Track QUIC fabric stream capacity

agents/rap-node-agent/internal/mesh/fabric_quic_transport.go

@@ -17,10 +17,12 @@ import (
 
 const fabricQUICNextProto = "rap-fabric-data-session-v1"
 const defaultQUICFabricConnIdleTTL = 5 * time.Minute
+const defaultQUICFabricMaxStreamsPerConn = 64
 
 type QUICFabricTransport struct {
 	Config            *quic.Config
 	IdleTTL           time.Duration
+	MaxStreamsPerConn int
 	mu                sync.Mutex
 	conns             map[string]*quicFabricConnEntry
 	stats             QUICFabricTransportStats
@@ -33,11 +35,15 @@ type QUICFabricTransportStats struct {
 	ClosedEvicted      uint64 `json:"closed_evicted"`
 	CloseAllCalls      uint64 `json:"close_all_calls"`
 	IdleEvicted        uint64 `json:"idle_evicted"`
+	StreamOpens        uint64 `json:"stream_opens"`
+	StreamCloses       uint64 `json:"stream_closes"`
+	StreamLimitRejects uint64 `json:"stream_limit_rejects"`
 }
 
 type QUICFabricTransportSnapshot struct {
 	SchemaVersion string                   `json:"schema_version"`
 	ActiveCount   int                      `json:"active_count"`
+	ActiveStreams int                      `json:"active_streams"`
 	Stats         QUICFabricTransportStats `json:"stats"`
 }
 
@@ -52,15 +58,18 @@ type quicFabricSession struct {
 	maxPayload int
 	timeout    time.Duration
 	closeConn  bool
+	transport  *QUICFabricTransport
+	connKey    string
 }
 
 type quicFabricConnEntry struct {
 	conn          *quic.Conn
 	lastUsed      time.Time
+	activeStreams int
 }
 
 func NewQUICFabricTransport(config *quic.Config) *QUICFabricTransport {
-	return &QUICFabricTransport{Config: config, IdleTTL: defaultQUICFabricConnIdleTTL, conns: map[string]*quicFabricConnEntry{}}
+	return &QUICFabricTransport{Config: config, IdleTTL: defaultQUICFabricConnIdleTTL, MaxStreamsPerConn: defaultQUICFabricMaxStreamsPerConn, conns: map[string]*quicFabricConnEntry{}}
 }
 
 func quicTLSConfigForTarget(target FabricTransportTarget) *tls.Config {
@@ -105,12 +114,16 @@ func (t *QUICFabricTransport) Connect(ctx context.Context, target FabricTranspor
 			tlsConfig.NextProtos = []string{fabricQUICNextProto}
 		}
 	}
-	conn, closeConn, err := t.connectConn(ctx, target, tlsConfig)
+	conn, connKey, closeConn, err := t.connectConn(ctx, target, tlsConfig)
 	if err != nil {
 		return nil, err
 	}
+	if err := t.reserveStream(connKey, conn); err != nil {
+		return nil, err
+	}
 	stream, err := conn.OpenStreamSync(ctx)
 	if err != nil {
+		t.releaseStream(connKey)
 		t.evictConn(target, conn)
 		if closeConn {
 			_ = conn.CloseWithError(1, "open stream failed")
@@ -138,20 +151,22 @@ func (t *QUICFabricTransport) Connect(ctx context.Context, target FabricTranspor
 		maxPayload: maxPayload,
 		timeout:    target.Timeout,
 		closeConn:  closeConn,
+		transport:  t,
+		connKey:    connKey,
 	}
 	go session.readLoop(context.Background())
 	return session, nil
 }
 
