Add ability to set outgouing interface (only Linux support)

cmd/ping/ping.go

@@ -13,7 +13,7 @@ import (
 var usage = `
 Usage:
 
-    ping [-c count] [-i interval] [-t timeout] [--privileged] host
+    ping [-c count] [-i interval] [-t timeout] [-I iface] [--privileged] host
 
 Examples:
 
@@ -37,11 +37,12 @@ Examples:
 `
 
 func main() {
-	timeout := flag.Duration("t", time.Second*100000, "")
-	interval := flag.Duration("i", time.Second, "")
-	count := flag.Int("c", -1, "")
-	size := flag.Int("s", 24, "")
-	ttl := flag.Int("l", 64, "TTL")
+	timeout := flag.Duration("t", time.Second*100000, "time to wait for response")
+	interval := flag.Duration("i", time.Second, "interval between sending each packet")
+	count := flag.Int("c", -1, "stop after replies")
+	size := flag.Int("s", 24, "number of data bytes to be sent")
+	ttl := flag.Int("l", 64, "define time to live")
+	iface := flag.String("I", "", "interface name")
 	privileged := flag.Bool("privileged", false, "")
 	flag.Usage = func() {
 		fmt.Print(usage)
@@ -90,6 +91,7 @@ func main() {
 	pinger.Interval = *interval
 	pinger.Timeout = *timeout
 	pinger.TTL = *ttl
+	pinger.Iface = *iface
 	pinger.SetPrivileged(*privileged)
 
 	fmt.Printf("PING %s (%s):\n", pinger.Addr(), pinger.IPAddr())

packetconn.go

@@ -1,8 +1,11 @@
 package ping
 
 import (
+	"errors"
 	"net"
+	"reflect"
 	"runtime"
+	"syscall"
 	"time"
 
 	"golang.org/x/net/icmp"
@@ -18,6 +21,7 @@ type packetConn interface {
 	SetReadDeadline(t time.Time) error
 	WriteTo(b []byte, dst net.Addr) (int, error)
 	SetTTL(ttl int)
+	BindToDevice(iface string) error
 }
 
 type icmpConn struct {
@@ -37,6 +41,38 @@ func (c *icmpConn) SetReadDeadline(t time.Time) error {
 	return c.c.SetReadDeadline(t)
 }
 
+func getConnFD(conn *icmp.PacketConn) (fd int) {
+	var packetConn reflect.Value
+
+	defer func() {
+		if r := recover(); r != nil {
+			fd = -1
+		}
+	}()
+
+	if conn.IPv4PacketConn() != nil {
+		packetConn = reflect.ValueOf(conn.IPv4PacketConn().PacketConn)
+	} else if conn.IPv6PacketConn() != nil {
+		packetConn = reflect.ValueOf(conn.IPv6PacketConn().PacketConn)
+	} else {
+		return -1
+	}
+
+	netFD := reflect.Indirect(reflect.Indirect(packetConn).FieldByName("fd"))
+	pollFD := netFD.FieldByName("pfd")
+	systemFD := pollFD.FieldByName("Sysfd")
+	return int(systemFD.Int())
+}
+
+func (c *icmpConn) BindToDevice(ifName string) error {
+	if runtime.GOOS == "linux" {
+		if fd := getConnFD(c.c); fd >= 0 {
+			return syscall.BindToDevice(fd, ifName)
+		}
+	}
+	return errors.New("bind to interface unsupported") // FIXME: or nil
+}
+
 func (c *icmpConn) WriteTo(b []byte, dst net.Addr) (int, error) {
 	if c.c.IPv6PacketConn() != nil {
 		if err := c.c.IPv6PacketConn().SetHopLimit(c.ttl); err != nil {

ping.go

@@ -182,6 +182,9 @@ type Pinger struct {
 	// Source is the source IP address
 	Source string
 
+	// Iface used to send/recv ICMP messages
+	Iface string
+
 	// Channel and mutex used to communicate when the Pinger should stop between goroutines.
 	done chan interface{}
 	lock sync.Mutex
@@ -418,6 +421,12 @@ func (p *Pinger) Run() error {
 	}
 	defer conn.Close()
 
