disable GSO if sending fails for a particular remote address

mock_raw_conn_test.go

@@ -0,0 +1,122 @@
+// Code generated by MockGen. DO NOT EDIT.
+// Source: github.com/quic-go/quic-go (interfaces: RawConn)
+
+// Package quic is a generated GoMock package.
+package quic
+
+import (
+	net "net"
+	reflect "reflect"
+	time "time"
+
+	gomock "github.com/golang/mock/gomock"
+)
+
+// MockRawConn is a mock of RawConn interface.
+type MockRawConn struct {
+	ctrl     *gomock.Controller
+	recorder *MockRawConnMockRecorder
+}
+
+// MockRawConnMockRecorder is the mock recorder for MockRawConn.
+type MockRawConnMockRecorder struct {
+	mock *MockRawConn
+}
+
+// NewMockRawConn creates a new mock instance.
+func NewMockRawConn(ctrl *gomock.Controller) *MockRawConn {
+	mock := &MockRawConn{ctrl: ctrl}
+	mock.recorder = &MockRawConnMockRecorder{mock}
+	return mock
+}
+
+// EXPECT returns an object that allows the caller to indicate expected use.
+func (m *MockRawConn) EXPECT() *MockRawConnMockRecorder {
+	return m.recorder
+}
+
+// Close mocks base method.
+func (m *MockRawConn) Close() error {
+	m.ctrl.T.Helper()
+	ret := m.ctrl.Call(m, "Close")
+	ret0, _ := ret[0].(error)
+	return ret0
+}
+
+// Close indicates an expected call of Close.
+func (mr *MockRawConnMockRecorder) Close() *gomock.Call {
+	mr.mock.ctrl.T.Helper()
+	return mr.mock.ctrl.RecordCallWithMethodType(mr.mock, "Close", reflect.TypeOf((*MockRawConn)(nil).Close))
+}
+
+// LocalAddr mocks base method.
+func (m *MockRawConn) LocalAddr() net.Addr {
+	m.ctrl.T.Helper()
+	ret := m.ctrl.Call(m, "LocalAddr")
+	ret0, _ := ret[0].(net.Addr)
+	return ret0
+}
+
+// LocalAddr indicates an expected call of LocalAddr.
+func (mr *MockRawConnMockRecorder) LocalAddr() *gomock.Call {
+	mr.mock.ctrl.T.Helper()
+	return mr.mock.ctrl.RecordCallWithMethodType(mr.mock, "LocalAddr", reflect.TypeOf((*MockRawConn)(nil).LocalAddr))
+}
+
+// ReadPacket mocks base method.
+func (m *MockRawConn) ReadPacket() (receivedPacket, error) {
+	m.ctrl.T.Helper()
+	ret := m.ctrl.Call(m, "ReadPacket")
+	ret0, _ := ret[0].(receivedPacket)
+	ret1, _ := ret[1].(error)
+	return ret0, ret1
+}
+
+// ReadPacket indicates an expected call of ReadPacket.
+func (mr *MockRawConnMockRecorder) ReadPacket() *gomock.Call {
+	mr.mock.ctrl.T.Helper()
+	return mr.mock.ctrl.RecordCallWithMethodType(mr.mock, "ReadPacket", reflect.TypeOf((*MockRawConn)(nil).ReadPacket))
+}
+
+// SetReadDeadline mocks base method.
+func (m *MockRawConn) SetReadDeadline(arg0 time.Time) error {
+	m.ctrl.T.Helper()
+	ret := m.ctrl.Call(m, "SetReadDeadline", arg0)
+	ret0, _ := ret[0].(error)
+	return ret0
+}
+
+// SetReadDeadline indicates an expected call of SetReadDeadline.
+func (mr *MockRawConnMockRecorder) SetReadDeadline(arg0 interface{}) *gomock.Call {
+	mr.mock.ctrl.T.Helper()
+	return mr.mock.ctrl.RecordCallWithMethodType(mr.mock, "SetReadDeadline", reflect.TypeOf((*MockRawConn)(nil).SetReadDeadline), arg0)
+}
+
+// WritePacket mocks base method.
+func (m *MockRawConn) WritePacket(arg0 []byte, arg1 net.Addr, arg2 []byte) (int, error) {
+	m.ctrl.T.Helper()
+	ret := m.ctrl.Call(m, "WritePacket", arg0, arg1, arg2)
+	ret0, _ := ret[0].(int)
+	ret1, _ := ret[1].(error)
+	return ret0, ret1
+}
+
+// WritePacket indicates an expected call of WritePacket.
+func (mr *MockRawConnMockRecorder) WritePacket(arg0, arg1, arg2 interface{}) *gomock.Call {
+	mr.mock.ctrl.T.Helper()
+	return mr.mock.ctrl.RecordCallWithMethodType(mr.mock, "WritePacket", reflect.TypeOf((*MockRawConn)(nil).WritePacket), arg0, arg1, arg2)
+}
+
+// capabilities mocks base method.
+func (m *MockRawConn) capabilities() connCapabilities {
+	m.ctrl.T.Helper()
+	ret := m.ctrl.Call(m, "capabilities")
+	ret0, _ := ret[0].(connCapabilities)
+	return ret0
+}
+
+// capabilities indicates an expected call of capabilities.
+func (mr *MockRawConnMockRecorder) capabilities() *gomock.Call {
+	mr.mock.ctrl.T.Helper()
+	return mr.mock.ctrl.RecordCallWithMethodType(mr.mock, "capabilities", reflect.TypeOf((*MockRawConn)(nil).capabilities))
+}

