Write to Client UDP Socket in Go

Check the below samples for client/server communication over UDP. The sendResponse routine is for sending response back to client.

udpclient.go

package main
import (
    "fmt"
    "net"
    "bufio"
)

func main() {
    p :=  make([]byte, 2048)
    conn, err := net.Dial("udp", "127.0.0.1:1234")
    if err != nil {
        fmt.Printf("Some error %v", err)
        return
    }
    fmt.Fprintf(conn, "Hi UDP Server, How are you doing?")
    _, err = bufio.NewReader(conn).Read(p)
    if err == nil {
        fmt.Printf("%s\n", p)
    } else {
        fmt.Printf("Some error %v\n", err)
    }
    conn.Close()
}

udpserver.go

package main
import (
    "fmt" 
    "net"  
)


func sendResponse(conn *net.UDPConn, addr *net.UDPAddr) {
    _,err := conn.WriteToUDP([]byte("From server: Hello I got your message "), addr)
    if err != nil {
        fmt.Printf("Couldn't send response %v", err)
    }
}


func main() {
    p := make([]byte, 2048)
    addr := net.UDPAddr{
        Port: 1234,
        IP: net.ParseIP("127.0.0.1"),
    }
    ser, err := net.ListenUDP("udp", &addr)
    if err != nil {
        fmt.Printf("Some error %v\n", err)
        return
    }
    for {
        _,remoteaddr,err := ser.ReadFromUDP(p)
        fmt.Printf("Read a message from %v %s \n", remoteaddr, p)
        if err !=  nil {
            fmt.Printf("Some error  %v", err)
            continue
        }
        go sendResponse(ser, remoteaddr)
    }
}

hello_echo.go

 package main                                                                                                          

 import (                                                                                                              
     "bufio"                                                                                                           
     "fmt"                                                                                                             
     "net"                                                                                                             
     "time"                                                                                                            
 )                                                                                                                     

 const proto, addr = "udp", ":8888"                                                                                    

 func main() {  

     go func() {                                                                                                       
         conn, _ := net.ListenPacket(proto, addr)                                                                      
         buf := make([]byte, 1024)                                                                                     
         n, dst, _ := conn.ReadFrom(buf)                                                                               
         fmt.Println("serv recv", string(buf[:n]))                                                                     
         conn.WriteTo(buf, dst)                                                                                        
     }()        

     time.Sleep(1 * time.Second)   

     conn, _ := net.Dial(proto, addr)                                                                                  
     conn.Write([]byte("hello\n"))                                                                                     
     buf, _, _ := bufio.NewReader(conn).ReadLine()                                                                     
     fmt.Println("clnt recv", string(buf))                                                                             
 }                                                                                                                     

The gist is here:

https://gist.github.com/winlinvip/e8665ba888e2fd489ccd5a449fadfa73

server.go

/*
Usage:
    go run server.go
See https://gist.github.com/winlinvip/e8665ba888e2fd489ccd5a449fadfa73
See https://stackoverflow.com/a/70576851/17679565
See https://github.com/ossrs/srs/issues/2843
 */
package main

import (
    "fmt"
    "net"
    "os"
    "strconv"
)

func main() {
    serverPort := 8000
    if len(os.Args) > 1 {
        if v,err := strconv.Atoi(os.Args[1]); err != nil {
            fmt.Printf("Invalid port %v, err %v", os.Args[1], err)
            os.Exit(-1)
        } else {
            serverPort = v
        }
    }

    addr := net.UDPAddr{
        Port: serverPort,
        IP:   net.ParseIP("0.0.0.0"),
    }
    server, err := net.ListenUDP("udp", &addr)
    if err != nil {
        fmt.Printf("Listen err %v\n", err)
        os.Exit(-1)
    }
    fmt.Printf("Listen at %v\n", addr.String())

    for {
        p := make([]byte, 1024)
        nn, raddr, err := server.ReadFromUDP(p)
        if err != nil {
            fmt.Printf("Read err  %v", err)
            continue
        }

        msg := p[:nn]
        fmt.Printf("Received %v %s\n", raddr, msg)

        go func(conn *net.UDPConn, raddr *net.UDPAddr, msg []byte) {
            _, err := conn.WriteToUDP([]byte(fmt.Sprintf("Pong: %s", msg)), raddr)
            if err != nil {
                fmt.Printf("Response err %v", err)
            }
        }(server, raddr, msg)
    }
}

client.go

/*
Usage:
    go run client.go
    go run client.go 101.201.77.240
See https://gist.github.com/winlinvip/e8665ba888e2fd489ccd5a449fadfa73
See https://stackoverflow.com/a/70576851/17679565
See https://github.com/ossrs/srs/issues/2843
*/
package main

import (
    "fmt"
    "net"
    "os"
    "strings"
)

func main() {
    serverEP := "127.0.0.1"
    if len(os.Args) > 1 {
        serverEP = os.Args[1]
    }
    if !strings.Contains(serverEP, ":") {
        serverEP = fmt.Sprintf("%v:8000", serverEP)
    }

    conn, err := net.Dial("udp", serverEP)
    if err != nil {
        fmt.Printf("Dial err %v", err)
        os.Exit(-1)
    }
    defer conn.Close()

    msg := "Hello, UDP server"
    fmt.Printf("Ping: %v\n", msg)
    if _, err = conn.Write([]byte(msg)); err != nil {
        fmt.Printf("Write err %v", err)
        os.Exit(-1)
    }

    p := make([]byte, 1024)
    nn, err := conn.Read(p)
    if err != nil {
        fmt.Printf("Read err %v\n", err)
        os.Exit(-1)
    }

    fmt.Printf("%v\n", string(p[:nn]))
}