Network Working Group T. Berners-Lee

Request for Comments: 1945 MIT/LCS

Category: Informational R. Fielding

UC Irvine

H. Frystyk

MIT/LCS

May 1996

 

 

Hypertext Transfer Protocol -- HTTP/1.0

 

Status of This Memo

 

This memo provides information for the Internet community. This memo

does not specify an Internet standard of any kind. Distribution of

this memo is unlimited.

 

IESG Note:

 

The IESG has concerns about this protocol, and expects this document

to be replaced relatively soon by a standards track document.

 

Abstract

 

The Hypertext Transfer Protocol (HTTP) is an application-level

protocol with the lightness and speed necessary for distributed,

collaborative, hypermedia information systems. It is a generic,

stateless, object-oriented protocol which can be used for many tasks,

such as name servers and distributed object management systems,

through extension of its request methods (commands). A feature of

HTTP is the typing of data representation, allowing systems to be

built independently of the data being transferred.

 

HTTP has been in use by the World-Wide Web global information

initiative since 1990. This specification reflects common usage of

the protocol referred to as "HTTP/1.0".

 

Table of Contents

 

1. Introduction .............................................. 4

1.1 Purpose .............................................. 4

1.2 Terminology .......................................... 4

1.3 Overall Operation .................................... 6

1.4 HTTP and MIME ........................................ 8

2. Notational Conventions and Generic Grammar ................ 8

2.1 Augmented BNF ........................................ 8

2.2 Basic Rules .......................................... 10

3. Protocol Parameters ....................................... 12

 

 

 

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3.1 HTTP Version ......................................... 12

3.2 Uniform Resource Identifiers ......................... 14

3.2.1 General Syntax ................................ 14

3.2.2 http URL ...................................... 15

3.3 Date/Time Formats .................................... 15

3.4 Character Sets ....................................... 17

3.5 Content Codings ...................................... 18

3.6 Media Types .......................................... 19

3.6.1 Canonicalization and Text Defaults ............ 19

3.6.2 Multipart Types ............................... 20

3.7 Product Tokens ....................................... 20

4. HTTP Message .............................................. 21

4.1 Message Types ........................................ 21

4.2 Message Headers ...................................... 22

4.3 General Header Fields ................................ 23

5. Request ................................................... 23

5.1 Request-Line ......................................... 23

5.1.1 Method ........................................ 24

5.1.2 Request-URI ................................... 24

5.2 Request Header Fields ................................ 25

6. Response .................................................. 25

6.1 Status-Line .......................................... 26

6.1.1 Status Code and Reason Phrase ................. 26

6.2 Response Header Fields ............................... 28

7. Entity .................................................... 28

7.1 Entity Header Fields ................................. 29

7.2 Entity Body .......................................... 29

7.2.1 Type .......................................... 29

7.2.2 Length ........................................ 30

8. Method Definitions ........................................ 30

8.1 GET .................................................. 31

8.2 HEAD ................................................. 31

8.3 POST ................................................. 31

9. Status Code Definitions ................................... 32

9.1 Informational 1xx .................................... 32

9.2 Successful 2xx ....................................... 32

9.3 Redirection 3xx ...................................... 34

9.4 Client Error 4xx ..................................... 35

9.5 Server Error 5xx ..................................... 37

10. Header Field Definitions .................................. 37

10.1 Allow ............................................... 38

10.2 Authorization ....................................... 38

10.3 Content-Encoding .................................... 39

10.4 Content-Length ...................................... 39

10.5 Content-Type ........................................ 40

10.6 Date ................................................ 40

10.7 Expires ............................................. 41

10.8 From ................................................ 42

 

 

 

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10.9 If-Modified-Since ................................... 42

10.10 Last-Modified ....................................... 43

10.11 Location ............................................ 44

10.12 Pragma .............................................. 44

10.13 Referer ............................................. 44

10.14 Server .............................................. 45

10.15 User-Agent .......................................... 46

10.16 WWW-Authenticate .................................... 46

11. Access Authentication ..................................... 47

11.1 Basic Authentication Scheme ......................... 48

12. Security Considerations ................................... 49

12.1 Authentication of Clients ........................... 49

12.2 Safe Methods ........................................ 49

12.3 Abuse of Server Log Information ..................... 50

12.4 Transfer of Sensitive Information ................... 50

12.5 Attacks Based On File and Path Names ................ 51

13. Acknowledgments ........................................... 51

14. References ................................................ 52

15. Authors' Addresses ........................................ 54

Appendix A. Internet Media Type message/http ................ 55

Appendix B. Tolerant Applications ........................... 55

Appendix C. Relationship to MIME ............................ 56

C.1 Conversion to Canonical Form ......................... 56

C.2 Conversion of Date Formats ........................... 57

C.3 Introduction of Content-Encoding ..................... 57

C.4 No Content-Transfer-Encoding ......................... 57

C.5 HTTP Header Fields in Multipart Body-Parts ........... 57

Appendix D. Additional Features ............................. 57

D.1 Additional Request Methods ........................... 58

D.1.1 PUT ........................................... 58

D.1.2 DELETE ........................................ 58

D.1.3 LINK .......................................... 58

D.1.4 UNLINK ........................................ 58

D.2 Additional Header Field Definitions .................. 58

D.2.1 Accept ........................................ 58

D.2.2 Accept-Charset ................................ 59

D.2.3 Accept-Encoding ............................... 59

D.2.4 Accept-Language ............................... 59

D.2.5 Content-Language .............................. 59

D.2.6 Link .......................................... 59

D.2.7 MIME-Version .................................. 59

D.2.8 Retry-After ................................... 60

D.2.9 Title ......................................... 60

D.2.10 URI ........................................... 60

 

 

 

 

 

 

 

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1. Introduction

 

1.1 Purpose

 

The Hypertext Transfer Protocol (HTTP) is an application-level

protocol with the lightness and speed necessary for distributed,

collaborative, hypermedia information systems. HTTP has been in use

by the World-Wide Web global information initiative since 1990. This

specification reflects common usage of the protocol referred too as

"HTTP/1.0". This specification describes the features that seem to be

consistently implemented in most HTTP/1.0 clients and servers. The

specification is split into two sections. Those features of HTTP for

which implementations are usually consistent are described in the

main body of this document. Those features which have few or

inconsistent implementations are listed in Appendix D.

 

Practical information systems require more functionality than simple

retrieval, including search, front-end update, and annotation. HTTP

allows an open-ended set of methods to be used to indicate the

purpose of a request. It builds on the discipline of reference

provided by the Uniform Resource Identifier (URI) [2], as a location

(URL) [4] or name (URN) [16], for indicating the resource on which a

method is to be applied. Messages are passed in a format similar to

that used by Internet Mail [7] and the Multipurpose Internet Mail

Extensions (MIME) [5].

 

HTTP is also used as a generic protocol for communication between

user agents and proxies/gateways to other Internet protocols, such as

SMTP [12], NNTP [11], FTP [14], Gopher [1], and WAIS [8], allowing

basic hypermedia access to resources available from diverse

applications and simplifying the implementation of user agents.

 

1.2 Terminology

 

This specification uses a number of terms to refer to the roles

played by participants in, and objects of, the HTTP communication.

 

connection

 

A transport layer virtual circuit established between two

application programs for the purpose of communication.

 

message

 

The basic unit of HTTP communication, consisting of a structured

sequence of octets matching the syntax defined in Section 4 and

transmitted via the connection.

 

 

 

 

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request

 

An HTTP request message (as defined in Section 5).

 

response

 

An HTTP response message (as defined in Section 6).

 

resource

 

A network data object or service which can be identified by a

URI (Section 3.2).

 

entity

 

A particular representation or rendition of a data resource, or

reply from a service resource, that may be enclosed within a

request or response message. An entity consists of

metainformation in the form of entity headers and content in the

form of an entity body.

 

client

 

An application program that establishes connections for the

purpose of sending requests.

 

user agent

 

The client which initiates a request. These are often browsers,

editors, spiders (web-traversing robots), or other end user

tools.

 

server

 

An application program that accepts connections in order to

service requests by sending back responses.

 

origin server

 

The server on which a given resource resides or is to be created.

 

proxy

 

An intermediary program which acts as both a server and a client

for the purpose of making requests on behalf of other clients.

Requests are serviced internally or by passing them, with

possible translation, on to other servers. A proxy must

interpret and, if necessary, rewrite a request message before

 

 

 

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forwarding it. Proxies are often used as client-side portals

through network firewalls and as helper applications for

handling requests via protocols not implemented by the user

agent.

 

gateway

 

A server which acts as an intermediary for some other server.

Unlike a proxy, a gateway receives requests as if it were the

origin server for the requested resource; the requesting client

may not be aware that it is communicating with a gateway.

Gateways are often used as server-side portals through network

firewalls and as protocol translators for access to resources

stored on non-HTTP systems.

 

tunnel

 

A tunnel is an intermediary program which is acting as a blind

relay between two connections. Once active, a tunnel is not

considered a party to the HTTP communication, though the tunnel

may have been initiated by an HTTP request. The tunnel ceases to

exist when both ends of the relayed connections are closed.

Tunnels are used when a portal is necessary and the intermediary

cannot, or should not, interpret the relayed communication.

 

cache

 

A program's local store of response messages and the subsystem

that controls its message storage, retrieval, and deletion. A

cache stores cachable responses in order to reduce the response

time and network bandwidth consumption on future, equivalent

requests. Any client or server may include a cache, though a

cache cannot be used by a server while it is acting as a tunnel.

 

Any given program may be capable of being both a client and a server;

our use of these terms refers only to the role being performed by the

program for a particular connection, rather than to the program's

capabilities in general. Likewise, any server may act as an origin

server, proxy, gateway, or tunnel, switching behavior based on the

nature of each request.

 

1.3 Overall Operation

 

The HTTP protocol is based on a request/response paradigm. A client

establishes a connection with a server and sends a request to the

server in the form of a request method, URI, and protocol version,

followed by a MIME-like message containing request modifiers, client

information, and possible body content. The server responds with a

 

 

 

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status line, including the message's protocol version and a success

or error code, followed by a MIME-like message containing server

information, entity metainformation, and possible body content.

 

Most HTTP communication is initiated by a user agent and consists of

a request to be applied to a resource on some origin server. In the

simplest case, this may be accomplished via a single connection (v)

between the user agent (UA) and the origin server (O).

 

request chain ------------------------>

UA -------------------v------------------- O

<----------------------- response chain

 

A more complicated situation occurs when one or more intermediaries

are present in the request/response chain. There are three common

forms of intermediary: proxy, gateway, and tunnel. A proxy is a

forwarding agent, receiving requests for a URI in its absolute form,

rewriting all or parts of the message, and forwarding the reformatted

request toward the server identified by the URI. A gateway is a

receiving agent, acting as a layer above some other server(s) and, if

necessary, translating the requests to the underlying server's

protocol. A tunnel acts as a relay point between two connections

without changing the messages; tunnels are used when the

communication needs to pass through an intermediary (such as a

firewall) even when the intermediary cannot understand the contents

of the messages.

 

request chain -------------------------------------->

UA -----v----- A -----v----- B -----v----- C -----v----- O

<------------------------------------- response chain

 

The figure above shows three intermediaries (A, B, and C) between the

user agent and origin server. A request or response message that

travels the whole chain must pass through four separate connections.

This distinction is important because some HTTP communication options

may apply only to the connection with the nearest, non-tunnel

neighbor, only to the end-points of the chain, or to all connections

along the chain. Although the diagram is linear, each participant may

be engaged in multiple, simultaneous communications. For example, B

may be receiving requests from many clients other than A, and/or

forwarding requests to servers other than C, at the same time that it

is handling A's request.

 

Any party to the communication which is not acting as a tunnel may

employ an internal cache for handling requests. The effect of a cache

is that the request/response chain is shortened if one of the

participants along the chain has a cached response applicable to that

request. The following illustrates the resulting chain if B has a

 

 

 

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cached copy of an earlier response from O (via C) for a request which

has not been cached by UA or A.

 

request chain ---------->

UA -----v----- A -----v----- B - - - - - - C - - - - - - O

<--------- response chain

 

Not all responses are cachable, and some requests may contain

modifiers which place special requirements on cache behavior. Some

HTTP/1.0 applications use heuristics to describe what is or is not a

"cachable" response, but these rules are not standardized.

