request-URI to the new
reference returned by the server, where possible.
It is possible for the server to send this status code in response
to a request using the PUT, POST, or DELETE methods. However, as
this might change the conditions under which the request was
issued, the user agent must not automatically redirect the request
unless it can be confirmed by the user.
302 Moved Temporarily
o Following: any method
o Required headers: URI-header, Location
The requested resource resides temporarily under a different URI.
Since the redirection may be altered on occasion, the client should
on future requests from the user continue to use the original
Request-URI and not the URI returned in the URI-header field and
Location fields.
It is possible for the server to send this status code in response
to a request using the PUT, POST, or DELETE methods. However, as
this might change the conditions under which the request was
issued, the user agent must not automatically redirect the request
unless it can be confirmed by the user.
303 Method
This code is obsolete.
304 Not Modified
o Following: conditional GET
o Required headers: none
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 shall
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 and which may have
changed independently of the entity's Last-Modified date. Examples
of relevant header fields include: Date, Server, and Expires.
6.2.3 Client Error 4xx
The 4xx class of status codes 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 is encouraged to 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.
400 Bad Request
The request had bad syntax or was inherently impossible to be
satisfied. The client is discouraged from repeating the request
without modifications.
401 Unauthorized
o Required headers: WWW-Authenticate
The request requires user authentication. The response must include
a WWW-Authenticate header field (Section 6.3.4) containing a
challenge applicable to the requested resource. The client may
repeat the request with a suitable Authorization header field.
HTTP access authentication is explained in Section 10.
402 Payment Required
This code is not currently supported, but is reserved for future
use.
403 Forbidden
The request is forbidden because of some reason that remains
unknown to the client. Authorization will not help and the request
should not be repeated. This status code can be used if the server
does not want to make public why the request cannot be fulfilled.
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 method) that an
old resource is permanently unavailable and has no forwarding
address.
405 Method Not Allowed
o Required headers: Allow
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 method's for the
requested resource.
406 None Acceptable
o Required headers: Content-*, where applicable to the Request-URI
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. The response must include (when
applicable) the Content-Type, Content-Encoding, and Content-
Language of the resource, and is encouraged to include the
resource's complete metainformation. No Entity-Body can be included
in the response.
407 Proxy Authentication Required
This code is reserved for future use. It is similar to
"401 Unauthorized", but indicates that the client must first
authenticate itself with the proxy. HTTP/1.0 does not provide a
means for proxy authentication -- this feature will be available in
future versions.
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 request. If
versioning is being used and the entity being PUT includes changes
to a resource which conflict with those made by an earlier (third-
party) request, the server may use the "409 Conflict" response to
indicate that it can't complete the PUT. In this case, the response
entity may contain a list of the differences between the two
versions.
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 are encouraged to
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" can
be used instead.
The "410 Gone" 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.
6.2.4 Server Errors 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 is encouraged to 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 received an invalid response from the gateway or
upstream server it accessed in attempting to complete 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 a "500 Internal
Server Error".
Note: The presence 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 did not receive a timely response from the gateway or
upstream server it accessed in attempting to complete the request.
6.3 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 the server
itself.
Response-Header= Public
| Retry-After
| Server
| WWW-Authenticate
| extension-header
Although additional response header fields may be implemented via
the extension mechanism, applications which do not recognize those
fields should treat them as Entity-Header fields.
6.3.1 Public
The Public 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 7.1.1) 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/1.0 in Section
5.2.
Public = "Public" ":" 1#method
Example of use:
Public: OPTIONS, MGET, MHEAD
This header field applies only to the current connection. 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.
6.3.2 Retry-After
The Retry-After header field can be used with "503 Service
Unavailable" to indicate how long the service is expected to be
unavailable to the requesting client. The value of this field can
be either an full 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.
6.3.3 Server
The Server header field contains information about the software
being used by the origin server program handling the request. The
field is analogous to the User-Agent field and has the following
format:
Server = "Server" ":" 1*( product )
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 4.3.2.
6.3.4 WWW-Authenticate
The WWW-Authenticate header field must be included as part of a
"401 Unauthorized" response. The field value consists of a
challenge that indicates the authentication scheme and parameters
applicable to the Request-URI.
WWW-Authenticate = "WWW-Authenticate" ":" challenge
The HTTP access authentication process is described in Section 10.
