advertize the max_ack_delay in the transport parameters

client.go

@@ -352,6 +352,7 @@ func (c *client) createNewTLSSession(version protocol.VersionNumber) error {
 		IdleTimeout:                    c.config.IdleTimeout,
 		MaxBidiStreams:                 uint64(c.config.MaxIncomingStreams),
 		MaxUniStreams:                  uint64(c.config.MaxIncomingUniStreams),
+		MaxAckDelay:                    protocol.MaxAckDelay,
 		AckDelayExponent:               protocol.AckDelayExponent,
 		DisableMigration:               true,
 	}

internal/ackhandler/received_packet_handler.go

@@ -11,8 +11,6 @@ import (
 )
 
 const (
-	// maximum delay that can be applied to an ACK for an ack-eliciting packet
-	ackSendDelay = 25 * time.Millisecond
 	// initial maximum number of ack-eliciting packets received before sending an ack.
 	initialAckElicitingPacketsBeforeAck = 2
 	// number of ack-eliciting that an ACK is sent for

internal/ackhandler/received_packet_tracker.go

@@ -16,8 +16,8 @@ type receivedPacketTracker struct {
 
 	packetHistory *receivedPacketHistory
 
-	ackSendDelay time.Duration
-	rttStats     *congestion.RTTStats
+	maxAckDelay time.Duration
+	rttStats    *congestion.RTTStats
 
 	packetsReceivedSinceLastAck             int
 	ackElicitingPacketsReceivedSinceLastAck int
@@ -37,7 +37,7 @@ func newReceivedPacketTracker(
 ) *receivedPacketTracker {
 	return &receivedPacketTracker{
 		packetHistory: newReceivedPacketHistory(),
-		ackSendDelay:  ackSendDelay,
+		maxAckDelay:   protocol.MaxAckDelay,
 		rttStats:      rttStats,
 		logger:        logger,
 		version:       version,
@@ -126,7 +126,7 @@ func (h *receivedPacketTracker) maybeQueueAck(packetNumber protocol.PacketNumber
 				}
 			} else if h.ackAlarm.IsZero() {
 				// wait for the minimum of the ack decimation delay or the delayed ack time before sending an ack
-				ackDelay := utils.MinDuration(ackSendDelay, time.Duration(float64(h.rttStats.MinRTT())*float64(ackDecimationDelay)))
+				ackDelay := utils.MinDuration(h.maxAckDelay, time.Duration(float64(h.rttStats.MinRTT())*float64(ackDecimationDelay)))
 				h.ackAlarm = rcvTime.Add(ackDelay)
 				if h.logger.Debug() {
 					h.logger.Debugf("\tSetting ACK timer to min(1/4 min-RTT, max ack delay): %s (%s from now)", ackDelay, time.Until(h.ackAlarm))
@@ -141,9 +141,9 @@ func (h *receivedPacketTracker) maybeQueueAck(packetNumber protocol.PacketNumber
 				h.ackQueued = true
 			} else if h.ackAlarm.IsZero() {
 				if h.logger.Debug() {
-					h.logger.Debugf("\tSetting ACK timer to max ack delay: %s", ackSendDelay)
+					h.logger.Debugf("\tSetting ACK timer to max ack delay: %s", h.maxAckDelay)
 				}
-				h.ackAlarm = rcvTime.Add(ackSendDelay)
+				h.ackAlarm = rcvTime.Add(h.maxAckDelay)
 			}
 		}
 		// If there are new missing packets to report, set a short timer to send an ACK.

internal/ackhandler/received_packet_tracker_test.go

@@ -151,7 +151,7 @@ var _ = Describe("Received Packet Tracker", func() {
 				err = tracker.ReceivedPacket(12, rcvTime, true)
 				Expect(err).ToNot(HaveOccurred())
 				Expect(tracker.ackQueued).To(BeFalse())
-				Expect(tracker.GetAlarmTimeout()).To(Equal(rcvTime.Add(ackSendDelay)))
+				Expect(tracker.GetAlarmTimeout()).To(Equal(rcvTime.Add(protocol.MaxAckDelay)))
 			})
 
 			It("queues an ACK if it was reported missing before", func() {

internal/protocol/params.go

@@ -125,3 +125,6 @@ const DefaultConnectionIDLength = 4
 
 // AckDelayExponent is the ack delay exponent used when sending ACKs.
 const AckDelayExponent = 3
+
+// MaxAckDelay is the maximum time by which we delay sending ACKs.
+const MaxAckDelay = 25 * time.Millisecond

server.go

@@ -445,6 +445,7 @@ func (s *server) createNewSession(
 		IdleTimeout:                    s.config.IdleTimeout,
 		MaxBidiStreams:                 uint64(s.config.MaxIncomingStreams),
 		MaxUniStreams:                  uint64(s.config.MaxIncomingUniStreams),
+		MaxAckDelay:                    protocol.MaxAckDelay,
 		AckDelayExponent:               protocol.AckDelayExponent,
 		DisableMigration:               true,
 		StatelessResetToken:            &token,