 

On the Internet, HTTP communication generally takes place over TCP/IP

connections. The default port is TCP 80 [15], but other ports can be

used. This does not preclude HTTP from being implemented on top of

any other protocol on the Internet, or on other networks. HTTP only

presumes a reliable transport; any protocol that provides such

guarantees can be used, and the mapping of the HTTP/1.0 request and

response structures onto the transport data units of the protocol in

question is outside the scope of this specification.

 

Except for experimental applications, current practice requires that

the connection be established by the client prior to each request and

closed by the server after sending the response. Both clients and

servers should be aware that either party may close the connection

prematurely, due to user action, automated time-out, or program

failure, and should handle such closing in a predictable fashion. In

any case, the closing of the connection by either or both parties

always terminates the current request, regardless of its status.

 

1.4 HTTP and MIME

 

HTTP/1.0 uses many of the constructs defined for MIME, as defined in

RFC 1521 [5]. Appendix C describes the ways in which the context of

HTTP allows for different use of Internet Media Types than is

typically found in Internet mail, and gives the rationale for those

differences.

 

2. Notational Conventions and Generic Grammar

 

2.1 Augmented BNF

 

All of the mechanisms specified in this document are described in

both prose and an augmented Backus-Naur Form (BNF) similar to that

used by RFC 822 [7]. Implementors will need to be familiar with the

notation in order to understand this specification. The augmented BNF

includes the following constructs:

 

 

 

 

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name = definition

 

The name of a rule is simply the name itself (without any

enclosing "<" and ">") and is separated from its definition by

the equal character "=". Whitespace is only significant in that

indentation of continuation lines is used to indicate a rule

definition that spans more than one line. Certain basic rules

are in uppercase, such as SP, LWS, HT, CRLF, DIGIT, ALPHA, etc.

Angle brackets are used within definitions whenever their

presence will facilitate discerning the use of rule names.

 

"literal"

 

Quotation marks surround literal text. Unless stated otherwise,

the text is case-insensitive.

 

rule1 | rule2

 

Elements separated by a bar ("I") are alternatives,

e.g., "yes | no" will accept yes or no.

 

(rule1 rule2)

 

Elements enclosed in parentheses are treated as a single

element. Thus, "(elem (foo | bar) elem)" allows the token

sequences "elem foo elem" and "elem bar elem".

 

*rule

 

The character "*" preceding an element indicates repetition. The

full form is "<n>*<m>element" indicating at least <n> and at

most <m> occurrences of element. Default values are 0 and

infinity so that "*(element)" allows any number, including zero;

"1*element" requires at least one; and "1*2element" allows one

or two.

 

[rule]

 

Square brackets enclose optional elements; "[foo bar]" is

equivalent to "*1(foo bar)".

 

N rule

 

Specific repetition: "<n>(element)" is equivalent to

"<n>*<n>(element)"; that is, exactly <n> occurrences of

(element). Thus 2DIGIT is a 2-digit number, and 3ALPHA is a

string of three alphabetic characters.

 

 

 

 

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#rule

 

A construct "#" is defined, similar to "*", for defining lists

of elements. The full form is "<n>#<m>element" indicating at

least <n> and at most <m> elements, each separated by one or

more commas (",") and optional linear whitespace (LWS). This

makes the usual form of lists very easy; a rule such as

"( *LWS element *( *LWS "," *LWS element ))" can be shown as

"1#element". Wherever this construct is used, null elements are

allowed, but do not contribute to the count of elements present.

That is, "(element), , (element)" is permitted, but counts as

only two elements. Therefore, where at least one element is

required, at least one non-null element must be present. Default

values are 0 and infinity so that "#(element)" allows any

number, including zero; "1#element" requires at least one; and

"1#2element" allows one or two.

 

; comment

 

A semi-colon, set off some distance to the right of rule text,

starts a comment that continues to the end of line. This is a

simple way of including useful notes in parallel with the

specifications.

 

implied *LWS

 

The grammar described by this specification is word-based.

Except where noted otherwise, linear whitespace (LWS) can be

included between any two adjacent words (token or

quoted-string), and between adjacent tokens and delimiters

(tspecials), without changing the interpretation of a field. At

least one delimiter (tspecials) must exist between any two

tokens, since they would otherwise be interpreted as a single

token. However, applications should attempt to follow "common

form" when generating HTTP constructs, since there exist some

implementations that fail to accept anything beyond the common

forms.

 

2.2 Basic Rules

 

The following rules are used throughout this specification to

describe basic parsing constructs. The US-ASCII coded character set

is defined by [17].

 

OCTET = <any 8-bit sequence of data>

CHAR = <any US-ASCII character (octets 0 - 127)>

UPALPHA = <any US-ASCII uppercase letter "A".."Z">

LOALPHA = <any US-ASCII lowercase letter "a".."z">

 

 

 

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ALPHA = UPALPHA | LOALPHA

DIGIT = <any US-ASCII digit "0".."9">

CTL = <any US-ASCII control character

(octets 0 - 31) and DEL (127)>

CR = <US-ASCII CR, carriage return (13)>

LF = <US-ASCII LF, linefeed (10)>

SP = <US-ASCII SP, space (32)>

HT = <US-ASCII HT, horizontal-tab (9)>

<"> = <US-ASCII double-quote mark (34)>

 

HTTP/1.0 defines the octet sequence CR LF as the end-of-line marker

for all protocol elements except the Entity-Body (see Appendix B for

tolerant applications). The end-of-line marker within an Entity-Body

is defined by its associated media type, as described in Section 3.6.

 

CRLF = CR LF

 

HTTP/1.0 headers may be folded onto multiple lines if each

continuation line begins with a space or horizontal tab. All linear

whitespace, including folding, has the same semantics as SP.

 

LWS = [CRLF] 1*( SP | HT )

 

However, folding of header lines is not expected by some

applications, and should not be generated by HTTP/1.0 applications.

 

The TEXT rule is only used for descriptive field contents and values

that are not intended to be interpreted by the message parser. Words

of *TEXT may contain octets from character sets other than US-ASCII.

 

TEXT = <any OCTET except CTLs,

but including LWS>

 

Recipients of header field TEXT containing octets outside the US-

ASCII character set may assume that they represent ISO-8859-1

characters.

 

Hexadecimal numeric characters are used in several protocol elements.

 

HEX = "A" | "B" | "C" | "D" | "E" | "F"

| "a" | "b" | "c" | "d" | "e" | "f" | DIGIT

 

Many HTTP/1.0 header field values consist of words separated by LWS

or special characters. These special characters must be in a quoted

string to be used within a parameter value.

 

word = token | quoted-string

 

 

 

 

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token = 1*<any CHAR except CTLs or tspecials>

 

tspecials = "(" | ")" | "<" | ">" | "@"

| "," | ";" | ":" | "\" | <">

| "/" | "[" | "]" | "?" | "="

| "{" | "}" | SP | HT

 

Comments may be included in some HTTP header fields by surrounding

the comment text with parentheses. Comments are only allowed in

fields containing "comment" as part of their field value definition.

In all other fields, parentheses are considered part of the field

value.

 

comment = "(" *( ctext | comment ) ")"

ctext = <any TEXT excluding "(" and ")">

 

A string of text is parsed as a single word if it is quoted using

double-quote marks.

 

quoted-string = ( <"> *(qdtext) <"> )

 

qdtext = <any CHAR except <"> and CTLs,

but including LWS>

 

Single-character quoting using the backslash ("\") character is not

permitted in HTTP/1.0.

 

3. Protocol Parameters

 

3.1 HTTP Version

 

HTTP uses a "<major>.<minor>" numbering scheme to indicate versions

of the protocol. The protocol versioning policy is intended to allow

the sender to indicate the format of a message and its capacity for

understanding further HTTP communication, rather than the features

obtained via that communication. No change is made to the version

number for the addition of message components which do not affect

communication behavior or which only add to extensible field values.

The <minor> number is incremented when the changes made to the

protocol add features which do not change the general message parsing

algorithm, but which may add to the message semantics and imply

additional capabilities of the sender. The <major> number is

incremented when the format of a message within the protocol is

changed.

 

The version of an HTTP message is indicated by an HTTP-Version field

in the first line of the message. If the protocol version is not

specified, the recipient must assume that the message is in the

 

 

 

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simple HTTP/0.9 format.

 

HTTP-Version = "HTTP" "/" 1*DIGIT "." 1*DIGIT

 

Note that the major and minor numbers should be treated as separate

integers and that each may be incremented higher than a single digit.

Thus, HTTP/2.4 is a lower version than HTTP/2.13, which in turn is

lower than HTTP/12.3. Leading zeros should be ignored by recipients

and never generated by senders.

 

This document defines both the 0.9 and 1.0 versions of the HTTP

protocol. Applications sending Full-Request or Full-Response

messages, as defined by this specification, must include an HTTP-

Version of "HTTP/1.0".

 

HTTP/1.0 servers must:

 

o recognize the format of the Request-Line for HTTP/0.9 and

HTTP/1.0 requests;

 

o understand any valid request in the format of HTTP/0.9 or

HTTP/1.0;

 

o respond appropriately with a message in the same protocol

version used by the client.

 

HTTP/1.0 clients must:

 

o recognize the format of the Status-Line for HTTP/1.0 responses;

 

o understand any valid response in the format of HTTP/0.9 or

HTTP/1.0.

 

Proxy and gateway applications must be careful in forwarding requests

that are received in a format different than that of the

application's native HTTP version. Since the protocol version

indicates the protocol capability of the sender, a proxy/gateway must

never send a message with a version indicator which is greater than

its native version; if a higher version request is received, the

proxy/gateway must either downgrade the request version or respond

with an error. Requests with a version lower than that of the

application's native format may be upgraded before being forwarded;

the proxy/gateway's response to that request must follow the server

requirements listed above.

 

 

 

 

 

 

 

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3.2 Uniform Resource Identifiers

 

URIs have been known by many names: WWW addresses, Universal Document

Identifiers, Universal Resource Identifiers [2], and finally the

combination of Uniform Resource Locators (URL) [4] and Names (URN)

[16]. As far as HTTP is concerned, Uniform Resource Identifiers are

simply formatted strings which identify--via name, location, or any

other characteristic--a network resource.

 

3.2.1 General Syntax

 

URIs in HTTP can be represented in absolute form or relative to some

known base URI [9], depending upon the context of their use. The two

forms are differentiated by the fact that absolute URIs always begin

with a scheme name followed by a colon.

 

URI = ( absoluteURI | relativeURI ) [ "#" fragment ]

 

absoluteURI = scheme ":" *( uchar | reserved )

 

relativeURI = net_path | abs_path | rel_path

 

net_path = "//" net_loc [ abs_path ]

abs_path = "/" rel_path

rel_path = [ path ] [ ";" params ] [ "?" query ]

 

path = fsegment *( "/" segment )

fsegment = 1*pchar

segment = *pchar

 

params = param *( ";" param )

param = *( pchar | "/" )

 

scheme = 1*( ALPHA | DIGIT | "+" | "-" | "." )

net_loc = *( pchar | ";" | "?" )

query = *( uchar | reserved )

fragment = *( uchar | reserved )

 

pchar = uchar | ":" | "@" | "&" | "=" | "+"

uchar = unreserved | escape

unreserved = ALPHA | DIGIT | safe | extra | national

 

escape = "%" HEX HEX

reserved = ";" | "/" | "?" | ":" | "@" | "&" | "=" | "+"

extra = "!" | "*" | "'" | "(" | ")" | ","

safe = "$" | "-" | "_" | "."

unsafe = CTL | SP | <"> | "#" | "%" | "<" | ">"

national = <any OCTET excluding ALPHA, DIGIT,

 

 

 

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reserved, extra, safe, and unsafe>

 

For definitive information on URL syntax and semantics, see RFC 1738

[4] and RFC 1808 [9]. The BNF above includes national characters not

allowed in valid URLs as specified by RFC 1738, since HTTP servers

are not restricted in the set of unreserved characters allowed to

represent the rel_path part of addresses, and HTTP proxies may

receive requests for URIs not defined by RFC 1738.

 

3.2.2 http URL

 

The "http" scheme is used to locate network resources via the HTTP

protocol. This section defines the scheme-specific syntax and

semantics for http URLs.

