It must be noted that a file does not have an inherent "content-
type" per se. A file is a bunch of bytes, and has a name. When
you download a file from a Web server, the server infers a
content-type (such as "application/pdf") from whatever clues it
can find, mostly the so-called "extension" (the few letters at
the end of the file name; e.g. " .pdf" is assumed to indicate a
PDF file), and sometimes the file contents themselves: for
instance, when a Web server distributes an HTML file, it also
looks within the file header for a "meta" tag which would
override the default choice for Content-type, like this: <meta
http-equiv="content-type" content="text/html;charset=UTF-8" />
So you have two operations on your server: upload, and download.
Upload is mostly safe: the file comes, and is stored. Download
can be a worry: when an administrator will download a file, he
will do so by clicking on some link within a Web browser, and
the Web server will infer a content-type, as described above.
The Web browser will then u