Re: [Cbor] [art] Artart early review of draft-ietf-cbor-file-magic-02

Michael Richardson <mcr+ietf@sandelman.ca> Thu, 26 August 2021 18:27 UTC

Return-Path: <mcr+ietf@sandelman.ca>
X-Original-To: cbor@ietfa.amsl.com
Delivered-To: cbor@ietfa.amsl.com
Received: from localhost (localhost [127.0.0.1]) by ietfa.amsl.com (Postfix) with ESMTP id 60E573A0303; Thu, 26 Aug 2021 11:27:55 -0700 (PDT)
X-Virus-Scanned: amavisd-new at amsl.com
X-Spam-Flag: NO
X-Spam-Score: -1.899
X-Spam-Level:
X-Spam-Status: No, score=-1.899 tagged_above=-999 required=5 tests=[BAYES_00=-1.9, SPF_HELO_NONE=0.001, SPF_PASS=-0.001, URIBL_BLOCKED=0.001] autolearn=ham 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 KKfEqUxbxXOw; Thu, 26 Aug 2021 11:27:49 -0700 (PDT)
Received: from tuna.sandelman.ca (tuna.sandelman.ca [IPv6:2607:f0b0:f:3:216:3eff:fe7c:d1f3]) (using TLSv1.2 with cipher ADH-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by ietfa.amsl.com (Postfix) with ESMTPS id D32CC3A02F7; Thu, 26 Aug 2021 11:27:48 -0700 (PDT)
Received: from localhost (localhost [127.0.0.1]) by tuna.sandelman.ca (Postfix) with ESMTP id 205F43898C; Thu, 26 Aug 2021 14:33:21 -0400 (EDT)
Received: from tuna.sandelman.ca ([127.0.0.1]) by localhost (localhost [127.0.0.1]) (amavisd-new, port 10024) with LMTP id U7fEcPR3ZZoV; Thu, 26 Aug 2021 14:33:15 -0400 (EDT)
Received: from sandelman.ca (obiwan.sandelman.ca [209.87.249.21]) by tuna.sandelman.ca (Postfix) with ESMTP id 3EDD938980; Thu, 26 Aug 2021 14:33:15 -0400 (EDT)
Received: from localhost (localhost [IPv6:::1]) by sandelman.ca (Postfix) with ESMTP id 5952D5E5; Thu, 26 Aug 2021 14:27:38 -0400 (EDT)
From: Michael Richardson <mcr+ietf@sandelman.ca>
To: worley@ariadne.com (Dale R. Worley), Bernard Aboba <bernard.aboba@gmail.com>, art@ietf.org, cbor@ietf.org, draft-ietf-cbor-file-magic.all@ietf.org
In-Reply-To: <874kbcaoic.fsf@hobgoblin.ariadne.com>
References: <874kbcaoic.fsf@hobgoblin.ariadne.com>
X-Mailer: MH-E 8.6+git; nmh 1.7+dev; GNU Emacs 26.1
X-Face: $\n1pF)h^`}$H>Hk{L"x@)JS7<%Az}5RyS@k9X%29-lHB$Ti.V>2bi.~ehC0; <'$9xN5Ub# z!G,p`nR&p7Fz@^UXIn156S8.~^@MJ*mMsD7=QFeq%AL4m<nPbLgmtKK-5dC@#:k
MIME-Version: 1.0
Content-Type: multipart/signed; boundary="=-=-="; micalg=pgp-sha512; protocol="application/pgp-signature"
Date: Thu, 26 Aug 2021 14:27:38 -0400
Message-ID: <26202.1630002458@localhost>
Archived-At: <https://mailarchive.ietf.org/arch/msg/cbor/3ey4egI-jbQWDrMa25tfkUv3rz0>
Subject: Re: [Cbor] [art] Artart early review of draft-ietf-cbor-file-magic-02
X-BeenThere: cbor@ietf.org
X-Mailman-Version: 2.1.29
Precedence: list
List-Id: "Concise Binary Object Representation \(CBOR\)" <cbor.ietf.org>
List-Unsubscribe: <https://www.ietf.org/mailman/options/cbor>, <mailto:cbor-request@ietf.org?subject=unsubscribe>
List-Archive: <https://mailarchive.ietf.org/arch/browse/cbor/>
List-Post: <mailto:cbor@ietf.org>
List-Help: <mailto:cbor-request@ietf.org?subject=help>
List-Subscribe: <https://www.ietf.org/mailman/listinfo/cbor>, <mailto:cbor-request@ietf.org?subject=subscribe>
X-List-Received-Date: Thu, 26 Aug 2021 18:27:56 -0000

Dale R. Worley <worley@ariadne.com> wrote:
    > There's an odd characteristic about this document, not in its content,
    > but in its style.  It's written as a proposal (a word which is used
    > several times), and yet it's intended to be a BCP, which tells people
    > what do to.

Yes, fair point.
1) It was written as an invididual draft originally, and sought feedback.
   (Request for Comments...)

2) It's a protocol for writing a protocol really.
   Each author that has something they want to mark up are told to think
   about the different parts, and then register something and document it in
   their document.
   So it's more of a framework for CBOR authors to follow.
   That's perhaps why it's not as authoritative as normal.

    > A magic number is ideally a unique fingerprint, present in the first
    > 4 or 8 bytes of the file, which does not change when the contents
    > change, and does not depend upon the length of the file.

    > (Though it would be more accurate to say, "... present at a defined
    > location in the first few bytes of the file ...".)  If this was a
    > specification, it would say essentially the same fact as "This scheme
    > has the desired property of magic numbers of having a unique fingerprint
    > at a fixed location near the beginning of the data."

Good comments.
I can re-edit to be more authoritative if you like.

    > I get the sense that the authors are ambivalent whether they are saying
    > what implementers should do, or just floating an idea.  Though I don't
    > know if that is accurate.

    > As far as content goes, I favor the "tag wrapped" version over the "tag
    > sequence", as it has assured upward-compatibility (if the implementation
    > follows the requirement to ignore unknown tags).

I also prefer it, although I implemented the tag sequence in the protocol
that made me write this document.

    > In particular, if the data consists of a sequence of CBOR items, each one could be tagged (if
    > they might differ) or only the first one be tagged (if they don't).  But
    > that's a different matter.

--
Michael Richardson <mcr+IETF@sandelman.ca>   . o O ( IPv6 IøT consulting )
           Sandelman Software Works Inc, Ottawa and Worldwide