Wow, what an exciting topic! Move on quickly to the next one, unless you're interested!

Here's the problem: You've got a PHP download script on your site, and your customers are downloading ZIP files, but when they try to open the file, it says its corrupt!

You can't work it out, because the files are fine when you upload them, and the customer is actually downloading a file. You've tried every combination of "header.." in your PHP, and still it's rubbish...

I had this problem when I tried to get OsCommerce to include a Content-Length header so that the user would know how long the download would take.

The reason the problem occurred was because OsCommerce had gzip compression on, and for some reason when you combine this with a Content-Length header, it truncates the file.

Eg: a test.zip file of actual size 5388599 bytes would be downloaded as a file of 5388599 bytes if I didn't have a
header('Content-Length: '.filesize(etc...));
statement, or as a file of 5387710 bytes when I did! Both times the Content-Length header reported 5388599 bytes, the correct size.

The answer: get rid of the Content-Length header, or turn off gzip compression. In OsCommerce this is done in the admin / configuration / gzip compression panel. I've hard-coded it into the PHP so that I can have gzip for the rest of the site, and just not for downloads.

Hopefully MGBT's downloads will work again now...

=== Edit 2nd Feb 2011 ===

I've had this re-occuring, the hardcoded fix in my osCommerce files stopped working thanks to some change at my host, so now I've got these lines in the .htaccess file for my whole site, and they stop any downloads from osCommerce being gzipped:

# this stops download files being gzipped
SetEnvIfNoCase Request_URI catalog/download\.php$ no-gzip dont-vary

(make sure that second line starting "SetEnvIfNoCase" is all on one line)