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
This section specifies the format and semantics of the 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
| Content-Encoding
| Content-Language
| Content-Length
| Content-Transfer-Encoding
| Content-Type
| Derived-From
| Expires
| Last-Modified
| Link
| Location
| Title
| URI-header
| Version
| extension-header
extension-header = HTTP-header
Each entity header field is explained in the subsections below.
Other header fields are allowed but cannot be assumed to be
recognizable by the recipient. Unknown header fields should be
ignored by the recipient and forwarded by proxies.
Note: It has been proposed that any HTML metainformation
element (allowed within the <HEAD> element of a document) be
a valid candidate for an HTTP entity header. This document
defines two header fields, Link and Title, which are both
examples of this. Base will be used in future versions of
HTTP.
7.1.1 Allow
The Allow 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; it must be present in a response with status
code "405 Method Not Allowed".
Allow = "Allow" ":" 1#method
Example of use:
Allow: GET, HEAD, PUT
This does not prevent a client from trying other methods. However,
it is recommended that the indications given by this field be
followed. This field has no default value; if left undefined, the
set of allowed methods is defined by the origin server at the time
of each request.
If a response passes through a proxy which does not understand one
or more of the methods indicated in the Allow header, the proxy
must not modify the Allow header; the user agent may have other
means of communicating with the origin server.
7.1.2 Content-Encoding
The Content-Encoding header field is used as a modifier to the
media-type. When present, its value indicates what additional
encoding mechanism has been applied to the resource, and thus what
decoding mechanism must be applied in order to obtain the media-
type referenced by the Content-Type header field. The 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" ":" encoding-mechanism
Encoding mechanisms are defined in Section 8.4. 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.
7.1.3 Content-Language
The Content-Language 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 8.2. 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
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 audience. In this case, the Content-Language should
only include "en".
Content-Language may be applied to any media type -- it should not
be considered limited to textual documents.
7.1.4 Content-Length
The Content-Length 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
Although it is not required, applications are strongly encouraged
to use this field to indicate the size of the Entity-Body to be
transferred, regardless of the media type of the entity.
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.
7.1.5 Content-Transfer-Encoding
The Content-Transfer-Encoding (CTE) header indicates what (if any)
type of transformation has been applied to the entity in order to
safely transfer it between the sender and the recipient. This
differs from the Content-Encoding in that the CTE is a property of
the message, not of the original resource.
Content-Transfer-Encoding
= "Content-Transfer-Encoding" ":" transfer-encoding
Transfer encodings are defined in Section 8.5. Because all HTTP
transactions take place on an 8-bit clean connection, the default
Content-Transfer-Encoding for all messages is binary. However, HTTP
may be used to transfer MIME messages which already have a defined
CTE. An example is:
Content-Transfer-Encoding: quoted-printable
Many older HTTP/1.0 applications do not understand the Content-
Transfer-Encoding header. However, since it may appear in any MIME
message (i.e. entities retrieved via a gateway to a MIME-conformant
protocol), future HTTP/1.0 applications are required to understand
it upon receipt. Gateways are the only HTTP applications that would
generate a CTE.
7.1.6 Content-Type
The Content-Type 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 8.1. An example of the field is
Content-Type: text/html; charset=ISO-8859-4
The Content-Type header field has no default value. Further
discussion of methods for identifying the media type of an entity
is provided in Section 7.2.1.
7.1.7 Derived-From
The Derived-From 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" ":" version-tag
An example use of the field is:
Derived-From: 2.1.1
A longer example of version control is included in Appendix C. The
Derived-From field is required for PUT requests if the entity being
put was previously retrieved from the same URI and a Version header
was included with the entity when it was last retrieved.
7.1.8 Expires
The Expires field gives the date/time after which the entity should
be considered stale. This allows information providers to suggest
the volatility of the resource. Caching clients (including proxies)
must not cache this copy of the resource beyond the date given,
unless its status has been updated by a later check of the origin
server. 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 are strongly
encouraged to 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
The Expires field has no default value. 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, copies of 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.
Note: Applications are encouraged to be tolerant of bad or
misinformed implementations of the Expires header. In
particular, recipients may wish to recognize a delta-seconds
value (any decimal integer) as representing the number of
seconds after receipt of the message that its contents
should be considered expired. Likewise, a value of zero (0)
or an invalid date format may be considered equivalent to an
"expires immediately." Although these values are not
legitimate for HTTP/1.0, a robust implementation is always
desirable.
