Added cancelled handler. Fixes #88

src/mcp/server/__init__.py

@@ -68,7 +68,7 @@ async def main():
 import logging
 import warnings
 from collections.abc import Awaitable, Callable
-from typing import Any, Sequence
+from typing import Any, Optional, Sequence
 
 from anyio.streams.memory import MemoryObjectReceiveStream, MemoryObjectSendStream
 from pydantic import AnyUrl
@@ -379,6 +379,20 @@ async def handler(req: types.ProgressNotification):
 
         return decorator
 
+    def cancellation_notification(self):
+        def decorator(
+            func: Callable[[Optional[int], Optional[str]], Awaitable[None]],
+        ):
+            logger.debug("Registering handler for ProgressNotification")
+
+            async def handler(req: types.CancellationNotification):
+                await func(req.params.requestId, req.params.reason)
+
+            self.notification_handlers[types.CancellationNotification] = handler
+            return func
+
+        return decorator
+
     def completion(self):
         """Provides completions for prompts and resource templates"""
 

src/mcp/types.py

@@ -1,4 +1,4 @@
-from typing import Any, Generic, Literal, TypeVar
+from typing import Any, Generic, Literal, Optional, TypeVar
 
 from pydantic import BaseModel, ConfigDict, FileUrl, RootModel
 from pydantic.networks import AnyUrl
@@ -325,6 +325,21 @@ class ProgressNotificationParams(NotificationParams):
     model_config = ConfigDict(extra="allow")
 
 
+class CancelledParams(BaseModel):
+    requestId: Optional[int] = None
+    reason: Optional[str] = ""
+
+
+class CancellationNotification(Notification):
+    """
+    An out-of-band notification used to inform the receiver of a progress update for a
+    long-running request.
+    """
+
+    method: Literal["cancelled"]
+    params: CancelledParams
+
+
 class ProgressNotification(Notification):
     """
     An out-of-band notification used to inform the receiver of a progress update for a
@@ -997,7 +1012,10 @@ class ClientRequest(
 
 class ClientNotification(
     RootModel[
-        ProgressNotification | InitializedNotification | RootsListChangedNotification
+        ProgressNotification
+        | InitializedNotification
+        | RootsListChangedNotification
+        | CancellationNotification
     ]
 ):
     pass
@@ -1019,6 +1037,7 @@ class ServerNotification(
         | ResourceListChangedNotification
         | ToolListChangedNotification
         | PromptListChangedNotification
+        | CancellationNotification
     ]
 ):
     pass