-func (t *QUICFabricTransport) connectConn(ctx context.Context, target FabricTransportTarget, tlsConfig *tls.Config) (*quic.Conn, bool, error) {
+func (t *QUICFabricTransport) connectConn(ctx context.Context, target FabricTransportTarget, tlsConfig *tls.Config) (*quic.Conn, string, bool, error) {
 	if t == nil {
 		conn, err := quic.DialAddr(ctx, target.Endpoint, tlsConfig, nil)
-		return conn, true, err
+		return conn, "", true, err
 	}
 	key := quicFabricConnKey(target)
 	if key == "" {
 		conn, err := quic.DialAddr(ctx, target.Endpoint, tlsConfig, t.Config)
-		return conn, true, err
+		return conn, "", true, err
 	}
 	t.mu.Lock()
 	t.pruneIdleLocked(time.Now())
@@ -164,7 +179,7 @@ func (t *QUICFabricTransport) connectConn(ctx context.Context, target FabricTran
 			entry.lastUsed = time.Now()
 			t.stats.Reuses++
 			t.mu.Unlock()
-			return entry.conn, false, nil
+			return entry.conn, key, false, nil
 		}
 	}
 	t.mu.Unlock()
@@ -174,7 +189,7 @@ func (t *QUICFabricTransport) connectConn(ctx context.Context, target FabricTran
 		t.mu.Lock()
 		t.stats.OpenFailures++
 		t.mu.Unlock()
-		return nil, false, err
+		return nil, "", false, err
 	}
 	t.mu.Lock()
 	t.pruneIdleLocked(time.Now())
@@ -188,7 +203,7 @@ func (t *QUICFabricTransport) connectConn(ctx context.Context, target FabricTran
 			t.stats.Reuses++
 			t.mu.Unlock()
 			_ = conn.CloseWithError(0, "duplicate connection")
-			return existing.conn, false, nil
+			return existing.conn, key, false, nil
 		}
 	}
 	if t.conns == nil {
@@ -197,7 +212,46 @@ func (t *QUICFabricTransport) connectConn(ctx context.Context, target FabricTran
 	t.conns[key] = &quicFabricConnEntry{conn: conn, lastUsed: time.Now()}
 	t.stats.Opens++
 	t.mu.Unlock()
-	return conn, false, nil
+	return conn, key, false, nil
+}
+
+func (t *QUICFabricTransport) reserveStream(key string, conn *quic.Conn) error {
+	if t == nil || key == "" {
+		return nil
+	}
+	t.mu.Lock()
+	defer t.mu.Unlock()
+	entry := t.conns[key]
+	if entry == nil || entry.conn != conn {
+		return fmt.Errorf("quic fabric connection is not cached")
+	}
+	limit := t.MaxStreamsPerConn
+	if limit <= 0 {
+		limit = defaultQUICFabricMaxStreamsPerConn
+	}
+	if entry.activeStreams >= limit {
+		t.stats.StreamLimitRejects++
+		return fmt.Errorf("quic fabric stream limit reached")
+	}
+	entry.activeStreams++
+	entry.lastUsed = time.Now()
+	t.stats.StreamOpens++
+	return nil
+}
+
+func (t *QUICFabricTransport) releaseStream(key string) {
+	if t == nil || key == "" {
+		return
+	}
+	t.mu.Lock()
+	if entry := t.conns[key]; entry != nil {
+		if entry.activeStreams > 0 {
+			entry.activeStreams--
+		}
+		entry.lastUsed = time.Now()
+		t.stats.StreamCloses++
+	}
+	t.mu.Unlock()
 }
 
