为什么我的UDP拨号程序也没有监听？

Question

I have two programs, a listener and a dialer. I want a two way street of UDP communication on the same port. My Listener as expected reads the datagram sent from the dialer, then sends back 5 datagrams of its own. Only trouble is, my dialer isn't reading it.

I tried using net.DialUDP but when I use that, 0 datagrams get sent from the dialer.

listener - Works great

func main() {

addr := net.UDPAddr{
    Port: 7000,
    IP:   net.ParseIP("127.0.0.1"),
}
conn, err := net.ListenUDP("udp", &addr)

defer conn.Close()
if err != nil {
    panic(err)
}

i := 0

b := make([]byte, 10)
conn.ReadFromUDP(b)
fmt.Println(string(b[:]))
for i < 5 {

    conn.WriteToUDP([]byte("sending back"), &addr)
    i++
}
}

Dialer that sends datagram but cannot read them

func main() {
sock, _ := net.Dial("udp", "127.0.0.1:7000")
buf := make([]byte, 100)

_, werr := sock.Write([]byte("first send"))
if werr != nil {
    fmt.Println(werr)
}
sock.Read(buf)

fmt.Println(string(buf[:]))
}

Dialer that doesn't send any datagrams

func main() {

remote, _ := net.ResolveUDPAddr("udp", "127.0.0.1:7000")
sock, _ := net.DialUDP("udp", nil, remote)

buf := make([]byte, 10)

for {
    sock.WriteToUDP([]byte("first send"), remote)
    sock.ReadFromUDP(buf)
    fmt.Println(string(buf[:]))

}
}

Answer 1

When in doubt, just use ListenUDP. It will both send and receive datagrams.

sock, _ := net.Dial("udp", "127.0.0.1:7000")

This creates a net.Conn, which is only a basic connection interface. You have to assert it as a *net.UDPConn to get the actual UDP methods to work.

sock, _ := net.DialUDP("udp", nil, remote)

This creates a "connected" UDP socket, and uses the bare Write method to send to a single remote address.