One document matched: draft-fielding-http-spec-00.txt
Network Working Group T. Berners-Lee
INTERNET-DRAFT R. T. Fielding
<draft-fielding-http-spec-00.txt> H. Frystyk Nielsen
Expires May 28, 1995 November 28, 1994
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
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Internet-Drafts are draft documents valid for a maximum of six
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To learn the current status of any Internet-Draft, please check
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Distribution of this document is unlimited. Please send comments
to the proposed HTTP working group at <http-wg@cuckoo.hpl.hp.com>.
Discussions of the working group are archived at
<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@info.cern.ch> 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 and negotiation of data
representation, allowing systems to be built independently of the
data being transferred.
HTTP has been in use by the World-Wide Web global information
initiative since 1990. This specification reflects preferred usage
of the protocol referred to as "HTTP/1.0", and is compatible with
the most commonly used HTTP server and client programs implemented
prior to November 1994.
Table of Contents
1. Introduction
1.1 Purpose
1.2 Overall Operation
1.3 Terminology
2. Notational Conventions and Generic Grammar
2.1 Augmented BNF
2.2 Basic Rules
3. HTTP Message
3.1 Header Fields
3.2 Object Body
4. Usage of RFC 822 and MIME Constructs
4.1 Date/Time Format
4.2 Content Types
4.2.1 Multipart Types
4.2.1.1 Multipart/alternative
4.2.1.2 Multipart/mixed
4.2.1.3 Multipart/parallel
4.2.1.4 Other Multipart Types
4.3 General Message Header Fields
4.3.1 Date
4.3.2 Forwarded
4.3.3 Message-ID
4.3.4 MIME-Version
5. Request
5.1 Request-Line
5.2 Method
5.2.1 GET
5.2.2 HEAD
5.2.3 POST
5.2.3.1 Returned Object Headers
5.2.3.2 Link Type
5.2.3.3 Submission
5.2.4 PUT
5.2.5 DELETE
5.3 HTTP-Version
5.4 Universal Resource Identifier
5.5 Request Header Fields
5.5.1 User-Agent
5.5.2 If-Modified-Since
5.5.3 Pragma
5.5.4 Authorization
5.5.5 Proxy-Authorization
5.5.6 Referer
5.5.7 From
5.5.8 Accept
5.5.9 Accept-Encoding
5.5.10 Accept-Language
6. Response
6.1 Status-Line
6.2 HTTP Version
6.3 Status Codes and Reason Phrases
6.3.1 Successful 2xx
6.3.2 Redirection 3xx
6.3.3 Client Error 4xx
6.3.4 Server Errors 5xx
6.4 Response Header Fields
6.4.1 Server
6.4.2 WWW-Authenticate
6.4.3 Proxy-Authenticate
7. Object Header Fields
7.1 Allow
7.2 Content-Length
7.3 Content-Type
7.4 Content-Encoding
7.5 Content-Transfer-Encoding
7.6 Content-Language
7.7 Expires
7.8 Last-Modified
7.9 URI Header
7.10 Location
7.11 Version
7.12 Derived-From
7.13 Release
7.14 Title
7.15 Link
8. HTTP Negotiation Algorithm
9. Basic Access Authentication Scheme
10. Registration Authority
11. Security Considerations
11.1 Authentication of Clients
11.2 Idempotent Methods
11.3 Abuse of Server Log Information
12. Acknowledgments
13. References
14. Authors Addresses
Appendix A. Format of a uuencoded file
Appendix B. Server tolerance of bad clients
Appendix C. Client tolerance of bad servers
C.1 Back compatibility
C.2 White space
1. Introduction
1.1 Purpose
The Hypertext Transfer Protocol (HTTP) is an application-level
protocol with the lightness and speed necessary for distributed,
collaborative, hypermedia information systems. HTTP has been in use
by the World-Wide Web global information initiative since 1990.
This specification reflects preferred usage of the protocol
referred to as "HTTP/1.0". This specification does not necessarily
reflect the "current practice" of any single HTTP server or client
implementation. It does, however, seek to remain compatible with
existing implementations wherever possible, and should be
considered the reference for future implementations of HTTP/1.0.
Practical information systems require more functionality than
simple retrieval, including search, front-end update, and
annotation. HTTP/1.0 allows an open-ended set of methods to be used
to indicate the purpose of a request. It builds on the discipline
of reference provided by the Universal Resource Identifier (URI)
[2], as a location (URL) [3, 8] or name (URN), for indicating the
object on which a method is to be applied. In addition, messages
are passed in a format similar to that used by Internet Mail [6]
and the Multipurpose Internet Mail Extensions (MIME) [4].
HTTP/1.0 is also used for communication between user agents and
various gateways, allowing hypermedia access to existing Internet
protocols like SMTP [11], NNTP [10], FTP [13], Gopher [1], and WAIS
[7]. HTTP/1.0 is designed to allow such gateways, via proxy agents,
without any loss of the data conveyed by those earlier protocols.
1.2 Overall Operation
The HTTP protocol is based on a request/response paradigm. A
requesting program (termed a client) establishes a connection with
a receiving program (termed a server) and sends a request to the
server in the form of a request method, URI, and protocol version,
followed by a MIME-like message containing request modifiers,
client information, and possible body content. The server responds
with a status line (including its protocol version and a success or
error code), followed by a MIME-like message containing server
information, object metainformation, and possible body content. It
should be noted that a given program may be capable of being both a
client and a server; our use of those terms refers only to the role
being performed by the program during a particular connection,
rather than to the program's purpose in general.
On the Internet, the communication generally takes place over a
TCP/IP connection. The default port is TCP 80 [14], but other ports
can be used. This does not preclude the HTTP/1.0 protocol from
being implemented on top of any other protocol on the Internet, or
on other networks. The mapping of the HTTP/1.0 request and response
structures onto the transport data units of the protocol in
question is outside the scope of this specification.
For most current implementations, the connection is established by
the client prior to each request and closed by the server after
sending the response. However, this is not a feature of the
protocol and is not required by this specification. Both clients
and servers must be capable of handling cases where either party
closes the connection prematurely, due to user action, automated
time-out, or program failure. In any case, the closing of the
connection by either or both parties always terminates the current
request, regardless of its status.
1.3 Terminology
This specification uses a number of terms to refer to the roles
played by participants in, and objects of, the HTTP communication.
connection
A virtual circuit connecting two parties for the purpose of
communication.
request
An HTTP request message (as defined in Section 5).
response
An HTTP response message (as defined in Section 6).
resource
A network data object or service, identified by a URI
client
A program that establishes connections for the purpose of
sending requests.
user agent
The client program which is closest to the user and which
initiates requests at their behest.
server
A program that accepts connections in order to service requests
by sending back responses
origin server
The server from which a given resource originates.
proxy
An intermediary program which acts as both a server and a client
for the purpose of forwarding requests. Proxies are often used
to act as a portal through a network firewall. A proxy agent
accepts requests from other clients and services them either
internally or by passing them (with possible translation) on to
other servers. A caching proxy is a proxy agent with a local
cache of server responses -- frequently requested objects can be
serviced from the cache rather than from the origin server. A
proxy server is a proxy agent that also acts as an origin server.
gateway
A proxy agent which services HTTP requests by translation into
protocols other than HTTP. The reply sent from the remote server
to the gateway is likewise translated into HTTP before being
forwarded to the user agent.
2. Notational Conventions and Generic Grammar
2.1 Augmented BNF
All of the mechanisms specified in this document are described in
both prose and the augmented Backus-Naur Form (BNF) of RFC 822 [6].
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, TAB, 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 slash ("/") are alternatives, e.g. "foo
/ bar" will accept foo or bar.
(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 (","). This makes the usual form of lists very easy;
a rule such as
"(element *("," 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.
2.2 Basic Rules
; (Dec. Octet)
OCTET = <any 8-bit character> ; ( 0-255 )
CHAR = <any US-ASCII character> ; (0 - 127) [16]
HIGHALPHA = <any US-ASCII uppercase ; ( 65 - 90 )
letter>
LOWALPHA = <any US-ASCII lowercase ; ( 97 -122 )
letter>
ALPHA = HIGHALPHA / LOWALPHA
DIGIT = <any US-ASCII digit
"0" through "9"> ; ( 48 - 57 )
CTL = <any US-ASCII control ; ( 0 - 31 )
and DEL> ; ( 127 )
CR = <US-ASCII CR,
carriage return> ; ( 13 )
LF = <US-ASCII LF, linefeed> ; ( 10 )
SP = <US-ASCII SP, space> ; ( 32 )
HTAB = <US-ASCII HT,
horizontal-tab> ; ( 9 )
<"> = <US-ASCII quote mark> ; ( 34 )
CRLF = CR LF
LWSP-char = SP / HTAB ; semantics = SP
linear-white-space ; semantics = SP
= 1*( [CRLF] LWSP-char) ; CRLF => folding
tspecials = "(" / ")" / "<" / ">" / "@"
/ "," / ";" / ":" / "\" / <">
/ "/" / "[" / "]" / "?" / "="
; tspecials must be in quoted-string to use within
; parameter values
token = 1*<any CHAR except SP,
CTLs, or tspecials>
quoted-string = <"> *(qtext) <">
qtext = <any CHAR excepting <">, "'" & CR,
& including linear-white-space>
phrase = 1*word
word = token / quoted-string
delimiters = tspecials / linear-white-space
text = <any CHAR, ; for generic
including bare CR, ; field contents
but NOT including CRLF>
3. HTTP Message
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 [6] for transferring data objects. Both messages may
include optional header fields (a.k.a. "headers") and an object
body. The object body is separated from the headers by a null line
(i.e., a line with nothing preceding the CRLF).
