(feat.) Check if the MongoDB port is open before binding to it

src/main/java/emu/lunarcore/database/DatabaseManager.java

@@ -2,6 +2,7 @@ package emu.lunarcore.database;
 
 import java.util.stream.Stream;
 
+import emu.lunarcore.util.Utils;
 import org.bson.codecs.configuration.CodecRegistries;
 import org.reflections.Reflections;
 
@@ -41,11 +42,12 @@ public final class DatabaseManager {
 
     public DatabaseManager(DatabaseInfo info, ServerType type) {
         // Variables
+        var internalConfig = LunarCore.getConfig().getInternalMongoServer();
         String connectionString = info.getUri();
 
         // Local mongo server
-        if (info.isUseInternal()) {
-            connectionString = startInternalMongoServer(LunarCore.getConfig().getInternalMongoServer());
+        if (info.isUseInternal() && Utils.isPortOpen(internalConfig.getAddress(), internalConfig.getPort())) {
+            connectionString = startInternalMongoServer(internalConfig);
             LunarCore.getLogger().info("Using local mongo server at " + server.getConnectionString());
         }
 

src/main/java/emu/lunarcore/util/Utils.java

@@ -1,6 +1,10 @@
 package emu.lunarcore.util;
 
 import java.io.File;
+import java.net.InetAddress;
+import java.net.InetSocketAddress;
+import java.net.ServerSocket;
+import java.net.Socket;
 import java.util.Base64;
 import java.util.List;
 import java.util.concurrent.ThreadLocalRandom;
@@ -157,4 +161,21 @@ public class Utils {
     public static byte[] base64Decode(String toDecode) {
         return Base64.getDecoder().decode(toDecode);
     }
+
+    /**
+     * Checks if a port is open on a given host.
+     *
+     * @param host The host to check.
+     * @param port The port to check.
+     * @return True if the port is open, false otherwise.
+     */
+    public static boolean isPortOpen(String host, int port) {
+        try (var serverSocket = new ServerSocket()) {
+            serverSocket.setReuseAddress(false);
+            serverSocket.bind(new InetSocketAddress(InetAddress.getByName(host), port), 1);
+            return true;
+        } catch (Exception ex) {
+            return false;
+        }
+    }
 }