Fix for Using addons wont allow players to connect #3359

[cwisniew]

Identify the Bug or Feature request

resolves #3359

Description of the Change

Fixes the problems where the add on wasn't always fetched from the server correctly, and the issue that was causing the asset to be created empty.

Possible Drawbacks

None foreseeable.

Documentation Notes

None required as this should allow addons to be used as already documented.

Release Notes

• Fixed an issue where using add-ons would cause problems for players trying to connect if they did not already have the add on.

---

This change is 

[kwvanderlinde]

A consequence of recognizing application/zip as Asset.Type.MTLIB is that I can now drag and drop other zip files into a campaign where previously I would be prevented from doing so. E.g., before this change, if I tried to drag a .mttable file onto a map, I would get this dialog:

But after this change I would just get a blank token with a broken image:

If this is deemed acceptable, then I am okay with this change. Otherwise a better approach may be to force the type of the asset that is passed to AddOnLibraryImporter.importFromAsset() rather than having the MTLIB type be auto-detected for all zip files.

[cwisniew]

I think the ability to drag those types of files onto the map but only get a red X and nothing further is done with them is going to be a source of confusion. I will have to update the fix as a suggested.

[cwisniew]

Fixed, sadly it wasn't an issue with AddonImport, (that already does the correct thing) the issue is with asset transfer at which point the client doesn't know what was sent it just knows something was sent so it tries to create an asset before saving it to the asset cache.

I have added the ability for the getMediaType() to check the contents of a zip file to see if it is an addon and only return MTLIB in that case. Since the file is not passed for the version used in the drag and drop code it will not allow you to drop a mtlib (or any zip file).

In the future this could be extended to support drag and drop of mtlib files importing an add on library (same goes for maps and tables I guess) but it is beyond the scope of this fix.

[kwvanderlinde]

Reviewed 1 of 2 files at r2, 3 of 3 files at r3, all commit messages.
Reviewable status: complete! all files reviewed, all discussions resolved (waiting on @cwisniew)