Hypertext Transfer Protocol -- HTTP/1.0
draft-ietf-http-v10-spec-04

HTTP Working Group T. Berners-Lee, MIT/LCS
INTERNET-DRAFT R. Fielding, UC Irvine
<draft-ietf-http-v10-spec-04.txt> H. Frystyk, MIT/LCS
Expires April 14, 1996 October 14, 1995
 Hypertext Transfer Protocol -- HTTP/1.0
Status of this Memo
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Abstract
 The Hypertext Transfer Protocol (HTTP) is an application-level 
 protocol with the lightness and speed necessary for distributed, 
 collaborative, hypermedia information systems. It is a generic, 
 stateless, object-oriented protocol which can be used for many 
 tasks, such as name servers and distributed object management 
 systems, through extension of its request methods (commands). A 
 feature of HTTP is the typing of data representation, allowing 
 systems to be built independently of the data being transferred.
 HTTP has been in use by the World-Wide Web global information 
 initiative since 1990. This specification reflects common usage of 
 the protocol referred to as "HTTP/1.0".
Table of Contents
 1. Introduction
 1.1 Purpose
 1.2 Terminology
 1.3 Overall Operation
 2. Notational Conventions and Generic Grammar
 2.1 Augmented BNF
 2.2 Basic Rules
 3. Protocol Parameters
 3.1 HTTP Version
 3.2 Uniform Resource Identifiers
 3.2.1 General Syntax
 3.2.2 http URL
 3.3 Date/Time Formats
 3.4 Character Sets
 3.5 Content Codings
 3.6 Media Types
 3.6.1 Canonicalization and Text Defaults
 3.6.2 Multipart Types
 3.7 Product Tokens
 4. HTTP Message
 4.1 Message Types
 4.2 Message Headers
 4.3 General Header Fields
 5. Request
 5.1 Request-Line
 5.1.1 Method
 5.1.2 Request-URI
 5.2 Request Header Fields
 6. Response
 6.1 Status-Line
 6.1.1 Status Code and Reason Phrase
 6.2 Response Header Fields
 7. Entity
 7.1 Entity Header Fields
 7.2 Entity Body
 7.2.1 Type
 7.2.2 Length
 8. Method Definitions
 8.1 GET
 8.2 HEAD
 8.3 POST
 9. Status Code Definitions
 9.1 Informational 1xx
 9.2 Successful 2xx
 9.3 Redirection 3xx
 9.4 Client Error 4xx
 9.5 Server Error 5xx
 10. Header Field Definitions
 10.1 Allow
 10.2 Authorization
 10.3 Content-Encoding
 10.4 Content-Length
 10.5 Content-Type
 10.6 Date
 10.7 Expires
 10.8 From
 10.9 If-Modified-Since
 10.10 Last-Modified
 10.11 Location
 10.12 MIME-Version
 10.13 Pragma
 10.14 Referer
 10.15 Server
 10.16 User-Agent
 10.17 WWW-Authenticate
 
 11. Access Authentication
 11.1 Basic Authentication Scheme
 12. Security Considerations
 12.1 Authentication of Clients
 12.2 Safe Methods
 12.3 Abuse of Server Log Information
 12.4 Transfer of Sensitive Information
 13. Acknowledgments
 14. References
 15. Authors' Addresses
 Appendix A. Internet Media Type message/http
 Appendix B. Tolerant Applications
 Appendix C. Relationship to MIME
 C.1 Conversion to Canonical Form
 C.1.1 Representation of Line Breaks
 C.1.2 Default Character Set
 C.2 Conversion of Date Formats
 C.3 Introduction of Content-Encoding
 C.4 No Content-Transfer-Encoding
1. Introduction
1.1 Purpose
 The Hypertext Transfer Protocol (HTTP) is an application-level 
 protocol with the lightness and speed necessary for distributed, 
 collaborative, hypermedia information systems. HTTP has been in use 
 by the World-Wide Web global information initiative since 1990. 
 This specification reflects common usage of the protocol referred 
 to as "HTTP/1.0". This specification is not intended to become an 
 Internet standard; rather, it defines those features of the HTTP 
 protocol that can reasonably be expected of any implementation 
 which claims to be using HTTP/1.0.
 Practical information systems require more functionality than 
 simple retrieval, including search, front-end update, and 
 annotation. HTTP allows an open-ended set of methods to be used to 
 indicate the purpose of a request. It builds on the discipline of 
 reference provided by the Uniform Resource Identifier (URI) [2], as 
 a location (URL) [4] or name (URN) [16], for indicating the 
 resource on which a method is to be applied. Messages are passed in 
 a format similar to that used by Internet Mail [7] and the 
 Multipurpose Internet Mail Extensions (MIME) [5].
 HTTP is also used as a generic protocol for communication between 
 user agents and proxies/gateways to other Internet protocols, such 
 as SMTP [12], NNTP [11], FTP [14], Gopher [1], and WAIS [8], 
 allowing basic hypermedia access to resources available from 
 diverse applications and simplifying the implementation of user 
 agents.
1.2 Terminology
 This specification uses a number of terms to refer to the roles 
 played by participants in, and objects of, the HTTP communication.
 connection
 A transport layer virtual circuit established between two 
 application programs for the purpose of communication.
 message
 The basic unit of HTTP communication, consisting of a structured 
 sequence of octets matching the syntax defined in Section 4 and 
 transmitted via the connection.
 request
 An HTTP request message (as defined in Section 5).
 response
 An HTTP response message (as defined in Section 6).
 resource
 A network data object or service which can be identified by a 
 URI (Section 3.2).
 entity
 A particular representation or rendition of a data resource, or 
 reply from a service resource, that may be enclosed within a 
 request or response message. An entity consists of 
 metainformation in the form of entity headers and content in the 
 form of an entity body.
 client
 An application program that establishes connections for the 
 purpose of sending requests.
 user agent
 The client which initiates a request. These are often browsers, 
 editors, spiders (web-traversing robots), or other end user 
 tools.
 server
 An application program that accepts connections in order to 
 service requests by sending back responses.
 origin server
 The server on which a given resource resides or is to be created.
 proxy
 An intermediary program which acts as both a server and a client 
 for the purpose of making requests on behalf of other clients. 
 Requests are serviced internally or by passing them, with 
 possible translation, on to other servers. A proxy must 
 interpret and, if necessary, rewrite a request message before 
 forwarding it. Proxies are often used as client-side portals 
 through network firewalls and as helper applications for 
 handling requests via protocols not implemented by the user 
 agent.
 gateway
 A server which acts as an intermediary for some other server. 
 Unlike a proxy, a gateway receives requests as if it were the 
 origin server for the requested resource; the requesting client 
 may not be aware that it is communicating with a gateway. 
 Gateways are often used as server-side portals through network 
 firewalls and as protocol translators for access to resources 
 stored on non-HTTP systems.
 tunnel
 A tunnel is an intermediary program which is acting as a blind 
 relay between two connections. Once active, a tunnel is not 
 considered a party to the HTTP communication, though the tunnel 
 may have been initiated by an HTTP request. A tunnel is closed 
 when both ends of the relayed connections are closed. Tunnels 
 are used when a portal is necessary and the intermediary cannot, 
 or should not, interpret the relayed communication.
 cache
 A program's local store of response messages and the subsystem 
 that controls its message storage, retrieval, and deletion. A 
 cache stores cachable responses in order to reduce the response 
 time and network bandwidth consumption on future, equivalent 
 requests. Any client or server may include a cache, though a 
 cache cannot be used by a server while it is acting as a tunnel.
 Any given program may be capable of being both a client and a 
 server; our use of these terms refers only to the role being 
 performed by the program for a particular connection, rather than 
 to the program's capabilities in general. Likewise, any server may 
 act as an origin server, proxy, gateway, or tunnel, switching 
 behavior based on the nature of each request.
1.3 Overall Operation
 The HTTP protocol is based on a request/response paradigm. A client 
 establishes a connection with a server and sends a request to the 
 server in the form of a request method, URI, and protocol version, 
 followed by a MIME-like message containing request modifiers, 
 client information, and possible body content. The server responds 
 with a status line, including the message's protocol version and a 
 success or error code, followed by a MIME-like message containing 
 server information, entity metainformation, and possible body 
 content.
 Most HTTP communication is initiated by a user agent and consists 
 of a request to be applied to a resource on some origin server. In 
 the simplest case, this may be accomplished via a single connection 
 (v) between the user agent (UA) and the origin server (O).
 request chain ------------------------>
 UA -------------------v------------------- O
 <----------------------- response chain
 A more complicated situation occurs when one or more intermediaries 
 are present in the request/response chain. There are three common 
 forms of intermediary: proxy, gateway, and tunnel. A proxy is a 
 forwarding agent, receiving requests for a URI in its absolute 
 form, rewriting all or parts of the message, and forwarding the 
 reformatted request toward the server identified by the URI. A 
 gateway is a receiving agent, acting as a layer above some other 
 server(s) and, if necessary, translating the requests to the 
 underlying server's protocol. A tunnel acts as a relay point 
 between two connections without changing the messages; tunnels are 
 used when the communication needs to pass through an intermediary 
 (such as a firewall) even when the intermediary cannot understand 
 the contents of the messages.
 request chain -------------------------------------->
 UA -----v----- A -----v----- B -----v----- C -----v----- O
 <------------------------------------- response chain
 The figure above shows three intermediaries (A, B, and C) between 
 the user agent and origin server. A request or response message 
 that travels the whole chain must pass through four separate 
 connections. This distinction is important because some HTTP 
 communication options may apply only to the connection with the 
 nearest, non-tunnel neighbor, only to the end-points of the chain, 
 or to all connections along the chain. Although the diagram is 
 linear, each participant may be engaged in multiple, simultaneous 
 communications. For example, B may be receiving requests from many 
 clients other than A, and/or forwarding requests to servers other 
 than C, at the same time that it is handling A's request.
 Any party to the communication which is not acting as a tunnel may 
 employ an internal cache for handling requests. The effect of a 
 cache is that the request/response chain is shortened if one of the 
 participants along the chain has a cached response applicable to 
 that request. The following illustrates the resulting chain if B 
 has a cached copy of an earlier response from O (via C) for a 
 request which has not been cached by UA or A.
 request chain ---------->
 UA -----v----- A -----v----- B - - - - - - C - - - - - - O
 <--------- response chain
 Not all responses are cachable, and some requests may contain 
 modifiers which place special requirements on cache behavior. 
 Historically, HTTP/1.0 applications have not adequately defined 
 what is or is not a "cachable" response.
 On the Internet, HTTP communication generally takes place over 
 TCP/IP connections. The default port is TCP 80 [15], but other 
 ports can be used. This does not preclude HTTP from being 
 implemented on top of any other protocol on the Internet, or on 
 other networks. HTTP only presumes a reliable transport; any 
 protocol that provides such guarantees can be used, and the mapping 
 of the HTTP/1.0 request and response structures onto the transport 
 data units of the protocol in question is outside the scope of this 
 specification.
 Current practice requires that the connection be established by the 
 client prior to each request and closed by the server after sending 
 the response. Both clients and servers must be capable of handling 
 cases where either party closes the connection prematurely, due to 
 user action, automated time-out, or program failure. In any case, 
 the closing of the connection by either or both parties always 
 terminates the current request, regardless of its status.
2. Notational Conventions and Generic Grammar
2.1 Augmented BNF
 All of the mechanisms specified in this document are described in 
 both prose and an augmented Backus-Naur Form (BNF) similar to that 
 used by RFC 822 [7]. Implementors will need to be familiar with the 
 notation in order to understand this specification. The augmented 
 BNF includes the following constructs:
 name = definition
 The name of a rule is simply the name itself (without any 
 enclosing "<" and ">") and is separated from its definition by 
 the equal character "=". Whitespace is only significant in that 
 indentation of continuation lines is used to indicate a rule 
 definition that spans more than one line. Certain basic rules 
 are in uppercase, such as SP, LWS, HT, CRLF, DIGIT, ALPHA, etc. 
 Angle brackets are used within definitions whenever their 
 presence will facilitate discerning the use of rule names.
