clockserver.go

// Clockserver publishes time on a given port as command line argument
// Usage: TZ=US/Eastern ./exercise8_1 8000 &

package main

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

func main() {
	port := os.Args[1]
	listener, err := net.Listen("tcp", fmt.Sprintf("localhost:%s", port))
	if err != nil {
		log.Fatal(err)
	}

	for {
		conn, err := listener.Accept()
		if err != nil {
			log.Print(err)
			continue
		}
		go handleConn(conn)
	}
}

func handleConn(c net.Conn) {
	defer c.Close()
	for {
		_, err := io.WriteString(c, time.Now().Format("03:04:05PM\n"))
		if err != nil {
			return
		}
		time.Sleep(1 * time.Second)
	}
}

clockwall.go

// Clockwall shows multiple times concurrently
// usage: ./clockwall NewYork=localhost:8000 Tokyo=localhost:8010
package main

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

func displayClock(timeZone, serverAddr, serverPort string, wg *sync.WaitGroup) {
	defer wg.Done()
	conn, err := net.Dial("tcp", fmt.Sprintf("%s:%s", serverAddr, serverPort))
	if err != nil {
		log.Fatal(err)
	}
	defer conn.Close()
	s := bufio.NewScanner(conn)
	for s.Scan() {
		fmt.Fprintf(os.Stdout, "%-15s: %s\n", timeZone, s.Text())
	}
}

func main() {
	// read params
	var wg sync.WaitGroup
	for _, arg := range os.Args[1:] {
		pArr := strings.Split(arg,"=")
		timeZone := pArr[0]
		serverAddr := strings.Split(pArr[1],":")[0]
		serverPort := strings.Split(pArr[1],":")[1]
		wg.Add(1)
		go displayClock(timeZone, serverAddr, serverPort, &wg)
	}
	wg.Wait()
}