feat: add MCP support (#20716)
Co-authored-by: QuantumGhost <obelisk.reg+git@gmail.com>
This commit is contained in:
Novice
397
api/core/mcp/session/base_session.py
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397
api/core/mcp/session/base_session.py
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@@ -0,0 +1,397 @@
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import logging
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import queue
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from collections.abc import Callable
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from concurrent.futures import ThreadPoolExecutor
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from contextlib import ExitStack
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from datetime import timedelta
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from types import TracebackType
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from typing import Any, Generic, Self, TypeVar
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from httpx import HTTPStatusError
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from pydantic import BaseModel
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from core.mcp.error import MCPAuthError, MCPConnectionError
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from core.mcp.types import (
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CancelledNotification,
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ClientNotification,
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ClientRequest,
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ClientResult,
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ErrorData,
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JSONRPCError,
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JSONRPCMessage,
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JSONRPCNotification,
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JSONRPCRequest,
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JSONRPCResponse,
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MessageMetadata,
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RequestId,
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RequestParams,
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ServerMessageMetadata,
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ServerNotification,
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ServerRequest,
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ServerResult,
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SessionMessage,
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)
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SendRequestT = TypeVar("SendRequestT", ClientRequest, ServerRequest)
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SendResultT = TypeVar("SendResultT", ClientResult, ServerResult)
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SendNotificationT = TypeVar("SendNotificationT", ClientNotification, ServerNotification)
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ReceiveRequestT = TypeVar("ReceiveRequestT", ClientRequest, ServerRequest)
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ReceiveResultT = TypeVar("ReceiveResultT", bound=BaseModel)
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ReceiveNotificationT = TypeVar("ReceiveNotificationT", ClientNotification, ServerNotification)
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DEFAULT_RESPONSE_READ_TIMEOUT = 1.0
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class RequestResponder(Generic[ReceiveRequestT, SendResultT]):
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"""Handles responding to MCP requests and manages request lifecycle.
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This class MUST be used as a context manager to ensure proper cleanup and
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cancellation handling:
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Example:
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with request_responder as resp:
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resp.respond(result)
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The context manager ensures:
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1. Proper cancellation scope setup and cleanup
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2. Request completion tracking
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3. Cleanup of in-flight requests
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"""
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request: ReceiveRequestT
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_session: Any
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_on_complete: Callable[["RequestResponder[ReceiveRequestT, SendResultT]"], Any]
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def __init__(
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self,
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request_id: RequestId,
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request_meta: RequestParams.Meta | None,
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request: ReceiveRequestT,
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session: """BaseSession[
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SendRequestT,
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SendNotificationT,
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SendResultT,
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ReceiveRequestT,
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ReceiveNotificationT
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]""",
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on_complete: Callable[["RequestResponder[ReceiveRequestT, SendResultT]"], Any],
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) -> None:
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self.request_id = request_id
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self.request_meta = request_meta
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self.request = request
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self._session = session
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self._completed = False
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self._on_complete = on_complete
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self._entered = False # Track if we're in a context manager
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def __enter__(self) -> "RequestResponder[ReceiveRequestT, SendResultT]":
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"""Enter the context manager, enabling request cancellation tracking."""
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self._entered = True
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return self
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def __exit__(
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self,
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exc_type: type[BaseException] | None,
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exc_val: BaseException | None,
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exc_tb: TracebackType | None,
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) -> None:
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"""Exit the context manager, performing cleanup and notifying completion."""
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try:
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if self._completed:
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self._on_complete(self)
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finally:
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self._entered = False
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def respond(self, response: SendResultT | ErrorData) -> None:
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"""Send a response for this request.
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Must be called within a context manager block.
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Raises:
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RuntimeError: If not used within a context manager
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AssertionError: If request was already responded to
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"""
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if not self._entered:
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raise RuntimeError("RequestResponder must be used as a context manager")
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assert not self._completed, "Request already responded to"
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self._completed = True
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self._session._send_response(request_id=self.request_id, response=response)
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def cancel(self) -> None:
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"""Cancel this request and mark it as completed."""
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if not self._entered:
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raise RuntimeError("RequestResponder must be used as a context manager")
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self._completed = True # Mark as completed so it's removed from in_flight
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# Send an error response to indicate cancellation
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self._session._send_response(
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request_id=self.request_id,
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response=ErrorData(code=0, message="Request cancelled", data=None),
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)
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class BaseSession(
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Generic[
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SendRequestT,
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SendNotificationT,
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SendResultT,
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ReceiveRequestT,
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ReceiveNotificationT,
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],
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):
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"""
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Implements an MCP "session" on top of read/write streams, including features
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like request/response linking, notifications, and progress.