 "literal"
 Quotation marks surround literal text. Unless stated otherwise, 
 the text is case-insensitive.
 rule1 | rule2
 Elements separated by a bar ("I") are alternatives,
 e.g., "yes | no" will accept yes or no.
 (rule1 rule2)
 Elements enclosed in parentheses are treated as a single 
 element. Thus, "(elem (foo | bar) elem)" allows the token 
 sequences "elem foo elem" and "elem bar elem".
 *rule
 The character "*" preceding an element indicates repetition. The 
 full form is "<n>*<m>element" indicating at least <n> and at 
 most <m> occurrences of element. Default values are 0 and 
 infinity so that "*(element)" allows any number, including zero; 
 "1*element" requires at least one; and "1*2element" allows one 
 or two.
 [rule]
 Square brackets enclose optional elements; "[foo bar]" is 
 equivalent to "*1(foo bar)".
 N rule
 Specific repetition: "<n>(element)" is equivalent to 
 "<n>*<n>(element)"; that is, exactly <n> occurrences of 
 (element). Thus 2DIGIT is a 2-digit number, and 3ALPHA is a 
 string of three alphabetic characters.
 #rule
 A construct "#" is defined, similar to "*", for defining lists 
 of elements. The full form is "<n>#<m>element" indicating at 
 least <n> and at most <m> elements, each separated by one or 
 more commas (",") and optional linear whitespace (LWS). This 
 makes the usual form of lists very easy; a rule such as 
 "( *LWS element *( *LWS "," *LWS element ))" can be shown as 
 "1#element". Wherever this construct is used, null elements are 
 allowed, but do not contribute to the count of elements present. 
 That is, "(element), , (element)" is permitted, but counts as 
 only two elements. Therefore, where at least one element is 
 required, at least one non-null element must be present. Default 
 values are 0 and infinity so that "#(element)" allows any 
 number, including zero; "1#element" requires at least one; and 
 "1#2element" allows one or two.
 ; comment
 A semi-colon, set off some distance to the right of rule text, 
 starts a comment that continues to the end of line. This is a 
 simple way of including useful notes in parallel with the 
 specifications.
 implied *LWS
 The grammar described by this specification is word-based. 
 Except where noted otherwise, linear whitespace (LWS) can be 
 included between any two adjacent words (token or 
 quoted-string), and between adjacent tokens and delimiters 
 (tspecials), without changing the interpretation of a field. 
 However, applications should attempt to follow "common form" 
 when generating HTTP constructs, since there exist some 
 implementations that fail to accept anything beyond the common 
 forms.
2.2 Basic Rules
 The following rules are used throughout this specification to 
 describe basic parsing constructs. The US-ASCII coded character set 
 is defined by [17].
 OCTET = <any 8-bit sequence of data>
 CHAR = <any US-ASCII character (octets 0 - 127)>
 UPALPHA = <any US-ASCII uppercase letter "A".."Z">
 LOALPHA = <any US-ASCII lowercase letter "a".."z">
 ALPHA = UPALPHA | LOALPHA
 DIGIT = <any US-ASCII digit "0".."9">
 CTL = <any US-ASCII control character
 (octets 0 - 31) and DEL (127)>
 CR = <US-ASCII CR, carriage return (13)>
 LF = <US-ASCII LF, linefeed (10)>
 SP = <US-ASCII SP, space (32)>
 HT = <US-ASCII HT, horizontal-tab (9)>
 <"> = <US-ASCII double-quote mark (34)>
 HTTP/1.0 defines the octet sequence CR LF as the end-of-line marker 
 for all protocol elements except the Entity-Body (see Appendix B 
 for tolerant applications). The end-of-line marker within an 
 Entity-Body is defined by its associated media type, as described 
 in Section 3.6.
 CRLF = CR LF
 HTTP/1.0 headers may be folded onto multiple lines if each 
 continuation line begins with a space or horizontal tab. All linear 
 whitespace, including folding, has the same semantics as SP.
 LWS = [CRLF] 1*( SP | HT )
 However, folding of header lines is not expected by some 
 applications, and should not be generated by HTTP/1.0 applications.
 The TEXT rule is only used for descriptive field contents and 
 values that are not intended to be interpreted by the message 
 parser. Words of *TEXT may contain octets from character sets other 
 than US-ASCII.
 TEXT = <any OCTET except CTLs,
 but including LWS>
 Recipients of header field TEXT containing octets outside the 
 US-ASCII character set may assume that they represent ISO-8859-1 
 characters.
 Many HTTP/1.0 header field values consist of words separated by LWS 
 or special characters. These special characters must be in a quoted 
 string to be used within a parameter value.
 word = token | quoted-string
 token = 1*<any CHAR except CTLs or tspecials>
 tspecials = "(" | ")" | "<" | ">" | "@"
 | "," | ";" | ":" | "\" | <">
 | "/" | "[" | "]" | "?" | "="
 | "{" | "}" | SP | HT
 Comments may be included in some HTTP header fields by surrounding 
 the comment text with parentheses. Comments are only allowed in 
 fields containing "comment" as part of their field value definition.
 comment = "(" *( ctext | comment ) ")"
 ctext = <any TEXT excluding "(" and ")">
 A string of text is parsed as a single word if it is quoted using 
 double-quote marks.
 quoted-string = ( <"> *(qdtext) <"> )
 qdtext = <any CHAR except <"> and CTLs,
 but including LWS>
 Single-character quoting using the backslash ("\") character is not 
 permitted in HTTP/1.0.
3. Protocol Parameters
3.1 HTTP Version
 HTTP uses a "<major>.<minor>" numbering scheme to indicate versions 
 of the protocol. The protocol versioning policy is intended to 
 allow the sender to indicate the format of a message and its 
 capacity for understanding further HTTP communication, rather than 
 the features obtained via that communication. No change is made to 
 the version number for the addition of message components which do 
 not affect communication behavior or which only add to extensible 
 field values. The <minor> number is incremented when the changes 
 made to the protocol add features which do not change the general 
 message parsing algorithm, but which may add to the message 
 semantics and imply additional capabilities of the sender. The 
 <major> number is incremented when the format of a message within 
 the protocol is changed.
 The version of an HTTP message is indicated by an HTTP-Version 
 field in the first line of the message. If the protocol version is 
 not specified, the recipient must assume that the message is in the 
 simple HTTP/0.9 format.
 HTTP-Version = "HTTP" "/" 1*DIGIT "." 1*DIGIT
 Note that the major and minor numbers should be treated as separate 
 integers and that each may be incremented higher than a single 
 digit. Thus, HTTP/2.4 is a lower version than HTTP/2.13, which in 
 turn is lower than HTTP/12.3. Leading zeros should be ignored by 
 recipients and never generated by senders.
 This document defines both the 0.9 and 1.0 versions of the HTTP 
 protocol. Applications sending Full-Request or Full-Response 
 messages, as defined by this specification, must include an 
 HTTP-Version of "HTTP/1.0".
 HTTP/1.0 servers must:
 o recognize the format of the Request-Line for HTTP/0.9 and 
 HTTP/1.0 requests;
 o understand any valid request in the format of HTTP/0.9 or 
 HTTP/1.0;
 o respond appropriately with a message in the same protocol 
 version used by the client.
 HTTP/1.0 clients must:
 o recognize the format of the Status-Line for HTTP/1.0 responses;
 o understand any valid response in the format of HTTP/0.9 or 
 HTTP/1.0.
 Proxy and gateway applications must be careful in forwarding 
 requests that are received in a format different than that of the 
 application's native HTTP version. Since the protocol version 
 indicates the protocol capability of the sender, a proxy/gateway 
 must never send a message with a version indicator which is greater 
 than its native version; if a higher version request is received, 
 the proxy/gateway must either downgrade the request version or 
 respond with an error. Requests with a version lower than that of 
 the application's native format may be upgraded before being 
 forwarded; the proxy/gateway's response to that request must follow 
 the normal server requirements.
3.2 Uniform Resource Identifiers
 URIs have been known by many names: WWW addresses, Universal 
 Document Identifiers, Universal Resource Identifiers [2], and 
 finally the combination of Uniform Resource Locators (URL) [4] and 
 Names (URN) [16]. As far as HTTP is concerned, Uniform Resource 
 Identifiers are simply formatted strings which identify--via name, 
 location, or any other characteristic--a network resource.
3.2.1 General Syntax
 URIs in HTTP/1.0 can be represented in absolute form or relative to 
 some known base URI [9], depending upon the context of their use. 
 The two forms are differentiated by the fact that absolute URIs 
 always begin with a scheme name followed by a colon.
 URI = ( absoluteURI | relativeURI ) [ "#" fragment ]
 absoluteURI = scheme ":" *( uchar | reserved )
 relativeURI = net_path | abs_path | rel_path
 net_path = "//" net_loc [ abs_path ]
 abs_path = "/" rel_path
 rel_path = [ path ] [ ";" params ] [ "?" query ]
 path = fsegment *( "/" segment )
 fsegment = 1*pchar
 segment = *pchar
 params = param *( ";" param )
 param = *( pchar | "/" )
 scheme = 1*( ALPHA | DIGIT | "+" | "-" | "." )
 net_loc = *( pchar | ";" | "?" )
 query = *( uchar | reserved )
 fragment = *( uchar | reserved )
 pchar = uchar | ":" | "@" | "&" | "="
 uchar = unreserved | escape
 unreserved = ALPHA | DIGIT | safe | extra | national
 escape = "%" hex hex
 hex = "A" | "B" | "C" | "D" | "E" | "F"
 | "a" | "b" | "c" | "d" | "e" | "f" | DIGIT
 reserved = ";" | "/" | "?" | ":" | "@" | "&" | "="
 safe = "$" | "-" | "_" | "." | "+"
 extra = "!" | "*" | "'" | "(" | ")" | ","
 national = <any OCTET excluding CTLs, SP,
 ALPHA, DIGIT, reserved, safe, and extra>
 For definitive information on URL syntax and semantics, see RFC 
 1738 [4] and RFC 1808 [9]. The BNF above includes national 
 characters not allowed in valid URLs as specified by RFC 1738, 
 since HTTP servers are not restricted in the set of unreserved 
 characters allowed to represent the rel_path part of addresses, and 
 HTTP proxies may receive requests for URIs not defined by RFC 1738.
3.2.2 http URL
 The "http" scheme is used to locate network resources via the HTTP 
 protocol. This section defines the scheme-specific syntax and 
 semantics for http URLs.
 http_URL = "http:" "//" host [ ":" port ] abs_path
 host = <A legal Internet host domain name
 or IP address (in dotted-decimal form),
 as defined by Section 2.1 of RFC 1123>
 port = *DIGIT
 If the port is empty or not given, port 80 is assumed. The 
 semantics are that the identified resource is located at the server 
 listening for TCP connections on that port of that host, and the 
 Request-URI for the resource is abs_path. If the abs_path is not 
 present in the URL, it must be given as "/" when used as a 
 Request-URI.
 Note: Although the HTTP protocol is independent of the 
 transport layer protocol, the http URL only identifies 
 resources by their TCP location, and thus non-TCP resources 
 must be identified by some other URI scheme.
 The canonical form for "http" URLs is obtained by converting any 
 UPALPHA characters in host to their LOALPHA equivalent (hostnames 
 are case-insensitive), eliding the [ ":" port ] if the port is 80, 
 and replacing an empty abs_path with "/".
3.3 Date/Time Formats
 HTTP/1.0 applications have historically allowed three different 
 formats for the representation of date/time stamps:
 1994年11月06日 08:49:37 GMT ; RFC 822, updated by RFC 1123
 Sunday, 06-Nov-94 08:49:37 GMT ; RFC 850, obsoleted by RFC 1036
 Sun Nov 6 08:49:37 1994 ; ANSI C's asctime() format
 The first format is preferred as an Internet standard and 
 represents a fixed-length subset of that defined by RFC 1123 [6] 
 (an update to RFC 822 [7]). The second format is in common use, but 
 is based on the obsolete RFC 850 [10] date format and lacks a 
 four-digit year. HTTP/1.0 clients and servers that parse the date 
 value should accept all three formats, though they must never 
 generate the third (asctime) format.
