PlaneShift

I think many thing can be specified directly in skin definition file, though I am not sure whether it's possible for this. Anyway, I vote for splitting the files to say maximally 30MB parts so it will speed up the updates and lower bandwidth. That is for both meshes.zip and materials.zip

Indeed the solution of bdiff is a nice and elegant one, but it comes at a price: it's causing the update file to almost alwayws include, in effect, the entire materials.zip. The reason is that the zip structure changes the entire file whenever even the tiniest of changes has been made to the archive.

That means that even if you only change a file of 10 KB to an archive, the binary diff is unable to find a set of small changes and instead is forced to exchange the entire file. This is a major inefficiency in using zip (or, AFAICT, most somewhat advanced compressors) together with bdiff in this role. Since the material files are pretty likely to change in any given update, this leads to every single player having to download essentially the whole materials.zip with each update, likely draining significant bandwidth from the server as-is (160MB*100 players*10 updates/month=160GB/month), plus requiring the server to store all this theoretically redundant information because the updater must be able to bootstrap from any version to the current one (which is a really nice feature IMO).

I assume that because of the compression, there's no space-efficient archive format that keeps most of the file constant, so it might be necessary to use eg. tar alongside zip and bdiff. The resulting process would be:
- unzip the file, yielding a tar file
- apply binary diff to tar file
- zip the tar file

That way, the updater would still be (reasonably) independant on the compressor used (in that it would just be a program called and not intrinsic to the updater as it used to be), while reducing the required download size significantly.
The drawbacks of course would be
- extra code to handle the generic decompression
- the associated case-logic to support uncompressed files, and / or only do this for files specified in an extra "format" file
- the inability for players to use the simple (and ATM ubiquitous) zip format only
- the increased memory requirement for the temporary uncompressed file

The latter might be mostly compensated by decompressing to disk, since ATM the downloaded file also takes up lots of space on the drive.

Thus, even without caring about user-modifications (for which the aforementioned override folder would be the better anyway), the update process would benefit from smaller files.

Setting New

This patch loads all zip-files from the path "/planeshift/art/mods/", so it's not necessary to modify the "materials.zip" or other files from PS.
These files are loaded in alphabetic order. If there are e.g. double dds-files, the dds from the first zip-packet gets loaded.
The zip-packets must contain a "mod.xml" with the following content:
<xml>

  <mod_information>
      <name>NAME</name>
      <author>AUTHOR</author>
      <description>DESCRIPTION</description>
  </mod_information>
  <mount_path>MOUNT PATH</mount_path>

</xml>

Patch: http://pastebin.com/w0sVANKM

- There are no more corrupted files → saves bandwidth
- it's easy to handle with the modular zip-file strukture - > possible to deactivate mods fast

I think above patch deserves a separate task to clarify votes for each feature request.
Even though closely related, splitting the materials.zip is not exactly the same as providing better support for other mods than art/skins/

i'm not really planning to implement a feature to mod graphics. it goes under mesh mods to find items fast in a place

I am adding some missing icons into these huge files, like delta blades and so, but on every update it's "repaired" and I need to do it again. It could be good to be able to insert separate mod that would fix this until it will be fixed in the main zip file. Even I don't know why it's not already fixed while these icons was included just few versions ago.
About repair - I suggest to make pslaunch to download zip files into *.zip.download file first (i.e. meshes.zip.download) and after the file is fully downloaded, rename it into *.zip (meshes.zip in this example), it could save time and bandwidth by stopping the update and using the old file in these cases, when it's not needed.
When it's possible, where should I put the missing icons without adding them into the huge zip file?