Hypertext Transfer Protocol -- HTTP/1.0
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Hypertext Transfer Protocol -- HTTP/1.0
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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RFC 1945 HTTP/1.0 May 1996
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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RFC 1945 HTTP/1.0 May 1996
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.
Berners-Lee, et al Informational [Page 18]
RFC 1945 HTTP/1.0 May 1996
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.
Berners-Lee, et al Informational [Page 19]
RFC 1945 HTTP/1.0 May 1996
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
Berners-Lee, et al Informational [Page 20]
RFC 1945 HTTP/1.0 May 1996
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
Berners-Lee, et al Informational [Page 21]
RFC 1945 HTTP/1.0 May 1996
| 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.
Berners-Lee, et al Informational [Page 22]
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