add real-time infrastructure (#137)

* setup infra for pusher service

* setup client sdk for pusher service

* fix: ping parse failure

* fix: send pong back to client

avoid disconnections every 2.5 minutes

* increase replicas

* feat: show presence and compose indicator

go/internal/pusher/server.go

@@ -0,0 +1,90 @@
+package pusher
+
+import (
+	"context"
+	"log/slog"
+	"net/http"
+
+	"github.com/flowy-live/llink/genproto/llink/pusher"
+	"github.com/flowy-live/llink/internal/auth"
+	"github.com/google/uuid"
+	"nhooyr.io/websocket"
+)
+
+// Server handles WebSocket upgrades and gRPC presence queries.
+type Server struct {
+	pbpusher.UnimplementedPusherServiceServer
+
+	hub     *Hub
+	bridge  *RedisBridge
+	authSvc auth.AuthService
+}
+
+// NewServer creates a new pusher server.
+func NewServer(hub *Hub, bridge *RedisBridge, authSvc auth.AuthService) *Server {
+	return &Server{
+		hub:     hub,
+		bridge:  bridge,
+		authSvc: authSvc,
+	}
+}
+
+// HandleWebSocket handles the WebSocket upgrade and connection lifecycle.
+func (s *Server) HandleWebSocket(w http.ResponseWriter, r *http.Request) {
+	// Authenticate via query param (WebSocket upgrade can't use custom headers)
+	token := r.URL.Query().Get("token")
+	if token == "" {
+		http.Error(w, "token required", http.StatusUnauthorized)
+		return
+	}
+
+	session, err := s.authSvc.GetSession(r.Context(), token)
+	if err != nil {
+		http.Error(w, "unauthorized", http.StatusUnauthorized)
+		return
+	}
+
+	// Accept WebSocket upgrade
+	ws, err := websocket.Accept(w, r, &websocket.AcceptOptions{
+		// Allow all origins for now — CORS is handled at the gateway level
+		InsecureSkipVerify: true,
+	})
+	if err != nil {
+		slog.Error("websocket accept failed", "error", err)
+		return
+	}
+
+	connID := uuid.New().String()
+	conn := newConn(connID, session.HumanId, ws)
+
+	slog.Info("websocket connected", "connId", connID, "humanId", session.HumanId)
+
+	ctx, cancel := context.WithCancel(r.Context())
+	defer cancel()
+
+	// WritePump runs in a separate goroutine
+	go conn.WritePump(ctx)
+
+	// ReadPump blocks until the connection closes
+	conn.ReadPump(ctx, s.hub)
+
+	slog.Info("websocket disconnected", "connId", connID, "humanId", session.HumanId)
+}
+
+// BulkGetPresence implements the gRPC PusherService.
+func (s *Server) BulkGetPresence(ctx context.Context, req *pbpusher.BulkGetPresenceRequest) (*pbpusher.BulkGetPresenceResponse, error) {
+	presence, err := s.bridge.GetPresence(ctx, req.ChannelIds)
+	if err != nil {
+		return nil, err
+	}
+
+	resp := &pbpusher.BulkGetPresenceResponse{
+		Presences: make(map[string]*pbpusher.ChannelPresence, len(presence)),
+	}
+	for chID, humanIDs := range presence {
+		resp.Presences[chID] = &pbpusher.ChannelPresence{
+			HumanIds: humanIDs,
+		}
+	}
+	return resp, nil
+}