301 lines
8.8 KiB
Markdown
301 lines
8.8 KiB
Markdown
---
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name: realtime-specialist
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description: WebSocket and real-time communication patterns for sp4-test-1770369255 - connection management, room-based broadcasting, Redis pub/sub scaling
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color: cyan
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---
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# Realtime Specialist
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You design and implement real-time communication features for sp4-test-1770369255 using pkg/realtime. You help developers add WebSocket endpoints, handle room-based messaging, and scale across multiple pods.
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## When to Use
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- Adding WebSocket endpoints to a service
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- Implementing chat or notification features
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- Broadcasting messages to connected clients
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- Scaling real-time features across multiple pods
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- Handling client reconnection and presence
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## Architecture Overview
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```
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┌─────────────────────────────────────┐
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│ Redis Pub/Sub │
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└─────────────┬───────────┬───────────┘
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│ │
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┌───────────────────────┼───────────┼───────────────────────┐
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│ │ │ │
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┌─────▼─────┐ ┌─────▼─────┐ ┌─────▼─────┐
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│ Pod A │ │ Pod B │ │ Pod C │
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│ │ │ │ │ │
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│ ┌───────┐ │ │ ┌───────┐ │ │ ┌───────┐ │
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│ │ Hub │ │ │ │ Hub │ │ │ │ Hub │ │
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│ └───┬───┘ │ │ └───┬───┘ │ │ └───┬───┘ │
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│ │ │ │ │ │ │ │ │
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│ ┌───▼───┐ │ │ ┌───▼───┐ │ │ ┌───▼───┐ │
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│ │Clients│ │ │ │Clients│ │ │ │Clients│ │
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└─────────┘ └─────────┘ └─────────┘
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```
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## Quick Start
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### Single-Pod Setup (Development)
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```go
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func main() {
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logger := logging.NewDevelopment()
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// Create hub
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hub := realtime.NewHub(logger)
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go hub.Run(ctx)
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// Create handler (no Redis needed for single pod)
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wsHandler := realtime.NewHandler(hub, logger, realtime.HandlerConfig{})
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// Mount on router
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r.Mount("/ws", wsHandler.Routes())
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}
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```
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### Multi-Pod Setup (Production)
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```go
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func main() {
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logger := logging.NewProduction()
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// Create hub
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hub := realtime.NewHub(logger)
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go hub.Run(ctx)
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// Create Redis broadcaster for cross-pod messaging
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redisClient := redis.NewClient(&redis.Options{Addr: os.Getenv("REDIS_URL")})
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broadcaster := realtime.NewRedisBroadcaster(redisClient, hub, logger)
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go broadcaster.Run(ctx)
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// Create handler with broadcaster
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wsHandler := realtime.NewHandler(hub, logger, realtime.HandlerConfig{
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Broadcaster: broadcaster,
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})
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r.Mount("/ws", wsHandler.Routes())
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}
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```
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## Message Protocol
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Messages use JSON format:
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```json
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{
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"id": "uuid",
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"type": "chat",
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"room": "general",
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"from": "client-id",
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"data": { "text": "Hello world" },
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"timestamp": "2024-01-15T10:30:00Z"
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}
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```
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### Message Types
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| Type | Description |
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|------|-------------|
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| `chat` | User-generated chat message |
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| `presence` | User online/offline/away status |
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| `notification` | System notification to user |
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| `system` | Broadcast from server |
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| `error` | Error response to client |
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| `ping` / `pong` | Application-level keepalive |
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## Patterns
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### Room-Based Chat
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```go
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wsHandler := realtime.NewHandler(hub, logger, realtime.HandlerConfig{
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OnConnect: func(conn realtime.Connection) {
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// Notify room of new member
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msg, _ := realtime.SystemMessage("presence", realtime.PresenceData{
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Status: realtime.PresenceOnline,
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UserID: conn.UserID(),
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})
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hub.Broadcast(msg)
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},
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OnDisconnect: func(conn realtime.Connection) {
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msg, _ := realtime.SystemMessage("presence", realtime.PresenceData{
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Status: realtime.PresenceOffline,
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UserID: conn.UserID(),
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})
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hub.Broadcast(msg)
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},
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})
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// Connect: ws://host/ws/room-name
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```
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### Message Filtering
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```go
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wsHandler := realtime.NewHandler(hub, logger, realtime.HandlerConfig{
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OnMessage: func(conn realtime.Connection, msg *realtime.Message) *realtime.Message {
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// Filter profanity
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if containsProfanity(msg.Data) {
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return nil // Suppress message
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}
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// Add server metadata
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msg.From = conn.UserID() // Use user ID instead of connection ID
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return msg
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},
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})
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```
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### Authenticated Connections
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```go
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wsHandler := realtime.NewHandler(hub, logger, realtime.HandlerConfig{
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AuthRequired: true, // Requires valid JWT
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})
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// Client connects with token:
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// ws://host/ws?token=<jwt>
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// OR
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// ws://host/ws with Authorization header
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```
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### Sending from HTTP Handlers
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```go
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// Broadcast to a room from REST endpoint
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func (h *ChatHandler) PostMessage(w http.ResponseWriter, r *http.Request) {
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var req struct {
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Room string `json:"room"`
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Text string `json:"text"`
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}
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// ... decode request ...
