Python MCP Server: Create & Learn
DataScienceQ🐍 Building Your Own Minecraft Protocol (MCP) Server with Python
The term "MCP Server" in the context of Python development most commonly refers to a custom server built to interact with the Minecraft Protocol. This protocol is the intricate set of rules and data formats that a Minecraft client uses to communicate with a Minecraft server. Building your own allows for deep customization and understanding of game mechanics.
What is MCP (Minecraft Protocol) and Its Uses?
The Minecraft Protocol defines how Minecraft clients (Java Edition) exchange information with game servers. It's a complex, stateful, binary protocol built on top of TCP/IP.
Uses of Building a Custom MCP Server:
• Educational Purposes: A fantastic way to learn about network programming, binary data manipulation, state machines, and reverse engineering protocols.
• Custom Game Modes/Mechanics: Implement unique gameplay experiences, minigames, or rule sets not possible with standard server software (like Spigot, Paper, Fabric, or vanilla).
• Botting and Automation: Develop intelligent bots that can interact with existing Minecraft servers, perform tasks, or simulate players.
• Proxies and Intermediaries: Create proxies that modify client-server communication, add custom features, security layers, or performance optimizations.
• Testing and Development Tools: Build custom test environments or tools for mod developers.
• Learning Client-Side Behavior: By observing and responding to client packets, one can gain insight into how the Minecraft client works internally.
Core Concepts of the Minecraft Protocol
Before diving into Python implementation, understanding these concepts is crucial:
• TCP/IP: All communication happens over TCP sockets, ensuring reliable, ordered delivery.
• Packet-Based: Data is exchanged in discrete units called "packets." Each packet has a length, a unique ID, and a payload.
• States: The protocol operates in different states, each with its own set of valid packet IDs and expected behaviors:
Handshaking: Initial connection, client sends desired protocol version and next state.
Status: Used for pinging a server to get basic information (player count, MOTD).
Login: Client authenticates with the server.
Play: The main game state, where all in-game interactions occur (movement, chat, block changes).
• Binary Data: Packet payloads consist of various binary data types:
VarInt: Variable-length integer, critical for packet IDs and lengths.
String: Length-prefixed UTF-8 encoded string.
Byte, Short, Int, Long: Standard fixed-size integers.
Float, Double: Floating-point numbers.
Boolean: Single byte (0x00 for false, 0x01 for true).
Arrays, NBT (Named Binary Tag): More complex data structures.
• Compression: After the Handshaking and Login states, servers typically enable Zlib compression for Play state packets to reduce bandwidth.
• Encryption: After successful login, communication is encrypted using AES with a shared secret.
Challenges of Building an MCP Server
• Protocol Complexity: The Minecraft protocol is incredibly detailed and constantly evolving with new game versions. A full implementation is a significant undertaking.
• State Management: Tracking the state (Handshaking, Login, Play) and associated data (player UUID, username, position) for each connected client is complex.
• Performance: Python's Global Interpreter Lock (GIL) can be a bottleneck for highly concurrent servers. asyncio is often preferred over traditional threading for I/O-bound tasks like network communication.
• Error Handling: Robust error handling is essential for dealing with malformed packets, network issues, and unexpected client behavior.
How to Build Your Own MCP Server with Python
This guide will provide a basic framework for handling the initial Handshaking and Login phases using Python's asyncio for concurrent client handling.
Prerequisites
• Python 3.7+
• asyncio (built-in for async networking)
• struct (built-in for packing/unpacking binary data)
• zlib (built-in for compression, if implementing Play state)
• PyCryptodome (or similar, for AES encryption, if implementing Play state with encryption)
• The [Minecraft Protocol Wiki](https://wiki.vg/Protocol) is your absolute best friend for packet formats.
1. Packet Structure and VarInt
Every packet starts with its total Length (as a VarInt), followed by its Packet ID (as a VarInt), and then the actual Data.
The VarInt is crucial. It's an integer that can take anywhere from 1 to 5 bytes, depending on its value.
import struct
import asyncio
import logging
logging.basicConfig(level=logging.INFO, format='%(asctime)s - %(levelname)s - %(message)s')
# --- VarInt Implementation ---
# This is a critical utility for reading/writing Minecraft protocol integers.
def read_varint(reader):
"""Reads a VarInt from an asyncio StreamReader."""
value = 0
num_read = 0
while True:
byte = yield from reader.readexactly(1)
byte = byte[0]
value |= (byte & 0x7F) << (7 * num_read)
if not (byte & 0x80):
break
num_read += 1
if num_read > 5:
raise ValueError("VarInt is too big!")
return value
def write_varint(value):
"""Writes a VarInt to bytes."""