mockgen.go

@@ -5,6 +5,9 @@ package quic
 //go:generate sh -c "go run github.com/golang/mock/mockgen -build_flags=\"-tags=gomock\" -package quic -self_package github.com/quic-go/quic-go -destination mock_send_conn_test.go github.com/quic-go/quic-go SendConn"
 type SendConn = sendConn
 
+//go:generate sh -c "go run github.com/golang/mock/mockgen -build_flags=\"-tags=gomock\" -package quic -self_package github.com/quic-go/quic-go -destination mock_raw_conn_test.go github.com/quic-go/quic-go RawConn"
+type RawConn = rawConn
+
 //go:generate sh -c "go run github.com/golang/mock/mockgen -build_flags=\"-tags=gomock\" -package quic -self_package github.com/quic-go/quic-go -destination mock_sender_test.go github.com/quic-go/quic-go Sender"
 type Sender = sender
 

packet_handler_map.go

@@ -26,9 +26,9 @@ type connCapabilities struct {
 // rawConn is a connection that allow reading of a receivedPackeh.
 type rawConn interface {
 	ReadPacket() (receivedPacket, error)
-	// The size parameter is used for GSO.
+	// WritePacket writes a packet on the wire.
-	// If GSO is not support, len(b) must be equal to size.
+	// If GSO is enabled, it's the caller's responsibility to set the correct control message.
-	WritePacket(b []byte, size uint16, addr net.Addr, oob []byte) (int, error)
+	WritePacket(b []byte, addr net.Addr, oob []byte) (int, error)
 	LocalAddr() net.Addr
 	SetReadDeadline(time.Time) error
 	io.Closer

send_conn.go

@@ -1,10 +1,12 @@
 package quic
 
 import (
+	"fmt"
 	"math"
 	"net"
 
 	"github.com/quic-go/quic-go/internal/protocol"
+	"github.com/quic-go/quic-go/internal/utils"
 )
 
 // A sendConn allows sending using a simple Write() on a non-connected packet conn.
@@ -20,61 +22,84 @@ type sendConn interface {
 type sconn struct {
 	rawConn
 
+	localAddr  net.Addr
 	remoteAddr net.Addr
+
+	logger utils.Logger
+
 	info packetInfo
 	oob  []byte
+	// If GSO enabled, and we receive a GSO error for this remote address, GSO is disabled.
+	gotGSOError bool
 }
 
 var _ sendConn = &sconn{}
 
-func newSendConn(c rawConn, remote net.Addr) *sconn {
+func newSendConn(c rawConn, remote net.Addr, info packetInfo, logger utils.Logger) *sconn {
-	sc := &sconn{
+	localAddr := c.LocalAddr()
-		rawConn:    c,
+	if info.addr.IsValid() {
-		remoteAddr: remote,
+		if udpAddr, ok := localAddr.(*net.UDPAddr); ok {
+			addrCopy := *udpAddr
+			addrCopy.IP = info.addr.AsSlice()
+			localAddr = &addrCopy
 		}
-	if c.capabilities().GSO {
-		// add 32 bytes, so we can add the UDP_SEGMENT msg
-		sc.oob = make([]byte, 0, 32)
 	}
-	return sc
-}
 
-func newSendConnWithPacketInfo(c rawConn, remote net.Addr, info packetInfo) *sconn {
 	oob := info.OOB()
-	if c.capabilities().GSO {
 	// add 32 bytes, so we can add the UDP_SEGMENT msg
 	l := len(oob)
 	oob = append(oob, make([]byte, 32)...)
 	oob = oob[:l]
-	}
 	return &sconn{
 		rawConn:    c,
+		localAddr:  localAddr,
 		remoteAddr: remote,
 		info:       info,
 		oob:        oob,
+		logger:     logger,
 	}
 }
 
 func (c *sconn) Write(p []byte, size protocol.ByteCount) error {
+	if !c.capabilities().GSO {
+		if protocol.ByteCount(len(p)) != size {
+			panic(fmt.Sprintf("inconsistent packet size (%d vs %d)", len(p), size))
+		}
+		_, err := c.WritePacket(p, c.remoteAddr, c.oob)
+		return err
+	}
+	// GSO is supported. Append the control message and send.
 	if size > math.MaxUint16 {
 		panic("size overflow")
 	}
-	_, err := c.WritePacket(p, uint16(size), c.remoteAddr, c.oob)
+	_, err := c.WritePacket(p, c.remoteAddr, appendUDPSegmentSizeMsg(c.oob, uint16(size)))
+	if err != nil && isGSOError(err) {
+		// disable GSO for future calls
+		c.gotGSOError = true
+		if c.logger.Debug() {
+			c.logger.Debugf("GSO failed when sending to %s", c.remoteAddr)
+		}
+		// send out the packets one by one
+		for len(p) > 0 {
+			l := len(p)
+			if l > int(size) {
+				l = int(size)
+			}
+			if _, err := c.WritePacket(p[:l], c.remoteAddr, c.oob); err != nil {
+				return err
+			}
+			p = p[l:]
+		}
+		return nil
+	}
 	return err
 }
 
-func (c *sconn) RemoteAddr() net.Addr {
+func (c *sconn) capabilities() connCapabilities {
-	return c.remoteAddr
+	capabilities := c.rawConn.capabilities()
+	capabilities.GSO = !c.gotGSOError
+	return capabilities
 }
 
-func (c *sconn) LocalAddr() net.Addr {
+func (c *sconn) RemoteAddr() net.Addr { return c.remoteAddr }
-	addr := c.rawConn.LocalAddr()
+func (c *sconn) LocalAddr() net.Addr  { return c.localAddr }
-	if c.info.addr.IsValid() {
-		if udpAddr, ok := addr.(*net.UDPAddr); ok {
-			addrCopy := *udpAddr
-			addrCopy.IP = c.info.addr.AsSlice()
-			addr = &addrCopy
-		}
-	}
-	return addr
-}

send_conn_test.go

@@ -2,46 +2,81 @@ package quic
 
 import (
 	"net"
+	"net/netip"
 
+	"github.com/quic-go/quic-go/internal/utils"
+
+	"github.com/golang/mock/gomock"
 	. "github.com/onsi/ginkgo/v2"
 	. "github.com/onsi/gomega"
 )
 
+// Only if appendUDPSegmentSizeMsg actually appends a message (and isn't only a stub implementation),
+// GSO is actually supported on this platform.
+var platformSupportsGSO = len(appendUDPSegmentSizeMsg([]byte{}, 1337)) > 0
+
 var _ = Describe("Connection (for sending packets)", func() {
-	var (
+	remoteAddr := &net.UDPAddr{IP: net.IPv4(192, 168, 100, 200), Port: 1337}
-		c          sendConn
-		packetConn *MockPacketConn
-		addr       net.Addr
-	)
 