Full-Request = Request-Line ; see Section 5.1
*General-Header ; see Section 4.3
*Request-Header ; see Section 5.5
*Object-Header ; see Section 7
CRLF
[ Object-Body ]
Full-Response = Status-Line ; see Section 6.1
*General-Header ; see Section 4.3
*Response-Header ; see Section 6.4
*Object-Header ; see Section 7
CRLF
[ Object-Body ]
3.1 Header Fields
HTTP header fields, which include Request-Header, Response-Header,
General-Header, Object-Header, and extension fields, follow the
same generic format as that given in Section 3.1 of RFC 822 [6].
Each header field consists of a name followed by a colon (":") and
the field value. The field value may be preceded by any amount of
linear-white-space, though a single SP is preferred. Header fields
can be extended over multiple lines by preceding each extra line
with one or more linear white-space characters.
HTTP-header = field-name ":" [ field-value ] CRLF
field-name = 1*<any CHAR, excluding CTLs, SP, and ":">
field-value = *( field-content / comment )
[ CRLF 1*LWSP-char field-value ]
field-content = <the US-ASCII characters making up the
field-value and consisting of combinations
of token, tspecials, and quoted-string,
or else consisting of text>
The order in which header fields are received is not significant.
However, it is considered "good practice" to send General-Header
fields first, followed by Request-Header or Response-Header fields
prior to the Object-Header fields. Comments can be included in HTTP
header fields by surrounding the comment text with parentheses.
However, because HTTP is rarely seen by human eyes, use of comments
is discouraged.
comment = "(" *(ctext / comment) ")"
ctext = <any CHAR excluding "(", ")", "` & CR,
& including linear-white-space>
3.2 Object Body
The data object (if any) sent with an HTTP/1.0 request or response
is in a format and encoding defined by the Object-Header fields,
the default being of type "plain/text" with "binary" encoding. Note
that, while all other information in the request or response is in
US-ASCII with lines delimited by CRLF, the Object-Body may contain
8-bit binary data.
Object-Body = *OCTET
The actual length, encoding, and data type of the Object-Body is
determined via the header fields Content-Length, Content-Encoding,
Content-Transfer-Encoding, and Content-Type, similar to those
defined by MIME [4]. If the Content-Length header field is present,
its value in bytes (number of octets) represents the length of the
Object-Body. Otherwise, the body length is determined either by a
heuristic function of the Content-Type and Content-Encoding, or by
the closing of the connection by the server.
Note: Closing the connection cannot be used to indicate content-
length when the data object is part of a request message,
as it leaves no possibility for the server to send back a
response.
4. Usage of RFC 822 and MIME Constructs
HTTP/1.0 reuses many of the constructs defined for Internet Mail
(RFC 822, [6]) and the Multipurpose Internet Mail Extensions (MIME,
[4]) to allow objects to be transmitted in an open variety of
representations. However, because it is not limited by the
restrictions of existing mail protocols and gateways, HTTP does not
obey some of the constraints imposed by RFC 822 and MIME for mail
transport. This section describes how these common constructs are
defined within HTTP.
4.1 Date/Time Format
For historical reasons, HTTP/1.0 allows 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 [5]
(an update to RFC 822 [6]). The second format is in common use
today, but is based on the obsolete RFC 850 [9] date format and
lacks a four-digit year. HTTP/1.0 clients and servers must accept
all three formats, though they should never generate the third
(asctime) format. It is strongly recommended that future clients
and servers only generate the RFC 1123 format for representing
date/time stamps in HTTP/1.0 requests and responses.
All HTTP/1.0 date/time stamps must be represented in Universal Time
(UT), also known as Greenwich Mean Time (GMT), without exception.
This is indicated in the first two formats by the inclusion of
"GMT" as the three-letter abbreviation for time zone, and should be
assumed when reading the asctime format.
HTTP-date = rfc1123-date / rfc850-date / asctime-date
rfc1123-date = wkday "," SP date1 SP time SP "GMT"
rfc850-date = weekday "," SP date2 SP time SP "GMT"
asctime-date = wkday SP date3 SP time SP 4DIGIT
date1 = 2DIGIT SP month SP 4DIGIT
; day month year (e.g. 02 Jun 1982)
date2 = 2DIGIT "-" month "-" 2DIGIT
; day-month-year (e.g. 02-Jun-82)
date3 = month SP ( 2DIGIT / ( SP 1DIGIT ))
; month day (e.g. Jun 2)
time = 2DIGIT ":" 2DIGIT ":" 2DIGIT
; 00:00:00 - 23:59:59
wkday = "Mon" / "Tue" / "Wed"
/ "Thu" / "Fri" / "Sat" / "Sun"
weekday = "Monday" / "Tuesday" / "Wednesday"
/ "Thursday" / "Friday" / "Saturday" / "Sunday"
month = "Jan" / "Feb" / "Mar" / "Apr"
/ "May" / "Jun" / "Jul" / "Aug"
/ "Sep" / "Oct" / "Nov" / "Dec"
It should be noted that the 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.
4.2 Content Types
HTTP uses Internet Media Types [12], formerly referred to as MIME
Content-Types [4], in order to provide open and extensible data
typing and type negotiation. For mail applications, where there is
no type negotiation between sender and receiver, it is reasonable
to put strict limits on the set of allowed content types. With
HTTP, however, user agents can identify acceptable media types as
part of the connection, and thus are allowed more freedom in the
use of non-registered types. The following grammar for media types
is a superset of that for MIME.
media-type = type "/" subtype *( ";" parameter)
type = token ; case-insensitive
subtype = token ; case-insensitive
parameter = attribute "=" value
attribute = token ; case-insensitive
value = token / quoted-string ; sometimes
; case-sensitive
4.2.1 Multipart Types
HTTP provides for a number of "multipart" types -- encapsulations of
several object body parts within a single message's Object-Body.
Multipart responses should only be used when the user agent has
indicated acceptability of the multipart type in addition to the
content types of each constituent body part.
As in MIME [4], all multipart types share a common syntax and must
include a boundary parameter as part of the media-type. Unlike in
MIME, the boundary parameter must always be enclosed in quotes
(<">) and multipart body parts may contain HTTP header fields which
are significant to the meaning of that part.
boundary = 0*69( bchar / SP ) bchar
bchar = DIGIT / ALPHA / "'" / "(" / ")" / "+"
/ "_" / "," / "-" / "." / "/" / ":" / "=" / "?"
The Object-Body of a multipart message is specified as follows:
multipart-body = discard-text 1*encapsulation
close-delimiter discard-text
encapsulation = delimiter body-part CRLF
delimiter = "--" boundary CRLF
; taken from Content-type field. There must
; be no space between "--" and boundary.
close-delimiter = "--" boundary "--" CRLF
; Again, no space by "--"
discard-text = *(*text CRLF)
; to be ignored upon receipt
body-part = *Object-Header
CRLF
[ Object-Body ] ; May be recursive
; if boundary differs
A URI-header field (Section 7.9) should be included in the body-
part for each enclosed object which can be identified by a URI.
4.2.1.1 Multipart/alternative
The "multipart/alternative" content-type is used in MIME to send
content-type variants of a single entity when the receiver's
capabilities are not known. This is not the case with HTTP.
Multipart/alternative can be used to provide metainformation of
many instances of an object, as in the case of a redirection
response. This allows, for example, URIs of a set of instances of
an object to be returned by a name server.
4.2.1.2 Multipart/mixed
The "multipart/mixed" media type can be used when the first body-
part contains references to other parts which the server wishes to
send at the same time. For example, the first body-part could be an
HTML document and the following body-parts could be annotations
upon that document. However, the use of multipart/mixed is strongly
discouraged in cases where the related objects are likely to have
already been retrieved and cached by the user agent or a caching
proxy.
4.2.1.3 Multipart/parallel
The "multipart/parallel" media type is identical to
multipart/mixed, but with the additional semantics that the parts
should be presented simultaneously by the user agent. This type
would be appropriate for situations where simultaneous presentation
is an important aspect of the information, such as for audio-
annotated slides and movies.
4.2.1.4 Other Multipart Types
The other multipart types defined by IANA [14] 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.
4.3 General Message Header Fields
There are a few header fields which have general applicability for
both request and response messages, but which do not apply to the
communicating parties or the object being transferred. Although
none of the General-Header fields are required, they are all
strongly recommended (where appropriate) and should be implemented
by future HTTP/1.0 clients and servers. These headers apply only to
the message being transmitted.
General-Header = Date
/ Forwarded
/ Message-ID
/ MIME-Version
4.3.1 Date
The Date header represents the date and time at which the message
was originated, having the same semantics as orig-date in RFC 822.
Note that only user agents and origin servers can originate a
message. However, if a message is received via direct connection
with the user agent (in the case of requests) or the origin server
(in the case of responses), then the default date can be assumed to
be the current date at the receiving end. However, since the date--
as it is believed by the origin--is important for evaluating cached
responses, origin servers should always include a Date header. A
received message which does not have a Date header field should be
assigned one by the receiver if and only if the message will be
cached by that receiver or gatewayed via a protocol which requires
a Date. The field value is an HTTP-date, as described in Section
4.1.
Date = "Date" ":" HTTP-date
An example is
Date: Tue, 15 Nov 1994 08:12:31 GMT
Only one Date header field is allowed per message.
