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Re: Multiple header fields with the same field name - unwritten assumption about quoted commas in values?

From: Piotr Dobrogost <p@ietf.dobrogost.net>
Date: Wed, 9 Jan 2013 18:05:40 +0100
Message-ID: <CAA6tFMvRPngM3oRYRUW4mTJDzs98wznqMEJiFeQgyLBzApX1xg@mail.gmail.com>
To: ietf-http-wg <ietf-http-wg@w3.org>
On Wed, Jan 9, 2013 at 5:38 PM, Julian Reschke <julian.reschke@gmx.de> wrote:
> On 2013-01-09 17:29, Zhong Yu wrote:
>> The commas in entity tags are "quoted", so it's not a problem for a
>> generic parser which pairs quotes.
>>      If-Match: "12,34", W/"56,78"
> But they do not use the quoted-string ABNF production (anymore). Note that
> that would imply handling of "\" which we found almost nobody does. This
> also means that just "pairing" double quotes is not sufficient.

I'm not sure I follow - I'll try to rephrase it. In the past entity
tags were specified as using quoted-string ABNF production but because
existing implementations did not implemented this grammar production
fully (they did not handle backslash as they should) you removed this
production from specs. The outcome is that "standard" parser which
parses quoted-string ABNF production can't parse entity tags anymore.
Does it mean that If-Match header field's value does no longer is in
the form of comma-separated list [i.e., #(values)] thus there can't be
multiple If-Match header fields?

>> The Link header can contain unquoted commas, since comma is legal in URIs
>>      Link: </page,6>; rel="Previous",  </page,8>; rel="Next"
>> fortunately these commas will be surround by <>, no ambiguity there.
> Yes, but the parser needs to understand the ABNF of the field value in order
> to decide which is which.

This leads to some questions:
What are the requirements on parser of conforming user agent in regard
to parsing header fields' values? Is it required to parse header
fields' values of all registered header fields? Is it required to
parse header fields' values for header fields which it handles? Is it
required to parse quoted-string values?

Piotr Dobrogost
Received on Wednesday, 9 January 2013 17:06:36 UTC

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