Re: empty lists?, was: Last Call: <draft-ietf-httpbis-header-structure-18.txt> (Structured Field Values for HTTP) to Proposed Standard

Benjamin Kaduk <bkaduk@akamai.com> Tue, 19 May 2020 02:56 UTC

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Date: Mon, 18 May 2020 19:55:45 -0700
From: Benjamin Kaduk <bkaduk@akamai.com>
To: Julian Reschke <julian.reschke@gmx.de>
Cc: Mark Nottingham <mnot@mnot.net>, last-call@ietf.org, httpbis-chairs@ietf.org, HTTP Working Group <ietf-http-wg@w3.org>, Barry Leiba <barryleiba@gmail.com>, draft-ietf-httpbis-header-structure@ietf.org
Message-ID: <20200519025544.GF3811@akamai.com>
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Subject: Re: empty lists?, was: Last Call: <draft-ietf-httpbis-header-structure-18.txt> (Structured Field Values for HTTP) to Proposed Standard
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On Tue, May 19, 2020 at 04:49:58AM +0200, Julian Reschke wrote:
> On 19.05.2020 01:20, Mark Nottingham wrote:
> > 
> > 
> > > On 19 May 2020, at 7:23 am, Benjamin Kaduk <bkaduk@akamai.com> wrote:
> > > 
> > > > > You saw
> > > > > 
> > > > >     An empty List is denoted by not serializing the field at all.
> > > > > 
> > > > > right?
> > > > 
> > > > That's about serialization.
> > > > 
> > > > 4.2.1 seems to parse an empty string into an empty list.
> > > > 
> > > > AFAICT, that's in conflict with the ABNF.
> > > 
> > > Thanks for clarifying.
> > 
> > As per S 1.2 [1], the ABNF is not for parsing; it's for 'illustrat[ing] the range of acceptable wire representations.'
> > 
> > The ABNF requires at least one member because sending an empty field value is not good practice; it's not something we encourage.
> > ...
> 
> So the real inconsistency here is that sending an empty value is not ok
> (forbidden?, not encouraged?), but an empty string is a valid parser input.

That does seem like a key topic for the DISCUSS ballot I just submitted.
(I wanted to get the rest of my comments available, and don't intend for
my DISCUSS text to be "the final word"; let's please continue this discussion
and go for clarity.)

-Ben