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

connection/quic.go

@@ -30,7 +30,6 @@ const (
 	HTTPMethodKey = "HttpMethod"
 	// HTTPHostKey is used to get or set http Method in QUIC ALPN if the underlying proxy connection type is HTTP.
 	HTTPHostKey = "HttpHost"
-	MaxDatagramFrameSize = 1220
 )
 
 // QUICConnection represents the type that facilitates Proxying via QUIC streams.

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
+	// Max transmission unit to receive from the transport
-	MTU() uint
+	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 {
+func (mt *mockQUICTransport) ReceiveMTU() uint {
-	return 1220
+	return 1217
 }
 
 func (mt *mockQUICTransport) newRequest(ctx context.Context, sessionID uuid.UUID, payload []byte) error {

quic/datagram.go

@@ -9,7 +9,9 @@ import (
 )
 
 const (
-	MaxDatagramFrameSize = 1220
+	// Max datagram frame size is limited to 1220 https://github.com/lucas-clemente/quic-go/blob/v0.24.0/internal/protocol/params.go#L138
+	// However, 3 more bytes are reserved https://github.com/lucas-clemente/quic-go/blob/v0.24.0/internal/wire/datagram_frame.go#L61
+	MaxDatagramFrameSize = 1217
 	sessionIDLen         = len(uuid.UUID{})
 )
 
@@ -34,7 +36,7 @@ func NewDatagramMuxer(quicSession quic.Session) (*DatagramMuxer, error) {
 func (dm *DatagramMuxer) SendTo(sessionID uuid.UUID, payload []byte) error {
 	if len(payload) > MaxDatagramFrameSize-sessionIDLen {
 		// TODO: TUN-5302 return ICMP packet too big message
-		return fmt.Errorf("origin UDP payload has %d bytes, which exceeds transport MTU %d", len(payload), MaxDatagramFrameSize-sessionIDLen)
+		return fmt.Errorf("origin UDP payload has %d bytes, which exceeds transport MTU %d", len(payload), dm.SendMTU())
 	}
 	msgWithID, err := SuffixSessionID(sessionID, payload)
 	if err != nil {
@@ -57,7 +59,13 @@ func (dm *DatagramMuxer) ReceiveFrom() (uuid.UUID, []byte, error) {
 	return ExtractSessionID(msg)
 }
 
-func (dm *DatagramMuxer) MTU() uint {
+// Maximum application payload to send through QUIC datagram frame
+func (dm *DatagramMuxer) SendMTU() uint {
+	return uint(MaxDatagramFrameSize - sessionIDLen)
+}
+
+// Maximum expected bytes to read from QUIC datagram frame
+func (dm *DatagramMuxer) ReceiveMTU() uint {
 	return MaxDatagramFrameSize
 }
 

quic/datagram_test.go

@@ -1,10 +1,20 @@
 package quic
 
 import (
+	"bytes"
+	"context"
+	"crypto/rand"
+	"crypto/rsa"
+	"crypto/tls"
+	"crypto/x509"
+	"encoding/pem"
+	"math/big"
 	"testing"
 
 	"github.com/google/uuid"
+	"github.com/lucas-clemente/quic-go"
 	"github.com/stretchr/testify/require"
+	"golang.org/x/sync/errgroup"
 )
 
 var (
@@ -39,3 +49,91 @@ func TestSuffixSessionIDError(t *testing.T) {
 	_, err = SuffixSessionID(testSessionID, msg)
 	require.Error(t, err)
 }
+
+func TestMaxDatagramPayload(t *testing.T) {
+	payload := make([]byte, MaxDatagramFrameSize-sessionIDLen)
+
+	quicConfig := &quic.Config{
+		KeepAlive:       true,
+		EnableDatagrams: true,
+	}
+	quicListener := newQUICListener(t, quicConfig)
+	defer quicListener.Close()
+
+	errGroup, ctx := errgroup.WithContext(context.Background())
+	// Run edge side of datagram muxer
+	errGroup.Go(func() error {
+		// Accept quic connection
+		quicSession, err := quicListener.Accept(ctx)
+		require.NoError(t, err)
+
+		muxer, err := NewDatagramMuxer(quicSession)
+		require.NoError(t, err)
+
+		sessionID, receivedPayload, err := muxer.ReceiveFrom()
+		require.NoError(t, err)
+		require.Equal(t, testSessionID, sessionID)
+		require.True(t, bytes.Equal(payload, receivedPayload))
+
+		return nil
+	})
+
+	// Run cloudflared side of datagram muxer
+	errGroup.Go(func() error {
+		tlsClientConfig := &tls.Config{
+			InsecureSkipVerify: true,
+			NextProtos:         []string{"argotunnel"},
+		}
+		// Establish quic connection
+		quicSession, err := quic.DialAddrEarly(quicListener.Addr().String(), tlsClientConfig, quicConfig)
+		require.NoError(t, err)
+
+		muxer, err := NewDatagramMuxer(quicSession)
+		require.NoError(t, err)
+
+		err = muxer.SendTo(testSessionID, payload)
+		require.NoError(t, err)
+
+		// Payload larger than transport MTU, should return an error
+		largePayload := append(payload, byte(1))
+		err = muxer.SendTo(testSessionID, largePayload)
+		require.Error(t, err)
+
+		return nil
+	})
+
+	require.NoError(t, errGroup.Wait())
+}
+
+func newQUICListener(t *testing.T, config *quic.Config) quic.Listener {
+	// Create a simple tls config.
+	tlsConfig := generateTLSConfig()
+
+	listener, err := quic.ListenAddr("127.0.0.1:0", tlsConfig, config)
+	require.NoError(t, err)
+
+	return listener
+}
+
+func generateTLSConfig() *tls.Config {
+	key, err := rsa.GenerateKey(rand.Reader, 1024)
+	if err != nil {
+		panic(err)
+	}
+	template := x509.Certificate{SerialNumber: big.NewInt(1)}
+	certDER, err := x509.CreateCertificate(rand.Reader, &template, &template, &key.PublicKey, key)
+	if err != nil {
+		panic(err)
+	}
+	keyPEM := pem.EncodeToMemory(&pem.Block{Type: "RSA PRIVATE KEY", Bytes: x509.MarshalPKCS1PrivateKey(key)})
+	certPEM := pem.EncodeToMemory(&pem.Block{Type: "CERTIFICATE", Bytes: certDER})
+
+	tlsCert, err := tls.X509KeyPair(certPEM, keyPEM)
+	if err != nil {
+		panic(err)
+	}
+	return &tls.Config{
+		Certificates: []tls.Certificate{tlsCert},
+		NextProtos:   []string{"argotunnel"},
+	}
+}