Re: [http-state] Is this an omission in the parser rules of draft-ietf-httpstate-cookie-21?

"Roy T. Fielding" <fielding@gbiv.com> Tue, 15 February 2011 03:23 UTC

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From: "Roy T. Fielding" <fielding@gbiv.com>
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Date: Mon, 14 Feb 2011 19:23:26 -0800
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To: Adam Barth <ietf@adambarth.com>
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Subject: Re: [http-state] Is this an omission in the parser rules of draft-ietf-httpstate-cookie-21?
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On Feb 4, 2011, at 11:29 AM, Adam Barth wrote:
> On Fri, Feb 4, 2011 at 11:24 AM, Roy T. Fielding <fielding@gbiv.com>; wrote:
>> On Feb 4, 2011, at 10:51 AM, Adam Barth wrote:
>>> On Fri, Feb 4, 2011 at 10:47 AM, Remy Lebeau <remy@lebeausoftware.org>; wrote:
>>>> -------- Original Message --------
>>>> Subject: Re: [http-state] Is this an omission in the parser rules of
>>>> draft-ietf-httpstate-cookie-21?
>>>> From: Adam Barth
>>>> Date: Fri, February 04, 2011 10:19 am
>>>> To: Remy Lebeau
>>>> Cc: http-state@ietf.org
>>>> 
>>>>> The draft gives user agents precise
>>>>> instructions for how to parse all
>>>>> manner of cookies, including cookies with
>>>>> values that contain quote characters. That
>>>>> information is contained in Section 5
>>>> 
>>>> I have re-read Section 5 and I do not see its grammar or parsing rules
>>>> accounting for quoted-string values at all. It only says to remove WSP
>>>> characters surrounding extracted names and values, and quote characters
>>>> are not part of the WSP definition. So what am I missing? Where exactly
>>>> does it say how to unquote a quoted-string used in attribute values?
>>> 
>>> Precisely.  It does not say to unquote a quoted-string because that's
>>> not how cookies work.  The role of the quote character is cookies is
>>> identical to the role of the "!" character.  That is, neither play a
>>> special role in the protocol.  Any representations by the contrary by
>>> 2109 or any other document are fiction and have only caused pain and
>>> misery in the world.
>> 
>> That may be, but the grammar for server generation of set-cookie
>> values is clearly wrong because use of DQUOTE in cookie values is
>> common (roughly 10% of the values in my browser cookie store) and
>> previously defined, even if we consider DQUOTE to be part of the
>> value string.  Let's just change the generating grammar for value to
>> match how cookies are actually parsed and only exclude characters
>> that are known to cause failures.
> 
> The grammar is not used for parsing.  Parsing is defined in Section 5,
> not Section 4.

Parsing for user agents is defined in section 5.  Servers have to
parse cookies as well, and the grammar provided in section 4 is wrong
for both generation and parsing.

Why do you want to push forward a document with a known error in the
grammar?  Just fix it.

This is not a trivial detail.  As written, the specification says
server developers SHOULD break sites like amazon.com.

   cookie-value      = token / ""

The correct grammar is in the original Netscape cookie spec: "This
string is a sequence of characters excluding semi-colon, comma and
white space."  Which easily translates (conservatively) into

   cookie-value      = %x21-2B / %x2D-3A / %x3C-7E / %x80-FF

and it does not conflict with section 5.

....Roy