 func (t *QUICFabricTransport) evictConn(target FabricTransportTarget, conn *quic.Conn) {
@@ -230,6 +284,9 @@ func (t *QUICFabricTransport) pruneIdleLocked(now time.Time) {
 			continue
 		}
 		if !entry.lastUsed.IsZero() && now.Sub(entry.lastUsed) > ttl {
+			if entry.activeStreams > 0 {
+				continue
+			}
 			_ = entry.conn.CloseWithError(0, "idle")
 			delete(t.conns, key)
 			t.stats.IdleEvicted++
@@ -285,6 +342,7 @@ func (t *QUICFabricTransport) Snapshot() QUICFabricTransportSnapshot {
 			snapshot.Stats.ClosedEvicted++
 		default:
 			snapshot.ActiveCount++
+			snapshot.ActiveStreams += entry.activeStreams
 		}
 	}
 	return snapshot
@@ -329,6 +387,9 @@ func (s *quicFabricSession) Close() error {
 		if s.stream != nil {
 			err = s.stream.Close()
 		}
+		if s.transport != nil {
+			s.transport.releaseStream(s.connKey)
+		}
 		if s.conn != nil {
 			if s.closeConn {
 				_ = s.conn.CloseWithError(0, "closed")

agents/rap-node-agent/internal/mesh/fabric_quic_transport_test.go

@@ -224,7 +224,9 @@ func TestQUICFabricTransportPrunesIdleConnections(t *testing.T) {
 	if err != nil {
 		t.Fatalf("connect: %v", err)
 	}
-	defer session.Close()
+	if err := session.Close(); err != nil {
+		t.Fatalf("close session: %v", err)
+	}
 	time.Sleep(time.Millisecond)
 
 	snapshot := transport.Snapshot()
@@ -233,6 +235,51 @@ func TestQUICFabricTransportPrunesIdleConnections(t *testing.T) {
 	}
 }
 
+func TestQUICFabricTransportLimitsStreamsPerConnection(t *testing.T) {
+	server, err := StartQUICFabricServer(context.Background(), QUICFabricServerConfig{
+		ListenAddr: "127.0.0.1:0",
+		TLSConfig:  testQUICTLSConfig(t),
+	})
+	if err != nil {
+		t.Fatalf("start quic fabric server: %v", err)
+	}
+	defer server.Close()
+
+	ctx, cancel := context.WithTimeout(context.Background(), 3*time.Second)
+	defer cancel()
+	transport := NewQUICFabricTransport(nil)
+	transport.MaxStreamsPerConn = 1
+	defer transport.Close()
+	target := FabricTransportTarget{
+		PeerID:   "node-b",
+		Endpoint: server.Addr().String(),
+		TLSConfig: &tls.Config{
+			InsecureSkipVerify: true,
+			NextProtos:         []string{fabricQUICNextProto},
+		},
+		Timeout: time.Second,
+	}
+	first, err := transport.Connect(ctx, target)
+	if err != nil {
+		t.Fatalf("first connect: %v", err)
+	}
+	if _, err := transport.Connect(ctx, target); err == nil {
+		t.Fatal("second connect succeeded past stream limit")
+	}
+	snapshot := transport.Snapshot()
+	if snapshot.ActiveStreams != 1 || snapshot.Stats.StreamLimitRejects != 1 {
+		t.Fatalf("unexpected stream limit snapshot: %+v", snapshot)
+	}
+	if err := first.Close(); err != nil {
+		t.Fatalf("close first stream: %v", err)
+	}
+	second, err := transport.Connect(ctx, target)
+	if err != nil {
+		t.Fatalf("connect after release: %v", err)
+	}
+	defer second.Close()
+}
+
 func TestQUICFabricServerHandlesFabricFrames(t *testing.T) {
 	var events []FabricSessionEventLogEntry
 	server, err := StartQUICFabricServer(context.Background(), QUICFabricServerConfig{

docs/architecture/DISTRIBUTED_FABRIC_NODE_PROTOCOL_PLAN.md

@@ -361,6 +361,9 @@ opens logical fabric-session streams on top, with heartbeat telemetry for QUIC
 connection opens, reuses, evictions, and active count.
 Cached QUIC connections are pruned by idle TTL, preventing long-running agents
 from holding unused peer connections indefinitely.
+QUIC carrier connections now track active logical streams and enforce a
+per-connection stream limit, exposing stream opens/closes and limit rejects in
+transport telemetry.
 
 Deliverables: