golang net package simulation

Let's make some fun to simulation  Server - Client.

 

1.  socket

I implement a echo server and use telnet to simulate the socket client.

in this way,  we don't need to implement our socket client but can test our client server in a standard way.

It can support multiple telnet clients concurrently. The behavior is as bellow.

when user input "BYE",  the connect to server shuts down.

code snippet:

package main

import (
    "bufio"
    "fmt"
    "io"
    "log"
    "net"
    "strings"
)

func main() {
    // Listen on TCP port 2000 on all interfaces.
    l, err := net.Listen("tcp", ":2000")
    if err != nil {
        log.Fatal(err)
    }
    defer l.Close()

    for {
        // Wait for a connection.
        conn, err := l.Accept()
        if err != nil {
            log.Fatal(err)
        }
        fmt.Println("INFO: accept a client")

        // Handle the connection in a new goroutine.
        go func(c net.Conn) {
            defer c.Close()

            rd := bufio.NewReader(c)
            for {
                line, _, err := rd.ReadLine()
                if err != nil && err != io.EOF {
                    log.Fatal(err)
                }

                s := string(line)
                fmt.Println("LOG:", s)

                //since rd.ReadLine() has trimed last "\n", append here to echo
                _, err = conn.Write([]byte("ECHO:" + s + "\r\n"))
                if err != nil {
                    log.Fatal(err)
                }

                if strings.ToLower(s) == "bye" {
                    fmt.Println("INFO: client closed")
                    break
                }
            }
        }(conn)
    }
}

 

2. http.Client