-	BeforeEach(func() {
+	It("gets the local and remote addresses", func() {
-		addr = &net.UDPAddr{IP: net.IPv4(192, 168, 100, 200), Port: 1337}
+		localAddr := &net.UDPAddr{IP: net.IPv4(192, 168, 0, 1), Port: 1234}
-		packetConn = NewMockPacketConn(mockCtrl)
+		rawConn := NewMockRawConn(mockCtrl)
-		rawConn, err := wrapConn(packetConn)
+		rawConn.EXPECT().LocalAddr().Return(localAddr)
-		Expect(err).ToNot(HaveOccurred())
+		c := newSendConn(rawConn, remoteAddr, packetInfo{}, utils.DefaultLogger)
-		c = newSendConnWithPacketInfo(rawConn, addr, packetInfo{})
+		Expect(c.LocalAddr().String()).To(Equal("192.168.0.1:1234"))
-	})
-
-	It("writes", func() {
-		packetConn.EXPECT().WriteTo([]byte("foobar"), addr)
-		Expect(c.Write([]byte("foobar"), 6)).To(Succeed())
-	})
-
-	It("gets the remote address", func() {
 		Expect(c.RemoteAddr().String()).To(Equal("192.168.100.200:1337"))
 	})
 
-	It("gets the local address", func() {
+	It("uses the local address from the packet info", func() {
-		addr := &net.UDPAddr{
+		localAddr := &net.UDPAddr{IP: net.IPv4(192, 168, 0, 1), Port: 1234}
-			IP:   net.IPv4(192, 168, 0, 1),
+		rawConn := NewMockRawConn(mockCtrl)
-			Port: 1234,
+		rawConn.EXPECT().LocalAddr().Return(localAddr)
-		}
+		c := newSendConn(rawConn, remoteAddr, packetInfo{addr: netip.AddrFrom4([4]byte{127, 0, 0, 42})}, utils.DefaultLogger)
-		packetConn.EXPECT().LocalAddr().Return(addr)
+		Expect(c.LocalAddr().String()).To(Equal("127.0.0.42:1234"))
-		Expect(c.LocalAddr()).To(Equal(addr))
 	})
 
-	It("closes", func() {
+	if platformSupportsGSO {
-		packetConn.EXPECT().Close()
+		It("writes with GSO", func() {
-		Expect(c.Close()).To(Succeed())
+			rawConn := NewMockRawConn(mockCtrl)
+			rawConn.EXPECT().LocalAddr()
+			rawConn.EXPECT().capabilities().Return(connCapabilities{GSO: true}).AnyTimes()
+			c := newSendConn(rawConn, remoteAddr, packetInfo{}, utils.DefaultLogger)
+			rawConn.EXPECT().WritePacket([]byte("foobar"), remoteAddr, gomock.Any()).Do(func(_ []byte, _ net.Addr, oob []byte) {
+				msg := appendUDPSegmentSizeMsg([]byte{}, 3)
+				Expect(oob).To(Equal(msg))
 			})
+			Expect(c.Write([]byte("foobar"), 3)).To(Succeed())
+		})
+
+		It("disables GSO if writing fails", func() {
+			rawConn := NewMockRawConn(mockCtrl)
+			rawConn.EXPECT().LocalAddr()
+			rawConn.EXPECT().capabilities().Return(connCapabilities{GSO: true}).AnyTimes()
+			c := newSendConn(rawConn, remoteAddr, packetInfo{}, utils.DefaultLogger)
+			Expect(c.capabilities().GSO).To(BeTrue())
+			gomock.InOrder(
+				rawConn.EXPECT().WritePacket([]byte("foobar"), remoteAddr, gomock.Any()).DoAndReturn(func(_ []byte, _ net.Addr, oob []byte) (int, error) {
+					msg := appendUDPSegmentSizeMsg([]byte{}, 3)
+					Expect(oob).To(Equal(msg))
+					return 0, errGSO
+				}),
+				rawConn.EXPECT().WritePacket([]byte("foo"), remoteAddr, []byte{}).Return(3, nil),
+				rawConn.EXPECT().WritePacket([]byte("bar"), remoteAddr, []byte{}).Return(3, nil),
+			)
+			Expect(c.Write([]byte("foobar"), 3)).To(Succeed())
+			Expect(c.capabilities().GSO).To(BeFalse()) // GSO support is now disabled
+			// make sure we actually enforce that
+			Expect(func() { c.Write([]byte("foobar"), 3) }).To(PanicWith("inconsistent packet size (6 vs 3)"))
+		})
+	} else {
+		It("writes without GSO", func() {
+			remoteAddr := &net.UDPAddr{IP: net.IPv4(192, 168, 100, 200), Port: 1337}
+			rawConn := NewMockRawConn(mockCtrl)
+			rawConn.EXPECT().LocalAddr()
+			rawConn.EXPECT().capabilities()
+			c := newSendConn(rawConn, remoteAddr, packetInfo{}, utils.DefaultLogger)
+			rawConn.EXPECT().WritePacket([]byte("foobar"), remoteAddr, nil)
+			Expect(c.Write([]byte("foobar"), 6)).To(Succeed())
+		})
+	}
 })

