Detects interface status on linux

src/tun_linux.go

@@ -6,6 +6,7 @@ package main
 import (
 	"encoding/binary"
 	"errors"
+	"fmt"
 	"golang.org/x/sys/unix"
 	"net"
 	"os"
@@ -13,12 +14,93 @@ import (
 	"unsafe"
 )
 
-const CloneDevicePath = "/dev/net/tun"
+// #include <string.h>
+// #include <unistd.h>
+// #include <net/if.h>
+// #include <netinet/in.h>
+// #include <linux/netlink.h>
+// #include <linux/rtnetlink.h>
+//
+// /* Creates a netlink socket
+//  * listening to the RTMGRP_LINK multicast group
+//  */
+//
+// int bind_rtmgrp() {
+//   int nl_sock = socket(AF_NETLINK, SOCK_RAW, NETLINK_ROUTE);
+//   if (nl_sock < 0)
+//     return -1;
+//
+//	 struct sockaddr_nl addr;
+//   memset ((void *) &addr, 0, sizeof (addr));
+//   addr.nl_family = AF_NETLINK;
+//   addr.nl_pid = getpid ();
+//   addr.nl_groups = RTMGRP_LINK | RTMGRP_IPV4_IFADDR | RTMGRP_IPV6_IFADDR;
+//
+//   if (bind(nl_sock, (struct sockaddr *) &addr, sizeof (addr)) < 0)
+//     return -1;
+//
+//   return nl_sock;
+// }
+import "C"
+
+const (
+	CloneDevicePath = "/dev/net/tun"
+	IFReqSize       = unix.IFNAMSIZ + 64
+)
 
 type NativeTun struct {
 	fd     *os.File
+	index  int
 	name   string
-	events chan TUNEvent
+	errors chan error    // async error handling
+	events chan TUNEvent //
+}
+
+func (tun *NativeTun) RoutineNetlinkListener() {
+	sock := int(C.bind_rtmgrp())
+	if sock < 0 {
+		tun.errors <- errors.New("Failed to create netlink event listener")
+		return
+	}
+
+	for msg := make([]byte, 1<<16); ; {
+
+		msgn, _, _, _, err := unix.Recvmsg(sock, msg[:], nil, 0)
+		if err != nil {
+			tun.errors <- fmt.Errorf("Failed to receive netlink message: %s", err.Error())
+			return
+		}
+
+		for remain := msg[:msgn]; len(remain) >= unix.SizeofNlMsghdr; {
+
+			hdr := *(*unix.NlMsghdr)(unsafe.Pointer(&remain[0]))
+
+			if int(hdr.Len) > len(remain) {
+				break
+			}
+
+			switch hdr.Type {
+			case unix.NLMSG_DONE:
+				remain = []byte{}
+
+			case unix.RTM_NEWLINK:
+				info := *(*unix.IfInfomsg)(unsafe.Pointer(&remain[unix.SizeofNlMsghdr]))
+
+				if info.Flags&unix.IFF_RUNNING != 0 {
+					tun.events <- TUNEventUp
+				}
+
+				if info.Flags&unix.IFF_RUNNING == 0 {
+					tun.events <- TUNEventDown
+				}
+
+				remain = remain[hdr.Len:]
+
+			default:
+				remain = remain[hdr.Len:]
+			}
+		}
+	}
 }
 
 func (tun *NativeTun) isUp() (bool, error) {
@@ -30,6 +112,46 @@ func (tun *NativeTun) Name() string {
 	return tun.name
 }
 
+func toInt32(val []byte) int {
+	n := binary.LittleEndian.Uint32(val[:4])
+	if n >= (1 << 31) {
+		return int(n-(1<<31)) - (1 << 31)
+	}
+	return int(n)
+}
+
+func getDummySock() (int, error) {
+	return unix.Socket(
+		unix.AF_INET,
+		unix.SOCK_DGRAM,
+		0,
+	)
+}
+
+func getIFIndex(name string) (int, error) {
+	fd, err := getDummySock()
+	if err != nil {
+		return 0, err
+	}
+
+	defer unix.Close(fd)
+
+	var ifr [IFReqSize]byte
+	copy(ifr[:], name)
+	_, _, errno := unix.Syscall(
+		unix.SYS_IOCTL,
+		uintptr(fd),
+		uintptr(unix.SIOCGIFINDEX),
+		uintptr(unsafe.Pointer(&ifr[0])),
+	)
+
+	if errno != 0 {
+		return 0, errno
+	}
+
+	return toInt32(ifr[unix.IFNAMSIZ:]), nil
+}
+
 func (tun *NativeTun) setMTU(n int) error {
 
 	// open datagram socket
@@ -48,7 +170,7 @@ func (tun *NativeTun) setMTU(n int) error {
 
 	// do ioctl call
 
-	var ifr [64]byte
+	var ifr [IFReqSize]byte
 	copy(ifr[:], tun.name)
 	binary.LittleEndian.PutUint32(ifr[16:20], uint32(n))
 	_, _, errno := unix.Syscall(
@@ -83,7 +205,7 @@ func (tun *NativeTun) MTU() (int, error) {
 
 	// do ioctl call
 
-	var ifr [64]byte
+	var ifr [IFReqSize]byte
 	copy(ifr[:], tun.name)
 	_, _, errno := unix.Syscall(
 		unix.SYS_IOCTL,
@@ -109,7 +231,12 @@ func (tun *NativeTun) Write(d []byte) (int, error) {
 }
 
 func (tun *NativeTun) Read(d []byte) (int, error) {
+	select {
+	case err := <-tun.errors:
+		return 0, err
+	default:
 		return tun.fd.Read(d)
+	}
 }
 
 func (tun *NativeTun) Events() chan TUNEvent {
@@ -131,11 +258,11 @@ func CreateTUN(name string) (TUNDevice, error) {
 
 	// create new device
 
-	var ifr [64]byte
+	var ifr [IFReqSize]byte
 	var flags uint16 = unix.IFF_TUN | unix.IFF_NO_PI
 	nameBytes := []byte(name)
 	if len(nameBytes) >= unix.IFNAMSIZ {
-		return nil, errors.New("Name size too long")
+		return nil, errors.New("Interface name too long")
 	}
 	copy(ifr[:], nameBytes)
 	binary.LittleEndian.PutUint16(ifr[16:], flags)
@@ -147,7 +274,7 @@ func CreateTUN(name string) (TUNDevice, error) {
 		uintptr(unsafe.Pointer(&ifr[0])),
 	)
 	if errno != 0 {
-		return nil, errors.New("Failed to create tun, ioctl call failed")
+		return nil, errno
 	}
 
 	// read (new) name of interface
@@ -158,13 +285,21 @@ func CreateTUN(name string) (TUNDevice, error) {
 		fd:     fd,
 		name:   newName,
 		events: make(chan TUNEvent, 5),
+		errors: make(chan error, 5),
 	}
 
-	// TODO: Wait for device to be upped
-	device.events <- TUNEventUp
+	// fetch IF index
+
+	device.index, err = getIFIndex(device.name)
+	if err != nil {
+		return nil, err
+	}
+
+	go device.RoutineNetlinkListener()
 
 	// set default MTU
 
-	err = device.setMTU(DefaultMTU)
-	return device, err
+	fmt.Println(device)
+
+	return device, device.setMTU(DefaultMTU)
 }