CODEWITHSUNDEEP
java
Johannes Trümpelmann
Johannes Trümpelmann

Reputation: 993

Add a timeout when creating a new Socket

I have a local network with DHCP and a few PCs. One of these should be my Server and get automatically connected to all others (clients). My idea was this: First, I create a server on every client (CServer) that is listening for a client programm from the server (SClient). When the SClient connects to a CServer, the SClient sends the CServer his IP, so he knows there will be the server on this IP. Then after trying all IPs in his IP range (e.g. 192.168.1.xxx), he starts the real server and all the clients connect to the known server IP. But when I try the following, the SClient just freezes at the first IP, when trying to connect to 192.168.1.0. How can i define a timeout or something similar that lets the SClient drop the unsuccessful connection and going on with 192.168.1.1?

import java.lang.*;
import java.io.*;
import java.net.*;

class SClient {
    public SClient() {
        for(int i = 120; i < 125; i++){
            try{
                InetAddress addr = InetAddress.getLocalHost();
                String addrs = addr+"";
                String ip = addrs.substring(addrs.indexOf("/")+1);
                Socket s1 = new Socket("192.168.1." + i, 1254);

                OutputStream s1out = s1.getOutputStream();
                DataOutputStream dos = new DataOutputStream (s1out);
                dos.writeUTF(ip);
                dos.close();
                s1out.close();
                s1.close();
            }catch(IOException e){}
        }
    }
}

and

import java.lang.*;
import java.io.*;
import java.net.*;

class CServer {
    public CServer() throws IOException{
        ServerSocket s = new ServerSocket(1254);

        while(true){
            Socket s1=s.accept();
            InputStream s1In = s1.getInputStream();
            DataInputStream dis = new DataInputStream(s1In);
            String st = new String (dis.readUTF());
            System.out.println(st);
            dis.close();
            s1In.close();
            s1.close();
    }
}

}

Upvotes: 13

Views: 10893

Answers (2)

Johannes Tr&#252;mpelmann
Johannes Tr&#252;mpelmann

Reputation: 993

I've found a solution for my problem. It was just initializing the Socket not with

Socket s1 = new Socket("192.168.1." + i, 1254);

but with

Socket s1 = new Socket();
s1.setSoTimeout(200);
s1.connect(new InetSocketAddress("192.168.1." + i, 1254), 200);

Thanks anyway!

Upvotes: 38

Perception
Perception

Reputation: 80633

It's much easier to do this with UDP. The general logic would be:

  1. Identify a well known port for 'discovery'
  2. Any machine that starts up sends out a 'Query Master Server' message
  3. If a response is not received to that message within a time frame you define, then the machine that sent it automatically designates itself as being the server.
  4. Henceforth, any machine that sends out a 'Query Master Server' message will get a response back from the master, with its IP address and a 'communication port'
  5. Connect from the new machine to the server on the communication port and start sending messages.

You might run into situations where more than one server thinks it is the master in this scenario, and then you would need a conflict resolution process, but the outline should give you a general idea of a process that will work for you.

Upvotes: 0

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