fix: Handle SSE Disconnects Properly When use starlette middleware

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

@@ -89,9 +89,9 @@ async def get_prompt(
         )
 
     if transport == "sse":
+        from mcp.server.fastmcp.server import SilentResponse
         from mcp.server.sse import SseServerTransport
         from starlette.applications import Starlette
-        from starlette.responses import Response
         from starlette.routing import Mount, Route
 
         sse = SseServerTransport("/messages/")
@@ -103,7 +103,7 @@ async def handle_sse(request):
                 await app.run(
                     streams[0], streams[1], app.create_initialization_options()
                 )
-            return Response()
+            return SilentResponse()
 
         starlette_app = Starlette(
             debug=True,

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

@@ -56,9 +56,9 @@ async def read_resource(uri: AnyUrl) -> str | bytes:
         return SAMPLE_RESOURCES[name]["content"]
 
     if transport == "sse":
+        from mcp.server.fastmcp.server import SilentResponse
         from mcp.server.sse import SseServerTransport
         from starlette.applications import Starlette
-        from starlette.responses import Response
         from starlette.routing import Mount, Route
 
         sse = SseServerTransport("/messages/")
@@ -70,7 +70,7 @@ async def handle_sse(request):
                 await app.run(
                     streams[0], streams[1], app.create_initialization_options()
                 )
-            return Response()
+            return SilentResponse()
 
         starlette_app = Starlette(
             debug=True,

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

@@ -57,9 +57,9 @@ async def list_tools() -> list[types.Tool]:
         ]
 
     if transport == "sse":
+        from mcp.server.fastmcp.server import SilentResponse
         from mcp.server.sse import SseServerTransport
         from starlette.applications import Starlette
-        from starlette.responses import Response
         from starlette.routing import Mount, Route
 
         sse = SseServerTransport("/messages/")
@@ -71,7 +71,7 @@ async def handle_sse(request):
                 await app.run(
                     streams[0], streams[1], app.create_initialization_options()
                 )
-            return Response()
+            return SilentResponse()
 
         starlette_app = Starlette(
             debug=True,

src/mcp/server/fastmcp/server.py

@@ -52,6 +52,16 @@
 logger = get_logger(__name__)
 
 
+class SilentResponse(Response):
+    """A response that does not send any HTTP response back to the client."""
+
+    def __init__(self) -> None:
+        super().__init__()
+
+    async def __call__(self, scope: Scope, receive: Receive, send: Send) -> None:
+        return
+
+
 class Settings(BaseSettings, Generic[LifespanResultT]):
     """FastMCP server settings.
 
@@ -748,7 +758,7 @@ async def handle_sse(scope: Scope, receive: Receive, send: Send):
                     streams[1],
                     self._mcp_server.create_initialization_options(),
                 )
-            return Response()
+            return SilentResponse()
 
         # Create routes
         routes: list[Route | Mount] = []

src/mcp/server/sse.py

@@ -23,7 +23,7 @@ async def handle_sse(request):
                 streams[0], streams[1], app.create_initialization_options()
             )
         # Return empty response to avoid NoneType error
-        return Response()
+        return SilentResponse()
 
     # Create and run Starlette app
     starlette_app = Starlette(routes=routes)

tests/server/test_sse_security.py

@@ -10,10 +10,10 @@
 import uvicorn
 from starlette.applications import Starlette
 from starlette.requests import Request
-from starlette.responses import Response
 from starlette.routing import Mount, Route
 
 from mcp.server import Server
+from mcp.server.fastmcp.server import SilentResponse
 from mcp.server.sse import SseServerTransport
 from mcp.server.transport_security import TransportSecuritySettings
 from mcp.types import Tool
@@ -55,7 +55,7 @@ async def handle_sse(request: Request):
         except ValueError as e:
             # Validation error was already handled inside connect_sse
             logger.debug(f"SSE connection failed validation: {e}")
-        return Response()
+        return SilentResponse()
 
     routes = [
         Route("/sse", endpoint=handle_sse),

tests/shared/test_sse.py

@@ -19,6 +19,7 @@
 from mcp.client.session import ClientSession
 from mcp.client.sse import sse_client
 from mcp.server import Server
+from mcp.server.fastmcp.server import SilentResponse
 from mcp.server.sse import SseServerTransport
 from mcp.server.transport_security import TransportSecuritySettings
 from mcp.shared.exceptions import McpError
@@ -91,7 +92,7 @@ def make_server_app() -> Starlette:
     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()
+        return SilentResponse()
 
     app = Starlette(
         routes=[
@@ -354,7 +355,7 @@ def run_context_server(server_port: int) -> None:
     async def handle_sse(request: Request) -> Response:
         async with sse.connect_sse(request.scope, request.receive, request._send) as streams:
             await context_server.run(streams[0], streams[1], context_server.create_initialization_options())
-        return Response()
+        return SilentResponse()
 
     app = Starlette(
         routes=[