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

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

Return-Path: <worley@alum.mit.edu>
X-Original-To: mmusic@ietfa.amsl.com
Delivered-To: mmusic@ietfa.amsl.com
Received: from localhost (localhost [127.0.0.1]) by ietfa.amsl.com (Postfix) with ESMTP id 514EA129417 for <mmusic@ietfa.amsl.com>; Thu, 12 Jan 2017 06:33:38 -0800 (PST)
X-Virus-Scanned: amavisd-new at amsl.com
X-Spam-Flag: NO
X-Spam-Score: -1.934
X-Spam-Level:
X-Spam-Status: No, score=-1.934 tagged_above=-999 required=5 tests=[BAYES_00=-1.9, HEADER_FROM_DIFFERENT_DOMAINS=0.001, RCVD_IN_DNSWL_LOW=-0.7, SPF_SOFTFAIL=0.665] autolearn=no autolearn_force=no
Received: from mail.ietf.org ([4.31.198.44]) by localhost (ietfa.amsl.com [127.0.0.1]) (amavisd-new, port 10024) with ESMTP id TC73I1voTrhT for <mmusic@ietfa.amsl.com>; Thu, 12 Jan 2017 06:33:36 -0800 (PST)
Received: from resqmta-po-04v.sys.comcast.net (resqmta-po-04v.sys.comcast.net [IPv6:2001:558:fe16:19:96:114:154:163]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by ietfa.amsl.com (Postfix) with ESMTPS id DD47D1293F0 for <mmusic@ietf.org>; Thu, 12 Jan 2017 06:33:36 -0800 (PST)
Received: from resomta-po-05v.sys.comcast.net ([96.114.154.229]) by resqmta-po-04v.sys.comcast.net with SMTP id RgRbct12brdcjRgRbcw76f; Thu, 12 Jan 2017 14:33:35 +0000
Received: from hobgoblin.ariadne.com ([IPv6:2601:192:4603:9471:222:fbff:fe91:d396]) by resomta-po-05v.sys.comcast.net with SMTP id RgRVcUUvrmBhGRgRWc0tju; Thu, 12 Jan 2017 14:33:33 +0000
Received: from hobgoblin.ariadne.com (hobgoblin.ariadne.com [127.0.0.1]) by hobgoblin.ariadne.com (8.14.7/8.14.7) with ESMTP id v0CEXTQZ000738; Thu, 12 Jan 2017 09:33:29 -0500
Received: (from worley@localhost) by hobgoblin.ariadne.com (8.14.7/8.14.7/Submit) id v0CEXRwf000734; Thu, 12 Jan 2017 09:33:27 -0500
X-Authentication-Warning: hobgoblin.ariadne.com: worley set sender to worley@alum.mit.edu using -f
From: worley@ariadne.com (Dale R. Worley)
To: RFC Errata System <rfc-editor@rfc-editor.org>
In-Reply-To: <20170112050406.13897B81A86@rfc-editor.org>
Sender: worley@ariadne.com (Dale R. Worley)
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)
X-BeenThere: mmusic@ietf.org
X-Mailman-Version: 2.1.17
Precedence: list
List-Id: Multiparty Multimedia Session Control Working Group <mmusic.ietf.org>
List-Unsubscribe: <https://www.ietf.org/mailman/options/mmusic>, <mailto:mmusic-request@ietf.org?subject=unsubscribe>
List-Archive: <https://mailarchive.ietf.org/arch/browse/mmusic/>
List-Post: <mailto:mmusic@ietf.org>
List-Help: <mailto:mmusic-request@ietf.org?subject=help>
List-Subscribe: <https://www.ietf.org/mailman/listinfo/mmusic>, <mailto:mmusic-request@ietf.org?subject=subscribe>
X-List-Received-Date: Thu, 12 Jan 2017 14:33:38 -0000

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