 Note: Recipients of date values are encouraged to be robust 
 in accepting date values that may have been generated by 
 non-HTTP applications, as is sometimes the case when 
 retrieving or posting messages via proxies/gateways to SMTP 
 or NNTP.
 All HTTP/1.0 date/time stamps must be represented in Universal Time 
 (UT), also known as Greenwich Mean Time (GMT), without exception. 
 This is indicated in the first two formats by the inclusion of 
 "GMT" as the three-letter abbreviation for time zone, and should be 
 assumed when reading the asctime format.
 HTTP-date = rfc1123-date | rfc850-date | asctime-date
 rfc1123-date = wkday "," SP date1 SP time SP "GMT"
 rfc850-date = weekday "," SP date2 SP time SP "GMT"
 asctime-date = wkday SP date3 SP time SP 4DIGIT
 date1 = 2DIGIT SP month SP 4DIGIT
 ; day month year (e.g., 02 Jun 1982)
 date2 = 2DIGIT "-" month "-" 2DIGIT
 ; day-month-year (e.g., 02-Jun-82)
 date3 = month SP ( 2DIGIT | ( SP 1DIGIT ))
 ; month day (e.g., Jun 2)
 time = 2DIGIT ":" 2DIGIT ":" 2DIGIT
 ; 00:00:00 - 23:59:59
 wkday = "Mon" | "Tue" | "Wed"
 | "Thu" | "Fri" | "Sat" | "Sun"
 weekday = "Monday" | "Tuesday" | "Wednesday"
 | "Thursday" | "Friday" | "Saturday" | "Sunday"
 month = "Jan" | "Feb" | "Mar" | "Apr"
 | "May" | "Jun" | "Jul" | "Aug"
 | "Sep" | "Oct" | "Nov" | "Dec"
 Note: HTTP/1.0 requirements for the date/time stamp format 
 apply only to their usage within the protocol stream. 
 Clients and servers are not required to use these formats 
 for user presentation, request logging, etc.
3.4 Character Sets
 HTTP uses the same definition of the term "character set" as that 
 described for MIME:
 The term "character set" is used in this document to 
 refer to a method used with one or more tables to convert 
 a sequence of octets into a sequence of characters. Note 
 that unconditional conversion in the other direction is 
 not required, in that not all characters may be available 
 in a given character set and a character set may provide 
 more than one sequence of octets to represent a 
 particular character. This definition is intended to 
 allow various kinds of character encodings, from simple 
 single-table mappings such as US-ASCII to complex table 
 switching methods such as those that use ISO 2022's 
 techniques. However, the definition associated with a 
 MIME character set name must fully specify the mapping to 
 be performed from octets to characters. In particular, 
 use of external profiling information to determine the 
 exact mapping is not permitted.
 HTTP character sets are identified by case-insensitive tokens. The 
 complete set of tokens are defined by the IANA Character Set 
 registry [15]. However, because that registry does not define a 
 single, consistent token for each character set, we define here the 
 preferred names for those character sets most likely to be used 
 with HTTP entities. These character sets include those registered 
 by RFC 1521 [5] -- the US-ASCII [17] and ISO-8859 [18] character 
 sets -- and other names specifically recommended for use within MIME 
 charset parameters.
 charset = "US-ASCII"
 | "ISO-8859-1" | "ISO-8859-2" | "ISO-8859-3"
 | "ISO-8859-4" | "ISO-8859-5" | "ISO-8859-6"
 | "ISO-8859-7" | "ISO-8859-8" | "ISO-8859-9"
 | "ISO-2022-JP" | "ISO-2022-JP-2" | "ISO-2022-KR"
 | "UNICODE-1-1" | "UNICODE-1-1-UTF-7" | "UNICODE-1-1-UTF-8"
 | token
 Although HTTP allows an arbitrary token to be used as a charset 
 value, any token that has a predefined value within the IANA 
 Character Set registry [15] must represent the character set 
 defined by that registry. Applications should limit their use of 
 character sets to those defined by the IANA registry.
 Note: This use of the term "character set" is more commonly 
 referred to as a "character encoding." However, since HTTP 
 and MIME share the same registry, it is important that the 
 terminology also be shared.
3.5 Content Codings
 Content coding values are used to indicate an encoding 
 transformation that has been applied to a resource. Content codings 
 are primarily used to allow a document to be compressed or 
 encrypted without losing the identity of its underlying media type. 
 Typically, the resource is stored in this encoding and only decoded 
 before rendering or analogous usage.
 content-coding = "x-gzip" | "x-compress" | token
 Note: For future compatibility, HTTP/1.0 applications should 
 consider "gzip" and "compress" to be equivalent to "x-gzip" 
 and "x-compress", respectively.
 All content-coding values are case-insensitive. HTTP/1.0 uses 
 content-coding values in the Content-Encoding (Section 10.3) header 
 field. Although the value describes the content-coding, what is 
 more important is that it indicates what decoding mechanism will be 
 required to remove the encoding. Note that a single program may be 
 capable of decoding multiple content-coding formats. Two values are 
 defined by this specification:
 x-gzip
 An encoding format produced by the file compression program 
 "gzip" (GNU zip) developed by Jean-loup Gailly. This format is 
 typically a Lempel-Ziv coding (LZ77) with a 32 bit CRC. Gzip is 
 available from the GNU project at 
 <URL:ftp://prep.ai.mit.edu/pub/gnu/>.
 x-compress
 The encoding format produced by the file compression program 
 "compress". This format is an adaptive Lempel-Ziv-Welch coding 
 (LZW).
 Note: Use of program names for the identification of 
 encoding formats is not desirable and should be discouraged 
 for future encodings. Their use here is representative of 
 historical practice, not good design.
3.6 Media Types
 HTTP uses Internet Media Types [13] in the Content-Type header 
 field (Section 10.5) in order to provide open and extensible data 
 typing. For mail applications, where there is no type negotiation 
 between sender and recipient, it is reasonable to put strict limits 
 on the set of allowed media types. With HTTP, where the sender and 
 recipient can communicate directly, applications are allowed more 
 freedom in the use of non-registered types. The following grammar 
 for media types is a superset of that for MIME because it does not 
 restrict itself to the official IANA and x-token types.
 media-type = type "/" subtype *( ";" parameter )
 type = token
 subtype = token
 Parameters may follow the type/subtype in the form of 
 attribute/value pairs.
 parameter = attribute "=" value
 attribute = token
 value = token | quoted-string
 The type, subtype, and parameter attribute names are 
 case-insensitive. Parameter values may or may not be 
 case-sensitive, depending on the semantics of the parameter name. 
 LWS must not be generated between the type and subtype, nor between 
 an attribute and its value.
 Many current applications do not recognize media type parameters. 
 Since parameters are a fundamental aspect of media types, this must 
 be considered an error in those applications. Nevertheless, 
 HTTP/1.0 applications should only use media type parameters when 
 they are necessary to define the content of a message.
 If a given media-type value has been registered by the IANA, any 
 use of that value must be indicative of the registered data format. 
 Although HTTP allows the use of non-registered media types, such 
 usage must not conflict with the IANA registry. Data providers are 
 strongly encouraged to register their media types with IANA via the 
 procedures outlined in RFC 1590 [13].
 All media-type's registered by IANA must be preferred over 
 extension tokens. However, HTTP does not limit applications to the 
 use of officially registered media types, nor does it encourage the 
 use of an "x-" prefix for unofficial types outside of explicitly 
 short experimental use between consenting applications.
3.6.1 Canonicalization and Text Defaults
 Media types are registered in a canonical form. In general, entity 
 bodies transferred via HTTP must be represented in the appropriate 
 canonical form prior to transmission. If the body has been encoded 
 via a Content-Encoding, the data must be in canonical form prior to 
 that encoding. However, HTTP modifies the canonical form 
 requirements for media of primary type "text" and for "application" 
 types consisting of text-like records.
 HTTP redefines the canonical form of text media to allow multiple 
 octet sequences to indicate a text line break. In addition to the 
 preferred form of CRLF, HTTP applications must accept a bare CR or 
 LF alone as representing a single line break in text media. 
 Furthermore, if the text media is represented in a character set 
 which does not use octets 13 and 10 for CR and LF respectively, as 
 is the case for some multi-byte character sets, HTTP allows the use 
 of whatever octet sequence(s) is defined by that character set to 
 represent the equivalent of CRLF, bare CR, and bare LF. It is 
 assumed that any recipient capable of using such a character set 
 will know the appropriate octet sequence for representing line 
 breaks within that character set.
 Note: This interpretation of line breaks applies only to the 
 contents of an Entity-Body and only after any 
 Content-Encoding has been removed. All other HTTP constructs 
 use CRLF exclusively to indicate a line break. Content 
 codings define their own line break requirements.
 A recipient of an HTTP text entity should translate the received 
 entity line breaks to the local line break conventions before 
 saving the entity external to the application and its cache; 
 whether this translation takes place immediately upon receipt of 
 the entity, or only when prompted by the user, is entirely up to 
 the individual application.
 HTTP also redefines the default character set for text media in an 
 entity body. If a textual media type defines a charset parameter 
 with a registered default value of "US-ASCII", HTTP changes the 
 default to be "ISO-8859-1". Since the ISO-8859-1 [18] character set 
 is a superset of US-ASCII [17], this has no effect upon the 
 interpretation of entity bodies which only contain octets within 
 the US-ASCII set (0 - 127). The presence of a charset parameter 
 value in a Content-Type header field overrides the default.
 It is recommended that the character set of an entity body be 
 labelled as the lowest common denominator of the character codes 
 used within a document, with the exception that no label is 
 preferred over the labels US-ASCII or ISO-8859-1.
3.6.2 Multipart Types
 MIME provides for a number of "multipart" types -- encapsulations of 
 several entities within a single message's Entity-Body. The 
 multipart types registered by IANA [15] do not have any special 
 meaning for HTTP/1.0, though user agents may need to understand 
 each type in order to correctly interpret the purpose of each 
 body-part. Ideally, an HTTP user agent should follow the same or 
 similar behavior as a MIME user agent does upon receipt of a 
 multipart type.
 As in MIME [5], all multipart types share a common syntax and must 
 include a boundary parameter as part of the media type value. The 
 message body is itself a protocol element and must therefore use 
 only CRLF to represent line breaks between body-parts. Unlike in 
 MIME, multipart body-parts may contain HTTP header fields which are 
 significant to the meaning of that part.
3.7 Product Tokens
 Product tokens are used to allow communicating applications to 
 identify themselves via a simple product token, with an optional 
 slash and version designator. Most fields using product tokens also 
 allow subproducts which form a significant part of the application 
 to be listed, separated by whitespace. By convention, the products 
 are listed in order of their significance for identifying the 
 application.
 product = token ["/" product-version]
 product-version = token
 Examples:
 User-Agent: CERN-LineMode/2.15 libwww/2.17b3
 Server: Apache/0.8.4
 Product tokens should be short and to the point -- use of them for 
 advertizing or other non-essential information is explicitly 
 forbidden. Although any token character may appear in a 
 product-version, this token should only be used for a version 
 identifier (i.e., successive versions of the same product should 
 only differ in the product-version portion of the product value).
4. HTTP Message
4.1 Message Types
 HTTP messages consist of requests from client to server and 
 responses from server to client.
 HTTP-message = Simple-Request ; HTTP/0.9 messages
 | Simple-Response
 | Full-Request ; HTTP/1.0 messages
 | Full-Response
 Full-Request and Full-Response use the generic message format of 
 RFC 822 [7] for transferring entities. Both messages may include 
 optional header fields (also known as "headers") and an entity 
 body. The entity body is separated from the headers by a null line 
 (i.e., a line with nothing preceding the CRLF).
 Full-Request = Request-Line ; Section 5.1
 *( General-Header ; Section 4.3
 | Request-Header ; Section 5.2
 | Entity-Header ) ; Section 7.1
 CRLF
 [ Entity-Body ] ; Section 7.2
 Full-Response = Status-Line ; Section 6.1
 *( General-Header ; Section 4.3
 | Response-Header ; Section 6.2
 | Entity-Header ) ; Section 7.1
 CRLF
 [ Entity-Body ] ; Section 7.2
 Simple-Request and Simple-Response do not allow the use of any 
 header information and are limited to a single request method (GET).
