Thread: Socket not working well

Hi everyone,

I'm trying to do a PortScanner that really works, I've searched some tutorials about a PortScanner in java at google and I noted that the basic ideia that people use is:

1-Create a Socket object with host and port;
2-If the port is open you close the socket, else the IOException will catch it.

The big deal is that I tryed this code and it didnt works, it says that are ports opened in my machine when they werent opened. So I decide a different way as this:

PHP Code:


try {  
  
        Socket clientSocket = new Socket("127.0.0.1", 2020);  
        clientSocket.setSoTimeout(3000);  
  
        DataInputStream inFromServer = new DataInputStream(clientSocket.getInputStream());  
  
        // Issue is here :(  
        System.out.println(""+inFromServer.readInt());  
  
        clientSocket.close();  
  
  
    } catch (SocketTimeoutException ex) {  
        System.out.println("Timeout exceed");  
    } catch (ConnectException ex) {  
        System.out.println("Port closed");  
    } catch (IOException e) {  
        System.out.println("Doesnt connect");  
    }  
  
} 


But it's not working well too. If the host doesnt have a port open at 2020 it works fine, the method readInt() return me -1, but when the port is opened, the method readInt(); return nothing to me and my code get freeze because it's waiting for a response of the host.

Does anybody know how can i fix this? Or an other better way to code a Port Scanner?

Thanks everybody!

You should be using another method to test for port availability. Try 123099's method but include a DatagramSocket to chekc for UDP availability as well.