 

http_URL = "http:" "//" host [ ":" port ] [ abs_path ]

 

host = <A legal Internet host domain name

or IP address (in dotted-decimal form),

as defined by Section 2.1 of RFC 1123>

 

port = *DIGIT

 

If the port is empty or not given, port 80 is assumed. The semantics

are that the identified resource is located at the server listening

for TCP connections on that port of that host, and the Request-URI

for the resource is abs_path. If the abs_path is not present in the

URL, it must be given as "/" when used as a Request-URI (Section

5.1.2).

 

Note: Although the HTTP protocol is independent of the transport

layer protocol, the http URL only identifies resources by their

TCP location, and thus non-TCP resources must be identified by

some other URI scheme.

 

The canonical form for "http" URLs is obtained by converting any

UPALPHA characters in host to their LOALPHA equivalent (hostnames are

case-insensitive), eliding the [ ":" port ] if the port is 80, and

replacing an empty abs_path with "/".

 

3.3 Date/Time Formats

 

HTTP/1.0 applications have historically allowed three different

formats for the representation of date/time stamps:

 

Sun, 06 Nov 1994 08:49:37 GMT ; RFC 822, updated by RFC 1123

Sunday, 06-Nov-94 08:49:37 GMT ; RFC 850, obsoleted by RFC 1036

Sun Nov 6 08:49:37 1994 ; ANSI C's asctime() format

 

 

 

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The first format is preferred as an Internet standard and represents

a fixed-length subset of that defined by RFC 1123 [6] (an update to

RFC 822 [7]). The second format is in common use, but is based on the

obsolete RFC 850 [10] date format and lacks a four-digit year.

HTTP/1.0 clients and servers that parse the date value should accept

all three formats, though they must never generate the third

(asctime) format.

 

Note: Recipients of date values are encouraged to be robust in

accepting date values that may have been generated by non-HTTP

applications, as is sometimes the case when retrieving or posting

messages via proxies/gateways to SMTP or NNTP.

 

All HTTP/1.0 date/time stamps must be represented in Universal Time

(UT), also known as Greenwich Mean Time (GMT), without exception.

This is indicated in the first two formats by the inclusion of "GMT"

as the three-letter abbreviation for time zone, and should be assumed

when reading the asctime format.

 

HTTP-date = rfc1123-date | rfc850-date | asctime-date

 

rfc1123-date = wkday "," SP date1 SP time SP "GMT"

rfc850-date = weekday "," SP date2 SP time SP "GMT"

asctime-date = wkday SP date3 SP time SP 4DIGIT

 

date1 = 2DIGIT SP month SP 4DIGIT

; day month year (e.g., 02 Jun 1982)

date2 = 2DIGIT "-" month "-" 2DIGIT

; day-month-year (e.g., 02-Jun-82)

date3 = month SP ( 2DIGIT | ( SP 1DIGIT ))

; month day (e.g., Jun 2)

 

time = 2DIGIT ":" 2DIGIT ":" 2DIGIT

; 00:00:00 - 23:59:59

 

wkday = "Mon" | "Tue" | "Wed"

| "Thu" | "Fri" | "Sat" | "Sun"

 

weekday = "Monday" | "Tuesday" | "Wednesday"

| "Thursday" | "Friday" | "Saturday" | "Sunday"

 

month = "Jan" | "Feb" | "Mar" | "Apr"

| "May" | "Jun" | "Jul" | "Aug"

| "Sep" | "Oct" | "Nov" | "Dec"

 

Note: HTTP 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

 

 

 

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presentation, request logging, etc.

 

3.4 Character Sets

 

HTTP uses the same definition of the term "character set" as that

described for MIME:

 

The term "character set" is used in this document to refer to a

method used with one or more tables to convert a sequence of

octets into a sequence of characters. Note that unconditional

conversion in the other direction is not required, in that not all

characters may be available in a given character set and a

character set may provide more than one sequence of octets to

represent a particular character. This definition is intended to

allow various kinds of character encodings, from simple single-

table mappings such as US-ASCII to complex table switching methods

such as those that use ISO 2022's techniques. However, the

definition associated with a MIME character set name must fully

specify the mapping to be performed from octets to characters. In

particular, use of external profiling information to determine the

exact mapping is not permitted.

 

Note: This use of the term "character set" is more commonly

referred to as a "character encoding." However, since HTTP and

MIME share the same registry, it is important that the terminology

also be shared.

 

HTTP character sets are identified by case-insensitive tokens. The

complete set of tokens are defined by the IANA Character Set registry

[15]. However, because that registry does not define a single,

consistent token for each character set, we define here the preferred

names for those character sets most likely to be used with HTTP

entities. These character sets include those registered by RFC 1521

[5] -- the US-ASCII [17] and ISO-8859 [18] character sets -- and

other names specifically recommended for use within MIME charset

parameters.

 

charset = "US-ASCII"

| "ISO-8859-1" | "ISO-8859-2" | "ISO-8859-3"

| "ISO-8859-4" | "ISO-8859-5" | "ISO-8859-6"

| "ISO-8859-7" | "ISO-8859-8" | "ISO-8859-9"

| "ISO-2022-JP" | "ISO-2022-JP-2" | "ISO-2022-KR"

| "UNICODE-1-1" | "UNICODE-1-1-UTF-7" | "UNICODE-1-1-UTF-8"

| token

 

Although HTTP allows an arbitrary token to be used as a charset

value, any token that has a predefined value within the IANA

Character Set registry [15] must represent the character set defined

 

 

 

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by that registry. Applications should limit their use of character

sets to those defined by the IANA registry.

 

The character set of an entity body should be labelled as the lowest

common denominator of the character codes used within that body, with

the exception that no label is preferred over the labels US-ASCII or

ISO-8859-1.

 

3.5 Content Codings

 

Content coding values are used to indicate an encoding transformation

that has been applied to a resource. Content codings are primarily

used to allow a document to be compressed or encrypted without losing

the identity of its underlying media type. Typically, the resource is

stored in this encoding and only decoded before rendering or

analogous usage.

 

content-coding = "x-gzip" | "x-compress" | token

 

Note: For future compatibility, HTTP/1.0 applications should

consider "gzip" and "compress" to be equivalent to "x-gzip"

and "x-compress", respectively.

 

All content-coding values are case-insensitive. HTTP/1.0 uses

content-coding values in the Content-Encoding (Section 10.3) header

field. Although the value describes the content-coding, what is more

important is that it indicates what decoding mechanism will be

required to remove the encoding. Note that a single program may be

capable of decoding multiple content-coding formats. Two values are

defined by this specification:

 

x-gzip

An encoding format produced by the file compression program

"gzip" (GNU zip) developed by Jean-loup Gailly. This format is

typically a Lempel-Ziv coding (LZ77) with a 32 bit CRC.

 

x-compress

The encoding format produced by the file compression program

"compress". This format is an adaptive Lempel-Ziv-Welch coding

(LZW).

 

Note: Use of program names for the identification of

encoding formats is not desirable and should be discouraged

for future encodings. Their use here is representative of

historical practice, not good design.

 

 

 

 

 

 

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3.6 Media Types

 

HTTP uses Internet Media Types [13] in the Content-Type header field

(Section 10.5) in order to provide open and extensible data typing.

 

media-type = type "/" subtype *( ";" parameter )

type = token

subtype = token

 

Parameters may follow the type/subtype in the form of attribute/value

pairs.

 

parameter = attribute "=" value

attribute = token

value = token | quoted-string

 

The type, subtype, and parameter attribute names are case-

insensitive. Parameter values may or may not be case-sensitive,

depending on the semantics of the parameter name. LWS must not be

generated between the type and subtype, nor between an attribute and

its value. Upon receipt of a media type with an unrecognized

parameter, a user agent should treat the media type as if the

unrecognized parameter and its value were not present.

 

Some older HTTP applications do not recognize media type parameters.

HTTP/1.0 applications should only use media type parameters when they

are necessary to define the content of a message.

 

Media-type values are registered with the Internet Assigned Number

Authority (IANA [15]). The media type registration process is

outlined in RFC 1590 [13]. Use of non-registered media types is

discouraged.

 

3.6.1 Canonicalization and Text Defaults

 

Internet media types are registered with a canonical form. In

general, an Entity-Body transferred via HTTP must be represented in

the appropriate canonical form prior to its transmission. If the body

has been encoded with a Content-Encoding, the underlying data should

be in canonical form prior to being encoded.

 

Media subtypes of the "text" type use CRLF as the text line break

when in canonical form. However, HTTP allows the transport of text

media with plain CR or LF alone representing a line break when used

consistently within the Entity-Body. HTTP applications must accept

CRLF, bare CR, and bare LF as being representative of a line break in

text media received via HTTP.

 

 

 

 

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In addition, if the text media is represented in a character set that

does not use octets 13 and 10 for CR and LF respectively, as is the

case for some multi-byte character sets, HTTP allows the use of

whatever octet sequences are defined by that character set to

represent the equivalent of CR and LF for line breaks. This

flexibility regarding line breaks applies only to text media in the

Entity-Body; a bare CR or LF should not be substituted for CRLF

within any of the HTTP control structures (such as header fields and

multipart boundaries).

 

The "charset" parameter is used with some media types to define the

character set (Section 3.4) of the data. When no explicit charset

parameter is provided by the sender, media subtypes of the "text"

type are defined to have a default charset value of "ISO-8859-1" when

received via HTTP. Data in character sets other than "ISO-8859-1" or

its subsets must be labelled with an appropriate charset value in

order to be consistently interpreted by the recipient.

 

Note: Many current HTTP servers provide data using charsets other

than "ISO-8859-1" without proper labelling. This situation reduces

interoperability and is not recommended. To compensate for this,

some HTTP user agents provide a configuration option to allow the

user to change the default interpretation of the media type

character set when no charset parameter is given.

 

3.6.2 Multipart Types

 

MIME provides for a number of "multipart" types -- encapsulations of

several entities within a single message's Entity-Body. The multipart

types registered by IANA [15] do not have any special meaning for

HTTP/1.0, though user agents may need to understand each type in

order to correctly interpret the purpose of each body-part. An HTTP

user agent should follow the same or similar behavior as a MIME user

agent does upon receipt of a multipart type. HTTP servers should not

assume that all HTTP clients are prepared to handle multipart types.

 

All multipart types share a common syntax and must include a boundary

parameter as part of the media type value. The message body is itself

a protocol element and must therefore use only CRLF to represent line

breaks between body-parts. Multipart body-parts may contain HTTP

header fields which are significant to the meaning of that part.

 

3.7 Product Tokens

 

Product tokens are used to allow communicating applications to

identify themselves via a simple product token, with an optional

slash and version designator. Most fields using product tokens also

allow subproducts which form a significant part of the application to

 

 

 

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be listed, separated by whitespace. By convention, the products are

listed in order of their significance for identifying the

application.

 

product = token ["/" product-version]

product-version = token

 

Examples:

 

User-Agent: CERN-LineMode/2.15 libwww/2.17b3

 

Server: Apache/0.8.4

 

Product tokens should be short and to the point -- use of them for

advertizing or other non-essential information is explicitly

forbidden. Although any token character may appear in a product-

version, this token should only be used for a version identifier

(i.e., successive versions of the same product should only differ in

the product-version portion of the product value).

 

4. HTTP Message

 

4.1 Message Types

 

HTTP messages consist of requests from client to server and responses

from server to client.

 

HTTP-message = Simple-Request ; HTTP/0.9 messages

| Simple-Response

| Full-Request ; HTTP/1.0 messages

| Full-Response

 

Full-Request and Full-Response use the generic message format of RFC

822 [7] for transferring entities. Both messages may include optional

header fields (also known as "headers") and an entity body. The

entity body is separated from the headers by a null line (i.e., a

line with nothing preceding the CRLF).

 

Full-Request = Request-Line ; Section 5.1

*( General-Header ; Section 4.3

| Request-Header ; Section 5.2

| Entity-Header ) ; Section 7.1

CRLF

[ Entity-Body ] ; Section 7.2

 

Full-Response = Status-Line ; Section 6.1

*( General-Header ; Section 4.3

| Response-Header ; Section 6.2

 

 

 

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| Entity-Header ) ; Section 7.1

CRLF

[ Entity-Body ] ; Section 7.2

 

Simple-Request and Simple-Response do not allow the use of any header

information and are limited to a single request method (GET).

 

Simple-Request = "GET" SP Request-URI CRLF

 

Simple-Response = [ Entity-Body ]

 

Use of the Simple-Request format is discouraged because it prevents

the server from identifying the media type of the returned entity.

