conn: separate gso and sticky control

Android wants GSO but not sticky.

Signed-off-by: Jason A. Donenfeld <Jason@zx2c4.com>

conn/bind_std.go

@@ -65,7 +65,7 @@ func NewStdNetBind() Bind {
 				msgs := make([]ipv6.Message, IdealBatchSize)
 				for i := range msgs {
 					msgs[i].Buffers = make(net.Buffers, 1)
-					msgs[i].OOB = make([]byte, controlSize)
+					msgs[i].OOB = make([]byte, stickyControlSize+gsoControlSize)
 				}
 				return &msgs
 			},

conn/gso_default.go

@@ -0,0 +1,21 @@
+//go:build !linux
+
+/* SPDX-License-Identifier: MIT
+ *
+ * Copyright (C) 2017-2023 WireGuard LLC. All Rights Reserved.
+ */
+
+package conn
+
+// getGSOSize parses control for UDP_GRO and if found returns its GSO size data.
+func getGSOSize(control []byte) (int, error) {
+	return 0, nil
+}
+
+// setGSOSize sets a UDP_SEGMENT in control based on gsoSize.
+func setGSOSize(control *[]byte, gsoSize uint16) {
+}
+
+// gsoControlSize returns the recommended buffer size for pooling sticky and UDP
+// offloading control data.
+const gsoControlSize = 0

conn/gso_linux.go

@@ -0,0 +1,65 @@
+//go:build linux
+
+/* SPDX-License-Identifier: MIT
+ *
+ * Copyright (C) 2017-2023 WireGuard LLC. All Rights Reserved.
+ */
+
+package conn
+
+import (
+	"fmt"
+	"unsafe"
+
+	"golang.org/x/sys/unix"
+)
+
+const (
+	sizeOfGSOData = 2
+)
+
+// getGSOSize parses control for UDP_GRO and if found returns its GSO size data.
+func getGSOSize(control []byte) (int, error) {
+	var (
+		hdr  unix.Cmsghdr
+		data []byte
+		rem  = control
+		err  error
+	)
+
+	for len(rem) > unix.SizeofCmsghdr {
+		hdr, data, rem, err = unix.ParseOneSocketControlMessage(rem)
+		if err != nil {
+			return 0, fmt.Errorf("error parsing socket control message: %w", err)
+		}
+		if hdr.Level == unix.SOL_UDP && hdr.Type == unix.UDP_GRO && len(data) >= sizeOfGSOData {
+			var gso uint16
+			copy(unsafe.Slice((*byte)(unsafe.Pointer(&gso)), sizeOfGSOData), data[:sizeOfGSOData])
+			return int(gso), nil
+		}
+	}
+	return 0, nil
+}
+
+// setGSOSize sets a UDP_SEGMENT in control based on gsoSize. It leaves existing
+// data in control untouched.
+func setGSOSize(control *[]byte, gsoSize uint16) {
+	existingLen := len(*control)
+	avail := cap(*control) - existingLen
+	space := unix.CmsgSpace(sizeOfGSOData)
+	if avail < space {
+		return
+	}
+	*control = (*control)[:cap(*control)]
+	gsoControl := (*control)[existingLen:]
+	hdr := (*unix.Cmsghdr)(unsafe.Pointer(&(gsoControl)[0]))
+	hdr.Level = unix.SOL_UDP
+	hdr.Type = unix.UDP_SEGMENT
+	hdr.SetLen(unix.CmsgLen(sizeOfGSOData))
+	copy((gsoControl)[unix.SizeofCmsghdr:], unsafe.Slice((*byte)(unsafe.Pointer(&gsoSize)), sizeOfGSOData))
+	*control = (*control)[:existingLen+space]
+}
+
+// gsoControlSize returns the recommended buffer size for pooling UDP
+// offloading control data.
+var gsoControlSize = unix.CmsgSpace(sizeOfGSOData)

conn/sticky_default.go

@@ -35,17 +35,8 @@ func getSrcFromControl(control []byte, ep *StdNetEndpoint) {
 func setSrcControl(control *[]byte, ep *StdNetEndpoint) {
 }
 
-// getGSOSize parses control for UDP_GRO and if found returns its GSO size data.
+// stickyControlSize returns the recommended buffer size for pooling sticky
-func getGSOSize(control []byte) (int, error) {
-	return 0, nil
-}
-
-// setGSOSize sets a UDP_SEGMENT in control based on gsoSize.
-func setGSOSize(control *[]byte, gsoSize uint16) {
-}
-
-// controlSize returns the recommended buffer size for pooling sticky and UDP
 // offloading control data.
-const controlSize = 0
+const stickyControlSize = 0
 
 const StdNetSupportsStickySockets = false

conn/sticky_linux.go

@@ -8,7 +8,6 @@
 package conn
 
 import (
-	"fmt"
 	"net/netip"
 	"unsafe"
 
