Exercise 8.1: Modify clock2 to support incoming parameters as port numbers, then write a clockwall program that communicates with multiple clock servers at the same time, reads the time from multiple servers, and displays all service transfers in a table at once The result is similar to the clock wall you see in some offices. If you have geographically distributed servers available, have those servers run on different machines; or run multiple different instances on the same machine that listen on different ports and pretend to be in different time zones . Like the following:
$ TZ=US/Eastern ./clock2 -port 8010 &
$ TZ=Asia/Tokyo ./clock2 -port 8020 &
$ TZ=Europe/London ./clock2 -port 8030 &
$ clockwall NewYork=localhost:8010 Tokyo=localhost:8020 London=localhost:8030
clock2.go
package main import ( "flag" "io" "log" "net" "time" ) //Support incoming parameters as port numbers var port = flag.String("port", "8000", "Please enter the port") func main() { flag.Parse() listener, err := net.Listen("tcp", "localhost:"+*port) if err != nil { log.Fatal(err) } for { conn, err := listener.Accept() if err != nil { log.Print(err) // e.g., connection aborted continue } go handleConn(conn) //Create new goroutines to handle the connection } } func handleConn(c net.Conn) { defer c.Close() for { _, err := io.WriteString(c, time.Now().Format("15:04:05\n")) if err != nil { return // e.g., client disconnected } time.Sleep(1 * time.Second) } }
clockwall.go
// Netcat1 is a read-only TCP client. package main import ( "io" "log" "net" "os" "strings" "time" ) func main() { for _, v := range os.Args[1:] { keyValue := strings.Split(v, "=") go connTcp(keyValue[1]) } for { time.Sleep(1 * time.Second) } } func connTcp(uri string) { conn, err := net.Dial("tcp", uri) if err != nil { log.Fatal(err) } defer conn.Close() mustCopy(os.Stdout, conn) } func mustCopy(dst io.Writer, src io.Reader) { if _, err := io.Copy(dst, src); err != nil { log.Fatal(err) } }