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This class is a context manager that automatically starts processing
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messages when entered.
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"""
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_response_streams: dict[RequestId, queue.Queue[JSONRPCResponse | JSONRPCError]]
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_request_id: int
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_in_flight: dict[RequestId, RequestResponder[ReceiveRequestT, SendResultT]]
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_receive_request_type: type[ReceiveRequestT]
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_receive_notification_type: type[ReceiveNotificationT]
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def __init__(
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self,
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read_stream: queue.Queue,
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write_stream: queue.Queue,
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receive_request_type: type[ReceiveRequestT],
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receive_notification_type: type[ReceiveNotificationT],
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# If none, reading will never time out
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read_timeout_seconds: timedelta | None = None,
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) -> None:
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self._read_stream = read_stream
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self._write_stream = write_stream
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self._response_streams = {}
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self._request_id = 0
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self._receive_request_type = receive_request_type
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self._receive_notification_type = receive_notification_type
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self._session_read_timeout_seconds = read_timeout_seconds
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self._in_flight = {}
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self._exit_stack = ExitStack()
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def __enter__(self) -> Self:
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self._executor = ThreadPoolExecutor()
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self._receiver_future = self._executor.submit(self._receive_loop)
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return self
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def check_receiver_status(self) -> None:
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if self._receiver_future.done():
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self._receiver_future.result()
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def __exit__(
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self, exc_type: type[BaseException] | None, exc_val: BaseException | None, exc_tb: TracebackType | None
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) -> None:
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self._exit_stack.close()
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self._read_stream.put(None)
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self._write_stream.put(None)
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def send_request(
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self,
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request: SendRequestT,
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result_type: type[ReceiveResultT],
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request_read_timeout_seconds: timedelta | None = None,
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metadata: MessageMetadata = None,
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) -> ReceiveResultT:
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"""
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Sends a request and wait for a response. Raises an McpError if the
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response contains an error. If a request read timeout is provided, it
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will take precedence over the session read timeout.
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Do not use this method to emit notifications! Use send_notification()
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instead.
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"""
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self.check_receiver_status()
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request_id = self._request_id
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self._request_id = request_id + 1
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response_queue: queue.Queue[JSONRPCResponse | JSONRPCError] = queue.Queue()
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self._response_streams[request_id] = response_queue
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try:
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jsonrpc_request = JSONRPCRequest(
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jsonrpc="2.0",
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id=request_id,
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**request.model_dump(by_alias=True, mode="json", exclude_none=True),
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)
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self._write_stream.put(SessionMessage(message=JSONRPCMessage(jsonrpc_request), metadata=metadata))
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timeout = DEFAULT_RESPONSE_READ_TIMEOUT
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if request_read_timeout_seconds is not None:
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timeout = float(request_read_timeout_seconds.total_seconds())
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elif self._session_read_timeout_seconds is not None:
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timeout = float(self._session_read_timeout_seconds.total_seconds())
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while True:
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try:
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response_or_error = response_queue.get(timeout=timeout)
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break
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except queue.Empty:
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self.check_receiver_status()
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continue
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if response_or_error is None:
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raise MCPConnectionError(
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ErrorData(
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code=500,
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message="No response received",
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)
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)
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elif isinstance(response_or_error, JSONRPCError):
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if response_or_error.error.code == 401:
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raise MCPAuthError(
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ErrorData(code=response_or_error.error.code, message=response_or_error.error.message)
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)
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else:
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raise MCPConnectionError(
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ErrorData(code=response_or_error.error.code, message=response_or_error.error.message)
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)
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else:
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return result_type.model_validate(response_or_error.result)
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finally:
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self._response_streams.pop(request_id, None)
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def send_notification(
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self,
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notification: SendNotificationT,
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related_request_id: RequestId | None = None,
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) -> None:
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"""
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Emits a notification, which is a one-way message that does not expect
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a response.
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"""
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self.check_receiver_status()
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# Some transport implementations may need to set the related_request_id
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# to attribute to the notifications to the request that triggered them.
