[LRUG] IE headers and exporting data in CSV files

[Joel Chippindale]

Thanks for this, it's all very helpful, but as you say, it'll be down to a
bit of experimentation, I'll post the results when I get a chance.
J.

2009/8/4 Chris Mear <chrismear at gmail.com>

> It seems to be a workaround for this issue with IE failing to download
> filed specified via a Content-Disposition header, when the connection is
> made over HTTPS:
>
> http://support.microsoft.com/?kbid=323308
>
> The root of the issue seems to be that when IE downloads and then
> saves/launches a file, it downloads it to a temporary store first.
> Unfortunately, it appears to use the same store for ordinary caching and the
> temporary download scratch space, so if a "don't cache" regime is in effect
> (which it is by default on HTTPS, or because you've specified no caching in
> your HTTP headers), it doesn't write the file to disk (or quickly deletes it
> or something) and then can't find it when it tries to save (copy/move) it to
> the user's desired location.
>
> This incantation of headers looks like it works by using the Pragma header
> to allow *some kind* of disk caching in IE (i.e. it's not set to
> 'no-cache'), but at the same time setting a Cache-Control header that makes
> IE not *really* cache it -- I'm guessing just to make sure it actually hits
> the server and downloads new data if you revisit the URL.
>
> According to this MSDN blog post, the post-check=0 and pre-check=0 aren't
> strictly necessary:
>
>
> http://blogs.msdn.com/ieinternals/archive/2009/07/20/Using-post_2D00_check-and-pre_2D00_check-cache-directives.aspx
>
> that is, according to the specs -- who knows what the actual behaviour of
> the software is.
>
> A quick trawl through the MS KB turns up issues like this attached to IE 5
> and IE 6, but nothing specifically to IE 7 -- however, would be best to
> test.
>
> There's also some other Content-Disposition--related bugs in IE, to do with
> things like not setting the filename properly, or miss-guessing the content
> type (various versions of IE actually do magic number sniffing on the file
> content to check the content type, apparently as a security feature to stop
> people disguising executables as images or whatever), which you can turn up
> by searching the KB for IE articles containing 'Content-Disposition'. It may
> be that this incantation works around some of those as well.
>
> Chris
>
>
>
> On 4 Aug 2009, at 12:35, Joel Chippindale wrote:
>
>  I've seen the following hack for setting the headers for IE in Ruby on
>> Rails when serving CSV files all over the place (for example
>> http://vikasnandal.blogspot.com/2008/03/how-to-export-data-to-csv-in-ruby-on.html
>> ).
>>
>> However I've never seen an explanation as to why it might be needed.
>>
>> Can any of you knowledgeable LRUGers enlighten me as to what the problem
>> with IE that it is meant to resolve is and if so, which versions of IE it is
>> a problem with and finally what happens if you don't include do these IE
>> specific headers?
>>
>> #this is required if you want this to work with IE
>> if request.env['HTTP_USER_AGENT'] =~ /msie/i
>>  headers['Pragma'] = 'public'
>>  headers["Content-type"] = "text/plain"
>>  headers['Cache-Control'] = 'no-cache, must-revalidate, post-check=0,
>> pre-check=0'
>>  headers['Content-Disposition'] = "attachment; filename=\"#{filename}\""
>>  headers['Expires'] = "0"
>> else
>>  headers["Content-Type"] ||= 'text/csv'
>>  headers["Content-Disposition"] = "attachment; filename=\"#{filename}\""
>> end
>>
>> J.
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>>
>
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