7.1.9 Last-Modified
The Last-Modified 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 receiver
should interpret it: if the receiver 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-mod date.
For entities with dynamically included parts, it may be the most
recent of the set of last-mod dates of 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. In any case, the recipient should only know (and
care) about the result -- whatever gets stuck in the Last-Modified
field -- and not worry about how that result was obtained.
7.1.10 Link
The Link header 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 [4].
Link = "Link" ":" 1#("<" URI ">"
[ ";" "rel" "=" relation ]
[ ";" "rev" "=" relation ]
[ ";" "title" "=" quoted-string ] )
relation = sgml-name
sgml-name = ALPHA *( ALPHA | DIGIT | "." | "-" )
Relation values are not case-sensitive and may be extended within
the constraints of the sgmlname syntax. There are no predefined
link relationship values for HTTP/1.0. 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 the entity is previous to chapter2
in a logical navigation path. The second indicates that the
publisher of the resource is identified by the given e-mail address.
7.1.11 Location
The Location header field is an earlier form of the URI-header and
is considered obsolete. However, HTTP/1.0 applications should
continue to support the Location header in order to properly
interface with older applications. The purpose of Location is
identical to that of the URI-header, except that no variants can be
specified and only one absolute location URL is allowed.
Location = "Location" ":" URI
An example is
Location: http://info.cern.ch/hypertext/WWW/NewLocation.html
7.1.12 Title
The Title header field indicates the title of the entity
Title = "Title" ":" *text
An example of the field is
Title: Hypertext Transfer Protocol -- HTTP/1.0
This field is to be considered isomorphic with the <TITLE> element
in HTML [4].
7.1.13 URI
The URI-header field may contain one or more Universal Resource
Identifiers (URIs) by which the resource origin of the entity can
be identified. There is no guarantee that the resource can be
accessed using the URI(s) specified. This field is required for the
201, 301, and 302 response messages, and may be included in any
message that contains resource metainformation.
URI-header = "URI" ":" 1#( "<" URI ">" [ ";" vary ] )
vary = "vary" "=" <"> 1#vary-dimension <">
vary-dimension = "type" | "language" | "version" | "encoding"
| "charset" | "user-agent" | extension-vary
extension-vary = token
Any URI specified in this field can be either absolute or relative
to the URI given in the Request-Line. The URI-header improves upon
the Location header field described in Section 7.1.11. For
backwards compatibility with older clients, servers are encouraged
to include both header fields in 301 and 302 responses.
The URI-header may also be used by a client performing a POST
request to suggest a URI for the new entity. Whether or not the
suggested URI is used is entirely up to the server to decide. In
any case, the server's response must include the actual URI(s) of
the new resource if one is successfully created (status 201).
If a URI refers to a set of variants, then the dimensions of that
variance must be given with a vary parameter. One example is:
URI: <http://info.cern.ch/hypertext/WWW/TheProject.multi>;
vary="type,language"
which indicates that the URI covers a group of entities that vary
in media type and natural language. A request for that URI will
result in a response that depends upon the client's request headers
for Accept and Accept-Language. Similar dimensions exist for the
Accept-Encoding, Accept-Charset, Version, and User-Agent header
fields, as demonstrated in the following example.
URI: <TheProject.ps>;vary="encoding,version",
<TheProject.html>;vary="user-agent,charset,version"
The vary parameter has an important effect on cache management,
particularly for caching proxies which service a diverse set of
user agents. Since the response to one user agent may differ from
the response to a second user agent if the two agents have
differing request profiles, a caching proxy must keep track of the
content metainformation for resources with varying dimensions.
Thus, the vary parameter tells the caching proxy what entity
headers must be part of the key for caching that URI. When the
caching proxy gets a request for that URI, it must forward the
request toward the origin server if the request profile includes a
variant dimension that has not already been cached.
7.1.14 Version
The Version field defines the version tag associated with a
rendition of an evolving entity. Together with the Derived-From
field described in Section 7.1.7, 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.
Version = "Version" ":" version-tag
version-tag = token | quoted-string
Examples of the Version field include:
Version: 2.1.2
Version: "Fred 19950116-12:26:48"
Version: 2.5a4-omega7
The version tag should be considered opaque to all parties but the
origin server. A user agent can request a particular version of an
entity by including its tag in a Version header as part of the
request. Similarly, a user agent may suggest a value for the
version of an entity transferred via a PUT or POST request.
However, only the origin server can reliably assign or increment
the version tag of an entity.
