bareiron

Minimalist Minecraft server for memory-restrictive embedded systems.

The goal of this project is to enable hosting Minecraft servers on very weak devices, such as the ESP32. The project's priorities are, in order: memory usage, performance, and features. Because of this, compliance with vanilla Minecraft is not guaranteed, nor is it a goal of the project.

• Minecraft version: 1.21.8
• Protocol version: 772

[!WARNING] Currently, only the vanilla client is officially supported. Issues have been reported when using Fabric or similar.

Quick start

For PC x86_64 platforms, grab the latest build binary (https://github.com/p2r3/bareiron/releases/download/latest/bareiron.exe) and run it. The file is a Cosmopolitan polyglot (https://github.com/jart/cosmopolitan), which means it'll run on Windows, Linux, and possibly Mac, despite the file extension. Note that the server's default settings cannot be reconfigured without compiling from source.

For microcontrollers, see the section on compilation below.

Compilation

Before compiling, you'll need to dump registry data from a vanilla Minecraft server. On Linux, this can be done automatically using the extract_registries.sh script. Otherwise, the manual process is as follows: create a folder called notchian here, and put a Minecraft server JAR in it. Then, follow this guide (https://minecraft.wiki/w/Minecraft_Wiki:Projects/wiki.vg_merge/Data_Generators) to dump all of the registries (use the second command with the --all flag). Finally, run build_registries.js with either bun (https://bun.sh/), node (https://nodejs.org/en/download), or deno (https://docs.deno.com/runtime/getting_started/installation/).

• To compile on Linux, install gcc and run ./build.sh.
• For compiling on Windows, there are a few options:
  • To compile a native Windows binary: install MSYS2 (https://www.msys2.org/) and open the "MSYS2 MINGW64" shell. From there, run pacman -Sy mingw-w64-x86_64-gcc, navigate to this project's directory, and run ./build.sh.
  • To compile a native 32-bit binary (compatible with Windows 95/98, but why would you ever want that), use the same steps above, except with pacman -Sy mingw-w64-cross-gcc and ./build.sh --9x.
  • To compile a MSYS2-linked binary: install MSYS2 (https://www.msys2.org/), and open the "MSYS2 MSYS" shell. From there, install gcc (run pacman -Sy gcc), navigate to this project's directory and run ./build.sh.
  • To compile and run a Linux binary from Windows: install WSL, and from there install gcc and run ./build.sh in this project's directory.
• To target an ESP variant, set up a PlatformIO project (select the ESP-IDF framework, not Arduino) and clone this repository on top of it. See Configuration below for further steps. For better performance, consider changing the clock speed and enabling compiler optimizations. If you don't know how to do this, there are plenty of resources online.

Configuration

Configuring the server requires compiling it from its source code as described in the section above.

Most user-friendly configuration options are available in include/globals.h, including WiFi credentials for embedded setups. Some other details, like the MOTD or starting time of day, can be found in src/globals.c. For everything else, you'll have to dig through the code.

Here's a summary of some of the more important yet less trivial options for those who plan to use this on a real microcontroller with real players:

• Depending on the player count, the performance of the MCU, and the bandwidth of your network, player position broadcasting could potentially throttle your connection. If you find this to be the case, try commenting out BROADCAST_ALL_MOVEMENT and SCALE_MOVEMENT_UPDATES_TO_PLAYER_COUNT. This will tie movement to the tickrate. If this change makes movement too choppy, you can decrease TIME_BETWEEN_TICKS at the cost of more compute.
• If you experience crashes or instability related to chests or water, those features can be disabled with ALLOW_CHESTS and DO_FLUID_FLOW, respectively.
• If you find frequent repeated chunk generation to choke the server, increasing VISITED_HISTORY might help. There isn't that much of a memory footprint for this - increasing it to 64 for example would only take up 240 extra bytes per allocated player.

Non-volatile storage (optional)

This section applies to those who target ESP variants and wish to persist world data after a shutdown. This is not necessary on PC platforms, as world and player data is written to world.bin by default.

The simplest way to accomplish this is to set up LittleFS in PlatformIO and comment out the #ifndef surrounding SYNC_WORLD_TO_DISK in globals.h. Since flash writes are typically slow and blocking, you'll likely want to uncomment DISK_SYNC_BLOCKS_ON_INTERVAL. Depending on the flash size of your board, you may also have to decrease MAX_BLOCK_CHANGES, so that the world data fits in your LittleFS partition.

If using an SD card module or other virtual file system, you'll have to implement the filesystem setup routine on your own. The built-in serializer should still work though, as it uses POSIX filesystem calls.

Alternatively, if you can't set up a file system, you can dump and upload world data over TCP. This can be enabled by uncommenting DEV_ENABLE_BEEF_DUMPS in globals.h. Note: this system implements no security or authentication. With this option enabled, anyone with access to the server can upload arbitrary world data.

Contribution

• Create issues and discuss with the maintainer(s) before making pull requests. Even for small changes.
• Follow the existing code style. Ensure that your changes fit in with the surrounding code, even if you disagree with the style. Pull requests with inconsistent style will be nitpicked.
• Test your code before creating a pull request or requesting a review, regardless of how "simple" your change is. It's a basic form of respect towards the maintainer and reviewer.
• Development tooling and compilation improvements are not welcome, unless you've worked with the codebase long enough to have noticed practical shortcomings in that area. Adding a single compiler flag is not a meaningful first contribution.
• For information on the Minecraft server protocol, refer to the wiki (https://minecraft.wiki/w/Java_Edition_protocol/Packets). For everything else, use a search engine (https://google.com).