Re: [Extra] Adam Roach's No Objection on draft-ietf-extra-imap-fetch-preview-03: (with COMMENT)

"Alexey Melnikov" <aamelnikov@fastmail.fm> Thu, 11 April 2019 10:23 UTC

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Date: Thu, 11 Apr 2019 06:23:23 -0400
From: "Alexey Melnikov" <aamelnikov@fastmail.fm>
To: "Michael Slusarz" <michael.slusarz=40open-xchange.com@dmarc.ietf.org>, "Adam Roach" <adam@nostrum.com>, "Adam Roach via Datatracker" <noreply@ietf.org>, "The IESG" <iesg@ietf.org>
Cc: extra@ietf.org, "Bron Gondwana" <brong@fastmailteam.com>, extra-chairs@ietf.org, draft-ietf-extra-imap-fetch-preview@ietf.org
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Subject: Re: [Extra] =?utf-8?q?Adam_Roach=27s_No_Objection_on_draft-ietf-extr?= =?utf-8?q?a-imap-fetch-preview-03=3A_=28with_COMMENT=29?=
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Hi Michael,

On Thu, Apr 11, 2019, at 4:46 AM, Michael Slusarz wrote:
> Adam,
> 
> Thanks for your comments.  Discussion below.
> 
> > On April 8, 2019 at 2:38 PM Adam Roach via Datatracker <noreply@ietf.org> wrote:
> > ----------------------------------------------------------------------
> > COMMENT:
> > ----------------------------------------------------------------------
> >
> > §3.1:
> > 
> > >  These algorithms MUST be one
> > >  of the algorithms identified as supported in the PREVIEW capability
> > >  responses.
> > 
> > This is confusing, as "algorithms" and "one of" don't make sense with each
> > other. Is it meant to say something like "...MUST be a subset of the
> > algorithms..."?
> 
> Noted that the topic of multiple algorithm selection is being discussed 
> in Barry's DISCUSS.
> 
> That being said, if multiple algorithm support is decided to be kept, 
> what about changing this to:
> 
> "All algorithms specified in the list MUST be identified as being 
> supported by the server by appearing in a PREVIEW capability response." 
> (or "PREVIEW= capability response" maybe?)

You already need to deal with unrecognized algorithms (the text you suggested below), so having a MUST here doesn't make sense.

> > §3.1:
> > 
> > >  If a client requests an algorithm that is unsupported,
> > >  the server MUST return a tagged BAD response.
> > 
> > This appear to be underspecified, or at least nonintuitive. As written,
> > it seems to say that an algorithm list of (known-1, known-2, unknown, known-3)
> > would be considered invalid, even though there are plenty of supported,
> > requested algorithms that could be used. Is this actually intended to be an
> > error? If so, please make it explicit, as it's pretty counterintuitive.
> > 
> > (As an aside: it's also unnecessarily fragile from an interop perspective, so I
> > would suggest that this is not the desired behavior: I believe you want to
> > return an error only when *none* of the requested algorithms are supported).
> 
> See Barry's DISCUSS response.  Agreed that error handling is not 
> specified adequately in current text.
> 
> To mirror duplicate algorithm language, how about: "Unsupported 
> algorithms in the list MUST be ignored. If the list contains no 
> supported algorithms, the server MUST return a tagged BAD response to 
> the FETCH command."

This looks reasonable to me.

> > ---------------------------------------------------------------------------
> > 
> > §6, example 5:
> > 
> > >    C: E1 CAPABILITY
> > >    S: * CAPABILITY IMAP4rev1 PREVIEW=FUZZY SEARCHRES
> > >    S: E1 OK Capability command completed.
> > >    [...a mailbox is SELECTed...]
> > >    C: E2 SEARCH RETURN (SAVE) FROM "FOO"
> > >    C: E3 FETCH $ (UID PREVIEW (LAZY=FUZZY))
> > 
> > This example shows the use of a modifier ("LAZY") with an algorithm; however,
> > this modifier doesn't appear to be advertised by the server in its CAPABILITY
> > line. If I understand how this is supposed to work (looking at the definitions
> > in section 7), I would have expected:
> > 
> >      S: * CAPABILITY IMAP4rev1 PREVIEW=FUZZY PREVIEW=LAZY SEARCHRES
> > 
> > I'll note that this syntax effectively places algorithms and modifiers in the
> > same namespace, although IANA doesn't seem to be given any explicit
> > instructions about this. I think this needs to be cleaned up prior to
> > publication.  I would make this last point a DISCUSS, except that it appears
> > to be covered by Benjamin's DISCUSS already.
> 
> This has been discussed in several other places already.  I am 
> proposing removing priority modifier extensions, which would address 
> this concern.

I think this is a reasonable course of action.

Best Regards,
Alexey