7.2 Entity Body
The entity-body (if any) sent with an HTTP/1.0 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. This specification defines two
request methods, "POST" and "PUT", that allow an entity-body. In
general, the presence of an entity-body in a request is signaled by
the inclusion of a Content-Length and/or Content-Transfer-Encoding
header field in the request message headers.
Note: Most current implementations of the POST and PUT
methods require a valid Content-Length header field. This
can cause problems for some systems that do not know the
size of the entity-body before transmission. Experimental
implementations (and future versions of HTTP) may use a
packetized Content-Transfer-Encoding to obviate the need for
a Content-Length.
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 Content header fields
may lead one to believe they should. Similarly, the responses "204
No Content", "304 Not Modified", and "406 None Acceptable" must not
include a body.
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 Content-Transfer-Encoding. These define a
three-layer, ordered encoding model:
entity-body <-
Content-Transfer-Encoding( Content-Encoding( Content-Type ) )
The default for both encodings is none (i.e., the identity
function). A Content-Type specifies the media type of the
underlying data. A Content-Encoding may be used to indicate an
additional encoding mechanism applied to the type (usually for the
purpose of data compression) that is a property of the resource
requested. A Content-Transfer-Encoding may be applied by a
transport agent to ensure safe and/or proper transfer of the
message. Note that the Content-Transfer-Encoding is a property of
the message, not of the resource.
The Content-Type header field has no default value. If and only if
the media type is not given by a Content-Type header (as is always
the case for Simple-Response messages), the receiver may attempt to
guess the media type via inspection of its content and/or the name
extension(s) of the URL used to access the resource. If the media
type remains unknown, the receiver 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 (number of octets)
represents the length of the Entity-Body. Otherwise, the body
length is determined by the Content-Type (for types with an
explicit end-of-body delimiter), the Content-Transfer-Encoding (for
packetized encodings), or the closing of the connection by the
server. Note that the latter cannot be used to indicate the end of
a request body, since it leaves no possibility for the server to
send back a response.
Note: Some older servers supply an invalid Content-Length
when sending a document that contains server-side includes
dynamically inserted into the data stream. It must be
emphasized that this will not be tolerated by future
versions of HTTP. Unless the client knows that it is
receiving a response from a compliant server, it should not
depend on the Content-Length value being correct.
8. Content Parameters
8.1 Media Types
HTTP uses Internet Media Types [15], formerly referred to as MIME
Content-Types [6], in order to provide open and extensible data
typing and type negotiation. For mail applications, where there is
no type negotiation between sender and receiver, it is reasonable
to put strict limits on the set of allowed media types. With HTTP,
however, user agents can identify acceptable media types as part of
the connection, and thus 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 not case-
sensitive. Parameter values may or may not be case-sensitive,
depending on the semantics of the parameter name. No LWS is allowed
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 [15].
All media-type's registered by IANA must be preferred over
extension tokens. However, HTTP does not limit conforming
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.
8.1.1 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 Content-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 Content-
Transfer-Encoding and/or Content-Encoding has been removed.
All other HTTP constructs use CRLF exclusively to indicate a
line break. Encoding mechanisms 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 character set ISO-8859-1 [19]
is a superset of USASCII [18], this has no effect upon the
interpretation of entity bodies which only contain octets within
the US-ASCII set (0 - 127). The presence of a charset parameter
value in a Content-Type header field overrides the default.
HTTP does not require that the character set of an entity body be
labelled as the lowest common denominator of the character codes
used within a document.
8.1.2 Multipart Types
MIME provides for a number of "multipart" types -- encapsulations of
several entities within a single message's Entity-Body. The
multipart types registered by IANA [17] do not have any special
meaning for HTTP/1.0, though user agents may need to understand
each type in order to correctly interpret the purpose of each body-
part. Ideally, an HTTP user agent should follow the same or similar
behavior as a MIME user agent does upon receipt of a multipart type.
As in MIME [6], all multipart types share a common syntax 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, multipart body-parts may contain HTTP header fields which are
significant to the meaning of that part.
A URI-header field (Section 7.1.13) should be included in the body-
part for each enclosed entity that can be identified by a URI.
8.2 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.
The HTTP/1.0 protocol uses language tags within the Accept-Language
and Content-Language 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 to be
treated as 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.
