Init

src/main/java/net/rubeta/legacyping/LegacyPing.java

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+package net.rubeta.legacyping;
+
+import org.bukkit.configuration.file.FileConfiguration;
+import org.bukkit.plugin.java.JavaPlugin;
+
+import java.io.IOException;
+import java.util.logging.Level;
+
+public final class LegacyPing extends JavaPlugin {
+    private ServerThread serverThread;
+
+    @Override
+    public void onEnable() {
+        this.saveDefaultConfig();
+        final FileConfiguration config = this.getConfig();
+        try {
+            this.serverThread = new ServerThread(this.getServer(), config.getString("host", "0.0.0.0"),  config.getInt("port", 25566));
+            this.serverThread.start();
+        } catch (IOException e) {
+            this.getLogger().log(Level.WARNING, "Failed to create ServerSocket", e);
+            this.getPluginLoader().disablePlugin(this);
+        }
+    }
+
+    @Override
+    public void onDisable() {
+        if (this.serverThread != null) {
+            this.serverThread.shutdown();
+        }
+    }
+}

src/main/java/net/rubeta/legacyping/ServerThread.java

@@ -0,0 +1,79 @@
+package net.rubeta.legacyping;
+
+import org.bukkit.Server;
+
+import java.io.*;
+import java.net.InetAddress;
+import java.net.ServerSocket;
+import java.net.Socket;
+import java.util.Arrays;
+import java.util.concurrent.TimeUnit;
+import java.util.concurrent.atomic.AtomicBoolean;
+
+public class ServerThread extends Thread {
+
+    // Queries start
+    private static final byte[] RUBETA_MODDED_CLIENT = new byte[]{0, 0, 0, 1, (byte) 254};
+
+    // Queries end
+    private final ServerSocket serverSocket;
+    private final AtomicBoolean working = new AtomicBoolean(false);
+    private final Server minecraftServer;
+
+    public ServerThread(final Server server, final String host, int port) throws IOException {
+        this.minecraftServer = server;
+        final InetAddress address = InetAddress.getByName(host);
+        this.serverSocket = new ServerSocket(port, 10, address);
+        this.serverSocket.setSoTimeout((int) TimeUnit.SECONDS.toMillis(10L));
+    }
+
+    @Override
+    public void run() {
+        this.working.set(true);
+        while (this.working.get() || !this.serverSocket.isClosed()) {
+            try {
+                final Socket newConnection = this.serverSocket.accept();
+                final InputStream inputStream = newConnection.getInputStream();
+                final ByteArrayOutputStream result = new ByteArrayOutputStream();
+                byte[] buffer = new byte[16];
+                for (int length; (length = inputStream.read(buffer)) != -1; ) {
+                    result.write(buffer, 0, length);
+                }
+                final byte[] query = result.toByteArray();
+                final OutputStream outputStream = newConnection.getOutputStream();
+                if (Arrays.equals(RUBETA_MODDED_CLIENT, query)) {
+                    this.responseForRuBetaModdedClient(outputStream);
+                } else if (false) {
+
+                }
+                newConnection.close();
+            } catch (IOException ignore) {
+            }
+        }
+    }
+
+    public void shutdown() {
+        this.working.set(false);
+        try {
+            this.serverSocket.close();
+        } catch (IOException ignore) {
+        }
+    }
+
+    private void responseForRuBetaModdedClient(final OutputStream outputStream) throws IOException {
+        final ByteArrayOutputStream result = new ByteArrayOutputStream();
+        final DataOutputStream dos = new DataOutputStream(result);
+        dos.write(255); // Packet 0xFF (PacketDisconnect)
+        final String response = this.minecraftServer.getMotd()
+                + '\u0000' + this.minecraftServer.getOnlinePlayers().size()
+                + '\u0000' + this.minecraftServer.getMaxPlayers();
+        dos.writeShort(response.length());
+        for (char c : response.toCharArray()) {
+            dos.writeChar(c);
+        }
+        // Packet data end
+        final DataOutputStream clientOutput = new DataOutputStream(outputStream);
+        clientOutput.writeInt(result.size());
+        clientOutput.write(result.toByteArray());
+    }
+}