TUN-5590: QUIC datagram max user payload is 1217 bytes

datagramsession/session.go

@@ -54,7 +54,7 @@ func (s *Session) Serve(ctx context.Context, closeAfterIdle time.Duration) (clos
 	go func() {
 		// QUIC implementation copies data to another buffer before returning https://github.com/lucas-clemente/quic-go/blob/v0.24.0/session.go#L1967-L1975
 		// This makes it safe to share readBuffer between iterations
-		readBuffer := make([]byte, s.transport.MTU())
+		readBuffer := make([]byte, s.transport.ReceiveMTU())
 		for {
 			if err := s.dstToTransport(readBuffer); err != nil {
 				s.closeChan <- err

datagramsession/transport.go

@@ -8,6 +8,6 @@ type transport interface {
 	SendTo(sessionID uuid.UUID, payload []byte) error
 	// ReceiveFrom reads the next datagram from the transport
 	ReceiveFrom() (uuid.UUID, []byte, error)
-	// Max transmission unit of the transport
-	MTU() uint
+	// Max transmission unit to receive from the transport
+	ReceiveMTU() uint
 }

datagramsession/transport_test.go

@@ -22,8 +22,8 @@ func (mt *mockQUICTransport) ReceiveFrom() (uuid.UUID, []byte, error) {
 	return mt.reqChan.Receive(context.Background())
 }
 
-func (mt *mockQUICTransport) MTU() uint {
-	return 1220
+func (mt *mockQUICTransport) ReceiveMTU() uint {
+	return 1217
 }
 
 func (mt *mockQUICTransport) newRequest(ctx context.Context, sessionID uuid.UUID, payload []byte) error {