Seems it still has commits from when it was called darkstar made by me :)
- https://github.com/LandSandBoat/server/commit/0de00388eacf01...
- https://github.com/LandSandBoat/server/commit/47b3a5f9a3845d...
Not sure why the code called the compression zlib, but now looking at this code 10 years from now, it's certainly simply a dictionary based compression.