Hypertext Transfer Protocol -- HTTP/1.0
draft-ietf-http-v10-spec-04
The information below is for an old version of the document that is already published as an RFC.
| Document | Type |
This is an older version of an Internet-Draft that was ultimately published as RFC 1945.
|
|
|---|---|---|---|
| Authors | Henrik Nielsen , Roy T. Fielding , Tim Berners-Lee | ||
| Last updated | 2023-08-30 (Latest revision 1995-10-16) | ||
| Replaces | draft-fielding-http-spec | ||
| RFC stream | Internet Engineering Task Force (IETF) | ||
| Intended RFC status | Informational | ||
| Formats | |||
| Additional resources | Mailing list discussion | ||
| Stream | WG state | (None) | |
| Document shepherd | (None) | ||
| IESG | IESG state | Became RFC 1945 (Informational) | |
| Consensus boilerplate | Unknown | ||
| Telechat date | (None) | ||
| Responsible AD | (None) | ||
| Send notices to | (None) |
draft-ietf-http-v10-spec-04
HTTP Working Group T. Berners-Lee, MIT/LCS
INTERNET-DRAFT R. Fielding, UC Irvine
<draft-ietf-http-v10-spec-04.txt> H. Frystyk, MIT/LCS
Expires April 14, 1996 October 14, 1995
Hypertext Transfer Protocol -- HTTP/1.0
Status of this Memo
This document is an Internet-Draft. Internet-Drafts are working
documents of the Internet Engineering Task Force (IETF), its areas,
and its working groups. Note that other groups may also distribute
working documents as Internet-Drafts.
Internet-Drafts are draft documents valid for a maximum of six
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Distribution of this document is unlimited. Please send comments to
the HTTP working group at <http-wg@cuckoo.hpl.hp.com>. Discussions
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<URL:http://www.ics.uci.edu/pub/ietf/http/>. General discussions
about HTTP and the applications which use HTTP should take place on
the <www-talk@w3.org> mailing list.
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 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 common usage of
the protocol referred to as "HTTP/1.0".
Table of Contents
1. Introduction
1.1 Purpose
1.2 Terminology
1.3 Overall Operation
2. Notational Conventions and Generic Grammar
2.1 Augmented BNF
2.2 Basic Rules
3. Protocol Parameters
3.1 HTTP Version
3.2 Uniform Resource Identifiers
3.2.1 General Syntax
3.2.2 http URL
3.3 Date/Time Formats
3.4 Character Sets
3.5 Content Codings
3.6 Media Types
3.6.1 Canonicalization and Text Defaults
3.6.2 Multipart Types
3.7 Product Tokens
4. HTTP Message
4.1 Message Types
4.2 Message Headers
4.3 General Header Fields
5. Request
5.1 Request-Line
5.1.1 Method
5.1.2 Request-URI
5.2 Request Header Fields
6. Response
6.1 Status-Line
6.1.1 Status Code and Reason Phrase
6.2 Response Header Fields
7. Entity
7.1 Entity Header Fields
7.2 Entity Body
7.2.1 Type
7.2.2 Length
8. Method Definitions
8.1 GET
8.2 HEAD
8.3 POST
9. Status Code Definitions
9.1 Informational 1xx
9.2 Successful 2xx
9.3 Redirection 3xx
9.4 Client Error 4xx
9.5 Server Error 5xx
10. Header Field Definitions
10.1 Allow
10.2 Authorization
10.3 Content-Encoding
10.4 Content-Length
10.5 Content-Type
10.6 Date
10.7 Expires
10.8 From
10.9 If-Modified-Since
10.10 Last-Modified
10.11 Location
10.12 MIME-Version
10.13 Pragma
10.14 Referer
10.15 Server
10.16 User-Agent
10.17 WWW-Authenticate
11. Access Authentication
11.1 Basic Authentication Scheme
12. Security Considerations
12.1 Authentication of Clients
12.2 Safe Methods
12.3 Abuse of Server Log Information
12.4 Transfer of Sensitive Information
13. Acknowledgments
14. References
15. Authors' Addresses
Appendix A. Internet Media Type message/http
Appendix B. Tolerant Applications
Appendix C. Relationship to MIME
C.1 Conversion to Canonical Form
C.1.1 Representation of Line Breaks
C.1.2 Default Character Set
C.2 Conversion of Date Formats
C.3 Introduction of Content-Encoding
C.4 No Content-Transfer-Encoding
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 common usage of the protocol referred
to as "HTTP/1.0". This specification is not intended to become an
Internet standard; rather, it defines those features of the HTTP
protocol that can reasonably be expected of any implementation
which claims to be using HTTP/1.0.
Practical information systems require more functionality than
simple retrieval, including search, front-end update, and
annotation. HTTP allows an open-ended set of methods to be used to
indicate the purpose of a request. It builds on the discipline of
reference provided by the Uniform Resource Identifier (URI) [2], as
a location (URL) [4] or name (URN) [16], 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 [7] and the
Multipurpose Internet Mail Extensions (MIME) [5].
HTTP is also used as a generic protocol for communication between
user agents and proxies/gateways to other Internet protocols, such
as SMTP [12], NNTP [11], FTP [14], Gopher [1], and WAIS [8],
allowing basic hypermedia access to resources available from
diverse applications and simplifying the implementation of user
agents.
1.2 Terminology
This specification uses a number of terms to refer to the roles
played by participants in, and objects of, the HTTP communication.
connection
A transport layer virtual circuit established between two
application programs for the purpose of communication.
message
The basic unit of HTTP communication, consisting of a structured
sequence of octets matching the syntax defined in Section 4 and
transmitted via the connection.
request
An HTTP request message (as defined in Section 5).
response
An HTTP response message (as defined in Section 6).
resource
A network data object or service which can be identified by a
URI (Section 3.2).
entity
A particular representation or rendition of a data resource, or
reply from a service resource, that may be enclosed within a
request or response message. An entity consists of
metainformation in the form of entity headers and content in the
form of an entity body.
client
An application program that establishes connections for the
purpose of sending requests.
user agent
The client which initiates a request. These are often browsers,
editors, spiders (web-traversing robots), or other end user
tools.
server
An application program that accepts connections in order to
service requests by sending back responses.
origin server
The server on which a given resource resides or is to be created.
proxy
An intermediary program which acts as both a server and a client
for the purpose of making requests on behalf of other clients.
Requests are serviced internally or by passing them, with
possible translation, on to other servers. A proxy must
interpret and, if necessary, rewrite a request message before
forwarding it. Proxies are often used as client-side portals
through network firewalls and as helper applications for
handling requests via protocols not implemented by the user
agent.
gateway
A server which acts as an intermediary for some other server.
Unlike a proxy, a gateway receives requests as if it were the
origin server for the requested resource; the requesting client
may not be aware that it is communicating with a gateway.
Gateways are often used as server-side portals through network
firewalls and as protocol translators for access to resources
stored on non-HTTP systems.
tunnel
A tunnel is an intermediary program which is acting as a blind
relay between two connections. Once active, a tunnel is not
considered a party to the HTTP communication, though the tunnel
may have been initiated by an HTTP request. A tunnel is closed
when both ends of the relayed connections are closed. Tunnels
are used when a portal is necessary and the intermediary cannot,
or should not, interpret the relayed communication.
cache
A program's local store of response messages and the subsystem
that controls its message storage, retrieval, and deletion. A
cache stores cachable responses in order to reduce the response
time and network bandwidth consumption on future, equivalent
requests. Any client or server may include a cache, though a
cache cannot be used by a server while it is acting as a tunnel.
Any given program may be capable of being both a client and a
server; our use of these terms refers only to the role being
performed by the program for a particular connection, rather than
to the program's capabilities in general. Likewise, any server may
act as an origin server, proxy, gateway, or tunnel, switching
behavior based on the nature of each request.
1.3 Overall Operation
The HTTP protocol is based on a request/response paradigm. A client
establishes a connection with a server and sends a request to the
server in the form of a request method, URI, and protocol version,
followed by a MIME-like message containing request modifiers,
client information, and possible body content. The server responds
with a status line, including the message's protocol version and a
success or error code, followed by a MIME-like message containing
server information, entity metainformation, and possible body
content.
Most HTTP communication is initiated by a user agent and consists
of a request to be applied to a resource on some origin server. In
the simplest case, this may be accomplished via a single connection
(v) between the user agent (UA) and the origin server (O).
request chain ------------------------>
UA -------------------v------------------- O
<----------------------- response chain
A more complicated situation occurs when one or more intermediaries
are present in the request/response chain. There are three common
forms of intermediary: proxy, gateway, and tunnel. A proxy is a
forwarding agent, receiving requests for a URI in its absolute
form, rewriting all or parts of the message, and forwarding the
reformatted request toward the server identified by the URI. A
gateway is a receiving agent, acting as a layer above some other
server(s) and, if necessary, translating the requests to the
underlying server's protocol. A tunnel acts as a relay point
between two connections without changing the messages; tunnels are
used when the communication needs to pass through an intermediary
(such as a firewall) even when the intermediary cannot understand
the contents of the messages.
request chain -------------------------------------->
UA -----v----- A -----v----- B -----v----- C -----v----- O
<------------------------------------- response chain
The figure above shows three intermediaries (A, B, and C) between
the user agent and origin server. A request or response message
that travels the whole chain must pass through four separate
connections. This distinction is important because some HTTP
communication options may apply only to the connection with the
nearest, non-tunnel neighbor, only to the end-points of the chain,
or to all connections along the chain. Although the diagram is
linear, each participant may be engaged in multiple, simultaneous
communications. For example, B may be receiving requests from many
clients other than A, and/or forwarding requests to servers other
than C, at the same time that it is handling A's request.