Note: An earlier version of this document incorrectly specified
that this field should contain the creation date of the
enclosed data object. This has been changed to reflect
actual (and proper) usage.
4.3.2 Forwarded
The Forwarded header is to be used by gateways and proxy agents to
indicate the intermediate steps between the user agent and the
server (on requests) and between the origin server and the client
(on responses). It is analogous to the "Received" field of RFC 822
and is intended to be used for tracing transport problems and
avoiding request loops.
Forwarded = "Forwarded" ":" "by" URI [ "(" product ")" ]
[ "for" FQDN ]
FQDN = <Fully-Qualified Domain Name>
In the following example, a message is sent from a client on
ptsun00.cern.ch to a server at www.ics.uci.edu port 80 via an
intermediate HTTP proxy agent at info.cern.ch port 8000. The
request received by the server at www.ics.uci.edu will then have
the following Forwarded header field:
Forwarded: by http://info.cern.ch:8000/ for ptsun00.cern.ch
Multiple Forwarded header fields are allowed and should represent
each gateway or proxy agent that has forwarded the message. It is
strongly recommended that proxy agents used as a portal through a
network firewall do not, by default, send out information about the
internal hosts within the firewall region. This information should
only be propagated if explicitly enabled. If not enabled, the for
token and FQDN should not be included in the field value.
4.3.3 Message-ID
The Message-ID field in HTTP is identical to that used by Internet
Mail and USENET messages, as defined in [9]. That is, it gives the
message a single, unique identifier which can be used for
identifying the message (not its contents) for "much longer" than
the expected lifetime of that message.
Message-ID = "Message-ID" ":" "<" addr-spec ">"
addr-spec = unique-string "@" FQDN
unique-string = <1*CHAR, not including whitespace or ">">
where unique-string must be unique within the host specified by
FQDN. An example is
Message-ID: <9411151630.4256@info.cern.ch>
which is composed using the time, date and process-ID on the host
info.cern.ch.
Note: Unlike the URI-header field, the Message-ID does not give
a way of accessing the resource, so the Message-ID cannot
be used to refer to that resource. However, in the case
of USENET news articles, the Message-ID may in fact be
used within a URI for retrieval of the message via NNTP.
4.3.4 MIME-Version
HTTP/1.0 messages may include a single MIME-Version header field to
indicate what version of the MIME protocol was used to construct
the message. It is important to note, however, that this should not
be considered as an indication of full compliance with MIME as it
has been defined in [4]. Gateways are responsible for ensuring this
compliance (where possible) when exporting HTTP messages to strict
MIME environments.
MIME-Version = "MIME-Version" ":" 1*DIGIT "." 1*DIGIT
MIME version "1.0" is the default for use in HTTP/1.0.
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 object
requested, the identifier of the object, 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. However,
applications using HTTP/0.9 should be upgraded to HTTP/1.0.
Request = Simple-Request / Full-Request
Simple-Request = "GET" URI CRLF ; HTTP/0.9 request
Full-Request = Request-Line ; see Section 5.1
*General-Header ; see Section 4.3
*Request-Header ; see Section 5.5
*Object-Header ; see Section 7
CRLF
[ Object-Body ] ; see Section 3.2
If an HTTP/1.0 server receives a Simple-Request, it must respond
with an HTTP/0.9 Simple-Response. Similarly, if a client 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.
5.1 Request-Line
The Request-Line begins with a method token, followed by the URI
and the protocol version, and ending with CRLF. The elements are
separated by LWSP-chars. No CR or LF are allowed except in the
final CRLF sequence.
Request-Line = Method URI HTTP-Version CRLF
5.2 Method
The Method token indicates the method to be performed on the object
identified by the URI. The method is case-sensitive and extensible.
Method = "GET" / "HEAD" ; case-sensitive
/ "PUT" / "POST"
/ "DELETE" / extension-method
extension-method = token
The methods GET and HEAD must be supported by all conforming
HTTP/1.0 servers. The list of methods acceptable by a specific
object can be specified in an "Allow" Object-Header (Section 7.1).
However, the client is always notified through the return code of
the response whether a method is currently allowed on a specific
URI, as this can change dynamically. The set of common methods for
HTTP/1.0 are specified below. Although this set can be easily
expanded, additional methods cannot be assumed to share the same
semantics for separately extended clients and servers. In order to
maintain compatibility, the semantic definition for extension
methods should be registered with the HTTP registration authority
(Section 10). Servers should return the Status-Code "501 Not
Implemented" if the method is unknown.
5.2.1 GET
The GET method means retrieve whatever data is identified by the
URI. In the case where the URI refers to a data-producing process,
or a script which can be run by such a process, it is the produced
data which shall be returned as the Object-Body in the response and
not the source text of the script or process.
If supported by the server, the GET method can be used for text
searches. The URI used in the request is the URI identifying the
object, suffixed by a "?" character and the text to be searched as
specified by RFC 1630 [2]. If the object being searched is in fact
itself the result of a search (i.e. the URI contains a "?"), then
those search terms are first stripped off, so the search is
performed on the original object. The body part of the response
shall, except in the case of error situations, always be the result
of the search.
5.2.2 HEAD
The HEAD method is similar to GET but the server may not return any
Object-Body in the response. This method can be used for obtaining
metainformation about the object identified by the URI such as the
last-modified date for use in caching schemes etc.
5.2.3 POST
The POST method is used to request that the origin server accept
the enclosed object as a new subordinate of the object given by the
request URI. Depending upon the URI in question, this new object
may be a document annotation, a message intended for a bulletin
board or newsgroup, an additional item to be appended to a list, or
a block of data (usually a form) to be processed via a gateway
program.
The POST method is designed as a generic way to allow a user agent
to add more information to a server without insisting that it be
stored under a specific URI. Where possible and appropriate, a new
URI will be allocated by the origin server and returned to the
client for future reference to that object. Note that this is not
the case when the HTTP protocol is used by user agent posting a
SMTP mail message through a proxy agent. The posted object is
considered to be subordinate to the specified URI, in the way that
a file is subordinate to a directory containing it, or a news
article is subordinate to a newsgroup to which it is posted.
The POST method is designed to allow a uniform function to cover
o Annotation of existing documents;
o Posting a message to a bulletin board topic, newsgroup,
mailing list, or similar group of articles;
o Providing form data to a gateway program;
o Extending a document during authorship.
The user agent may not assume any postconditions of the method in
terms of web topology. For example, if a POST is accepted, the
effect may be delayed or overruled by human moderation, batch
processing, etc. The user agent should not be surprised if a link
is not immediately (or never) created.
If the URI does not refer to a gateway, the origin server is
requested to see to the storage of the new object. That is, the
origin server does not have to store it permanently, but should (if
the method was successful) return a URI by which the object can be
referenced and later retrieved. The semantics of this method imply
nothing of any undertakings by the origin server to maintain the
availability of the object.
If the user agent includes a URI-header in the request, the server
should treat that URI as advisory only. It may store the object
under a different URI, in which case the origin server must inform
the user agent of the new URI via a URI-header in the response.
5.2.3.1 Returned Object Headers
The POST method shall return a set (possibly empty) of object
headers for the newly posted object. The server may return the
entire metainformation for the object (as in the HEAD method), or a
subset of it. The posted object should not be returned in the
response, though the response Object-Body may include a status or
error message which references the new object.
5.2.3.2 Link Type
The Link header field described in Section 7.15 may be specified by
explicitly giving a (possibly reverse) link in the Object-Header of
the linked object. If one or more Link's are contained in the
Object-Header, then this information should be used. If no such
link or links are specified, then the server should generate a
link. The link type in this case is determined by the server.
Note: The server may perform other operations as a result of
the new object being added: lists and indexes might be
updated, for example. However, no mandatory operation is
imposed on the origin server.
5.2.3.3 Submission
When articles are submitted, the analogy of being added to a body
of knowledge by being linked is close. When a form is submitted,
this can be done with POST, though in this case side-effects will
be expected.
5.2.4 PUT
The PUT method specifies that the data in the Object-Body of the
request is to be stored under the supplied URI. If the URI points
to an already existing object, the enclosed object should be
considered a modified version of the one residing on the origin
server. If the URI does not point to an existing object, and that
URI is capable of being defined as a new object from the requesting
user agent, the origin server can place the object at that URI.
The actual method for determining how the object is placed, and
what happens to its predecessor, is defined entirely by the
individual origin server. If version control is implemented by the
origin server, the Version, Derived-From, and Release header fields
should be used to help identify and control revisions to an object.
5.2.5 DELETE
The DELETE method requests that the server delete the object
corresponding to the given URI. After a successful DELETE request,
the URI becomes invalid for any future references. This method can
at all times be overridden by human interaction or other means on
the remote server, so the client cannot be guaranteed that the
operation has been carried out, even if the status code returned
from the server indicates that the action has been completed
successfully.
5.3 HTTP-Version
The HTTP-Version element defines the version of the HTTP protocol
being used for the request. If the protocol version is not
specified, the server shall assume that the client uses HTTP
version 0.9 and the response should be formatted as a Simple-
Response.
HTTP-Version = "HTTP" "/" 1*DIGIT "." 1*DIGIT
Full-Request messages which obey the protocol defined by this
document should use an HTTP-Version of "HTTP/1.0".
