Fix NoneType return starlette/routing.py line 74,

Author: Hoa Lam

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

@@ -91,6 +91,7 @@ async def get_prompt(
         from mcp.server.sse import SseServerTransport
         from starlette.applications import Starlette
         from starlette.routing import Mount, Route
+        from starlette.responses import Response
 
         sse = SseServerTransport("/messages/")
 
@@ -101,6 +102,7 @@ async def handle_sse(request):
                 await app.run(
                     streams[0], streams[1], app.create_initialization_options()
                 )
+            return Response("MCP SSE")
 
         starlette_app = Starlette(
             debug=True,

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

@@ -47,6 +47,7 @@ async def read_resource(uri: FileUrl) -> str | bytes:
         from mcp.server.sse import SseServerTransport
         from starlette.applications import Starlette
         from starlette.routing import Mount, Route
+        from starlette.responses import Response
 
         sse = SseServerTransport("/messages/")
 
@@ -57,6 +58,7 @@ async def handle_sse(request):
                 await app.run(
                     streams[0], streams[1], app.create_initialization_options()
                 )
+            return Response("MCP SSE")
 
         starlette_app = Starlette(
             debug=True,

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

@@ -61,16 +61,17 @@ async def list_tools() -> list[types.Tool]:
         from mcp.server.sse import SseServerTransport
         from starlette.applications import Starlette
         from starlette.routing import Mount, Route
+        from starlette.responses import Response
 
         sse = SseServerTransport("/messages/")
-
         async def handle_sse(request):
             async with sse.connect_sse(
                 request.scope, request.receive, request._send
             ) as streams:
                 await app.run(
                     streams[0], streams[1], app.create_initialization_options()
                 )
+            return Response("MCP SSE")
 
         starlette_app = Starlette(
             debug=True,

src/mcp/server/fastmcp/server.py

@@ -13,6 +13,8 @@
 
 import anyio
 import pydantic_core
+import starlette
+import starlette.responses
 import uvicorn
 from pydantic import BaseModel, Field
 from pydantic.networks import AnyUrl
@@ -475,6 +477,7 @@ async def run_stdio_async(self) -> None:
 
     async def run_sse_async(self) -> None:
         """Run the server using SSE transport."""
+        from starlette.responses import Response
         from starlette.applications import Starlette
         from starlette.routing import Mount, Route
 
@@ -489,6 +492,7 @@ async def handle_sse(request):
                     streams[1],
                     self._mcp_server.create_initialization_options(),
                 )
+            return Response("OK")
 
         starlette_app = Starlette(
             debug=self.settings.debug,

src/mcp/server/sse.py

@@ -6,6 +6,8 @@
 Example usage:
 ```
     # Create an SSE transport at an endpoint
+    from starlette.responses import Response
+
     sse = SseServerTransport("/messages/")
 
     # Create Starlette routes for SSE and message handling
@@ -22,6 +24,7 @@ async def handle_sse(request):
             await app.run(
                 streams[0], streams[1], app.create_initialization_options()
             )
+        return Response("MCP SSE")
 
     # Create and run Starlette app
     starlette_app = Starlette(routes=routes)

tests/shared/test_sse.py

@@ -80,16 +80,19 @@ async def handle_call_tool(name: str, args: dict) -> list[TextContent]:
 # Test fixtures
 def make_server_app() -> Starlette:
     """Create test Starlette app with SSE transport"""
+    from starlette.responses import Response
+
     sse = SseServerTransport("/messages/")
     server = ServerTest()
 
-    async def handle_sse(request: Request) -> None:
+    async def handle_sse(request: Request) -> Response:
         async with sse.connect_sse(
             request.scope, request.receive, request._send
         ) as streams:
             await server.run(
                 streams[0], streams[1], server.create_initialization_options()
             )
+        return Response("MCP SSE")
 
     app = Starlette(
         routes=[