ping_test.go

func TestPingGoogle(t *testing.T) {
	if testing.Short() {
		t.Skip("to avoid external network")
	}
	switch runtime.GOOS {
	case "darwin":
	case "linux":
		t.Log("you may need to adjust the net.ipv4.ping_group_range kernel state")
	default:
		t.Skipf("not supported on %q", runtime.GOOS)
	}

	for i, tt := range pingGoogleTests {
		if tt.network[:2] == "ip" && os.Getuid() != 0 {
			continue
		}
		c, err := icmp.ListenPacket(tt.network, tt.address)
		if err != nil {
			t.Error(err)
			continue
		}
		defer c.Close()

		// MODIFIED BEGIN
		if err := c.IPv4PacketConn().SetTTL(1); err != nil {
			t.Fatal(err)
		}
		// MODIFIED END

		dst, err := googleAddr(c, tt.protocol)
		if err != nil {
			t.Error(err)
			continue
		}

		wm := icmp.Message{
			Type: tt.mtype, Code: 0,
			Body: &icmp.Echo{
				ID: os.Getpid() & 0xffff, Seq: 1 << uint(i),
				Data: []byte("HELLO-R-U-THERE"),
			},
		}
		wb, err := wm.Marshal(nil)
		if err != nil {
			t.Error(err)
			continue
		}
		if n, err := c.WriteTo(wb, dst); err != nil {
			t.Error(err, dst)
			continue
		} else if n != len(wb) {
			t.Errorf("got %v; want %v", n, len(wb))
			continue
		}

		rb := make([]byte, 1500)
		n, peer, err := c.ReadFrom(rb)
		if err != nil {
			t.Error(err)
			continue
		}
		rm, err := icmp.ParseMessage(tt.protocol, rb[:n])
		if err != nil {
			t.Error(err)
			continue
		}
		switch rm.Type {
		case ipv4.ICMPTypeEchoReply, ipv6.ICMPTypeEchoReply:
			t.Logf("got reflection from %v", peer)
		default:
			t.Errorf("got %+v; want echo reply", rm)
		}
	}
}