5.4 Universal Resource Identifier
The URI is a Universal Resource Identifier, as defined in RFC 1630
[2], and identifies the object upon which to apply the request. It
can either be a URL (Uniform Resource Locator [3]) or a URN
(Uniform Resource Name). At the time of this writing, no suitable
naming system exists for URNs, but this protocol will accept such
names so long as they do not include whitespace and are
distinguishable from the existing URL name space.
URI = <As defined in RFC 1630>
Unless the server is being used as a proxy, a partial URI shall be
given with the assumptions of the protocol (http) and host name
(the server's address) being obvious. That is, if the full URI
looks like
http://info.cern.ch/hypertext/WWW/TheProject.html
then the corresponding partial URI in the Simple-Request or Full-
Request is
/hypertext/WWW/TheProject.html
In the case of a client sending a request through a proxy or
gateway, the protocol and host name must be explicitly declared.
Note: The URI should be encoded using the escaping scheme
described in [2]. Note that escaping is permitted for any
character but the default escaping should be limited to
reserved characters and characters which are considered
unsafe.
Note: The part of an URL after the host name and optional port
number is completely opaque to the client: The client may
make no deductions, such as the file type, about the
object based on the URL pointing to it.
5.5 Request Header Fields
The request header fields provide the possibility for the client to
pass additional information about the request and the client itself
to the server. All header fields are RFC 822 conforming and are
optional for the client to transmit. However, the client is
strongly encouraged to specify as many as possible.
Request-Header = User-Agent
/ If-Modified-Since
/ Pragma
/ Authorization
/ Proxy-Authorization
/ Referer
/ From
/ Accept
/ Accept-Encoding
/ Accept-Language
These header fields are explained in the following subsections.
Unknown header fields should be considered Object-Header fields.
5.5.1 User-Agent
The User-Agent field contains information about the user agent
originating the request. This is for statistical purposes, the
tracing of protocol violations, and automated recognition of user
agents for the sake of tailoring responses to avoid particular user
agent limitations or features. Although it is not required, user
agents should always include this field with requests. The field
can contain multiple tokens specifying the product name, with an
optional slash and version designator, and other products which
form a significant part of the user agent. By convention, the
products are listed in order of their significance for identifying
the application.
User-Agent = "User-Agent" ":" 1*product
product = token ["/" product-version]
product-version = 1*DIGIT "." 1*DIGIT
Example:
User-Agent: CERN-LineMode/2.15 libwww/2.17
Product tokens should be short and to the point -- use of this field
for advertizing or other non-essential information is explicitly
deprecated and will be considered as non-cormance to the protocol.
See Section 6.4.1 for a description of what should be done for
requests passed through a gateway or proxy.
Note: Some current proxiy applications append their product
information to the list in the User-Agent field. This is
no longer recommended, since it makes machine
interpretation of these fields ambiguous.
5.5.2 If-Modified-Since
The If-Modified-Since header field is used with the GET method to
make it conditional: if the requested document has not been
modified since the time specified in this field, the document will
not be returned from the server; instead, a "304 Not Modified"
response will be returned without any Object-Body. The format of
this field is an absolute date and time in the HTTP-date format of
Section 4.1:
If-Modified-Since = "If-Modified-Since" ":" HTTP-date
An example of the field is:
If-Modified-Since: Sat, 29 Oct 1994 19:43:31 GMT
The purpose of this feature is to allow efficient updates of local
cache information with a minimum amount of transaction overhead.
The same functionality can be obtained, though with much greater
overhead, by issuing a HEAD request possibly followed by a GET
request.
5.5.3 Pragma
Pragma directives should be understood by servers to which they are
relevant, e.g. a proxy. They give the client the possibility of
affecting the default behavior of the server. The syntax is the
same as for other multiple-value fields in HTTP, however the
current specification only contains one valid parameter:
Pragma = "Pragma" ":" 1*#pragma-param
pragma-param = "no-cache" / extension-pragma
extension-pragma = token
When the "no-cache" parameter is present, a caching proxy should
not return a document from the cache even though it has not
expired, but it should always request the document from the actual
server.
Note: Pragmas should be passed through by proxies even though
they might have significance to the proxy itself. This is
necessary in cases when the request has to go through
many proxies, and the pragma may affect all of them. It
is not possible to specify a pragma for a specific proxy;
however, any pragma-param not relevant to a gateway or
proxy should be ignored.
5.5.4 Authorization
This version of the HTTP protocol contains a simple access
authentication scheme which is explained in Section 9. The
Authorization header field identifies the user requesting a URI on
an HTTP server.
Authorization = "Authorization" ":" (("Basic" uu-encoded)
/ (extension-scheme extension-encrypted))
uu-encoded = <UU encoding of userid-password>
userid-password = [word] ":" [word]
extension-scheme = token
extension-encrypted = token
The format of this field is in extensible form so that it can
handle other and more advanced encryption schemes. The first word
is a specification of the authorization system in use followed by
the encrypted version of the User-ID and the password separated by
a ":" in clear text. It is important to note that the Basic scheme
only provides a low-level security similar to the methods used by
unmodified FTP, Telnet, etc.
Note: The specification indicates that the userid-password can
be the sequence ":" as both the User-ID and the password
are optional, however it is not the recommended usage.
5.5.5 Proxy-Authorization
The Proxy-Authorization header field allows the client to identify
itself (or its user) to a proxy agent which requires
authentication. The format is the same as for Authorization.
Proxy-Authorization = "Proxy-Authorization" ":"
(("Basic" uu-encoded)
/(extension-scheme extension-encrypted))
Unlike Authorization, the Proxy-Authorization applies only to the
current connection and must not be passed on to higher-level
servers or proxies.
5.5.6 Referer
The Referer field allows the client to specify, for the server's
benefit, the address (URI) of the document (or element within the
document) from which the URI in the request was obtained. This
allows a server to generate lists of back-links to documents, for
interest, logging, optimized caching etc. It also allows bad links
to be traced for maintenance. The format of the field is:
Referer = "Referer" ":" URI
Example:
Referer: http://info.cern.ch/hypertext/DataSources/Overview.html
If a partial URI is given, then it should be parsed relative to the
URI of the object of the request.
Note: The Referer field allows reading patterns to be studied,
and reverse links drawn, however, the field may in fact
contain a secure URI, whose revelation itself can be
considered as a breach of security. It is therefore
strongly recommended that the user be able to disable and
enable this field prior to a request.
5.5.7 From
The From header field, if given, should contain an Internet e-mail
address for the human user who controls the requesting user agent.
It should contain a machine-usable address as defined by addr-spec
in RFC 822:
From = "From" ":" addr-spec
An example is:
From: webmaster@w3.org
This header field may be used for logging purposes and as a means
for identifying the source of invalid or unwanted requests. It
should not be used as an insecure form of access protection. The
interpretation of this field is that the request is being performed
on behalf of the person given, who accepts responsibility for the
method performed. In particular, robot agents should include this
header so that the person responsible for running the robot can be
contacted if problems occur on the receiving end.
The Internet e-mail address in this field does not have to
correspond to the Internet host which issued the request. (For
example, when a request is passed through a gateway or proxy agent,
then the original issuer's address should be used). The address
should, if possible, be a valid Internet e-mail address, whether or
not it is in fact an Internet e-mail address or the Internet e-mail
representation of an address on some other mail system.
Note: The client should not send the From header field without
the user's approval, as it may conflict with the user's
privacy interests or their site's security policy. It is
strongly recommended that the user be able to disable,
enable, and modify the value of this field at any time
prior to a request.
5.5.8 Accept
This field contains a list of representation schemes (Content-Type
metainformation tokens) which are accepted in the response to the
request. The set given may of course vary from request to request
from the same client.
The field may be wrapped onto several lines according to RFC 822,
and also more than one occurrence of the field is allowed with the
significance being the same as if all the entries has been in one
field. The format of each entry in the list is:
Accept = "Accept" ":"
1#( ("*" / type) "/" ("*" / subtype)
*(";" accept-param) )
accept-param = ("q" "=" ( "0" / "1" / float) )
/ ("mxb" "=" 1*DIGIT)
float = < ANSI-C floating point text representation,
where (0.0 < float < 1.0) >
q is the quality factor of how well the client can handle the
content type and mxb is the maximum accepted size of the Object-
Body in number of octets. The definition does not prohibit
duplicate accept-param's, but leaves the interpretation undefined.
See Section 8 for a description of the negotiation algorithm and
penalty model. A quality factor of 0 is equivalent to not sending
an accept header field containing the actual content-type. The
default values are: q=1 and mxb=infinity.
In order to save time, and also allow clients to receive content
types of which they may not be aware, an asterisk "*" may be used
in place of either the type token and/or the subtype token. The
example
Accept: audio/*; q=0.2, audio/basic
should verbally be interpreted as "if you have audio/basic, send
it; otherwise send me some other audio".
If no accept field is present, then it is assumed that the client
accepts all formats with quality factor 1. This is equivalent to
the client sending the following accept header field:
Accept: */*; q=1
or
Accept: */*
A more elaborate example is
Accept: text/plain; q=0.5, text/html,
text/x-dvi; q=0.8; mxb=100000, text/x-c
Verbally, this should be interpreted as "text/html and text/x-c are
the preferred content types, but if they do not exist then send the
Object-Body in text/x-dvi if the object is less than 100000 bytes.
If this is not the case then send text/plain".
Note: The client should not try to divine which content types
are relevant to send in the request header on behalf of
the information given in the URI, for example by looking
at the file suffix in a URL. This information is
completely opaque to the client.
