fix(pico): use O(1) session indexing and harden websocket concurrency handling (#1970)

* perf(pico): implement O(1) session lookup for pico connections

- Replace `sync.Map` with `connections` and `sessionConnections`.
- Add `addConnection`, `removeConnection`, `sessionConnectionsSnapshot`, and `takeAllConnections` with `connsMu` for concurrency.
- `broadcastToSession` now dispatches directly to `sessionConnections`.
- Add `newUniqueConnID` to avoid UUID collision/overwrites.
- Ensure `Stop` and `readLoop` use the new helpers for safe cleanup and correct `connCount` updates.

* refactor(pico): replace addConnection with createAndAddConnection for atomic connID generation

* refactor(pico): clear connections in one time to improve perf

Co-authored-by: Copilot <175728472+Copilot@users.noreply.github.com>

* fix(pico): keep connCount consistent with connection indexes

* refactor(pico): make connCount a regular int guarded by connsMu

* fix(pico): enforce MaxConnections atomically on registration

* fix(pico): use temporary over-limit error and remove conn counter

---------

Co-authored-by: Copilot <175728472+Copilot@users.noreply.github.com>

pkg/channels/pico/pico.go

@@ -56,8 +56,9 @@ type PicoChannel struct {
 	*channels.BaseChannel
 	config             config.PicoConfig
 	upgrader           websocket.Upgrader
-	connections sync.Map // connID → *picoConn
+	connections        map[string]*picoConn            // connID -> *picoConn
-	connCount   atomic.Int32
+	sessionConnections map[string]map[string]*picoConn // sessionID -> connID -> *picoConn
+	connsMu            sync.RWMutex
 	ctx                context.Context
 	cancel             context.CancelFunc
 }
@@ -92,9 +93,104 @@ func NewPicoChannel(cfg config.PicoConfig, messageBus *bus.MessageBus) (*PicoCha
 			ReadBufferSize:  1024,
 			WriteBufferSize: 1024,
 		},
+		connections:        make(map[string]*picoConn),
+		sessionConnections: make(map[string]map[string]*picoConn),
 	}, nil
 }
 
+// createAndAddConnection checks MaxConnections and registers a connection atomically.
+func (c *PicoChannel) createAndAddConnection(conn *websocket.Conn, sessionID string, maxConns int) (*picoConn, error) {
+	c.connsMu.Lock()
+	defer c.connsMu.Unlock()
+	if len(c.connections) >= maxConns {
+		return nil, channels.ErrTemporary
+	}
+
+	var connID string
+	for {
+		connID = uuid.New().String()
+		if _, exists := c.connections[connID]; !exists {
+			break
+		}
+	}
+
+	pc := &picoConn{
+		id:        connID,
+		conn:      conn,
+		sessionID: sessionID,
+	}
+
+	c.connections[pc.id] = pc
+	bySession, ok := c.sessionConnections[pc.sessionID]
+	if !ok {
+		bySession = make(map[string]*picoConn)
+		c.sessionConnections[pc.sessionID] = bySession
+	}
+	bySession[pc.id] = pc
+
+	return pc, nil
+}
+
+// removeConnection deletes a connection from indexes and returns it when found.
+func (c *PicoChannel) removeConnection(connID string) *picoConn {
+	c.connsMu.Lock()
+	defer c.connsMu.Unlock()
+
+	pc, ok := c.connections[connID]
+	if !ok {
+		return nil
+	}
+
+	delete(c.connections, connID)
+	if bySession, ok := c.sessionConnections[pc.sessionID]; ok {
+		delete(bySession, connID)
+		if len(bySession) == 0 {
+			delete(c.sessionConnections, pc.sessionID)
+		}
+	}
+
+	return pc
+}
+
+// takeAllConnections snapshots and clears all connection indexes.
+func (c *PicoChannel) takeAllConnections() []*picoConn {
+	c.connsMu.Lock()
+	defer c.connsMu.Unlock()
+
+	all := make([]*picoConn, 0, len(c.connections))
+	for _, pc := range c.connections {
+		all = append(all, pc)
+	}
+	clear(c.connections)
+	clear(c.sessionConnections)
+
+	return all
+}
+
+// sessionConnectionsSnapshot returns all active connections for a session.
+func (c *PicoChannel) sessionConnectionsSnapshot(sessionID string) []*picoConn {
+	c.connsMu.RLock()
+	defer c.connsMu.RUnlock()
+
+	bySession, ok := c.sessionConnections[sessionID]
+	if !ok || len(bySession) == 0 {
+		return nil
+	}
+
+	conns := make([]*picoConn, 0, len(bySession))
+	for _, pc := range bySession {
+		conns = append(conns, pc)
+	}
+	return conns
+}
+
+// currentConnCount returns a lock-protected snapshot of active connection count.
+func (c *PicoChannel) currentConnCount() int {
+	c.connsMu.RLock()
+	defer c.connsMu.RUnlock()
+	return len(c.connections)
+}
+
 // Start implements Channel.
 func (c *PicoChannel) Start(ctx context.Context) error {
 	logger.InfoC("pico", "Starting Pico Protocol channel")
@@ -110,13 +206,9 @@ func (c *PicoChannel) Stop(ctx context.Context) error {
 	c.SetRunning(false)
 
