Network Working Group R. Fielding Request for Comments: 2616 ...

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Fielding, et al. Standards Track [Page 21]RFC 2616 HTTP/1.1 June 1999The term "character set" is used in this document to refer to amethod used with one or more tables to convert a sequence of octetsinto a sequence of characters. Note that unconditional conversion inthe other direction is not required, in that not all characters maybe available in a given character set and a character set may providemore than one sequence of octets to represent a particular character.This definition is intended to allow various kinds of characterencoding, from simple single-table mappings such as US-ASCII tocomplex table switching methods such as those that use ISO-2022'stechniques. However, the definition associated with a MIME characterset name MUST fully specify the mapping to be performed from octetsto characters. In particular, use of external profiling informationto determine the exact mapping is not permitted.Note: This use of the term "character set" is more commonlyreferred to as a "character encoding." However, since HTTP andMIME share the same registry, it is important that the terminologyalso be shared.HTTP character sets are identified by case-insensitive tokens. Thecomplete set of tokens is defined by the IANA Character Set registry[19].charset = tokenAlthough HTTP allows an arbitrary token to be used as a charsetvalue, any token that has a predefined value within the IANACharacter Set registry [19] MUST represent the character set definedby that registry. Applications SHOULD limit their use of charactersets to those defined by the IANA registry.Implementors should be aware of IETF character set requirements [38][41].3.4.1 Missing CharsetSome HTTP/1.0 software has interpreted a Content-Type header withoutcharset parameter incorrectly to mean "recipient should guess."Senders wishing to defeat this behavior MAY include a charsetparameter even when the charset is ISO-8859-1 and SHOULD do so whenit is known that it will not confuse the recipient.
Unfortunately, some older HTTP/1.0 clients did not deal properly withan explicit charset parameter. HTTP/1.1 recipients MUST respect thecharset label provided by the sender; and those user agents that havea provision to "guess" a charset MUST use the charset from theFielding, et al. Standards Track [Page 22]RFC 2616 HTTP/1.1 June 1999content-type field if they support that charset, rather than therecipient's preference, when initially displaying a document. Seesection 3.7.1.3.5 Content CodingsContent coding values indicate an encoding transformation that hasbeen or can be applied to an entity. Content codings are primarilyused to allow a document to be compressed or otherwise usefullytransformed without losing the identity of its underlying media typeand without loss of information. Frequently, the entity is stored incoded form, transmitted directly, and only decoded by the recipient.content-coding = tokenAll content-coding values are case-insensitive. HTTP/1.1 usescontent-coding values in the Accept-Encoding (section 14.3) andContent-Encoding (section 14.11) header fields. Although the valuedescribes the content-coding, what is more important is that itindicates what decoding mechanism will be required to remove theencoding.The Internet Assigned Numbers Authority (IANA) acts as a registry forcontent-coding value tokens. Initially, the registry contains thefollowing tokens:gzip An encoding format produced by the file compression program"gzip" (GNU zip) as described in RFC 1952 [25]. This format is aLempel-Ziv coding (LZ77) with a 32 bit CRC.compressThe encoding format produced by the common UNIX file compressionprogram "compress". This format is an adaptive Lempel-Ziv-Welchcoding (LZW).Use of program names for the identification of encoding formats
Page 2: eferred to as "HTTP/1.1", and is an
Page 5 and 6: 12.1 Server-driven Negotiation ....
Page 7 and 8: 14.40 Trailer .....................
Page 9 and 10: 1.2 RequirementsThe key words "MUST
Page 12 and 13: Fielding, et al. Standards Track [P
Page 14 and 15: equest chain ----------------------
Page 16 and 17: Elements separated by a bar ("|") a
Page 18 and 19: HTTP/1.1 header field values can be
Page 20 and 21: An application that sends a request
Page 22 and 23: 3.2.3 URI ComparisonWhen comparing
Page 26 and 27: is not desirable and is discouraged
Page 28 and 29: CRLFchunk = chunk-size [ chunk-exte
Page 30 and 31: When in canonical form, media subty
Page 32 and 33: 3.9 Quality ValuesHTTP content nego
Page 34 and 35: RFC 2616 HTTP/1.1 June 1999HTTP/1.1
Page 36 and 37: message-body = entity-body| Transfe
Page 38 and 39: in advance.Messages MUST NOT includ
Page 40 and 41: equested resource, and 501 (Not Imp
Page 42 and 43: names) MUST use the following rules
Page 44 and 45: values for the first digit:- 1xx: I
Page 48 and 49: how the transfer-length of a messag
Page 50 and 51: connection-token close.If either th
Page 52 and 53: idempotent (see section 9.1.2). Non
Page 54 and 55: compatibility with RFC 2068, a serv
Page 56 and 57: If at any point an error status is
Page 58 and 59: optional features implemented by th
Page 60 and 61: - Extending a database through an a
Page 62 and 63: intervention (or other means) on th
Page 64 and 65: 10.1.2 101 Switching ProtocolsThe s
Page 66 and 67: esponse MAY include new or updated
Page 70 and 71: The response MUST include the follo
Page 72 and 73: If the client is sending data, a se
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If the response could be unacceptab
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10.4.15 414 Request-URI Too LongThe
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10.5.5 504 Gateway TimeoutThe serve
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Fielding, et al. Standards Track [P
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Caching would be useless if it did
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Warning (but without removing any e
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If the user has overridden the basi
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in the past. This means that the re
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RFC 2616 HTTP/1.1 June 1999the time
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simple:response_is_fresh = (freshne
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match.In HTTP/1.1, a conditional re
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validators or strong validators. Cl
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- MAY send a weak entity tag instea
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Unless specifically constrained by
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warn-code 1xx, which are deleted ev
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for the associated entity, its enti
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- DELETE- POSTIn order to prevent d
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The Accept request-header field can
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image/jpeg = 0.5text/html;level=2 =
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Note: If the request does not inclu
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Accept-Ranges: bytesbut are not req
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containing an Authorization field,
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- Restrictions on what may be store
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improve privacy in some cases, we c
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must-revalidateBecause a cache MAY
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understand.For example, consider a
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new coding is known to be acceptabl
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14.14 Content-LocationThe Content-L
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Note: while the definition of Conte
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server SHOULD return them in the or
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Some origin server implementations
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Expires = "Expires" ":" HTTP-dateAn
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A client MUST include a Host header
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een modified since the date given b
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RFC 2616 HTTP/1.1 June 1999If none
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14.29 Last-ModifiedThe Last-Modifie
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MAY require that behavior be consis
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yte-ranges-specifier = bytes-unit "
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Content) instead of 200 (OK).- The
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The TE request-header field indicat
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a cache cannot determine from the r
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SHOULD NOT, by default, forward the
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this user agent behavior in mind.Re
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designers and implementors be parti
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strongly correlated to the membersh
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serious security considerations. Co
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The HTTP protocol has evolved consi
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Protocol -- HTTP/1.0", RFC 1945, Ma
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Implementation and Analysis", RFC 1
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University of California, IrvineIrv
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Notes:1) Additional CRLFs may prece
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full compliance with the MIME proto
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ead chunk-size and CRLF}read entity
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- understand any valid response in
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CREATE had a race that required an
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also needed to be a general header,
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Network Working Group R. Fielding Request for Comments: 2616 ...

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