Init

.gitignore

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+# User-specific stuff
+.idea/
+
+*.iml
+*.ipr
+*.iws
+
+# IntelliJ
+out/
+
+# Compiled class file
+*.class
+
+# Log file
+*.log
+
+# BlueJ files
+*.ctxt
+
+# Package Files #
+*.jar
+*.war
+*.nar
+*.ear
+*.zip
+*.tar.gz
+*.rar
+
+# virtual machine crash logs, see http://www.java.com/en/download/help/error_hotspot.xml
+hs_err_pid*
+
+*~
+
+# temporary files which can be created if a process still has a handle open of a deleted file
+.fuse_hidden*
+
+# KDE directory preferences
+.directory
+
+# Linux trash folder which might appear on any partition or disk
+.Trash-*
+
+# .nfs files are created when an open file is removed but is still being accessed
+.nfs*
+
+# General
+.DS_Store
+.AppleDouble
+.LSOverride
+
+# Icon must end with two \r
+Icon
+
+# Thumbnails
+._*
+
+# Files that might appear in the root of a volume
+.DocumentRevisions-V100
+.fseventsd
+.Spotlight-V100
+.TemporaryItems
+.Trashes
+.VolumeIcon.icns
+.com.apple.timemachine.donotpresent
+
+# Directories potentially created on remote AFP share
+.AppleDB
+.AppleDesktop
+Network Trash Folder
+Temporary Items
+.apdisk
+
+# Windows thumbnail cache files
+Thumbs.db
+Thumbs.db:encryptable
+ehthumbs.db
+ehthumbs_vista.db
+
+# Dump file
+*.stackdump
+
+# Folder config file
+[Dd]esktop.ini
+
+# Recycle Bin used on file shares
+$RECYCLE.BIN/
+
+# Windows Installer files
+*.cab
+*.msi
+*.msix
+*.msm
+*.msp
+
+# Windows shortcuts
+*.lnk
+
+target/
+
+pom.xml.tag
+pom.xml.releaseBackup
+pom.xml.versionsBackup
+pom.xml.next
+
+release.properties
+dependency-reduced-pom.xml
+buildNumber.properties
+.mvn/timing.properties
+.mvn/wrapper/maven-wrapper.jar
+.flattened-pom.xml
+
+# Common working directory
+run/

pom.xml

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+<?xml version="1.0" encoding="UTF-8"?>
+<project xmlns="http://maven.apache.org/POM/4.0.0"
+         xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
+         xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
+    <modelVersion>4.0.0</modelVersion>
+
+    <groupId>net.rubeta</groupId>
+    <artifactId>LegacyPing</artifactId>
+    <version>1.0-SNAPSHOT</version>
+    <packaging>jar</packaging>
+
+    <name>LegacyPing</name>
+
+    <properties>
+        <java.version>1.8</java.version>
+        <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
+    </properties>
+
+    <build>
+        <plugins>
+            <plugin>
+                <groupId>org.apache.maven.plugins</groupId>
+                <artifactId>maven-compiler-plugin</artifactId>
+                <version>3.8.1</version>
+                <configuration>
+                    <source>${java.version}</source>
+                    <target>${java.version}</target>
+                </configuration>
+            </plugin>
+            <!--plugin>
+                <groupId>org.apache.maven.plugins</groupId>
+                <artifactId>maven-shade-plugin</artifactId>
+                <version>3.2.4</version>
+                <executions>
+                    <execution>
+                        <phase>package</phase>
+                        <goals>
+                            <goal>shade</goal>
+                        </goals>
+                        <configuration>
+                            <createDependencyReducedPom>false</createDependencyReducedPom>
+                        </configuration>
+                    </execution>
+                </executions>
+            </plugin-->
+        </plugins>
+        <resources>
+            <resource>
+                <directory>src/main/resources</directory>
+                <filtering>true</filtering>
+            </resource>
+        </resources>
+    </build>
+
+    <dependencies>
+        <dependency>
+            <groupId>org.bukkit</groupId>
+            <artifactId>crutchbukkitmodded</artifactId>
+            <version>0.0.1-SNAPSHOT</version>
+            <scope>provided</scope>
+        </dependency>
+    </dependencies>
+</project>

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

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+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());
+    }
+}

src/main/resources/config.yml

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+host: '0.0.0.0'
+port: 25566

src/main/resources/plugin.yml

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+name: LegacyPing
+version: '${project.version}'
+main: net.rubeta.legacyping.LegacyPing