bot/docs/concepts/architecture.md

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WebSocket gateway architecture, components, and client flows	Working on gateway protocol, clients, or transports	Gateway Architecture

Gateway architecture

Last updated: 2026-01-22

Overview

• A single long‑lived Gateway owns all messaging surfaces (WhatsApp via Baileys, Telegram via grammY, Slack, Discord, Signal, iMessage, WebChat).
• Control-plane clients (macOS app, CLI, web UI, automations) connect to the Gateway over WebSocket on the configured bind host (default 127.0.0.1:18789).
• Nodes (macOS/iOS/Android/headless) also connect over WebSocket, but declare role: node with explicit caps/commands.
• One Gateway per host; it is the only place that opens a WhatsApp session.
• The canvas host is served by the Gateway HTTP server under:
  • /__bot__/canvas/ (agent-editable HTML/CSS/JS)
  • /__bot__/a2ui/ (A2UI host) It uses the same port as the Gateway (default 18789).

Components and flows

Gateway (daemon)

• Maintains provider connections.
• Exposes a typed WS API (requests, responses, server‑push events).
• Validates inbound frames against JSON Schema.
• Emits events like agent, chat, presence, health, heartbeat, cron.

Clients (mac app / CLI / web admin)

• One WS connection per client.
• Send requests (health, status, send, agent, system-presence).
• Subscribe to events (tick, agent, presence, shutdown).

Nodes (macOS / iOS / Android / headless)

• Connect to the same WS server with role: node.
• Provide a device identity in connect; pairing is device‑based (role node) and approval lives in the device pairing store.
• Expose commands like canvas.*, camera.*, screen.record, location.get.

Protocol details:

• Gateway protocol

WebChat

• Static UI that uses the Gateway WS API for chat history and sends.
• In remote setups, connects through the same SSH/Tailscale tunnel as other clients.

Connection lifecycle (single client)

sequenceDiagram
    participant Client
    participant Gateway

    Client->>Gateway: req:connect
    Gateway-->>Client: res (ok)
    Note right of Gateway: or res error + close
    Note left of Client: payload=hello-ok<br>snapshot: presence + health

    Gateway-->>Client: event:presence
    Gateway-->>Client: event:tick

    Client->>Gateway: req:agent
    Gateway-->>Client: res:agent<br>ack {runId, status:"accepted"}
    Gateway-->>Client: event:agent<br>(streaming)
    Gateway-->>Client: res:agent<br>final {runId, status, summary}

Wire protocol (summary)

• Transport: WebSocket, text frames with JSON payloads.
• First frame must be connect.
• After handshake:
  • Requests: {type:"req", id, method, params} → {type:"res", id, ok, payload|error}
  • Events: {type:"event", event, payload, seq?, stateVersion?}
• If BOT_GATEWAY_TOKEN (or --token) is set, connect.params.auth.token must match or the socket closes.
• Idempotency keys are required for side‑effecting methods (send, agent) to safely retry; the server keeps a short‑lived dedupe cache.
• Nodes must include role: "node" plus caps/commands/permissions in connect.

Pairing + local trust

• All WS clients (operators + nodes) include a device identity on connect.
• New device IDs require pairing approval; the Gateway issues a device token for subsequent connects.
• Local connects (loopback or the gateway host’s own tailnet address) can be auto‑approved to keep same‑host UX smooth.
• All connects must sign the connect.challenge nonce.
• Signature payload v3 also binds platform + deviceFamily; the gateway pins paired metadata on reconnect and requires repair pairing for metadata changes.
• Non‑local connects still require explicit approval.
• Gateway auth (gateway.auth.*) still applies to all connections, local or remote.

Details: Gateway protocol, Pairing, Security.

Protocol typing and codegen

• TypeBox schemas define the protocol.
• JSON Schema is generated from those schemas.
• Swift models are generated from the JSON Schema.

Remote access

• Preferred: Tailscale or VPN.

• Alternative: SSH tunnel

  ssh -N -L 18789:127.0.0.1:18789 user@host
  

• The same handshake + auth token apply over the tunnel.

• TLS + optional pinning can be enabled for WS in remote setups.

Operations snapshot

• Start: hanzo-bot gateway (foreground, logs to stdout).
• Health: health over WS (also included in hello-ok).
• Supervision: launchd/systemd for auto‑restart.

Invariants

• Exactly one Gateway controls a single Baileys session per host.
• Handshake is mandatory; any non‑JSON or non‑connect first frame is a hard close.
• Events are not replayed; clients must refresh on gaps.