Note: In earlier versions of this document, the mxs parameter
defined the maximum acceptable delay in seconds before
the response would arrive. This has been removed as the
server has no means of obtaining a usable reference
value. However, this does not prevent the client from
internally measuring the response time and optimize the
accept header field accordingly by using the quality
factor.
5.5.9 Accept-Encoding
This header field is similar to the Accept header field, but lists
the Content-Encoding types which are acceptable in the response.
The Content-Encoding field is described in Section 7.4. The formal
definition is:
Accept-Encoding = "Accept-Encoding" ":" 1#encoding-mechanism
encoding-mechanism = "x-compress" / "x-gzip" / extension-encoding
extension-encoding = token
Example
Accept-Encoding: x-compress
5.5.10 Accept-Language
The "Accept-Language" field is similar to the accept header field,
but it lists the set of natural languages accepted in the response.
The language-encoding field is described in Section 7.6. The format
of the field is defined as:
Accept-Language = "Accept-Language" ":"
1#(language-dialect *1(";" language-param) )
language-dialect = ("*" / language) ["/" ("*" / dialect) ]
language-param = "q" "=" ( "0" / "1" / float)
language = <As defined in ISO 639 but case-insensitive>
dialect = <As defined in ISO 3166 but case-insensitive>
As with the Accept field, a quality factor q can be specified which
in this case describe the level of intelligibility to the user. The
default value is q=1. The definition does not prohibit duplicate
language-param's, but leaves the interpretation undefined. An
example of it's use is
Accept-Language: dk, en/gb; q=0.5
meaning: "If you have a Danish version, send it; else if you have
an British English version, send it".
Note: If the server can not serve the request with the language
specified or if the languages specified only represent a
subset in case of a multi-linguistic data object, it is
not illegal to serve the request in an unspecified
language. The character "*" can be used to indicate "any
language" and/or "any dialect".
Note: As intelligibility is highly dependent on the individual
user, it is recommended that any client applications
makes the choice of linguistic preferences available to
the user.
6. Response
If the client has issued an HTTP request, the response from the
server shall consist of the following:
Response = Simple-Response / Full-Response
Simple-Response = [Object-Body]
Full-Response = Status-Line ; see Section 6.1
*General-Header ; see Section 4.3
*Response-Header ; see Section 6.4
*Object-Header ; see Section 7
CRLF
[ Object-Body ] ; see Section 3.2
A Simple-Response should only be sent in response to an HTTP/0.9
Simple-Request. Note that the Simple-Response consists only of the
object that was requested and is terminated by the server closing
the connection.
6.1 Status-Line
The Status-Line should, like the Request-Line, consist only of the
elements specified separated by LWSP-chars. That is, no CR or LF
are allowed except in the final CRLF sequence.
Status-Line = HTTP-Version Status-Code Reason-Phrase CRLF
6.2 HTTP Version
The HTTP-Version field identifies the protocol version being used
by the server. The format of this field is identical to the
corresponding HTTP-Version field in the Request-Line described in
Section 5.3.
6.3 Status Codes and Reason Phrases
The Status-Code field contains an 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 the Reason-Phrase or to pass it on to the human user.
Status-Code = 3DIGIT
Reason-Phrase = *token
All responses, regardless of the Status-Code, may contain an Object-
Header and/or an Object-Body. This can either be the object pointed
to by the requested URI or an object containing further explanation
of the Status-Code. In the latter case, the preferred content-type
is "text/html", but "text/plain" is also accepted. As for the
Reason-Phrase, it is not mandatory for the client to pass any
explanation information in the Object-Body to the user.
The first digit of the Status-Code defines the class of responses
known to HTTP. The last two digits do not have any categorization
role. There are 5 values for the first digit:
o 1xx: Not used, but reserved for future use
o 2xx: Success - The requested action was successfully received
and understood
o 3xx: Redirection - Further action must be taken in order to
complete the request
o 4xx: Client Error - The request contains bad syntax or is
inherently impossible to fulfill
o 5xx: Server Error - The server could not fulfill the request
The values of the numeric status codes, and a default set of
corresponding Reason-Phrase's, are presented below. Every Status-
Code has a description of which method it can follow and any
metainformation required in the HTTP-header. The Status-Code of any
extension-method is not defined in this document, and no rules are
given for introducing additional codes.
6.3.1 Successful 2xx
This class of status codes indicates that the client's request was
successfully received and understood.
200 OK
o Following: GET, HEAD, POST
o Required metainformation: none
The request could be fulfilled and an Object-Header should be
returned to the client in the response. In the case of GET, the
response should also contain an Object-Body.
201 Created
o Following: POST, PUT
o Required metainformation: URI-header
This indicates that the POST has been successful or that the PUT
resulted in a new object. The newly created object can be
referenced by the URI returned in the URI-header field in the
response. This action can, at any time, be overridden at the origin
server (possibly by human intervention), so this status code is no
guarantee that the object continue to be available at teh given URI.
202 Accepted
o Following: GET, HEAD, PUT, POST, DELETE
o Required metainformation: none
The request has been accepted for processing, but the processing
has not been completed. The request may or may not eventually be
acted upon, as it may be disallowed when processing actually takes
place. There is no facility for resending a status code from an
asynchronous operations such as this.
203 Provisional Information
o Following: GET, HEAD, POST
o Required metainformation: none
When received in the response, this indicates that the returned
metainformation in the HTTP-header is not the definitive set as
available from the origin server, but is gathered from a local or a
third party copy. The set presented can either be a subset or a
superset of the original version, for example including annotation
information about the data object.
204 No Response
o Following: GET, HEAD, POST
o Required metainformation: none
The server has received the request but there is no information to
send back, and the client should stay in the same document view.
This is mainly to allow input for scripts without changing the
document at the same time.
205 Deleted
o Following: DELETE
o Required metainformation: none
The DELETE method was successful and the object has been removed by
the requested server. This action can at any time be overridden by
the origin server, for example by human interaction, so this status
code is no guarantee that the operation has in fact been carried
out.
206 Modified
o Following: PUT
o Required metainformation: none
The PUT method was successful and the object has been modified on
the requested server. This action can at any time be overridden at
the origin server, for example by human interaction so this status
code is no guarantee that the operation has in fact been carried
out.
6.3.2 Redirection 3xx
This class of status codes indicates that further action needs to
be taken by the client in order to fulfill the request. The action
required can normally be carried out by the client without
interaction with the user, but it is strongly recommended that this
only takes place if the method used in the request is either GET or
HEAD.
301 Moved Permanently
o Following: GET, HEAD, POST, PUT
o Required metainformation: URI-header, Location
The object requested has been assigned a new permanent URI, and any
future references to this object must be done using the returned
URI.
Note: It is possible for the server to send back this status
code in response to a request using the PUT and POST
methods. However, as this might change the conditions
under which the request was issued, the user agent should
not automatically redirect the request unless it can be
confirmed by the user.
Note: Clients with link editing capabilities are encouraged to
automatically relink references to the URI requested to
the new reference returned by the server, where possible.
302 Moved Temporarily
o Following: GET, HEAD, POST, PUT
o Required metainformation: URI-header, Location
The data requested resides temporarily under a different URI. As
the redirection may be altered on occasion, the client should on
future requests from the user continue to use the original URI used
for this request and not the URI returned in the URI-header field.
Note: It is possible for the server to send back this status
code in response to a request using the PUT and POST
methods. However, as this might change the conditions
under which the request was issued, the user agent should
not automatically redirect the request unless it can be
confirmed by the user.
303 Method
o Required metainformation: none
This code is obsolete.
304 Not Modified
o Following: conditional GET
o Required metainformation: none
If the client has performed a conditional GET request and access is
allowed, but the document has not been modified since the date and
time specified in the If-Modified-Since field, the server shall
respond with this status code and must not send the Object-Body to
the client. Metainformation contained in the response should only
contain information relevant to cache managers and which may have
changed independently of the object's Last-Modified date. Examples
of relevant header fields are: Date, Server, and Expires, however
none of them are mandatory.
6.3.3 Client Error 4xx
The 4xx class of status codes is intended for cases in which the
client seems to have erred. The codes can follow any method
described in Section 5.2, and the set consists of:
400 Bad Request
o Required metainformation: none
The request had bad syntax or was inherently impossible to be
satisfied. The client is discouraged from repeating the request
without modifications.
401 Unauthorized
o Required metainformation: WWW-Authenticate
The server must return a WWW-Authenticate header field as described
in Section 6.4.2 containing a list of authorization schemes in
which at least one must be fulfilled in order for the client to
obtain the Object-Body. The client should then retry the request
with a suitable Authorization header field. The HTTP access
authentication scheme is explained in Section 9.
402 Payment Required
o Required metainformation: none
This code is not currently supported, but is reserved for future
use.
403 Forbidden
o Required metainformation: none
The request is, for some reason unknown to the client, forbidden.
Authorization will not help and the request should not be repeated.
This status code can also be used if the server does not want to
make public whether the request can not be fulfilled due to
insufficient authorization from the client or because the object
does not exist.
404 Not Found
o Required metainformation: none
The server has not found anything matching the URI given. No
indication is given whether the condition is temporary or permanent.
405 Method Not Allowed
o Required metainformation: Allow
The method specified in the Request-Line is not allowed for the
object identified by the URI. The server should send back an Allow
header containing a list of valid method's as explained in Section
7.1.
406 None Acceptable
o Required metainformation: Content-Type, Content-Encoding,
Content-Language
The server has found an object matching the URI given, but not one
that matches all of the conditions identified in the Accept, Accept-
Encoding, and Accept-Language request headers. The response should
include at least the Content-Type, the Content-Encoding, and the
Content-Language, but is encouraged to include the object's
complete metainformation. No Object-Body can be included in the
response.
