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

From: Zhong Yu <zhong.j.yu@gmail.com>
Date: Wed, 9 Jan 2013 10:29:51 -0600
Message-ID: <CACuKZqHDWbNMiwjkxvBuAt-UEg_tjzEvFZsyXM2U+5H5qxK76A@mail.gmail.com>
To: Julian Reschke <julian.reschke@gmx.de>
Cc: Piotr Dobrogost <p@ietf.dobrogost.net>, ietf-http-wg@w3.org
On Wed, Jan 9, 2013 at 5:00 AM, Julian Reschke <julian.reschke@gmx.de> wrote:
> On 2013-01-09 03:22, Zhong Yu wrote:
>>
>> On Tue, Jan 8, 2013 at 6:28 PM, Piotr Dobrogost <p@ietf.dobrogost.net>
>> wrote:
>>>
>>> Hi!
>>>
>>> In
>>> http://trac.tools.ietf.org/html/draft-ietf-httpbis-p1-messaging-21#section-3.2
>>> one reads
>>>
>>> "Multiple header fields with the same field name MUST NOT be sent in a
>>>   message unless the entire field value for that header field is
>>>   defined as a comma-separated list [i.e., #(values)]."
>>>
>>> Is the unwritten assumption that each value out of "values" has no
>>> unquoted comma?
>>
>>
>> Good question. I think it is true for all headers defined in the spec
>> that use the #rule; I guess it is intended to be true in general.
>
>
> It's a good idea to do, but not always the case. Example: "If-Match" and
> "If-None-Match". So to separate values in a list production, code needs to
> understand the syntax of the individual values.

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"

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.

The same bis section also specifically mentions the exception to
`Set-Cookie` - each cookie must be declared in its own line, because
unquoted comma can appear in the line

    Set-Cookie: name=value; path=/ab,1; expires=Wed, 09 Jun 2021 10:18:14 GMT

If we are to put multiple cookies on one line, the comma in the expiry
date does not cause ambiguity, but the comma in the path value could

    Set-Cookie: n1=v1; path=/ab,1 , n2=v2

Zhong Yu
Received on Wednesday, 9 January 2013 16:30:21 GMT

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