LIS 525 - MIME

It may be the MIME type and not the extension as such that tells the browser how to treat a downloaded file.

Netscape Navigator has its own set of associations for MIME types. If a MIME type lacks an association, the user gets a message asking what should be done with the file. For example, the FIMS intranet server associates the MIME type application/x-msaccess with Microsoft Access databases, but Navigator may not recognize this MIME type and, if you attempt to access an .mdb file with Navigator you may see a message like the following

Problems can arise if a provider uploads a file with an extension that does not have a MIME type association on the server (or has the wrong MIME type association). For example, the University's public server publish.uwo.ca lacks a MIME type association for the extension *.the. Instead, it applies the default type text/plain. So, if, in Navigator, you try to access http://publish.uwo.ca/~craven/523/craven.the, Navigator will display a page of strange characters, instead of prompting you for where to store a copy of the file.

Other browsers look at the extension and other file features to determine what to do with the file.

Firefox only allows you either to download the file or to cancel the request. In addition to these two choices, Opera and Internet Explorer also allow you to open the file and will call up the correct application to do so, after issuing a warning.

For more technical details on how IE determines MIME types, see:

MIME Types in Apache

In Apache, the MIME type for files with particular extensions can be set with the AddType directive. Syntax: AddType MIME-type extension [extension] ... For example,
AddType image/gif .gif
.

A default MIME type for other extensions can be set with the DefaultType directive. Syntax: DefaultType MIME-type.

Web Hosting Services and MIME Types

Few Web hosting services allow explicitly for customized MIME types, probably because only a few types of Web site need them and most browsers can deal with MIME type errors anyway.
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Last updated December 21, 2007.
This page maintained by Prof. Tim Craven
E-mail (text/plain only): craven@uwo.ca
Faculty of Information and Media Studies
University of Western Ontario,
London, Ontario
Canada, N6A 5B7