407 Proxy Authentication Required
o Required metainformation: Proxy-Authenticate
This code is similar to "401 Unauthorized" but it indicates that
the user agent must first authenticate itself with the proxy. The
proxy must return a Proxy-Authenticate header field as described in
Section 6.4.3 containing a list of authorization schemes in which
at least one must be fulfilled in order for the client to use the
proxy. The client should then create a new request with the proxy
as the server destination and with a suitable Proxy-Authorization
header field. The HTTP access authentication scheme is explained in
Section 9.
408 Request Timeout
o Required metainformation: none
This code indicates that the client did not produce a request
within a time that the server was prepared to wait. If the client
is still actively generating the request, it should immediately
stop sending further information to the server.
6.3.4 Server Errors 5xx
Response status codes beginning with the digit "5" indicate cases
in which the server is aware that it has erred or is incapable of
performing the request. These codes can follow any method at any
time.
Note: For all of the 5xx codes, the server is encouraged to
send back an HTTP-header and an Object-Body containing an
explanation of the error situation, and whether it is a
temporary or permanent condition.
500 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 fulfil
the request.
502 Bad Gateway
This is equivalent to "500 Internal Error", but for the case of a
gateway or proxy accessing some other service, this indicates that
the response from the other service was invalid. As from the point
of view of the client and the HTTP transaction, the other service
is hidden within the gateway or proxy, this may be treated
identically to "500 Internal Error", but has more diagnostic value.
503 Service Unavailable
The server is currently unable to handle the request. This can
either be due to overload of the server or servicing of the server.
The implication is that this is a temporary condition which may be
alleviated at other times.
504 Gateway Timeout
This is equivalent to "500 Internal Error", but for the case of a
gateway or proxy accessing some other service, this indicates that
the response from the other service did not return within a time
that the gateway was prepared to wait. As from the point of view of
the client and the HTTP transaction, the other service is hidden
within the gateway or proxy, this may be treated identically to
"500 Internal Error", but has more diagnostic value.
6.4 Response Header Fields
The response header fields provide the server the possibility to
pass additional information about the response which can not be
placed in the Status-Line. These header fields are not intended to
give information about an Object-Body returned in the response but
uniquely about the server itself. The Object-Header fields which
should be used for the latter purpose are described in Section 7.
The response header fields specified in this document are:
Response-Header = Server
/ WWW-Authenticate
/ Proxy-Authenticate
Unknown header fields should be considered Object-Header fields.
6.4.1 Server
This field contains information about the server software program
used for handling the request. The field is equivalent to the User-
Agent field in the request and has the following format:
Server = "Server" ":" 1*product
Example:
Server: CERN/3.0 libwww/2.17
If the request is going through a gateway or proxy, then these
applications must not add their data to the list received. Instead,
they should use the Forwarded field described in Section 4.3.1.
6.4.2 WWW-Authenticate
The WWW-Authenticate header field must be included as part of the
response if the server sends back a "401 Unauthorized" Status-Code
on a request from the client as part of the Basic Authentication
Scheme described in Section 9. This header field indicates the
authentication scheme used and the realm in which the requested URI
belongs. The syntax is defined as:
WWW-Authenticate = "WWW-Authenticate" ":" ("Basic" realm)
/ (extension-scheme realm)
realm = token
The contents of this field is extensible as is the case for the
Authorization field in the request header. The first word is a
specification of the authorization system in use followed by the
realm of the protected URI requested.
6.4.3 Proxy-Authenticate
The Proxy-Authenticate header field must be included as part of the
response if the proxy sends back a "407 Proxy Authentication
Required" Status-Code on a request from the client. This header
field indicates the authentication scheme used and the realm in
which the requested URI belongs. The syntax is defined as:
Proxy-Authenticate = "Proxy-Authenticate" ":" ("Basic" realm)
/ (extension-scheme realm)
realm = token
Unlike WWW-Authenticate, the Proxy-Authenticate applies only to the
current connection and must not be passed on to lower-level user
agents or proxies.
7. Object Header Fields
Any Full-Request or Full-Response message can contain Object-Header
fields and an Object-Body as defined in Section 3. This section
specifies the format and contents of the Object-Header fields.
Object-Header fields define metainformation about the Object-Body.
All are optional, but applications are strongly encouraged to
specify as many as possible. This document defines the following
header fields:
Object-Header = Allow
/ Content-Length
/ Content-Type
/ Content-Encoding
/ Content-Transfer-Encoding
/ Content-Language
/ Expires
/ Last-Modified
/ URI-header
/ Location
/ Version
/ Derived-From
/ Release
/ Title
/ Link
/ extension-header
extension-header = HTTP-header
In this section, recipient refers to either the client or the
server, depending on who receives the object. Each object header
field is explained in the subsections below. Other header fields
are allowed but cannot be assumed to be recognizable by the
recipient. Unknown header fields should be ignored by the
recipient, but passed on to downstream recipients (if any).
7.1 Allow
The "Allow" header field lists the set of methods supported by the
object identified by the requested URI. The purpose of this field
is strictly to inform the recipient of valid methods associated
with the object. This does not prevent the client from trying other
methods. However, it is recommended to follow the indications given
in this field. If not specified, the default value of the allowed
methods equals the total set of methods described in Section 5.2.
The format of the field is:
Allow = "Allow" ":" 1#method
Example of use:
Allow: GET, HEAD, PUT
7.2 Content-Length
This field indicates in number of octets the size of the Object-
Body sent to the recipient. The format of the field is
Content-Length = "Content-Length" ":" 1*DIGIT
An example is
Content-Length: 3495
Even though it is not mandatory, applications are strongly
encouraged to use this field to indicated the size of the Object-
Body to be transferred no matter of the content-type of the object.
Note: Any Content-Length of size greater than or equal to zero
is a valid value. The field has no default value.
Note: The meaning of this field is significantly different from
the corresponding specification in the MIME
specifications where it is an optional field used within
the "message/external-body" Content-Type. In HTTP, it
should be used whereever possible.
7.3 Content-Type
The format of this field which is also described in Section 4.2 is
defined as:
Content-Type = "Content-Type" ":" media-type
An example of the field is
Content-Type: text/html; charset=ISO-8859-1
Note: All content types defined by MIME including extension
tokens are of course valid tokens. The field has no
default value.
7.4 Content-Encoding
The Content-Encoding header field, unique to HTTP, is used as a
modifier to the content-type. When present, its value indicates the
encoding mechanism applied to the associated Object-Body prior to
it being enclosed in the message, and thus what decoding mechanism
must be applied in order to obtain the media type referenced by the
Content-Type header field. This is primarily used to allow object
compression without losing the identity of the underlying media
type. It has the following format:
Content-Encoding = "Content-Encoding" ":" encoding-mechanism
An example of its use is
Content-Encoding: x-gzip
Note: The Content-Encoding field differs from the "Content-
Transfer-Encoding" field defined as encoding in the MIME
specifications. The purpose of the "Content-Transfer-
Encoding" field is "to indicate the type of
transformation that has been used in order to represent
the object in an acceptable manner for transport". The
Content-Encoding field is used to indicate any form of
compression mechanism used to decrease the amount of data
to be transported. The result after encoding can still be
any type defined by the Content-Transfer-Encoding field.
7.5 Content-Transfer-Encoding
Because all HTTP communication takes place on an 8-bit clean
connection, the default content-transfer-encoding for all messages
is "binary". Note that this differs from the required default in
MIME [4], so gateways between HTTP and MIME-compliant protocols
should add an explicit "Content-Transfer-Encoding: binary" to the
message header if one is not already present.
Content-Transfer-Encoding
= type [ "/" subtype ] *( ";" parameter )
7.6 Content-Language
The Content-Language field describes the natural language of the
Object-Body. It is defined as:
Content-Language = "Content-Language" ":" 1#lang-dia
lang-dia = language ["/" dialect ]
An example of its use is
Content-Language: dk
means that the content of the message is in Danish with no dialect
specified. The example
Content-Language: en/gb, dk
means that the language is Danish and British English.
Note: Multi-linguistic data objects can be described using a
list of lang-dia codes. This document does not specify
any means to indicates the amount of different natural
languages represented in the data object.
Note: This field can be defined, not only for textual documents
but also for audio and possibly other media as well. It
should not be considered limited to data objects of type
"text".
7.7 Expires
The Expires field gives the date and time after which the
information given ceases to be valid and should be retrieved again
if it has been kept as a local copy. This allows control of caching
mechanisms, but the date and time indicated does not necessarily
imply that the original object will cease to exist. This is
completely controlled by the server. The format is an absolute date
and time as defined by HTTP-date in Section 4.1. The formal
description is
Expires = "Expires" ":" HTTP-date
and an example of the use is
Expires: Thu, 01 Dec 1994 16:00:00 GMT
Note: This field can also be used for automatic refreshing of
dynamic or volatile data. However, this is completely
dependent on the implementation of the client application
to automatically issue a new request when the object has
expired.
Note: Data objects generated by data-producing processes, or
scripts which can be run by such processes, are often
dynamic by nature. Therefore it is strongly recommended
that such data objects do contain an Expires header field.
