Allow Quarkus to pick a random debug port

core/deployment/src/main/java/io/quarkus/deployment/dev/QuarkusDevModeLauncher.java

@@ -7,6 +7,7 @@
 import java.io.IOException;
 import java.io.ObjectOutputStream;
 import java.net.InetAddress;
+import java.net.ServerSocket;
 import java.net.Socket;
 import java.net.URI;
 import java.net.UnknownHostException;
@@ -40,7 +41,7 @@
 
 public abstract class QuarkusDevModeLauncher {
     final Pattern validDebug = Pattern.compile("^(true|false|client|[0-9]+)$");
-    final Pattern validPort = Pattern.compile("^[0-9]+$");
+    final Pattern validPort = Pattern.compile("^-?[0-9]+$");
 
     public class Builder<R extends QuarkusDevModeLauncher, B extends Builder<R, B>> {
 
@@ -369,7 +370,7 @@ protected void prepare() throws Exception {
             }
         }
         if (port <= 0) {
-            throw new Exception("The specified debug port must be greater than 0");
+            port = getRandomPort();
         }
 
         if (debug != null && debug.equalsIgnoreCase("client")) {
@@ -479,6 +480,12 @@ protected void prepare() throws Exception {
         }
     }
 
+    private int getRandomPort() throws IOException {
+        try (ServerSocket socket = new ServerSocket(0)) {
+            return socket.getLocalPort();
+        }
+    }
+
     private InetAddress getInetAddress(String host) throws UnknownHostException {
         if ("localhost".equals(host)) {
             return InetAddress.getByAddress(new byte[] { 127, 0, 0, 1 });