RustNotMC

A survival game built on a Minecraft 1.12.2 client as the rendering platform, with its own server, its own protocol and its own accounts.

Repositories

Repository	License	What lives there
rsx-client	MIT	Loader, mod API, client hooks, deobfuscation tools
rsx-protocol	MIT	Wire format, packet schemas, shared simulation library
rsx-plugin-api	MIT	Interfaces for server-side content
rsx-server-core	proprietary	Tick loop, world, entities, scaling
rsx-auth	proprietary	Accounts, tokens, revocation

Target

Base platform is Minecraft 1.12.2, forked into our own source tree so the game is moddable from the start rather than patched from outside.

• game fork: Java 17, compiled by game-fork\scripts\prepare-game.ps1
• loader and mod API: Java 17
• mods: Java only

Capacity target is 200 players on 4 cores and 8 GB of RAM, scaling to 500 on larger hardware.

The fork

The client is not wrapped around the game jar. game-fork rebuilds it from the verified vanilla jar into readable source, and the loader is an ordinary part of that game rather than an agent injected into someone else's process.

vanilla client-1.12.2.jar   verified Mojang signature
  -> mcp-1.12.2-srg.zip    3344 classes, 20817 members
  -> merge with MCP CSVs   9991 fields, 18715 methods renamed
  -> SpecialSource          3310 classes in MCP names
  -> FernFlower            2050 source files
  -> hand patches + rules   114 patches, one regex rule
  -> javac                  3268 classes, clean

prepare-game.ps1 runs the whole thing and is idempotent. Hand fixes live in game-fork\patches\decompiler-fixes.txt and are re-applied on every run, so regenerating the tree never loses them.

Compiling clean proves nothing. Decompilation quietly breaks code that still compiles, still has the right methods and still runs: an entity that compares itself with itself never leaves the ground, a list indexed by entity id removes the wrong player. Every patch here was checked against the original bytecode with javap, and tools\javap_diff.py is the tool that makes that comparison usable. The self-comparison finder and the remove-by-index finder both came out of this class of bug.

The fork holds Mojang-derived code and is not published. What ships in the open repository is the loader, the mod API and the build tools.

Modding

Mods are jars with a descriptor at META-INF/rsxmod.properties:

id=rsxm-demo
name=RustNotMC Demo
version=1.1.0
env=CLIENT
entrypoint=net.rustnotmc.demo.DemoMod
access=hud,commands,files
depends.core=>=1.0

env is CLIENT, SERVER or BOTH. The loader runs on the client today; the field exists so a mod that targets both sides does not need a format change when the loader moves to the server.

Each mod gets its own class loader. Load order comes from the dependency graph, not from filenames. Shutdown runs in reverse.

What a mod may touch

A client mod changes what the client shows. It never decides what is true about the world: the server owns the world, the inventory, the player and the network. Capabilities are only granted when something actually checks them.

Capability	Grants	Checked
CORE	lifecycle, logging, own mod directory	always
HUD	draw overlays through the game's font	granted from descriptor
INPUT	read keyboard and mouse state	granted from descriptor
COMMANDS	register commands the player can type	granted from descriptor
FILES	a directory of its own under run/mods/<id>	granted from descriptor
REFLECTION	reach into game internals	never automatic, operator consent

WORLD, PLAYER, NETWORK, TEXT, INPUT and COMMAND were removed: they were advertised but not enforced, so a descriptor could claim them and receive nothing. A capability that cannot be granted is worse than an absent one.

Commands carry a scope. CLIENT commands run on the client and are never sent anywhere. SERVER and BOTH commands are registered but deliberately not executed on the client, because the server is what has to see them and decide.

The client API contains no game types at all, which is what lets the loader build and test with the game closed: the SPI is implemented on the game side and the API never depends on it. tick() advances on the client's own tick, not on frames, so a mod counts the same twenty steps a second at 60 fps and at 240.

Building

rsx-client\scripts\build.ps1           # dist\rsx-loader.jar
rsx-client\scripts\test.ps1            # self test, 128 checks
game-fork\scripts\prepare-game.ps1     # rebuild the fork from the vanilla jar
game-fork\scripts\compile-game.ps1     # compile only, fast iteration
rsx-client\scripts\run-game.ps1        # launch the client

Only a JDK is required. No Gradle, no network once the mappings are cached.

Assets

The client will not run without a real asset tree, and the launcher on this machine keeps assets the modern way: indexes/1.12.json pointing at objects/<aa>/<sha1>. A 1.12.2 client reads neither. It wants <assetsDir>/minecraft/<path>.

Pointing --assetsDir straight at the object store does not look broken. Text and textures come from the jar, so the game looks complete, but every sound has been an asset since 1.7.3 and none of them are on disk: the sound engine starts, play() is called, nothing is found, and paulscode says nothing. tools\materialize_assets.py lays the tree out and run-game.ps1 calls it on every launch, so this cannot be forgotten again.

Tools

Script	Purpose
rsx-client\tools\merge_srg_mcp.py	vanilla SRG plus MCP CSVs into one obf to MCP SRG
rsx-client\tools\apply_patches.py	re-applies the hand fixes, fails loudly if one misses
rsx-client\tools\add_patch.py	appends a reviewed patch to the fix file
rsx-client\tools\fix_stale_locals.py	FernFlower's stale local references, scoped per method
rsx-client\tools\fix_generic_casts.py	inserts the cast where a generic loses its type parameter
rsx-client\tools\fix_decompiler_rules.py	systematic rewrites that would be hundreds of patches
rsx-client\tools\show_errors.py	javac errors next to the source line that caused them
rsx-client\tools\struct_diff.py	class-by-class comparison against the reference, plus orphan analysis
rsx-client\tools\javap_diff.py	instruction-level comparison, normalising constant pool and offsets
rsx-client\tools\find_self_comparisons.py	finds x == x, the decompiler's signature bug
rsx-client\tools\find_remove_index_bugs.py	finds List<Integer>.remove(int) where an object was meant
rsx-client\tools\find_callers.py	who calls a field or method, via the constant pool
rsx-client\tools\materialize_assets.py	lays the asset tree out from the index and object store
rsx-client\tools\ogg_duration.py	real length of an ogg, to tell a short file from a cut-off one
rsx-client\tools\stage_run.py	writes the runtime classpath
rsx-client\tools\fetch_missing.py	pulls natives into the local run directory

Legal

Minecraft is a trademark of Mojang Studios. This project is not affiliated with or endorsed by Mojang or Microsoft. Game assets are not redistributed here.