wire: write configured value of max_udp_payload_size transport parameter

connection.go

@@ -299,6 +299,7 @@ var newConnection = func(
 		MaxUniStreamNum:                 protocol.StreamNum(s.config.MaxIncomingUniStreams),
 		MaxAckDelay:                     protocol.MaxAckDelayInclGranularity,
 		AckDelayExponent:                protocol.AckDelayExponent,
+		MaxUDPPayloadSize:               protocol.MaxPacketBufferSize,
 		DisableActiveMigration:          true,
 		StatelessResetToken:             &statelessResetToken,
 		OriginalDestinationConnectionID: origDestConnID,
@@ -410,6 +411,7 @@ var newClientConnection = func(
 		MaxBidiStreamNum:               protocol.StreamNum(s.config.MaxIncomingStreams),
 		MaxUniStreamNum:                protocol.StreamNum(s.config.MaxIncomingUniStreams),
 		MaxAckDelay:                    protocol.MaxAckDelayInclGranularity,
+		MaxUDPPayloadSize:              protocol.MaxPacketBufferSize,
 		AckDelayExponent:               protocol.AckDelayExponent,
 		DisableActiveMigration:         true,
 		// For interoperability with quic-go versions before May 2023, this value must be set to a value

internal/wire/transport_parameter_test.go

@@ -103,6 +103,7 @@ var _ = Describe("Transport Parameters", func() {
 			AckDelayExponent:                13,
 			MaxAckDelay:                     42 * time.Millisecond,
 			ActiveConnectionIDLimit:         2 + getRandomValueUpTo(math.MaxInt64-2),
+			MaxUDPPayloadSize:               1200 + protocol.ByteCount(getRandomValue()-1200),
 			MaxDatagramFrameSize:            protocol.ByteCount(getRandomValue()),
 		}
 		data := params.Marshal(protocol.PerspectiveServer)
@@ -124,6 +125,7 @@ var _ = Describe("Transport Parameters", func() {
 		Expect(p.AckDelayExponent).To(Equal(uint8(13)))
 		Expect(p.MaxAckDelay).To(Equal(42 * time.Millisecond))
 		Expect(p.ActiveConnectionIDLimit).To(Equal(params.ActiveConnectionIDLimit))
+		Expect(p.MaxUDPPayloadSize).To(Equal(params.MaxUDPPayloadSize))
 		Expect(p.MaxDatagramFrameSize).To(Equal(params.MaxDatagramFrameSize))
 	})
 

internal/wire/transport_parameters.go

@@ -358,7 +358,9 @@ func (p *TransportParameters) Marshal(pers protocol.Perspective) []byte {
 	// idle_timeout
 	b = p.marshalVarintParam(b, maxIdleTimeoutParameterID, uint64(p.MaxIdleTimeout/time.Millisecond))
 	// max_packet_size
-	b = p.marshalVarintParam(b, maxUDPPayloadSizeParameterID, uint64(protocol.MaxPacketBufferSize))
+	if p.MaxUDPPayloadSize > 0 {
+		b = p.marshalVarintParam(b, maxUDPPayloadSizeParameterID, uint64(p.MaxUDPPayloadSize))
+	}
 	// max_ack_delay
 	// Only send it if is different from the default value.
 	if p.MaxAckDelay != protocol.DefaultMaxAckDelay {