 Simple-Request = "GET" SP Request-URI CRLF
 Simple-Response = [ Entity-Body ]
 Use of the Simple-Request format is discouraged because it prevents 
 the server from identifying the media type of the returned entity.
4.2 Message Headers
 HTTP header fields, which include General-Header (Section 4.3), 
 Request-Header (Section 5.2), Response-Header (Section 6.2), and 
 Entity-Header (Section 7.1) fields, follow the same generic format 
 as that given in Section 3.1 of RFC 822 [7]. Each header field 
 consists of a name followed immediately by a colon (":"), a single 
 space (SP) character, and the field value. Field names are 
 case-insensitive. Header fields can be extended over multiple lines 
 by preceding each extra line with at least one SP or HT, though 
 this is not recommended.
 HTTP-header = field-name ":" [ field-value ] CRLF
 field-name = token
 field-value = *( field-content | LWS )
 field-content = <the OCTETs making up the field-value
 and consisting of either *TEXT or combinations
 of token, tspecials, and quoted-string>
 The order in which header fields are received is not significant. 
 However, it is "good practice" to send General-Header fields first, 
 followed by Request-Header or Response-Header fields prior to the 
 Entity-Header fields.
 Multiple HTTP-header fields with the same field-name may be present 
 in a message if and only if the entire field-value for that header 
 field is defined as a comma-separated list [i.e., #(values)]. It 
 must be possible to combine the multiple header fields into one 
 "field-name: field-value" pair, without changing the semantics of 
 the message, by appending each subsequent field-value to the first, 
 each separated by a comma.
4.3 General Header Fields
 There are a few header fields which have general applicability for 
 both request and response messages, but which do not apply to the 
 entity being transferred. These headers apply only to the message 
 being transmitted.
 General-Header = Date ; Section 10.6
 | MIME-Version ; Section 10.12
 | Pragma ; Section 10.13
 General header field names can be extended reliably only in 
 combination with a change in the protocol version. However, new or 
 experimental header fields may be given the semantics of general 
 header fields if all parties in the communication recognize them to 
 be general header fields. Unknown header fields are treated as 
 Entity-Header fields.
5. Request
 A request message from a client to a server includes, within the 
 first line of that message, the method to be applied to the 
 resource, the identifier of the resource, and the protocol version 
 in use. For backwards compatibility with the more limited HTTP/0.9 
 protocol, there are two valid formats for an HTTP request:
 Request = Simple-Request | Full-Request
 Simple-Request = "GET" SP Request-URI CRLF
 Full-Request = Request-Line ; Section 5.1
 *( General-Header ; Section 4.3
 | Request-Header ; Section 5.2
 | Entity-Header ) ; Section 7.1
 CRLF
 [ Entity-Body ] ; Section 7.2
 If an HTTP/1.0 server receives a Simple-Request, it must respond 
 with an HTTP/0.9 Simple-Response. An HTTP/1.0 client capable of 
 receiving a Full-Response should never generate a Simple-Request.
5.1 Request-Line
 The Request-Line begins with a method token, followed by the 
 Request-URI and the protocol version, and ending with CRLF. The 
 elements are separated by SP characters. No CR or LF are allowed 
 except in the final CRLF sequence.
 Request-Line = Method SP Request-URI SP HTTP-Version CRLF
 Note that the difference between a Simple-Request and the 
 Request-Line of a Full-Request is the presence of the HTTP-Version 
 field and the availability of methods other than GET.
5.1.1 Method
 The Method token indicates the method to be performed on the 
 resource identified by the Request-URI. The method is 
 case-sensitive.
 Method = "GET" ; Section 8.1
 | "HEAD" ; Section 8.2
 | "POST" ; Section 8.3
 | extension-method
 extension-method = token
 The list of methods acceptable by a specific resource can change 
 dynamically; the client is notified through the return code of the 
 response if a method is not allowed on a resource. Servers should 
 return the status code 501 (not implemented) if the method is 
 unknown or not implemented.
 The methods commonly used by HTTP/1.0 applications are fully 
 defined in Section 8.
5.1.2 Request-URI
 The Request-URI is a Uniform Resource Identifier (Section 3.2) and 
 identifies the resource upon which to apply the request.
 Request-URI = absoluteURI | abs_path
 The two options for Request-URI are dependent on the nature of the 
 request.
 The absoluteURI form is only allowed when the request is being made 
 to a proxy. The proxy is requested to forward the request and 
 return the response. If the request is GET or HEAD and a prior 
 response is cached, the proxy may use the cached message if it 
 passes any restrictions in the Expires header field. Note that the 
 proxy may forward the request on to another proxy or directly to 
 the server specified by the absoluteURI. In order to avoid request 
 loops, a proxy must be able to recognize all of its server names, 
 including any aliases, local variations, and the numeric IP 
 address. An example Request-Line would be:
 GET http://www.w3.org/hypertext/WWW/TheProject.html HTTP/1.0
 The most common form of Request-URI is that used to identify a 
 resource on an origin server or gateway. In this case, only the 
 absolute path of the URI is transmitted (see Section 3.2.1, 
 abs_path). For example, a client wishing to retrieve the resource 
 above directly from the origin server would create a TCP connection 
 to port 80 of the host "www.w3.org" and send the line:
 GET /hypertext/WWW/TheProject.html HTTP/1.0
 followed by the remainder of the Full-Request. Note that the 
 absolute path cannot be empty; if none is present in the original 
 URI, it must be given as "/" (the server root).
 The Request-URI is transmitted as an encoded string, where some 
 characters may be escaped using the "% hex hex" encoding defined by 
 RFC 1738 [4]. The origin server must decode the Request-URI in 
 order to properly interpret the request.
5.2 Request Header Fields
 The request header fields allow the client to pass additional 
 information about the request, and about the client itself, to the 
 server. All header fields are optional and conform to the generic 
 HTTP-header syntax.
 Request-Header = Authorization ; Section 10.2
 | From ; Section 10.8
 | If-Modified-Since ; Section 10.9
 | Referer ; Section 10.14
 | User-Agent ; Section 10.16
 Request-Header field names can be extended reliably only in 
 combination with a change in the protocol version. However, new or 
 experimental header fields may be given the semantics of request 
 header fields if all parties in the communication recognize them to 
 be request header fields. Unknown header fields are treated as 
 Entity-Header fields.
6. Response
 After receiving and interpreting a request message, a server 
 responds in the form of an HTTP response message.
 Response = Simple-Response | Full-Response
 Simple-Response = [ Entity-Body ]
 Full-Response = Status-Line ; Section 6.1
 *( General-Header ; Section 4.3
 | Response-Header ; Section 6.2
 | Entity-Header ) ; Section 7.1
 CRLF
 [ Entity-Body ] ; Section 7.2
 A Simple-Response should only be sent in response to an HTTP/0.9 
 Simple-Request or if the server only supports the more limited 
 HTTP/0.9 protocol. If a client sends an HTTP/1.0 Full-Request and 
 receives a response that does not begin with a Status-Line, it 
 should assume that the response is a Simple-Response and parse it 
 accordingly. Note that the Simple-Response consists only of the 
 entity body and is terminated by the server closing the connection.
6.1 Status-Line
 The first line of a Full-Response message is the Status-Line, 
 consisting of the protocol version followed by a numeric status 
 code and its associated textual phrase, with each element separated 
 by SP characters. No CR or LF is allowed except in the final CRLF 
 sequence.
 Status-Line = HTTP-Version SP Status-Code SP Reason-Phrase CRLF
 Since a status line always begins with the protocol version and 
 status code
 "HTTP/" 1*DIGIT "." 1*DIGIT SP 3DIGIT SP
 (e.g., "HTTP/1.0 200 "), the presence of that expression is 
 sufficient to differentiate a Full-Response from a Simple-Response. 
 Although the Simple-Response format may allow such an expression to 
 occur at the beginning of an entity body, and thus cause a 
 misinterpretation of the message if it was given in response to a 
 Full-Request, most HTTP/0.9 servers are limited to responses of 
 type "text/html" and therefore would never generate such a response.
6.1.1 Status Code and Reason Phrase
 The Status-Code element is a 3-digit integer result code of the 
 attempt to understand and satisfy the request. The Reason-Phrase is 
 intended to give a short textual description of the Status-Code. 
 The Status-Code is intended for use by automata and the 
 Reason-Phrase is intended for the human user. The client is not 
 required to examine or display the Reason-Phrase.
 The first digit of the Status-Code defines the class of response. 
 The last two digits do not have any categorization role. There are 
 5 values for the first digit:
 o 1xx: Informational - Not used, but reserved for future use
 o 2xx: Success - The action was successfully received, 
 understood, and accepted.
 o 3xx: Redirection - Further action must be taken in order to 
 complete the request
 o 4xx: Client Error - The request contains bad syntax or cannot 
 be fulfilled
 o 5xx: Server Error - The server failed to fulfill an apparently 
 valid request
 The individual values of the numeric status codes defined for 
 HTTP/1.0, and an example set of corresponding Reason-Phrase's, are 
 presented below. The reason phrases listed here are only 
 recommended -- they may be replaced by local equivalents without 
 affecting the protocol. These codes are fully defined in Section 9.
 Status-Code = "200" ; OK
 | "201" ; Created
 | "202" ; Accepted
 | "204" ; No Content
 | "301" ; Moved Permanently
 | "302" ; Moved Temporarily
 | "304" ; Not Modified
 | "400" ; Bad Request
 | "401" ; Unauthorized
 | "403" ; Forbidden
 | "404" ; Not Found
 | "500" ; Internal Server Error
 | "501" ; Not Implemented
 | "502" ; Bad Gateway
 | "503" ; Service Unavailable
 | extension-code
 extension-code = 3DIGIT
 Reason-Phrase = *<TEXT, excluding CR, LF>
 HTTP status codes are extensible, but the above codes are the only 
 ones generally recognized in current practice. HTTP applications 
 are not required to understand the meaning of all registered status 
 codes, though such understanding is obviously desirable. However, 
 applications must understand the class of any status code, as 
 indicated by the first digit, and treat any unknown response as 
 being equivalent to the x00 status code of that class. For example, 
 if an unknown status code of 421 is received by the client, it can 
 safely assume that there was something wrong with its request and 
 treat the response as if it had received a 400 status code. In such 
 cases, user agents should present to the user the entity returned 
 with the response, since that entity is likely to include 
 human-readable information which will explain the unusual status.
6.2 Response Header Fields
 The response header fields allow the server to pass additional 
 information about the response which cannot be placed in the 
 Status-Line. These header fields are not intended to give 
 information about an Entity-Body returned in the response, but 
 about the server itself.
 Response-Header = Location ; Section 10.11
 | Server ; Section 10.15
 | WWW-Authenticate ; Section 10.17
 Response-Header field names can be extended reliably only in 
 combination with a change in the protocol version. However, new or 
 experimental header fields may be given the semantics of response 
 header fields if all parties in the communication recognize them to 
 be response header fields. Unknown header fields are treated as 
 Entity-Header fields.
7. Entity
 Full-Request and Full-Response messages may transfer an entity 
 within some requests and responses. An entity consists of 
 Entity-Header fields and (usually) an Entity-Body. In this section, 
 both sender and recipient refer to either the client or the server, 
 depending on who sends and who receives the entity.
7.1 Entity Header Fields
 Entity-Header fields define optional metainformation about the 
 Entity-Body or, if no body is present, about the resource 
 identified by the request.
 Entity-Header = Allow ; Section 10.1
 | Content-Encoding ; Section 10.3
 | Content-Length ; Section 10.4
 | Content-Type ; Section 10.5
 | Expires ; Section 10.7
 | Last-Modified ; Section 10.10
 | extension-header
 extension-header = HTTP-header
 The extension-header mechanism allows additional Entity-Header 
 fields to be defined without changing the protocol, but these 
 fields cannot be assumed to be recognizable by the recipient. 
 Unknown header fields should be ignored by the recipient and 
 forwarded by proxies.
7.2 Entity Body
 The entity body (if any) sent with an HTTP/1.0 request or response 
 is in a format and encoding defined by the Entity-Header fields.