Any party to the communication which is not acting as a tunnel may
employ an internal cache for handling requests. The effect of a
cache is that the request/response chain is shortened if one of the
participants along the chain has a cached response applicable to
that request. The following illustrates the resulting chain if B
has a cached copy of an earlier response from O (via C) for a
request which has not been cached by UA or A.
request chain ---------->
UA -----v----- A -----v----- B - - - - - - C - - - - - - O
<--------- response chain
Not all responses are cachable, and some requests may contain
modifiers which place special requirements on cache behavior.
Historically, HTTP/1.0 applications have not adequately defined
what is or is not a "cachable" response.
On the Internet, HTTP communication generally takes place over
TCP/IP connections. The default port is TCP 80 [15], but other
ports can be used. This does not preclude HTTP from being
implemented on top of any other protocol on the Internet, or on
other networks. HTTP only presumes a reliable transport; any
protocol that provides such guarantees can be used, and the mapping
of the HTTP/1.0 request and response structures onto the transport
data units of the protocol in question is outside the scope of this
specification.
Current practice requires that the connection be established by the
client prior to each request and closed by the server after sending
the response. Both clients and servers must be capable of handling
cases where either party closes the connection prematurely, due to
user action, automated time-out, or program failure. In any case,
the closing of the connection by either or both parties always
terminates the current request, regardless of its status.
2. Notational Conventions and Generic Grammar
2.1 Augmented BNF
All of the mechanisms specified in this document are described in
both prose and an augmented Backus-Naur Form (BNF) similar to that
used by RFC 822 [7]. Implementors will need to be familiar with the
notation in order to understand this specification. The augmented
BNF includes the following constructs:
name = definition
The name of a rule is simply the name itself (without any
enclosing "<" and ">") and is separated from its definition by
the equal character "=". Whitespace is only significant in that
indentation of continuation lines is used to indicate a rule
definition that spans more than one line. Certain basic rules
are in uppercase, such as SP, LWS, HT, CRLF, DIGIT, ALPHA, etc.
Angle brackets are used within definitions whenever their
presence will facilitate discerning the use of rule names.
"literal"
Quotation marks surround literal text. Unless stated otherwise,
the text is case-insensitive.
rule1 | rule2
Elements separated by a bar ("I") are alternatives,
e.g., "yes | no" will accept yes or no.
(rule1 rule2)
Elements enclosed in parentheses are treated as a single
element. Thus, "(elem (foo | bar) elem)" allows the token
sequences "elem foo elem" and "elem bar elem".
*rule
The character "*" preceding an element indicates repetition. The
full form is "<n>*<m>element" indicating at least <n> and at
most <m> occurrences of element. Default values are 0 and
infinity so that "*(element)" allows any number, including zero;
"1*element" requires at least one; and "1*2element" allows one
or two.
[rule]
Square brackets enclose optional elements; "[foo bar]" is
equivalent to "*1(foo bar)".
N rule
Specific repetition: "<n>(element)" is equivalent to
"<n>*<n>(element)"; that is, exactly <n> occurrences of
(element). Thus 2DIGIT is a 2-digit number, and 3ALPHA is a
string of three alphabetic characters.
#rule
A construct "#" is defined, similar to "*", for defining lists
of elements. The full form is "<n>#<m>element" indicating at
least <n> and at most <m> elements, each separated by one or
more commas (",") and optional linear whitespace (LWS). This
makes the usual form of lists very easy; a rule such as
"( *LWS element *( *LWS "," *LWS element ))" can be shown as
"1#element". Wherever this construct is used, null elements are
allowed, but do not contribute to the count of elements present.
That is, "(element), , (element)" is permitted, but counts as
only two elements. Therefore, where at least one element is
required, at least one non-null element must be present. Default
values are 0 and infinity so that "#(element)" allows any
number, including zero; "1#element" requires at least one; and
"1#2element" allows one or two.
; comment
A semi-colon, set off some distance to the right of rule text,
starts a comment that continues to the end of line. This is a
simple way of including useful notes in parallel with the
specifications.
implied *LWS
The grammar described by this specification is word-based.
Except where noted otherwise, linear whitespace (LWS) can be
included between any two adjacent words (token or
quoted-string), and between adjacent tokens and delimiters
(tspecials), without changing the interpretation of a field.
However, applications should attempt to follow "common form"
when generating HTTP constructs, since there exist some
implementations that fail to accept anything beyond the common
forms.
2.2 Basic Rules
The following rules are used throughout this specification to
describe basic parsing constructs. The US-ASCII coded character set
is defined by [17].
OCTET = <any 8-bit sequence of data>
CHAR = <any US-ASCII character (octets 0 - 127)>
UPALPHA = <any US-ASCII uppercase letter "A".."Z">
LOALPHA = <any US-ASCII lowercase letter "a".."z">
ALPHA = UPALPHA | LOALPHA
DIGIT = <any US-ASCII digit "0".."9">
CTL = <any US-ASCII control character
(octets 0 - 31) and DEL (127)>
CR = <US-ASCII CR, carriage return (13)>
LF = <US-ASCII LF, linefeed (10)>
SP = <US-ASCII SP, space (32)>
HT = <US-ASCII HT, horizontal-tab (9)>
<"> = <US-ASCII double-quote mark (34)>
HTTP/1.0 defines the octet sequence CR LF as the end-of-line marker
for all protocol elements except the Entity-Body (see Appendix B
for tolerant applications). The end-of-line marker within an
Entity-Body is defined by its associated media type, as described
in Section 3.6.
CRLF = CR LF
HTTP/1.0 headers may be folded onto multiple lines if each
continuation line begins with a space or horizontal tab. All linear
whitespace, including folding, has the same semantics as SP.
LWS = [CRLF] 1*( SP | HT )
However, folding of header lines is not expected by some
applications, and should not be generated by HTTP/1.0 applications.
The TEXT rule is only used for descriptive field contents and
values that are not intended to be interpreted by the message
parser. Words of *TEXT may contain octets from character sets other
than US-ASCII.
TEXT = <any OCTET except CTLs,
but including LWS>
Recipients of header field TEXT containing octets outside the
US-ASCII character set may assume that they represent ISO-8859-1
characters.
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 | HT
Comments may be included in some HTTP header fields by surrounding
the comment text with parentheses. Comments are only allowed in
fields containing "comment" as part of their field value definition.
comment = "(" *( ctext | comment ) ")"
ctext = <any TEXT excluding "(" and ")">
A string of text is parsed as a single word if it is quoted using
double-quote marks.
quoted-string = ( <"> *(qdtext) <"> )
qdtext = <any CHAR except <"> and CTLs,
but including LWS>
Single-character quoting using the backslash ("\") character is not
permitted in HTTP/1.0.
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 zeros 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/1.0 servers must:
o recognize the format of the Request-Line for HTTP/0.9 and
HTTP/1.0 requests;
o understand any valid request in the format of HTTP/0.9 or
HTTP/1.0;
o respond appropriately with a message in the same protocol
version used by the client.
HTTP/1.0 clients must:
o recognize the format of the Status-Line for HTTP/1.0 responses;
o understand any valid response in the format of HTTP/0.9 or
HTTP/1.0.
Proxy and gateway applications must be careful in forwarding
requests that are received in a format different than that of the
application's native HTTP version. Since the protocol version
indicates the protocol capability of the sender, a proxy/gateway
must never send a message with a version indicator which is greater
than its native version; if a higher version request is received,
the proxy/gateway must either downgrade the request version or
respond with an error. Requests with a version lower than that of
the application's native format may be upgraded before being
forwarded; the proxy/gateway's response to that request must follow
the normal server requirements.
3.2 Uniform Resource Identifiers
URIs have been known by many names: WWW addresses, Universal
Document Identifiers, Universal Resource Identifiers [2], and
finally the combination of Uniform Resource Locators (URL) [4] and
Names (URN) [16]. As far as HTTP is concerned, Uniform Resource
Identifiers are simply formatted strings which identify--via name,
location, or any other characteristic--a network resource.
3.2.1 General Syntax
URIs in HTTP/1.0 can be represented in absolute form or relative to
some known base URI [9], depending upon the context of their use.
The two forms are differentiated by the fact that absolute URIs
always begin with a scheme name followed by a colon.
URI = ( absoluteURI | relativeURI ) [ "#" fragment ]
absoluteURI = scheme ":" *( uchar | reserved )
relativeURI = net_path | abs_path | rel_path
net_path = "//" net_loc [ abs_path ]
abs_path = "/" rel_path
rel_path = [ path ] [ ";" params ] [ "?" query ]
path = fsegment *( "/" segment )
fsegment = 1*pchar
segment = *pchar
params = param *( ";" param )
param = *( pchar | "/" )
scheme = 1*( ALPHA | DIGIT | "+" | "-" | "." )
net_loc = *( pchar | ";" | "?" )
query = *( uchar | reserved )
fragment = *( uchar | reserved )
pchar = uchar | ":" | "@" | "&" | "="
uchar = unreserved | escape
unreserved = ALPHA | DIGIT | safe | extra | national
escape = "%" hex hex
hex = "A" | "B" | "C" | "D" | "E" | "F"
| "a" | "b" | "c" | "d" | "e" | "f" | DIGIT
reserved = ";" | "/" | "?" | ":" | "@" | "&" | "="
safe = "$" | "-" | "_" | "." | "+"
extra = "!" | "*" | "'" | "(" | ")" | ","
national = <any OCTET excluding CTLs, SP,
ALPHA, DIGIT, reserved, safe, and extra>
For definitive information on URL syntax and semantics, see RFC
1738 [4] and RFC 1808 [9]. The BNF above includes national
characters not allowed in valid URLs as specified by RFC 1738,
since HTTP servers are not restricted in the set of unreserved
characters allowed to represent the rel_path part of addresses, and
HTTP proxies may receive requests for URIs not defined by RFC 1738.
