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Old 09-29-2007, 11:24 AM   #1
Steve Rindsberg
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Default New extensions need new MIME types?

The new version of MS Office comes with some new file types/file extensions. I'm wondering whether that'll create new problems for web server administrators and users.

A user on another forum reported that when she opens a .PPTX (Office 2007/PowerPoint) file she created and saved on her own computer, all's well. But when she opens a file someone else sent her, Windows Exporer treats it as a ZIP file.

"Opens" might mean any of several things; we're trying to get her to give us specifics, and it may have nothing whatever to do with web sites/servers. Time will tell.

But one other member asked whether the files from someone else had been posted to a web site, thinking that the mime type may not have been correctly set for PPTX files.

Which got me wondering: what *would* happen if the web server doesn't know what a .PPTX file is. Would it just tell the browser "Beats me, man. Here. You figure it out."

And might the browser look for file signatures of some sort? Since PPTX files are, in fact, ZIP archives, it'd find a file sig for ZIP, in this case.

   
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Old 09-30-2007, 01:12 AM   #2
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Quote:
Originally Posted by Steve Rindsberg View Post
Which got me wondering: what *would* happen if the web server doesn't know what a .PPTX file is. Would it just tell the browser "Beats me, man. Here. You figure it out."
On the server one normally defines not only a list of specific mime types (a web server tends to come with a predefined list), but also a default. So if a file has an extension that's not in its list of defined mime types, the web server will serve it as the default type - which will create problems with many browsers. (The default is usually set to plain text.)

Internet Explorer, of course, ignores the mime type in the normal HTTP header completely and looks only at the extension to look that up in its own list of mime types in the Registry (at least that's where they are no Windows, I don't know what IE/Mac does). You can force it to use a mime type by setting a Content-disposition header, but that works for downloads only, not linked files.

This is not the case for things like linked stylesheets though, where IE derives the type from the type attribute in the link tag. Firefox does no such thing, and if a stylesheet is not served with the appropriate mime type, it will not "execute" it.

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Originally Posted by Steve Rindsberg
And might the browser look for file signatures of some sort? Since PPTX files are, in fact, ZIP archives, it'd find a file sig for ZIP, in this case.
I'm not aware of browsers doing that for all cases, though they must do it for image types in order to display them properly.

   
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Old 09-30-2007, 07:25 AM   #3
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Thanks ... that's all helpful to know.

But re the browser looking at file signatures:

>>I'm not aware of browsers doing that for all cases, though they must do it for image types in order to display them properly.

Ie, on systems that don't necessarily use extensions.

It'd be fun to cobble up a set of image, zip and other files with no extensions, wrong extensions and unknown extensions to see what browsers make of them. Send me a few hours and I'll get right on it.

   
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Old 09-30-2007, 11:05 AM   #4
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hour, hour, hour

That enough?

   
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Old 09-30-2007, 07:32 PM   #5
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Well ... enough for a start. And with already interesting results:

http://www.rdpslides.com/browsertests/

Opera treats the extensionless files as text but MSIE6 must be doing some file sniffing ... it displays JPGs and PNGs with or without extension.

   
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Old 10-01-2007, 01:38 AM   #6
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IE5 also clearly does some sniffing, but obviously only for "web images", in your samples that's only JPG and PNG. Interestingly, this version of IE has limited support for PNG in that it will dislpay one if it's teh src of an img element, but as a "bare" link (in which case you'll get a download prompt); this behavior is extended to your extension-less samples. PCX (with or without extension) is shown as text, TGA (with or without extension) results in a blank page.

Firefox also shows only the "web formats" (JPG and PNG); PCX and TGA are shown as text; all "extension-less" links result in text.

BTW, this behavior also demonstrates that you have no content management on your server; with content management, a file can be sepcified without an extension, buit teh server then lokos at what format the browser prefers and serves that (for instance GIF in preference to PNG). If this happens, normal browsers would then look at the Content-Type HTTP header to see what they're actually getting, while IE (I think) would do its sniffing thing - but for both, an extension-less image would still result in an actual image being shown, if the server can find a type matching the browser's preference.

   
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Old 10-01-2007, 03:21 AM   #7
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I get the same results as Marjolein using Konqueror in Linux. Only the png and jpg with extension display as images. A touch disappointing really given that Linux traditionally doesn't link file types to extensions - I had hoped Konqueror would sniff out the mime type.

Presumably Safari should exhibit similar behaviour as it's based on Konqueror.

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Old 10-01-2007, 06:12 AM   #8
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Quote:
Originally Posted by Steve Rindsberg View Post
Well ... enough for a start. And with already interesting results:

http://www.rdpslides.com/browsertests/

Opera treats the extensionless files as text but MSIE6 must be doing some file sniffing ... it displays JPGs and PNGs with or without extension.
From a Mac:

Safari 2.0.4 was disappointing, saw only the jpg and png with extensions; those two without extension appeared as text (full of question marks too). The two unfamiliar formats (pcx and tga) showed absolutely blank pages.

With Firefox 2.0.0.7 and Netscape Nav 2.0b3, I got something from all of them. Only the jpg and png with extensions appeared, however. Without, I got a couple of lines of text. All the others showed a full screen of text.

   
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Old 10-01-2007, 07:52 AM   #9
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Default GIF as a Web Site Format?

What about GIF as a web site format?

This Compuserve image format was in use before the Internet became a public service.
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Old 10-01-2007, 08:12 AM   #10
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What about GIF as a web site format?

This Compuserve image format was in use before the Internet became a public service.
I suppose you mean the World Wide Web - CompuServe was using the Internet long before "PPP" was a "secret" service and shortly after you could connect to the WWW.

   
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