 Entity-Body = *OCTET
 An entity body is included with a request message only when the 
 request method calls for one. The presence of an entity body in a 
 request is signaled by the inclusion of a Content-Length header 
 field in the request message headers. HTTP/1.0 requests containing 
 an entity body must include a valid Content-Length header field.
 For response messages, whether or not an entity body is included 
 with a message is dependent on both the request method and the 
 response code. All responses to the HEAD request method must not 
 include a body, even though the presence of entity header fields 
 may lead one to believe they do. All 1xx (informational), 204 (no 
 content), and 304 (not modified) responses must not include a body. 
 All other responses must include an entity body or a Content-Length 
 header field defined with a value of zero (0).
7.2.1 Type
 When an Entity-Body is included with a message, the data type of 
 that body is determined via the header fields Content-Type and 
 Content-Encoding. These define a two-layer, ordered encoding model:
 entity-body := Content-Encoding( Content-Type( data ) )
 A Content-Type specifies the media type of the underlying data. A 
 Content-Encoding may be used to indicate any additional content 
 coding applied to the type, usually for the purpose of data 
 compression, that is a property of the resource requested. The 
 default for the content encoding is none (i.e., the identity 
 function).
 Any HTTP/1.0 message containing an entity body should include a 
 Content-Type header field defining the media type of that body. If 
 and only if the media type is not given by a Content-Type header, 
 as is the case for Simple-Response messages, the recipient may 
 attempt to guess the media type via inspection of its content 
 and/or the name extension(s) of the URL used to identify the 
 resource. If the media type remains unknown, the recipient should 
 treat it as type "application/octet-stream".
7.2.2 Length
 When an Entity-Body is included with a message, the length of that 
 body may be determined in one of two ways. If a Content-Length 
 header field is present, its value in bytes represents the length 
 of the Entity-Body. Otherwise, the body length is determined by the 
 closing of the connection by the server.
 Closing the connection cannot be used to indicate the end of a 
 request body, since it leaves no possibility for the server to send 
 back a response. Therefore, HTTP/1.0 requests containing an entity 
 body must include a valid Content-Length header field. If a request 
 contains an entity body and Content-Length is not specified, and 
 the server does not recognize or cannot calculate the length from 
 other fields, then the server should send a 400 (bad request) 
 response.
 Note: Some older servers supply an invalid Content-Length 
 when sending a document that contains server-side includes 
 dynamically inserted into the data stream. It must be 
 emphasized that this will not be tolerated by future 
 versions of HTTP. Unless the client knows that it is 
 receiving a response from a compliant server, it should not 
 depend on the Content-Length value being correct.
8. Method Definitions
 The set of common methods for HTTP/1.0 is defined below. Although 
 this set can be expanded, additional methods cannot be assumed to 
 share the same semantics for separately extended clients and 
 servers.
8.1 GET
 The GET method means retrieve whatever information (in the form of 
 an entity) is identified by the Request-URI. If the Request-URI 
 refers to a data-producing process, it is the produced data which 
 shall be returned as the entity in the response and not the source 
 text of the process, unless that text happens to be the output of 
 the process.
 The semantics of the GET method changes to a "conditional GET" if 
 the request message includes an If-Modified-Since header field. A 
 conditional GET method requests that the identified resource be 
 transferred only if it has been modified since the date given by 
 the If-Modified-Since header, as described in Section 10.9. The 
 conditional GET method is intended to reduce network usage by 
 allowing cached entities to be refreshed without requiring multiple 
 requests or transferring unnecessary data.
8.2 HEAD
 The HEAD method is identical to GET except that the server must not 
 return any Entity-Body in the response. The metainformation 
 contained in the HTTP headers in response to a HEAD request should 
 be identical to the information sent in response to a GET request. 
 This method can be used for obtaining metainformation about the 
 resource identified by the Request-URI without transferring the 
 Entity-Body itself. This method is often used for testing hypertext 
 links for validity, accessibility, and recent modification.
 There is no "conditional HEAD" request analogous to the conditional 
 GET. If an If-Modified-Since header field is included with a HEAD 
 request, it should be ignored.
8.3 POST
 The POST method is used to request that the destination server 
 accept the entity enclosed in the request as a new subordinate of 
 the resource identified by the Request-URI in the Request-Line. 
 POST is designed to allow a uniform method to cover the following 
 functions:
 o Annotation of existing resources; 
 o Posting a message to a bulletin board, newsgroup, mailing list, 
 or similar group of articles;
 o Providing a block of data, such as the result of submitting a 
 form [3], to a data-handling process;
 o Extending a database through an append operation.
 The actual function performed by the POST method is determined by 
 the server and is usually dependent on the Request-URI. The posted 
 entity is subordinate to that URI in the same way that a file is 
 subordinate to a directory containing it, a news article is 
 subordinate to a newsgroup to which it is posted, or a record is 
 subordinate to a database.
 A successful POST does not require that the entity be created as a 
 resource on the origin server or made accessible for future 
 reference. That is, the action performed by the POST method might 
 not result in a resource that can be identified by a URI. In this 
 case, either 200 (ok) or 204 (no content) is the appropriate 
 response status, depending on whether or not the response includes 
 an entity that describes the result.
 If a resource has been created on the origin server, the response 
 should be 201 (created) and contain an entity (preferably of type 
 "text/html") which describes the status of the request and refers 
 to the new resource.
 A valid Content-Length is required on all HTTP/1.0 POST requests. 
 An HTTP/1.0 server should respond with a 400 (bad request) message 
 if it cannot determine the length of the request message's content.
 Applications must not cache responses to a POST request.
9. Status Code Definitions
 Each Status-Code is described below, including a description of 
 which method(s) it can follow and any metainformation required in 
 the response.
9.1 Informational 1xx
 This class of status code indicates a provisional response, 
 consisting only of the Status-Line and optional headers, and is 
 terminated by an empty line. HTTP/1.0 does not define any 1xx 
 status codes and they are not a valid response to a HTTP/1.0 
 request. However, they may be useful for experimental applications 
 which are outside the scope of this specification.
9.2 Successful 2xx
 This class of status code indicates that the client's request was 
 successfully received, understood, and accepted.
 200 OK
 The request has succeeded. The information returned with the 
 response is dependent on the method used in the request, as follows:
 GET an entity corresponding to the requested resource is sent 
 in the response;
 HEAD the response must only contain the header information and 
 no Entity-Body;
 POST an entity describing or containing the result of the action.
 201 Created
 The request has been fulfilled and resulted in a new resource being 
 created. The newly created resource can be referenced by the URI(s) 
 returned in the entity of the response. The origin server should 
 create the resource before using this Status-Code. If the action 
 cannot be carried out immediately, the server must include in the 
 response body a description of when the resource will be available; 
 otherwise, the server should respond with 202 (accepted).
 Of the methods defined by this specification, only POST can create 
 a resource.
 202 Accepted
 The request has been accepted for processing, but the processing 
 has not been completed. The request may or may not eventually be 
 acted upon, as it may be disallowed when processing actually takes 
 place. There is no facility for re-sending a status code from an 
 asynchronous operation such as this.
 The 202 response is intentionally non-committal. Its purpose is to 
 allow a server to accept a request for some other process (perhaps 
 a batch-oriented process that is only run once per day) without 
 requiring that the user agent's connection to the server persist 
 until the process is completed. The entity returned with this 
 response should include an indication of the request's current 
 status and either a pointer to a status monitor or some estimate of 
 when the user can expect the request to be fulfilled.
 204 No Content
 The server has fulfilled the request but there is no new 
 information to send back. If the client is a user agent, it should 
 not change its document view from that which caused the request to 
 be generated. This response is primarily intended to allow input 
 for scripts or other actions to take place without causing a change 
 to the user agent's active document view. The response may include 
 new metainformation in the form of entity headers, which should 
 apply to the document currently in the user agent's active view.
9.3 Redirection 3xx
 This class of status code indicates that further action needs to be 
 taken by the user agent in order to fulfill the request. The action 
 required can sometimes be carried out by the user agent without 
 interaction with the user, but it is strongly recommended that this 
 only take place if the method used in the request is GET or HEAD. A 
 user agent should never automatically redirect a request more than 
 5 times, since such redirections usually indicate an infinite loop.
 300 Multiple Choices
 This response code is not directly used by HTTP/1.0 applications, 
 but serves as the default for interpreting the 3xx class of 
 responses.
 The requested resource is available at one or more locations. 
 Unless it was a HEAD request, the response should include an entity 
 containing a list of resource characteristics and locations from 
 which the user or user agent can choose the one most appropriate. 
 If the server has a preferred choice, it should include the URL in 
 a Location field; user agents may use this field value for 
 automatic redirection.
 301 Moved Permanently
 The requested resource has been assigned a new permanent URL and 
 any future references to this resource should be done using that 
 URL. Clients with link editing capabilities should automatically 
 relink references to the Request-URI to the new reference returned 
 by the server, where possible.
 The new URL must be given by the Location field in the response. 
 Unless it was a HEAD request, the Entity-Body of the response 
 should contain a short note with a hyperlink to the new URL.
 If the 301 status code is received in response to a request using 
 the POST method, the user agent must not automatically redirect the 
 request unless it can be confirmed by the user, since this might 
 change the conditions under which the request was issued.
 302 Moved Temporarily
 The requested resource resides temporarily under a different URL. 
 Since the redirection may be altered on occasion, the client should 
 continue to use the Request-URI for future requests.
 The URL must be given by the Location field in the response. Unless 
 it was a HEAD request, the Entity-Body of the response should 
 contain a short note with a hyperlink to the new URI(s).
 If the 302 status code is received in response to a request using 
 the POST method, the user agent must not automatically redirect the 
 request unless it can be confirmed by the user, since this might 
 change the conditions under which the request was issued.
 304 Not Modified
 If the client has performed a conditional GET request and access is 
 allowed, but the document has not been modified since the date and 
 time specified in the If-Modified-Since field, the server must 
 respond with this status code and not send an Entity-Body to the 
 client. Header fields contained in the response should only include 
 information which is relevant to cache managers or which may have 
 changed independently of the entity's Last-Modified date. Examples 
 of relevant header fields include: Date, Server, and Expires. A 
 cache should update its cached entity to reflect any new field 
 values given in the 304 response.
9.4 Client Error 4xx
 The 4xx class of status code is intended for cases in which the 
 client seems to have erred. If the client has not completed the 
 request when a 4xx code is received, it should immediately cease 
 sending data to the server. Except when responding to a HEAD 
 request, the server should include an entity containing an 
 explanation of the error situation, and whether it is a temporary 
 or permanent condition. These status codes are applicable to any 
 request method.
 Note: If the client is sending data, server implementations 
 on TCP should be careful to ensure that the client 
 acknowledges receipt of the packet(s) containing the 
 response prior to closing the input connection. If the 
 client continues sending data to the server after the close, 
 the server's controller will send a reset packet to the 
 client, which may erase the client's unacknowledged input 
 buffers before they can be read and interpreted by the HTTP 
 application.
 400 Bad Request
 The request could not be understood by the server due to malformed 
 syntax. The client should not repeat the request without 
 modifications.
 401 Unauthorized
 The request requires user authentication. The response must include 
 a WWW-Authenticate header field (Section 10.17) containing a 
 challenge applicable to the requested resource. The client may 
 repeat the request with a suitable Authorization header field 
 (Section 10.2). If the request already included Authorization 
 credentials, then the 401 response indicates that authorization has 
 been refused for those credentials. If the 401 response contains 
 the same challenge as the prior response, and the user agent has 
 already attempted authentication at least once, then the user 
 should be presented the entity that was given in the response, 
 since that entity may include relevent diagnostic information. HTTP 
 access authentication is explained in Section 11.
 403 Forbidden
 The server understood the request, but is refusing to fulfill it. 
 Authorization will not help and the request should not be repeated. 
 If the request method was not HEAD and the server wishes to make 
 public why the request has not been fulfilled, it should describe 
 the reason for the refusal in the entity body. This status code is 
 commonly used when the server does not wish to reveal exactly why 
 the request has been refused, or when no other response is 
 applicable.