 	// Close all connections
-	c.connections.Range(func(key, value any) bool {
+	for _, pc := range c.takeAllConnections() {
-		if pc, ok := value.(*picoConn); ok {
 		pc.close()
 	}
-		c.connections.Delete(key)
-		return true
-	})
 
 	if c.cancel != nil {
 		c.cancel()
@@ -133,8 +225,8 @@ func (c *PicoChannel) WebhookPath() string { return "/pico/" }
 func (c *PicoChannel) ServeHTTP(w http.ResponseWriter, r *http.Request) {
 	path := strings.TrimPrefix(r.URL.Path, "/pico")
 
-	switch {
+	switch path {
-	case path == "/ws" || path == "/ws/":
+	case "/ws", "/ws/":
 		c.handleWebSocket(w, r)
 	default:
 		http.NotFound(w, r)
@@ -208,12 +300,7 @@ func (c *PicoChannel) broadcastToSession(chatID string, msg PicoMessage) error {
 	msg.SessionID = sessionID
 
 	var sent bool
-	c.connections.Range(func(key, value any) bool {
+	for _, pc := range c.sessionConnectionsSnapshot(sessionID) {
-		pc, ok := value.(*picoConn)
-		if !ok {
-			return true
-		}
-		if pc.sessionID == sessionID {
 		if err := pc.writeJSON(msg); err != nil {
 			logger.DebugCF("pico", "Write to connection failed", map[string]any{
 				"conn_id": pc.id,
@@ -223,8 +310,6 @@ func (c *PicoChannel) broadcastToSession(chatID string, msg PicoMessage) error {
 			sent = true
 		}
 	}
-		return true
-	})
 
 	if !sent {
 		return fmt.Errorf("no active connections for session %s: %w", sessionID, channels.ErrSendFailed)
@@ -250,7 +335,7 @@ func (c *PicoChannel) handleWebSocket(w http.ResponseWriter, r *http.Request) {
 	if maxConns <= 0 {
 		maxConns = 100
 	}
-	if int(c.connCount.Load()) >= maxConns {
+	if c.currentConnCount() >= maxConns {
 		http.Error(w, "too many connections", http.StatusServiceUnavailable)
 		return
 	}
@@ -275,15 +360,17 @@ func (c *PicoChannel) handleWebSocket(w http.ResponseWriter, r *http.Request) {
 		sessionID = uuid.New().String()
 	}
 
-	pc := &picoConn{
+	pc, err := c.createAndAddConnection(conn, sessionID, maxConns)
-		id:        uuid.New().String(),
+	if err != nil {
-		conn:      conn,
+		_ = conn.WriteControl(
-		sessionID: sessionID,
+			websocket.CloseMessage,
+			websocket.FormatCloseMessage(websocket.CloseTryAgainLater, "too many connections"),
+			time.Now().Add(2*time.Second),
+		)
+		_ = conn.Close()
+		return
 	}
 
-	c.connections.Store(pc.id, pc)
-	c.connCount.Add(1)
-
 	logger.InfoCF("pico", "WebSocket client connected", map[string]any{
 		"conn_id":    pc.id,
 		"session_id": sessionID,
@@ -341,12 +428,12 @@ func (c *PicoChannel) matchedSubprotocol(r *http.Request) string {
 func (c *PicoChannel) readLoop(pc *picoConn) {
 	defer func() {
 		pc.close()
-		c.connections.Delete(pc.id)
+		if removed := c.removeConnection(pc.id); removed != nil {
-		c.connCount.Add(-1)
 			logger.InfoCF("pico", "WebSocket client disconnected", map[string]any{
-			"conn_id":    pc.id,
+				"conn_id":    removed.id,
-			"session_id": pc.sessionID,
+				"session_id": removed.sessionID,
 			})
+		}
 	}()
 