server.go

@@ -632,7 +632,7 @@ func (s *baseServer) handleInitialImpl(p receivedPacket, hdr *wire.Header) error
 			tracer = config.Tracer(context.WithValue(context.Background(), ConnectionTracingKey, tracingID), protocol.PerspectiveServer, connID)
 		}
 		conn = s.newConn(
-			newSendConnWithPacketInfo(s.conn, p.remoteAddr, p.info),
+			newSendConn(s.conn, p.remoteAddr, p.info, s.logger),
 			s.connHandler,
 			origDestConnID,
 			retrySrcConnID,
@@ -742,7 +742,7 @@ func (s *baseServer) sendRetry(remoteAddr net.Addr, hdr *wire.Header, info packe
 	if s.tracer != nil {
 		s.tracer.SentPacket(remoteAddr, &replyHdr.Header, protocol.ByteCount(len(buf.Data)), nil)
 	}
-	_, err = s.conn.WritePacket(buf.Data, uint16(len(buf.Data)), remoteAddr, info.OOB())
+	_, err = s.conn.WritePacket(buf.Data, remoteAddr, info.OOB())
 	return err
 }
 
@@ -841,7 +841,7 @@ func (s *baseServer) sendError(remoteAddr net.Addr, hdr *wire.Header, sealer han
 	if s.tracer != nil {
 		s.tracer.SentPacket(remoteAddr, &replyHdr.Header, protocol.ByteCount(len(b.Data)), []logging.Frame{ccf})
 	}
-	_, err = s.conn.WritePacket(b.Data, uint16(len(b.Data)), remoteAddr, info.OOB())
+	_, err = s.conn.WritePacket(b.Data, remoteAddr, info.OOB())
 	return err
 }
 
@@ -879,7 +879,7 @@ func (s *baseServer) maybeSendVersionNegotiationPacket(p receivedPacket) {
 	if s.tracer != nil {
 		s.tracer.SentVersionNegotiationPacket(p.remoteAddr, src, dest, s.config.Versions)
 	}
-	if _, err := s.conn.WritePacket(data, uint16(len(data)), p.remoteAddr, p.info.OOB()); err != nil {
+	if _, err := s.conn.WritePacket(data, p.remoteAddr, p.info.OOB()); err != nil {
 		s.logger.Debugf("Error sending Version Negotiation: %s", err)
 	}
 }

sys_conn.go

@@ -1,7 +1,6 @@
 package quic
 
 import (
-	"fmt"
 	"log"
 	"net"
 	"os"
@@ -105,10 +104,7 @@ func (c *basicConn) ReadPacket() (receivedPacket, error) {
 	}, nil
 }
 