 

4.2 Message Headers

 

HTTP header fields, which include General-Header (Section 4.3),

Request-Header (Section 5.2), Response-Header (Section 6.2), and

Entity-Header (Section 7.1) fields, follow the same generic format as

that given in Section 3.1 of RFC 822 [7]. Each header field consists

of a name followed immediately by a colon (":"), a single space (SP)

character, and the field value. Field names are case-insensitive.

Header fields can be extended over multiple lines by preceding each

extra line with at least one SP or HT, though this is not

recommended.

 

HTTP-header = field-name ":" [ field-value ] CRLF

 

field-name = token

field-value = *( field-content | LWS )

 

field-content = <the OCTETs making up the field-value

and consisting of either *TEXT or combinations

of token, tspecials, and quoted-string>

 

The order in which header fields are received is not significant.

However, it is "good practice" to send General-Header fields first,

followed by Request-Header or Response-Header fields prior to the

Entity-Header fields.

 

Multiple HTTP-header fields with the same field-name may be present

in a message if and only if the entire field-value for that header

field is defined as a comma-separated list [i.e., #(values)]. It must

be possible to combine the multiple header fields into one "field-

name: field-value" pair, without changing the semantics of the

message, by appending each subsequent field-value to the first, each

separated by a comma.

 

 

 

 

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4.3 General Header Fields

 

There are a few header fields which have general applicability for

both request and response messages, but which do not apply to the

entity being transferred. These headers apply only to the message

being transmitted.

 

General-Header = Date ; Section 10.6

| Pragma ; Section 10.12

 

General header field names can be extended reliably only in

combination with a change in the protocol version. However, new or

experimental header fields may be given the semantics of general

header fields if all parties in the communication recognize them to

be general header fields. Unrecognized header fields are treated as

Entity-Header fields.

 

5. Request

 

A request message from a client to a server includes, within the

first line of that message, the method to be applied to the resource,

the identifier of the resource, and the protocol version in use. For

backwards compatibility with the more limited HTTP/0.9 protocol,

there are two valid formats for an HTTP request:

 

Request = Simple-Request | Full-Request

 

Simple-Request = "GET" SP Request-URI CRLF

 

Full-Request = Request-Line ; Section 5.1

*( General-Header ; Section 4.3

| Request-Header ; Section 5.2

| Entity-Header ) ; Section 7.1

CRLF

[ Entity-Body ] ; Section 7.2

 

If an HTTP/1.0 server receives a Simple-Request, it must respond with

an HTTP/0.9 Simple-Response. An HTTP/1.0 client capable of receiving

a Full-Response should never generate a Simple-Request.

 

5.1 Request-Line

 

The Request-Line begins with a method token, followed by the

Request-URI and the protocol version, and ending with CRLF. The

elements are separated by SP characters. No CR or LF are allowed

except in the final CRLF sequence.

 

Request-Line = Method SP Request-URI SP HTTP-Version CRLF

 

 

 

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Note that the difference between a Simple-Request and the Request-

Line of a Full-Request is the presence of the HTTP-Version field and

the availability of methods other than GET.

 

5.1.1 Method

 

The Method token indicates the method to be performed on the resource

identified by the Request-URI. The method is case-sensitive.

 

Method = "GET" ; Section 8.1

| "HEAD" ; Section 8.2

| "POST" ; Section 8.3

| extension-method

 

extension-method = token

 

The list of methods acceptable by a specific resource can change

dynamically; the client is notified through the return code of the

response if a method is not allowed on a resource. Servers should

return the status code 501 (not implemented) if the method is

unrecognized or not implemented.

 

The methods commonly used by HTTP/1.0 applications are fully defined

in Section 8.

 

5.1.2 Request-URI

 

The Request-URI is a Uniform Resource Identifier (Section 3.2) and

identifies the resource upon which to apply the request.

 

Request-URI = absoluteURI | abs_path

 

The two options for Request-URI are dependent on the nature of the

request.

 

The absoluteURI form is only allowed when the request is being made

to a proxy. The proxy is requested to forward the request and return

the response. If the request is GET or HEAD and a prior response is

cached, the proxy may use the cached message if it passes any

restrictions in the Expires header field. Note that the proxy may

forward the request on to another proxy or directly to the server

specified by the absoluteURI. In order to avoid request loops, a

proxy must be able to recognize all of its server names, including

any aliases, local variations, and the numeric IP address. An example

Request-Line would be:

 

GET http://www.w3.org/pub/WWW/TheProject.html HTTP/1.0

 

 

 

 

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The most common form of Request-URI is that used to identify a

resource on an origin server or gateway. In this case, only the

absolute path of the URI is transmitted (see Section 3.2.1,

abs_path). For example, a client wishing to retrieve the resource

above directly from the origin server would create a TCP connection

to port 80 of the host "www.w3.org" and send the line:

 

GET /pub/WWW/TheProject.html HTTP/1.0

 

followed by the remainder of the Full-Request. Note that the absolute

path cannot be empty; if none is present in the original URI, it must

be given as "/" (the server root).

 

The Request-URI is transmitted as an encoded string, where some

characters may be escaped using the "% HEX HEX" encoding defined by

RFC 1738 [4]. The origin server must decode the Request-URI in order

to properly interpret the request.

 

5.2 Request Header Fields

 

The request header fields allow the client to pass additional

information about the request, and about the client itself, to the

server. These fields act as request modifiers, with semantics

equivalent to the parameters on a programming language method

(procedure) invocation.

 

Request-Header = Authorization ; Section 10.2

| From ; Section 10.8

| If-Modified-Since ; Section 10.9

| Referer ; Section 10.13

| User-Agent ; Section 10.15

 

Request-Header field names can be extended reliably only in

combination with a change in the protocol version. However, new or

experimental header fields may be given the semantics of request

header fields if all parties in the communication recognize them to

be request header fields. Unrecognized header fields are treated as

Entity-Header fields.

 

6. Response

 

After receiving and interpreting a request message, a server responds

in the form of an HTTP response message.

 

Response = Simple-Response | Full-Response

 

Simple-Response = [ Entity-Body ]

 

 

 

 

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Full-Response = Status-Line ; Section 6.1

*( General-Header ; Section 4.3

| Response-Header ; Section 6.2

| Entity-Header ) ; Section 7.1

CRLF

[ Entity-Body ] ; Section 7.2

 

A Simple-Response should only be sent in response to an HTTP/0.9

Simple-Request or if the server only supports the more limited

HTTP/0.9 protocol. If a client sends an HTTP/1.0 Full-Request and

receives a response that does not begin with a Status-Line, it should

assume that the response is a Simple-Response and parse it

accordingly. Note that the Simple-Response consists only of the

entity body and is terminated by the server closing the connection.

 

6.1 Status-Line

 

The first line of a Full-Response message is the Status-Line,

consisting of the protocol version followed by a numeric status code

and its associated textual phrase, with each element separated by SP

characters. No CR or LF is allowed except in the final CRLF sequence.

 

Status-Line = HTTP-Version SP Status-Code SP Reason-Phrase CRLF

 

Since a status line always begins with the protocol version and

status code

 

"HTTP/" 1*DIGIT "." 1*DIGIT SP 3DIGIT SP

 

(e.g., "HTTP/1.0 200 "), the presence of that expression is

sufficient to differentiate a Full-Response from a Simple-Response.

Although the Simple-Response format may allow such an expression to

occur at the beginning of an entity body, and thus cause a

misinterpretation of the message if it was given in response to a

Full-Request, most HTTP/0.9 servers are limited to responses of type

"text/html" and therefore would never generate such a response.

 

6.1.1 Status Code and Reason Phrase

 

The Status-Code element is a 3-digit integer result code of the

attempt to understand and satisfy the request. The Reason-Phrase is

intended to give a short textual description of the Status-Code. The

Status-Code is intended for use by automata and the Reason-Phrase is

intended for the human user. The client is not required to examine or

display the Reason-Phrase.

 

 

 

 

 

 

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The first digit of the Status-Code defines the class of response. The

last two digits do not have any categorization role. There are 5

values for the first digit:

 

o 1xx: Informational - Not used, but reserved for future use

 

o 2xx: Success - The action was successfully received,

understood, and accepted.

 

o 3xx: Redirection - Further action must be taken in order to

complete the request

 

o 4xx: Client Error - The request contains bad syntax or cannot

be fulfilled

 

o 5xx: Server Error - The server failed to fulfill an apparently

valid request

 

The individual values of the numeric status codes defined for

HTTP/1.0, and an example set of corresponding Reason-Phrase's, are

presented below. The reason phrases listed here are only recommended

-- they may be replaced by local equivalents without affecting the

protocol. These codes are fully defined in Section 9.

 

Status-Code = "200" ; OK

| "201" ; Created

| "202" ; Accepted

| "204" ; No Content

| "301" ; Moved Permanently

| "302" ; Moved Temporarily

| "304" ; Not Modified

| "400" ; Bad Request

| "401" ; Unauthorized

| "403" ; Forbidden

| "404" ; Not Found

| "500" ; Internal Server Error

| "501" ; Not Implemented

| "502" ; Bad Gateway

| "503" ; Service Unavailable

| extension-code

 

extension-code = 3DIGIT

 

Reason-Phrase = *<TEXT, excluding CR, LF>

 

HTTP status codes are extensible, but the above codes are the only

ones generally recognized in current practice. HTTP applications are

not required to understand the meaning of all registered status

 

 

 

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codes, though such understanding is obviously desirable. However,

applications must understand the class of any status code, as

indicated by the first digit, and treat any unrecognized response as

being equivalent to the x00 status code of that class, with the

exception that an unrecognized response must not be cached. For

example, if an unrecognized status code of 431 is received by the

client, it can safely assume that there was something wrong with its

request and treat the response as if it had received a 400 status

code. In such cases, user agents should present to the user the

entity returned with the response, since that entity is likely to

include human-readable information which will explain the unusual

status.

 

6.2 Response Header Fields

 

The response header fields allow the server to pass additional

information about the response which cannot be placed in the Status-

Line. These header fields give information about the server and about

further access to the resource identified by the Request-URI.

 

Response-Header = Location ; Section 10.11

| Server ; Section 10.14

| WWW-Authenticate ; Section 10.16

 

Response-Header field names can be extended reliably only in

combination with a change in the protocol version. However, new or

experimental header fields may be given the semantics of response

header fields if all parties in the communication recognize them to

be response header fields. Unrecognized header fields are treated as

Entity-Header fields.

 

7. Entity

 

Full-Request and Full-Response messages may transfer an entity within

some requests and responses. An entity consists of Entity-Header

fields and (usually) an Entity-Body. In this section, both sender and

recipient refer to either the client or the server, depending on who

sends and who receives the entity.

 

 

 

 

 

 

 

 

 

 

 

 

 

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7.1 Entity Header Fields

 

Entity-Header fields define optional metainformation about the

Entity-Body or, if no body is present, about the resource identified

by the request.

 

Entity-Header = Allow ; Section 10.1

| Content-Encoding ; Section 10.3

| Content-Length ; Section 10.4

| Content-Type ; Section 10.5

| Expires ; Section 10.7

| Last-Modified ; Section 10.10

| extension-header

 

extension-header = HTTP-header

 

The extension-header mechanism allows additional Entity-Header fields

to be defined without changing the protocol, but these fields cannot

be assumed to be recognizable by the recipient. Unrecognized header

fields should be ignored by the recipient and forwarded by proxies.

 

7.2 Entity Body

 

The entity body (if any) sent with an HTTP request or response is in

a format and encoding defined by the Entity-Header fields.

 

Entity-Body = *OCTET

 

An entity body is included with a request message only when the

request method calls for one. The presence of an entity body in a

request is signaled by the inclusion of a Content-Length header field

in the request message headers. HTTP/1.0 requests containing an

entity body must include a valid Content-Length header field.

 

For response messages, whether or not an entity body is included with

a message is dependent on both the request method and the response

code. All responses to the HEAD request method must not include a

body, even though the presence of entity header fields may lead one

to believe they do. All 1xx (informational), 204 (no content), and

304 (not modified) responses must not include a body. All other

responses must include an entity body or a Content-Length header

field defined with a value of zero (0).

 

7.2.1 Type

 

When an Entity-Body is included with a message, the data type of that

body is determined via the header fields Content-Type and Content-

Encoding. These define a two-layer, ordered encoding model:

 

 

 

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entity-body := Content-Encoding( Content-Type( data ) )

 

A Content-Type specifies the media type of the underlying data. A

Content-Encoding may be used to indicate any additional content

coding applied to the type, usually for the purpose of data

compression, that is a property of the resource requested. The

default for the content encoding is none (i.e., the identity

function).

