Subject: [Sip] Error in RFC 3261 definition of the Accept header syntax

From: Pekka Pessi <[email-masked]>
Date: Tue, 20 Apr 2004 16:27:33 +0300

Hello all,

RFC 3261 defines the Accept header as follows:

20.1 Accept

   The Accept header field follows the syntax defined in [H14.1].  The
   semantics are also identical, with the exception that if no Accept
   header field is present, the server SHOULD assume a default value of
   application/sdp.

[H14.1] refers to RFC 2616 section 14.1, which plainly states that
there must be a q parameter between media-type-specific parameters
and other accept-parameters, IOW the first accept-parameter must
always be q parameter.

Now, the grammar part in RFC 3261 defines syntax for the Accept
header as follows:

Accept         =  "Accept" HCOLON
                   [ accept-range *(COMMA accept-range) ]
accept-range   =  media-range *(SEMI accept-param)
media-range    =  ( "*/*"
                  / ( m-type SLASH "*" )
                  / ( m-type SLASH m-subtype )
                  ) *( SEMI m-parameter )
accept-param   =  ("q" EQUAL qvalue) / generic-param

The error was introduced during the great grammar rewrite, I
believe. The RFC3261-style syntax following the [H14.1] would be
as follows:

Accept         =  "Accept" HCOLON
                   [ accept-range *(COMMA accept-range) ]
accept-range   =  media-range [ accept-params ]
media-range    =  ( "*/*"
                  / ( m-type SLASH "*" )
                  / ( m-type SLASH m-subtype )
                  ) *( SEMI m-parameter )
accept-params   =  SEMI "q" EQUAL qvalue *(SEMI generic-param)

--Pekka

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