TCP Server & Client

main.go

package main

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

const thisAddr = "10.22.20.129"

func main() {
	fmt.Println("Hello. This is your IP to share: ", thisAddr)
	fmt.Print("Wait for someone or start a connection? ([w]/s) ")
	ans := ""
	if n, err := fmt.Scanln(&ans); err != nil && n != 0 {
		log.Fatal(err)
	}
	switch strings.TrimSpace(ans) {
	case "w", "":
		waitForConnections(thisAddr)
	case "s":
		fmt.Print("IP of the computer? ")
		ip, err := scanIPV4()
		if err != nil {
			log.Fatal(err)
		}
		connectToIP(ip)
	default:
		log.Fatal("invalid")
	}
}

func waitForConnections(thisAddr string) {
	l, err := net.Listen("tcp", thisAddr+":1289")
	if err != nil {
		log.Fatal(err)
	}
	defer l.Close()
	fmt.Println("Waiting for someone to join...")

	conn, err := l.Accept()
	if err != nil {
		log.Fatal(err)
	}
	defer conn.Close()

	fmt.Println("Connection established: ", conn.RemoteAddr().String())

	go receive(conn)
	send(conn)
}

func connectToIP(ip string) {
	conn, err := net.Dial("tcp", net.JoinHostPort(ip, "1289"))
	if err != nil {
		log.Fatal(err)
	}
	defer conn.Close()
	fmt.Println("\nConnection established: ", conn.RemoteAddr().String())

	go receive(conn)
	send(conn)
}

func receive(conn net.Conn) {
	buf := bufio.NewReader(conn)
	for {
		data, err := buf.ReadString('\n')
		if err != nil {
			log.Fatal(err)
		}
		fmt.Printf("\b\b\b\b\b\b\b\b[them]:\t%s\n[you]:\t", strings.TrimSpace(data))
	}
}

func send(conn net.Conn) {
	s := bufio.NewScanner(os.Stdin)
	for {
		fmt.Print("[you]:\t")
		msg, err := scanStr(s)
		if err != nil {
			log.Fatal(err)
		}

		if _, err := conn.Write([]byte(msg)); err != nil {
			log.Fatal(err)
		}
	}
}

func scanStr(s *bufio.Scanner) (string, error) {
	if s.Scan() {
		return s.Text(), nil
	}
	err := s.Err()
	return "", err
}

func scanIPV4() (ip string, err error) {
	s := bufio.NewScanner(os.Stdin)
	if s.Scan() {
		ip, err = s.Text(), nil
	}
	err = s.Err()
	if err != nil {
		return
	}

	res := net.ParseIP(ip)
	if res == nil {
		err = &net.ParseError{}
		return
	}
	ip = res.To4().String()

	return
}