3.2.2 http URL
The "http" scheme is used to locate network resources via the HTTP
protocol. This section defines the scheme-specific syntax and
semantics for http URLs.
http_URL = "http:" "//" host [ ":" port ] abs_path
host = <A legal Internet host domain name
or IP address (in dotted-decimal form),
as defined by Section 2.1 of RFC 1123>
port = *DIGIT
If the port is empty or not given, port 80 is assumed. The
semantics are that the identified resource is located at the server
listening for TCP connections on that port of that host, and the
Request-URI for the resource is abs_path. If the abs_path is not
present in the URL, it must be given as "/" when used as a
Request-URI.
Note: Although the HTTP protocol is independent of the
transport layer protocol, the http URL only identifies
resources by their TCP location, and thus non-TCP resources
must be identified by some other URI scheme.
The canonical form for "http" URLs is obtained by converting any
UPALPHA characters in host to their LOALPHA equivalent (hostnames
are case-insensitive), eliding the [ ":" port ] if the port is 80,
and replacing an empty abs_path with "/".
3.3 Date/Time Formats
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 [6]
(an update to RFC 822 [7]). The second format is in common use, but
is based on the obsolete RFC 850 [10] date format and lacks a
four-digit year. HTTP/1.0 clients and servers that parse the date
value should accept all three formats, though they must never
generate the third (asctime) format.
Note: Recipients of date values are encouraged to be robust
in accepting date values that may have been generated by
non-HTTP applications, as is sometimes the case when
retrieving or posting messages via proxies/gateways to SMTP
or NNTP.
All HTTP/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"
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.
3.4 Character Sets
HTTP uses the same definition of the term "character set" as that
described for MIME:
The term "character set" is used in this document to
refer to a method used with one or more tables to convert
a sequence of octets into a sequence of characters. Note
that unconditional conversion in the other direction is
not required, in that not all characters may be available
in a given character set and a character set may provide
more than one sequence of octets to represent a
particular character. This definition is intended to
allow various kinds of character encodings, from simple
single-table mappings such as US-ASCII to complex table
switching methods such as those that use ISO 2022's
techniques. However, the definition associated with a
MIME character set name must fully specify the mapping to
be performed from octets to characters. In particular,
use of external profiling information to determine the
exact mapping is not permitted.
HTTP character sets are identified by case-insensitive tokens. The
complete set of tokens are defined by the IANA Character Set
registry [15]. However, because that registry does not define a
single, consistent token for each character set, we define here the
preferred names for those character sets most likely to be used
with HTTP entities. These character sets include those registered
by RFC 1521 [5] -- the US-ASCII [17] and ISO-8859 [18] character
sets -- and other names specifically recommended for use within MIME
charset parameters.
charset = "US-ASCII"
| "ISO-8859-1" | "ISO-8859-2" | "ISO-8859-3"
| "ISO-8859-4" | "ISO-8859-5" | "ISO-8859-6"
| "ISO-8859-7" | "ISO-8859-8" | "ISO-8859-9"
| "ISO-2022-JP" | "ISO-2022-JP-2" | "ISO-2022-KR"
| "UNICODE-1-1" | "UNICODE-1-1-UTF-7" | "UNICODE-1-1-UTF-8"
| token
Although HTTP allows an arbitrary token to be used as a charset
value, any token that has a predefined value within the IANA
Character Set registry [15] must represent the character set
defined by that registry. Applications should limit their use of
character sets to those defined by the IANA registry.
Note: This use of the term "character set" is more commonly
referred to as a "character encoding." However, since HTTP
and MIME share the same registry, it is important that the
terminology also be shared.
3.5 Content Codings
Content coding values are used to indicate an encoding
transformation that has been applied to a resource. Content codings
are primarily used to allow a document to be compressed or
encrypted without losing the identity of its underlying media type.
Typically, the resource is stored in this encoding and only decoded
before rendering or analogous usage.
content-coding = "x-gzip" | "x-compress" | token
Note: For future compatibility, HTTP/1.0 applications should
consider "gzip" and "compress" to be equivalent to "x-gzip"
and "x-compress", respectively.
All content-coding values are case-insensitive. HTTP/1.0 uses
content-coding values in the Content-Encoding (Section 10.3) header
field. Although the value describes the content-coding, what is
more important is that it indicates what decoding mechanism will be
required to remove the encoding. Note that a single program may be
capable of decoding multiple content-coding formats. Two values are
defined by this specification:
x-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/>.
x-compress
The encoding format produced by the file compression program
"compress". This format is an adaptive Lempel-Ziv-Welch coding
(LZW).
Note: Use of program names for the identification of
encoding formats is not desirable and should be discouraged
for future encodings. Their use here is representative of
historical practice, not good design.
3.6 Media Types
HTTP uses Internet Media Types [13] in the Content-Type header
field (Section 10.5) in order to provide open and extensible data
typing. For mail applications, where there is no type negotiation
between sender and recipient, it is reasonable to put strict limits
on the set of allowed media types. With HTTP, where the sender and
recipient can communicate directly, applications are allowed more
freedom in the use of non-registered types. The following grammar
for media types is a superset of that for MIME because it does not
restrict itself to the official IANA and x-token types.
media-type = type "/" subtype *( ";" parameter )
type = token
subtype = token
Parameters may follow the type/subtype in the form of
attribute/value pairs.
parameter = attribute "=" value
attribute = token
value = token | quoted-string
The type, subtype, and parameter attribute names are
case-insensitive. Parameter values may or may not be
case-sensitive, depending on the semantics of the parameter name.
LWS must not be generated between the type and subtype, nor between
an attribute and its value.
Many current applications do not recognize media type parameters.
Since parameters are a fundamental aspect of media types, this must
be considered an error in those applications. Nevertheless,
HTTP/1.0 applications should only use media type parameters when
they are necessary to define the content of a message.
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 [13].
All media-type's registered by IANA must be preferred over
extension tokens. However, HTTP does not limit applications to the
use of officially registered media types, nor does it encourage the
use of an "x-" prefix for unofficial types outside of explicitly
short experimental use between consenting applications.
3.6.1 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, 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-Encoding has been removed. All other HTTP constructs
use CRLF exclusively to indicate a line break. Content
codings define their own line break requirements.
A recipient of an HTTP text entity should translate the received
entity line breaks to the local line break conventions before
saving the entity external to the application and its cache;
whether this translation takes place immediately upon receipt of
the entity, or only when prompted by the user, is entirely up to
the individual application.
HTTP also redefines the default character set for text media in an
entity body. If a textual media type defines a charset parameter
with a registered default value of "US-ASCII", HTTP changes the
default to be "ISO-8859-1". Since the ISO-8859-1 [18] character set
is a superset of US-ASCII [17], 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.
It is recommended that the character set of an entity body be
labelled as the lowest common denominator of the character codes
used within a document, with the exception that no label is
preferred over the labels US-ASCII or ISO-8859-1.
3.6.2 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 [15] 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 [5], 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.
3.7 Product Tokens
Product tokens are used to allow communicating applications to
identify themselves via a simple product token, with an optional
slash and version designator. Most fields using product tokens also
allow subproducts which form a significant part of the application
to be listed, separated by whitespace. By convention, the products
are listed in order of their significance for identifying the
application.
product = token ["/" product-version]
product-version = token
Examples:
User-Agent: CERN-LineMode/2.15 libwww/2.17b3
Server: Apache/0.8.4
Product tokens should be short and to the point -- use of them for
advertizing or other non-essential information is explicitly
forbidden. Although any token character may appear in a
product-version, this token should only be used for a version
identifier (i.e., successive versions of the same product should
only differ in the product-version portion of the product value).
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 [7] for transferring entities. Both messages may include
optional header fields (also known as "headers") and an entity
body. The entity body is separated from the headers by a null line
(i.e., a line with nothing preceding the CRLF).
Full-Request = Request-Line ; Section 5.1
*( General-Header ; Section 4.3
| Request-Header ; Section 5.2
| Entity-Header ) ; Section 7.1
CRLF
[ Entity-Body ] ; Section 7.2
Full-Response = Status-Line ; Section 6.1
*( General-Header ; Section 4.3
| Response-Header ; Section 6.2
| Entity-Header ) ; Section 7.1
CRLF
[ Entity-Body ] ; Section 7.2
Simple-Request and Simple-Response do not allow the use of any
header information and are limited to a single request method (GET).
Simple-Request = "GET" SP Request-URI CRLF
Simple-Response = [ Entity-Body ]
Use of the Simple-Request format is discouraged because it prevents
the server from identifying the media type of the returned entity.
4.2 Message Headers
HTTP header fields, which include General-Header (Section 4.3),
Request-Header (Section 5.2), Response-Header (Section 6.2), and
Entity-Header (Section 7.1) fields, follow the same generic format
as that given in Section 3.1 of RFC 822 [7]. Each header field
consists of a name followed immediately by a colon (":"), a single
space (SP) character, and the field value. Field names are
case-insensitive. Header fields can be extended over multiple lines
by preceding each extra line with at least one SP or HT, though
this is not recommended.