 

Any HTTP/1.0 message containing an entity body should include a

Content-Type header field defining the media type of that body. If

and only if the media type is not given by a Content-Type header, as

is the case for Simple-Response messages, the recipient may attempt

to guess the media type via inspection of its content and/or the name

extension(s) of the URL used to identify the resource. If the media

type remains unknown, the recipient should treat it as type

"application/octet-stream".

 

7.2.2 Length

 

When an Entity-Body is included with a message, the length of that

body may be determined in one of two ways. If a Content-Length header

field is present, its value in bytes represents the length of the

Entity-Body. Otherwise, the body length is determined by the closing

of the connection by the server.

 

Closing the connection cannot be used to indicate the end of a

request body, since it leaves no possibility for the server to send

back a response. Therefore, HTTP/1.0 requests containing an entity

body must include a valid Content-Length header field. If a request

contains an entity body and Content-Length is not specified, and the

server does not recognize or cannot calculate the length from other

fields, then the server should send a 400 (bad request) response.

 

Note: Some older servers supply an invalid Content-Length when

sending a document that contains server-side includes dynamically

inserted into the data stream. It must be emphasized that this

will not be tolerated by future versions of HTTP. Unless the

client knows that it is receiving a response from a compliant

server, it should not depend on the Content-Length value being

correct.

 

8. Method Definitions

 

The set of common methods for HTTP/1.0 is defined below. Although

this set can be expanded, additional methods cannot be assumed to

share the same semantics for separately extended clients and servers.

 

 

 

 

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8.1 GET

 

The GET method means retrieve whatever information (in the form of an

entity) is identified by the Request-URI. If the Request-URI refers

to a data-producing process, it is the produced data which shall be

returned as the entity in the response and not the source text of the

process, unless that text happens to be the output of the process.

 

The semantics of the GET method changes to a "conditional GET" if the

request message includes an If-Modified-Since header field. A

conditional GET method requests that the identified resource be

transferred only if it has been modified since the date given by the

If-Modified-Since header, as described in Section 10.9. The

conditional GET method is intended to reduce network usage by

allowing cached entities to be refreshed without requiring multiple

requests or transferring unnecessary data.

 

8.2 HEAD

 

The HEAD method is identical to GET except that the server must not

return any Entity-Body in the response. The metainformation contained

in the HTTP headers in response to a HEAD request should be identical

to the information sent in response to a GET request. This method can

be used for obtaining metainformation about the resource identified

by the Request-URI without transferring the Entity-Body itself. This

method is often used for testing hypertext links for validity,

accessibility, and recent modification.

 

There is no "conditional HEAD" request analogous to the conditional

GET. If an If-Modified-Since header field is included with a HEAD

request, it should be ignored.

 

8.3 POST

 

The POST method is used to request that the destination server accept

the entity enclosed in the request as a new subordinate of the

resource identified by the Request-URI in the Request-Line. POST is

designed to allow a uniform method to cover the following functions:

 

o Annotation of existing resources;

 

o Posting a message to a bulletin board, newsgroup, mailing list,

or similar group of articles;

 

o Providing a block of data, such as the result of submitting a

form [3], to a data-handling process;

 

o Extending a database through an append operation.

 

 

 

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The actual function performed by the POST method is determined by the

server and is usually dependent on the Request-URI. The posted entity

is subordinate to that URI in the same way that a file is subordinate

to a directory containing it, a news article is subordinate to a

newsgroup to which it is posted, or a record is subordinate to a

database.

 

A successful POST does not require that the entity be created as a

resource on the origin server or made accessible for future

reference. That is, the action performed by the POST method might not

result in a resource that can be identified by a URI. In this case,

either 200 (ok) or 204 (no content) is the appropriate response

status, depending on whether or not the response includes an entity

that describes the result.

 

If a resource has been created on the origin server, the response

should be 201 (created) and contain an entity (preferably of type

"text/html") which describes the status of the request and refers to

the new resource.

 

A valid Content-Length is required on all HTTP/1.0 POST requests. An

HTTP/1.0 server should respond with a 400 (bad request) message if it

cannot determine the length of the request message's content.

 

Applications must not cache responses to a POST request because the

application has no way of knowing that the server would return an

equivalent response on some future request.

 

9. Status Code Definitions

 

Each Status-Code is described below, including a description of which

method(s) it can follow and any metainformation required in the

response.

 

9.1 Informational 1xx

 

This class of status code indicates a provisional response,

consisting only of the Status-Line and optional headers, and is

terminated by an empty line. HTTP/1.0 does not define any 1xx status

codes and they are not a valid response to a HTTP/1.0 request.

However, they may be useful for experimental applications which are

outside the scope of this specification.

 

9.2 Successful 2xx

 

This class of status code indicates that the client's request was

successfully received, understood, and accepted.

 

 

 

 

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200 OK

 

The request has succeeded. The information returned with the

response is dependent on the method used in the request, as follows:

 

GET an entity corresponding to the requested resource is sent

in the response;

 

HEAD the response must only contain the header information and

no Entity-Body;

 

POST an entity describing or containing the result of the action.

 

201 Created

 

The request has been fulfilled and resulted in a new resource being

created. The newly created resource can be referenced by the URI(s)

returned in the entity of the response. The origin server should

create the resource before using this Status-Code. If the action

cannot be carried out immediately, the server must include in the

response body a description of when the resource will be available;

otherwise, the server should respond with 202 (accepted).

 

Of the methods defined by this specification, only POST can create a

resource.

 

202 Accepted

 

The request has been accepted for processing, but the processing

has not been completed. The request may or may not eventually be

acted upon, as it may be disallowed when processing actually takes

place. There is no facility for re-sending a status code from an

asynchronous operation such as this.

 

The 202 response is intentionally non-committal. Its purpose is to

allow a server to accept a request for some other process (perhaps

a batch-oriented process that is only run once per day) without

requiring that the user agent's connection to the server persist

until the process is completed. The entity returned with this

response should include an indication of the request's current

status and either a pointer to a status monitor or some estimate of

when the user can expect the request to be fulfilled.

 

204 No Content

 

The server has fulfilled the request but there is no new

information to send back. If the client is a user agent, it should

not change its document view from that which caused the request to

 

 

 

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be generated. This response is primarily intended to allow input

for scripts or other actions to take place without causing a change

to the user agent's active document view. The response may include

new metainformation in the form of entity headers, which should

apply to the document currently in the user agent's active view.

 

9.3 Redirection 3xx

 

This class of status code indicates that further action needs to be

taken by the user agent in order to fulfill the request. The action

required may be carried out by the user agent without interaction

with the user if and only if the method used in the subsequent

request is GET or HEAD. A user agent should never automatically

redirect a request more than 5 times, since such redirections usually

indicate an infinite loop.

 

300 Multiple Choices

 

This response code is not directly used by HTTP/1.0 applications,

but serves as the default for interpreting the 3xx class of

responses.

 

The requested resource is available at one or more locations.

Unless it was a HEAD request, the response should include an entity

containing a list of resource characteristics and locations from

which the user or user agent can choose the one most appropriate.

If the server has a preferred choice, it should include the URL in

a Location field; user agents may use this field value for

automatic redirection.

 

301 Moved Permanently

 

The requested resource has been assigned a new permanent URL and

any future references to this resource should be done using that

URL. Clients with link editing capabilities should automatically

relink references to the Request-URI to the new reference returned

by the server, where possible.

 

The new URL must be given by the Location field in the response.

Unless it was a HEAD request, the Entity-Body of the response

should contain a short note with a hyperlink to the new URL.

 

If the 301 status code is received in response to a request using

the POST method, the user agent must not automatically redirect the

request unless it can be confirmed by the user, since this might

change the conditions under which the request was issued.

 

 

 

 

 

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Note: When automatically redirecting a POST request after

receiving a 301 status code, some existing user agents will

erroneously change it into a GET request.

 

302 Moved Temporarily

 

The requested resource resides temporarily under a different URL.

Since the redirection may be altered on occasion, the client should

continue to use the Request-URI for future requests.

 

The URL must be given by the Location field in the response. Unless

it was a HEAD request, the Entity-Body of the response should

contain a short note with a hyperlink to the new URI(s).

 

If the 302 status code is received in response to a request using

the POST method, the user agent must not automatically redirect the

request unless it can be confirmed by the user, since this might

change the conditions under which the request was issued.

 

Note: When automatically redirecting a POST request after

receiving a 302 status code, some existing user agents will

erroneously change it into a GET request.

 

304 Not Modified

 

If the client has performed a conditional GET request and access is

allowed, but the document has not been modified since the date and

time specified in the If-Modified-Since field, the server must

respond with this status code and not send an Entity-Body to the

client. Header fields contained in the response should only include

information which is relevant to cache managers or which may have

changed independently of the entity's Last-Modified date. Examples

of relevant header fields include: Date, Server, and Expires. A

cache should update its cached entity to reflect any new field

values given in the 304 response.

 

9.4 Client Error 4xx

 

The 4xx class of status code is intended for cases in which the

client seems to have erred. If the client has not completed the

request when a 4xx code is received, it should immediately cease

sending data to the server. Except when responding to a HEAD request,

the server should include an entity containing an explanation of the

error situation, and whether it is a temporary or permanent

condition. These status codes are applicable to any request method.

 

 

 

 

 

 

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Note: If the client is sending data, server implementations on TCP

should be careful to ensure that the client acknowledges receipt

of the packet(s) containing the response prior to closing the

input connection. If the client continues sending data to the

server after the close, the server's controller will send a reset

packet to the client, which may erase the client's unacknowledged

input buffers before they can be read and interpreted by the HTTP

application.

 

400 Bad Request

 

The request could not be understood by the server due to malformed

syntax. The client should not repeat the request without

modifications.

 

401 Unauthorized

 

The request requires user authentication. The response must include

a WWW-Authenticate header field (Section 10.16) containing a

challenge applicable to the requested resource. The client may

repeat the request with a suitable Authorization header field

(Section 10.2). If the request already included Authorization

credentials, then the 401 response indicates that authorization has

been refused for those credentials. If the 401 response contains

the same challenge as the prior response, and the user agent has

already attempted authentication at least once, then the user

should be presented the entity that was given in the response,

since that entity may include relevant diagnostic information. HTTP

access authentication is explained in Section 11.

 

403 Forbidden

 

The server understood the request, but is refusing to fulfill it.

Authorization will not help and the request should not be repeated.

If the request method was not HEAD and the server wishes to make

public why the request has not been fulfilled, it should describe

the reason for the refusal in the entity body. This status code is

commonly used when the server does not wish to reveal exactly why

the request has been refused, or when no other response is

applicable.

 

404 Not Found

 

The server has not found anything matching the Request-URI. No

indication is given of whether the condition is temporary or

permanent. If the server does not wish to make this information

available to the client, the status code 403 (forbidden) can be

used instead.

 

 

 

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9.5 Server Error 5xx

 

Response status codes beginning with the digit "5" indicate cases in

which the server is aware that it has erred or is incapable of

performing the request. If the client has not completed the request

when a 5xx code is received, it should immediately cease sending data

to the server. Except when responding to a HEAD request, the server

should include an entity containing an explanation of the error

situation, and whether it is a temporary or permanent condition.

These response codes are applicable to any request method and there

are no required header fields.

 

500 Internal Server Error

 

The server encountered an unexpected condition which prevented it

from fulfilling the request.

 

501 Not Implemented

 

The server does not support the functionality required to fulfill

the request. This is the appropriate response when the server does

not recognize the request method and is not capable of supporting

it for any resource.

 

502 Bad Gateway

 

The server, while acting as a gateway or proxy, received an invalid

response from the upstream server it accessed in attempting to

fulfill the request.

 

503 Service Unavailable

 

The server is currently unable to handle the request due to a

temporary overloading or maintenance of the server. The implication

is that this is a temporary condition which will be alleviated

after some delay.

 

Note: The existence of the 503 status code does not imply

that a server must use it when becoming overloaded. Some

servers may wish to simply refuse the connection.

 

10. Header Field Definitions

 

This section defines the syntax and semantics of all commonly used

HTTP/1.0 header fields. For general and entity header fields, both

sender and recipient refer to either the client or the server,

depending on who sends and who receives the message.

