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Message-ID: <88e286470807230542g36a81818yd1eaf8f7ece49b5c@mail.gmail.com>
Date: Wed, 23 Jul 2008 22:42:19 +1000
From: "Graham Dumpleton" <graham.dumple...@gmail.com>
To: modwsgi@googlegroups.com
Subject: Re: [modwsgi] wsgi.file_wrapper and range headers
In-Reply-To: <4505ad26-38f8-4ce8-a013-86c71c41d...@l64g2000hse.googlegroups.com>
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References: <4505ad26-38f8-4ce8-a013-86c71c41d...@l64g2000hse.googlegroups.com>

2008/7/23 Graham Carlyle <gra...@grahamcarlyle.com>:
>
> Hi
>
> I'm using django with mod_wsgi to dynamically serve some PDFs from a
> website. I'm patching django in order to utilise the file_wrapper
> speedup...
>
> http://code.djangoproject.com/ticket/7894
>
> So my question is .. how can i support range headers with the
> file_wrapper speedup? My tests suggest that the range header is being
> ignored with the whole file being returned.
>
> I'm trying to get this to work as it seems the Adobe Acrobat 7.0 PDF
> plug-in on Windows causes Firefox to fail downloading the PDF unless
> it can retrieve the file using range headers.
>
> I'm guessing that mod_wsgi isn't trying to support the range header
> and so I either have to deal with it in my webapp which seems a shame
> as apache already has the functionality, or I have to use something
> like a caching proxy infront of apache (say squid).

You would have to handle range headers yourself in application that is
just how WSGI is. That is, WSGI expects everything to be done in
application.

For it to work, just open file in 'rb' mode, seek to appropriate
position in file, set Content-Length for how much you want sent and
then wrap it in wsgi.file_wrapper and return it.

Note that mod_wsgi is however probably the only WSGI hosting mechanism
available which will actually look at the Content-Length returned for
wsgi.file_wrapper and only send that much of the file from the current
seek position. All other WSGI hosting adapters I have seen will just
return from current seek position to end of file. Thus the others
could return much more data than necessary and it would be up to
client to ignore what was returned in excess of the content length.

Even the FileWrapper example in WSGI PEP explaining what to use when
wsgi.file_wrapper isn't supported by WSGI adapter doesn't look at
Content-Length. Thus, if using FileWrapper to support other WSGI
adapters without wsgi.file_wrapper extension, you may want to modify
the FileWrapper example from WSGI PEP to honour Content-Length.

That all said, you may thus have problems adding this support in
Django if mod_wsgi which handles it properly.

Graham