Fix: avoid extra copy on windows

core/device/tun/io_unix.go

@@ -0,0 +1,29 @@
+// +build darwin freebsd linux,!amd64,!arm64 openbsd
+
+package tun
+
+import (
+	"github.com/xjasonlyu/tun2socks/common/pool"
+)
+
+const offset = 4 /* 4 bytes TUN_PI */
+
+func (t *TUN) Read(packet []byte) (n int, err error) {
+	buf := pool.Get(offset + len(packet))
+	defer pool.Put(buf)
+
+	if n, err = t.nt.Read(buf, offset); err != nil {
+		return
+	}
+
+	copy(packet, buf[offset:offset+n])
+	return
+}
+
+func (t *TUN) Write(packet []byte) (int, error) {
+	buf := pool.Get(offset + len(packet))
+	defer pool.Put(buf)
+
+	copy(buf[offset:], packet)
+	return t.nt.Write(buf[:offset+len(packet)], offset)
+}

core/device/tun/io_windows.go

@@ -0,0 +1,11 @@
+package tun
+
+const offset = 0
+
+func (t *TUN) Read(packet []byte) (int, error) {
+	return t.nt.Read(packet, offset)
+}
+
+func (t *TUN) Write(packet []byte) (int, error) {
+	return t.nt.Write(packet, offset)
+}

core/device/tun/offset_unix.go

@@ -1,5 +0,0 @@
-// +build darwin freebsd linux openbsd
-
-package tun
-
-const offset = 4 /* 4 bytes TUN_PI */

core/device/tun/offset_windows.go

@@ -1,3 +0,0 @@
-package tun
-
-const offset = 0

core/device/tun/tun_linux_64bit.go

@@ -108,5 +108,3 @@ func setMTU(name string, n uint32) error {
 
 	return nil
 }
-
-var _ = offset /* ignore static check */

core/device/tun/tun_wg.go

@@ -5,7 +5,6 @@ package tun
 import (
 	"fmt"
 
-	"github.com/xjasonlyu/tun2socks/common/pool"
 	"github.com/xjasonlyu/tun2socks/core/device"
 	"github.com/xjasonlyu/tun2socks/core/device/rwbased"
 
@@ -48,26 +47,6 @@ func Open(opts ...Option) (device.Device, error) {
 	return t, nil
 }
 
-func (t *TUN) Read(packet []byte) (n int, err error) {
-	buf := pool.Get(offset + len(packet))
-	defer pool.Put(buf)
-
-	if n, err = t.nt.Read(buf, offset); err != nil {
-		return
-	}
-
-	copy(packet, buf[offset:offset+n])
-	return
-}
-
-func (t *TUN) Write(packet []byte) (int, error) {
-	buf := pool.Get(offset + len(packet))
-	defer pool.Put(buf)
-
-	copy(buf[offset:], packet)
-	return t.nt.Write(buf[:offset+len(packet)], offset)
-}
-
 func (t *TUN) Name() string {
 	name, _ := t.nt.Name()
 	return name