 404 Not Found
 The server has not found anything matching the Request-URI. No 
 indication is given of whether the condition is temporary or 
 permanent. If the server does not wish to make this information 
 available to the client, the status code 403 (forbidden) can be 
 used instead.
9.5 Server Error 5xx
 Response status codes beginning with the digit "5" indicate cases 
 in which the server is aware that it has erred or is incapable of 
 performing the request. If the client has not completed the request 
 when a 5xx code is received, it should immediately cease sending 
 data to the server. Except when responding to a HEAD request, the 
 server should include an entity containing an explanation of the 
 error situation, and whether it is a temporary or permanent 
 condition. These response codes are applicable to any request 
 method and there are no required header fields.
 500 Internal Server Error
 The server encountered an unexpected condition which prevented it 
 from fulfilling the request. 
 501 Not Implemented
 The server does not support the functionality required to fulfill 
 the request. This is the appropriate response when the server does 
 not recognize the request method and is not capable of supporting 
 it for any resource.
 502 Bad Gateway
 The server, while acting as a gateway or proxy, received an invalid 
 response from the upstream server it accessed in attempting to 
 fulfill the request.
 503 Service Unavailable
 The server is currently unable to handle the request due to a 
 temporary overloading or maintenance of the server. The implication 
 is that this is a temporary condition which will be alleviated 
 after some delay.
 Note: The existence of the 503 status code does not imply 
 that a server must use it when becoming overloaded. Some 
 servers may wish to simply refuse the connection.
10. Header Field Definitions
 This section defines the syntax and semantics of all commonly used 
 HTTP/1.0 header fields. For general and entity header fields, both 
 sender and recipient refer to either the client or the server, 
 depending on who sends and who receives the message.
10.1 Allow
 The Allow entity-header field lists the set of methods supported by 
 the resource identified by the Request-URI. The purpose of this 
 field is strictly to inform the recipient of valid methods 
 associated with the resource. The Allow header field is not 
 permitted in a request using the POST method, and thus should be 
 ignored if it is received as part of a POST entity.
 Allow = "Allow" ":" 1#method
 Example of use:
 Allow: GET, HEAD
 This field cannot prevent a client from trying other methods. 
 However, the indications given by the Allow header field value 
 should be followed. The actual set of allowed methods is defined by 
 the origin server at the time of each request.
 A proxy must not modify the Allow header field even if it does not 
 understand all the methods specified, since the user agent may have 
 other means of communicating with the origin server.
 The Allow header field does not indicate what methods are 
 implemented by the server.
10.2 Authorization
 A user agent that wishes to authenticate itself with a 
 server--usually, but not necessarily, after receiving a 401 
 response--may do so by including an Authorization request-header 
 field with the request. The Authorization field value consists of 
 credentials containing the authentication information of the user 
 agent for the realm of the resource being requested.
 Authorization = "Authorization" ":" credentials
 HTTP access authentication is described in Section 11. If a request 
 is authenticated and a realm specified, the same credentials should 
 be valid for all other requests within this realm.
 Responses to requests containing an Authorization field are not 
 cachable.
10.3 Content-Encoding
 The Content-Encoding entity-header field is used as a modifier to 
 the media-type. When present, its value indicates what additional 
 content coding has been applied to the resource, and thus what 
 decoding mechanism must be applied in order to obtain the 
 media-type referenced by the Content-Type header field. The 
 Content-Encoding is primarily used to allow a document to be 
 compressed without losing the identity of its underlying media type.
 Content-Encoding = "Content-Encoding" ":" content-coding
 Content codings are defined in Section 3.5. An example of its use is
 Content-Encoding: x-gzip
 The Content-Encoding is a characteristic of the resource identified 
 by the Request-URI. Typically, the resource is stored with this 
 encoding and is only decoded before rendering or analogous usage.
10.4 Content-Length
 The Content-Length entity-header field indicates the size of the 
 Entity-Body, in decimal number of octets, sent to the recipient or, 
 in the case of the HEAD method, the size of the Entity-Body that 
 would have been sent had the request been a GET.
 Content-Length = "Content-Length" ":" 1*DIGIT
 An example is
 Content-Length: 3495
 Applications should use this field to indicate the size of the 
 Entity-Body to be transferred, regardless of the media type of the 
 entity. A valid Content-Length field value is required on all 
 HTTP/1.0 request messages containing an entity body.
 Any Content-Length greater than or equal to zero is a valid value. 
 Section 7.2.2 describes how to determine the length of a response 
 entity body if a Content-Length is not given.
 Note: The meaning of this field is significantly different 
 from the corresponding definition in MIME, where it is an 
 optional field used within the "message/external-body" 
 content-type. In HTTP, it should be used whenever the 
 entity's length can be determined prior to being transferred.
10.5 Content-Type
 The Content-Type entity-header field indicates the media type of 
 the Entity-Body sent to the recipient or, in the case of the HEAD 
 method, the media type that would have been sent had the request 
 been a GET.
 Content-Type = "Content-Type" ":" media-type
 Media types are defined in Section 3.6. An example of the field is
 Content-Type: text/html
 Further discussion of methods for identifying the media type of an 
 entity is provided in Section 7.2.1.
10.6 Date
 The Date general-header field represents the date and time at which 
 the message was originated, having the same semantics as orig-date 
 in RFC 822. The field value is an HTTP-date, as described in 
 Section 3.3.
 Date = "Date" ":" HTTP-date
 An example is
 Date: 1994年11月15日 08:12:31 GMT
 If a message is received via direct connection with the user agent 
 (in the case of requests) or the origin server (in the case of 
 responses), then the date can be assumed to be the current date at 
 the receiving end. However, since the date--as it is believed by the 
 origin--is important for evaluating cached responses, origin servers 
 should always include a Date header. Clients should only send a 
 Date header field in messages that include an entity body, as in 
 the case of the POST request, and even then it is optional. A 
 received message which does not have a Date header field should be 
 assigned one by the recipient if the message will be cached by that 
 recipient or gatewayed via a protocol which requires a Date.
 In theory, the date should represent the moment just before the 
 entity is generated. In practice, the date can be generated at any 
 time during the message origination without affecting its semantic 
 value.
 Note: An earlier version of this document incorrectly 
 specified that this field should contain the creation date 
 of the enclosed Entity-Body. This has been changed to 
 reflect actual (and proper) usage.
10.7 Expires
 The Expires entity-header field gives the date/time after which the 
 entity should be considered stale. This allows information 
 providers to suggest the volatility of the resource, or a date 
 after which the information may no longer be valid. Applications 
 must not cache this entity beyond the date given. The presence of 
 an Expires field does not imply that the original resource will 
 change or cease to exist at, before, or after that time. However, 
 information providers that know or even suspect that a resource 
 will change by a certain date should include an Expires header with 
 that date. The format is an absolute date and time as defined by 
 HTTP-date in Section 3.3.
 Expires = "Expires" ":" HTTP-date
 An example of its use is
 Expires: 1994年12月01日 16:00:00 GMT
 If the date given is equal to or earlier than the value of the Date 
 header, the recipient must not cache the enclosed entity. If a 
 resource is dynamic by nature, as is the case with many 
 data-producing processes, entities from that resource should be 
 given an appropriate Expires value which reflects that dynamism.
 The Expires field cannot be used to force a user agent to refresh 
 its display or reload a resource; its semantics apply only to 
 caching mechanisms, and such mechanisms need only check a 
 resource's expiration status when a new request for that resource 
 is initiated.
 User agents often have history mechanisms, such as "Back" buttons 
 and history lists, which can be used to redisplay an entity 
 retrieved earlier in a session. By default, the Expires field does 
 not apply to history mechanisms. If the entity is still in storage, 
 a history mechanism should display it even if the entity has 
 expired, unless the user has specifically configured the agent to 
 refresh expired history documents.
 Note: Applications are encouraged to be tolerant of bad or 
 misinformed implementations of the Expires header. A value 
 of zero (0) or an invalid date format should be considered 
 equivalent to an "expires immediately." Although these 
 values are not legitimate for HTTP/1.0, a robust 
 implementation is always desirable.
10.8 From
 The From request-header field, if given, should contain an Internet 
 e-mail address for the human user who controls the requesting user 
 agent. The address should be machine-usable, as defined by mailbox 
 in RFC 822 [7] (as updated by RFC 1123 [6]):
 From = "From" ":" mailbox
 An example is:
 From: webmaster@w3.org
 This header field may be used for logging purposes and as a means 
 for identifying the source of invalid or unwanted requests. It 
 should not be used as an insecure form of access protection. The 
 interpretation of this field is that the request is being performed 
 on behalf of the person given, who accepts responsibility for the 
 method performed. In particular, robot agents should include this 
 header so that the person responsible for running the robot can be 
 contacted if problems occur on the receiving end.
 The Internet e-mail address in this field may be separate from the 
 Internet host which issued the request. For example, when a request 
 is passed through a proxy, the original issuer's address should be 
 used.
 Note: The client should not send the From header field 
 without the user's approval, as it may conflict with the 
 user's privacy interests or their site's security policy. It 
 is strongly recommended that the user be able to disable, 
 enable, and modify the value of this field at any time prior 
 to a request.
10.9 If-Modified-Since
 The If-Modified-Since request-header field is used with the GET 
 method to make it conditional: if the requested resource has not 
 been modified since the time specified in this field, a copy of the 
 resource will not be returned from the server; instead, a 304 (not 
 modified) response will be returned without any Entity-Body.
 If-Modified-Since = "If-Modified-Since" ":" HTTP-date
 An example of the field is:
 If-Modified-Since: 1994年10月29日 19:43:31 GMT
 A conditional GET method requests that the identified resource be 
 transferred only if it has been modified since the date given by 
 the If-Modified-Since header. The algorithm for determining this 
 includes the following cases:
 a) If the request would normally result in anything other than 
 a 200 (ok) status, or if the passed If-Modified-Since date 
 is invalid, the response is exactly the same as for a 
 normal GET. A date which is later than the server's current 
 time is invalid.
 b) If the resource has been modified since the 
 If-Modified-Since date, the response is exactly the same as 
 for a normal GET.
 c) If the resource has not been modified since a valid 
 If-Modified-Since date, the server shall return a 304 (not 
 modified) response.
 The purpose of this feature is to allow efficient updates of cached 
 information with a minimum amount of transaction overhead.
10.10 Last-Modified
 The Last-Modified entity-header field indicates the date and time 
 at which the sender believes the resource was last modified. The 
 exact semantics of this field are defined in terms of how the 
 recipient should interpret it: if the recipient has a copy of this 
 resource which is older than the date given by the Last-Modified 
 field, that copy should be considered stale.
 Last-Modified = "Last-Modified" ":" HTTP-date
 An example of its use is
 Last-Modified: 1994年11月15日 12:45:26 GMT
 The exact meaning of this header field depends on the 
 implementation of the sender and the nature of the original 
 resource. For files, it may be just the file system last-modified 
 time. For entities with dynamically included parts, it may be the 
 most recent of the set of last-modify times for its component 
 parts. For database gateways, it may be the last-update timestamp 
 of the record. For virtual objects, it may be the last time the 
 internal state changed.
 An origin server must not send a Last-Modified date which is later 
 than the server's time of message origination. In such cases, where 
 the resource's last modification would indicate some time in the 
 future, the server must replace that date with the message 
 origination date.
10.11 Location
 The Location response-header field defines the exact location of 
 the resource that was identified by the Request-URI. For 3xx 
 responses, the location must indicate the server's preferred URL 
 for automatic redirection to the resource. Only one absolute URL is 
 allowed.
 Location = "Location" ":" absoluteURI
 An example is
 Location: http://www.w3.org/hypertext/WWW/NewLocation.html
10.12 MIME-Version
 HTTP is not a MIME-compliant protocol (see Appendix C). However, 
 HTTP/1.0 messages may include a single MIME-Version general-header 
 field to indicate what version of the MIME protocol was used to 
 construct the message. Use of the MIME-Version header field should 
 indicate that the message is in full compliance with the MIME 
 protocol (as defined in [5]). Unfortunately, some older versions of 
 HTTP/1.0 clients and servers use this field indiscriminately, and 
 thus recipients must not take it for granted that the message is 
 indeed in full compliance with MIME. Proxies and gateways are 
 responsible for ensuring this compliance (where possible) when 
 exporting HTTP messages to strict MIME environments. Future 
 HTTP/1.0 applications must only use MIME-Version when the message 
 is fully MIME-compliant.