 	readTimeout := time.Duration(c.config.ReadTimeout) * time.Second

pkg/channels/pico/pico_test.go

@@ -0,0 +1,144 @@
+package pico
+
+import (
+	"context"
+	"errors"
+	"fmt"
+	"sync"
+	"testing"
+
+	"github.com/sipeed/picoclaw/pkg/bus"
+	"github.com/sipeed/picoclaw/pkg/channels"
+	"github.com/sipeed/picoclaw/pkg/config"
+)
+
+func newTestPicoChannel(t *testing.T) *PicoChannel {
+	t.Helper()
+
+	cfg := config.PicoConfig{}
+	cfg.SetToken("test-token")
+	ch, err := NewPicoChannel(cfg, bus.NewMessageBus())
+	if err != nil {
+		t.Fatalf("NewPicoChannel: %v", err)
+	}
+
+	ch.ctx = context.Background()
+	return ch
+}
+
+func TestCreateAndAddConnection_RespectsMaxConnectionsConcurrently(t *testing.T) {
+	ch := newTestPicoChannel(t)
+
+	const (
+		maxConns   = 5
+		goroutines = 64
+		sessionID  = "session-a"
+	)
+
+	var wg sync.WaitGroup
+	var mu sync.Mutex
+	successCount := 0
+	errCount := 0
+
+	wg.Add(goroutines)
+	for i := 0; i < goroutines; i++ {
+		go func() {
+			defer wg.Done()
+
+			pc, err := ch.createAndAddConnection(nil, sessionID, maxConns)
+			mu.Lock()
+			defer mu.Unlock()
+
+			if err == nil {
+				successCount++
+				if pc == nil {
+					t.Errorf("pc is nil on success")
+				}
+				return
+			}
+			if !errors.Is(err, channels.ErrTemporary) {
+				t.Errorf("unexpected error: %v", err)
+				return
+			}
+			errCount++
+		}()
+	}
+	wg.Wait()
+
+	if successCount > maxConns {
+		t.Fatalf("successCount=%d > maxConns=%d", successCount, maxConns)
+	}
+	if successCount+errCount != goroutines {
+		t.Fatalf("success=%d err=%d total=%d want=%d", successCount, errCount, successCount+errCount, goroutines)
+	}
+	if got := ch.currentConnCount(); got != maxConns {
+		t.Fatalf("currentConnCount=%d want=%d", got, maxConns)
+	}
+}
+
+func TestRemoveConnection_CleansBothIndexes(t *testing.T) {
+	ch := newTestPicoChannel(t)
+
+	pc, err := ch.createAndAddConnection(nil, "session-cleanup", 10)
+	if err != nil {
+		t.Fatalf("createAndAddConnection: %v", err)
+	}
+
+	removed := ch.removeConnection(pc.id)
+	if removed == nil {
+		t.Fatal("removeConnection returned nil")
+	}
+
+	ch.connsMu.RLock()
+	defer ch.connsMu.RUnlock()
+
+	if _, ok := ch.connections[pc.id]; ok {
+		t.Fatalf("connID %s still exists in connections", pc.id)
+	}
+	if _, ok := ch.sessionConnections[pc.sessionID]; ok {
+		t.Fatalf("session %s still exists in sessionConnections", pc.sessionID)
+	}
+	if got := len(ch.connections); got != 0 {
+		t.Fatalf("len(connections)=%d want=0", got)
+	}
+}
+
+func TestBroadcastToSession_TargetsOnlyRequestedSession(t *testing.T) {
+	ch := newTestPicoChannel(t)
+
+	target := &picoConn{id: "target", sessionID: "s-target"}
+	target.closed.Store(true)
+	ch.addConnForTest(target)
+
+	other := &picoConn{id: "other", sessionID: "s-other"}
+	ch.addConnForTest(other)
+
+	err := ch.broadcastToSession("pico:s-target", newMessage(TypeMessageCreate, map[string]any{"content": "hello"}))
+	if err == nil {
+		t.Fatal("expected send failure due to closed target connection")
+	}
+	if !errors.Is(err, channels.ErrSendFailed) {
+		t.Fatalf("expected ErrSendFailed, got %v", err)
+	}
+}
+
+func (c *PicoChannel) addConnForTest(pc *picoConn) {
+	c.connsMu.Lock()
+	defer c.connsMu.Unlock()
+	if c.connections == nil {
+		c.connections = make(map[string]*picoConn)
+	}
+	if c.sessionConnections == nil {
+		c.sessionConnections = make(map[string]map[string]*picoConn)
+	}
+	if _, exists := c.connections[pc.id]; exists {
+		panic(fmt.Sprintf("duplicate conn id in test: %s", pc.id))
+	}
+	c.connections[pc.id] = pc
+	bySession, ok := c.sessionConnections[pc.sessionID]
+	if !ok {
+		bySession = make(map[string]*picoConn)
+		c.sessionConnections[pc.sessionID] = bySession
+	}
+	bySession[pc.id] = pc
+}