Please don't refer to some comment. Put all the relevant information into your Pull Request and also testing instructions so it can be tested.

This issue was mentioned by Victor Vogel at
http://joomlacode.org/gf/project/joomla/tracker/?action=TrackerItemEdit&tracker_item_id=33910&start=0
but has nothing to do with original issue there and is not a WAMP or XAMPP issue.

Test (XAMPP and/or online):

• Install staging package where https://github.com/joomla/joomla-cms/pull/3182/files is applied already
• Backend > Extensions > Install from URL
• Enter URL http://getk2.org/downloads/?f=K2_v2.6.8.zip

• Try to install ==> Error Unable to find install package

• Apply my PR ==> Installation works

• Tested with other URLs that already worked before. Still successfull installations.

Installation fails because of
[Content-Disposition] => attachment; filename=K2_v2.6.8.zip;
See semicolon at the end!

In tmp folder a file is created
K2_v2.6.8.zip;
See semicolon at the end!

So, JArchive::extract(...) fails because of unknown archive type zip;
See semicolon at the end!

Presence of semicolons in [Content-Disposition] was not discussed in #3182 , just quotes.

Thanks, I see now what you mean.

I wonder why getk2.org has a semicolon after the filename to begin with. Is that valid syntax according to RFCs? The examples I found all either quote the filename or just put the filename without any quotes. I didn't see an example ending the filename with a semicolon.

I just want to rule out it's not a bug in getk2.org itself.

The semicolon is a valid separator character in the syntax of Content-Disposition headers. As such, it should not be considered part of the filename.

See: http://tools.ietf.org/html/rfc6266

@chrisdavenport & @illovo Thanks for the explanations.

I could reproduce the problem using the webinstaller and trying to install K2. PR fixes the issue.
Also code looks fine.