 MIME-Version = "MIME-Version" ":" 1*DIGIT "." 1*DIGIT
 MIME version "1.0" is the default for use in HTTP/1.0. However, 
 HTTP/1.0 message parsing and semantics are defined by this document 
 and not the MIME specification.
10.13 Pragma
 The Pragma general-header field is used to include 
 implementation-specific directives that may apply to any recipient 
 along the request/response chain. All pragma directives specify 
 optional behavior from the viewpoint of the protocol; however, some 
 systems may require that behavior be consistent with the directives.
 Pragma = "Pragma" ":" 1#pragma-directive
 pragma-directive = "no-cache" | extension-pragma
 extension-pragma = token [ "=" word ]
 When the "no-cache" directive is present in a request message, an 
 application should forward the request toward the origin server 
 even if it has a cached copy of what is being requested. This 
 allows a client to insist upon receiving an authoritative response 
 to its request. It also allows a client to refresh a cached copy 
 which is known to be corrupted or stale.
 Pragma directives must be passed through by a proxy or gateway 
 application, regardless of their significance to that application, 
 since the directives may be applicable to all recipients along the 
 request/response chain. It is not possible to specify a pragma for 
 a specific recipient; however, any pragma directive not relevant to 
 a recipient should be ignored by that recipient.
10.14 Referer
 The Referer request-header field allows the client to specify, for 
 the server's benefit, the address (URI) of the resource from which 
 the Request-URI was obtained. This allows a server to generate 
 lists of back-links to resources for interest, logging, optimized 
 caching, etc. It also allows obsolete or mistyped links to be 
 traced for maintenance. The Referer field must not be sent if the 
 Request-URI was obtained from a source that does not have its own 
 URI, such as input from the user keyboard.
 Referer = "Referer" ":" ( absoluteURI | relativeURI )
 Example:
 Referer: http://www.w3.org/hypertext/DataSources/Overview.html
 If a partial URI is given, it should be interpreted relative to the 
 Request-URI. The URI must not include a fragment.
 Note: Because the source of a link may be private 
 information or may reveal an otherwise private information 
 source, it is strongly recommended that the user be able to 
 select whether or not the Referer field is sent. For 
 example, a browser client could have a toggle switch for 
 browsing openly/anonymously, which would respectively 
 enable/disable the sending of Referer and From information.
10.15 Server
 The Server response-header field contains information about the 
 software used by the origin server to handle the request. The field 
 can contain multiple product tokens (Section 3.7) and comments 
 identifying the server and any significant subproducts. By 
 convention, the product tokens are listed in order of their 
 significance for identifying the application.
 Server = "Server" ":" 1*( product | comment )
 Example:
 Server: CERN/3.0 libwww/2.17
 If the response is being forwarded through a proxy, the proxy 
 application must not add its data to the product list.
 Note: Revealing the specific software version of the server 
 may allow the server machine to become more vulnerable to 
 attacks against software that is known to contain security 
 holes. Server implementors are encouraged to make this field 
 a configurable option.
10.16 User-Agent
 The User-Agent request-header field contains information about the 
 user agent originating the request. This is for statistical 
 purposes, the tracing of protocol violations, and automated 
 recognition of user agents for the sake of tailoring responses to 
 avoid particular user agent limitations. Although it is not 
 required, user agents should include this field with requests. The 
 field can contain multiple product tokens (Section 3.7) and 
 comments identifying the agent and any subproducts which form a 
 significant part of the user agent. By convention, the product 
 tokens are listed in order of their significance for identifying 
 the application.
 User-Agent = "User-Agent" ":" 1*( product | comment )
 Example:
 User-Agent: CERN-LineMode/2.15 libwww/2.17b3
 Note: Some current proxy applications append their product 
 information to the list in the User-Agent field. This is not 
 recommended, since it makes machine interpretation of these 
 fields ambiguous.
10.17 WWW-Authenticate
 The WWW-Authenticate response-header field must be included in 401 
 (unauthorized) response messages. The field value consists of at 
 least one challenge that indicates the authentication scheme(s) and 
 parameters applicable to the Request-URI.
 WWW-Authenticate = "WWW-Authenticate" ":" 1#challenge
 The HTTP access authentication process is described in Section 11. 
 User agents must take special care in parsing the WWW-Authenticate 
 field value if it contains more than one challenge, or if more than 
 one WWW-Authenticate header field is provided, since the contents 
 of a challenge may itself contain a comma-separated list of 
 authentication parameters.
11. Access Authentication
 HTTP provides a simple challenge-response authentication mechanism 
 which may be used by a server to challenge a client request and by 
 a client to provide authentication information. It uses an 
 extensible, case-insensitive token to identify the authentication 
 scheme, followed by a comma-separated list of attribute-value pairs 
 which carry the parameters necessary for achieving authentication 
 via that scheme.
 auth-scheme = token
 auth-param = token "=" quoted-string
 The 401 (unauthorized) response message is used by an origin server 
 to challenge the authorization of a user agent. This response must 
 include a WWW-Authenticate header field containing at least one 
 challenge applicable to the requested resource.
 challenge = auth-scheme 1*SP realm *( "," auth-param )
 realm = "realm" "=" realm-value
 realm-value = quoted-string
 The realm attribute (case-insensitive) is required for all 
 authentication schemes which issue a challenge. The realm value 
 (case-sensitive), in combination with the canonical root URL of the 
 server being accessed, defines the protection space. These realms 
 allow the protected resources on a server to be partitioned into a 
 set of protection spaces, each with its own authentication scheme 
 and/or authorization database. The realm value is a string, 
 generally assigned by the origin server, which may have additional 
 semantics specific to the authentication scheme.
 A user agent that wishes to authenticate itself with a 
 server--usually, but not necessarily, after receiving a 401 
 response--may do so by including an Authorization header field with 
 the request. The Authorization field value consists of credentials 
 containing the authentication information of the user agent for the 
 realm of the resource being requested.
 credentials = basic-credentials
 | ( auth-scheme #auth-param )
 The domain over which credentials can be automatically applied by a 
 user agent is determined by the protection space. If a prior 
 request has been authorized, the same credentials may be reused for 
 all other requests within that protection space for a period of 
 time determined by the authentication scheme, parameters, and/or 
 user preference. Unless otherwise defined by the authentication 
 scheme, a single protection space cannot extend outside the scope 
 of its server.
 If the server does not wish to accept the credentials sent with a 
 request, it should return a 403 (forbidden) response.
 The HTTP protocol does not restrict applications to this simple 
 challenge-response mechanism for access authentication. Additional 
 mechanisms may be used, such as encryption at the transport level 
 or via message encapsulation, and with additional header fields 
 specifying authentication information. However, these additional 
 mechanisms are not defined by this specification.
 Proxies must be completely transparent regarding user agent 
 authentication. That is, they must forward the WWW-Authenticate and 
 Authorization headers untouched, and must not cache the response to 
 a request containing Authorization. HTTP/1.0 does not provide a 
 means for a client to be authenticated with a proxy.
11.1 Basic Authentication Scheme
 The "basic" authentication scheme is based on the model that the 
 user agent must authenticate itself with a user-ID and a password 
 for each realm. The realm value should be considered an opaque 
 string which can only be compared for equality with other realms on 
 that server. The server will authorize the request only if it can 
 validate the user-ID and password for the protection space of the 
 Request-URI. There are no optional authentication parameters.
 Upon receipt of an unauthorized request for a URI within the 
 protection space, the server should respond with a challenge like 
 the following:
 WWW-Authenticate: Basic realm="WallyWorld"
 where "WallyWorld" is the string assigned by the server to identify 
 the protection space of the Request-URI.
 To receive authorization, the client sends the user-ID and 
 password, separated by a single colon (":") character, within a 
 base64 [5] encoded string in the credentials.
 basic-credentials = "Basic" SP basic-cookie
 basic-cookie = <base64 [5] encoding of userid-password,
 except not limited to 76 char/line>
 userid-password = [ token ] ":" *TEXT
 If the user agent wishes to send the user-ID "Aladdin" and password 
 "open sesame", it would use the following header field:
 Authorization: Basic QWxhZGRpbjpvcGVuIHNlc2FtZQ==
 The basic authentication scheme is a non-secure method of filtering 
 unauthorized access to resources on an HTTP server. It is based on 
 the assumption that the connection between the client and the 
 server can be regarded as a trusted carrier. As this is not 
 generally true on an open network, the basic authentication scheme 
 should be used accordingly. In spite of this, clients should 
 implement the scheme in order to communicate with servers that use 
 it.
12. Security Considerations
 This section is meant to inform application developers, information 
 providers, and users of the security limitations in HTTP/1.0 as 
 described by this document. The discussion does not include 
 definitive solutions to the problems revealed, though it does make 
 some suggestions for reducing security risks.
12.1 Authentication of Clients
 As mentioned in Section 11.1, the Basic authentication scheme is 
 not a secure method of user authentication, nor does it prevent the 
 Entity-Body from being transmitted in clear text across the 
 physical network used as the carrier. HTTP/1.0 does not prevent 
 additional authentication schemes and encryption mechanisms from 
 being employed to increase security.
12.2 Safe Methods
 The writers of client software should be aware that the software 
 represents the user in their interactions over the Internet, and 
 should be careful to allow the user to be aware of any actions they 
 may take which may have an unexpected significance to themselves or 
 others.
 In particular, the convention has been established that the GET and 
 HEAD methods should never have the significance of taking an action 
 other than retrieval. These methods should be considered "safe." 
 This allows user agents to represent other methods, such as POST, 
 in a special way, so that the user is made aware of the fact that a 
 possibly unsafe action is being requested.
 Naturally, it is not possible to ensure that the server does not 
 generate side-effects as a result of performing a GET request; in 
 fact, some dynamic resources consider that a feature. The important 
 distinction here is that the user did not request the side-effects, 
 so therefore cannot be held accountable for them.
12.3 Abuse of Server Log Information
 A server is in the position to save personal data about a user's 
 requests which may identify their reading patterns or subjects of 
 interest. This information is clearly confidential in nature and 
 its handling may be constrained by law in certain countries. People 
 using the HTTP protocol to provide data are responsible for 
 ensuring that such material is not distributed without the 
 permission of any individuals that are identifiable by the 
 published results.
12.4 Transfer of Sensitive Information
 Like any generic data transfer protocol, HTTP cannot regulate the 
 content of the data that is transferred, nor is there any a priori 
 method of determining the sensitivity of any particular piece of 
 information within the context of any given request. Therefore, 
 applications should supply as much control over this information as 
 possible to the provider of that information. Three header fields 
 are worth special mention in this context: Server, Referer and From.
 Revealing the specific software version of the server may allow the 
 server machine to become more vulnerable to attacks against 
 software that is known to contain security holes. Implementors 
 should make the Server header field a configurable option.
 The Referer field allows reading patterns to be studied and reverse 
 links drawn. Although it can be very useful, its power can be 
 abused if user details are not separated from the information 
 contained in the Referer. Even when the personal information has 
 been removed, the Referer field may indicate a private document's 
 URI whose publication would be inappropriate.
 The information sent in the From field might conflict with the 
 user's privacy interests or their site's security policy, and hence 
 it should not be transmitted without the user being able to 
 disable, enable, and modify the contents of the field. The user 
 must be able to set the contents of this field within a user 
 preference or application defaults configuration.
 We suggest, though do not require, that a convenient toggle 
 interface be provided for the user to enable or disable the sending 
 of From and Referer information.
13. Acknowledgments
 This specification makes heavy use of the augmented BNF and generic 
 constructs defined by David H. Crocker for RFC 822 [7]. Similarly, 
 it reuses many of the definitions provided by Nathaniel Borenstein 
 and Ned Freed for MIME [5]. We hope that their inclusion in this 
 specification will help reduce past confusion over the relationship 
 between HTTP/1.0 and Internet mail message formats.
