在Go中使用UDP的客户端/服务器

Question

I'm using gob to send messages from client to serve and this is working, however when the server response to client this don't read from connection.

func servidor(porta int){
var site string

addr := net.UDPAddr{
    Port: porta,
    IP: net.ParseIP("localhost"),
}

conn, erro := net.ListenUDP("udp", &addr)
verificaErro(erro)

enc := gob.NewEncoder(conn)
dec := gob.NewDecoder(conn)

dec.Decode(&site)

enc.Encode(site)

}

func cliente(site string){
porta := "1200"
conn := ConnectToSocket("localhost:"+porta)

enc := gob.NewEncoder(conn)
dec := gob.NewDecoder(conn)

enc.Encode("Test")
dec.Decode(&site)

fmt.Println(site)

}

How can I solve this problem?

Answer 1

There are two issues:

• UDP is a packet based protocol, but gob is expecting a stream. The encoder can call the connection Write method multiple times when encoding a value. Each write sends a packet. You probably want one packet per encoded value.
• Gob streams have state. The encoder sends information about any type once and expects the decoder to remember the information. Even if the gob encoder calls Write exactly once per encoded value, packets sent by subsequent writes will not include the type information.

The fix is to encode to a buffer and send that buffer:

var buf Bytes.Buffer
if err := gob.NewEncoder(&buf).Encode(value); err != nil {
   // handle error
}
_, err := c.WriteTo(buf.Bytes(), addr)

Receive to a buffer and decode from that buffer:

buf := make([]byte, 1024)
n, addr, err := c.ReadFrom(buf)
if err != nil {
   // handle error
}
if err := gob.NewDecoder(bytes.NewReader(buf[:n])).Decode(&v); err != nil {
   // handle error
}