 

 

 

 

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10.1 Allow

 

The Allow entity-header field lists the set of methods supported by

the resource identified by the Request-URI. The purpose of this field

is strictly to inform the recipient of valid methods associated with

the resource. The Allow header field is not permitted in a request

using the POST method, and thus should be ignored if it is received

as part of a POST entity.

 

Allow = "Allow" ":" 1#method

 

Example of use:

 

Allow: GET, HEAD

 

This field cannot prevent a client from trying other methods.

However, the indications given by the Allow header field value should

be followed. The actual set of allowed methods is defined by the

origin server at the time of each request.

 

A proxy must not modify the Allow header field even if it does not

understand all the methods specified, since the user agent may have

other means of communicating with the origin server.

 

The Allow header field does not indicate what methods are implemented

by the server.

 

10.2 Authorization

 

A user agent that wishes to authenticate itself with a server--

usually, but not necessarily, after receiving a 401 response--may do

so by including an Authorization request-header field with the

request. The Authorization field value consists of credentials

containing the authentication information of the user agent for the

realm of the resource being requested.

 

Authorization = "Authorization" ":" credentials

 

HTTP access authentication is described in Section 11. If a request

is authenticated and a realm specified, the same credentials should

be valid for all other requests within this realm.

 

Responses to requests containing an Authorization field are not

cachable.

 

 

 

 

 

 

 

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10.3 Content-Encoding

 

The Content-Encoding entity-header field is used as a modifier to the

media-type. When present, its value indicates what additional content

coding has been applied to the resource, and thus what decoding

mechanism must be applied in order to obtain the media-type

referenced by the Content-Type header field. The Content-Encoding is

primarily used to allow a document to be compressed without losing

the identity of its underlying media type.

 

Content-Encoding = "Content-Encoding" ":" content-coding

 

Content codings are defined in Section 3.5. An example of its use is

 

Content-Encoding: x-gzip

 

The Content-Encoding is a characteristic of the resource identified

by the Request-URI. Typically, the resource is stored with this

encoding and is only decoded before rendering or analogous usage.

 

10.4 Content-Length

 

The Content-Length entity-header field indicates the size of the

Entity-Body, in decimal number of octets, sent to the recipient or,

in the case of the HEAD method, the size of the Entity-Body that

would have been sent had the request been a GET.

 

Content-Length = "Content-Length" ":" 1*DIGIT

 

An example is

 

Content-Length: 3495

 

Applications should use this field to indicate the size of the

Entity-Body to be transferred, regardless of the media type of the

entity. A valid Content-Length field value is required on all

HTTP/1.0 request messages containing an entity body.

 

Any Content-Length greater than or equal to zero is a valid value.

Section 7.2.2 describes how to determine the length of a response

entity body if a Content-Length is not given.

 

Note: The meaning of this field is significantly different from

the corresponding definition in MIME, where it is an optional

field used within the "message/external-body" content-type. In

HTTP, it should be used whenever the entity's length can be

determined prior to being transferred.

 

 

 

 

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10.5 Content-Type

 

The Content-Type entity-header field indicates the media type of the

Entity-Body sent to the recipient or, in the case of the HEAD method,

the media type that would have been sent had the request been a GET.

 

Content-Type = "Content-Type" ":" media-type

 

Media types are defined in Section 3.6. An example of the field is

 

Content-Type: text/html

 

Further discussion of methods for identifying the media type of an

entity is provided in Section 7.2.1.

 

10.6 Date

 

The Date general-header field represents the date and time at which

the message was originated, having the same semantics as orig-date in

RFC 822. The field value is an HTTP-date, as described in Section

3.3.

 

Date = "Date" ":" HTTP-date

 

An example is

 

Date: Tue, 15 Nov 1994 08:12:31 GMT

 

If a message is received via direct connection with the user agent

(in the case of requests) or the origin server (in the case of

responses), then the date can be assumed to be the current date at

the receiving end. However, since the date--as it is believed by the

origin--is important for evaluating cached responses, origin servers

should always include a Date header. Clients should only send a Date

header field in messages that include an entity body, as in the case

of the POST request, and even then it is optional. A received message

which does not have a Date header field should be assigned one by the

recipient if the message will be cached by that recipient or

gatewayed via a protocol which requires a Date.

 

In theory, the date should represent the moment just before the

entity is generated. In practice, the date can be generated at any

time during the message origination without affecting its semantic

value.

 

Note: An earlier version of this document incorrectly specified

that this field should contain the creation date of the enclosed

Entity-Body. This has been changed to reflect actual (and proper)

 

 

 

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usage.

 

10.7 Expires

 

The Expires entity-header field gives the date/time after which the

entity should be considered stale. This allows information providers

to suggest the volatility of the resource, or a date after which the

information may no longer be valid. Applications must not cache this

entity beyond the date given. The presence of an Expires field does

not imply that the original resource will change or cease to exist

at, before, or after that time. However, information providers that

know or even suspect that a resource will change by a certain date

should include an Expires header with that date. The format is an

absolute date and time as defined by HTTP-date in Section 3.3.

 

Expires = "Expires" ":" HTTP-date

 

An example of its use is

 

Expires: Thu, 01 Dec 1994 16:00:00 GMT

 

If the date given is equal to or earlier than the value of the Date

header, the recipient must not cache the enclosed entity. If a

resource is dynamic by nature, as is the case with many data-

producing processes, entities from that resource should be given an

appropriate Expires value which reflects that dynamism.

 

The Expires field cannot be used to force a user agent to refresh its

display or reload a resource; its semantics apply only to caching

mechanisms, and such mechanisms need only check a resource's

expiration status when a new request for that resource is initiated.

 

User agents often have history mechanisms, such as "Back" buttons and

history lists, which can be used to redisplay an entity retrieved

earlier in a session. By default, the Expires field does not apply to

history mechanisms. If the entity is still in storage, a history

mechanism should display it even if the entity has expired, unless

the user has specifically configured the agent to refresh expired

history documents.

 

Note: Applications are encouraged to be tolerant of bad or

misinformed implementations of the Expires header. A value of zero

(0) or an invalid date format should be considered equivalent to

an "expires immediately." Although these values are not legitimate

for HTTP/1.0, a robust implementation is always desirable.

 

 

 

 

 

 

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10.8 From

 

The From request-header field, if given, should contain an Internet

e-mail address for the human user who controls the requesting user

agent. The address should be machine-usable, as defined by mailbox in

RFC 822 [7] (as updated by RFC 1123 [6]):

 

From = "From" ":" mailbox

 

An example is:

 

From: webmaster@w3.org

 

This header field may be used for logging purposes and as a means for

identifying the source of invalid or unwanted requests. It should not

be used as an insecure form of access protection. The interpretation

of this field is that the request is being performed on behalf of the

person given, who accepts responsibility for the method performed. In

particular, robot agents should include this header so that the

person responsible for running the robot can be contacted if problems

occur on the receiving end.

 

The Internet e-mail address in this field may be separate from the

Internet host which issued the request. For example, when a request

is passed through a proxy, the original issuer's address should be

used.

 

Note: The client should not send the From header field without the

user's approval, as it may conflict with the user's privacy

interests or their site's security policy. It is strongly

recommended that the user be able to disable, enable, and modify

the value of this field at any time prior to a request.

 

10.9 If-Modified-Since

 

The If-Modified-Since request-header field is used with the GET

method to make it conditional: if the requested resource has not been

modified since the time specified in this field, a copy of the

resource will not be returned from the server; instead, a 304 (not

modified) response will be returned without any Entity-Body.

 

If-Modified-Since = "If-Modified-Since" ":" HTTP-date

 

An example of the field is:

 

If-Modified-Since: Sat, 29 Oct 1994 19:43:31 GMT

 

 

 

 

 

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A conditional GET method requests that the identified resource be

transferred only if it has been modified since the date given by the

If-Modified-Since header. The algorithm for determining this includes

the following cases:

 

a) If the request would normally result in anything other than

a 200 (ok) status, or if the passed If-Modified-Since date

is invalid, the response is exactly the same as for a

normal GET. A date which is later than the server's current

time is invalid.

 

b) If the resource has been modified since the

If-Modified-Since date, the response is exactly the same as

for a normal GET.

 

c) If the resource has not been modified since a valid

If-Modified-Since date, the server shall return a 304 (not

modified) response.

 

The purpose of this feature is to allow efficient updates of cached

information with a minimum amount of transaction overhead.

 

10.10 Last-Modified

 

The Last-Modified entity-header field indicates the date and time at

which the sender believes the resource was last modified. The exact

semantics of this field are defined in terms of how the recipient

should interpret it: if the recipient has a copy of this resource

which is older than the date given by the Last-Modified field, that

copy should be considered stale.

 

Last-Modified = "Last-Modified" ":" HTTP-date

 

An example of its use is

 

Last-Modified: Tue, 15 Nov 1994 12:45:26 GMT

 

The exact meaning of this header field depends on the implementation

of the sender and the nature of the original resource. For files, it

may be just the file system last-modified time. For entities with

dynamically included parts, it may be the most recent of the set of

last-modify times for its component parts. For database gateways, it

may be the last-update timestamp of the record. For virtual objects,

it may be the last time the internal state changed.

 

An origin server must not send a Last-Modified date which is later

than the server's time of message origination. In such cases, where

the resource's last modification would indicate some time in the

 

 

 

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future, the server must replace that date with the message

origination date.

 

10.11 Location

 

The Location response-header field defines the exact location of the

resource that was identified by the Request-URI. For 3xx responses,

the location must indicate the server's preferred URL for automatic

redirection to the resource. Only one absolute URL is allowed.

 

Location = "Location" ":" absoluteURI

 

An example is

 

Location: http://www.w3.org/hypertext/WWW/NewLocation.html

 

10.12 Pragma

 

The Pragma general-header field is used to include implementation-

specific directives that may apply to any recipient along the

request/response chain. All pragma directives specify optional

behavior from the viewpoint of the protocol; however, some systems

may require that behavior be consistent with the directives.

 

Pragma = "Pragma" ":" 1#pragma-directive

 

pragma-directive = "no-cache" | extension-pragma

extension-pragma = token [ "=" word ]

 

When the "no-cache" directive is present in a request message, an

application should forward the request toward the origin server even

if it has a cached copy of what is being requested. This allows a

client to insist upon receiving an authoritative response to its

request. It also allows a client to refresh a cached copy which is

known to be corrupted or stale.

 

Pragma directives must be passed through by a proxy or gateway

application, regardless of their significance to that application,

since the directives may be applicable to all recipients along the

request/response chain. It is not possible to specify a pragma for a

specific recipient; however, any pragma directive not relevant to a

recipient should be ignored by that recipient.

 

10.13 Referer

 

The Referer request-header field allows the client to specify, for

the server's benefit, the address (URI) of the resource from which

the Request-URI was obtained. This allows a server to generate lists

 

 

 

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of back-links to resources for interest, logging, optimized caching,

etc. It also allows obsolete or mistyped links to be traced for

maintenance. The Referer field must not be sent if the Request-URI

was obtained from a source that does not have its own URI, such as

input from the user keyboard.

 

Referer = "Referer" ":" ( absoluteURI | relativeURI )

 

Example:

 

Referer: http://www.w3.org/hypertext/DataSources/Overview.html

 

If a partial URI is given, it should be interpreted relative to the

Request-URI. The URI must not include a fragment.

 

Note: Because the source of a link may be private information or

may reveal an otherwise private information source, it is strongly

recommended that the user be able to select whether or not the

Referer field is sent. For example, a browser client could have a

toggle switch for browsing openly/anonymously, which would

respectively enable/disable the sending of Referer and From

information.

 

10.14 Server

 

The Server response-header field contains information about the

software used by the origin server to handle the request. The field

can contain multiple product tokens (Section 3.7) and comments

identifying the server and any significant subproducts. By

convention, the product tokens are listed in order of their

significance for identifying the application.

 

Server = "Server" ":" 1*( product | comment )

 

Example:

 

Server: CERN/3.0 libwww/2.17

 

If the response is being forwarded through a proxy, the proxy

application must not add its data to the product list.

 

Note: Revealing the specific software version of the server may

allow the server machine to become more vulnerable to attacks

against software that is known to contain security holes. Server

implementors are encouraged to make this field a configurable

option.

 

 

 

 

 

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Note: Some existing servers fail to restrict themselves to the

product token syntax within the Server field.