HTTP-header = field-name ":" [ field-value ] CRLF
field-name = token
field-value = *( field-content | LWS )
field-content = <the OCTETs making up the field-value
and consisting of either *TEXT or combinations
of token, tspecials, and quoted-string>
The order in which header fields are received is not significant.
However, it is "good practice" to send General-Header fields first,
followed by Request-Header or Response-Header fields prior to the
Entity-Header fields.
Multiple HTTP-header fields with the same field-name may be present
in a message if and only if the entire field-value for that header
field is defined as a comma-separated list [i.e., #(values)]. It
must be possible to combine the multiple header fields into one
"field-name: field-value" pair, without changing the semantics of
the message, by appending each subsequent field-value to the first,
each separated by a comma.
4.3 General Header Fields
There are a few header fields which have general applicability for
both request and response messages, but which do not apply to the
entity being transferred. These headers apply only to the message
being transmitted.
General-Header = Date ; Section 10.6
| MIME-Version ; Section 10.12
| Pragma ; Section 10.13
General header field names can be extended reliably only in
combination with a change in the protocol version. However, new or
experimental header fields may be given the semantics of general
header fields if all parties in the communication recognize them to
be general header fields. Unknown header fields are treated as
Entity-Header fields.
5. Request
A request message from a client to a server includes, within the
first line of that message, the method to be applied to the
resource, the identifier of the resource, and the protocol version
in use. For backwards compatibility with the more limited HTTP/0.9
protocol, there are two valid formats for an HTTP request:
Request = Simple-Request | Full-Request
Simple-Request = "GET" SP Request-URI CRLF
Full-Request = Request-Line ; Section 5.1
*( General-Header ; Section 4.3
| Request-Header ; Section 5.2
| Entity-Header ) ; Section 7.1
CRLF
[ Entity-Body ] ; Section 7.2
If an HTTP/1.0 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 and the availability of methods other than GET.
5.1.1 Method
The Method token indicates the method to be performed on the
resource identified by the Request-URI. The method is
case-sensitive.
Method = "GET" ; Section 8.1
| "HEAD" ; Section 8.2
| "POST" ; Section 8.3
| extension-method
extension-method = token
The list of methods acceptable by a specific resource can change
dynamically; the client is notified through the return code of the
response if a method is not allowed on a resource. Servers should
return the status code 501 (not implemented) if the method is
unknown or not implemented.
The methods commonly used by HTTP/1.0 applications are fully
defined in Section 8.
5.1.2 Request-URI
The Request-URI is a Uniform Resource Identifier (Section 3.2) and
identifies the resource upon which to apply the request.
Request-URI = absoluteURI | abs_path
The two options for Request-URI are dependent on the nature of the
request.
The absoluteURI form is only allowed when the request is being made
to a proxy. The proxy is requested to forward the request and
return the response. If the request is GET or HEAD and a prior
response is cached, the proxy may use the cached message if it
passes any restrictions in the Expires header field. Note that the
proxy may forward the request on to another proxy or directly to
the server specified by the absoluteURI. In order to avoid request
loops, a proxy must be able to recognize all of its server names,
including any aliases, local variations, and the numeric IP
address. An example Request-Line would be:
GET http://www.w3.org/hypertext/WWW/TheProject.html HTTP/1.0
The most common form of Request-URI is that used to identify a
resource on an origin server or gateway. In this case, only the
absolute path of the URI is transmitted (see Section 3.2.1,
abs_path). For example, a client wishing to retrieve the resource
above directly from the origin server would create a TCP connection
to port 80 of the host "www.w3.org" and send the line:
GET /hypertext/WWW/TheProject.html HTTP/1.0
followed by the remainder of the Full-Request. Note that the
absolute path cannot be empty; if none is present in the original
URI, it must be given as "/" (the server root).
The Request-URI is transmitted as an encoded string, where some
characters may be escaped using the "% hex hex" encoding defined by
RFC 1738 [4]. The origin server must decode the Request-URI in
order to properly interpret the request.
5.2 Request Header Fields
The request header fields allow the client to pass additional
information about the request, and about the client itself, to the
server. All header fields are optional and conform to the generic
HTTP-header syntax.
Request-Header = Authorization ; Section 10.2
| From ; Section 10.8
| If-Modified-Since ; Section 10.9
| Referer ; Section 10.14
| User-Agent ; Section 10.16
Request-Header field names can be extended reliably only in
combination with a change in the protocol version. However, new or
experimental header fields may be given the semantics of request
header fields if all parties in the communication recognize them to
be request header fields. Unknown header fields are treated as
Entity-Header fields.
6. Response
After receiving and interpreting a request message, a server
responds in the form of an HTTP response message.
Response = Simple-Response | Full-Response
Simple-Response = [ Entity-Body ]
Full-Response = Status-Line ; Section 6.1
*( General-Header ; Section 4.3
| Response-Header ; Section 6.2
| Entity-Header ) ; Section 7.1
CRLF
[ Entity-Body ] ; Section 7.2
A Simple-Response should only be sent in response to an HTTP/0.9
Simple-Request or if the server only supports the more limited
HTTP/0.9 protocol. If a client sends an HTTP/1.0 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 and
status code
"HTTP/" 1*DIGIT "." 1*DIGIT SP 3DIGIT SP
(e.g., "HTTP/1.0 200 "), the presence of that expression is
sufficient to differentiate a Full-Response from a Simple-Response.
Although the Simple-Response format may allow such an expression to
occur at the beginning of an entity body, and thus cause a
misinterpretation of the message if it was given in response to a
Full-Request, most HTTP/0.9 servers are limited to responses of
type "text/html" and therefore would never generate such a response.
6.1.1 Status Code and Reason Phrase
The Status-Code element is a 3-digit integer result code of the
attempt to understand and satisfy the request. The Reason-Phrase is
intended to give a short textual description of the Status-Code.
The Status-Code is intended for use by automata and the
Reason-Phrase is intended for the human user. The client is not
required to examine or display the Reason-Phrase.
The first digit of the Status-Code defines the class of response.
The last two digits do not have any categorization role. There are
5 values for the first digit:
o 1xx: Informational - 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. These codes are fully defined in Section 9.
Status-Code = "200" ; OK
| "201" ; Created
| "202" ; Accepted
| "204" ; No Content
| "301" ; Moved Permanently
| "302" ; Moved Temporarily
| "304" ; Not Modified
| "400" ; Bad Request
| "401" ; Unauthorized
| "403" ; Forbidden
| "404" ; Not Found
| "500" ; Internal Server Error
| "501" ; Not Implemented
| "502" ; Bad Gateway
| "503" ; Service Unavailable
| extension-code
extension-code = 3DIGIT
Reason-Phrase = *<TEXT, excluding CR, LF>
HTTP status codes are extensible, but the above codes are the only
ones generally recognized in current practice. HTTP applications
are not required to understand the meaning of all registered status
codes, though such understanding is obviously desirable. However,
applications must understand the class of any status code, as
indicated by the first digit, and treat any unknown 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 should present to the user the entity returned
with the response, since that entity is likely to include
human-readable information which will explain the unusual status.
6.2 Response Header Fields
The response header fields allow the server to pass additional
information about the response which cannot be placed in the
Status-Line. These header fields are not intended to give
information about an Entity-Body returned in the response, but
about the server itself.
Response-Header = Location ; Section 10.11
| Server ; Section 10.15
| WWW-Authenticate ; Section 10.17
Response-Header field names can be extended reliably only in
combination with a change in the protocol version. However, new or
experimental header fields may be given the semantics of response
header fields if all parties in the communication recognize them to
be response header fields. Unknown header fields are treated as
Entity-Header fields.
7. Entity
Full-Request and Full-Response messages may transfer an entity
within some requests and responses. An entity consists of
Entity-Header fields and (usually) an Entity-Body. In this section,
both sender and recipient refer to either the client or the server,
depending on who sends and who receives the entity.
7.1 Entity Header Fields
Entity-Header fields define optional metainformation about the
Entity-Body or, if no body is present, about the resource
identified by the request.
Entity-Header = Allow ; Section 10.1
| Content-Encoding ; Section 10.3
| Content-Length ; Section 10.4
| Content-Type ; Section 10.5
| Expires ; Section 10.7
| Last-Modified ; Section 10.10
| extension-header
extension-header = HTTP-header
The extension-header mechanism allows additional Entity-Header
fields to be defined without changing the protocol, but these
fields cannot be assumed to be recognizable by the recipient.
Unknown header fields should be ignored by the recipient and
forwarded by proxies.
7.2 Entity Body
The entity body (if any) sent with an HTTP/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. The presence of an entity body in a
request is signaled by the inclusion of a Content-Length header
field in the request message headers. HTTP/1.0 requests containing
an entity body must include a valid Content-Length header field.
For response messages, whether or not an entity body is included
with a message is dependent on both the request method and the
response code. All responses to the HEAD request method must not
include a body, even though the presence of entity header fields
may lead one to believe they do. All 1xx (informational), 204 (no
content), and 304 (not modified) responses must not include a body.
All other responses must include an entity body or a Content-Length
header field defined with a value of zero (0).
7.2.1 Type
When an Entity-Body is included with a message, the data type of
that body is determined via the header fields Content-Type and
Content-Encoding. These define a two-layer, ordered encoding model:
entity-body := Content-Encoding( Content-Type( data ) )
A Content-Type specifies the media type of the underlying data. A
Content-Encoding may be used to indicate any additional content
coding applied to the type, usually for the purpose of data
compression, that is a property of the resource requested. The
default for the content encoding is none (i.e., the identity
function).