-func (c *basicConn) WritePacket(b []byte, packetSize uint16, addr net.Addr, _ []byte) (n int, err error) {
+func (c *basicConn) WritePacket(b []byte, addr net.Addr, _ []byte) (n int, err error) {
-	if uint16(len(b)) != packetSize {
-		panic(fmt.Sprintf("inconsistent length. got: %d. expected %d", packetSize, len(b)))
-	}
 	return c.PacketConn.WriteTo(b, addr)
 }
 

sys_conn_df_linux.go

@@ -4,11 +4,7 @@ package quic
 
 import (
 	"errors"
-	"log"
-	"os"
-	"strconv"
 	"syscall"
-	"unsafe"
 
 	"golang.org/x/sys/unix"
 
@@ -38,43 +34,9 @@ func setDF(rawConn syscall.RawConn) (bool, error) {
 	return true, nil
 }
 
-func maybeSetGSO(rawConn syscall.RawConn) bool {
-	enable, _ := strconv.ParseBool(os.Getenv("QUIC_GO_ENABLE_GSO"))
-	if !enable {
-		return false
-	}
-
-	var setErr error
-	if err := rawConn.Control(func(fd uintptr) {
-		setErr = unix.SetsockoptInt(int(fd), syscall.IPPROTO_UDP, unix.UDP_SEGMENT, 1)
-	}); err != nil {
-		setErr = err
-	}
-	if setErr != nil {
-		log.Println("failed to enable GSO")
-		return false
-	}
-	return true
-}
-
 func isSendMsgSizeErr(err error) bool {
 	// https://man7.org/linux/man-pages/man7/udp.7.html
 	return errors.Is(err, unix.EMSGSIZE)
 }
 
-func isRecvMsgSizeErr(err error) bool { return false }
+func isRecvMsgSizeErr(error) bool { return false }
-
-func appendUDPSegmentSizeMsg(b []byte, size uint16) []byte {
-	startLen := len(b)
-	const dataLen = 2 // payload is a uint16
-	b = append(b, make([]byte, unix.CmsgSpace(dataLen))...)
-	h := (*unix.Cmsghdr)(unsafe.Pointer(&b[startLen]))
-	h.Level = syscall.IPPROTO_UDP
-	h.Type = unix.UDP_SEGMENT
-	h.SetLen(unix.CmsgLen(dataLen))
-
-	// UnixRights uses the private `data` method, but I *think* this achieves the same goal.
-	offset := startLen + unix.CmsgSpace(0)
-	*(*uint16)(unsafe.Pointer(&b[offset])) = size
-	return b
-}

sys_conn_helper_linux.go

@@ -4,8 +4,11 @@ package quic
 
 import (
 	"encoding/binary"
+	"errors"
 	"net/netip"
+	"os"
 	"syscall"
+	"unsafe"
 
 	"golang.org/x/sys/unix"
 )
@@ -48,3 +51,30 @@ func parseIPv4PktInfo(body []byte) (ip netip.Addr, ifIndex uint32, ok bool) {
 	}
 	return netip.AddrFrom4(*(*[4]byte)(body[8:12])), binary.LittleEndian.Uint32(body), true
 }
+
+func appendUDPSegmentSizeMsg(b []byte, size uint16) []byte {
+	startLen := len(b)
+	const dataLen = 2 // payload is a uint16
+	b = append(b, make([]byte, unix.CmsgSpace(dataLen))...)
+	h := (*unix.Cmsghdr)(unsafe.Pointer(&b[startLen]))
+	h.Level = syscall.IPPROTO_UDP
+	h.Type = unix.UDP_SEGMENT
+	h.SetLen(unix.CmsgLen(dataLen))
+
+	// UnixRights uses the private `data` method, but I *think* this achieves the same goal.
+	offset := startLen + unix.CmsgSpace(0)
+	*(*uint16)(unsafe.Pointer(&b[offset])) = size
+	return b
+}
+
+func isGSOError(err error) bool {
+	var serr *os.SyscallError
+	if errors.As(err, &serr) {
+		// EIO is returned by udp_send_skb() if the device driver does not have tx checksums enabled,
+		// which is a hard requirement of UDP_SEGMENT. See:
+		// https://git.kernel.org/pub/scm/docs/man-pages/man-pages.git/tree/man7/udp.7?id=806eabd74910447f21005160e90957bde4db0183#n228
+		// https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/net/ipv4/udp.c?h=v6.2&id=c9c3395d5e3dcc6daee66c6908354d47bf98cb0c#n942
+		return serr.Err == unix.EIO
+	}
+	return false
+}

