Re: [MMUSIC] [Editorial Errata Reported] RFC4566 (4903)

worley@ariadne.com (Dale R. Worley) Thu, 12 January 2017 14:33 UTC

From: worley@ariadne.com
To: RFC Errata System <rfc-editor@rfc-editor.org>
In-Reply-To: <20170112050406.13897B81A86@rfc-editor.org>
Sender: worley@ariadne.com
Date: Thu, 12 Jan 2017 09:33:27 -0500
Message-ID: <87ziiw73go.fsf@hobgoblin.ariadne.com>
Archived-At: <https://mailarchive.ietf.org/arch/msg/mmusic/LmL7SUbMeYJgrcj6hUe3j8MgcJU>
Cc: ben@nostrum.com, block.rxckin.beats@gmail.com, mmusic@ietf.org, aamelnikov@fastmail.fm, fandreas@cisco.com, M.Handley@cs.ucl.ac.uk, csp@csperkins.org, van@packetdesign.com, rfc-editor@rfc-editor.org
Subject: Re: [MMUSIC] [Editorial Errata Reported] RFC4566 (4903)
Precedence: list

RFC Errata System <rfc-editor@rfc-editor.org> writes:
> Original Text

>    connection-field =    [%x63 "=" nettype SP addrtype SP
>                          connection-address CRLF]
>                          ;a connection field must be present
>                          ;in every media description or at the
>                          ;session-level

> Corrected Text

>    connection-field =    %x63 "=" nettype SP addrtype SP
>                          connection-address CRLF
>                          ;a connection field must be present
>                          ;in every media description or at the
>                          ;session-level
>

> in BNF of SDP, connection-field itself is optional [0, 1], but
> media-description has multiple [0,) connection-field.  it seems
> conflict, because multiple of optional fields doesn't finish because
> multiple filed can't find when to end.

As a grammar, a set of BNF productions, the original text is correct.
The erratum is correct that parser generators may have a difficult time
processing that grammar, but strictly speaking, that is not a problem
with the RFC.

Personally, I do not like the style of the grammar, which is to present
all of the alternatives as required and then each alternative contains
its own optionality.  That is,

   session-description = proto-version
                         origin-field
                         session-name-field
                         information-field
                         uri-field
                         email-fields
			 [...]

   information-field =   [%x69 "=" text CRLF]

   uri-field =           [%x75 "=" uri CRLF]

   email-fields =        *(%x65 "=" email-address CRLF)

I would prefer

   session-description = proto-version
                         origin-field
                         session-name-field
                         [information-field]
                         [uri-field]
                         *email-field
			 [...]

   information-field =   %x69 "=" text CRLF

   uri-field =           %x75 "=" uri CRLF

   email-field =         %x65 "=" email-address CRLF

But that is a style issue, and it is best to define connection-field
using the same style as every other field.

Dale

[MMUSIC] [Editorial Errata Reported] RFC4566 (490… RFC Errata System
Re: [MMUSIC] [Editorial Errata Reported] RFC4566 … Dale R. Worley