src/main/java/com/it_jaros/networkScanner/Scanner.java


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package com.it_jaros.networkScanner;

import java.io.IOException;
import java.net.ConnectException;
import java.net.InetSocketAddress;
import java.net.Socket;
import java.util.List;
import java.util.Queue;
import java.util.concurrent.ConcurrentLinkedQueue;
import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;
import java.util.concurrent.Semaphore;
import java.util.concurrent.TimeUnit;
import java.util.concurrent.atomic.AtomicLong;
import java.util.concurrent.locks.LockSupport;

public class Scanner {
                
    private Counter counter = new Counter();
    
    public Scanner() {}

    public List<Integer> scanPorts(ScanTarget
     target) {
        return scanPorts(target.address(), target.openSocketLimit(), target.delayInMillis());
    }

    public List<Integer> scanPorts(String address, int socketLimit, int delayInMillis) {
        Queue<Integer> openPorts = new ConcurrentLinkedQueue<>();
        Semaphore socketCap = new Semaphore(socketLimit);
        long delayInNanos = TimeUnit.MILLISECONDS.toNanos(Math.max(0, delayInMillis));
        AtomicLong nextStartNanos = new AtomicLong(System.nanoTime());
        try (ExecutorService executor = Executors.newVirtualThreadPerTaskExecutor()) {
            for (int port = 1; port < 65536; port++) {
                final int currentPort = port;
                executor.submit(() -> {
                    if (delayInNanos > 0) {
                        long mySlot = nextStartNanos.getAndAdd(delayInNanos);
                        long wait = mySlot - System.nanoTime();
                        if (wait > 0) LockSupport.parkNanos(wait);
                    }
                    socketCap.acquireUninterruptibly();
                    counter.inc();
                    try (Socket socket = new Socket()) {
                        socket.connect(new InetSocketAddress(address, currentPort));
                        openPorts.add(currentPort);
                    } catch (ConnectException ignored) {
                    } catch (IOException e) {
                        System.out.println(e.getClass().getSimpleName() + ": " + e.getMessage());
                    } finally {
                        counter.dec();
                        socketCap.release();
                    }
                });
            }
        }
        System.out.println("Peak concurrent connects: " + counter.max());
        return openPorts.stream().toList();
    }
}