Note: Earlier versions of this document specified an
incomplete language tag, where values were limited to ISO
639 language abbreviations with an optional ISO 3166 country
code appended after an underscore ("_") or slash ("/")
character. This format was abandoned in favor of the
recently proposed standard for Internet protocols.
8.3 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.
Character sets are identified by case-insensitive tokens. The
complete set of allowed charset values are defined by the IANA
Character Set registry [17]. 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. This set of charset values
includes those registered by RFC 1521 [6] -- the US-ASCII [18] and
ISO8859 [19] character sets -- and other character set 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 character
set value, any token that has a predefined value within the IANA
Character Set registry [17] must represent the character set
defined by that registry. Applications are encouraged, but not
required, to limit their use of character sets to those defined by
the IANA registry.
8.4 Encoding Mechanisms
Encoding mechanism values are used to indicate an encoding
transformation that has been or can be applied to a resource.
Encoding mechanisms 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 with this
encoding and is only decoded before rendering or analogous usage.
encoding-mechanism = "gzip" | "compress" | token
Note: For historical reasons, HTTP/1.0 applications should
consider "x-gzip" and "x-compress" to be equivalent to
"gzip" and "compress", respectively.
All encoding-mechanism values are case-insensitive. HTTP/1.0 uses
encoding-mechanism values in the Accept-Encoding (Section 5.4.3)
and Content-Encoding (Section 7.1.2) header fields. Although the
value describes the encoding-mechanism, 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 encoding-mechanism 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).
8.5 Transfer Encodings
Transfer encoding 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. Transfer encodings are only used with entities destined
for or retrieved from MIME-conformant systems, and thus will rarely
occur in an HTTP/1.0 message. This differs from an encoding-
mechanism in that the transfer encoding is a property of the
message, not of the original resource.
transfer-encoding = "binary" | "8bit" | "7bit"
| "quoted-printable" | "base64"
| token
All transfer-encoding values are case-insensitive. HTTP/1.0 uses
transfer-encoding values in the Accept-Encoding (Section 5.4.3) and
Content-Transfer-Encoding (Section 7.1.5) header fields.
The values "7bit", "8bit", and "binary" are used to indicate that
no transfer encoding has been performed. Instead, they describe the
sort of encoding that might be needed for transmission through an
unsafe transport system. Binary indicates that the body may contain
any set of octets. 8bit adds the restrictions that CR and LF
characters only occur as part of CRLF line separators, all lines
are short (less than 1000 octets), and no NULs (octet 0) are
present. 7bit adds a further restriction that all octets are 7-bit
US-ASCII characters.
The "quoted-printable" and "base64" values indicate that the
associated encoding (as defined in MIME [6]) has been applied to
the body. These encodings consist entirely of 7-bit US-ASCII
characters.
9. Content Negotiation
Content negotiation is an optional feature of the HTTP protocol. It
is designed to allow for preemptive selection of a preferred
content representation, within a single request-response round-trip,
and without intervention from the user. However, this may not
always be desirable for the user and is sometimes unnecessary for
the content provider. Implementors are encouraged to 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. If
there are no variant forms of the resource, the "negotiation" is
limited to whether or not that single media type is acceptable
under the constraints given by the Accept request header field
(if any).
If variants are available, those variants that are completely
unacceptable should be removed from consideration first.
Unacceptable variants include those with a Content-Encoding not
listed in an Accept-Encoding field, those with a character subset
(other than the default ISO-8859-1) not listed in an Accept-Charset
field, and those with a media type not within any of the media
ranges of an explicitly constrained Accept field (or listed with a
zero quality parameter).
If no acceptable variants remain at this point, the server should
respond with a "406 None Acceptable" response message. If more than
one variant remains, and at least one has a Content-Language within
those listed by an Accept-Language field, any variants which do not
match the language constraint are removed from further
consideration.
If multiple choices still remain, the selection is further winnowed
by calculating and comparing the relative quality of the available
media types. The calculated weights are normalized to a real number
in the range 0 through 1, where 0 is the minimum and 1 the maximum
value. The following parameters are included in the calculation:
q The quality factor chosen by the user agent (and
configurable by the user) that represents the desirability
of that media type. In this case, desirability is usually a
measure of the clients ability to faithfully represent the
contents of that media type to the user. The value is in
the range [0,1], where the default value is 1.
qs The quality factor, as chosen by the server (via some
unspecified mechanism), to represent the relative quality
of a particular variant representation of the 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 has the same range and
default as q.
mxb The maximum number of bytes in the Entity-Body accepted by
the client. The default value is mxb=undefined
(i.e. infinity).
bs The actual number of bytes in the Entity-Body for a
particular source representation. This should equal the
value sent as Content-Length. The default value is 0.
