A simple echo server testing a few interesting Go language features, goroutines and channels.

echo-client.go

package main

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

func main() {
	servAddr := "localhost:3540"
	tcpAddr, err := net.ResolveTCPAddr("tcp", servAddr)
	if err != nil {
		println("ResolveTCPAddr failed:", err.Error())
		os.Exit(1)
	}
	for i := 0; i < 4096; i++ {
		fmt.Println("Echo client: ", i)
		go echo_client(tcpAddr, i)
	}
	fmt.Println("WAITING!")
	time.Sleep(5 * time.Minute)
}

func echo_client(tcpAddr *net.TCPAddr, i int) {
	strEcho := fmt.Sprintf("hello %d", i)
	conn, err := net.DialTCP("tcp", nil, tcpAddr)
	defer conn.Close()
	if err != nil {
		fmt.Println("Dial failed:", err.Error())
		os.Exit(1)
	}

	_, err = conn.Write([]byte(strEcho))
	if err != nil {
		println("Write to server failed:", err.Error())
		os.Exit(1)
	}

	println("write to server = ", strEcho)

	reply := make([]byte, 1024)

	_, err = conn.Read(reply)
	if err != nil {
		println("Write to server failed:", err.Error())
		os.Exit(1)
	}

	fmt.Println("reply from server=", string(reply))

	time.Sleep(5 * time.Minute)
	// time.Sleep(10 * time.Second)
}

echo-server.go

// $ 6g echo.go && 6l -o echo echo.6
// $ ./echo
//
//  ~ in another terminal ~
//
// $ nc localhost 3540

package main

import (
    "net"
    "bufio"
    "strconv"
    "fmt"
)

const PORT = 3540

func main() {
    server, err := net.Listen("tcp", ":" + strconv.Itoa(PORT))
    if server == nil {
        panic(fmt.Sprintln("couldn't start listening: " , err))
    }
    conns := clientConns(server)
    for {
        go handleConn(<-conns)
    }
}

func clientConns(listener net.Listener) chan net.Conn {
    ch := make(chan net.Conn)
    i := 0
    go func() {
        for {
            client, err := listener.Accept()
            if client == nil {
                fmt.Println("couldn't accept: ", err)
                continue
            }
            i++
            fmt.Printf("%d: %v <-> %v\n", i, client.LocalAddr(), client.RemoteAddr())
            ch <- client
        }
    }()
    return ch
}

func handleConn(client net.Conn) {
    b := bufio.NewReader(client)
    for {
        line, err := b.ReadBytes('\n')
        if err != nil { // EOF, or worse
            break
        }
        client.Write(line)
    }
}