simple-mcp-server

Okay, here's a basic outline and code snippets for a simple MCP (Minecraft Protocol) server implementation using Java Spring Boot. This will be a *very* simplified version, focusing on the core concepts of receiving and responding to a handshake packet. It won't handle full game logic, world data, or player interactions. This is a starting point. **Important Considerations:** * **Complexity:** The Minecraft Protocol is complex. This example only covers the initial handshake. Implementing a full server requires significant effort. * **Security:** This example is *not* secure. Real-world servers need proper authentication, encryption, and anti-cheat measures. * **Libraries:** While Spring Boot simplifies things, you'll likely need a library to handle the low-level details of the Minecraft Protocol (packet encoding/decoding). I'll show a basic example without a dedicated library, but for a real server, consider libraries like `minecraft-server-util` or similar. * **Asynchronous Handling:** Use asynchronous processing (e.g., `CompletableFuture`, `ExecutorService`) to avoid blocking the main thread when handling network operations. **1. Project Setup (Spring Boot)** * Create a new Spring Boot project using Spring Initializr ([https://start.spring.io/](https://start.spring.io/)). * Dependencies: You'll need at least `spring-boot-starter-web`. Consider adding `spring-boot-starter-logging` for better logging. **2. Core Components** * **MinecraftServer Class:** This class will manage the server socket and handle incoming connections. * **Packet Handling:** Functions to read and write Minecraft Protocol packets. * **Data Structures:** Classes to represent the data in the packets (e.g., Handshake). **3. Code Example (Simplified)** ```java import org.springframework.boot.SpringApplication; import org.springframework.boot.autoconfigure.SpringBootApplication; import org.springframework.stereotype.Component; import java.io.DataInputStream; import java.io.DataOutputStream; import java.io.IOException; import java.net.ServerSocket; import java.net.Socket; import java.nio.charset.StandardCharsets; import java.util.concurrent.ExecutorService; import java.util.concurrent.Executors; import org.slf4j.Logger; import org.slf4j.LoggerFactory; @SpringBootApplication public class MinecraftServerApplication { public static void main(String[] args) { SpringApplication.run(MinecraftServerApplication.class, args); } } @Component class MinecraftServer { private static final Logger logger = LoggerFactory.getLogger(MinecraftServer.class); private final int port = 25565; // Default Minecraft port private final ExecutorService executor = Executors.newFixedThreadPool(10); // Thread pool private ServerSocket serverSocket; public MinecraftServer() { startServer(); } private void startServer() { try { serverSocket = new ServerSocket(port); logger.info("Minecraft server started on port " + port); while (true) { Socket clientSocket = serverSocket.accept(); executor.submit(() -> handleClient(clientSocket)); // Handle in a separate thread } } catch (IOException e) { logger.error("Error starting server: " + e.getMessage(), e); } finally { if (serverSocket != null) { try { serverSocket.close(); } catch (IOException e) { logger.error("Error closing server socket: " + e.getMessage(), e); } } } } private void handleClient(Socket clientSocket) { try (DataInputStream in = new DataInputStream(clientSocket.getInputStream()); DataOutputStream out = new DataOutputStream(clientSocket.getOutputStream())) { logger.info("Client connected from " + clientSocket.getInetAddress()); // 1. Read the Handshake packet Handshake handshake = readHandshake(in); logger.info("Received handshake: " + handshake); // 2. Respond to the handshake (Status Response) sendStatusResponse(out); //3. Handle Ping handlePing(in, out); } catch (IOException e) { logger.error("Error handling client: " + e.getMessage(), e); } finally { try { clientSocket.close(); logger.info("Client disconnected from " + clientSocket.getInetAddress()); } catch (IOException e) { logger.error("Error closing client socket: " + e.getMessage(), e); } } } private Handshake readHandshake(DataInputStream in) throws IOException { // Read packet length (VarInt) int packetLength = readVarInt(in); // Read packet ID (VarInt) int packetId = readVarInt(in); if (packetId != 0x00) { throw new IOException("Expected handshake packet (ID 0x00), got " + packetId); } // Read protocol version (VarInt) int protocolVersion = readVarInt(in); // Read server address (String) String serverAddress = readString(in); // Read server port (Unsigned Short) int serverPort = in.readUnsignedShort(); // Read next state (VarInt) int nextState = readVarInt(in); return new Handshake(protocolVersion, serverAddress, serverPort, nextState); } private void sendStatusResponse(DataOutputStream out) throws IOException { // Create a simple JSON response String jsonResponse = "{\n" + " \"version\": {\n" + " \"name\": \"My Simple Server\",\n" + " \"protocol\": 757\n" + // Example protocol version " },\n" + " \"players\": {\n" + " \"max\": 100,\n" + " \"online\": 0\n" + " },\n" + " \"description\": {\n" + " \"text\": \"A simple Minecraft server\"\n" + " }\n" + "}"; byte[] jsonBytes = jsonResponse.getBytes(StandardCharsets.UTF_8); int dataLength = jsonBytes.length; // Packet ID for Status Response is 0x00 byte[] packetData = new byte[dataLength + varIntSize(dataLength) + varIntSize(0x00)]; int offset = 0; offset = writeVarInt(packetData, offset, dataLength + varIntSize(0x00)); // Packet Length offset = writeVarInt(packetData, offset, 0x00); // Packet ID System.arraycopy(jsonBytes, 0, packetData, offset, dataLength); // JSON Data out.write(packetData); out.flush(); } private void handlePing(DataInputStream in, DataOutputStream out) throws IOException { // Read packet length (VarInt) int packetLength = readVarInt(in); // Read packet ID (VarInt) int packetId = readVarInt(in); if (packetId != 0x01) { throw new IOException("Expected Ping packet (ID 0x01), got " + packetId); } // Read payload (long) long payload = in.readLong(); // Send Pong response sendPongResponse(out, payload); } private void sendPongResponse(DataOutputStream out, long payload) throws IOException { // Packet ID for Pong Response is 0x01 byte[] packetData = new byte[8 + varIntSize(8) + varIntSize(0x01)]; // 8 bytes for long payload int offset = 0; offset = writeVarInt(packetData, offset, 8 + varIntSize(0x01)); // Packet Length offset = writeVarInt(packetData, offset, 0x01); // Packet ID writeLong(packetData, offset, payload); // Payload out.write(packetData); out.flush(); } // Helper methods for reading and writing VarInts and Strings (Minecraft Protocol) private int readVarInt(DataInputStream in) throws IOException { int numRead = 0; int result = 0; byte read; do { read = in.readByte(); int value = (read & 0x7f); result |= (value << (7 * numRead)); numRead++; if (numRead > 5) { throw new RuntimeException("VarInt is too big"); } } while ((read & 0x80) != 0); return result; } private String readString(DataInputStream in) throws IOException { int length = readVarInt(in); byte[] bytes = new byte[length]; in.readFully(bytes); return new String(bytes, StandardCharsets.UTF_8); } private int writeVarInt(byte[] buffer, int offset, int value) { while (true) { if ((value & ~0x7F) == 0) { buffer[offset++] = (byte) value; return offset; } else { buffer[offset++] = (byte) ((value & 0x7F) | 0x80); value >>>= 7; } } } private int varIntSize(int value) { int size = 0; do { value >>>= 7; size++; } while (value != 0); return size; } private void writeLong(byte[] buffer, int offset, long value) { buffer[offset++] = (byte) (value >>> 0); buffer[offset++] = (byte) (value >>> 8); buffer[offset++] = (byte) (value >>> 16); buffer[offset++] = (byte) (value >>> 24); buffer[offset++] = (byte) (value >>> 32); buffer[offset++] = (byte) (value >>> 