The discrete mapping function is defined as:
{ if mxb=undefined, then (qs * q) }
Q(q,qs,mxb,bs) = { if mxb >= bs, then (qs * q) }
{ if mxb < bs, then 0 }
The variants with a maximal value for the Q function represent the
preferred representation(s) of the entity. If multiple
representations exist for a single media type (as would be the case
if they only varied by Content-Encoding), then the smallest
representation (lowest bs) is preferred.
Finally, there may still be multiple choices available to the user.
If so, the server may either choose one (possibly at random) from
those available and respond with "200 OK", or it may 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 (no such type is
available at the time of this writing).
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.
10. Access Authentication
HTTP provides a simple challenge-response authorization mechanism
which may be used by a server to challenge a client request and by
a client to provide authentication information. The mechanism uses
an extensible 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 = "Basic" | 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 the challenge
applicable to the requested resource.
challenge = auth-scheme 1*LWS realm [ "," 1#auth-param ]
realm = "Realm" "=" quoted-string
The realm attribute is required for all access authentication
schemes which issue a challenge. The realm value, in combination
with the root URL of the server being accessed, defines the
authorization space. These realms allow the protected resources on
a server to be partitioned into a set of authorization spaces, each
with its own authentication scheme and/or 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 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 = auth-scheme [ 1*LWS encoded-cookie ] #auth-param
encoded-cookie = 1*<any CHAR except CTLs or tspecials,
but including "=" and "/">
The domain over which credentials can be automatically applied by a
user agent is determined by the authorization space. If a request
is authenticated, the credentials can be reused for all other
requests within that authorization space for a period of time
determined by the authentication scheme, parameters, and/or user
preference.
The HTTP protocol does not restrict applications to this simple
challenge-response mechanism for access authentication. Additional
mechanisms may be used at the transport level, via message
encapsulation, and/or 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 access
authentication. That is, they must forward the WWW-Authenticate and
Authorization headers untouched. HTTP/1.0 does not provide a means
for a client to be authenticated with a proxy -- this feature will
be available in future versions of HTTP.
Note: The names Proxy-Authenticate and Proxy-Authorization
have been suggested as headers, analogous to WWW-Authenticate
and Authorization, but applying only to the immediate
connection with a proxy.
10.1 Basic Authentication Scheme
The basic authentication scheme is based on the model that the
client 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. The
server will service the request only if it can validate the user-ID
and password for the domain of the Request-URI.
basic-challenge = "Basic" SP realm
The client sends the user-ID and password (separated by a single
colon ":" character) within a base64 [6] encoded-cookie in the
credentials.
basic-credentials = "Basic" SP basic-cookie
basic-cookie = <base64 encoding of userid-password>
userid-password = [ token ] ":" *text
There are no optional authentication parameters for the basic
scheme. For example, 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 are strongly
encouraged to implement the scheme in order to communicate with
servers that use it.
11. Security Considerations
This section is meant to inform application developers, information
providers, and users of the security limitations in HTTP/1.0 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.
11.1 Authentication of Clients
As mentioned in Section 10.1, the Basic authentication scheme is
not considered to be 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/1.0 does
not prevent additional authentication schemes and encryption
mechanisms to be employed to increase security.
11.2 Idempotent Methods
The writers of client software should be aware that the software
represents the user in their interactions over the net, 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. The link "click here to subscribe"--causing the reading of a
special "magic" document--is open to abuse by others making a link
"click here to see a pretty picture." These methods should be
considered "safe" and should not have side effects. This allows the
client software to represent other methods (such as POST, PUT and
DELETE) in a special way, so that the user is aware of the fact
that an action is being requested.
11.3 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.
Two header fields are worth special mention in this context:
Referer and From. 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 have indicated
a secure document's URI, whose revelation itself would be a breach
of security.
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 active 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.
12. Acknowledgments
This specification makes heavy use of the augmented BNF and generic
constructs defined by David H. Crocker for RFC 822 [8]. Similarly,
it reuses many of the definitions provided by Nathaniel Borenstein
and Ned Freed for MIME [6]. We hope that their inclusion in this
specification will help reduce past confusion over the relationship
between HTTP/1.0 and Internet mail.
