server/sse: return response in handle_post_message

examples/servers/simple-prompt/mcp_simple_prompt/server.py

@@ -107,7 +107,7 @@ async def handle_sse(request):
                 )
 
         async def handle_messages(request):
-            await sse.handle_post_message(request.scope, request.receive, request._send)
+            return await sse.handle_post_message(request.scope, request.receive)
 
         starlette_app = Starlette(
             debug=True,

examples/servers/simple-resource/mcp_simple_resource/server.py

@@ -64,7 +64,7 @@ async def handle_sse(request):
                 )
 
         async def handle_messages(request):
-            await sse.handle_post_message(request.scope, request.receive, request._send)
+            return await sse.handle_post_message(request.scope, request.receive)
 
         starlette_app = Starlette(
             debug=True,

examples/servers/simple-tool/mcp_simple_tool/server.py

@@ -78,7 +78,7 @@ async def handle_sse(request):
                 )
 
         async def handle_messages(request):
-            await sse.handle_post_message(request.scope, request.receive, request._send)
+            return await sse.handle_post_message(request.scope, request.receive)
 
         starlette_app = Starlette(
             debug=True,

src/mcp/server/sse.py

@@ -24,7 +24,7 @@ async def handle_sse(request):
             )
 
     async def handle_messages(request):
-        await sse.handle_post_message(request.scope, request.receive, request._send)
+        return await sse.handle_post_message(request.scope, request.receive)
 
     # Create and run Starlette app
     starlette_app = Starlette(routes=routes)
@@ -133,31 +133,26 @@ async def sse_writer():
             logger.debug("Yielding read and write streams")
             yield (read_stream, write_stream)
 
-    async def handle_post_message(
-        self, scope: Scope, receive: Receive, send: Send
-    ) -> None:
+    async def handle_post_message(self, scope: Scope, receive: Receive) -> Response:
         logger.debug("Handling POST message")
         request = Request(scope, receive)
 
         session_id_param = request.query_params.get("session_id")
         if session_id_param is None:
             logger.warning("Received request without session_id")
-            response = Response("session_id is required", status_code=400)
-            return await response(scope, receive, send)
+            return Response("session_id is required", status_code=400)
 
         try:
             session_id = UUID(hex=session_id_param)
             logger.debug(f"Parsed session ID: {session_id}")
         except ValueError:
             logger.warning(f"Received invalid session ID: {session_id_param}")
-            response = Response("Invalid session ID", status_code=400)
-            return await response(scope, receive, send)
+            return Response("Invalid session ID", status_code=400)
 
         writer = self._read_stream_writers.get(session_id)
         if not writer:
             logger.warning(f"Could not find session for ID: {session_id}")
-            response = Response("Could not find session", status_code=404)
-            return await response(scope, receive, send)
+            return Response("Could not find session", status_code=404)
 
         json = await request.json()
         logger.debug(f"Received JSON: {json}")
@@ -167,12 +162,9 @@ async def handle_post_message(
             logger.debug(f"Validated client message: {message}")
         except ValidationError as err:
             logger.error(f"Failed to parse message: {err}")
-            response = Response("Could not parse message", status_code=400)
-            await response(scope, receive, send)
             await writer.send(err)
-            return
+            return Response("Could not parse message", status_code=400)
 
         logger.debug(f"Sending message to writer: {message}")
-        response = Response("Accepted", status_code=202)
-        await response(scope, receive, send)
         await writer.send(message)
+        return Response("Accepted", status_code=202)