Removed IFF_NO_PI from TUN linux

This change was needed for the Linux TUN status hack
to work properly (not increment the error counter).

This commit also updates the TUN interface to allow for
the construction / removal of the TUN info headers in-place.

src/receive.go

@@ -243,13 +243,24 @@ func (device *Device) RoutineDecryption() {
 			counter := elem.packet[MessageTransportOffsetCounter:MessageTransportOffsetContent]
 			content := elem.packet[MessageTransportOffsetContent:]
 
+			// expand nonce
+
+			nonce[0x4] = counter[0x0]
+			nonce[0x5] = counter[0x1]
+			nonce[0x6] = counter[0x2]
+			nonce[0x7] = counter[0x3]
+
+			nonce[0x8] = counter[0x4]
+			nonce[0x9] = counter[0x5]
+			nonce[0xa] = counter[0x6]
+			nonce[0xb] = counter[0x7]
+
 			// decrypt and release to consumer
 
 			var err error
-			copy(nonce[4:], counter)
 			elem.counter = binary.LittleEndian.Uint64(counter)
 			elem.packet, err = elem.keyPair.receive.Open(
-				elem.buffer[:0],
+				content[:0],
 				nonce[:],
 				content,
 				nil,
@@ -495,6 +506,7 @@ func (peer *Peer) RoutineSequentialReceiver() {
 			// wait for decryption
 
 			elem.mutex.Lock()
+
 			if elem.IsDropped() {
 				continue
 			}
@@ -603,8 +615,11 @@ func (peer *Peer) RoutineSequentialReceiver() {
 
 			// write to tun device
 
+			offset := MessageTransportOffsetContent
 			atomic.AddUint64(&peer.stats.rxBytes, uint64(len(elem.packet)))
-			_, err := device.tun.device.Write(elem.packet)
+			_, err := device.tun.device.Write(
+				elem.buffer[:offset+len(elem.packet)],
+				offset)
 			device.PutMessageBuffer(elem.buffer)
 			if err != nil {
 				logError.Println("Failed to write packet to TUN device:", err)

src/send.go

@@ -127,8 +127,9 @@ func (device *Device) RoutineReadFromTUN() {
 
 		// read packet
 
-		elem.packet = elem.buffer[MessageTransportHeaderSize:]
-		size, err := device.tun.device.Read(elem.packet)
+		offset := MessageTransportHeaderSize
+		size, err := device.tun.device.Read(elem.buffer[:], offset)
+
 		if err != nil {
 			logError.Println("Failed to read packet from TUN device:", err)
 			device.Close()
@@ -139,7 +140,7 @@ func (device *Device) RoutineReadFromTUN() {
 			continue
 		}
 
-		elem.packet = elem.packet[:size]
+		elem.packet = elem.buffer[offset : offset+size]
 
 		// lookup peer
 

src/tun.go

@@ -16,13 +16,13 @@ const (
 )
 
 type TUNDevice interface {
-	File() *os.File            // returns the file descriptor of the device
-	Read([]byte) (int, error)  // read a packet from the device (without any additional headers)
-	Write([]byte) (int, error) // writes a packet to the device (without any additional headers)
-	MTU() (int, error)         // returns the MTU of the device
-	Name() string              // returns the current name
-	Events() chan TUNEvent     // returns a constant channel of events related to the device
-	Close() error              // stops the device and closes the event channel
+	File() *os.File                 // returns the file descriptor of the device
+	Read([]byte, int) (int, error)  // read a packet from the device (without any additional headers)
+	Write([]byte, int) (int, error) // writes a packet to the device (without any additional headers)
+	MTU() (int, error)              // returns the MTU of the device
+	Name() string                   // returns the current name
+	Events() chan TUNEvent          // returns a constant channel of events related to the device
+	Close() error                   // stops the device and closes the event channel
 }
 
 func (device *Device) RoutineTUNEventReader() {

src/tun_linux.go

@@ -7,6 +7,7 @@ import (
 	"encoding/binary"
 	"errors"
 	"fmt"
+	"golang.org/x/net/ipv6"
 	"golang.org/x/sys/unix"
 	"net"
 	"os"
@@ -249,16 +250,41 @@ func (tun *NativeTun) MTU() (int, error) {
 	return int(val), nil
 }
 
-func (tun *NativeTun) Write(d []byte) (int, error) {
-	return tun.fd.Write(d)
+func (tun *NativeTun) Write(buff []byte, offset int) (int, error) {
+
+	// reserve space for header
+
+	buff = buff[offset-4:]
+
+	// add packet information header
+
+	buff[0] = 0x00
+	buff[1] = 0x00
+
+	if buff[4] == ipv6.Version<<4 {
+		buff[2] = 0x86
+		buff[3] = 0xdd
+	} else {
+		buff[2] = 0x08
+		buff[3] = 0x00
+	}
+
+	// write
+
+	return tun.fd.Write(buff)
 }
 
-func (tun *NativeTun) Read(d []byte) (int, error) {
+func (tun *NativeTun) Read(buff []byte, offset int) (int, error) {
 	select {
 	case err := <-tun.errors:
 		return 0, err
 	default:
-		return tun.fd.Read(d)
+		buff := buff[offset-4:]
+		n, err := tun.fd.Read(buff[:])
+		if n < 4 {
+			return 0, err
+		}
+		return n - 4, err
 	}
 }
 
@@ -306,7 +332,7 @@ func CreateTUN(name string) (TUNDevice, error) {
 	// create new device
 
 	var ifr [IFReqSize]byte
-	var flags uint16 = unix.IFF_TUN | unix.IFF_NO_PI
+	var flags uint16 = unix.IFF_TUN // | unix.IFF_NO_PI
 	nameBytes := []byte(name)
 	if len(nameBytes) >= unix.IFNAMSIZ {
 		return nil, errors.New("Interface name too long")