use a ringbuffer to store received packets in the connection (#4928)

Reduces memory usage by replacing a fixed-capacity channel (256) with a
ring buffer (initial capacity: 8). The buffer grows to 256 only when
many packets are enqueued.

connection.go

@@ -19,6 +19,7 @@ import (
 	"github.com/quic-go/quic-go/internal/protocol"
 	"github.com/quic-go/quic-go/internal/qerr"
 	"github.com/quic-go/quic-go/internal/utils"
+	"github.com/quic-go/quic-go/internal/utils/ringbuffer"
 	"github.com/quic-go/quic-go/internal/wire"
 	"github.com/quic-go/quic-go/logging"
 )
@@ -154,8 +155,10 @@ type connection struct {
 	oneRTTStream        *cryptoStream // only set for the server
 	cryptoStreamHandler cryptoStreamHandler
 
-	receivedPackets  chan receivedPacket
-	sendingScheduled chan struct{}
+	notifyReceivedPacket chan struct{}
+	sendingScheduled     chan struct{}
+	receivedPacketMx     sync.Mutex
+	receivedPackets      ringbuffer.RingBuffer[receivedPacket]
 
 	// closeChan is used to notify the run loop that it should terminate
 	closeChan chan struct{}
@@ -478,7 +481,8 @@ func (s *connection) preSetup() {
 		s.perspective,
 	)
 	s.framer = newFramer(s.connFlowController)
-	s.receivedPackets = make(chan receivedPacket, protocol.MaxConnUnprocessedPackets)
+	s.receivedPackets.Init(8)
+	s.notifyReceivedPacket = make(chan struct{}, 1)
 	s.closeChan = make(chan struct{}, 1)
 	s.sendingScheduled = make(chan struct{}, 1)
 	s.handshakeCompleteChan = make(chan struct{})
@@ -496,18 +500,14 @@ func (s *connection) run() (err error) {
 	defer func() { s.ctxCancel(err) }()
 
 	defer func() {
-		// Drain queued packets that will never be processed.
-		for {
-			select {
-			case p, ok := <-s.receivedPackets:
-				if !ok {
-					return
-				}
-				p.buffer.Decrement()
-				p.buffer.MaybeRelease()
-			default:
-				return
-			}
+		// drain queued packets that will never be processed
+		s.receivedPacketMx.Lock()
+		defer s.receivedPacketMx.Unlock()
+
+		for !s.receivedPackets.Empty() {
+			p := s.receivedPackets.PopFront()
+			p.buffer.Decrement()
+			p.buffer.MaybeRelease()
 		}
 	}()
 
@@ -574,8 +574,8 @@ runLoop:
 				// We do all the interesting stuff after the switch statement, so
 				// nothing to see here.
 			case <-sendQueueAvailable:
-			case firstPacket := <-s.receivedPackets:
-				wasProcessed, err := s.handlePackets(firstPacket)
+			case <-s.notifyReceivedPacket:
+				wasProcessed, err := s.handlePackets()
 				if err != nil {
 					s.setCloseError(&closeError{err: err})
 					break runLoop
@@ -784,32 +784,45 @@ func (s *connection) handleHandshakeConfirmed(now time.Time) error {
 	return nil
 }
 
-func (s *connection) handlePackets(firstPacket receivedPacket) (wasProcessed bool, _ error) {
-	wasProcessed, err := s.handleOnePacket(firstPacket)
-	if err != nil {
-		return false, err
-	}
-	// only process a single packet at a time before handshake completion
-	if !s.handshakeComplete {
-		return wasProcessed, nil
-	}
+func (s *connection) handlePackets() (wasProcessed bool, _ error) {
 	// Now process all packets in the receivedPackets channel.
 	// Limit the number of packets to the length of the receivedPackets channel,
 	// so we eventually get a chance to send out an ACK when receiving a lot of packets.
-	numPackets := len(s.receivedPackets)
-receiveLoop:
+	s.receivedPacketMx.Lock()
+	numPackets := s.receivedPackets.Len()
+	if numPackets == 0 {
+		s.receivedPacketMx.Unlock()
+		return false, nil
+	}
+
+	var hasMorePackets bool
 	for i := 0; i < numPackets; i++ {
+		if i > 0 {
+			s.receivedPacketMx.Lock()
+		}
+		p := s.receivedPackets.PopFront()
+		hasMorePackets = !s.receivedPackets.Empty()
+		s.receivedPacketMx.Unlock()
+
+		processed, err := s.handleOnePacket(p)
+		if err != nil {
+			return false, err
+		}
+		if processed {
+			wasProcessed = true
+		}
+		if !hasMorePackets {
+			break
+		}
+		// only process a single packet at a time before handshake completion
+		if !s.handshakeComplete {
+			break
+		}
+	}
+	if hasMorePackets {
 		select {
-		case p := <-s.receivedPackets:
-			processed, err := s.handleOnePacket(p)
-			if err != nil {
-				return false, err
-			}
-			if processed {
-				wasProcessed = true
-			}
+		case s.notifyReceivedPacket <- struct{}{}:
 		default:
-			break receiveLoop
 		}
 	}
 	return wasProcessed, nil
@@ -1392,14 +1405,22 @@ func (s *connection) handleFrame(
 
 // handlePacket is called by the server with a new packet
 func (s *connection) handlePacket(p receivedPacket) {
+	s.receivedPacketMx.Lock()
 	// Discard packets once the amount of queued packets is larger than
 	// the channel size, protocol.MaxConnUnprocessedPackets
-	select {
-	case s.receivedPackets <- p:
-	default:
+	if s.receivedPackets.Len() >= protocol.MaxConnUnprocessedPackets {
 		if s.tracer != nil && s.tracer.DroppedPacket != nil {
 			s.tracer.DroppedPacket(logging.PacketTypeNotDetermined, protocol.InvalidPacketNumber, p.Size(), logging.PacketDropDOSPrevention)
 		}
+		s.receivedPacketMx.Unlock()
+		return
+	}
+	s.receivedPackets.PushBack(p)
+	s.receivedPacketMx.Unlock()
+
+	select {
+	case s.notifyReceivedPacket <- struct{}{}:
+	default:
 	}
 }
 
@@ -1978,7 +1999,10 @@ func (s *connection) sendPacketsWithoutGSO(now time.Time) error {
 			return nil
 		}
 		// Prioritize receiving of packets over sending out more packets.
-		if len(s.receivedPackets) > 0 {
+		s.receivedPacketMx.Lock()
+		hasPackets := !s.receivedPackets.Empty()
+		s.receivedPacketMx.Unlock()
+		if hasPackets {
 			s.pacingDeadline = deadlineSendImmediately
 			return nil
 		}
@@ -2036,7 +2060,10 @@ func (s *connection) sendPacketsWithGSO(now time.Time) error {
 		}
 
 		// Prioritize receiving of packets over sending out more packets.
-		if len(s.receivedPackets) > 0 {
+		s.receivedPacketMx.Lock()
+		hasPackets := !s.receivedPackets.Empty()
+		s.receivedPacketMx.Unlock()
+		if hasPackets {
 			s.pacingDeadline = deadlineSendImmediately
 			return nil
 		}