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

Mark Nottingham <mnot@mnot.net> Mon, 18 May 2020 23:24 UTC

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From: Mark Nottingham <mnot@mnot.net>
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Date: Tue, 19 May 2020 09:20:57 +1000
Cc: "Julian F. Reschke" <julian.reschke@gmx.de>, 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
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To: Benjamin Kaduk <bkaduk@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 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.


> FWIW I already have a comment staged about how we seem to make the
> ABNF normative for serialization but the prose normative for parsing,
> which seems like a weird mismatch that requires justification.

ABNF isn't normative for serialisation; what led you to that conclusion? 



1. https://httpwg.org/http-extensions/draft-ietf-httpbis-header-structure.html#notational-conventions

--
Mark Nottingham   https://www.mnot.net/