7.8 Last-Modified
The Last-Modified field indicates the date and time of when the
data object was last modified. The format is an HTTP-date, as
described in Section 4.1, and the syntax is:
Last-Modified = "Last-Modified" ":" HTTP-date
An example of its use is
Last-Modified: Tue, 15 Nov 1994 12:45:26 GMT
Note: The definition of this header field does not specify what
is meant by "modification", as this depends on the actual
server implementation. In particular, the field is not
connected to any date and time indications given by the
operation system on which the server application is
running.
Note: If the expires header field is not present in the Object-
Header, then this field can be used by a cache mechanism
to estimate when the object expires.
7.9 URI Header
The URI-header field contains a URI by which the object may be
found. It should not be confused with the token in the Request-Line
described in Section 5.4. As for a normal request, there is no
guarantee that the object can be retrieved using the URI specified.
The field is normally a part of a response having Status-Code "301
Moved Permanently" or "302 Moved Temporarily".
URI-header = "URI" ":" 1#( URI [";" vary] )
vary = "vary" "=" <"> 1#vary-param <">
vary-param = "type" / "language" / "version" / "encoding"
/ extension-vary
extension-vary = token
If the URI is used to refer to a set of variants, then the
dimensions in which the variants may differ must be given with the
vary parameters.
Multiple occurrences of vary-param in the vary field give
alternative access names or addresses for the object. An example of
the field is:
URI: http://info.cern.ch/hypertext/WWW/TheProject.multi;
vary="type,language"
This indicates that the URI indicated covers a group of possible
data objects which varies in content-type and in natural language.
The client can specify which of these objects to be returned in the
response to a request using the request header fields: Accept,
Accept-Encoding, Accept-Language, and Version. Another example is:
URI: http://info.cern.ch/hypertext/WWW/TheProject.ps;
vary="encoding"
This indicates that the data object pointed to by the URI exists in
different encodings as defined by the Content-Encoding field.
7.10 Location
The Location header field is an earlier form of the URI-header and
is considered obsolete. However, HTTP/1.0 clients and servers
should continue to support the Location header in order to properly
interface with older applications. The purpose of Location is
identical to that of the URI-header, except that no variants can be
specified and only one location URI is allowed.
URI-header = "Location" ":" URI
7.11 Version
The Version field defines a version number referring to the current
contents of an evolving object resident on the origin server.
Together with the Derived-From field described in Section 7.12, it
allows groups of people to work simultaneously on the creation of a
work as an iterative process. The field should be used to indicate
evolution along a single path of a particular work. It should not
be used to indicate derived works or renditions in different
representations.
Version = "Version" ":" 1*DIGIT *( "." 1*DIGIT )
Note: The field should be present in the response if PUT is an
allowed method to perform on the object pointed to by the
requested URI. However the presence of the field can not
be taken as an indication whether PUT is allowed or not.
7.12 Derived-From
The Derived-From field contains the most recent value of the
Version field before any modifications local to the transmitting
application have been carried out on an evolving data object. The
definition of the field must therefore be similar to the Version
field described in Section 7.11:
Derived-From = "Derived-From" ":" 1*DIGIT *( "." 1*DIGIT )
The definition of this field allows both the server and the client
to employ a code management system to merge different versions of
an evolving data object. As for the Version field, the Derived-From
may only be used to indicate evolution along a single path of a
particular work. It should not be used to indicate derived works or
renditions in different representations.
Note: The definition allows different code management systems
to be employed by the involved parties. The only
requirement is a conforming mapping between any internal
versioning system and the one defined by Derived-From and
Version.
7.13 Release
This field is a string oriented value containing a code
representing the publisher's local versioning of the document, for
example relative to a local code management system. The definition
of this field contains no explicit semantics as publishers often
will have quite complex version information containing hidden local
semantics.
Release = "Release" ":" *text
Note: This field is significantly different from the Version
field defined in Section 7.11 which should be used
together with the PUT method. The Release does not have
an implied interpretation and can be used freely as
metainformation for any Object-Body. The value should be
considered opaque.
7.14 Title
This header field indicates the title of the document, which is not
to be considered as part of the object. The definition of the field
is:
Title = "Title" ":" *text
The field differs from the "Subject" field described in RFC 822 in
that title is defined by the creator/author of a data object, but
the "Subject" field is defined by the originator. The field is to
be considered isomorphic with the <TITLE> element in HTML [15].
7.15 Link
The Link header provides a means for describing the relationship
between HTTP-Object's. An object can have multiple Link elements
and can typically indicate relationships like hierarchical
structure. The field is semantically equivalent to the <LINK>
element in an HTML document.
Link = "Link" ":" 1#(URI *1(";" "REL" "=" relation) )
relation = "UseIndex" / "UseGlossary" / "Contents"
/ "Next" / "Previous" / "Parent"
/ "BookMark" / "Made" / "Help"
The reader is referred to the HTML specification [15] for a full
explanation of the semantics for LINK relationships. Examples of
usage include:
Link: http://info.cern.ch/previous; REL="Previous"
Link: mailto:timbl@info.cern.ch; REL="Made"
The first example indicates that this object is logically a
continuation of the previous object identified by the URI. The
second indicates that the author of the object is identified by the
given e-mail address.
Note: It has been proposed that any HTML metainformation
element (allowed within the <HEAD> as opposed to <BODY>
element of the document) be a valid candidate for an HTTP
object header. This document defines the two header
fields Link and Title which both are examples of this.
8. HTTP Negotiation Algorithm
The goal of the negotiation algorithm is to map a set of parameters
into a one-dimensional space where the calculated weights represent
the "degradation" figure of the data object. The maximum value of
this set represents the Content-Type in which the Object-Body
optimally should be returned to the client.
It is assumed that it is possible to assign an absolute value
representing the amount of loss of value when the data object is
rendered into a specific content-type. Whilst this is a very
subjective measurement, and in fact largely a function of the
document in question, the approximation is made that one can define
this degradation figure as a function of merely the representation
involved.
It is furthermore assumed that the cost to the user of viewing a
data object also is a function of the time taken for the
presentation. We first assume that the cost is linear in time, and
then assume that the time is linear in the size of the Object-Body.
The calculated weights are normalized to a real number between 0
and 1 where 0 is the minimum value and 1 is the maximum value. This
document defines the following parameters to be included in the
algorithm:
q The quality factor representing the level of degradation when
rendering the data object in a specific Content-Type in the
client application. The value is normalized so that q OE[0;1],
where the default value is q=1.
qs Equivalent to the q factor but for the server application in
case it can perform Content-Type conversions. The default value
is qs=1.
mxb The maximum number of bytes in the Object-Body accepted by the
client. The default value is mxb=undefined (i.e. infinity).
bs The actual number of bytes of the Object-Body as a function of
Content-Type and Content-Encoding. This value equals the value
send in the Content-Length field. The default value is bs=0.
The discrete mapping function is defined as:
{ if mxb=undefined, then (qs * q) }
Q(q,qs,mxb,bs) = { if mxb >= bs, then (qs * q) }
{ if mxb < bs, then 0 }
The maximum of the Q function represents the preferred content-type
to be used for transmitting the Object-Body to the client.
Note: It is not mandatory for the server application to
actually do the mapping and to determine the maximum
value and hence the optimal Content-Type to return to the
client. However, it is strongly recommended as it can
save a significant amount of bandwidth. The hope is that
fine decisions will not have to be made, as in most cases
the results for different formats will be very different,
and there will be a clear winner.
Note: The algorithm described does not take into account the
cost of any conversion performed by a gateway or proxy.
Although this is an important topic, it is considered
more important to maintain any gateways or proxy as
transparent parties in the transmission between the
client and the server.
9. Basic Access Authentication Scheme
The basic authentication scheme described here is to be considered
as a non-secure way 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 it not generally true, the basic access
authentication scheme should be used accordingly. However, it must
be implemented in order for an application to be HTTP 1.0
conforming.
The basic authentication scheme is based on the model that the
client must authenticate itself using a user-ID and a password. The
server will serve the request only if the server can validate the
authentication sent by the client, for example by using a password
file. The protected resources on the server can be divided into a
set of realms which can use different password files, so that
different realms can be accessible by different users.
A typical example of an authenticated request has one of the
following two profiles:
o The client requests a document without sending an
Authorization header field
o The server responds with a "401 Unauthorized" status code as
described in Section 6.3.3 and an WWW-Authenticate header
field
o The client knows already a valid user-ID and a password for
the realm indicated by the WWW-Authenticate header field or
it prompts the user.
o The clients generates a new request with an Authorization
header field
o The server replies with the requested data resource.
In this example, the client has no authorization information prior
to the initial request. In the next example, the client does have
such information due to a previous request within the realm
indicated by the server. The example would then look like:
o The client requests a document with an Authorization header
field
o The server replies with the requested data resource.
This specification of the HTTP protocol allows other authentication
schemes to be implemented using either the same frame as the basic
scheme or additional header fields. However, these can not be
assumed to be generally accepted by applications conforming to this
specification.
Note: The client is encouraged only to use the second approach
after it has verified that the requested URI is pointing
to a resource within the realm where the content of the
authorization header field is valid for accessing the URI.
Note: As described in Section 1.2, this specification does not
require that the connection be closed after each request.
However, when HTTP is used on top of TCP, it is
recommended that the connection be closed between the
first and second client request in an authenticated
request.
Note: Gateways and proxy agents shall be completely transparent
in the basic access authentication scheme. That is, they
must forward the WWW-Authenticate header and the
Authorization header untouched. In case a gateway or a
proxy wants to authenticate a client before a request is
forwarded to the server, it can be done using the scheme
presented above but not in the same authenticated request
as the one that the gateway or proxy is forwarding. That
is, it must be done using an explicit request from the
client to the gateway or proxy.
