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

From: Julian Reschke <julian.reschke@gmx.de>
Date: Wed, 09 Jan 2013 18:25:45 +0100
Message-ID: <50EDA819.4040402@gmx.de>
To: Zhong Yu <zhong.j.yu@gmail.com>
CC: Piotr Dobrogost <p@ietf.dobrogost.net>, ietf-http-wg@w3.org
On 2013-01-09 18:08, Zhong Yu wrote:
> On Wed, Jan 9, 2013 at 10:38 AM, Julian Reschke <julian.reschke@gmx.de> wrote:
>> On 2013-01-09 17:29, Zhong Yu wrote:
>>>
>>> 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"
>>
>>
>> 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
>
> Do you mean if a server responds
>
>      Entity-Tag: "abc\""
>
> most clients will fail to parse it? But if the server changes it to

What we tested is whether servers that send an ETag of "X" will also 
process "\X" and treat it as equivalent. I believe the outcome was that 
they don't.

>      Entity-Tag: "abc\"
>
> it'll fail on good clients which are conformant to RFC2616.

Yes. Do you have information that this happens in practice? ((a) servers 
using backslash in entity tags, and/or (b) clients parsing them as 
quoted-string?)

Best regards, Julian
Received on Wednesday, 9 January 2013 17:26:14 GMT

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