RegionIO

A Minecraft Java Edition server core written in Go, targeting version 26.1.2 (protocol 775). RegionIO implements the connection lifecycle (status → login → configuration → play), chunk streaming, block editing, and a vanilla-faithful overworld generator built on the real noise_router final_density tree.

Status

• Network: full handshake/status/login (offline mode)/configuration/play state machine with zlib compression, keep-alive, and chunk streaming.
• Registries: 28 synchronized registries + tags, captured verbatim from the 26.1.2 vanilla server and sent during configuration.
• World: in-memory chunk cache with memoized, compression-ready level_chunk_with_light frames; paletted block containers; heightmaps.
• Generation: bit-faithful overworld terrain from the embedded datapack (ImprovedNoise/PerlinNoise/BlendedNoise/NormalNoise + the density function interpreter), plus multi-noise biomes (per-chunk, surface layer) via the vanilla Climate finder over the official biome parameter table.
• Gameplay: creative block place/break, hotbar item→block mapping, chat, teleport ack, and a randomized bedrock floor / beach & gravel surface pass.

Build & run

go build ./...
go run ./cmd/regionio -seed 12345

The world seed defaults to 0; override it with the -seed flag or the REGIONIO_SEED environment variable. The server listens on 0.0.0.0:25565.

Testing

go test ./...

Parity tests (internal/world/vanilla_parity_test.go) compare generated surface heights against captures from the official server and skip when no capture is present.

Project layout

cmd/regionio/      entry point (config, listener, graceful shutdown)
internal/
  protocol/        wire primitives: VarInt, framing, compression, packet IDs
  nbt/             NBT encoder/decoder (with modified UTF-8)
  registry/        embedded synchronized registries + tags
  world/           chunk model, level_chunk encoder, cache, generators, biomes
  worldgen/        noise core + density-function interpreter + climate finder
  network/         per-connection state machine (handler/conn/play/login/...)
  server/          shared core: config, status response, profiles

Notes

The vanilla server.jar and its unpacked libraries//versions/ are not included (obtain them from Mojang). The embedded data under internal/ (registries, biome parameters, the overworld datapack) is derived from vanilla reports and is all that is required to build and run.