+	if p.Iface != "" {
+		if err = conn.BindToDevice(p.Iface); err != nil {
+			return err
+		}
+	}
+
 	conn.SetTTL(p.TTL)
 	return p.run(conn)
 }

ping_test.go

@@ -5,6 +5,7 @@ import (
 	"errors"
 	"fmt"
 	"net"
+	"runtime"
 	"runtime/debug"
 	"sync/atomic"
 	"testing"
@@ -385,6 +386,27 @@ func TestSetIPAddr(t *testing.T) {
 	AssertEqualStrings(t, googleaddr.String(), p.Addr())
 }
 
+func TestBindToDevice(t *testing.T) {
+	// Create a localhost ipv4 pinger
+	pinger := New("127.0.0.1")
+	pinger.ipv4 = true
+	pinger.Count = 1
+
+	// Set loopback interface: "lo"
+	pinger.Iface = "lo"
+	err := pinger.Run()
+	if runtime.GOOS == "linux" {
+		AssertNoError(t, err)
+	} else {
+		AssertError(t, err, "other platforms unsupported this feature")
+	}
+
+	// Set fake interface: "L()0pB@cK"
+	pinger.Iface = "L()0pB@cK"
+	err = pinger.Run()
+	AssertError(t, err, "device not found")
+}
+
 func TestEmptyIPAddr(t *testing.T) {
 	_, err := NewPinger("")
 	AssertError(t, err, "empty pinger did not return an error")
@@ -642,6 +664,7 @@ func (c testPacketConn) ICMPRequestType() icmp.Type        { return ipv4.ICMPTyp
 func (c testPacketConn) SetFlagTTL() error                 { return nil }
 func (c testPacketConn) SetReadDeadline(t time.Time) error { return nil }
 func (c testPacketConn) SetTTL(t int)                      {}
+func (c testPacketConn) BindToDevice(iface string) error   { return nil }
 
 func (c testPacketConn) ReadFrom(b []byte) (n int, ttl int, src net.Addr, err error) {
 	return 0, 0, nil, nil

utils_linux.go

@@ -1,7 +1,15 @@
-// +build linux
+//go:build linux
 
 package ping
 
+import (
+	"errors"
+	"reflect"
+	"syscall"
+
+	"golang.org/x/net/icmp"
+)
+
 // Returns the length of an ICMP message.
 func (p *Pinger) getMessageLength() int {
 	return p.Size + 8
@@ -17,3 +25,33 @@ func (p *Pinger) matchID(ID int) bool {
 	}
 	return true
 }
+
+func getConnFD(conn *icmp.PacketConn) (fd int) {
+	var packetConn reflect.Value
+
+	defer func() {
+		if r := recover(); r != nil {
+			fd = -1
+		}
+	}()
+
+	if conn.IPv4PacketConn() != nil {
+		packetConn = reflect.ValueOf(conn.IPv4PacketConn().PacketConn)
+	} else if conn.IPv6PacketConn() != nil {
+		packetConn = reflect.ValueOf(conn.IPv6PacketConn().PacketConn)
+	} else {
+		return -1
+	}
+
+	netFD := reflect.Indirect(reflect.Indirect(packetConn).FieldByName("fd"))
+	pollFD := netFD.FieldByName("pfd")
+	systemFD := pollFD.FieldByName("Sysfd")
+	return int(systemFD.Int())
+}
+
+func (c *icmpConn) BindToDevice(ifName string) error {
+	if fd := getConnFD(c.c); fd >= 0 {
+		return syscall.BindToDevice(fd, ifName)
+	}
+	return errors.New("bind to interface unsupported")
+}

utils_other.go

@@ -1,4 +1,4 @@
-// +build !linux,!windows
+//go:build !linux && !windows
 
 package ping
 
@@ -14,3 +14,7 @@ func (p *Pinger) matchID(ID int) bool {
 	}
 	return true
 }
+
+func (c *icmpConn) BindToDevice(ifName string) error {
+	return errors.New("bind to interface unsupported")
+}

utils_windows.go

@@ -1,4 +1,4 @@
-// +build windows
+//go:build windows
 
 package ping
 
@@ -22,3 +22,7 @@ func (p *Pinger) matchID(ID int) bool {
 	}
 	return true
 }
+
+func (c *icmpConn) BindToDevice(ifName string) error {
+	return errors.New("bind to interface unsupported")
+}