@@ -106,54 +105,8 @@ func setSrcControl(control *[]byte, ep *StdNetEndpoint) {
 	*control = append(*control, ep.src...)
 }
 
-const (
+// stickyControlSize returns the recommended buffer size for pooling sticky
-	sizeOfGSOData = 2
-)
-
-// getGSOSize parses control for UDP_GRO and if found returns its GSO size data.
-func getGSOSize(control []byte) (int, error) {
-	var (
-		hdr  unix.Cmsghdr
-		data []byte
-		rem  = control
-		err  error
-	)
-
-	for len(rem) > unix.SizeofCmsghdr {
-		hdr, data, rem, err = unix.ParseOneSocketControlMessage(rem)
-		if err != nil {
-			return 0, fmt.Errorf("error parsing socket control message: %w", err)
-		}
-		if hdr.Level == unix.SOL_UDP && hdr.Type == unix.UDP_GRO && len(data) >= sizeOfGSOData {
-			var gso uint16
-			copy(unsafe.Slice((*byte)(unsafe.Pointer(&gso)), sizeOfGSOData), data[:sizeOfGSOData])
-			return int(gso), nil
-		}
-	}
-	return 0, nil
-}
-
-// setGSOSize sets a UDP_SEGMENT in control based on gsoSize. It leaves existing
-// data in control untouched.
-func setGSOSize(control *[]byte, gsoSize uint16) {
-	existingLen := len(*control)
-	avail := cap(*control) - existingLen
-	space := unix.CmsgSpace(sizeOfGSOData)
-	if avail < space {
-		return
-	}
-	*control = (*control)[:cap(*control)]
-	gsoControl := (*control)[existingLen:]
-	hdr := (*unix.Cmsghdr)(unsafe.Pointer(&(gsoControl)[0]))
-	hdr.Level = unix.SOL_UDP
-	hdr.Type = unix.UDP_SEGMENT
-	hdr.SetLen(unix.CmsgLen(sizeOfGSOData))
-	copy((gsoControl)[unix.SizeofCmsghdr:], unsafe.Slice((*byte)(unsafe.Pointer(&gsoSize)), sizeOfGSOData))
-	*control = (*control)[:existingLen+space]
-}
-
-// controlSize returns the recommended buffer size for pooling sticky and UDP
 // offloading control data.
-var controlSize = unix.CmsgSpace(unix.SizeofInet6Pktinfo) + unix.CmsgSpace(sizeOfGSOData)
+var stickyControlSize = unix.CmsgSpace(unix.SizeofInet6Pktinfo)
 
 const StdNetSupportsStickySockets = true

conn/sticky_linux_test.go

@@ -60,7 +60,7 @@ func Test_setSrcControl(t *testing.T) {
 		}
 		setSrc(ep, netip.MustParseAddr("127.0.0.1"), 5)
 
-		control := make([]byte, controlSize)
+		control := make([]byte, stickyControlSize)
 
 		setSrcControl(&control, ep)
 
@@ -89,7 +89,7 @@ func Test_setSrcControl(t *testing.T) {
 		}
 		setSrc(ep, netip.MustParseAddr("::1"), 5)
 
-		control := make([]byte, controlSize)
+		control := make([]byte, stickyControlSize)
 
 		setSrcControl(&control, ep)
 
@@ -113,7 +113,7 @@ func Test_setSrcControl(t *testing.T) {
 	})
 
 	t.Run("ClearOnNoSrc", func(t *testing.T) {
-		control := make([]byte, controlSize)
+		control := make([]byte, stickyControlSize)
 		hdr := (*unix.Cmsghdr)(unsafe.Pointer(&control[0]))
 		hdr.Level = 1
 		hdr.Type = 2
@@ -129,7 +129,7 @@ func Test_setSrcControl(t *testing.T) {
 
 func Test_getSrcFromControl(t *testing.T) {
 	t.Run("IPv4", func(t *testing.T) {
-		control := make([]byte, controlSize)
+		control := make([]byte, stickyControlSize)
 		hdr := (*unix.Cmsghdr)(unsafe.Pointer(&control[0]))
 		hdr.Level = unix.IPPROTO_IP
 		hdr.Type = unix.IP_PKTINFO
@@ -149,7 +149,7 @@ func Test_getSrcFromControl(t *testing.T) {
 		}
 	})
 	t.Run("IPv6", func(t *testing.T) {
-		control := make([]byte, controlSize)
+		control := make([]byte, stickyControlSize)
 		hdr := (*unix.Cmsghdr)(unsafe.Pointer(&control[0]))
 		hdr.Level = unix.IPPROTO_IPV6
 		hdr.Type = unix.IPV6_PKTINFO