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Re: line folding - ABNF vs prose

From: Roy T. Fielding <fielding@gbiv.com>
Date: Wed, 27 Jul 2011 08:20:58 -0700
Cc: Julian Reschke <julian.reschke@gmx.de>, HTTP Working Group <ietf-http-wg@w3.org>
Message-Id: <8128AD88-175B-42FB-85AF-3B42704E0355@gbiv.com>
To: Willy Tarreau <w@1wt.eu>
On Jul 27, 2011, at 7:59 AM, Willy Tarreau wrote:

> On Wed, Jul 27, 2011 at 04:19:16PM +0200, Julian Reschke wrote:
>> On 2011-07-27 16:07, Willy Tarreau wrote:
>>> Replacing with a single SP is harder than replacing with any number of
>>> spaces. For instance, haproxy replaces the CRLF with a comma followed
>>> by a space so that the line is folded without moving a memory block,
>>> and it works quite well.
>>> 
>>> Maybe the intention was to replace with a single SP but the result is
>>> still valid with multiple spaces, so maybe we should explicitly allow
>>> them ? Anyway good catch on this impact on the ABNF !
>>> ...
>> 
>> That might be ok betweek words (tokens/quoted-strings), but might be a 
>> problem inside quoted-string...
> 
> But I thought we were only allowed to fold lines for headers which are
> defined as comma-separated lists, and to add a comma. So by definition
> we should not do that on a header that is not a list, and since a header
> which is not a list must not appear multiple times, this should not be
> a problem.

No, (un)folding long field values has nothing to do with combining multiple
header fields of the same name into a single value.

In any case, I don't think we should worry about extra spaces breaking a
quoted string that has been folded on whitespace.  HTTP does not have
semantically meaningful long quoted strings and normal clients do not
perform any folding (only test or evil clients).  What is important is
that recipients do not treat a folded line as an empty line indicating
the end of headers.

....Roy
Received on Wednesday, 27 July 2011 15:21:31 GMT

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