Any HTTP/1.0 message containing an entity body should include a
Content-Type header field defining the media type of that body. If
and only if the media type is not given by a Content-Type header,
as is the case for Simple-Response messages, the recipient may
attempt to guess the media type via inspection of its content
and/or the name extension(s) of the URL used to identify the
resource. If the media type remains unknown, the recipient should
treat it as type "application/octet-stream".
7.2.2 Length
When an Entity-Body is included with a message, the length of that
body may be determined in one of two ways. If a Content-Length
header field is present, its value in bytes represents the length
of the Entity-Body. Otherwise, the body length is determined by the
closing of the connection by the server.
Closing the connection cannot be used to indicate the end of a
request body, since it leaves no possibility for the server to send
back a response. Therefore, HTTP/1.0 requests containing an entity
body must include a valid Content-Length header field. If a request
contains an entity body and Content-Length is not specified, and
the server does not recognize or cannot calculate the length from
other fields, then the server should send a 400 (bad request)
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. Method Definitions
The set of common methods for HTTP/1.0 is defined below. Although
this set can be expanded, additional methods cannot be assumed to
share the same semantics for separately extended clients and
servers.
8.1 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, as described in Section 10.9. 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.
8.2 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" request analogous to the conditional
GET. If an If-Modified-Since header field is included with a HEAD
request, it should be ignored.
8.3 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, such as the result of submitting a
form [3], to a data-handling process;
o Extending a database through an append operation.
The actual function performed by the POST method is determined by
the server and is usually dependent on the Request-URI. The posted
entity is subordinate to that URI in the same way that a file is
subordinate to a directory containing it, a news article is
subordinate to a newsgroup to which it is posted, or a record is
subordinate to a database.
A successful POST does not require that the entity be created as a
resource on the origin server or made accessible for future
reference. That is, the action performed by the POST method might
not result in a resource that can be identified by a URI. In this
case, either 200 (ok) or 204 (no content) is the appropriate
response status, depending on whether or not the response includes
an entity that describes the result.
If a resource has been created on the origin server, the response
should be 201 (created) and contain an entity (preferably of type
"text/html") which describes the status of the request and refers
to the new resource.
A valid Content-Length is required on all HTTP/1.0 POST requests.
An HTTP/1.0 server should respond with a 400 (bad request) message
if it cannot determine the length of the request message's content.
Applications must not cache responses to a POST request.
9. Status Code Definitions
Each Status-Code is described below, including a description of
which method(s) it can follow and any metainformation required in
the response.
9.1 Informational 1xx
This class of status code indicates a provisional response,
consisting only of the Status-Line and optional headers, and is
terminated by an empty line. HTTP/1.0 does not define any 1xx
status codes and they are not a valid response to a HTTP/1.0
request. However, they may be useful for experimental applications
which are outside the scope of this specification.
9.2 Successful 2xx
This class of status code indicates that the client's request was
successfully received, understood, and accepted.
200 OK
The request has succeeded. The information returned with the
response is dependent on the method used in the request, as follows:
GET an entity corresponding to the requested resource is sent
in the response;
HEAD the response must only contain the header information and
no Entity-Body;
POST an entity describing or containing the result of the action.
201 Created
The request has been fulfilled and resulted in a new resource being
created. The newly created resource can be referenced by the URI(s)
returned in the entity of the response. The origin server should
create the resource before using this Status-Code. If the action
cannot be carried out immediately, the server must include in the
response body a description of when the resource will be available;
otherwise, the server should respond with 202 (accepted).
Of the methods defined by this specification, only POST can create
a resource.
202 Accepted
The request has been accepted for processing, but the processing
has not been completed. The request may or may not eventually be
acted upon, as it may be disallowed when processing actually takes
place. There is no facility for re-sending a status code from an
asynchronous operation such as this.
The 202 response is intentionally non-committal. Its purpose is to
allow a server to accept a request for some other process (perhaps
a batch-oriented process that is only run once per day) without
requiring that the user agent's connection to the server persist
until the process is completed. The entity returned with this
response should include an indication of the request's current
status and either a pointer to a status monitor or some estimate of
when the user can expect the request to be fulfilled.
204 No Content
The server has fulfilled the request but there is no new
information to send back. If the client is a user agent, it should
not change its document view from that which caused the request to
be generated. This response is primarily intended to allow input
for scripts or other actions to take place without causing a change
to the user agent's active document view. The response may include
new metainformation in the form of entity headers, which should
apply to the document currently in the user agent's active view.
9.3 Redirection 3xx
This class of status code indicates that further action needs to be
taken by the user agent in order to fulfill the request. The action
required can sometimes be carried out by the user agent without
interaction with the user, but it is strongly recommended that this
only take place if the method used in the request is GET or HEAD. A
user agent should never automatically redirect a request more than
5 times, since such redirections usually indicate an infinite loop.
300 Multiple Choices
This response code is not directly used by HTTP/1.0 applications,
but serves as the default for interpreting the 3xx class of
responses.
The requested resource is available at one or more locations.
Unless it was a HEAD request, the response should include an entity
containing a list of resource characteristics and locations from
which the user or user agent can choose the one most appropriate.
If the server has a preferred choice, it should include the URL in
a Location field; user agents may use this field value for
automatic redirection.
301 Moved Permanently
The requested resource has been assigned a new permanent URL and
any future references to this resource should be done using that
URL. Clients with link editing capabilities should automatically
relink references to the Request-URI to the new reference returned
by the server, where possible.
The new URL must be given by the Location field in the response.
Unless it was a HEAD request, the Entity-Body of the response
should contain a short note with a hyperlink to the new URL.
If the 301 status code is received in response to a request using
the POST method, the user agent must not automatically redirect the
request unless it can be confirmed by the user, since this might
change the conditions under which the request was issued.
302 Moved Temporarily
The requested resource resides temporarily under a different URL.
Since the redirection may be altered on occasion, the client should
continue to use the Request-URI for future requests.
The URL must be given by the Location field in the response. Unless
it was a HEAD request, the Entity-Body of the response should
contain a short note with a hyperlink to the new URI(s).
If the 302 status code is received in response to a request using
the POST method, the user agent must not automatically redirect the
request unless it can be confirmed by the user, since this might
change the conditions under which the request was issued.
304 Not Modified
If the client has performed a conditional GET request and access is
allowed, but the document has not been modified since the date and
time specified in the If-Modified-Since field, the server must
respond with this status code and not send an Entity-Body to the
client. Header fields contained in the response should only include
information which is relevant to cache managers or which may have
changed independently of the entity's Last-Modified date. Examples
of relevant header fields include: Date, Server, and Expires. A
cache should update its cached entity to reflect any new field
values given in the 304 response.
9.4 Client Error 4xx
The 4xx class of status code is intended for cases in which the
client seems to have erred. If the client has not completed the
request when a 4xx code is received, it should immediately cease
sending data to the server. Except when responding to a HEAD
request, the server should include an entity containing an
explanation of the error situation, and whether it is a temporary
or permanent condition. These status codes are applicable to any
request method.
Note: If the client is sending data, server implementations
on TCP should be careful to ensure that the client
acknowledges receipt of the packet(s) containing the
response prior to closing the input connection. If the
client continues sending data to the server after the close,
the server's controller will send a reset packet to the
client, which may erase the client's unacknowledged input
buffers before they can be read and interpreted by the HTTP
application.
400 Bad Request
The request could not be understood by the server due to malformed
syntax. The client should not repeat the request without
modifications.
401 Unauthorized
The request requires user authentication. The response must include
a WWW-Authenticate header field (Section 10.17) containing a
challenge applicable to the requested resource. The client may
repeat the request with a suitable Authorization header field
(Section 10.2). If the request already included Authorization
credentials, then the 401 response indicates that authorization has
been refused for those credentials. If the 401 response contains
the same challenge as the prior response, and the user agent has
already attempted authentication at least once, then the user
should be presented the entity that was given in the response,
since that entity may include relevent diagnostic information. HTTP
access authentication is explained in Section 11.
403 Forbidden
The server understood the request, but is refusing to fulfill it.
Authorization will not help and the request should not be repeated.
If the request method was not HEAD and the server wishes to make
public why the request has not been fulfilled, it should describe
the reason for the refusal in the entity body. This status code is
commonly used when the server does not wish to reveal exactly why
the request has been refused, or when no other response is
applicable.
404 Not Found
The server has not found anything matching the Request-URI. No
indication is given of whether the condition is temporary or
permanent. If the server does not wish to make this information
available to the client, the status code 403 (forbidden) can be
used instead.
9.5 Server Error 5xx
Response status codes beginning with the digit "5" indicate cases
in which the server is aware that it has erred or is incapable of
performing the request. If the client has not completed the request
when a 5xx code is received, it should immediately cease sending
data to the server. Except when responding to a HEAD request, the
server should include an entity containing an explanation of the
error situation, and whether it is a temporary or permanent
condition. These response codes are applicable to any request
method and there are no required header fields.
500 Internal Server Error
The server encountered an unexpected condition which prevented it
from fulfilling the request.
501 Not Implemented
The server does not support the functionality required to fulfill
the request. This is the appropriate response when the server does
not recognize the request method and is not capable of supporting
it for any resource.