sys_conn_helper_linux_test.go

@@ -1,22 +1,24 @@
-// We need root permissions to use RCVBUFFORCE.
+//go:build linux
-// This test is therefore only compiled when the root build flag is set.
-// It can only succeed if the tests are then also run with root permissions.
-//go:build linux && root
 
 package quic
 
 import (
+	"errors"
 	"net"
 	"os"
 
+	"golang.org/x/sys/unix"
+
 	. "github.com/onsi/ginkgo/v2"
 	. "github.com/onsi/gomega"
 )
 
+var errGSO = &os.SyscallError{Err: unix.EIO}
+
 var _ = Describe("forcing a change of send and receive buffer sizes", func() {
 	It("forces a change of the receive buffer size", func() {
 		if os.Getuid() != 0 {
-			Fail("Must be root to force change the receive buffer size")
+			Skip("Must be root to force change the receive buffer size")
 		}
 
 		c, err := net.ListenPacket("udp", "127.0.0.1:0")
@@ -43,7 +45,7 @@ var _ = Describe("forcing a change of send and receive buffer sizes", func() {
 
 	It("forces a change of the send buffer size", func() {
 		if os.Getuid() != 0 {
-			Fail("Must be root to force change the send buffer size")
+			Skip("Must be root to force change the send buffer size")
 		}
 
 		c, err := net.ListenPacket("udp", "127.0.0.1:0")
@@ -67,4 +69,10 @@ var _ = Describe("forcing a change of send and receive buffer sizes", func() {
 		//  The kernel doubles this value (to allow space for bookkeeping overhead)
 		Expect(size).To(Equal(2 * large))
 	})
+
+	It("detects GSO errors", func() {
+		Expect(isGSOError(errGSO)).To(BeTrue())
+		Expect(isGSOError(nil)).To(BeFalse())
+		Expect(isGSOError(errors.New("test"))).To(BeFalse())
+	})
 })

sys_conn_helper_nonlinux.go

@@ -4,3 +4,6 @@ package quic
 
 func forceSetReceiveBuffer(c any, bytes int) error { return nil }
 func forceSetSendBuffer(c any, bytes int) error    { return nil }
+
+func appendUDPSegmentSizeMsg(_ []byte, _ uint16) []byte { return nil }
+func isGSOError(error) bool                             { return false }

sys_conn_helper_nonlinux_test.go

@@ -0,0 +1,7 @@
+//go:build !linux
+
+package quic
+
+import "errors"
+
+var errGSO = errors.New("fake GSO error")

sys_conn_no_gso.go

@@ -1,8 +0,0 @@
-//go:build darwin || freebsd
-
-package quic
-
-import "syscall"
-
-func maybeSetGSO(_ syscall.RawConn) bool                { return false }
-func appendUDPSegmentSizeMsg(_ []byte, _ uint16) []byte { return nil }

sys_conn_oob.go

@@ -5,7 +5,6 @@ package quic
 import (
 	"encoding/binary"
 	"errors"
-	"fmt"
 	"log"
 	"net"
 	"net/netip"
@@ -128,10 +127,6 @@ func newConn(c OOBCapablePacketConn, supportsDF bool) (*oobConn, error) {
 		bc = ipv4.NewPacketConn(c)
 	}
 
