Chat Room

Real-time chat with Phoenix Channels, where each room is a supervised QuickBEAM runtime.

Architecture

  Browser A ──┐                              ┌── Browser B
  (WebSocket) │                              │ (WebSocket)
              ▼                              ▼
        ┌──────────────────────────────────────┐
        │          Phoenix.Endpoint             │
        │   Socket → Channel ("room:general")   │
        └──────────────┬───────────────────────┘
                       │
          Phoenix.PubSub ("room:general")
                       │
        ┌──────────────▼───────────────────────┐
        │      DynamicSupervisor               │
        │  ┌──────────┐  ┌──────────┐          │
        │  │ Room      │  │ Room      │  ...    │
        │  │ "general" │  │ "random"  │         │
        │  │ (QuickBEAM│  │ (QuickBEAM│         │
        │  │  runtime) │  │  runtime) │         │
        │  └─────┬─────┘  └──────────┘         │
        └────────┼─────────────────────────────┘
                 │
        ┌────────▼─────────────────────────────┐
        │     QuickJS context                   │
        │  state.messages = [...]               │
        │  BroadcastChannel("chat")             │
        │     │                                 │
        │     └→ Beam.callSync("broadcast", msg)│
        │          → Phoenix.PubSub.broadcast!  │
        └──────────────────────────────────────┘

How it works

1. Room per runtime — each chat room is a QuickBEAM runtime registered via Registry, supervised by DynamicSupervisor. Created on first message (lazy).
2. JS manages state — message history lives in the JS context as a plain array. No external database.
3. BroadcastChannel → PubSub — when JS calls channel.postMessage(msg), the BroadcastChannel (backed by :pg) triggers a handler that calls Phoenix.PubSub.broadcast!. All subscribed Phoenix Channels push the message to their WebSocket clients.
4. Phoenix Channels — clients connect via WebSocket, join room:<id>, receive history on join, and get live updates via PubSub.
5. Crash recovery — kill a room's process and it's cleaned up (transient restart). Next message to that room starts a fresh runtime.

Run

mix deps.get
mix run run.exs

Open http://localhost:4000 in multiple browser tabs.

Test

mix test

Key features demonstrated

• Actor-per-entity — one QuickBEAM runtime per room via Registry + DynamicSupervisor
• BroadcastChannel → Phoenix.PubSub — JS broadcasts become real-time WebSocket pushes
• Phoenix Channels — standard Phoenix real-time integration
• Lazy creation — rooms start on first use, no pre-provisioning
• OTP supervision — rooms are supervised, crash recovery is automatic
• Zero database — state lives in JS memory (add persistence via Beam.call handlers if needed)