 The HTTP protocol has evolved considerably over the past four 
 years. It has benefited from a large and active developer 
 community--the many people who have participated on the www-talk 
 mailing list--and it is that community which has been most 
 responsible for the success of HTTP and of the World-Wide Web in 
 general. Marc Andreessen, Robert Cailliau, Daniel W. Connolly,
 Bob Denny, Jean-Francois Groff, Phillip M. Hallam-Baker,
 Hakon W. Lie, Ari Luotonen, Rob McCool, Lou Montulli, Dave Raggett,
 Tony Sanders, and Marc VanHeyningen deserve special recognition for
 their efforts in defining aspects of the protocol for early versions
 of this specification.
 This document has benefited greatly from the comments of all those 
 participating in the HTTP-WG. In addition to those already 
 mentioned, the following individuals have contributed to this 
 specification:
 Gary Adams Harald Tveit Alvestrand
 Keith Ball Brian Behlendorf
 Paul Burchard Maurizio Codogno
 Mike Cowlishaw Roman Czyborra
 Michael A. Dolan John Franks
 Jim Gettys Marc Hedlund
 Koen Holtman Alex Hopmann
 Bob Jernigan Shel Kaphan
 Martijn Koster Dave Kristol
 Daniel LaLiberte Paul Leach
 Albert Lunde John C. Mallery
 Larry Masinter Mitra
 Gavin Nicol Bill Perry
 Jeffrey Perry Owen Rees
 David Robinson Marc Salomon
 Rich Salz Jim Seidman
 Chuck Shotton Eric W. Sink
 Simon E. Spero Robert S. Thau
 Francois Yergeau Mary Ellen Zurko
 Jean-Philippe Martin-Flatin
14. References
 [1] F. Anklesaria, M. McCahill, P. Lindner, D. Johnson, D. Torrey, 
 and B. Alberti. "The Internet Gopher Protocol: A distributed 
 document search and retrieval protocol." RFC 1436, University 
 of Minnesota, March 1993.
 [2] T. Berners-Lee. "Universal Resource Identifiers in WWW: A 
 Unifying Syntax for the Expression of Names and Addresses of 
 Objects on the Network as used in the World-Wide Web." RFC 
 1630, CERN, June 1994.
 [3] T. Berners-Lee and D. Connolly. "HyperText Markup Language 
 Specification - 2.0." Work in Progress 
 (draft-ietf-html-spec-05.txt), MIT/W3C, August 1995.
 [4] T. Berners-Lee, L. Masinter, and M. McCahill. "Uniform Resource 
 Locators (URL)." RFC 1738, CERN, Xerox PARC, University of 
 Minnesota, December 1994.
 [5] N. Borenstein and N. Freed. "MIME (Multipurpose Internet Mail 
 Extensions) Part One: Mechanisms for Specifying and Describing 
 the Format of Internet Message Bodies." RFC 1521, Bellcore, 
 Innosoft, September 1993.
 [6] R. Braden. "Requirements for Internet hosts - application and 
 support." STD 3, RFC 1123, IETF, October 1989.
 [7] D. H. Crocker. "Standard for the Format of ARPA Internet Text 
 Messages." STD 11, RFC 822, UDEL, August 1982.
 [8] F. Davis, B. Kahle, H. Morris, J. Salem, T. Shen, R. Wang, 
 J. Sui, and M. Grinbaum. "WAIS Interface Protocol Prototype 
 Functional Specification." (v1.5), Thinking Machines 
 Corporation, April 1990.
 [9] R. Fielding. "Relative Uniform Resource Locators." RFC 1808, 
 UC Irvine, June 1995.
 [10] M. Horton and R. Adams. "Standard for interchange of USENET 
 messages." RFC 1036 (Obsoletes RFC 850), AT&T Bell 
 Laboratories, Center for Seismic Studies, December 1987.
 [11] B. Kantor and P. Lapsley. "Network News Transfer Protocol: 
 A Proposed Standard for the Stream-Based Transmission of News." 
 RFC 977, UC San Diego, UC Berkeley, February 1986.
 [12] J. Postel. "Simple Mail Transfer Protocol." STD 10, RFC 821, 
 USC/ISI, August 1982.
 [13] J. Postel. "Media Type Registration Procedure." RFC 1590, 
 USC/ISI, March 1994.
 [14] J. Postel and J. K. Reynolds. "File Transfer Protocol (FTP)." 
 STD 9, RFC 959, USC/ISI, October 1985.
 [15] J. Reynolds and J. Postel. "Assigned Numbers." STD 2, RFC 1700, 
 USC/ISI, October 1994.
 [16] K. Sollins and L. Masinter. "Functional Requirements for 
 Uniform Resource Names." RFC 1737, MIT/LCS, Xerox Corporation, 
 December 1994.
 [17] US-ASCII. Coded Character Set - 7-Bit American Standard Code 
 for Information Interchange. Standard ANSI X3.4-1986, ANSI, 
 1986.
 [18] ISO-8859. International Standard -- Information Processing --
 8-bit Single-Byte Coded Graphic Character Sets --
 Part 1: Latin alphabet No. 1, ISO 8859-1:1987.
 Part 2: Latin alphabet No. 2, ISO 8859-2, 1987.
 Part 3: Latin alphabet No. 3, ISO 8859-3, 1988.
 Part 4: Latin alphabet No. 4, ISO 8859-4, 1988.
 Part 5: Latin/Cyrillic alphabet, ISO 8859-5, 1988.
 Part 6: Latin/Arabic alphabet, ISO 8859-6, 1987.
 Part 7: Latin/Greek alphabet, ISO 8859-7, 1987.
 Part 8: Latin/Hebrew alphabet, ISO 8859-8, 1988.
 Part 9: Latin alphabet No. 5, ISO 8859-9, 1990.
15. Authors' Addresses
 Tim Berners-Lee
 Director, W3 Consortium
 MIT Laboratory for Computer Science
 545 Technology Square
 Cambridge, MA 02139, U.S.A.
 Tel: +1 (617) 253 5702
 Fax: +1 (617) 258 8682
 Email: timbl@w3.org
 Roy T. Fielding
 Department of Information and Computer Science
 University of California
 Irvine, CA 92717-3425, U.S.A.
 Tel: +1 (714) 824-4049
 Fax: +1 (714) 824-4056
 Email: fielding@ics.uci.edu
 Henrik Frystyk Nielsen
 W3 Consortium
 MIT Laboratory for Computer Science
 545 Technology Square
 Cambridge, MA 02139, U.S.A.
 Tel: +1 (617) 258 8143
 Fax: +1 (617) 258 8682
 Email: frystyk@w3.org
Appendices
 These appendices are provided for informational reasons only -- they 
 do not form a part of the HTTP/1.0 specification.
A. Internet Media Type message/http
 In addition to defining the HTTP/1.0 protocol, this document serves 
 as the specification for the Internet media type "message/http". 
 The following is to be registered with IANA [13].
 Media Type name: message
 Media subtype name: http
 Required parameters: none
 Optional parameters: version, msgtype
 version: The HTTP-Version number of the enclosed message
 (e.g., "1.0"). If not present, the version can be
 determined from the first line of the body.
 msgtype: The message type -- "request" or "response". If 
 not present, the type can be determined from the 
 first line of the body.
 Encoding considerations: only "7bit", "8bit", or "binary" are 
 permitted
 Security considerations: none
B. Tolerant Applications
 Although this document specifies the requirements for the 
 generation of HTTP/1.0 messages, not all applications will be 
 correct in their implementation. We therefore recommend that 
 operational applications be tolerant of deviations whenever those 
 deviations can be interpreted unambiguously.
 Clients should be tolerant in parsing the Status-Line and servers 
 tolerant when parsing the Request-Line. In particular, they should 
 accept any amount of SP or HT characters between fields, even 
 though only a single SP is required.
 The line terminator for HTTP-header fields is the sequence CRLF. 
 However, we recommend that applications, when parsing such headers, 
 recognize a single LF as a line terminator and ignore the leading 
 CR.
C. Relationship to MIME
 HTTP/1.0 reuses many of the constructs defined for Internet Mail 
 (RFC 822 [7]) and the Multipurpose Internet Mail Extensions 
 (MIME [5]) to allow entities to be transmitted in an open variety 
 of representations and with extensible mechanisms. However, HTTP is 
 not a MIME-compliant application. HTTP's performance requirements 
 differ substantially from those of Internet mail. Since it is not 
 limited by the restrictions of existing mail protocols and SMTP 
 gateways, HTTP does not obey some of the constraints imposed by 
 RFC 822 and MIME for mail transport.
 This appendix describes specific areas where HTTP differs from 
 MIME. Proxies/gateways to MIME-compliant protocols must be aware of 
 these differences and provide the appropriate conversions where 
 necessary.
C.1 Conversion to Canonical Form
 MIME requires that an entity be converted to canonical form prior 
 to being transferred, as described in Appendix G of RFC 1521 [5]. 
 Although HTTP does require media types to be transferred in 
 canonical form, it changes the definition of "canonical form" for 
 text-based media types as described in Section 3.6.1.
C.1.1 Representation of Line Breaks
 MIME requires that the canonical form of any text type represent 
 line breaks as CRLF and forbids the use of CR or LF outside of line 
 break sequences. Since HTTP allows CRLF, bare CR, and bare LF (or 
 the octet sequence(s) to which they would be translated for the 
 given character set) to indicate a line break within text content, 
 recipients of an HTTP message cannot rely upon receiving 
 MIME-canonical line breaks in text.
 Where it is possible, a proxy or gateway from HTTP to a 
 MIME-compliant protocol should translate all line breaks within 
 text/* media types to the MIME canonical form of CRLF. However, 
 this may be complicated by the presence of a Content-Encoding and 
 by the fact that HTTP allows the use of some character sets which 
 do not use octets 13 and 10 to represent CR and LF, as is the case 
 for some multi-byte character sets. If canonicalization is 
 performed, the Content-Length header field value must be updated to 
 reflect the new body length.
C.1.2 Default Character Set
 MIME requires that all subtypes of the top-level Content-Type 
 "text" have a default character set of US-ASCII [17]. In contrast, 
 HTTP defines the default character set for "text" to be 
 ISO-8859-1 [18] (a superset of US-ASCII). Therefore, if a text/* 
 media type given in the Content-Type header field does not already 
 include an explicit charset parameter, the parameter
 ;charset="iso-8859-1"
 should be added by the proxy/gateway if the entity contains any 
 octets greater than 127.
C.2 Conversion of Date Formats
 HTTP/1.0 uses a restricted subset of date formats to simplify the 
 process of date comparison. Proxies/gateways from other protocols 
 should ensure that any Date header field present in a message 
 conforms to one of the HTTP/1.0 formats and rewrite the date if 
 necessary.
C.3 Introduction of Content-Encoding
 MIME does not include any concept equivalent to HTTP's 
 Content-Encoding header field. Since this acts as a modifier on the 
 media type, proxies/gateways to MIME-compliant protocols must 
 either change the value of the Content-Type header field or decode 
 the Entity-Body before forwarding the message.
 Note: Some experimental applications of Content-Type for 
 Internet mail have used a media-type parameter of 
 ";conversions=<content-coding>" to perform an equivalent 
 function as Content-Encoding. However, this parameter is not 
 part of the MIME specification at the time of this writing.
C.4 No Content-Transfer-Encoding
 HTTP does not use the Content-Transfer-Encoding (CTE) field of 
 MIME. Proxies/gateways from MIME-compliant protocols must remove 
 any non-identity CTE ("quoted-printable" or "base64") encoding 
 prior to delivering the response message to an HTTP client. 
 Proxies/gateways to MIME-compliant protocols are responsible for 
 ensuring that the message is in the correct format and encoding for 
 safe transport on that protocol, where "safe transport" is defined 
 by the limitations of the protocol being used. At a minimum, the 
 CTE field of
 Content-Transfer-Encoding: binary
 should be added by the proxy/gateway if it is unwilling to apply a 
 content transfer encoding.
 An HTTP client may include a Content-Transfer-Encoding as an 
 extension Entity-Header in a POST request when it knows the 
 destination of that request is a proxy/gateway to a MIME-compliant 
 protocol.