out = b''
while True:
byte = value & 0x7F
value >>= 7
if value:
byte |= 0x80
out += bytes([byte])
if not value:
break
return out
# --- Utility to read a length-prefixed string ---
def read_string(reader):
"""Reads a length-prefixed string (VarInt length) from a StreamReader."""
length = yield from read_varint(reader)
string_bytes = yield from reader.readexactly(length)
return string_bytes.decode('utf-8')
def write_string(s):
"""Writes a string with VarInt length prefix to bytes."""
s_bytes = s.encode('utf-8')
return write_varint(len(s_bytes)) + s_bytes2. Handling Client Connections (Asyncio Server)
An asyncio server is ideal for handling multiple concurrent clients without explicit threading.
class MinecraftClient:
def __init__(self, reader, writer):
self.reader = reader
self.writer = writer
self.state = "HANDSHAKING" # Current protocol state
self.protocol_version = -1
self.username = None
logging.info(f"New client connected from {self.writer.get_extra_info('peername')}")
async def _send_packet(self, packet_id, data):
"""Helper to send a packet."""
packet_id_bytes = write_varint(packet_id)
packet_data = packet_id_bytes + data
packet_length = write_varint(len(packet_data))
self.writer.write(packet_length + packet_data)
await self.writer.drain()
logging.debug(f"Sent packet ID: {hex(packet_id)} with data: {data.hex()}")
async def _handle_handshaking(self, packet_id, packet_data_reader):
"""Handles packets in the HANDSHAKING state."""
if packet_id == 0x00: # Handshake Packet
# The Handshake packet format:
# VarInt Protocol Version
# String Server Address
# Unsigned Short Server Port
# VarInt Next State (1 for Status, 2 for Login)
self.protocol_version = await read_varint(packet_data_reader)
server_address = await read_string(packet_data_reader)
server_port = struct.unpack('>H', await packet_data_reader.readexactly(2))[0]
next_state = await read_varint(packet_data_reader)
logging.info(f"Handshake from {self.writer.get_extra_info('peername')}: "
f"Protocol {self.protocol_version}, Addr: {server_address}:{server_port}, Next State: {next_state}")
if next_state == 1: # Status State
self.state = "STATUS"
elif next_state == 2: # Login State
self.state = "LOGIN"
else:
logging.warning(f"Unknown next state: {next_state}")
self.writer.close()
await self.writer.wait_closed()
else:
logging.warning(f"Unhandled packet ID {hex(packet_id)} in HANDSHAKING state.")
async def _handle_status(self, packet_id, packet_data_reader):
"""Handles packets in the STATUS state."""
if packet_id == 0x00: # Status Request
# Client requested server status
logging.info("Client requested server status.")
# Response: JSON string with server info
status_json = """
{
"version": {
"name": "1.16.5",
"protocol": 754
},
"players": {
"max": 100,
"online": 1,
"sample": [
{
"name": "PythonMCP",
"id": "4566e69f-c90a-48ee-89d4-cba5e05df1f6"
}
]
},
"description": {
"text": "A basic Python MCP server!"
},
"favicon": "data:image/png;base64,<YOUR_BASE64_FAVICON_HERE>"
}
""" # Replace <YOUR_BASE64_FAVICON_HERE> with an actual base64 encoded favicon image
await self._send_packet(0x00, write_string(status_json))
elif packet_id == 0x01: # Ping Request
# Client sent a ping packet (Long payload)
payload = struct.unpack('>Q', await packet_data_reader.readexactly(8))[0]
logging.info(f"Client sent ping with payload: {payload}")
# Respond with a Pong packet (same payload)
await self._send_packet(0x01, struct.pack('>Q', payload))
# After ping/pong, client might close connection
self.writer.close()
await self.writer.wait_closed()
else:
logging.warning(f"Unhandled packet ID {hex(packet_id)} in STATUS state.")
async def _handle_login(self, packet_id, packet_data_reader):
"""Handles packets in the LOGIN state."""
if packet_id == 0x00: # Login Start
# Client sent username
self.username = await read_string(packet_data_reader)
logging.info(f"Login request from username: {self.username}")
# For a very basic server, we'll just allow login without authentication
# Response: Login Success (Packet ID 0x02)
# Format: String UUID, String Username
# You'd generate a real UUID here
uuid_str = "00000000-0000-0000-0000-000000000000" # Placeholder UUID
login_success_data = write_string(uuid_str) + write_string(self.username)
await self._send_packet(0x02, login_success_data)
self.state = "PLAY"
logging.info(f"Client {self.username} logged in. Entering PLAY state.")
