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Re: header parsing, trailing OWS

From: Adrien de Croy <adrien@qbik.com>
Date: Thu, 08 Oct 2009 11:47:38 +1300
Message-ID: <4ACD1A8A.1070005@qbik.com>
To: David Morris <dwm@xpasc.com>
CC: Julian Reschke <julian.reschke@gmx.de>, ietf-http-wg@w3.org

Actually point b needs to be a MUST as well, since if it didn't remove 
the OWS when forwarding the message, it would be breaching a.


Adrien de Croy wrote:
>
> I think it must always be possible for an agent to remove the OWS 
> without breaking the meaning of the header.  We can't really allow a 
> situation where the OWS has some meaning, or is relied on, since that 
> then breaks all manner of things (e.g. such as comparison of selecting 
> headers for caches).
>
> If we take that to its logical conclusion there should be
>
> a) a MUST level requirement for implementations to not generate 
> extraneous OWS
> b) a SHOULD level requirement for intermediaries to remove extraneous OWS
> c) a requirement for caches and clients to remove OWS when using 
> headers - hard to tell whether should be SHOULD or MUST.
>
> regards
>
> Adrien
>
>
> David Morris wrote:
>>
>>
>> On Wed, 7 Oct 2009, Julian Reschke wrote:
>>> David Morris wrote:
>>>> On Thu, 24 Sep 2009, Julian Reschke wrote:
>>>>
>>>>> In the current edits, the last 'MAY' is a 'SHOULD', which makes it 
>>>>> read
>>>>>
>>>>> "A field value MAY be preceded by optional whitespace (OWS); a 
>>>>> single SP is preferred. The field value does not include any 
>>>>> leading or trailing white space: OWS occurring before the first 
>>>>> non-whitespace character of the field value or after the last 
>>>>> non-whitespace character of the field value is ignored and SHOULD 
>>>>> be removed without changing the meaning of the header field."
>>>>
>>>>
>>>> Doesn't read smoothly .... and infact turns into a directive rather 
>>>> than a permission.
>>>>
>>>> One alternate to illustrate my point ...
>>>>    "SHOULD be removed" --> "SHOULD be able to"
>>>> another ... replace the remainder after "the field value is ignored 
>>>> and"
>>>> with:
>>>>     "removing OWS before or after the field value SHOULD NOT change 
>>>> the
>>>>      meaning of the header field."
>>>
>>> I think we should just say:
>>>
>>> "OWS occurring before the first non-whitespace character of the 
>>> field value or after the last non-whitespace character of the field 
>>> value is ignored and can be removed without changing the meaning of 
>>> the header field."
>>>
>>> ...replacing the MAY in draft 07, and the SHOULD in the current 
>>> edits, by "can". RFC2119 terminology is not needed here.
>>
>> It seems to me that by not being more explicit, we harm 
>> interoperability.
>>
>> It seems obvious to me with your last proposal, that removing excess 
>> whitespace before interpreting a value is the only sensible 
>> interpretation, but I've seen enough sloppy coding to believe, that 
>> the proposed wording would be interpreted as one can ignore the 
>> existance of excess white space and use the value, white space and 
>> all in some comparison. Thus I'm in favor of as strong a wording as 
>> we can use at this stage of the progression to standard to say that 
>> excess white space MUST be removed for interpreting the value.
>>
>> Perhaps introduce the notion of canonical form for headers and values 
>> and require conversion to canonical form before processing the values 
>> in any context where the outcome would be different based on the 
>> existance of extraneous white space. Including (but not limited to) 
>> computation of a digest of header values, interptreting values, etc.
>>
>> Dave Morris
>>
>

-- 
Adrien de Croy - WinGate Proxy Server - http://www.wingate.com
Received on Wednesday, 7 October 2009 22:44:21 GMT

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