Back in my sixth semester Computer Networks lab, we had to write a simple
port scanner (port 0 to 1024). The basic principle was to see whether a connection could be made at a port. If connection can be made, it is open, or else it is closed. I had used the following code then. However, it took 17 minutes to perform the scan.
import java.io.IOException;
import java.net.InetAddress;
import java.net.Socket;
import java.net.UnknownHostException;
public class port_scanner {
static Socket soc;
public static void main(String[] args) throws IOException {
for(int i=1;i<1024;i++){
try{
soc= new Socket(InetAddress.getLocalHost(),i);
System.out.println("port "+i+" open");
soc.close();
}catch(IOException e){
System.out.println("port "+i+" closed");
}
}
}
}
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The better option was to use threading. I was lazy back then and the above program was sufficient to fetch me marks, and so I did not write a multi-threaded code. I needed to brush up threading because placements are going to start soon. Therefore, I implemented the multi-threaded version. It took just 2 seconds to perform the scan.
import java.io.IOException;
import java.net.InetAddress;
import java.net.Socket;
class myThread implements Runnable{
Thread t;
Socket soc;
boolean state=true;
int port;
myThread(int port){
this.port=port;
t=new Thread(this,"Thread");
t.start();
}
boolean getState(){
return state;
}
@Override
public void run(){
try{
soc= new Socket(InetAddress.getLocalHost(),port);
soc.close();
}catch(IOException e){
state=false;
}
}
}
public class new_prt {
static myThread threads[] = new myThread[1024];
public static void main(String args[]){
for(int j=0;j<1024;j++){
threads[j]=new myThread(i);
}
for(int j=0;j<1024;j++){
try{
threads[j].t.join();
if(threads[j].getState()==true)
System.out.println("port "+threads[j].port + " open");
else
System.out.println("port "+threads[j].port + " closed");
}catch(InterruptedException e){
}
}
}
}
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