-	// Try enabling GSO.
-	// This will only succeed on Linux, and only for kernels > 4.18.
-	supportsGSO := maybeSetGSO(rawConn)
-
 	msgs := make([]ipv4.Message, batchSize)
 	for i := range msgs {
 		// preallocate the [][]byte
@@ -144,7 +139,6 @@ func newConn(c OOBCapablePacketConn, supportsDF bool) (*oobConn, error) {
 		readPos:              batchSize,
 	}
 	oobConn.cap.DF = supportsDF
-	oobConn.cap.GSO = supportsGSO
 	for i := 0; i < batchSize; i++ {
 		oobConn.messages[i].OOB = make([]byte, oobBufferSize)
 	}
@@ -231,17 +225,9 @@ func (c *oobConn) ReadPacket() (receivedPacket, error) {
 }
 
 // WritePacket writes a new packet.
-// If the connection supports GSO (and we activated GSO support before),
+// If the connection supports GSO, it's the caller's responsibility to append the right control mesage.
-// it appends the UDP_SEGMENT size message to oob.
+func (c *oobConn) WritePacket(b []byte, addr net.Addr, oob []byte) (int, error) {
-// Callers are advised to make sure that oob has a sufficient capacity,
+	n, _, err := c.OOBCapablePacketConn.WriteMsgUDP(b, oob, addr.(*net.UDPAddr))
-// such that appending the UDP_SEGMENT size message doesn't cause an allocation.
-func (c *oobConn) WritePacket(b []byte, packetSize uint16, addr net.Addr, oob []byte) (n int, err error) {
-	if c.cap.GSO {
-		oob = appendUDPSegmentSizeMsg(oob, packetSize)
-	} else if uint16(len(b)) != packetSize {
-		panic(fmt.Sprintf("inconsistent length. got: %d. expected %d", packetSize, len(b)))
-	}
-	n, _, err = c.OOBCapablePacketConn.WriteMsgUDP(b, oob, addr.(*net.UDPAddr))
 	return n, err
 }
 

transport.go

@@ -179,7 +179,7 @@ func (t *Transport) dial(ctx context.Context, addr net.Addr, hostname string, tl
 		}
 		tlsConf.ServerName = hostname
 	}
-	return dial(ctx, newSendConn(t.conn, addr), t.connIDGenerator, t.handlerMap, tlsConf, conf, onClose, use0RTT)
+	return dial(ctx, newSendConn(t.conn, addr, packetInfo{}, utils.DefaultLogger), t.connIDGenerator, t.handlerMap, tlsConf, conf, onClose, use0RTT)
 }
 
 func (t *Transport) init(allowZeroLengthConnIDs bool) error {
@@ -195,7 +195,6 @@ func (t *Transport) init(allowZeroLengthConnIDs bool) error {
 				return
 			}
 		}
-		t.conn = conn
 
 		t.logger = utils.DefaultLogger // TODO: make this configurable
 		t.conn = conn
@@ -229,7 +228,7 @@ func (t *Transport) WriteTo(b []byte, addr net.Addr) (int, error) {
 	if err := t.init(false); err != nil {
 		return 0, err
 	}
-	return t.conn.WritePacket(b, uint16(len(b)), addr, nil)
+	return t.conn.WritePacket(b, addr, nil)
 }
 
 func (t *Transport) enqueueClosePacket(p closePacket) {
@@ -247,7 +246,7 @@ func (t *Transport) runSendQueue() {
 		case <-t.listening:
 			return
 		case p := <-t.closeQueue:
-			t.conn.WritePacket(p.payload, uint16(len(p.payload)), p.addr, p.info.OOB())
+			t.conn.WritePacket(p.payload, p.addr, p.info.OOB())
 		case p := <-t.statelessResetQueue:
 			t.sendStatelessReset(p)
 		}
@@ -408,7 +407,7 @@ func (t *Transport) sendStatelessReset(p receivedPacket) {
 	rand.Read(data)
 	data[0] = (data[0] & 0x7f) | 0x40
 	data = append(data, token[:]...)
-	if _, err := t.conn.WritePacket(data, uint16(len(data)), p.remoteAddr, p.info.OOB()); err != nil {
+	if _, err := t.conn.WritePacket(data, p.remoteAddr, p.info.OOB()); err != nil {
 		t.logger.Debugf("Error sending Stateless Reset to %s: %s", p.remoteAddr, err)
 	}
 }