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Re: Content-Disposition: *sender* advice

From: Julian Reschke <julian.reschke@gmx.de>
Date: Sat, 26 Feb 2011 12:12:23 +0100
Message-ID: <4D68E017.9050800@gmx.de>
To: HTTP Working Group <ietf-http-wg@w3.org>
On 25.02.2011 11:11, Julian Reschke wrote:
> On 24.02.2011 08:54, Julian Reschke wrote:
>> On 24.02.2011 06:39, Mark Nottingham wrote:
>>> I wouldn't say we break FireFox by recommending this ("breaking" means
>>> that C-D doesn't work at all, or produces garbage), and I wouldn't say
>>> they've been doing the right thing (because they implemented to prefer
>>> the non-internationalised filename).
>> When I said "break" I mean that sending a I18Nized filename will not
>> have the desired effect.
>> ...
> Looking at <https://bugzilla.mozilla.org/show_bug.cgi?id=588781#c21>,
> the fix will go into Firefox 5, which is planned to be 3 months behind
> Firefox 4.
> Optimally, this would be ~July 2011.
> On the other hand, to get to RFC we need
> - to do the IETF LC -> two weeks
> - get it through the IESG (I expect at least minimally one revision to
> be requested) -> ~ two months
> Once it's in the RFC publication queue, it'll take at least another six
> weeks... Which would be around the same time.
> Still, I'm very uncomfortable recommending something we're not sure will
> work when the RFC is published.
> ...

Ok, after lots of wordsmithing by Mark and myself we now have this:

-- snip --
Appendix D.  Advice on Generating Content-Disposition Header Fields

    To successfully interoperate with existing and future user agents,
    senders of the Content-Disposition header field are advised to:

    o  Include a 'filename' parameter when US-ASCII is sufficiently

    o  Use the 'token' form of the filename parameter only when it does
       not contain disallowed characters (e.g., spaces); in such cases,
       the quoted-string form should be used.

    o  Avoid including the percent character followed by two hexadecimal
       characters (e.g., %A9) in the filename parameter, since some
       existing implementations consider it to be an escape character,
       while others will pass it through unchanged.

    o  Avoid including the "\" character in the quoted-string form of the
       filename parameter, as escaping is not implemented by some user
       agents, and can be considered as an illegal path character.

    o  Avoid using non-ASCII characters in the filename parameter.
       Although most existing implementations will decode them as ISO-
       8859-1, some will apply heuristics to detect UTF-8, and thus might
       fail on certain names.

    o  Include a 'filename*' parameter where the desired filename cannot
       be expressed faithfully using the 'filename' form.  Note that
       legacy user agents will not process this, and will fall back to
       using the 'filename' parameter's content.

    o  When a 'filename*' parameter is sent, to also generate a
       'filename' parameter as a fallback for user agents that do not
       support the 'filename*' form, if possible.  This can be done by
       substituting characters with US-ASCII sequences (e.g., Unicode
       character point U+00E4 (LATIN SMALL LETTER A WITH DIARESIS) by
       "ae").  Note that this may not be possible in some locales.

    o  When a 'filename' parameter is included as a fallback (as per
       above), 'filename' should occur first, due to parsing problems in
       some existing implementations. [[fallbackbug: Firefox is known to
       pick the wrong parameter; a bug fix is scheduled for Firefox 5.

    o  Use UTF-8 as the encoding of the 'filename*' parameter, when
       present, because at least one existing implementation only
       implements that encoding.

    Note that this advice is based upon UA behaviour at the time of
    writing, and might be superseded.
    <http://purl.org/NET/http/content-disposition-tests> provides an
    overview of current levels of support in various implementations.
-- snip --

Where <http://purl.org/NET/http/content-disposition-tests> currently 
redirects to <http://greenbytes.de/tech/tc2231/>.

See <http://trac.tools.ietf.org/wg/httpbis/trac/changeset/1142>.

Best regards, Julian
Received on Saturday, 26 February 2011 11:13:11 UTC

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