502 Bad Gateway
The server, while acting as a gateway or proxy, received an invalid
response from the upstream server it accessed in attempting to
fulfill the request.
503 Service Unavailable
The server is currently unable to handle the request due to a
temporary overloading or maintenance of the server. The implication
is that this is a temporary condition which will be alleviated
after some delay.
Note: The existence of the 503 status code does not imply
that a server must use it when becoming overloaded. Some
servers may wish to simply refuse the connection.
10. Header Field Definitions
This section defines the syntax and semantics of all commonly used
HTTP/1.0 header fields. For general and entity header fields, both
sender and recipient refer to either the client or the server,
depending on who sends and who receives the message.
10.1 Allow
The Allow entity-header field lists the set of methods supported by
the resource identified by the Request-URI. The purpose of this
field is strictly to inform the recipient of valid methods
associated with the resource. The Allow header field is not
permitted in a request using the POST method, and thus should be
ignored if it is received as part of a POST entity.
Allow = "Allow" ":" 1#method
Example of use:
Allow: GET, HEAD
This field cannot prevent a client from trying other methods.
However, the indications given by the Allow header field value
should be followed. The actual set of allowed methods is defined by
the origin server at the time of each request.
A proxy must not modify the Allow header field even if it does not
understand all the methods specified, since the user agent may have
other means of communicating with the origin server.
The Allow header field does not indicate what methods are
implemented by the server.
10.2 Authorization
A user agent that wishes to authenticate itself with a
server--usually, but not necessarily, after receiving a 401
response--may do so by including an Authorization request-header
field with the request. The Authorization field value consists of
credentials containing the authentication information of the user
agent for the realm of the resource being requested.
Authorization = "Authorization" ":" credentials
HTTP access authentication is described in Section 11. If a request
is authenticated and a realm specified, the same credentials should
be valid for all other requests within this realm.
Responses to requests containing an Authorization field are not
cachable.
10.3 Content-Encoding
The Content-Encoding entity-header field is used as a modifier to
the media-type. When present, its value indicates what additional
content coding 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" ":" content-coding
Content codings are defined in Section 3.5. An example of its use is
Content-Encoding: x-gzip
The Content-Encoding is a characteristic of the resource identified
by the Request-URI. Typically, the resource is stored with this
encoding and is only decoded before rendering or analogous usage.
10.4 Content-Length
The Content-Length entity-header field indicates the size of the
Entity-Body, in decimal number of octets, sent to the recipient or,
in the case of the HEAD method, the size of the Entity-Body that
would have been sent had the request been a GET.
Content-Length = "Content-Length" ":" 1*DIGIT
An example is
Content-Length: 3495
Applications should use this field to indicate the size of the
Entity-Body to be transferred, regardless of the media type of the
entity. A valid Content-Length field value is required on all
HTTP/1.0 request messages containing an entity body.
Any Content-Length greater than or equal to zero is a valid value.
Section 7.2.2 describes how to determine the length of a response
entity body if a Content-Length is not given.
Note: The meaning of this field is significantly different
from the corresponding definition in MIME, where it is an
optional field used within the "message/external-body"
content-type. In HTTP, it should be used whenever the
entity's length can be determined prior to being transferred.
10.5 Content-Type
The Content-Type entity-header field indicates the media type of
the Entity-Body sent to the recipient or, in the case of the HEAD
method, the media type that would have been sent had the request
been a GET.
Content-Type = "Content-Type" ":" media-type
Media types are defined in Section 3.6. An example of the field is
Content-Type: text/html
Further discussion of methods for identifying the media type of an
entity is provided in Section 7.2.1.
10.6 Date
The Date general-header field represents the date and time at which
the message was originated, having the same semantics as orig-date
in RFC 822. The field value is an HTTP-date, as described in
Section 3.3.
Date = "Date" ":" HTTP-date
An example is
Date: Tue, 15 Nov 1994 08:12:31 GMT
If a message is received via direct connection with the user agent
(in the case of requests) or the origin server (in the case of
responses), then the date can be assumed to be the current date at
the receiving end. However, since the date--as it is believed by the
origin--is important for evaluating cached responses, origin servers
should always include a Date header. Clients should only send a
Date header field in messages that include an entity body, as in
the case of the POST request, and even then it is optional. A
received message which does not have a Date header field should be
assigned one by the recipient if the message will be cached by that
recipient or gatewayed via a protocol which requires a Date.
In theory, the date should represent the moment just before the
entity is generated. In practice, the date can be generated at any
time during the message origination without affecting its semantic
value.
Note: An earlier version of this document incorrectly
specified that this field should contain the creation date
of the enclosed Entity-Body. This has been changed to
reflect actual (and proper) usage.
10.7 Expires
The Expires entity-header field gives the date/time after which the
entity should be considered stale. This allows information
providers to suggest the volatility of the resource, or a date
after which the information may no longer be valid. Applications
must not cache this entity beyond the date given. The presence of
an Expires field does not imply that the original resource will
change or cease to exist at, before, or after that time. However,
information providers that know or even suspect that a resource
will change by a certain date should include an Expires header with
that date. The format is an absolute date and time as defined by
HTTP-date in Section 3.3.
Expires = "Expires" ":" HTTP-date
An example of its use is
Expires: Thu, 01 Dec 1994 16:00:00 GMT
If the date given is equal to or earlier than the value of the Date
header, the recipient must not cache the enclosed entity. If a
resource is dynamic by nature, as is the case with many
data-producing processes, entities from that resource should be
given an appropriate Expires value which reflects that dynamism.
The Expires field cannot be used to force a user agent to refresh
its display or reload a resource; its semantics apply only to
caching mechanisms, and such mechanisms need only check a
resource's expiration status when a new request for that resource
is initiated.
User agents often have history mechanisms, such as "Back" buttons
and history lists, which can be used to redisplay an entity
retrieved earlier in a session. By default, the Expires field does
not apply to history mechanisms. If the entity is still in storage,
a history mechanism should display it even if the entity has
expired, unless the user has specifically configured the agent to
refresh expired history documents.
Note: Applications are encouraged to be tolerant of bad or
misinformed implementations of the Expires header. A value
of zero (0) or an invalid date format should be considered
equivalent to an "expires immediately." Although these
values are not legitimate for HTTP/1.0, a robust
implementation is always desirable.
10.8 From
The From request-header field, if given, should contain an Internet
e-mail address for the human user who controls the requesting user
agent. The address should be machine-usable, as defined by mailbox
in RFC 822 [7] (as updated by RFC 1123 [6]):
From = "From" ":" mailbox
An example is:
From: webmaster@w3.org
This header field may be used for logging purposes and as a means
for identifying the source of invalid or unwanted requests. It
should not be used as an insecure form of access protection. The
interpretation of this field is that the request is being performed
on behalf of the person given, who accepts responsibility for the
method performed. In particular, robot agents should include this
header so that the person responsible for running the robot can be
contacted if problems occur on the receiving end.
The Internet e-mail address in this field may be separate from the
Internet host which issued the request. For example, when a request
is passed through a proxy, the original issuer's address should be
used.
Note: The client should not send the From header field
without the user's approval, as it may conflict with the
user's privacy interests or their site's security policy. It
is strongly recommended that the user be able to disable,
enable, and modify the value of this field at any time prior
to a request.
10.9 If-Modified-Since
The If-Modified-Since request-header field is used with the GET
method to make it conditional: if the requested resource has not
been modified since the time specified in this field, a copy of the
resource will not be returned from the server; instead, a 304 (not
modified) response will be returned without any Entity-Body.
If-Modified-Since = "If-Modified-Since" ":" HTTP-date
An example of the field is:
If-Modified-Since: Sat, 29 Oct 1994 19:43:31 GMT
A conditional GET method requests that the identified resource be
transferred only if it has been modified since the date given by
the If-Modified-Since header. The algorithm for determining this
includes the following cases:
a) If the request would normally result in anything other than
a 200 (ok) status, or if the passed If-Modified-Since date
is invalid, the response is exactly the same as for a
normal GET. A date which is later than the server's current
time is invalid.
b) If the resource has been modified since the
If-Modified-Since date, the response is exactly the same as
for a normal GET.
c) If the resource has not been modified since a valid
If-Modified-Since date, the server shall return a 304 (not
modified) response.
The purpose of this feature is to allow efficient updates of cached
information with a minimum amount of transaction overhead.
10.10 Last-Modified
The Last-Modified entity-header field indicates the date and time
at which the sender believes the resource was last modified. The
exact semantics of this field are defined in terms of how the
recipient should interpret it: if the recipient has a copy of this
resource which is older than the date given by the Last-Modified
field, that copy should be considered stale.
Last-Modified = "Last-Modified" ":" HTTP-date
An example of its use is
Last-Modified: Tue, 15 Nov 1994 12:45:26 GMT
The exact meaning of this header field depends on the
implementation of the sender and the nature of the original
resource. For files, it may be just the file system last-modified
time. For entities with dynamically included parts, it may be the
most recent of the set of last-modify times for its component
parts. For database gateways, it may be the last-update timestamp
of the record. For virtual objects, it may be the last time the
internal state changed.
An origin server must not send a Last-Modified date which is later
than the server's time of message origination. In such cases, where
the resource's last modification would indicate some time in the
future, the server must replace that date with the message
origination date.
10.11 Location
The Location response-header field defines the exact location of
the resource that was identified by the Request-URI. For 3xx
responses, the location must indicate the server's preferred URL
for automatic redirection to the resource. Only one absolute URL is
allowed.
