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Server-side 2026-07-28 stateless support: classifier, driver split, server/discover (#2928)

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Max 2026-06-21 19:34:17 +01:00 • committed by GitHub
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45
src/mcp/shared/jsonrpc_dispatcher.py
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@ -49,7 +49,7 @@ from mcp.types import (
RequestId,
)
__all__ = ["JSONRPCDispatcher"]
__all__ = ["JSONRPCDispatcher", "handler_exception_to_error_data"]
logger = logging.getLogger(__name__)
@ -67,6 +67,23 @@ PeerCancelMode = Literal["interrupt", "signal"]
the handler's scope; `"signal"` only sets `ctx.cancel_requested`."""
def handler_exception_to_error_data(exc: BaseException) -> ErrorData | None:
"""Map a handler-raised exception to its wire `ErrorData`.
The two rungs every dispatcher shares: an `MCPError` carries its own
`ErrorData`; a pydantic `ValidationError` is the spec's INVALID_PARAMS
with empty ``data`` (no pydantic text on the wire). Returns ``None`` for
any other exception so each caller applies its own catch-all -
`JSONRPCDispatcher` currently pins ``code=0`` for v1 compat,
`to_jsonrpc_response` uses `INTERNAL_ERROR`.
"""
if isinstance(exc, MCPError):
return exc.error
if isinstance(exc, ValidationError):
return ErrorData(code=INVALID_PARAMS, message="Invalid request parameters", data="")
return None
def _coerce_id(request_id: RequestId) -> RequestId:
"""Coerce a stringified int request ID back to int so a peer-echoed ID still correlates (matches the TS SDK)."""
if isinstance(request_id, str):
@ -667,7 +684,7 @@ class JSONRPCDispatcher(Dispatcher[TransportT]):
# anyio absorbs the scope's own cancel at __exit__, and
# `cancelled_caught` (unlike `cancel_called`) guarantees the
# result write above did not happen - no double response.
# TODO(maxisbey): spec says SHOULD NOT respond after cancel;
# TODO(L38): spec says SHOULD NOT respond after cancel;
# the existing server always has, so match that for now.
answer_write_started = True
await self._write_error(req.id, ErrorData(code=0, message="Request cancelled"))
@ -684,21 +701,17 @@ class JSONRPCDispatcher(Dispatcher[TransportT]):
describe=f"shutdown error response for request {req.id!r}",
)
raise
except MCPError as e:
await self._write_error(req.id, e.error)
except ValidationError:
# TODO(maxisbey): data="" pins existing-server compat (no pydantic
# text on the wire); revisit per the suite's divergence entry.
await self._write_error(
req.id, ErrorData(code=INVALID_PARAMS, message="Invalid request parameters", data="")
)
except Exception as e:
logger.exception("handler for %r raised", req.method)
# TODO(maxisbey): code=0 pins existing-server compat; JSON-RPC says
# INTERNAL_ERROR. Revisit per the suite's divergence entry.
await self._write_error(req.id, ErrorData(code=0, message=str(e)))
if self._raise_handler_exceptions:
raise
error = handler_exception_to_error_data(e)
if error is not None:
await self._write_error(req.id, error)
else:
logger.exception("handler for %r raised", req.method)
# TODO(L58): code=0 pins existing-server compat; JSON-RPC says
# INTERNAL_ERROR. Revisit per the suite's divergence entry.
await self._write_error(req.id, ErrorData(code=0, message=str(e)))
if self._raise_handler_exceptions:
raise
# No `_in_flight` pop here: the inner finally covers every path, and a late pop could evict a reused id.
def _allocate_id(self) -> int: