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https://github.com/aljazceru/mcp-python-sdk.git
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Initial import
This commit is contained in:
David Soria Parra
244
mcp_python/shared/session.py
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244
mcp_python/shared/session.py
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from contextlib import AbstractAsyncContextManager
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from typing import Generic, TypeVar
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import anyio
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import anyio.lowlevel
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from anyio.streams.memory import MemoryObjectReceiveStream, MemoryObjectSendStream
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from pydantic import BaseModel
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from mcp_python.shared.exceptions import McpError
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from mcp_python.types import (
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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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RequestParams,
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ServerNotification,
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ServerRequest,
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ServerResult,
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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(
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"ReceiveNotificationT", ClientNotification, ServerNotification
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)
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RequestId = str | int
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class RequestResponder(Generic[ReceiveRequestT, SendResultT]):
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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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) -> 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._responded = False
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async def respond(self, response: SendResultT | ErrorData) -> None:
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assert not self._responded, "Request already responded to"
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self._responded = True
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await self._session._send_response(
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request_id=self.request_id, response=response
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)
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class BaseSession(
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AbstractAsyncContextManager,
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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 like request/response linking, notifications, and progress.
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This class is an async context manager that automatically starts processing messages when entered.
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"""
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_response_streams: dict[
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RequestId, MemoryObjectSendStream[JSONRPCResponse | JSONRPCError]
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]
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_request_id: int
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def __init__(
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self,
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read_stream: MemoryObjectReceiveStream[JSONRPCMessage | Exception],
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write_stream: MemoryObjectSendStream[JSONRPCMessage],
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receive_request_type: type[ReceiveRequestT],
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receive_notification_type: type[ReceiveNotificationT],
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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._incoming_message_stream_writer, self._incoming_message_stream_reader = (
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anyio.create_memory_object_stream[
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RequestResponder[ReceiveRequestT, SendResultT]
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| ReceiveNotificationT
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| Exception
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]()
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)
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async def __aenter__(self):
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self._task_group = anyio.create_task_group()
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await self._task_group.__aenter__()
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self._task_group.start_soon(self._receive_loop)
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return self
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async def __aexit__(self, exc_type, exc_val, exc_tb):
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# Using BaseSession as a context manager should not block on exit (this would be very surprising behavior), so make sure to cancel the tasks in the task group.
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self._task_group.cancel_scope.cancel()
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return await self._task_group.__aexit__(exc_type, exc_val, exc_tb)
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async 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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) -> ReceiveResultT:
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"""
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Sends a request and wait for a response. Raises an McpError if the response contains an error.
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Do not use this method to emit notifications! Use send_notification() instead.
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"""
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request_id = self._request_id
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self._request_id = request_id + 1
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response_stream, response_stream_reader = anyio.create_memory_object_stream[
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JSONRPCResponse | JSONRPCError
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](1)
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self._response_streams[request_id] = response_stream
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jsonrpc_request = JSONRPCRequest(
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jsonrpc="2.0", id=request_id, **request.model_dump(by_alias=True, mode="json")
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)
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# TODO: Support progress callbacks
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await self._write_stream.send(JSONRPCMessage(jsonrpc_request))
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response_or_error = await response_stream_reader.receive()
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if isinstance(response_or_error, JSONRPCError):
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raise McpError(response_or_error.error)
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else:
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return result_type.model_validate(response_or_error.result)
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async def send_notification(self, notification: SendNotificationT) -> None:
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"""
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Emits a notification, which is a one-way message that does not expect a response.
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"""
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jsonrpc_notification = JSONRPCNotification(
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jsonrpc="2.0", **notification.model_dump(by_alias=True, mode="json")
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)
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await self._write_stream.send(JSONRPCMessage(jsonrpc_notification))
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async def _send_response(
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self, request_id: RequestId, response: SendResultT | ErrorData
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) -> 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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await self._write_stream.send(JSONRPCMessage(jsonrpc_error))
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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"),
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)
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await self._write_stream.send(JSONRPCMessage(jsonrpc_response))
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async def _receive_loop(self) -> None:
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async with (
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self._read_stream,
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self._write_stream,
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self._incoming_message_stream_writer,
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):
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async for message in self._read_stream:
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if isinstance(message, Exception):
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await self._incoming_message_stream_writer.send(message)
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elif isinstance(message.root, JSONRPCRequest):
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validated_request = self._receive_request_type.model_validate(
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message.root.model_dump(by_alias=True, mode="json")
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)
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responder = RequestResponder(
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request_id=message.root.id,
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request_meta=validated_request.root.params._meta
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if validated_request.root.params
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else None,
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request=validated_request,
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session=self,
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)
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await self._received_request(responder)
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if not responder._responded:
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await self._incoming_message_stream_writer.send(responder)
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elif isinstance(message.root, JSONRPCNotification):
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notification = self._receive_notification_type.model_validate(
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message.root.model_dump(by_alias=True, mode="json")
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)
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await self._received_notification(notification)
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await self._incoming_message_stream_writer.send(notification)
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else: # Response or error
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stream = self._response_streams.pop(message.root.id, None)
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if stream:
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await stream.send(message.root)
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else:
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await self._incoming_message_stream_writer.send(
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RuntimeError(
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f"Received response with an unknown request ID: {message}"
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)
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)
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async def _received_request(
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self, responder: RequestResponder[ReceiveRequestT, SendResultT]
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) -> None:
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"""
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Can be overridden by subclasses to handle a request without needing to listen on the message stream.
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If the request is responded to within this method, it will not be forwarded on to the message stream.
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"""
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async 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 to listen on the message stream.
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"""
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async 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 processed.
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"""
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@property
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def incoming_messages(
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self,
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) -> MemoryObjectReceiveStream[
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RequestResponder[ReceiveRequestT, SendResultT]
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| ReceiveNotificationT
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| Exception
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]:
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return self._incoming_message_stream_reader
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