Reviewed and added OSX patch

The patch was provided by:
Naveen Nathan <naveen@lastninja.net>

The following modifications to the patch was made:

- Added copyright notice
- Fixed file descriptor leak in .MTU() method
- Migrated to the new(er) golang.org/x/sys/unix package
- Removed non-functioning Daemonize method

src/daemon_darwin.go

@@ -0,0 +1,9 @@
+package main
+
+import (
+	"errors"
+)
+
+func Daemonize() error {
+	return errors.New("Not implemented on OSX")
+}

src/tun_darwin.go

@@ -0,0 +1,278 @@
+/* Copyright (c) 2016, Song Gao <song@gao.io>
+ * All rights reserved.
+ *
+ * Code from https://github.com/songgao/water
+ */
+
+package main
+
+import (
+	"encoding/binary"
+	"errors"
+	"fmt"
+	"golang.org/x/net/ipv4"
+	"golang.org/x/net/ipv6"
+	"golang.org/x/sys/unix"
+	"io"
+	"os"
+	"sync"
+	"unsafe"
+)
+
+const utunControlName = "com.apple.net.utun_control"
+
+// _CTLIOCGINFO value derived from /usr/include/sys/{kern_control,ioccom}.h
+const _CTLIOCGINFO = (0x40000000 | 0x80000000) | ((100 & 0x1fff) << 16) | uint32(byte('N'))<<8 | 3
+
+// sockaddr_ctl specifeid in /usr/include/sys/kern_control.h
+type sockaddrCtl struct {
+	scLen      uint8
+	scFamily   uint8
+	ssSysaddr  uint16
+	scID       uint32
+	scUnit     uint32
+	scReserved [5]uint32
+}
+
+var sockaddrCtlSize uintptr = 32
+
+func CreateTUN(name string) (ifce TUNDevice, err error) {
+	ifIndex := -1
+	fmt.Sscanf(name, "utun%d", &ifIndex)
+	if ifIndex < 0 {
+		return nil, fmt.Errorf("error parsing interface name %s, must be utun[0-9]+", name)
+	}
+
+	fd, err := unix.Socket(unix.AF_SYSTEM, unix.SOCK_DGRAM, 2)
+
+	if err != nil {
+		return nil, fmt.Errorf("error in unix.Socket: %v", err)
+	}
+
+	var ctlInfo = &struct {
+		ctlID   uint32
+		ctlName [96]byte
+	}{}
+
+	copy(ctlInfo.ctlName[:], []byte(utunControlName))
+
+	_, _, errno := unix.Syscall(
+		unix.SYS_IOCTL,
+		uintptr(fd),
+		uintptr(_CTLIOCGINFO),
+		uintptr(unsafe.Pointer(ctlInfo)),
+	)
+
+	if errno != 0 {
+		err = errno
+		return nil, fmt.Errorf("error in unix.Syscall(unix.SYS_IOTL, ...): %v", err)
+	}
+
+	sc := sockaddrCtl{
+		scLen:     uint8(sockaddrCtlSize),
+		scFamily:  unix.AF_SYSTEM,
+		ssSysaddr: 2,
+		scID:      ctlInfo.ctlID,
+		scUnit:    uint32(ifIndex) + 1,
+	}
+
+	scPointer := unsafe.Pointer(&sc)
+
+	_, _, errno = unix.RawSyscall(
+		unix.SYS_CONNECT,
+		uintptr(fd),
+		uintptr(scPointer),
+		uintptr(sockaddrCtlSize),
+	)
+
+	if errno != 0 {
+		err = errno
+		return nil, fmt.Errorf("error in unix.RawSyscall(unix.SYS_CONNECT, ...): %v", err)
+	}
+
+	// read (new) name of interface
+
+	var ifName struct {
+		name [16]byte
+	}
+	ifNameSize := uintptr(16)
+
+	_, _, errno = unix.Syscall6(
+		unix.SYS_GETSOCKOPT,
+		uintptr(fd),
+		2, /* #define SYSPROTO_CONTROL 2 */
+		2, /* #define UTUN_OPT_IFNAME 2 */
+		uintptr(unsafe.Pointer(&ifName)),
+		uintptr(unsafe.Pointer(&ifNameSize)), 0)
+
+	if errno != 0 {
+		err = errno
+		return nil, fmt.Errorf("error in unix.Syscall6(unix.SYS_GETSOCKOPT, ...): %v", err)
+	}
+
+	device := &tunReadCloser{
+		name: string(ifName.name[:ifNameSize-1 /* -1 is for \0 */]),
+		f:    os.NewFile(uintptr(fd), string(ifName.name[:])),
+		mtu:  1500,
+	}
+
+	// set default MTU
+
+	err = device.setMTU(DefaultMTU)
+
+	return device, err
+}
+
+// tunReadCloser is a hack to work around the first 4 bytes "packet
+// information" because there doesn't seem to be an IFF_NO_PI for darwin.
+type tunReadCloser struct {
+	name string
+	f    io.ReadWriteCloser
+	mtu  int
+
+	rMu  sync.Mutex
+	rBuf []byte
+
+	wMu  sync.Mutex
+	wBuf []byte
+}
+
+var _ io.ReadWriteCloser = (*tunReadCloser)(nil)
+
+func (t *tunReadCloser) Read(to []byte) (int, error) {
+	t.rMu.Lock()
+	defer t.rMu.Unlock()
+
+	if cap(t.rBuf) < len(to)+4 {
+		t.rBuf = make([]byte, len(to)+4)
+	}
+	t.rBuf = t.rBuf[:len(to)+4]
+
+	n, err := t.f.Read(t.rBuf)
+	copy(to, t.rBuf[4:])
+	return n - 4, err
+}
+
+func (t *tunReadCloser) Write(from []byte) (int, error) {
+
+	if len(from) == 0 {
+		return 0, unix.EIO
+	}
+
+	t.wMu.Lock()
+	defer t.wMu.Unlock()
+
+	if cap(t.wBuf) < len(from)+4 {
+		t.wBuf = make([]byte, len(from)+4)
+	}
+	t.wBuf = t.wBuf[:len(from)+4]
+
+	// determine the IP Family for the NULL L2 Header
+
+	ipVer := from[0] >> 4
+	if ipVer == ipv4.Version {
+		t.wBuf[3] = unix.AF_INET
+	} else if ipVer == ipv6.Version {
+		t.wBuf[3] = unix.AF_INET6
+	} else {
+		return 0, errors.New("Unable to determine IP version from packet.")
+	}
+
+	copy(t.wBuf[4:], from)
+
+	n, err := t.f.Write(t.wBuf)
+	return n - 4, err
+}
+
+func (t *tunReadCloser) Close() error {
+
+	// lock to make sure no read/write is in process.
+
+	t.rMu.Lock()
+	defer t.rMu.Unlock()
+
+	t.wMu.Lock()
+	defer t.wMu.Unlock()
+
+	return t.f.Close()
+}
+
+func (t *tunReadCloser) Name() string {
+	return t.name
+}
+
+func (t *tunReadCloser) setMTU(n int) error {
+
+	// open datagram socket
+
+	var fd int
+
+	fd, err := unix.Socket(
+		unix.AF_INET,
+		unix.SOCK_DGRAM,
+		0,
+	)
+
+	if err != nil {
+		return err
+	}
+
+	defer unix.Close(fd)
+
+	// do ioctl call
+
+	var ifr [32]byte
+	copy(ifr[:], t.name)
+	binary.LittleEndian.PutUint32(ifr[16:20], uint32(n))
+	_, _, errno := unix.Syscall(
+		unix.SYS_IOCTL,
+		uintptr(fd),
+		uintptr(unix.SIOCSIFMTU),
+		uintptr(unsafe.Pointer(&ifr[0])),
+	)
+
+	if errno != 0 {
+		return fmt.Errorf("Failed to set MTU on %s", t.name)
+	}
+
+	return nil
+}
+
+func (t *tunReadCloser) MTU() (int, error) {
+
+	// open datagram socket
+
+	fd, err := unix.Socket(
+		unix.AF_INET,
+		unix.SOCK_DGRAM,
+		0,
+	)
+
+	if err != nil {
+		return 0, err
+	}
+
+	defer unix.Close(fd)
+
+	// do ioctl call
+
+	var ifr [64]byte
+	copy(ifr[:], t.name)
+	_, _, errno := unix.Syscall(
+		unix.SYS_IOCTL,
+		uintptr(fd),
+		uintptr(unix.SIOCGIFMTU),
+		uintptr(unsafe.Pointer(&ifr[0])),
+	)
+	if errno != 0 {
+		return 0, fmt.Errorf("Failed to get MTU on %s", t.name)
+	}
+
+	// convert result to signed 32-bit int
+
+	val := binary.LittleEndian.Uint32(ifr[16:20])
+	if val >= (1 << 31) {
+		return int(val-(1<<31)) - (1 << 31), nil
+	}
+	return int(val), nil
+}