40); buffer[offset++] = (byte) (value >>> 48); buffer[offset++] = (byte) (value >>> 56); } } // Data class for the Handshake packet class Handshake { public int protocolVersion; public String serverAddress; public int serverPort; public int nextState; public Handshake(int protocolVersion, String serverAddress, int serverPort, int nextState) { this.protocolVersion = protocolVersion; this.serverAddress = serverAddress; this.serverPort = serverPort; this.nextState = nextState; } @Override public String toString() { return "Handshake{" + "protocolVersion=" + protocolVersion + ", serverAddress='" + serverAddress + '\'' + ", serverPort=" + serverPort + ", nextState=" + nextState + '}'; } } ``` **Explanation:** 1. **`MinecraftServerApplication`:** Standard Spring Boot application entry point. 2. **`MinecraftServer`:** * `@Component`: Makes this a Spring-managed bean. * `startServer()`: Creates a `ServerSocket` and listens for incoming connections. Uses a thread pool (`ExecutorService`) to handle each client connection asynchronously. * `handleClient()`: This is where the magic happens. It reads the handshake packet, sends a status response, and handles the ping. * `readHandshake()`: Reads the handshake packet data from the input stream. It reads VarInts and Strings according to the Minecraft Protocol. * `sendStatusResponse()`: Creates a simple JSON response (the server status) and sends it back to the client. This is what you see when you add a server to your Minecraft client. * `handlePing()`: Reads the ping packet and sends a pong response. * `readVarInt()`, `readString()`, `writeVarInt()`: Helper methods to read and write VarInts and Strings, which are used extensively in the Minecraft Protocol. VarInts are variable-length integers. 3. **`Handshake`:** A simple data class to hold the handshake information. **How to Run:** 1. Build the Spring Boot project (e.g., using Maven or Gradle). 2. Run the resulting JAR file. 3. In your Minecraft client, add a new server with the address `localhost` (or the IP address of your server). 4. You should see the server in the server list with the status information you provided in the `sendStatusResponse()` method. **Key Improvements and Next Steps:** * **Error Handling:** Add more robust error handling and logging. * **Configuration:** Externalize the server port and other settings using Spring Boot's configuration mechanisms. * **Minecraft Protocol Library:** Use a dedicated Minecraft Protocol library to simplify packet handling and ensure correctness. This will handle the complexities of VarInts, strings, and other data types. * **State Management:** Implement proper state management to track the client's connection state (handshake, status, login, play). * **Login:** Implement the login sequence to authenticate players. * **World Generation:** Generate or load a Minecraft world. * **Game Logic:** Implement the core game logic (player movement, block updates, etc.). * **Security:** Implement encryption (e.g., using the `net.minecraft.network.Encryption` class from a Minecraft server library) and authentication. * **Asynchronous I/O:** Use non-blocking I/O (NIO) for better performance. **Chinese Translation of Key Concepts:** * **Minecraft Protocol (MCP):** 我的世界协议 (Wǒ de Shìjiè Xiéyì) * **Handshake:** 握手 (Wòshǒu) * **Packet:** 数据包 (Shùjùbāo) * **Server:** 服务器 (Fúwùqì) * **Client:** 客户端 (Kèhùduān) * **VarInt:** 变长整数 (Biàn cháng zhěngshù) * **Status Response:** 状态响应 (Zhuàngtài xiǎngyìng) * **Ping:** 延迟测试 (Yánchí cèshì) / 心跳 (Xīntiào) * **Pong:** 延迟测试回应 (Yánchí cèshì huíyìng) / 心跳回应 (Xīntiào huíyìng) * **Thread Pool:** 线程池 (Xiànchéng chí) * **Asynchronous:** 异步 (Yìbù) * **Socket:** 套接字 (Tàojiēzì) This example provides a basic foundation. Building a full Minecraft server is a complex undertaking, but this should give you a good starting point. Remember to prioritize security and use appropriate libraries to handle the Minecraft Protocol correctly. Good luck!