116 lines
4.4 KiB
Python
116 lines
4.4 KiB
Python
"""
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Copyright 2024-2026 ReplyPier
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Licensed under the Apache License, Version 2.0 (the "License");
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you may not use this file except in compliance with the License.
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You may obtain a copy of the License at
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http://www.apache.org/licenses/LICENSE-2.0
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Unless required by applicable law or agreed to in writing, software
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distributed under the License is distributed on an "AS IS" BASIS,
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WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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See the License for the specific language governing permissions and
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limitations under the License.
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"""
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# An MCP tool's session, opened, held and closed by one task of its own.
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#
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# The MCP transports run inside anyio cancel scopes that belong to the task that
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# enters them. Entered from the request's own task, a refused streamable-HTTP
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# connect surfaced as a CancelledError instead of the error, and the leaked
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# scope cancelled the next connector in the same request too; closing from
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# another task failed with "exit cancel scope in a different task". The owner
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# task here enters and exits the tool's context itself, so a failure stays in it.
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import asyncio
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from typing import Optional
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from app.core.logger import get_logger
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logger = get_logger(__name__)
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CONNECTION_FAILED = "Could not connect to the server (refused, unreachable or not an MCP endpoint)"
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# Strong references to owner tasks being torn down; without them the loop can
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# garbage collect a task mid-flight.
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_closing: set = set()
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def _forget_outcome(task: asyncio.Task) -> None:
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"""Read a finished owner task's exception so asyncio doesn't log it as never
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retrieved; whoever cared has already reported it."""
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if not task.cancelled():
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task.exception()
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class HeldConnection:
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def __init__(self, tool):
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self.tool = tool
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self._opened = asyncio.Event()
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self._release = asyncio.Event()
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self._task: Optional[asyncio.Task] = None
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async def open(self, timeout: float) -> None:
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"""Connect within ``timeout`` seconds. Raises TimeoutError, or what the
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connect raised (ConnectionError when the transport only cancelled)."""
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self._task = asyncio.create_task(self._hold())
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self._task.add_done_callback(_forget_outcome)
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opened = asyncio.create_task(self._opened.wait())
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try:
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await asyncio.wait({opened, self._task}, timeout=timeout,
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return_when=asyncio.FIRST_COMPLETED)
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except asyncio.CancelledError:
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self._abandon() # the request itself was cancelled
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raise
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finally:
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opened.cancel()
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if self._opened.is_set():
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return
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if not self._task.done():
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self._abandon()
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raise asyncio.TimeoutError()
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if self._task.cancelled():
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raise ConnectionError(CONNECTION_FAILED)
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raise self._task.exception()
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async def _hold(self) -> None:
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await self.tool.__aenter__()
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try:
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self._opened.set()
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await self._release.wait()
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finally:
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await self.tool.__aexit__(None, None, None)
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def _abandon(self) -> None:
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"""Stop the owner without waiting: a STDIO server that never answered
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can leave its unwind blocked until the child process exits."""
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if self._task is not None and not self._task.done():
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self._task.cancel()
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_closing.add(self._task)
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self._task.add_done_callback(_closing.discard)
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async def close(self, timeout: float) -> None:
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"""Ask the owner task to exit the tool's context, waiting up to
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``timeout`` seconds before abandoning it. Never raises."""
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if self._task is None or self._task.done():
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return
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self._release.set()
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try:
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await asyncio.wait_for(asyncio.shield(self._task), timeout=timeout)
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except asyncio.TimeoutError:
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logger.debug("MCP tool did not close in time; abandoning it")
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self._abandon()
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except asyncio.CancelledError:
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current = asyncio.current_task()
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if current is not None and current.cancelling():
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self._abandon() # the caller itself is being cancelled
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raise
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# Otherwise the owner ended cancelled by its transport: it is closed.
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except Exception as e:
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logger.debug(f"MCP tool close raised (non-critical): {e}")
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def release(self) -> None:
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"""Close without waiting."""
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self._release.set()
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