The HTTP protocol has evolved considerably over the past three
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,
Phillip M. Hallam-Baker, Haringkon W. Lie, Ari Luotonen, Rob McCool,
Dave Raggett, Tony Sanders, and Marc VanHeyningen deserve special
recognition for their efforts in defining aspects of the protocol
for early versions of this specification.
This document has benefited greatly from the comments of all those
participating in the HTTPWG. 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 Michael A. Dolan
John Franks Alex Hopmann
Bob Jernigan Martijn Koster
Dave Kristol Daniel LaLiberte
Albert Lunde John C. Mallery
Larry Masinter Mitra
Gavin Nicol Marc Salomon
Chuck Shotton Eric W. Sink
Simon E. Spero
13. References
[1] H. T. Alvestrand. "Tags for the identification of languages."
RFC 1766, UNINETT, March 1995.
[2] F. Anklesaria, M. McCahill, P. Lindner, D. Johnson, D. Torrey,
and 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 and D. Connolly. "HyperText Markup Language
Specification - 2.0." Work in Progress (draft-ietf-html-spec-
01.txt), CERN, HaL Computer Systems, February 1995.
[5] T. Berners-Lee, L. Masinter, and M. McCahill. "Uniform Resource
Locators (URL)." RFC 1738, CERN, Xerox PARC, University of
Minnesota, October 1994.
[6] N. Borenstein and 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.
[7] R. Braden. "Requirements for Internet hosts - application and
support." STD 3, RFC 1123, IETF, October 1989.
[8] D. H. Crocker. "Standard for the Format of ARPA Internet Text
Messages." STD 11, RFC 822, UDEL, August 1982.
[9] F. Davis, B. Kahle, H. Morris, J. Salem, T. Shen, R. Wang,
J. Sui, and M. Grinbaum. "WAIS Interface Protocol Prototype
Functional Specification." (v1.5), Thinking Machines
Corporation, April 1990.
[10] R. T. Fielding. "Relative Uniform Resource Locators." Work in
Progress (draft-ietf-uri-relative-url-05.txt), UC Irvine,
January 1995.
[11] M. Horton and R. Adams. "Standard for interchange of USENET
messages." RFC 1036 (Obsoletes RFC 850), AT&T Bell
Laboratories, Center for Seismic Studies, December 1987.
[12] B. Kantor and 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.
[13] K. Moore. "MIME (Multipurpose Internet Mail Extensions) Part
Two: Message Header Extensions for Non-ASCII Text." RFC 1522,
University of Tennessee, September 1993.
[14] J. Postel. "Simple Mail Transfer Protocol." STD 10, RFC 821,
USC/ISI, August 1982.
[15] J. Postel. "Media Type Registration Procedure." RFC 1590,
USC/ISI, March 1994.
[16] J. Postel and J. K. Reynolds. "File Transfer Protocol (FTP)."
STD 9, RFC 959, USC/ISI, October 1985.
[17] J. Reynolds and J. Postel. "Assigned Numbers." STD 2, RFC 1700,
USC/ISI, October 1994.
[18] US-ASCII. Coded Character Set - 7-Bit American Standard Code for
Information Interchange. Standard ANSI X3.4-1986, ANSI, 1986.
[19] 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.
14. Authors' Addresses
Tim Berners-Lee
Director, W3 Consortium
MIT Laboratory for Computer Science
545 Technology Square
Cambridge, MA 02139, U.S.A.
Tel: +1 (617) 253 9670
Fax: +1 (617) 258 8682
Email: timbl@w3.org
Roy T. Fielding
Department of Information and Computer Science
University of California
Irvine, CA 92717-3425, U.S.A.
Tel: +1 (714) 824-4049
Fax: +1 (714) 824-4056
Email: fielding@ics.uci.edu
Henrik Frystyk Nielsen
World-Wide Web Project
CERN,
1211 Geneva 23, Switzerland
Tel: +41 (22) 767 8265
Fax: +41 (22) 767 8730
Email: frystyk@w3.org
Appendices
These appendices are provided for informational reasons only -- they
do not form a part of the HTTP/1.0 specification.
A. Internet Media Type message/http
In addition to defining the HTTP/1.0 protocol, this document serves
as the specification for the Internet media type "message/http".
The following is to be registered with IANA [15].