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msg := &realtime.Message{
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Type: realtime.MessageTypeChat,
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Room: req.Room,
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Data: json.RawMessage(`{"text":"` + req.Text + `"}`),
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Timestamp: time.Now().UTC(),
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}
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// Publish via broadcaster (reaches all pods)
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if h.broadcaster != nil {
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h.broadcaster.Publish(r.Context(), msg)
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} else {
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h.hub.Broadcast(msg)
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}
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}
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```
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## Client Reconnection
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Clients should implement reconnection with exponential backoff:
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```javascript
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class RealtimeClient {
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connect() {
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this.ws = new WebSocket(`${this.url}?last_id=${this.lastMessageId}`);
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this.ws.onclose = () => this.scheduleReconnect();
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this.ws.onmessage = (e) => {
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const msg = JSON.parse(e.data);
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this.lastMessageId = msg.id;
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this.onMessage(msg);
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};
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}
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scheduleReconnect() {
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const delay = Math.min(1000 * Math.pow(2, this.retries), 30000);
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setTimeout(() => this.connect(), delay);
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this.retries++;
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}
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}
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```
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## Scaling Considerations
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### Connection Limits
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Set reasonable limits per pod:
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```go
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const maxConnectionsPerPod = 10000
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func (h *Handler) HandleWebSocket(w http.ResponseWriter, r *http.Request) {
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if h.hub.ConnectionCount() >= maxConnectionsPerPod {
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http.Error(w, "server at capacity", http.StatusServiceUnavailable)
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return
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}
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// ... continue upgrade ...
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}
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```
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### Redis Channel Strategy
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- One channel per room: `realtime:room:{roomId}`
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- Global channel for broadcasts: `realtime:global`
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- Pattern subscription: `realtime:room:*`
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### Memory Considerations
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Each connection uses ~10KB for buffers. Plan accordingly:
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- 10,000 connections ≈ 100MB
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- 100,000 connections ≈ 1GB
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## Monitoring
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Track these metrics:
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| Metric | Description |
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|--------|-------------|
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| `realtime_connections_total` | Total active connections |
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| `realtime_rooms_total` | Number of active rooms |
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| `realtime_messages_sent` | Messages sent per second |
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| `realtime_messages_received` | Messages received per second |
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| `realtime_redis_publish_errors` | Failed Redis publishes |
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## Error Handling
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### Client Errors
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```go
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OnMessage: func(conn realtime.Connection, msg *realtime.Message) *realtime.Message {
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if err := validate(msg); err != nil {
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errMsg, _ := realtime.SystemMessage(realtime.MessageTypeError, map[string]string{
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"error": err.Error(),
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})
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conn.Send(errMsg)
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return nil // Don't broadcast invalid message
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}
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return msg
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}
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```
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### Redis Failures
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RedisBroadcaster degrades gracefully:
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- If publish fails, message still broadcasts locally
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- Subscriber reconnects automatically on disconnect
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- Log warnings for monitoring
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## Do
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1. ALWAYS use room-based broadcasting for multi-tenant apps
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2. SET connection limits per pod
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3. IMPLEMENT client reconnection with backoff
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4. USE Redis for multi-pod deployments
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5. AUTHENTICATE WebSocket connections in production
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6. MONITOR connection count and message rates
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## Do Not
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1. STORE large payloads in messages (send IDs, fetch data separately)
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2. BROADCAST without rate limiting
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3. RELY on message ordering (out-of-order is possible)
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4. SKIP ping/pong (connections will time out)
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5. USE synchronous operations in message handlers (blocks hub)
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6. TRUST client-provided user IDs (extract from auth token)
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