4 files changed, 153 insertions, 0 deletions
diff --git a/src/main/java/com/it_jaros/networkScanner/App.java b/src/main/java/com/it_jaros/networkScanner/App.java
new file mode 100644
index 0000000..5d52065
--- /dev/null
+++ b/src/main/java/com/it_jaros/networkScanner/App.java
@@ -0,0 +1,41 @@
+package com.it_jaros.networkScanner;
+
+import java.util.List;
+
+public class App {
+    public static void main(String[] args) {
+        Scanner scanner = new Scanner();
+        if (args.length < 1 || args[0] == "") {
+            usageAndExit();
+        }
+        String target = args[0];
+        System.out.printf(
+                "Scanning host=%s \n",
+                target);
+
+        try (FdCounter fd = new FdCounter()) {
+            fd.start(20); // sample every 20ms
+            List<Integer> openPorts = scanner.scanPorts(target, 10000);
+            printPorts(target, openPorts);
+            System.out.println("FD limit: " + fd.maxFds());
+            System.out.println("Peak open FDs during scan: " + fd.peakOpenFds());
+        }
+    }
+
+    public static void printPorts(String address, List<Integer> openPorts) {
+        System.out.println("Address:" + address);
+        openPorts.forEach((p) -> System.out.println("Open port: " + p));
+    }
+
+    private static void usageAndExit() {
+        System.err.println("""
+            Usage:
+              java -jar scanner.jar <host> 
+
+            Examples:
+              java -jar scanner.jar localhost
+              java -jar scanner.jar fd00::1 
+            """);
+        System.exit(1);
+    }
+}
diff --git a/src/main/java/com/it_jaros/networkScanner/Counter.java b/src/main/java/com/it_jaros/networkScanner/Counter.java
new file mode 100644
index 0000000..a4baec0
--- /dev/null
+++ b/src/main/java/com/it_jaros/networkScanner/Counter.java
@@ -0,0 +1,25 @@
+package com.it_jaros.networkScanner;
+
+import java.util.concurrent.atomic.AtomicInteger;
+
+public final class Counter {
+    private final AtomicInteger current = new AtomicInteger(0);
+    private final AtomicInteger max = new AtomicInteger(0);
+
+    public void inc() {
+        int now = current.incrementAndGet();
+        max.accumulateAndGet(now, Math::max);
+    }
+
+    public void dec() {
+        current.decrementAndGet();
+    }
+
+    public int current() {
+        return current.get();
+    }
+
+    public int max() {
+        return max.get();
+    }
+}
diff --git a/src/main/java/com/it_jaros/networkScanner/FdCounter.java b/src/main/java/com/it_jaros/networkScanner/FdCounter.java
new file mode 100644
index 0000000..05eb9a4
--- /dev/null
+++ b/src/main/java/com/it_jaros/networkScanner/FdCounter.java
@@ -0,0 +1,37 @@
+package com.it_jaros.networkScanner;
+
+import java.lang.management.ManagementFactory;
+import java.util.concurrent.Executors;
+import java.util.concurrent.ScheduledExecutorService;
+import java.util.concurrent.TimeUnit;
+import java.util.concurrent.atomic.AtomicLong;
+
+import com.sun.management.UnixOperatingSystemMXBean;
+
+public final class FdCounter implements AutoCloseable {
+    private final UnixOperatingSystemMXBean os =
+            (UnixOperatingSystemMXBean) ManagementFactory.getOperatingSystemMXBean();
+    private final ScheduledExecutorService ses =
+            Executors.newSingleThreadScheduledExecutor(Thread.ofPlatform().daemon().factory());
+    private final AtomicLong peak = new AtomicLong(0);
+
+    public void start(long everyMillis) {
+        ses.scheduleAtFixedRate(() -> {
+            long now = os.getOpenFileDescriptorCount();
+            peak.accumulateAndGet(now, Math::max);
+        }, 0, everyMillis, TimeUnit.MILLISECONDS);
+    }
+
+    public long peakOpenFds() {
+        return peak.get();
+    }
+
+    public long maxFds() {
+        return os.getMaxFileDescriptorCount();
+    }
+
+    @Override public void close() {
+        ses.shutdownNow();
+    }
+}
+
diff --git a/src/main/java/com/it_jaros/networkScanner/Scanner.java b/src/main/java/com/it_jaros/networkScanner/Scanner.java
new file mode 100644
index 0000000..1f71f56
--- /dev/null
+++ b/src/main/java/com/it_jaros/networkScanner/Scanner.java
@@ -0,0 +1,50 @@
+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;
+
+public class Scanner {
+                
+    private Counter counter = new Counter();
+    private final int socketLimitDefault = 1024;
+    
+    public Scanner() {}
+    
+    public List<Integer> scanPorts(String address) {
+        return scanPorts(address, socketLimitDefault);
+    }
+
+    public List<Integer> scanPorts(String address, int socketLimit) {
+        Queue<Integer> openPorts = new ConcurrentLinkedQueue<>();
+        Semaphore socketCap = new Semaphore(socketLimit);
+        try (ExecutorService executor = Executors.newVirtualThreadPerTaskExecutor()) {
+            for (int port = 1; port < 65536; port++) {
+                final int currentPort = port;
+                executor.submit(() -> {
+                    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();
+    }
+}