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

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Elements separated by a bar ("|") 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 "elemfoo elem" and "elem bar elem".*ruleThe character "*" preceding an element indicates repetition. Thefull form is "*element" indicating at least and at most occurrences of element. Default values are 0 and infinity sothat "*(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]" isequivalent to "*1(foo bar)".Fielding, et al. Standards Track [Page 14]RFC 2616 HTTP/1.1 June 1999N ruleSpecific repetition: "(element)" is equivalent to"*(element)"; that is, exactly occurrences of (element).Thus 2DIGIT is a 2-digit number, and 3ALPHA is a string of threealphabetic characters.#ruleA construct "#" is defined, similar to "*", for defining lists ofelements. The full form is "#element" indicating at least and at most elements, each separated by one or more commas(",") and OPTIONAL linear white space (LWS). This makes the usualform of lists very easy; a rule such as( *LWS element *( *LWS "," *LWS element ))can be shown as1#elementWherever this construct is used, null elements are allowed, but donot contribute to the count of elements present. That is,"(element), , (element) " is permitted, but counts as only twoelements. Therefore, where at least one element is required, atleast one non-null element MUST be present. Default values are 0and infinity so that "#element" allows any number, including zero;"1#element" requires at least one; and "1#2element" allows one ortwo.; 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 asimple way of including useful notes in parallel with thespecifications.implied *LWSThe grammar described by this specification is word-based. Exceptwhere noted otherwise, linear white space (LWS) can be includedbetween any two adjacent words (token or quoted-string), andbetween adjacent words and separators, without changing theinterpretation of a field. At least one delimiter (LWS and/orseparators) MUST exist between any two tokens (for the definitionof "token" below), since they would otherwise be interpreted as asingle token.2.2 Basic RulesThe following rules are used throughout this specification todescribe basic parsing constructs. The US-ASCII coded character setis defined by ANSI X3.4-1986 [21].Fielding, et al. Standards Track [Page 15]RFC 2616 HTTP/1.1 June 1999OCTET = CHAR = UPALPHA = LOALPHA = ALPHA = UPALPHA | LOALPHADIGIT = CTL = CR = LF = SP = HT =
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 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
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esponse MAY include new or updated
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Fielding, et al. Standards Track [P
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The response MUST include the follo
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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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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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