[Go] Simple example of how to use sockets for a basic, multithreaded, TCP based client-server communication.

client.go

package main

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

func main()  {
	arguments := os.Args
	if len(arguments) == 1 {
		fmt.Printf("Please provide address and port number in the form ADDR:PORT. (Call like this: %s ADDR:PORT)\n", arguments[0])
		return
	}

	service := arguments[1]
	tcpAddr, err := net.ResolveTCPAddr("tcp4", service)
	checkError(err)
	conn, err := net.DialTCP("tcp4", nil, tcpAddr)
	checkError(err)
	for {
		fmt.Print("Please enter a command: ")
		scanner := bufio.NewScanner(os.Stdin)
		scanner.Scan()
		input := scanner.Text()
		checkError(err)
		_, err = conn.Write([]byte(input + "\x04"))
		checkError(err)
		if input == "dc"{
			fmt.Println("Closing the connection and exiting client...")
			err = conn.Close()
			checkError(err)
			return
		}
		response, err := bufio.NewReader(conn).ReadString('\x04')
		response = strings.TrimSuffix(response, "\x04")
		checkError(err)
		fmt.Println(response + "\n")
	}
}

func checkError(err error)  {
	if err != nil {
		println("Program execution was aborted due to following ERROR: ", err.Error())
		os.Exit(1)
	}
}

server.go

package main

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

func main()  {
	arguments := os.Args
	if len(arguments) == 1 {
		fmt.Printf("Please provide the port number the server should listen on. (Call like this: %s PORT)\n", arguments[0])
		return
	}

	var service = ":" + arguments[1]
	tcpAddr, err := net.ResolveTCPAddr("tcp4", service)
	fmt.Printf("Starting local server @PORT %s\n\n", tcpAddr.String()[1:])
	checkError(err)
	listener, err := net.ListenTCP("tcp4", tcpAddr)
	checkError(err)
	for {
		conn, err := listener.Accept()
		fmt.Printf("Connected to client %s\n", conn.RemoteAddr())
		checkError(err)
		go handleConnection(conn)
	}
}

func handleConnection(conn net.Conn)  {
	fmt.Printf("Handling connection %s\n", conn.RemoteAddr())
	for {
		message, err := bufio.NewReader(conn).ReadString('\x04')
		message = strings.TrimSuffix(message, "\x04")
		fmt.Printf("Recived message \"%s\" from %s\n", message, conn.RemoteAddr())
		checkForConnDrop(err, conn)
		if err != nil {
			return
		}
		switch message {
		case "help":
			helpText := "List of available commands:\n\n" +
				"ping - Makes the server reply with a pong\n" +
				"time - The server replies with the current server time\n" +
				"echo [message]- The server echos back the [message]\n" +
				"dc - Closes the connection with the server\n" +
				"help - Gives you this list"
			_, err := conn.Write(prepareMessage(helpText))
			checkError(err)
		case "ping":
			_, err := conn.Write(prepareMessage("<- pong"))
			checkError(err)
		case "time":
			curTime := time.Now().Format(time.RFC822)
			_, err := conn.Write(prepareMessage(curTime))
			checkError(err)
		case "dc":
			fmt.Printf("Closing connection with client %s.\n", conn.RemoteAddr())
			err := conn.Close()
			checkError(err)
			return
		default:
			if strings.Contains(message, "echo") {
				message = strings.Replace(message, "echo ", "", 1)
				_, err := conn.Write(prepareMessage(message))
				checkError(err)
			} else {
				_, err := conn.Write(prepareMessage("The command " + message + " is unknown. For a list of available commands use \"help.\""))
				checkError(err)
			}
		}
	}
}

func checkError(err error)  {
	if err != nil {
		println("Program execution was aborted due to following ERROR: ", err.Error())
		os.Exit(1)
	}
}

func checkForConnDrop(err error, conn net.Conn) {
	if err != nil {
		fmt.Printf("Connection to client %s was aborted due to following ERROR: %s\n", conn.RemoteAddr().String(), err.Error())
	}
}

func prepareMessage(message string) []byte {
	return []byte(message + "\x04")
}