go-network[7]-udp

/* UDPDaytimeClient
 */
package main

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

func main() {
    if len(os.Args) != 2 {
        fmt.Fprintf(os.Stderr, "Usage: %s host:port", os.Args[0])
        os.Exit(1)
    }
    service := os.Args[1]

    udpAddr, err := net.ResolveUDPAddr("udp4", service)
    checkError(err)

    conn, err := net.DialUDP("udp", nil, udpAddr)
    checkError(err)

    _, err = conn.Write([]byte("anything"))
    checkError(err)

    var buf [512]byte
    n, err := conn.Read(buf[0:])
    checkError(err)

    fmt.Println(string(buf[0:n]))

    os.Exit(0)
}

func checkError(err error) {
    if err != nil {
        fmt.Fprintf(os.Stderr, "Fatal error %s", err.Error())
        os.Exit(1)
    }
}

/* UDPDaytimeServer
 */
package main

import (
	"fmt"
	"net"
	"os"
	"time"
)

func main() {

	service := ":1200"
	udpAddr, err := net.ResolveUDPAddr("udp4", service)
	checkError(err)

	conn, err := net.ListenUDP("udp", udpAddr)
	checkError(err)

	for {
		 handleClient(conn)
	}
}

func handleClient(conn *net.UDPConn) {

	var buf [512]byte

	_, addr, err := conn.ReadFromUDP(buf[0:])
	if err != nil {
		return
	}

	daytime := time.Now().String()

	conn.WriteToUDP([]byte(daytime), addr)
	conn.Close()
}

func checkError(err error) {
	if err != nil {
		fmt.Fprintf(os.Stderr, "Fatal error %s", err.Error())
		os.Exit(1)
	}
}