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jsonrpc_notification = JSONRPCNotification(
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jsonrpc="2.0",
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**notification.model_dump(by_alias=True, mode="json", exclude_none=True),
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)
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session_message = SessionMessage(
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message=JSONRPCMessage(jsonrpc_notification),
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metadata=ServerMessageMetadata(related_request_id=related_request_id) if related_request_id else None,
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)
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self._write_stream.put(session_message)
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def _send_response(self, request_id: RequestId, response: SendResultT | ErrorData) -> None:
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if isinstance(response, ErrorData):
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jsonrpc_error = JSONRPCError(jsonrpc="2.0", id=request_id, error=response)
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session_message = SessionMessage(message=JSONRPCMessage(jsonrpc_error))
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self._write_stream.put(session_message)
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else:
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jsonrpc_response = JSONRPCResponse(
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jsonrpc="2.0",
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id=request_id,
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result=response.model_dump(by_alias=True, mode="json", exclude_none=True),
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)
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session_message = SessionMessage(message=JSONRPCMessage(jsonrpc_response))
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self._write_stream.put(session_message)
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def _receive_loop(self) -> None:
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"""
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Main message processing loop.
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In a real synchronous implementation, this would likely run in a separate thread.
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"""
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while True:
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try:
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# Attempt to receive a message (this would be blocking in a synchronous context)
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message = self._read_stream.get(timeout=DEFAULT_RESPONSE_READ_TIMEOUT)
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if message is None:
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break
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if isinstance(message, HTTPStatusError):
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response_queue = self._response_streams.get(self._request_id - 1)
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if response_queue is not None:
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response_queue.put(
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JSONRPCError(
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jsonrpc="2.0",
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id=self._request_id - 1,
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error=ErrorData(code=message.response.status_code, message=message.args[0]),
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)
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)
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else:
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self._handle_incoming(RuntimeError(f"Received response with an unknown request ID: {message}"))
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elif isinstance(message, Exception):
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self._handle_incoming(message)
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elif isinstance(message.message.root, JSONRPCRequest):
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validated_request = self._receive_request_type.model_validate(
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message.message.root.model_dump(by_alias=True, mode="json", exclude_none=True)
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)
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responder = RequestResponder(
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request_id=message.message.root.id,
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request_meta=validated_request.root.params.meta if validated_request.root.params else None,
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request=validated_request,
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session=self,
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on_complete=lambda r: self._in_flight.pop(r.request_id, None),
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)
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self._in_flight[responder.request_id] = responder
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self._received_request(responder)
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if not responder._completed:
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self._handle_incoming(responder)
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elif isinstance(message.message.root, JSONRPCNotification):
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try:
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notification = self._receive_notification_type.model_validate(
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message.message.root.model_dump(by_alias=True, mode="json", exclude_none=True)
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)
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# Handle cancellation notifications
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if isinstance(notification.root, CancelledNotification):
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cancelled_id = notification.root.params.requestId
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if cancelled_id in self._in_flight:
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self._in_flight[cancelled_id].cancel()
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else:
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self._received_notification(notification)
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self._handle_incoming(notification)
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except Exception as e:
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# For other validation errors, log and continue
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logging.warning(f"Failed to validate notification: {e}. Message was: {message.message.root}")
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else: # Response or error
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response_queue = self._response_streams.get(message.message.root.id)
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if response_queue is not None:
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response_queue.put(message.message.root)
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else:
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self._handle_incoming(RuntimeError(f"Server Error: {message}"))
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except queue.Empty:
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continue
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except Exception as e:
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logging.exception("Error in message processing loop")
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raise
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def _received_request(self, responder: RequestResponder[ReceiveRequestT, SendResultT]) -> None:
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"""
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Can be overridden by subclasses to handle a request without needing to
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listen on the message stream.
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If the request is responded to within this method, it will not be
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forwarded on to the message stream.
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"""
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pass
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def _received_notification(self, notification: ReceiveNotificationT) -> None:
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"""
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Can be overridden by subclasses to handle a notification without needing
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to listen on the message stream.
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"""
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pass
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def send_progress_notification(
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self, progress_token: str | int, progress: float, total: float | None = None
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) -> None:
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"""
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Sends a progress notification for a request that is currently being
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processed.
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"""
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pass
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def _handle_incoming(
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self,
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req: RequestResponder[ReceiveRequestT, SendResultT] | ReceiveNotificationT | Exception,
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) -> None:
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"""A generic handler for incoming messages. Overwritten by subclasses."""
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pass
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