jscanner

commit d88400469de3ac51e5dd2998b3968759a4ea18a0
parent c9313a24375fb8ffe1db356770e24009bae36c8a
Author: Matthias Jaros <jaros@mailbox.org>
Date:   Mon, 16 Mar 2026 23:34:05 +0100

Added maxTargetLimit for a cap that defines how many targets are scanned
at the same time.

Diffstat:
M
src/main/java/com/it_jaros/network_scanner/App.java
 | 
4
++--
M
src/main/java/com/it_jaros/network_scanner/CliParser.java
 | 
11
++++++++---
M
src/main/java/com/it_jaros/network_scanner/ScanOptions.java
 | 
2
+-
M
src/main/java/com/it_jaros/network_scanner/Scanner.java
 | 
14
++++++++++++--

4 files changed, 23 insertions(+), 8 deletions(-)
diff --git a/src/main/java/com/it_jaros/network_scanner/App.java b/src/main/java/com/it_jaros/network_scanner/App.java
@@ -9,7 +9,7 @@ public class App {
         try {
             ScanOptions options = cliParser.parseArgs(args);
             Scanner scanner = new Scanner(options.openSocketLimit(), options.timeoutInMillis(),
-                    options.delayInMillis(), options.maxWorkersPerHost());
+                    options.delayInMillis(), options.maxWorkersPerHost(), options.maxTargetsLimit());
             printResults(scanner.scan(options));
         } catch (IllegalArgumentException e) {
             System.out.printf("Error while parsing arguments: %s", e.getMessage());
@@ -27,7 +27,7 @@ public class App {
         String ports = result.openPorts().stream().mapToObj(String::valueOf).collect(Collectors.joining(","));
         String output = "[" + result.target() + "]:";
         if (ports.isEmpty()) {
-            output = output + "No open ports found";
+            return;
         } else {
             output = output + ports;
         }
diff --git a/src/main/java/com/it_jaros/network_scanner/CliParser.java b/src/main/java/com/it_jaros/network_scanner/CliParser.java
@@ -15,6 +15,7 @@ public class CliParser {
         int delayInMillis = 0;
         int timeoutInMillis = 1000;
         int maxWorkersPerHost = 1000;
+        int maxTargetsLimit = 10;
         String ports = "1-1024";
         for (int i = 0; i < args.length; i++) {
             final String currentArg = args[i];
@@ -40,6 +41,9 @@ public class CliParser {
                     case "--maxWorkersPerHost", "-wh":
                         maxWorkersPerHost = Integer.parseInt(args[++i]);
                         break;
+                    case "--maxTargetsLimit", "-tl":
+                        maxTargetsLimit = Integer.parseInt(args[++i]);
+                        break;
                     case "--ports", "-p":
                         ports = args[++i];
                         break;
@@ -53,10 +57,10 @@ public class CliParser {
         }
 
         System.out.printf(
-                "Parsed arguments: targets('%s'), ports(%s), socketLimit(%s), delayInMillis(%s), timeoutInMillis(%s), maxWorkersPerHost(%s)%n",
-                targets, ports, socketLimit, delayInMillis, timeoutInMillis, maxWorkersPerHost);
+                "Parsed arguments: targets('%s'), ports(%s), socketLimit(%s), delayInMillis(%s), timeoutInMillis(%s), maxWorkersPerHost(%s), maxTargetsLimit(%s) %n",
+                targets, ports, socketLimit, delayInMillis, timeoutInMillis, maxWorkersPerHost, maxTargetsLimit);
         
-        return new ScanOptions(targets.stream().toList(), socketLimit, delayInMillis, timeoutInMillis, maxWorkersPerHost, ports);
+        return new ScanOptions(targets.stream().toList(), socketLimit, delayInMillis, timeoutInMillis, maxWorkersPerHost, maxTargetsLimit, ports);
     }
 
     public void usageAndExit() {
@@ -70,6 +74,7 @@ public class CliParser {
                     --timeout, -t:\t\tTimeout per connection attempt, 0 means infinite (Default: 1000)
                     --ports, -p:\t\tPorts to be scanned
                     --maxWorkersPerHost, -wh:\tVirtual Worker Threads run per target. Higher doesn't mean necessarily faster. But the more you use the more RAM is required (Default: 1000)
+                    --maxTargetsLimit, -tl:\\tMax number of targets that are scanned at the same time (Default: 10)
 
                 Examples:
                     java -jar scanner.jar localhost
diff --git a/src/main/java/com/it_jaros/network_scanner/ScanOptions.java b/src/main/java/com/it_jaros/network_scanner/ScanOptions.java
@@ -2,4 +2,4 @@ package com.it_jaros.network_scanner;
 
 import java.util.List;
 
-public record ScanOptions(List<String> targets, int openSocketLimit, int delayInMillis, int timeoutInMillis, int maxWorkersPerHost, String ports) {}
+public record ScanOptions(List<String> targets, int openSocketLimit, int delayInMillis, int timeoutInMillis, int maxWorkersPerHost, int maxTargetsLimit, String ports) {}
diff --git a/src/main/java/com/it_jaros/network_scanner/Scanner.java b/src/main/java/com/it_jaros/network_scanner/Scanner.java
@@ -26,12 +26,14 @@ public class Scanner {
     private final int timeoutInMillis;
     private final long delayInNanos;
     private final int maxWorkersPerHost;
+    private final int maxTargetsLimit;
 
-    public Scanner(int socketLimit, int timeoutInMillis, int delayInMillis, int maxWorkersPerHost) {
+    public Scanner(int socketLimit, int timeoutInMillis, int delayInMillis, int maxWorkersPerHost, int maxTargetsLimit) {
         this.timeoutInMillis = timeoutInMillis;
         this.delayInNanos = TimeUnit.MILLISECONDS.toNanos(Math.max(0, delayInMillis));
         this.socketLimit = new Semaphore(socketLimit);
         this.maxWorkersPerHost = maxWorkersPerHost;
+        this.maxTargetsLimit = maxTargetsLimit;
     }
 
     public List<ScanResult> scan(ScanOptions target) {
@@ -43,8 +45,16 @@ public class Scanner {
         progressBar.start();
         try (ExecutorService executor = Executors.newVirtualThreadPerTaskExecutor()) {
             List<Future<ScanResult>> futures = new ArrayList<>();
+            Semaphore maxTargets = new Semaphore(maxTargetsLimit);
             for (String target : targets) {
-                futures.add(executor.submit(() -> scanTarget(target, ports)));
+                maxTargets.acquireUninterruptibly();
+                futures.add(executor.submit(() -> {
+                    try {
+                        return scanTarget(target, ports);
+                    } finally {
+                        maxTargets.release();
+                    }
+                }));
             }
 
             futures.forEach((Future<ScanResult> f) -> {