When users try to download a Zip file from Moodle using Internet Explorer, the file is truncated. WinZip and Windows XP's internal zip-processing algorithms both complain that the file is corrupted. Please see the following course to reproduce the error:

http://elearning.lse.ac.uk/moodle-1.7/mod/resource/index.php?id=2

Log in as a guest. The enrolment key is 'testkey'. Try to download "test.zip", which should be 7,397 bytes. The size after downloading from IE is 7,334 bytes. I can reproduce the error using IE6 SP2 (6.0.2900.2180.xpsp_sp2_gdr_050301-1519) and IE 7.

A workaround exists, where the teacher can add "?forcedownload=true" after the filename. This is not ideal: we don't really want to be reminding our users to do this every time they upload a zip.

I have created a patch for lib/filelib.php which will set $forcedownload to true if the mimetype is 'application/zip'. It fixes the problem, and I haven't seen any adverse effects on other browsers. Please find it attached, and let me know if you find anything wrong.

Chris