Fix: fastmcp exit stuck

Author: PWZER

src/mcp/server/fastmcp/server.py

@@ -20,6 +20,7 @@
 from pydantic_settings import BaseSettings, SettingsConfigDict
 from starlette.applications import Starlette
 from starlette.requests import Request
+from starlette.responses import Response
 from starlette.routing import Mount, Route
 
 from mcp.server.fastmcp.exceptions import ResourceError
@@ -482,17 +483,20 @@ def sse_app(self) -> Starlette:
         """Return an instance of the SSE server app."""
         sse = SseServerTransport(self.settings.message_path)
 
-        async def handle_sse(request: Request) -> None:
-            async with sse.connect_sse(
-                request.scope,
-                request.receive,
-                request._send,  # type: ignore[reportPrivateUsage]
-            ) as streams:
-                await self._mcp_server.run(
-                    streams[0],
-                    streams[1],
-                    self._mcp_server.create_initialization_options(),
-                )
+        async def handle_sse(request: Request) -> Response:
+            with anyio.CancelScope() as cancel_scope:
+                async with sse.connect_sse(
+                    request.scope,
+                    request.receive,
+                    request._send,  # type: ignore[reportPrivateUsage]
+                    callback=lambda: cancel_scope.cancel(),
+                ) as streams:
+                    await self._mcp_server.run(
+                        streams[0],
+                        streams[1],
+                        self._mcp_server.create_initialization_options(),
+                    )
+            return Response(status_code=200)
 
         return Starlette(
             debug=self.settings.debug,