 

10.15 User-Agent

 

The User-Agent request-header field contains information about the

user agent originating the request. This is for statistical purposes,

the tracing of protocol violations, and automated recognition of user

agents for the sake of tailoring responses to avoid particular user

agent limitations. Although it is not required, user agents should

include this field with requests. The field can contain multiple

product tokens (Section 3.7) and comments identifying the agent and

any subproducts which form a significant part of the user agent. By

convention, the product tokens are listed in order of their

significance for identifying the application.

 

User-Agent = "User-Agent" ":" 1*( product | comment )

 

Example:

 

User-Agent: CERN-LineMode/2.15 libwww/2.17b3

 

Note: Some current proxy applications append their product

information to the list in the User-Agent field. This is not

recommended, since it makes machine interpretation of these

fields ambiguous.

 

Note: Some existing clients fail to restrict themselves to

the product token syntax within the User-Agent field.

 

10.16 WWW-Authenticate

 

The WWW-Authenticate response-header field must be included in 401

(unauthorized) response messages. The field value consists of at

least one challenge that indicates the authentication scheme(s) and

parameters applicable to the Request-URI.

 

WWW-Authenticate = "WWW-Authenticate" ":" 1#challenge

 

The HTTP access authentication process is described in Section 11.

User agents must take special care in parsing the WWW-Authenticate

field value if it contains more than one challenge, or if more than

one WWW-Authenticate header field is provided, since the contents of

a challenge may itself contain a comma-separated list of

authentication parameters.

 

 

 

 

 

 

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11. Access Authentication

 

HTTP provides a simple challenge-response authentication mechanism

which may be used by a server to challenge a client request and by a

client to provide authentication information. It uses an extensible,

case-insensitive token to identify the authentication scheme,

followed by a comma-separated list of attribute-value pairs which

carry the parameters necessary for achieving authentication via that

scheme.

 

auth-scheme = token

 

auth-param = token "=" quoted-string

 

The 401 (unauthorized) response message is used by an origin server

to challenge the authorization of a user agent. This response must

include a WWW-Authenticate header field containing at least one

challenge applicable to the requested resource.

 

challenge = auth-scheme 1*SP realm *( "," auth-param )

 

realm = "realm" "=" realm-value

realm-value = quoted-string

 

The realm attribute (case-insensitive) is required for all

authentication schemes which issue a challenge. The realm value

(case-sensitive), in combination with the canonical root URL of the

server being accessed, defines the protection space. These realms

allow the protected resources on a server to be partitioned into a

set of protection spaces, each with its own authentication scheme

and/or authorization database. The realm value is a string, generally

assigned by the origin server, which may have additional semantics

specific to the authentication scheme.

 

A user agent that wishes to authenticate itself with a server--

usually, but not necessarily, after receiving a 401 response--may do

so by including an Authorization header field with the request. The

Authorization field value consists of credentials containing the

authentication information of the user agent for the realm of the

resource being requested.

 

credentials = basic-credentials

| ( auth-scheme #auth-param )

 

The domain over which credentials can be automatically applied by a

user agent is determined by the protection space. If a prior request

has been authorized, the same credentials may be reused for all other

requests within that protection space for a period of time determined

 

 

 

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by the authentication scheme, parameters, and/or user preference.

Unless otherwise defined by the authentication scheme, a single

protection space cannot extend outside the scope of its server.

 

If the server does not wish to accept the credentials sent with a

request, it should return a 403 (forbidden) response.

 

The HTTP protocol does not restrict applications to this simple

challenge-response mechanism for access authentication. Additional

mechanisms may be used, such as encryption at the transport level or

via message encapsulation, and with additional header fields

specifying authentication information. However, these additional

mechanisms are not defined by this specification.

 

Proxies must be completely transparent regarding user agent

authentication. That is, they must forward the WWW-Authenticate and

Authorization headers untouched, and must not cache the response to a

request containing Authorization. HTTP/1.0 does not provide a means

for a client to be authenticated with a proxy.

 

11.1 Basic Authentication Scheme

 

The "basic" authentication scheme is based on the model that the user

agent must authenticate itself with a user-ID and a password for each

realm. The realm value should be considered an opaque string which

can only be compared for equality with other realms on that server.

The server will authorize the request only if it can validate the

user-ID and password for the protection space of the Request-URI.

There are no optional authentication parameters.

 

Upon receipt of an unauthorized request for a URI within the

protection space, the server should respond with a challenge like the

following:

 

WWW-Authenticate: Basic realm="WallyWorld"

 

where "WallyWorld" is the string assigned by the server to identify

the protection space of the Request-URI.

 

To receive authorization, the client sends the user-ID and password,

separated by a single colon (":") character, within a base64 [5]

encoded string in the credentials.

 

basic-credentials = "Basic" SP basic-cookie

 

basic-cookie = <base64 [5] encoding of userid-password,

except not limited to 76 char/line>

 

 

 

 

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userid-password = [ token ] ":" *TEXT

 

If the user agent wishes to send the user-ID "Aladdin" and password

"open sesame", it would use the following header field:

 

Authorization: Basic QWxhZGRpbjpvcGVuIHNlc2FtZQ==

 

The basic authentication scheme is a non-secure method of filtering

unauthorized access to resources on an HTTP server. It is based on

the assumption that the connection between the client and the server

can be regarded as a trusted carrier. As this is not generally true

on an open network, the basic authentication scheme should be used

accordingly. In spite of this, clients should implement the scheme in

order to communicate with servers that use it.

 

12. Security Considerations

 

This section is meant to inform application developers, information

providers, and users of the security limitations in HTTP/1.0 as

described by this document. The discussion does not include

definitive solutions to the problems revealed, though it does make

some suggestions for reducing security risks.

 

12.1 Authentication of Clients

 

As mentioned in Section 11.1, the Basic authentication scheme is not

a secure method of user authentication, nor does it prevent the

Entity-Body from being transmitted in clear text across the physical

network used as the carrier. HTTP/1.0 does not prevent additional

authentication schemes and encryption mechanisms from being employed

to increase security.

 

12.2 Safe Methods

 

The writers of client software should be aware that the software

represents the user in their interactions over the Internet, and

should be careful to allow the user to be aware of any actions they

may take which may have an unexpected significance to themselves or

others.

 

In particular, the convention has been established that the GET and

HEAD methods should never have the significance of taking an action

other than retrieval. These methods should be considered "safe." This

allows user agents to represent other methods, such as POST, in a

special way, so that the user is made aware of the fact that a

possibly unsafe action is being requested.

 

 

 

 

 

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Naturally, it is not possible to ensure that the server does not

generate side-effects as a result of performing a GET request; in

fact, some dynamic resources consider that a feature. The important

distinction here is that the user did not request the side-effects,

so therefore cannot be held accountable for them.

 

12.3 Abuse of Server Log Information

 

A server is in the position to save personal data about a user's

requests which may identify their reading patterns or subjects of

interest. This information is clearly confidential in nature and its

handling may be constrained by law in certain countries. People using

the HTTP protocol to provide data are responsible for ensuring that

such material is not distributed without the permission of any

individuals that are identifiable by the published results.

 

12.4 Transfer of Sensitive Information

 

Like any generic data transfer protocol, HTTP cannot regulate the

content of the data that is transferred, nor is there any a priori

method of determining the sensitivity of any particular piece of

information within the context of any given request. Therefore,

applications should supply as much control over this information as

possible to the provider of that information. Three header fields are

worth special mention in this context: Server, Referer and From.

 

Revealing the specific software version of the server may allow the

server machine to become more vulnerable to attacks against software

that is known to contain security holes. Implementors should make the

Server header field a configurable option.

 

The Referer field allows reading patterns to be studied and reverse

links drawn. Although it can be very useful, its power can be abused

if user details are not separated from the information contained in

the Referer. Even when the personal information has been removed, the

Referer field may indicate a private document's URI whose publication

would be inappropriate.

 

The information sent in the From field might conflict with the user's

privacy interests or their site's security policy, and hence it

should not be transmitted without the user being able to disable,

enable, and modify the contents of the field. The user must be able

to set the contents of this field within a user preference or

application defaults configuration.

 

We suggest, though do not require, that a convenient toggle interface

be provided for the user to enable or disable the sending of From and

Referer information.

 

 

 

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12.5 Attacks Based On File and Path Names

 

Implementations of HTTP origin servers should be careful to restrict

the documents returned by HTTP requests to be only those that were

intended by the server administrators. If an HTTP server translates

HTTP URIs directly into file system calls, the server must take

special care not to serve files that were not intended to be

delivered to HTTP clients. For example, Unix, Microsoft Windows, and

other operating systems use ".." as a path component to indicate a

directory level above the current one. On such a system, an HTTP

server must disallow any such construct in the Request-URI if it

would otherwise allow access to a resource outside those intended to

be accessible via the HTTP server. Similarly, files intended for

reference only internally to the server (such as access control

files, configuration files, and script code) must be protected from

inappropriate retrieval, since they might contain sensitive

information. Experience has shown that minor bugs in such HTTP server

implementations have turned into security risks.

 

13. Acknowledgments

 

This specification makes heavy use of the augmented BNF and generic

constructs defined by David H. Crocker for RFC 822 [7]. Similarly, it

reuses many of the definitions provided by Nathaniel Borenstein and

Ned Freed for MIME [5]. We hope that their inclusion in this

specification will help reduce past confusion over the relationship

between HTTP/1.0 and Internet mail message formats.

 

The HTTP protocol has evolved considerably over the past four years.

It has benefited from a large and active developer community--the

many people who have participated on the www-talk mailing list--and

it is that community which has been most responsible for the success

of HTTP and of the World-Wide Web in general. Marc Andreessen, Robert

Cailliau, Daniel W. Connolly, Bob Denny, Jean-Francois Groff, Phillip

M. Hallam-Baker, Hakon W. Lie, Ari Luotonen, Rob McCool, Lou

Montulli, Dave Raggett, Tony Sanders, and Marc VanHeyningen deserve

special recognition for their efforts in defining aspects of the

protocol for early versions of this specification.

 

Paul Hoffman contributed sections regarding the informational status

of this document and Appendices C and D.

 

 

 

 

 

 

 

 

 

 

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This document has benefited greatly from the comments of all those

participating in the HTTP-WG. In addition to those already mentioned,

the following individuals have contributed to this specification:

 

Gary Adams Harald Tveit Alvestrand

Keith Ball Brian Behlendorf

Paul Burchard Maurizio Codogno

Mike Cowlishaw Roman Czyborra

Michael A. Dolan John Franks

Jim Gettys Marc Hedlund

Koen Holtman Alex Hopmann

Bob Jernigan Shel Kaphan

Martijn Koster Dave Kristol

Daniel LaLiberte Paul Leach

Albert Lunde John C. Mallery

Larry Masinter Mitra

Jeffrey Mogul Gavin Nicol

Bill Perry Jeffrey Perry

Owen Rees Luigi Rizzo

David Robinson Marc Salomon

Rich Salz Jim Seidman

Chuck Shotton Eric W. Sink

Simon E. Spero Robert S. Thau

Francois Yergeau Mary Ellen Zurko

Jean-Philippe Martin-Flatin

 

14. References

 

[1] Anklesaria, F., McCahill, M., Lindner, P., Johnson, D.,

Torrey, D., and B. Alberti, "The Internet Gopher Protocol: A

Distributed Document Search and Retrieval Protocol", RFC 1436,

University of Minnesota, March 1993.

 

[2] Berners-Lee, T., "Universal Resource Identifiers in WWW: A

Unifying Syntax for the Expression of Names and Addresses of

Objects on the Network as used in the World-Wide Web",

RFC 1630, CERN, June 1994.

 

[3] Berners-Lee, T., and D. Connolly, "Hypertext Markup Language -

2.0", RFC 1866, MIT/W3C, November 1995.

 

[4] Berners-Lee, T., Masinter, L., and M. McCahill, "Uniform

Resource Locators (URL)", RFC 1738, CERN, Xerox PARC,

University of Minnesota, December 1994.

 

 

 

 

 

 

 

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RFC 1945 HTTP/1.0 May 1996

 

 

[5] Borenstein, N., and N. Freed, "MIME (Multipurpose Internet Mail

Extensions) Part One: Mechanisms for Specifying and Describing

the Format of Internet Message Bodies", RFC 1521, Bellcore,

Innosoft, September 1993.

 

[6] Braden, R., "Requirements for Internet hosts - Application and

Support", STD 3, RFC 1123, IETF, October 1989.