src/uapi_darwin.go

@@ -0,0 +1,83 @@
+package main
+
+import (
+	"fmt"
+	"net"
+	"os"
+	"time"
+)
+
+/* TODO:
+ * This code can be improved by using fsnotify once:
+ * https://github.com/fsnotify/fsnotify/pull/205
+ * Is merged
+ */
+
+type UAPIListener struct {
+	listener net.Listener // unix socket listener
+	connNew  chan net.Conn
+	connErr  chan error
+}
+
+func (l *UAPIListener) Accept() (net.Conn, error) {
+	for {
+		select {
+		case conn := <-l.connNew:
+			return conn, nil
+
+		case err := <-l.connErr:
+			return nil, err
+		}
+	}
+}
+
+func (l *UAPIListener) Close() error {
+	return l.listener.Close()
+}
+
+func (l *UAPIListener) Addr() net.Addr {
+	return nil
+}
+
+func NewUAPIListener(name string) (net.Listener, error) {
+
+	// open UNIX socket
+
+	socketPath := fmt.Sprintf("/var/run/wireguard/%s.sock", name)
+	listener, err := net.Listen("unix", socketPath)
+	if err != nil {
+		return nil, err
+	}
+
+	uapi := &UAPIListener{
+		listener: listener,
+		connNew:  make(chan net.Conn, 1),
+		connErr:  make(chan error, 1),
+	}
+
+	// watch for deletion of socket
+
+	go func(l *UAPIListener) {
+		for ; ; time.Sleep(time.Second) {
+			if _, err := os.Stat(socketPath); os.IsNotExist(err) {
+				l.connErr <- err
+				return
+			}
+		}
+	}(uapi)
+
+	// watch for new connections
+
+	go func(l *UAPIListener) {
+		for {
+			conn, err := l.listener.Accept()
+			if err != nil {
+				l.connErr <- err
+				break
+			}
+			l.connNew <- conn
+		}
+	}(uapi)
+
+	return uapi, nil
+}