Media Type name: message
Media subtype name: http
Required parameters: none
Optional parameters: version, type
version: The HTTP-Version number of the enclosed message
(e.g. "1.0"). If not present, the version can be
determined from the first line of the body.
type: 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. Minimum Compliance
Early reviews of this specification have indicated the need for a
statement of the minimum requirements for an implementation to be
considered in compliance with HTTP/1.0. This section will be
written soon.
Note: The primary difficulty in determining a standard for
minimum compliance rests in the fact that HTTP is a flexible
protocol which can be used for many purposes. The
requirements for special purpose applications often differ
from those of general purpose applications.
B.1 Servers
Servers have a special responsibility for being honest when
generating their responses to requesting clients. The Status-Code
sent in the Status-Line must correspond to the actual action taken
by the server. This is especially the case when the method used in
the request is one of PUT, POST, DELETE, LINK, and UNLINK. If a
Status-Code of 200 is returned, the client must be able to assume
that the action has been carried out. If the server is not able to
fulfill the requested action immediately, the correct status code
to use is "202 Accepted".
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.
C. Tolerant Applications
While it may be appropriate for testing applications to verify full
conformance to this specification, it is recommended that
operational applications be tolerant of deviations. This appendix
mentions the most important topics where tolerance is recommended.
C.1 Request-Line, Status-Line, and Header Fields
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 and HTAB characters between fields, even
though only a single SP is specified.
The line terminator for HTTP-header fields should be 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.
We recommend that servers allocate URIs free of "variant"
characters (characters whose representation differs in some of the
national variant character sets), punctuation characters, and
spaces. This makes URIs easier to handle by humans when the need
arises (such as for debugging or transmission through non hypertext
systems).
D. Relationship to MIME
HTTP/1.0 reuses many of the constructs defined for Internet Mail
(RFC 822 [8]) and the Multipurpose Internet Mail Extensions
(MIME [6]) to allow entities to be transmitted in an open variety
of representations and with extensible mechanisms. However, HTTP is
not a MIME-conforming 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
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. Gateways to MIME-compliant protocols must be aware of these
differences and provide the appropriate conversions where
necessary. No conversion should be necessary for a MIME-conforming
entity to be transferred using HTTP.
D.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 [6].
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 8.1.1.
D.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 gateway from HTTP to a MIME-conformant
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).
D.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 [18]. In contrast,
HTTP defines the default character set for "text" to be
ISO88591 [19] (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 gateway if the entity contains any octets
greater than 127.
D.2 Default Content-Transfer-Encoding
The default Content-Transfer-Encoding (CTE) for all MIME messages
is "7bit". In contrast, HTTP defines the default CTE to be
"binary". Therefore, if an entity does not include an explicit CTE
header field, the gateway should apply either the "quoted-printable"
or "base64" transfer encodings and add the appropriate
Content-Transfer-Encoding field. At a minimum, the explicit CTE
field of
Content-Transfer-Encoding: binary
should be added by the gateway if it is unwilling to apply a mail-
safe encoding.
D.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, gateways to MIME-conformant protocols should 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=<encoding-mechanisms>" to perform an
equivalent function as Content-Encoding. However, this
parameter is not part of the MIME specification at the time
of this writing.
E. Example of Version Control
This appendix gives an example on how the Entity-Header fields
Version and Derived-From can be used to apply version control to
the creation and parallel development of a work. In order to
simplify the example, only two user agents (A and B) are considered
together with an origin server S.
o A sends a POST request to S, including the header
"Version: 1.0" and an entity
o S replies "201 Created" to A, including the header
"Version: 1.0" and a URI-header which should be used for
future references
o A starts editing the entity
o B sends a GET request to S
o S replies "200 OK" to B, including the entity with a header
"Version: 1.0"
o B starts editing the entity
o B sends a PUT request to S, including the entity and a header
"Derived-From: 1.0"
o S replies "204 No Content" to B, including a header
"Version: 1.1" but no entity
o A sends a PUT request to S, including the entity and a header
"Derived-From: 1.0"
o S replies "409 Conflict" to A, including "Version: 1.1" and the
list of problems with merging A's changes to 1.0 with those
already applied for B and version 1.1
o A merges B's changes with its own, possibly with help from the
user of A
o A sends a PUT request to S including the entity and the header
"Derived-From: 1.1"
o S replies "204 No Content" to A, including the header
"Version: 1.2" but no entity
The example can be expanded to any number of involved user agents,
though the likelihood of conflicts and the difficulty of resolving
them may increase.
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