Question

I’m trying to make a Java TCP client and a node.js TCP server talk together.
This is my code at the moment :

• The Java client

  import java.net.;
  import java.io.;

  public class Client2{

  public static void main(String[] args)  throws Exception{
      Socket s = new Socket("192.168.1.35",8500);
      DataOutputStream dos = new DataOutputStream(s.getOutputStream());
      dos.writeUTF("abcdefgh");
      dos.close();
      s.close();
  }
  

  }

• the Node.js Server

  var net = require(‘net’),
  server = net.createServer();

  server.on(‘connection’, function (client) {

  console.log('Hello World !');
  
  client.on('data', function(data) {
  
      var message = data.toString('utf8');
      console.log('***' + message +'***');
  
  });
  

  });

  server.listen(8500);

This example will give this result back :

Hello World !
**abcdefgh***

• but with this as input :

  abcdefghijklmnopqrstuvwxyzabcdefghijklmnopqrstuvwxyzabcdefghijklmnopqrstuvwxyzabcdefghijklmnopqrstuvwxyzabcdefghijklmnopqrstuvwxyz

it gives this back :

Hello World !
***�abcdefghijklmnopqrstuvwxyzabcdefghijklmnopqrstuvwxyzabcdefghijklmnopqrstuvwxyzabcdefghijklmnopqrstuvwxyzabcdefghijklmnopqrstuvwxyz***

• with this input :

  qq32we3w87d 38s1d87s4df7s4d1+s2d7f+sfdsf4sà$àà3663%ç%&ç%&ç

it gives this back :

Hello World !
***@qq32we3w87d 38s1d87s4df7s4d1+s2d7f+sfdsf4sà$àà3663%ç%&ç%&ç***

tldr: Sometimes when logging the buffers, node adds characters (rectangles with numbers or ?) at the beginning or event cuts some characters at the start out.

– How can I log buffers and assign them to a variable the right way ?

Answer 1

I’m not an expert on DataOutputStream, but if it really is adding extra characters, you should use something else.

When I did server stuff, I used BufferedReader and BufferedWriter. It looks like this:

        Socket s = new Socket(<<WEB ADDRESS AS STRING>>,<<PORT NO AS INT>>);
        BufferedWriter bw = new BufferedWriter(new OutputStreamWriter(s.getOutputStream()));
        BufferedReader br = new BufferedReader(new InputStreamReader(s.getInputStream()));
        //left out a bunch of lines. This is where you should read the lines 
        //of input (with an inner loop) and send stuff back
        s.shutdownInput();
        bw.flush();
        s.shutdownOutput();

NOTE, IF YOU’RE GOING TO DEAL WITH LARGE PAGES, THIS COULD CAUSE A PROBLEM, AS THE BUFFEREDREADER AND BUFFEREDWRITER WILL FILL UP BEFORE YOU’RE READY. if this is a problem I’d look into the other Reader and Writer classes. They are quite plentiful, as I understand it, and one should suit your needs.