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.ArrayList;
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();
    private Semaphore socketCap;
    
    public Scanner(int socketLimit) {
        socketCap = new Semaphore(socketLimit);
    }

    public Scanner() {}

    public List<ScanResult> scanPorts(ScanOptions target) {
        return scanPorts(target.targets(), target.delayInMillis());
    }

    public List<ScanResult> scanPorts(List<String> targets, int delayInMillis) {
        List<ScanResult> results = new ArrayList<>();
        long delayInNanos = TimeUnit.MILLISECONDS.toNanos(Math.max(0, delayInMillis));
        try (ExecutorService executor = Executors.newVirtualThreadPerTaskExecutor()) {
            for (String target : targets) {
                results.add(scanTargetAsync(target, delayInNanos, executor));
            }
        }
        System.out.println("Peak concurrent connects: " + counter.max());
        return results;
    }

    private ScanResult scanTargetAsync(String target, long delayInNanos, ExecutorService executor) { 
        AtomicLong nextStartNanos = new AtomicLong(System.nanoTime());
        Queue<Integer> openPorts = new ConcurrentLinkedQueue<>();
        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(target, currentPort), 10000);
                    openPorts.add(currentPort);
                } catch (ConnectException ignored) {
                } catch (IOException e) {
                    System.out.println(e.getClass().getSimpleName() + ": " + e.getMessage());
                } finally {
                    counter.dec();
                    socketCap.release();
                }
            });
        }
        return new ScanResult(target, openPorts);
    }
}