Fix: Enhance ASGI Compliance and Robustness in router.py SSE Handling (#164)

* Fix: Ensure ASGI compliance in transport.py for POST message handling

- Modified mcpm.router.transport.py:

  - Refactored handle_post_message to correctly send a 202 Accepted response as a raw ASGI application before proceeding with internal message forwarding. It now implicitly returns None as expected.

(Note: Complementary ASGI fixes for mcpm.router.router.py's handle_sse were already present in the base branch 076a6bf)

* Fix: Enhance ASGI compliance in router.py SSE handling

---------

Co-authored-by: Jonathan Wang <[email protected]>

Author: iSevenDays

src/mcpm/router/router.py

@@ -7,6 +7,7 @@
 from collections import defaultdict
 from contextlib import asynccontextmanager
 from typing import Literal, Optional, Sequence, TextIO
+import asyncio
 
 import uvicorn
 from deprecated import deprecated
@@ -46,6 +47,21 @@
 logger = logging.getLogger(__name__)
 
 
+class NoOpsResponse(Response):
+    def __init__(self):
+        super().__init__(content=b"", status_code=204)
+
+    async def __call__(self, scope, receive, send):
+        await send(
+            {
+                "type": "http.response.start",
+                "status": self.status_code,
+                "headers": self.render_headers(),
+            }
+        )
+        await send({"type": "http.response.body", "body": b"", "more_body": False})
+
+
 class MCPRouter:
     """
     A router that aggregates multiple MCP servers (SSE/STDIO) and
@@ -615,17 +631,29 @@ async def get_sse_server_app(
         sse = RouterSseTransport("/messages/", api_key=api_key)
 
         async def handle_sse(request: Request) -> Response:
-            async with sse.connect_sse(
-                request.scope,
-                request.receive,
-                request._send,  # noqa: SLF001
-            ) as (read_stream, write_stream):
-                await self.aggregated_server.run(
-                    read_stream,
-                    write_stream,
-                    self.aggregated_server.initialization_options,
-                )
-            return Response()
+            try:
+                async with sse.connect_sse(
+                    request.scope,
+                    request.receive,
+                    request._send,  # noqa: SLF001
+                ) as (read_stream, write_stream):
+                    await self.aggregated_server.run(
+                        read_stream,
+                        write_stream,
+                        self.aggregated_server.initialization_options,
+                    )
+                    # Keep alive while client connected.
+                    # EventSourceResponse (inside connect_sse) manages the stream,
+                    # but this loop ensures this handler itself stays alive until disconnect.
+                    while not await request.is_disconnected():
+                        await asyncio.sleep(0.1)
+
+            except asyncio.CancelledError:
+                raise
+            except Exception as e:
+                logger.error(f"Unexpected error in handle_sse (router.py): {e}", exc_info=True)
+            finally:
+                return NoOpsResponse()
 
         lifespan_handler: t.Optional[Lifespan[Starlette]] = None
         if include_lifespan: