// runPayloadTransponder transmits IPv4 datagram payloads to the
// loopback address or interface and captures the loopback'd datagram
// payloads.
func runPayloadTransponder(t *testing.T, c *ipv4.PacketConn, wb []byte, dst net.Addr) {
cf := ipv4.FlagTTL | ipv4.FlagDst | ipv4.FlagInterface
rb := make([]byte, 1500)
for i, toggle := range []bool{true, false, true} {
if err := c.SetControlMessage(cf, toggle); err != nil {
t.Fatalf("ipv4.PacketConn.SetControlMessage failed: %v", err)
}
c.SetTOS(i + 1)
var ip net.IP
switch v := dst.(type) {
case *net.UDPAddr:
ip = v.IP
case *net.IPAddr:
ip = v.IP
}
if ip.IsMulticast() {
c.SetMulticastTTL(i + 1)
} else {
c.SetTTL(i + 1)
}
c.SetDeadline(time.Now().Add(100 * time.Millisecond))
if _, err := c.Write(wb, nil, dst); err != nil {
t.Fatalf("ipv4.PacketConn.Write failed: %v", err)
}
_, cm, _, err := c.Read(rb)
if err != nil {
t.Fatalf("ipv4.PacketConn.Read failed: %v", err)
}
t.Logf("rcvd cmsg: %v", cm)
}
}
