Slime is a Minecraft world file format described by the Hypixel developers on one of their dev blogs. This format was originally designed to store SkyBlock player islands. As so, the main focus of this format is small worlds, guaranteeing a higher compression rate, and using less disk space than Minecraft's default Region file format.
This projects provides a CraftBukkit Slime chunk loader based on "in-memory" worlds, which don't use disk storage at all. This is extremely useful for minigame servers, where the maps tend to be small (they fit nicely in memory), and no world saving is needed.
You can download the Bukkit plugin from the Releases page.
First, let's convert a region file-based world to a .slime file. Download slime-tools, and run the following command
java -jar slime-tools.jar <world folder> [coords] <chunk radius>where [coords] is a comma-separated coordinate list (e.g. 0,0,0) that represents the center of the world, and <chunk radius> is the side length of the square region to convert.
Next, move the generated .slime file into your server's world directory (e.g. world/), and rename it to chunks.slime.
Finally, move the Slime plugin to the server's plugins/ directory, and start it up.
The SkyBlock Slime world (Download)
The plugin will only inject the custom chunk loader into world directories that contain a chunks.slime file, and will fallback to the default region file-based chunk loader.
Note the plugin also sets the Slime world's ChunkGenerator to an empty chunk generator, so all non-populated chunks will be empty.
As we modify several NMS methods, there are some caveats:
- World saving is not implemented. This means the changes you make to the Slime world will be deleted upon restart.
- As we inject plugin classes into Java's system class loader, reloading this plugin may result in undefined behavior.
The former is ideal for minigame servers since the server doesn't need to serialize the world to NBT, resulting in less CPU and memory usage.
We "inject" the custom chunk loader by providing a ServerNBTManager that overrides the createChunkLoader. This method returns a SlimeChunkLoader, which is where the main program logic lies.
When the server starts, this loader reads the Slime world file located at <world-dir>/chunks.slime and creates ProtoSlimeChunk instances, which contain the raw chunk information.
Whenever the chunk is requested by the server, this proto chunk is converted into a regular NMS Chunk, with all its entities, blocks, skylight information...
This approach was taken for two reasons:
- Instantiating NMS
Chunks on startup uses much more CPU and memory than proto chunks. These only store the strictly necessary info in primitives. - On the other hand, waiting for a chunk load request to read the Slime file is too slow. Instead, the file reading is performed during startup. Converting a proto chunk into a NMS
Chunkis really cheap, since the data is already in memory.
Once a chunk is loaded, it will be kept in memory until the server shuts down. Successive loads will return the cached chunk instead of performing the proto conversion.
There's limited available information about the Slime format, so some assumptions were made. For example, the blog post doesn't detail the storage structure of multiple(?) slime files. We assumed they all fit in a single file, <world-dir>/chunks.slime.
The provided slime-tools JAR contains a saving reference implementation, and seems to be for version 1, since it doesn't include entity information.
This project supports both version 1 and 3 (spec) of the format.
- The Hypixel team (Minikloon in particular) for creating this world format.
- The JUnit team for creating the JUnit 5 testing framework.
- The Byte Buddy project contributors for their code generation library.
- Noobcrew for creating the SkyBlock map (which we run tests against).
Contributions are more than welcome. This project hasn't been fully tested, so please feel free to fix bugs, add documentation, tests...
Note you will need to manually run BuildTools to install Spigot 1.8.8 locally.