Go Echo Server and Client

client.go

package main

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

const (
	LOCAL_HOST         = "localhost"
	DEFAULT_LOCAL_PORT = "7070"

	REMOTE_HOST = "localhost"
	REMOTE_PORT = "8080"

	PING_PERIOD = 1 * time.Second
)

func main() {
	var localPort string
	if len(os.Args) <= 1 {
		localPort = DEFAULT_LOCAL_PORT
	} else {
		localPort = os.Args[1]
	}

	localAddr, err := net.ResolveTCPAddr("tcp", LOCAL_HOST+":"+localPort)
	exit_on_error(err)

	remoteAddr, err := net.ResolveTCPAddr("tcp", REMOTE_HOST+":"+REMOTE_PORT)
	exit_on_error(err)

	conn, err := net.DialTCP("tcp", localAddr, remoteAddr)
	exit_on_error(err)

	fmt.Printf("%s <--> %s\n", localAddr.String(), remoteAddr.String())

	for {
		time.Sleep(PING_PERIOD)
		ping(conn, "hello from "+localAddr.String())
	}
}

func ping(conn net.Conn, msg string) {
	_, err := conn.Write([]byte(msg))
	exit_on_error(err)

	fmt.Println("Sent", msg)

	buf := make([]byte, 512)
	_, err = conn.Read(buf)
	exit_on_error(err)

	fmt.Println("Got ", string(buf))
}

func exit_on_error(err error) {
	if err != nil {
		fmt.Println(err)
		os.Exit(1)
	}
}

server.go

package main

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

const (
	HOST = "localhost"
	PORT = "8080"
)

func main() {
	addr, err := net.ResolveTCPAddr("tcp", HOST+":"+PORT)
	exit_on_error(err)

	listener, err := net.ListenTCP("tcp", addr)
	exit_on_error(err)

	fmt.Println("Listening on port", PORT)

	for {
		conn, err := listener.Accept()
		if err != nil {
			fmt.Println(err)
		} else {
			go echo(conn)
		}
	}
}

func echo(conn net.Conn) {
	defer conn.Close()
	defer fmt.Println("")

	fmt.Printf("Connected to: %s\n", conn.RemoteAddr().String())

	for {
		buf := make([]byte, 512)
		_, err := conn.Read(buf)
		if err == io.EOF {
			return
		}
		if err != nil {
			fmt.Println("Error reading:")
			fmt.Println(err)
			continue
		}

		fmt.Println(fmt.Sprintf("[%s]", conn.RemoteAddr().String()), string(buf))

		_, err = conn.Write(buf)
		if err != nil {
			fmt.Println("Error writing:")
			fmt.Println(err)
			continue
		}
	}
}

func exit_on_error(err error) {
	if err != nil {
		fmt.Println(err)
		os.Exit(1)
	}
}