Server Overview

RabiRiichi.Server is an ASP.NET Core (net9.0) app that hosts the Core engine as a multiplayer service. It adds everything the headless engine deliberately leaves out: networking, rooms and seats, authentication, reconnection, AI substitution, and replays.

Architecture at a glance

The key ideas:

• One transport, gRPC-shaped. All traffic is Protobuf messages over a single /ws WebSocket. A WebSocketAdapter implements the gRPC streaming interfaces, so the connection/streaming code is transport-agnostic (a dormant gRPC endpoint exists but isn't mapped). See Transport & protocol.
• Single-writer concurrency. Nearly all room/user mutations run through one RoomTaskQueue (a bounded single-reader channel), giving lock-free-by- serialization semantics. Overload surfaces as a ResourceExhausted error.
• Durable connections. Each User owns a Connection that survives socket drops; a reconnect within a grace window resumes the same session, replays missed messages, and re-syncs game state.
• The engine bridge is ServerActionCenter, the server's IActionCenter. It serializes each event per seat (privacy-filtered), presents inquiries, and — for replays — captures a fully-revealed god-view stream.

The main pieces

Area	Files	Docs
Bootstrap / DI	Startup.cs	Running the server
Transport	WebSockets/, Connections/	Transport & protocol
Rooms & users	Models/	Rooms & users
Engine bridge	Connections/ServerActionCenter.cs	Transport, Replays
Replays	Services/ReplayStore.cs, ReplayCleanupService.cs	Replays
Auth	Auth/	Authentication
AI	Agents/	AI agents

Request lifecycle

1. A client opens /ws/public (anonymous) or /ws/connect (after a token handshake).
2. It sends a ClientMessageDto containing a ClientRequest (with a monotonic id).
3. The WebSocketController dispatches it on the RoomTaskQueue (HandlePublic / HandlePrivate).
4. The handler mutates room/user state or reads a replay, and returns a payload wrapped as a ServerMessageDto with respond_to = id so the client can correlate.
5. Server-initiated pushes (events, inquiries, room state, chat, heartbeats) flow as separate ServerMsg / EventMsg messages.

Read on: Transport & protocol.