 

[7] Crocker, D., "Standard for the Format of ARPA Internet Text

Messages", STD 11, RFC 822, UDEL, August 1982.

 

[8] F. Davis, B. Kahle, H. Morris, J. Salem, T. Shen, R. Wang,

J. Sui, and M. Grinbaum. "WAIS Interface Protocol Prototype

Functional Specification." (v1.5), Thinking Machines

Corporation, April 1990.

 

[9] Fielding, R., "Relative Uniform Resource Locators", RFC 1808,

UC Irvine, June 1995.

 

[10] Horton, M., and R. Adams, "Standard for interchange of USENET

Messages", RFC 1036 (Obsoletes RFC 850), AT&T Bell

Laboratories, Center for Seismic Studies, December 1987.

 

[11] Kantor, B., and P. Lapsley, "Network News Transfer Protocol:

A Proposed Standard for the Stream-Based Transmission of News",

RFC 977, UC San Diego, UC Berkeley, February 1986.

 

[12] Postel, J., "Simple Mail Transfer Protocol." STD 10, RFC 821,

USC/ISI, August 1982.

 

[13] Postel, J., "Media Type Registration Procedure." RFC 1590,

USC/ISI, March 1994.

 

[14] Postel, J., and J. Reynolds, "File Transfer Protocol (FTP)",

STD 9, RFC 959, USC/ISI, October 1985.

 

[15] Reynolds, J., and J. Postel, "Assigned Numbers", STD 2, RFC

1700, USC/ISI, October 1994.

 

[16] Sollins, K., and L. Masinter, "Functional Requirements for

Uniform Resource Names", RFC 1737, MIT/LCS, Xerox Corporation,

December 1994.

 

[17] US-ASCII. Coded Character Set - 7-Bit American Standard Code

for Information Interchange. Standard ANSI X3.4-1986, ANSI,

1986.

 

 

 

 

 

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[18] ISO-8859. International Standard -- Information Processing --

8-bit Single-Byte Coded Graphic Character Sets --

Part 1: Latin alphabet No. 1, ISO 8859-1:1987.

Part 2: Latin alphabet No. 2, ISO 8859-2, 1987.

Part 3: Latin alphabet No. 3, ISO 8859-3, 1988.

Part 4: Latin alphabet No. 4, ISO 8859-4, 1988.

Part 5: Latin/Cyrillic alphabet, ISO 8859-5, 1988.

Part 6: Latin/Arabic alphabet, ISO 8859-6, 1987.

Part 7: Latin/Greek alphabet, ISO 8859-7, 1987.

Part 8: Latin/Hebrew alphabet, ISO 8859-8, 1988.

Part 9: Latin alphabet No. 5, ISO 8859-9, 1990.

 

15. Authors' Addresses

 

Tim Berners-Lee

Director, W3 Consortium

MIT Laboratory for Computer Science

545 Technology Square

Cambridge, MA 02139, U.S.A.

 

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.

 

Fax: +1 (714) 824-4056

EMail: fielding@ics.uci.edu

 

 

Henrik Frystyk Nielsen

W3 Consortium

MIT Laboratory for Computer Science

545 Technology Square

Cambridge, MA 02139, U.S.A.

 

Fax: +1 (617) 258 8682

EMail: frystyk@w3.org

 

 

 

 

 

 

 

 

 

 

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Appendices

 

These appendices are provided for informational reasons only -- they

do not form a part of the HTTP/1.0 specification.

 

A. Internet Media Type message/http

 

In addition to defining the HTTP/1.0 protocol, this document serves

as the specification for the Internet media type "message/http". The

following is to be registered with IANA [13].

 

Media Type name: message

 

Media subtype name: http

 

Required parameters: none

 

Optional parameters: version, msgtype

 

version: The HTTP-Version number of the enclosed message

(e.g., "1.0"). If not present, the version can be

determined from the first line of the body.

 

msgtype: The message type -- "request" or "response". If

not present, the type can be determined from the

first line of the body.

 

Encoding considerations: only "7bit", "8bit", or "binary" are

permitted

 

Security considerations: none

 

B. Tolerant Applications

 

Although this document specifies the requirements for the generation

of HTTP/1.0 messages, not all applications will be correct in their

implementation. We therefore recommend that operational applications

be tolerant of deviations whenever those deviations can be

interpreted unambiguously.

 

Clients should be tolerant in parsing the Status-Line and servers

tolerant when parsing the Request-Line. In particular, they should

accept any amount of SP or HT characters between fields, even though

only a single SP is required.

 

The line terminator for HTTP-header fields is the sequence CRLF.

However, we recommend that applications, when parsing such headers,

recognize a single LF as a line terminator and ignore the leading CR.

 

 

 

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C. Relationship to MIME

 

HTTP/1.0 uses many of the constructs defined for Internet Mail (RFC

822 [7]) and the Multipurpose Internet Mail Extensions (MIME [5]) to

allow entities to be transmitted in an open variety of

representations and with extensible mechanisms. However, RFC 1521

discusses mail, and HTTP has a few features that are different than

those described in RFC 1521. These differences were carefully chosen

to optimize performance over binary connections, to allow greater

freedom in the use of new media types, to make date comparisons

easier, and to acknowledge the practice of some early HTTP servers

and clients.

 

At the time of this writing, it is expected that RFC 1521 will be

revised. The revisions may include some of the practices found in

HTTP/1.0 but not in RFC 1521.

 

This appendix describes specific areas where HTTP differs from RFC

1521. Proxies and gateways to strict MIME environments should be

aware of these differences and provide the appropriate conversions

where necessary. Proxies and gateways from MIME environments to HTTP

also need to be aware of the differences because some conversions may

be required.

 

C.1 Conversion to Canonical Form

 

RFC 1521 requires that an Internet mail entity be converted to

canonical form prior to being transferred, as described in Appendix G

of RFC 1521 [5]. Section 3.6.1 of this document describes the forms

allowed for subtypes of the "text" media type when transmitted over

HTTP.

 

RFC 1521 requires that content with a Content-Type of "text"

represent line breaks as CRLF and forbids the use of CR or LF outside

of line break sequences. HTTP allows CRLF, bare CR, and bare LF to

indicate a line break within text content when a message is

transmitted over HTTP.

 

Where it is possible, a proxy or gateway from HTTP to a strict RFC

1521 environment should translate all line breaks within the text

media types described in Section 3.6.1 of this document to the RFC

1521 canonical form of CRLF. Note, however, that this may be

complicated by the presence of a Content-Encoding and by the fact

that HTTP allows the use of some character sets which do not use

octets 13 and 10 to represent CR and LF, as is the case for some

multi-byte character sets.

 

 

 

 

 

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C.2 Conversion of Date Formats

 

HTTP/1.0 uses a restricted set of date formats (Section 3.3) to

simplify the process of date comparison. Proxies and gateways from

other protocols should ensure that any Date header field present in a

message conforms to one of the HTTP/1.0 formats and rewrite the date

if necessary.

 

C.3 Introduction of Content-Encoding

 

RFC 1521 does not include any concept equivalent to HTTP/1.0's

Content-Encoding header field. Since this acts as a modifier on the

media type, proxies and gateways from HTTP to MIME-compliant

protocols must either change the value of the Content-Type header

field or decode the Entity-Body before forwarding the message. (Some

experimental applications of Content-Type for Internet mail have used

a media-type parameter of ";conversions=<content-coding>" to perform

an equivalent function as Content-Encoding. However, this parameter

is not part of RFC 1521.)

 

C.4 No Content-Transfer-Encoding

 

HTTP does not use the Content-Transfer-Encoding (CTE) field of RFC

1521. Proxies and gateways from MIME-compliant protocols to HTTP must

remove any non-identity CTE ("quoted-printable" or "base64") encoding

prior to delivering the response message to an HTTP client.

 

Proxies and gateways from HTTP to MIME-compliant protocols are

responsible for ensuring that the message is in the correct format

and encoding for safe transport on that protocol, where "safe

transport" is defined by the limitations of the protocol being used.

Such a proxy or gateway should label the data with an appropriate

Content-Transfer-Encoding if doing so will improve the likelihood of

safe transport over the destination protocol.

 

C.5 HTTP Header Fields in Multipart Body-Parts

 

In RFC 1521, most header fields in multipart body-parts are generally

ignored unless the field name begins with "Content-". In HTTP/1.0,

multipart body-parts may contain any HTTP header fields which are

significant to the meaning of that part.

 

D. Additional Features

 

This appendix documents protocol elements used by some existing HTTP

implementations, but not consistently and correctly across most

HTTP/1.0 applications. Implementors should be aware of these

features, but cannot rely upon their presence in, or interoperability

 

 

 

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with, other HTTP/1.0 applications.

 

D.1 Additional Request Methods

 

D.1.1 PUT

 

The PUT method requests that the enclosed entity be stored under the

supplied Request-URI. If the Request-URI refers to an already

existing resource, the enclosed entity should be considered as a

modified version of the one residing on the origin server. If the

Request-URI does not point to an existing resource, and that URI is

capable of being defined as a new resource by the requesting user

agent, the origin server can create the resource with that URI.

 

The fundamental difference between the POST and PUT requests is

reflected in the different meaning of the Request-URI. The URI in a

POST request identifies the resource that will handle the enclosed

entity as data to be processed. That resource may be a data-accepting

process, a gateway to some other protocol, or a separate entity that

accepts annotations. In contrast, the URI in a PUT request identifies

the entity enclosed with the request -- the user agent knows what URI

is intended and the server should not apply the request to some other

resource.

 

D.1.2 DELETE

 

The DELETE method requests that the origin server delete the resource

identified by the Request-URI.

 

D.1.3 LINK

 

The LINK method establishes one or more Link relationships between

the existing resource identified by the Request-URI and other

existing resources.

 

D.1.4 UNLINK

 

The UNLINK method removes one or more Link relationships from the

existing resource identified by the Request-URI.

 

D.2 Additional Header Field Definitions

 

D.2.1 Accept

 

The Accept request-header field can be used to indicate a list of

media ranges which are acceptable as a response to the request. The

asterisk "*" character is used to group media types into ranges, with

"*/*" indicating all media types and "type/*" indicating all subtypes

 

 

 

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of that type. The set of ranges given by the client should represent

what types are acceptable given the context of the request.

 

D.2.2 Accept-Charset

 

The Accept-Charset request-header field can be used to indicate a

list of preferred character sets other than the default US-ASCII and

ISO-8859-1. This field allows clients capable of understanding more

comprehensive or special-purpose character sets to signal that

capability to a server which is capable of representing documents in

those character sets.

 

D.2.3 Accept-Encoding

 

The Accept-Encoding request-header field is similar to Accept, but

restricts the content-coding values which are acceptable in the

response.

 

D.2.4 Accept-Language

 

The Accept-Language request-header field is similar to Accept, but

restricts the set of natural languages that are preferred as a

response to the request.

 

D.2.5 Content-Language

 

The Content-Language entity-header field describes the natural

language(s) of the intended audience for the enclosed entity. Note

that this may not be equivalent to all the languages used within the

entity.

 

D.2.6 Link

 

The Link entity-header field provides a means for describing a

relationship between the entity and some other resource. An entity

may include multiple Link values. Links at the metainformation level

typically indicate relationships like hierarchical structure and

navigation paths.

 

D.2.7 MIME-Version

 

HTTP messages may include a single MIME-Version general-header field

to indicate what version of the MIME protocol was used to construct

the message. Use of the MIME-Version header field, as defined by RFC

1521 [5], should indicate that the message is MIME-conformant.

Unfortunately, some older HTTP/1.0 servers send it indiscriminately,

and thus this field should be ignored.

 

 

 

 

Berners-Lee, et al Informational [Page 59]

 

 

RFC 1945 HTTP/1.0 May 1996

 

 

D.2.8 Retry-After

 

The Retry-After response-header field can be used with a 503 (service

unavailable) response to indicate how long the service is expected to

be unavailable to the requesting client. The value of this field can

be either an HTTP-date or an integer number of seconds (in decimal)

after the time of the response.

 

D.2.9 Title

 

The Title entity-header field indicates the title of the entity.

 

D.2.10 URI

 

The URI entity-header field may contain some or all of the Uniform

Resource Identifiers (Section 3.2) by which the Request-URI resource

can be identified. There is no guarantee that the resource can be

accessed using the URI(s) specified.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

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