Campus-25/static/Servers/Tachyon/README.md

Tachyon — voice server for an NGO/LiteNetLib client

A clean-room, protocol-compatible voice server (project name Tachyon) for the Rec Room client's in-room proximity voice. Same clean-room posture as the sibling LuxonServer, but a different, unrelated protocol: compatibility logic is derived from public MIT sources (NGO, the community LiteNetLib transport, LiteNetLib itself) and from black-box observation of network traffic. The stack, bottom-up, is Dissonance over NGO over the RecRoom encrypt layer over LiteNetLib.

Two real clients hear each other through it, in plaintext, with no client patch — and voice is scoped to rooms server-side.

Layout

• src/ + CMakeLists.txt — Tachyon (C++23). Dependency-light: the LiteNetLib transport comes from the vendor/LiteNetLibPP submodule, hashing from the official single-header xxHash in third_party/, and the recflare room lookup from libcurl.

• patches/ — 0001-tachyon-packet-layer-hook.patch, applied to the LiteNetLibPP submodule at configure time (adds the datagram-layer hook the RecRoom 0x11 marker needs). See patches/README.md.

• docs/ngo-litenetlib-wire.md — the wire specification. Read this first.

• docs/tachyon-findings.md — client static-analysis findings (the full Tachyon stack).

• docs/client-agent-request-*.md — questions to the client-side static-analysis agent.

• tools/decode_lnl.py — decoder for hex-dump captures of LiteNetLib traffic.

• traffic.txt — an early capture of the client failing to connect (see spec §7).

• vendor/litenetlib, vendor/ngo, vendor/mcc — upstream reference clones, git-ignored and not built against; re-create if you need to re-check the spec:

  mkdir -p vendor && cd vendor
  git clone --filter=blob:none https://github.com/Unity-Technologies/com.unity.netcode.gameobjects.git ngo
  git clone --filter=blob:none https://github.com/Unity-Technologies/multiplayer-community-contributions.git mcc
  git clone --filter=blob:none https://github.com/RevenantX/LiteNetLib.git litenetlib
  

(A C#/.NET reference implementation lived in reference/ earlier and proved the protocol end to end; it has been removed now that the C++ server is the product. Old commits still have it.)

Build & run

Needs CMake, a C++23 compiler, libcurl-devel (room lookup) and openssl-devel (blob decryption) — e.g. sudo dnf install libcurl-devel openssl-devel. vendor/LiteNetLibPP is a submodule, so clone with it:

git clone --recurse-submodules <repo>        # or: git submodule update --init --recursive
cmake -S . -B build -DCMAKE_BUILD_TYPE=Release
cmake --build build -j
./build/tachyon --config tachyon.conf         # or all-flags; fork+dissonance+0x11+rooms are defaults

Settings load from a key = value config file (--config, see tachyon.conf.example); CLI flags override it. The RSA private key that decrypts the client's wire blobs (AT/VB/CKA/CIA/CPK) is set via private_key in the config or --private-key <file> — a .NET RSAKeyValue XML file.

Offline self-test (no network): ./build/tachyon --selftest [batch.hex] — checks packing, batch build↔parse + hashes (fork & stock), and Dissonance primitives; exit 0 = pass. An optional captured NGO batch (hex) is fed through the parser.

Flags: --no-fork / --no-dissonance / --no-encrypt / --no-rooms / --room-url <u> / --room-timeout <ms> / --ds-count-width N, plus logging: -v/--verbose (debug: per-message + per-relay), -q/--quiet (warnings/errors only), --log-level error|warn|info|debug. The default is info — a startup banner plus connect/disconnect/handshake lifecycle and all warnings, quiet enough to run as a service. It logs to stdout (line-buffered) and shuts down cleanly on SIGINT/SIGTERM (exit 0), so a minimal systemd unit is just:

[Service]
ExecStart=/path/to/tachyon --port 7777 --quiet
Restart=on-failure

With --verbose, a connection walks through, in order: LiteNetLib connect accepted → ConnectionRequest parsed → ConnectionApproved sent → room resolved (account=… -> room=…) → Dissonance HandshakeResponse → ClientState roster relays → [relay] … delivered=1/1 when same-room clients talk.

Current status

Works end to end against the real client (build 20250718.01): LiteNetLib (ProtocolId 13) + RecRoom 0x11 marker + forked NGO batch + the Tachyon "Carrot" approval + the Dissonance session/relay, all plaintext. Same-room clients hear each other; cross-room is silent; room membership follows players live as they switch rooms (resolved per handshake from recflare).

Scope

Connection handshake, time sync, the Dissonance session handshake, voice relay (ServerRelay unwrap + per-client fan-out), and server-side room scoping. Rooms come from recflare (GET <room-url>?id=<AccountId> → room instance id — there is no room id on the wire); each room gets its own Dissonance session, and the relay/roster are scoped to same-room peers, with a lookup-failure fail-safe that isolates the client. There is no object replication, no NetworkVariable sync and no scene management — the client build does not contain those message types.