golang tcp socket - process multiple messages

Question

I have this Go tcp socket

package main

import (
  "fmt"
  "io"
  "log"
  "net"
  "bytes"
)

func main() {

  l, err := net.Listen("tcp", ":1200")
  if err != nil {
    log.Fatal(err)
  }
  defer l.Close()
  for {

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

    go func(c net.Conn) {

      var buf bytes.Buffer
      io.Copy(&buf, c)
      fmt.Println("total size:", buf.Len())
      s := buf.String()
      println(s)

      c.Close()
    }(conn)
  }
}

accept a message, transform it to string and display it, but if the connection is not closed by the client I am not able to see the message showed on the server as expected

How is possible to send multiple message from the client without the need to close the client connection (by the client) ?

Here the client in NodeJs

var net = require('net');

let packet = {
              Target: { Host: "", Port: "9000" },
              Name: { Family: "Newmarch", Personal: "Jan" },
              Email: [
                      { Kind: "home", Address: "[email protected]"},
                      { Kind: "work", Address: "[email protected]"}
                     ]
}


var client = new net.Socket();
client.connect(1200, '0.0.0.0', function() {
  console.log('Connected');
  client.write( (new Buffer(JSON.stringify(packet), 'UTF-8')) );
  client.end();
  //client.write('\n');
});

client.on('data', function(data) {
  console.log('Received: ' + data);
  client.destroy();
});

client.on('close', function() {
  console.log('Connection closed');
});

Thanks valeriano cossu

As the answers mentioned you have to break your messages somehow. TCP itself is a streaming protocol, not a packet based one. — Kaveh Shahbazian

Unknown Unknown · Accepted Answer · 2016-09-07T11:23:23

Because you are getting a constant stream of data the server needs to know how to seperate messages. One way of doing that is using a new line character.

I have revised your code below.

Go server: package main

import (
    "bufio"
    "log"
    "net"
)

func main() {

    l, err := net.Listen("tcp", ":1200")
    if err != nil {
        log.Fatal(err)
    }
    defer l.Close()
    for {

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

        go func(c net.Conn) {
            for {
                message, err := bufio.NewReader(conn).ReadString('\n')
                if err != nil {
                    log.Printf("Error: %+v", err.Error())
                    return
                }

                log.Println("Message:", string(message))
            }
        }(conn)
    }
}

Nodejs client:

var net = require('net');

let packet = {
              Target: { Host: "", Port: "9000" },
              Name: { Family: "Newmarch", Personal: "Jan" },
              Email: [
                      { Kind: "home", Address: "[email protected]"},
                      { Kind: "work", Address: "[email protected]"}
                     ]
}


var client = new net.Socket();
client.connect(1200, '0.0.0.0', function() {
  console.log('Connected');

  // Send 10 messages
  for(var i = 0; i < 10; i++) {
    client.write( (new Buffer(JSON.stringify(packet), 'UTF-8')) );
    client.write('\n');
  }

  client.end();

});

client.on('data', function(data) {
  console.log('Received: ' + data);
  client.destroy();
});

client.on('close', function() {
  console.log('Connection closed');
});

golang tcp socket - process multiple messages

2 Answers