Location = "Location" ":" absoluteURI
An example is
Location: http://www.w3.org/hypertext/WWW/NewLocation.html
10.12 MIME-Version
HTTP is not a MIME-compliant protocol (see Appendix C). However,
HTTP/1.0 messages may include a single MIME-Version general-header
field to indicate what version of the MIME protocol was used to
construct the message. Use of the MIME-Version header field should
indicate that the message is in full compliance with the MIME
protocol (as defined in [5]). Unfortunately, some older versions of
HTTP/1.0 clients and servers use this field indiscriminately, and
thus recipients must not take it for granted that the message is
indeed in full compliance with MIME. Proxies and 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 fully MIME-compliant.
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.
10.13 Pragma
The Pragma general-header field is used to include
implementation-specific directives that may apply to any recipient
along the request/response chain. All pragma directives specify
optional behavior from the viewpoint of the protocol; however, some
systems may require that behavior be consistent with the directives.
Pragma = "Pragma" ":" 1#pragma-directive
pragma-directive = "no-cache" | extension-pragma
extension-pragma = token [ "=" word ]
When the "no-cache" directive is present in a request message, an
application should forward the request toward the origin server
even if it has a cached copy of what is being requested. This
allows a client to insist upon receiving an authoritative response
to its request. It also allows a client to refresh a cached copy
which is known to be corrupted or stale.
Pragma directives must be passed through by a proxy or gateway
application, regardless of their significance to that application,
since the directives may be applicable to all recipients along the
request/response chain. It is not possible to specify a pragma for
a specific recipient; however, any pragma directive not relevant to
a recipient should be ignored by that recipient.
10.14 Referer
The Referer request-header field allows the client to specify, for
the server's benefit, the address (URI) of the resource from which
the Request-URI was obtained. This allows a server to generate
lists of back-links to resources for interest, logging, optimized
caching, etc. It also allows obsolete or mistyped links to be
traced for maintenance. The Referer field must not be sent if the
Request-URI was obtained from a source that does not have its own
URI, such as input from the user keyboard.
Referer = "Referer" ":" ( absoluteURI | relativeURI )
Example:
Referer: http://www.w3.org/hypertext/DataSources/Overview.html
If a partial URI is given, it should be interpreted relative to the
Request-URI. The URI must not include a fragment.
Note: Because the source of a link may be private
information or may reveal an otherwise private information
source, it is strongly recommended that the user be able to
select whether or not the Referer field is sent. For
example, a browser client could have a toggle switch for
browsing openly/anonymously, which would respectively
enable/disable the sending of Referer and From information.
10.15 Server
The Server response-header field contains information about the
software used by the origin server to handle the request. The field
can contain multiple product tokens (Section 3.7) and comments
identifying the server and any significant subproducts. By
convention, the product tokens are listed in order of their
significance for identifying the application.
Server = "Server" ":" 1*( product | comment )
Example:
Server: CERN/3.0 libwww/2.17
If the response is being forwarded through a proxy, the proxy
application must not add its data to the product list.
Note: Revealing the specific software version of the server
may allow the server machine to become more vulnerable to
attacks against software that is known to contain security
holes. Server implementors are encouraged to make this field
a configurable option.
10.16 User-Agent
The User-Agent request-header field contains information about the
user agent originating the request. This is for statistical
purposes, the tracing of protocol violations, and automated
recognition of user agents for the sake of tailoring responses to
avoid particular user agent limitations. Although it is not
required, user agents should include this field with requests. The
field can contain multiple product tokens (Section 3.7) and
comments identifying the agent and any subproducts which form a
significant part of the user agent. By convention, the product
tokens are listed in order of their significance for identifying
the application.
User-Agent = "User-Agent" ":" 1*( product | comment )
Example:
User-Agent: CERN-LineMode/2.15 libwww/2.17b3
Note: Some current proxy applications append their product
information to the list in the User-Agent field. This is not
recommended, since it makes machine interpretation of these
fields ambiguous.
10.17 WWW-Authenticate
The WWW-Authenticate response-header field must be included in 401
(unauthorized) response messages. The field value consists of at
least one challenge that indicates the authentication scheme(s) and
parameters applicable to the Request-URI.
WWW-Authenticate = "WWW-Authenticate" ":" 1#challenge
The HTTP access authentication process is described in Section 11.
User agents must take special care in parsing the WWW-Authenticate
field value if it contains more than one challenge, or if more than
one WWW-Authenticate header field is provided, since the contents
of a challenge may itself contain a comma-separated list of
authentication parameters.
11. Access Authentication
HTTP provides a simple challenge-response authentication mechanism
which may be used by a server to challenge a client request and by
a client to provide authentication information. It uses an
extensible, case-insensitive token to identify the authentication
scheme, followed by a comma-separated list of attribute-value pairs
which carry the parameters necessary for achieving authentication
via that scheme.
auth-scheme = token
auth-param = token "=" quoted-string
The 401 (unauthorized) response message is used by an origin server
to challenge the authorization of a user agent. This response must
include a WWW-Authenticate header field containing at least one
challenge applicable to the requested resource.
challenge = auth-scheme 1*SP realm *( "," auth-param )
realm = "realm" "=" realm-value
realm-value = quoted-string
The realm attribute (case-insensitive) is required for all
authentication schemes which issue a challenge. The realm value
(case-sensitive), in combination with the canonical root URL of the
server being accessed, defines the protection space. These realms
allow the protected resources on a server to be partitioned into a
set of protection spaces, each with its own authentication scheme
and/or authorization database. The realm value is a string,
generally assigned by the origin server, which may have additional
semantics specific to the authentication scheme.
A user agent that wishes to authenticate itself with a
server--usually, but not necessarily, after receiving a 401
response--may do so by including an Authorization header field with
the request. The Authorization field value consists of credentials
containing the authentication information of the user agent for the
realm of the resource being requested.
credentials = basic-credentials
| ( auth-scheme #auth-param )
The domain over which credentials can be automatically applied by a
user agent is determined by the protection space. If a prior
request has been authorized, the same credentials may be reused for
all other requests within that protection space for a period of
time determined by the authentication scheme, parameters, and/or
user preference. Unless otherwise defined by the authentication
scheme, a single protection space cannot extend outside the scope
of its server.
If the server does not wish to accept the credentials sent with a
request, it should return a 403 (forbidden) response.
The HTTP protocol does not restrict applications to this simple
challenge-response mechanism for access authentication. Additional
mechanisms may be used, such as encryption at the transport level
or via message encapsulation, and with additional header fields
specifying authentication information. However, these additional
mechanisms are not defined by this specification.
Proxies must be completely transparent regarding user agent
authentication. That is, they must forward the WWW-Authenticate and
Authorization headers untouched, and must not cache the response to
a request containing Authorization. HTTP/1.0 does not provide a
means for a client to be authenticated with a proxy.
11.1 Basic Authentication Scheme
The "basic" authentication scheme is based on the model that the
user agent must authenticate itself with a user-ID and a password
for each realm. The realm value should be considered an opaque
string which can only be compared for equality with other realms on
that server. The server will authorize the request only if it can
validate the user-ID and password for the protection space of the
Request-URI. There are no optional authentication parameters.
Upon receipt of an unauthorized request for a URI within the
protection space, the server should respond with a challenge like
the following:
WWW-Authenticate: Basic realm="WallyWorld"
where "WallyWorld" is the string assigned by the server to identify
the protection space of the Request-URI.
To receive authorization, the client sends the user-ID and
password, separated by a single colon (":") character, within a
base64 [5] encoded string in the credentials.
basic-credentials = "Basic" SP basic-cookie
basic-cookie = <base64 [5] encoding of userid-password,
except not limited to 76 char/line>
userid-password = [ token ] ":" *TEXT
If the user agent wishes to send the user-ID "Aladdin" and password
"open sesame", it would use the following header field:
Authorization: Basic QWxhZGRpbjpvcGVuIHNlc2FtZQ==
The basic authentication scheme is a non-secure method of filtering
unauthorized access to resources on an HTTP server. It is based on
the assumption that the connection between the client and the
server can be regarded as a trusted carrier. As this is not
generally true on an open network, the basic authentication scheme
should be used accordingly. In spite of this, clients should
implement the scheme in order to communicate with servers that use
it.
12. 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.
12.1 Authentication of Clients
As mentioned in Section 11.1, the Basic authentication scheme is
not a secure method of user authentication, nor does it prevent the
Entity-Body from being transmitted in clear text across the
physical network used as the carrier. HTTP/1.0 does not prevent
additional authentication schemes and encryption mechanisms from
being employed to increase security.
12.2 Safe Methods
The writers of client software should be aware that the software
represents the user in their interactions over the Internet, and
should be careful to allow the user to be aware of any actions they
may take which may have an unexpected significance to themselves or
others.
In particular, the convention has been established that the GET and
HEAD methods should never have the significance of taking an action
other than retrieval. These methods should be considered "safe."
This allows user agents to represent other methods, such as POST,
in a special way, so that the user is made aware of the fact that a
possibly unsafe action is being requested.
Naturally, it is not possible to ensure that the server does not
generate side-effects as a result of performing a GET request; in
fact, some dynamic resources consider that a feature. The important
distinction here is that the user did not request the side-effects,
so therefore cannot be held accountable for them.
12.3 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.
12.4 Transfer of Sensitive Information
Like any generic data transfer protocol, HTTP cannot regulate the
content of the data that is transferred, nor is there any a priori
method of determining the sensitivity of any particular piece of
information within the context of any given request. Therefore,
applications should supply as much control over this information as
possible to the provider of that information. Three header fields
are worth special mention in this context: Server, Referer and From.
