Allow customization of the Starlette app (middleware, routes, etc)

[mconflitti-pbc]

Is your feature request related to a problem? Please describe.
Found that it has been useful in my fork of this repo to split out the creation of the starlette app into its own function so I can create it and customize it in my code before running it.

Describe the solution you'd like

    async def _create_sse_app(self):
        """Run the server using SSE transport."""
        from starlette.applications import Starlette
        from starlette.routing import Mount, Route

        sse = SseServerTransport("/messages/")

        async def handle_sse(request):
            async with sse.connect_sse(
                request.scope, request.receive, request._send
            ) as streams:
                await self._mcp_server.run(
                    streams[0],
                    streams[1],
                    self._mcp_server.create_initialization_options(),
                )

        starlette_app = Starlette(
            debug=self.settings.debug,
            routes=[
                Route("/sse", endpoint=handle_sse),
                Mount("/messages/", app=sse.handle_post_message),
            ],
        )
        
        return starlette_app

    async def run_sse_async(self) -> None:
        """Run the server using SSE transport."""
        starlette_app = self._create_sse_app()
        # ... rest is same

and then use this like:

mcp_server = FastMCP("example", transport="sse")

#...server set up

app = mcp_server._create_sse_app()
app.add_route(...)
app.add_middleware(...)

# run with this or the uvicorn cli
if __name__ == "__main__":
    uvicorn.run(app, host="0.0.0.0", port=8000)

Describe alternatives you've considered
none since it is currently contained in the run_sse_async function

[mconflitti-pbc]

This should also address a bug related to urllib url joining that truncates server urls paths when combininb /messages/ set in the transport object.

sse = SseServerTransport("/messages/")

For example, if joining http://localhost:8000/some/path/to/sse with /messages/, it will output: http://localhost:8000/messages

Removing the leading slash fixes this.

[panz2018]

I have developed web servers that integrate MCP SSE functionality:

• Using FastAPI: fastapi_mcp_sse
• Using Starlette: starlette_mcp_sse

These servers can be extended with custom routes while retaining full MCP SSE capabilities. Thus, it is possible to add any customization (middleware, routes, etc) in the fully developed FastAPI or Starlette servers.

[andrewburtnett]

I would also like the ability to add middleware and routes. We have specific requirements for healthchecks and request headers that would need to be handled by the MCP Server.

[epinault]

@panz2018 do you know if it is possible to extend the timeout for a request? I am getting timeout on slower request and I am unable to figure out an doc in starlette or uvicorn to extend it

[panz2018]

@panz2018 do you know if it is possible to extend the timeout for a request? I am getting timeout on slower request and I am unable to figure out an doc in starlette or uvicorn to extend it

Sorry, I have never faced this issue before.

[mconflitti-pbc]

@epinault check out the parameters for the sse_client transport here: https://github.com/modelcontextprotocol/python-sdk/blob/main/src/mcp/client/sse.py#L25

The default timeout is set to 5, but can be changed by passing in what you need.

[SinOverCos]

Is there a recommended solution for a health check endpoint that works today?

[felipeavilis]

Is there a recommended solution for a health check endpoint that works today?

The @panz2018 solution worked for my project.

• Unicorn for multithread;
• FastAPI for HTTP Requets (health check, etc) ;
• FastMCP for SSE and MPC requets;

#194 (comment)