Class JSONRPCDispatcher

src/mcp/shared/jsonrpc_dispatcher.py:229–770

`Dispatcher` over the `SessionMessage` stream contract. Explicit Protocol base so pyright checks conformance at the class definition.

class JSONRPCDispatcher(Dispatcher[TransportT]):
    """`Dispatcher` over the `SessionMessage` stream contract.

    Explicit Protocol base so pyright checks conformance at the class definition.
    """

    def __init__(
        self,
        read_stream: ReadStream[SessionMessage | Exception],
        write_stream: WriteStream[SessionMessage],
        *,
        transport_builder: Callable[[MessageMetadata], TransportT] | None = None,
        peer_cancel_mode: PeerCancelMode = "interrupt",
        raise_handler_exceptions: bool = False,
        inline_methods: frozenset[str] = frozenset(),
        on_stream_exception: Callable[[Exception], Awaitable[None]] | None = None,
    ) -> None:
        """Wire a dispatcher over a transport's `SessionMessage` stream pair.

        Args:
            transport_builder: Builds each message's `TransportContext` from
                its `SessionMessage.metadata`.
            raise_handler_exceptions: Re-raise handler exceptions out of
                `run()` after the error response is written.
            inline_methods: Methods awaited in the read loop before the next
                message is dequeued (e.g. `initialize`); an inline handler
                that awaits the peer deadlocks the parked loop.
            on_stream_exception: Observer for `Exception` items on the read
                stream; without it they are debug-logged and dropped. Awaited
                inline in the read loop, so a slow observer stalls dispatch.
        """
        self._read_stream = read_stream
        self._write_stream = write_stream
        # With transport_builder omitted, TransportT defaults to
        # TransportContext; pyright can't connect the two, hence the cast.
        self._transport_builder = cast(
            "Callable[[MessageMetadata], TransportT]",
            transport_builder or _default_transport_builder,
        )
        self._peer_cancel_mode: PeerCancelMode = peer_cancel_mode
        self._raise_handler_exceptions = raise_handler_exceptions
        self._inline_methods = inline_methods
        self.on_stream_exception = on_stream_exception
        """Observer for ``Exception`` items on the read stream. Mutable so a session can
        bind it after the dispatcher is built (e.g. ``ClientSession`` routing into
        ``message_handler``); only consulted inside ``run()`` so pre-enter assignment is safe."""

        self._next_id = 0
        self._pending: dict[RequestId, _Pending] = {}
        self._in_flight: dict[RequestId, _InFlight[TransportT]] = {}
        self._tg: anyio.abc.TaskGroup | None = None
        self._running = False
        self._closed = False

    async def send_raw_request(
        self,
        method: str,
        params: Mapping[str, Any] | None,