# In a real server, you'd now send Join Game, Player Position And Look, etc.
# Example: Send a simple chat message (Play state packet 0x0F, Serverbound is 0x03)
# For a server-to-client chat message (clientbound), the ID is 0x0F (pre-1.19)
# This is simplified and might not match exact protocol for all versions.
# Refer to wiki.vg for 'Clientbound Chat Message'
chat_json = f'{{"text":"Welcome to the Python server, {self.username}!"}}'
# Packet ID 0x0F (Clientbound Chat Message)
# Field: VarInt chat mode, String sender UUID, String message JSON, Optional String sender name
# For 1.16.5 (protocol 754), chat is 0x0F: String (JSON), Byte (Position), UUID (Sender)
chat_data = write_string(chat_json) + struct.pack('>B', 0) # Position 0 (chat message)
# Need to include sender UUID for newer versions. Skipping for this basic example.
# This packet format is version dependent.
# await self._send_packet(0x0F, chat_data) # This would typically be sent in PLAY state
else:
logging.warning(f"Unhandled packet ID {hex(packet_id)} in LOGIN state.")
async def handle_client(self):
"""Main loop for handling a single client's packets."""
try:
while True:
# Read packet length
packet_length = await read_varint(self.reader)
logging.debug(f"Received packet with length: {packet_length}")
# Read packet data (ID + Payload)
packet_data = await self.reader.readexactly(packet_length)
packet_data_reader = asyncio.StreamReader()
packet_data_reader.feed_data(packet_data)
# Read packet ID
packet_id = await read_varint(packet_data_reader)
logging.debug(f"Received packet ID: {hex(packet_id)} in {self.state} state.")
# Dispatch based on current state
if self.state == "HANDSHAKING":
await self._handle_handshaking(packet_id, packet_data_reader)
elif self.state == "STATUS":
await self._handle_status(packet_id, packet_data_reader)
elif self.state == "LOGIN":
await self._handle_login(packet_id, packet_data_reader)
elif self.state == "PLAY":
# This is where the bulk of game logic would go
logging.info(f"Received Play state packet ID {hex(packet_id)}. Not implemented.")
pass # Implement Play state packets here (e.g., client movement, chat)
except asyncio.IncompleteReadError:
logging.info(f"Client {self.writer.get_extra_info('peername')} disconnected gracefully.")
except Exception as e:
logging.error(f"Error handling client {self.writer.get_extra_info('peername')}: {e}")
finally:
self.writer.close()
await self.writer.wait_closed()
logging.info(f"Connection to {self.writer.get_extra_info('peername')} closed.")
async def start_server(host, port):
server = await asyncio.start_server(
lambda r, w: MinecraftClient(r, w).handle_client(),
host, port
)
addrs = ', '.join(str(sock.getsockname()) for sock in server.sockets)
logging.info(f"Serving on {addrs}")
async with server:
await server.serve_forever()
if __name__ == "__main__":
SERVER_HOST = '0.0.0.0'
SERVER_PORT = 25565 # Standard Minecraft port
try:
asyncio.run(start_server(SERVER_HOST, SERVER_PORT))
except KeyboardInterrupt:
logging.info("Server stopped by user.")How to Test This Basic Server
• Save the code: Save the Python code as mcp_server.py.
• Run the server: python mcp_server.py
• Open Minecraft Client:
For Status: In Minecraft Java Edition, go to "Multiplayer" -> "Direct Connection" (or add a server) and enter localhost:25565. You should see the server's MOTD "A basic Python MCP server!" and player count.
For Login: Attempt to connect. The client will try to log in. The server should print "Client {username} logged in. Entering PLAY state." Since the Play state isn't implemented, the client will likely disconnect after a short time or timeout, but the login phase itself would have occurred.
Further Steps and Complexities
• Full Play State Implementation: This involves handling hundreds of different packets for player movement, block interactions, inventory, entities, chat, chunk data, etc. This is the most complex part.
• Compression and Encryption: Crucial for robust and secure communication in the Play state.
• Player World Data: Managing player inventories, positions, health, and saving/loading this data.
• Chunk Generation: Sending map data (chunks) to clients.
• Entity Management: Tracking and updating other players, NPCs, and mobs.
• Threading vs. Asyncio: For very high-performance needs, multi-process or heavily optimized C/Rust extensions might be considered, but asyncio is generally sufficient for many custom server needs in Python.
• Existing Libraries: For a higher-level abstraction, libraries like pyminecraft or python-mc (though potentially less maintained or feature-rich than mysql-connector-python for SQL) might exist, but this article focuses on building from the ground up for educational purposes.
Building an MCP server is a deep dive into network programming and protocol implementation. It's challenging but offers unparalleled insight into how Minecraft works and provides a powerful platform for custom game experiences.
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