disable Path MTU Discovery on Windows

conn_generic.go

@@ -5,6 +5,8 @@ package quic
 
 import "net"
 
+const disablePathMTUDiscovery = false
+
 func newConn(c net.PacketConn) (connection, error) {
 	return &basicConn{PacketConn: c}, nil
 }

conn_helper_darwin.go

@@ -5,7 +5,10 @@ package quic
 
 import "golang.org/x/sys/unix"
 
-const msgTypeIPTOS = unix.IP_RECVTOS
+const (
+	msgTypeIPTOS            = unix.IP_RECVTOS
+	disablePathMTUDiscovery = false
+)
 
 const (
 	ipv4RECVPKTINFO = unix.IP_RECVPKTINFO

conn_helper_freebsd.go

@@ -5,7 +5,10 @@ package quic
 
 import "golang.org/x/sys/unix"
 
-const msgTypeIPTOS = unix.IP_RECVTOS
+const (
+	msgTypeIPTOS            = unix.IP_RECVTOS
+	disablePathMTUDiscovery = false
+)
 
 const (
 	ipv4RECVPKTINFO = 0x7

conn_helper_linux.go

@@ -5,7 +5,10 @@ package quic
 
 import "golang.org/x/sys/unix"
 
-const msgTypeIPTOS = unix.IP_TOS
+const (
+	msgTypeIPTOS            = unix.IP_TOS
+	disablePathMTUDiscovery = false
+)
 
 const (
 	ipv4RECVPKTINFO = unix.IP_PKTINFO

conn_windows.go

@@ -12,7 +12,10 @@ import (
 	"golang.org/x/sys/windows"
 )
 
-const IP_DONTFRAGMENT = 14
+const (
+	disablePathMTUDiscovery = true
+	IP_DONTFRAGMENT         = 14
+)
 
 func newConn(c OOBCapablePacketConn) (connection, error) {
 	rawConn, err := c.SyscallConn()

interface.go

@@ -283,6 +283,7 @@ type Config struct {
 	KeepAlive bool
 	// DisablePathMTUDiscovery disables Path MTU Discovery (RFC 8899).
 	// Packets will then be at most 1252 (IPv4) / 1232 (IPv6) bytes in size.
+	// Note that Path MTU discovery is always disabled on Windows, see https://github.com/lucas-clemente/quic-go/issues/3273.
 	DisablePathMTUDiscovery bool
 	// DisableVersionNegotiationPackets disables the sending of Version Negotiation packets.
 	// This can be useful if version information is exchanged out-of-band.

session.go

@@ -130,6 +130,10 @@ func (e *errCloseForRecreating) Error() string {
 var sessionTracingID uint64        // to be accessed atomically
 func nextSessionTracingID() uint64 { return atomic.AddUint64(&sessionTracingID, 1) }
 
+func pathMTUDiscoveryEnabled(config *Config) bool {
+	return !disablePathMTUDiscovery && !config.DisablePathMTUDiscovery
+}
+
 // A Session is a QUIC session
 type session struct {
 	// Destination connection ID used during the handshake.
@@ -743,7 +747,7 @@ func (s *session) maybeResetTimer() {
 			deadline = s.idleTimeoutStartTime().Add(s.idleTimeout)
 		}
 	}
-	if s.handshakeConfirmed && !s.config.DisablePathMTUDiscovery {
+	if s.handshakeConfirmed && pathMTUDiscoveryEnabled(s.config) {
 		if probeTime := s.mtuDiscoverer.NextProbeTime(); !probeTime.IsZero() {
 			deadline = utils.MinTime(deadline, probeTime)
 		}
@@ -807,7 +811,7 @@ func (s *session) handleHandshakeConfirmed() {
 	s.sentPacketHandler.SetHandshakeConfirmed()
 	s.cryptoStreamHandler.SetHandshakeConfirmed()
 
-	if !s.config.DisablePathMTUDiscovery {
+	if pathMTUDiscoveryEnabled(s.config) {
 		maxPacketSize := s.peerParams.MaxUDPPayloadSize
 		if maxPacketSize == 0 {
 			maxPacketSize = protocol.MaxByteCount
@@ -1768,7 +1772,7 @@ func (s *session) sendPacket() (bool, error) {
 		s.sendQueue.Send(packet.buffer)
 		return true, nil
 	}
-	if !s.config.DisablePathMTUDiscovery && s.mtuDiscoverer.ShouldSendProbe(now) {
+	if pathMTUDiscoveryEnabled(s.config) && s.mtuDiscoverer.ShouldSendProbe(now) {
 		packet, err := s.packer.PackMTUProbePacket(s.mtuDiscoverer.GetPing())
 		if err != nil {
 			return false, err

session_test.go

@@ -9,6 +9,7 @@ import (
 	"fmt"
 	"io"
 	"net"
+	"runtime"
 	"runtime/pprof"
 	"strings"
 	"time"
@@ -1681,6 +1682,7 @@ var _ = Describe("Session", func() {
 			time.Sleep(50 * time.Millisecond)
 		})
 
+		if runtime.GOOS != "windows" { // Path MTU Discovery is disabled on Windows
 			It("sends a Path MTU probe packet", func() {
 				mtuDiscoverer := NewMockMtuDiscoverer(mockCtrl)
 				sess.mtuDiscoverer = mtuDiscoverer
@@ -1708,6 +1710,7 @@ var _ = Describe("Session", func() {
 				sess.scheduleSending()
 				Eventually(written).Should(Receive())
 			})
+		}
 	})
 
 	Context("scheduling sending", func() {