Revealing the specific software version of the server may allow the
server machine to become more vulnerable to attacks against
software that is known to contain security holes. Implementors
should make the Server header field a configurable option.
The Referer field allows reading patterns to be studied and reverse
links drawn. Although it can be very useful, its power can be
abused if user details are not separated from the information
contained in the Referer. Even when the personal information has
been removed, the Referer field may indicate a private document's
URI whose publication would be inappropriate.
The information sent in the From field might conflict with the
user's privacy interests or their site's security policy, and hence
it should not be transmitted without the user being able to
disable, enable, and modify the contents of the field. The user
must be able to set the contents of this field within a user
preference or application defaults configuration.
We suggest, though do not require, that a convenient toggle
interface be provided for the user to enable or disable the sending
of From and Referer information.
13. Acknowledgments
This specification makes heavy use of the augmented BNF and generic
constructs defined by David H. Crocker for RFC 822 [7]. Similarly,
it reuses many of the definitions provided by Nathaniel Borenstein
and Ned Freed for MIME [5]. We hope that their inclusion in this
specification will help reduce past confusion over the relationship
between HTTP/1.0 and Internet mail message formats.
The HTTP protocol has evolved considerably over the past four
years. It has benefited from a large and active developer
community--the many people who have participated on the www-talk
mailing list--and it is that community which has been most
responsible for the success of HTTP and of the World-Wide Web in
general. Marc Andreessen, Robert Cailliau, Daniel W. Connolly,
Bob Denny, Jean-Francois Groff, Phillip M. Hallam-Baker,
Hakon W. Lie, Ari Luotonen, Rob McCool, Lou Montulli, 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 HTTP-WG. In addition to those already
mentioned, the following individuals have contributed to this
specification:
Gary Adams Harald Tveit Alvestrand
Keith Ball Brian Behlendorf
Paul Burchard Maurizio Codogno
Mike Cowlishaw Roman Czyborra
Michael A. Dolan John Franks
Jim Gettys Marc Hedlund
Koen Holtman Alex Hopmann
Bob Jernigan Shel Kaphan
Martijn Koster Dave Kristol
Daniel LaLiberte Paul Leach
Albert Lunde John C. Mallery
Larry Masinter Mitra
Gavin Nicol Bill Perry
Jeffrey Perry Owen Rees
David Robinson Marc Salomon
Rich Salz Jim Seidman
Chuck Shotton Eric W. Sink
Simon E. Spero Robert S. Thau
Francois Yergeau Mary Ellen Zurko
Jean-Philippe Martin-Flatin
14. References
[1] 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.
[2] 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.
[3] T. Berners-Lee and D. Connolly. "HyperText Markup Language
Specification - 2.0." Work in Progress
(draft-ietf-html-spec-05.txt), MIT/W3C, August 1995.
[4] T. Berners-Lee, L. Masinter, and M. McCahill. "Uniform Resource
Locators (URL)." RFC 1738, CERN, Xerox PARC, University of
Minnesota, December 1994.
[5] 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.
[6] R. Braden. "Requirements for Internet hosts - application and
support." STD 3, RFC 1123, IETF, October 1989.
[7] D. H. Crocker. "Standard for the Format of ARPA Internet Text
Messages." STD 11, RFC 822, UDEL, August 1982.
[8] 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.
[9] R. Fielding. "Relative Uniform Resource Locators." RFC 1808,
UC Irvine, June 1995.
[10] 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.
[11] 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.
[12] J. Postel. "Simple Mail Transfer Protocol." STD 10, RFC 821,
USC/ISI, August 1982.
[13] J. Postel. "Media Type Registration Procedure." RFC 1590,
USC/ISI, March 1994.
[14] J. Postel and J. K. Reynolds. "File Transfer Protocol (FTP)."
STD 9, RFC 959, USC/ISI, October 1985.
[15] J. Reynolds and J. Postel. "Assigned Numbers." STD 2, RFC 1700,
USC/ISI, October 1994.
[16] K. Sollins and L. Masinter. "Functional Requirements for
Uniform Resource Names." RFC 1737, MIT/LCS, Xerox Corporation,
December 1994.
[17] US-ASCII. Coded Character Set - 7-Bit American Standard Code
for Information Interchange. Standard ANSI X3.4-1986, ANSI,
1986.
[18] 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.
15. 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 5702
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
W3 Consortium
MIT Laboratory for Computer Science
545 Technology Square
Cambridge, MA 02139, U.S.A.
Tel: +1 (617) 258 8143
Fax: +1 (617) 258 8682
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 [13].
Media Type name: message
Media subtype name: http
Required parameters: none
Optional parameters: version, msgtype
version: The HTTP-Version number of the enclosed message
(e.g., "1.0"). If not present, the version can be
determined from the first line of the body.
msgtype: The message type -- "request" or "response". If
not present, the type can be determined from the
first line of the body.
Encoding considerations: only "7bit", "8bit", or "binary" are
permitted
Security considerations: none
B. Tolerant Applications
Although this document specifies the requirements for the
generation of HTTP/1.0 messages, not all applications will be
correct in their implementation. We therefore recommend that
operational applications be tolerant of deviations whenever those
deviations can be interpreted unambiguously.
Clients should be tolerant in parsing the Status-Line and servers
tolerant when parsing the Request-Line. In particular, they should
accept any amount of SP or HT characters between fields, even
though only a single SP is required.
The line terminator for HTTP-header fields is the sequence CRLF.
However, we recommend that applications, when parsing such headers,
recognize a single LF as a line terminator and ignore the leading
CR.
C. Relationship to MIME
HTTP/1.0 reuses many of the constructs defined for Internet Mail
(RFC 822 [7]) and the Multipurpose Internet Mail Extensions
(MIME [5]) to allow entities to be transmitted in an open variety
of representations and with extensible mechanisms. However, HTTP is
not a MIME-compliant application. HTTP's performance requirements
differ substantially from those of Internet mail. Since it is not
limited by the restrictions of existing mail protocols and SMTP
gateways, HTTP does not obey some of the constraints imposed by
RFC 822 and MIME for mail transport.
This appendix describes specific areas where HTTP differs from
MIME. Proxies/gateways to MIME-compliant protocols must be aware of
these differences and provide the appropriate conversions where
necessary.
C.1 Conversion to Canonical Form
MIME requires that an entity be converted to canonical form prior
to being transferred, as described in Appendix G of RFC 1521 [5].
Although HTTP does require media types to be transferred in
canonical form, it changes the definition of "canonical form" for
text-based media types as described in Section 3.6.1.
C.1.1 Representation of Line Breaks
MIME requires that the canonical form of any text type represent
line breaks as CRLF and forbids the use of CR or LF outside of line
break sequences. Since HTTP allows CRLF, bare CR, and bare LF (or
the octet sequence(s) to which they would be translated for the
given character set) to indicate a line break within text content,
recipients of an HTTP message cannot rely upon receiving
MIME-canonical line breaks in text.
Where it is possible, a proxy or gateway from HTTP to a
MIME-compliant protocol should translate all line breaks within
text/* media types to the MIME canonical form of CRLF. However,
this may be complicated by the presence of a Content-Encoding and
by the fact that HTTP allows the use of some character sets which
do not use octets 13 and 10 to represent CR and LF, as is the case
for some multi-byte character sets. If canonicalization is
performed, the Content-Length header field value must be updated to
reflect the new body length.
C.1.2 Default Character Set
MIME requires that all subtypes of the top-level Content-Type
"text" have a default character set of US-ASCII [17]. In contrast,
HTTP defines the default character set for "text" to be
ISO-8859-1 [18] (a superset of US-ASCII). Therefore, if a text/*
media type given in the Content-Type header field does not already
include an explicit charset parameter, the parameter
;charset="iso-8859-1"
should be added by the proxy/gateway if the entity contains any
octets greater than 127.
C.2 Conversion of Date Formats
HTTP/1.0 uses a restricted subset of date formats to simplify the
process of date comparison. Proxies/gateways from other protocols
should ensure that any Date header field present in a message
conforms to one of the HTTP/1.0 formats and rewrite the date if
necessary.
C.3 Introduction of Content-Encoding
MIME does not include any concept equivalent to HTTP's
Content-Encoding header field. Since this acts as a modifier on the
media type, proxies/gateways to MIME-compliant protocols must
either change the value of the Content-Type header field or decode
the Entity-Body before forwarding the message.
Note: Some experimental applications of Content-Type for
Internet mail have used a media-type parameter of
";conversions=<content-coding>" to perform an equivalent
function as Content-Encoding. However, this parameter is not
part of the MIME specification at the time of this writing.
C.4 No Content-Transfer-Encoding
HTTP does not use the Content-Transfer-Encoding (CTE) field of
MIME. Proxies/gateways from MIME-compliant protocols must remove
any non-identity CTE ("quoted-printable" or "base64") encoding
prior to delivering the response message to an HTTP client.
Proxies/gateways to MIME-compliant protocols are responsible for
ensuring that the message is in the correct format and encoding for
safe transport on that protocol, where "safe transport" is defined
by the limitations of the protocol being used. At a minimum, the
CTE field of
Content-Transfer-Encoding: binary
should be added by the proxy/gateway if it is unwilling to apply a
content transfer encoding.
An HTTP client may include a Content-Transfer-Encoding as an
extension Entity-Header in a POST request when it knows the
destination of that request is a proxy/gateway to a MIME-compliant
protocol.