mcpc 0.2.4

MCP Callback Protocol extension for enabling asynchronous tool callbacks and streaming updates from MCP clients

MCPC - Model Context Protocol Callback

MCPC is an extension to MCP (Model-Context-Protocol) that solves a critical limitation in LLM tool interactions: enabling continued conversations while running tools background tasks. It facilitates asynchronous two-way communication between LLMs and tools through the already existing MCP transport - no additional transport layer needed, while maintaining full backward compatibility.

What is MCPC?

MCPC is an extension to the MCP protocol, not a replacement. It builds upon the existing MCP infrastructure to add real-time two-way communication capabilities while maintaining full compatibility with standard MCP implementations.

MCPC solves a critical limitation in LLM tool interactions: enabling continuous two-way communication while running background tasks:

• Bidirectional communication between LLMs and tools using the same MCP transport
• Continuous conversation with LLMs during tool execution
• Real-time updates from background processes
• Asynchronous notifications when operations complete
• Support for indefinitely running tasks with streaming updates

Compatibility Matrix

Feature	Status	Notes
STDIO Transport	✅ Implemented	Full support for standard input/output transport
SSE Transport	⚠️ Limited Support	Standard MCP operations only, MCPC features pending
MCPC Client → Standard MCP Server	✅ Implemented	Full backward compatibility
Standard MCP Client → MCPC Server	✅ Implemented	Automatic fallback to synchronous results

Quick Installation

# With UV (recommended)
uv add mcpc

# With pip
pip install mcpc

Basic Client Usage

# Initialize the MCPC handler
mcpc_handler = MCPCHandler("my-provider")

# Define your event listener function
async def my_mcpc_listener(mcpc_message: MCPCMessage) -> None:
    print(f"Received MCPC message: {mcpc_message}")
    # Handle the message based on status
    if mcpc_message.type == "task" and mcpc_message.event == "complete":
        print(f"Task {mcpc_message.task_id} completed with result: {mcpc_message.result}")

# Add your event listener for MCPC Message
mcpc_handler.add_event_listener(my_mcpc_listener)

# Wrap the transport with MCPC event listeners
wrapped_transport = await mcpc_handler.wrap_streams(*transport)

# Create a ClientSession with the wrapped transport
session = await ClientSession(*wrapped_transport)

# Initialize MCPC features by checking for MCPC support
mcpc_supported = await mcpc_handler.init_mcpc(session)
if mcpc_supported:
    print(f"MCPC protocol v{mcpc_handler.protocol_version} supported")

Basic Server Usage

# Initialize MCPC helper
server = Server("my-provider")
mcpc = MCPCHelper("my-provider", transport_type="stdio")

@server.call_tool()
async def call_tool(name: str, arguments: Dict[str, Any]) -> List[TextContent]:
    metadata = arguments.pop("_metadata", {})
    session_id = metadata.get("mcpc_session_id", "default")
    task_id = metadata.get("mcpc_task_id", str(uuid.uuid4()))

    # Handle protocol information request
    if name == "_is_mcpc_enabled":
        client_info = arguments.get("mcpc_info")
        return mcpc.handle_protocol_info_request(client_info)

    if name == "process_data":
        async def process_data_task():
            await mcpc.send(mcpc.create_task_event(
                event="update",
                tool_name="process_data",
                session_id=session_id,
                task_id=task_id,
                result="Processing data..."
            ))
            await asyncio.sleep(3) # Simulate processing time
            await mcpc.send(mcpc.create_task_event(
                event="complete",
                tool_name="process_data",
                session_id=session_id,
                task_id=task_id,
                result={
                    YOUR_DATA_OBJECT
                }
            ))
        # Start a background task
        collected_messages = mcpc.start_task(task_id, process_data_task)

    # For standard MCP clients, return collected complete/failed messages
    if collected_messages:
        return mcpc.messages_to_text_content(collected_messages)

    # For MCPC clients, return immediate acknowledgment
    response = mcpc.create_task_event(
        event="created",
        tool_name="process_data",
        session_id=session_id,
        task_id=task_id,
        result=f"Started processing data_id={data_id}. Updates will stream in real-time."
    )
    return mcpc.messages_to_text_content([response])

Documentation

For detailed documentation, please see:

• Getting Started Guide - Installation and basic usage
• Server Implementation - How to implement MCPC in your server
• API Reference - Detailed API documentation
• Protocol Details - Message structure and protocol information
• Use Cases - Example scenarios and use cases

License

MIT