10. Registration Authority
The HTTP Registration Authority is responsible for maintaining
lists of:
o Authorization schemes (see Authorization: field above)
o Common method semantics
o Data format names (as MIME Content-Types or Internet Media
Types)
o Data encoding names (as MIME Content-Encoding))
It is proposed that the Internet Assigned Numbers Authority [14] or
their successors take this role.
11. Security Considerations
The following section reveals some of the security aspects of HTTP.
They are meant to inform application providers of the security
limitations in HTTP described by this document, but do not suggest
definitive solutions to the problems discussed.
11.1 Authentication of Clients
As mentioned in Section 9, the Basic Authentication scheme used in
HTTP is not to be considered as a secure way of protecting
information on servers, nor does it prevent the Object-Body from
being transmitted in clear text across the physical network used as
the carrier for HTTP. The protocol allows through the definition of
the relevant header field additional authentication schemes to be
employed to increase the security level.
11.2 Idempotent Methods
The writers of client software should be aware that the software
represents the user in their interactions over the net, and should
be careful to allow the user to be aware of any actions they may
take which may have an unexpected significance to themselves or
others.
In particular, the convention must be established that the GET and
HEAD methods never have the significance of taking an action. The
link "click here to subscribe"--causing the reading of a special
"magic" document--is open to abuse by others making a link "click
here to see a pretty picture". These methods should be considered
"safe" and should not have side effects. This allows the client
software to represent other methods (such as POST, PUT and DELETE)
in a special way, so that the user is aware of the fact that an
action is being requested.
11.3 Abuse of Server Log Information
A server is in the position to save personal data about information
requested by readers. This information is clearly confidential in
nature and its handling may be constrained by law in certain
countries. Server providers shall ensure that such material is not
distributed without the permission of any individuals that are
identifiable by the published results.
Two header fields are worth special mention in this context:
Referer and From. The Referer field allows reading patterns to be
studied and reverse links drawn. Although it can be very useful,
its power can be abused if user details are not separated from the
information contained in the Referer. Even when the personal
information has been removed, the Referer field may have indicated
a secure document's URI, whose revelation would itself be a breach
of security.
The information sent in the From field might conflict with the
user's privacy interests or their site's security policy, and hence
it should not be transmitted without the user being able to
disable, enable, and modify the contents of the field prior to a
request.
12. Acknowledgments
This specification makes heavy use of the augmented BNF and generic
constructs defined by David H. Crocker for RFC 822 [6]. Similarly,
it reuses the content-type definitions provided by Nathaniel
Borenstein and Ned Freed for MIME [4]. We hope that their inclusion
in this specification will help reduce past confusion over the
relationship between HTTP/1.0 and Internet mail.
The HTTP protocol has evolved considerably over the past three
years. It has benefited from a large and active developer community--
the many people who have participated on the www-talk mailing list--
and it is that community which has been most responsible for the
success of HTTP and of the World-Wide Web in general. Ari Luotonen,
Rob McCool, Tony Sanders, and Marc VanHeningen deserve special
recognition for their efforts in defining aspects of the protocol
for early versions of this specification. Bob Denny assisted in
proof-reading the specification and performing sanity-checks as it
was being rewritten.
13. 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, <URL:http://ds.internic.net/rfc/rfc1436.txt>,
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, <URL:http://ds.internic.net/rfc/rfc1630.txt>,
June 1994.
[3] T. Berners-Lee, L. Masinter, and M. McCahill. "Uniform Resource
Locators (URL)." Internet-Draft (work in progress), CERN, Xerox
PARC, University of Minnesota, <URL:http://ds.internic.net/
internet-drafts/draft-ietf-uri-url-08.txt>, October 1994.
[4] 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, <URL:http://ds.internic.net/rfc/rfc1521.ps>,
September 1993.
[5] R. Braden. "Requirements for Internet hosts - application and
support." STD 3, RFC 1123, IETF,
<URL:http://ds.internic.net/rfc/rfc1123.txt>, October 1989.
[6] D. H. Crocker. "Standard for the Format of ARPA Internet Text
Messages." STD 11, RFC 822, UDEL,
<URL:http://ds.internic.net/rfc/rfc822.txt>, August 1982.
[7] 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 Corp.,
<URL:ftp://quake.think.com/pub/wais/doc/protspec.txt>,
April 1990.
[8] R. Fielding. "Relative Uniform Resource Locators."
Internet-Draft (work in progress), UC Irvine,
<URL:http://ds.internic.net/internet-drafts/
draft-ietf-uri-relative-url-01.txt>, October 1994.
[9] M. Horton and R. Adams. "Standard for interchange of USENET
messages." RFC 1036 (Obsoletes RFC 850), AT&T Bell Labs,
Center for Seismic Studies, <URL:http://ds.internic.net/rfc/
rfc1036.txt>, December 1987.
[10] 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,
<URL:http://ds.internic.net/rfc/rfc977.txt>, February 1986.
[11] J. Postel. "Simple Mail Transfer Protocol." STD 10, RFC 821,
USC/ISI, <URL:http://ds.internic.net/rfc/rfc821.txt>,
August 1982.
[12] J. Postel. "Media Type Registration Procedure." RFC 1590,
USC/ISI, <URL:http://ds.internic.net/rfc/rfc1590.txt>,
March 1994.
[13] J. Postel and J. K. Reynolds. "File Transfer Protocol (FTP)."
STD 9, RFC 959, USC/ISI,
<URL:http://ds.internic.net/rfc/rfc959.txt>, October 1985.
[14] J. Reynolds and J. Postel. "Assigned Numbers." STD 2, RFC 1700,
USC/ISI, <URL:http://ds.internic.net/rfc/rfc1700.txt>,
October 1994.
[15] T. Berners-Lee, D. Connolly, et al. "HyperText Markup Language
Specification - 2.0." Internet-Draft (work in progress), CERN,
HaL Computer Systems,
<URL:http://www.ics.uci.edu/pub/ietf/html/>, November 1994.
[16] US-ASCII. "Coded Character Set - 7-Bit American Standard Code
for Information Interchange." Standard ANSI X3.4-1986, ANSI,
1986.
14. Authors Addresses
Tim Berners-Lee
Director, W3 Consortium
MIT Laboratory for Computer Science
545 Technology Square
Cambridge, MA 02139, U.S.A.
Tel: +1 (617) 253 9670
Fax: +1 (617) 258 8682
Email: timbl@w3.org
Roy T. Fielding
Department of Information and Computer Science
University of California
Irvine, CA 92717-3425, U.S.A.
Tel: +1 (714) 856-7308
Fax: +1 (714) 856-4056
Email: fielding@ics.uci.edu
Henrik Frystyk Nielsen
World-Wide Web Project
CERN,
1211 Geneva 23, Switzerland
Tel: +41 (22) 767 8265
Fax: +41 (22) 767 8730
Email: frystyk@w3.org
Appendices
These appendices are provided for informational reasons only -- they
do not form a part of the HTTP/1.0 specification.
A. Format of a uuencoded file
This section has been taken from the man page on uuencode on SunOS.
Files output by uuencode consist of a header line, followed by a
number of body lines, and a trailer line. uudecode will ignore any
lines preceding the header or following the trailer. Lines
preceding a header must not, of course, look like a header.
The header line is distinguished by having the first 6 characters
"begin ". The word begin is followed by a mode (in octal), and a
string which names the remote file. SP characters separate the
three items in the header line.
The body consists of a number of lines, each at most 62 characters
long (including the trailing LF). These consist of a character
count, followed by encoded characters, followed by a LF. The
character count is a single printing character, and represents an
integer, the number of bytes the rest of the line represents. Such
integers are always in the range from 0 to 63 and can be determined
by subtracting the character SP (octal 40) from the character.
Groups of 3 bytes are stored in 4 characters, 6 bits per character.
All are offset by a SP to make the characters printing. The last
line may be shorter than the normal 45 bytes. If the size is not a
multiple of 3, this fact can be determined by the value of the
count on the last line. Extra garbage will be included to make the
character count a multiple of 4. The body is terminated by a line
with a count of zero. This line consists of one ASCII SP.
The trailer line consists of end on a line by itself.
B. Server tolerance of bad clients
Whilst it is seen appropriate for testing parsers to check full
conformance to this specification, it is recommended that
operational parsers be tolerant of deviations.
In particular, lines should be regarded as terminated by the Line
Feed, and the preceding Carriage Return character ignored.
Any HTTP Header Field Name which is not recognized should be
ignored in operational parsers.
It is recommended that servers use URIs free of "variant"
characters whose representation differs in some of the national
variant character sets, punctuation characters, and spaces. This
will make URIs easier to handle by humans when the need (such as
debugging, or transmission through non hypertext systems) arises.
C. Client tolerance of bad servers
Servers not implementing the specification as written are not HTTP
compliant. Servers should always be made completely compliant.
However, clients should also tolerate deviant servers where
possible.
C.1 Back compatibility
In order that clients using the HTTP protocol should be able to
communicate with servers using the protocol originally implemented
in the W3 data model, clients should tolerate responses which do
not start with a numeric version number and response codes.
In this case, they should assume that the rest of the response is a
document body in type text/html.
C.2 White space
Clients should be tolerant in parsing response status lines, in
particular they should accept any sequence of white space (SP and
HTAB) characters between fields.
Lines should be regarded as terminated by a line feed (LF), and the
preceding carriage return (CR) character ignored.
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