test nested servers

pyproject.toml

@@ -83,7 +83,7 @@ asyncio_mode = "auto"
 asyncio_default_fixture_loop_scope = "session"
 asyncio_default_test_loop_scope = "session"
 filterwarnings = []
-timeout = 5
+timeout = 3
 
 [tool.pyright]
 include = ["src", "tests"]

src/fastmcp/server/http.py

@@ -110,7 +110,7 @@ def setup_auth_middleware_and_routes(
 def create_base_app(
     routes: list[Route | Mount],
     middleware: list[Middleware],
-    debug: bool,
+    debug: bool = False,
     lifespan: Callable | None = None,
 ) -> Starlette:
     """Create a base Starlette app with common middleware and routes.
@@ -127,17 +127,12 @@ def create_base_app(
     # Always add RequestContextMiddleware as the outermost middleware
     middleware.append(Middleware(RequestContextMiddleware))
 
-    # Create the app
-    app_kwargs = {
-        "debug": debug,
-        "routes": routes,
-        "middleware": middleware,
-    }
-
-    if lifespan:
-        app_kwargs["lifespan"] = lifespan
-
-    return Starlette(**app_kwargs)
+    return Starlette(
+        routes=routes,
+        middleware=middleware,
+        debug=debug,
+        lifespan=lifespan,
+    )
 
 
 def create_sse_app(
@@ -224,7 +219,11 @@ def create_sse_app(
         routes.extend(cast(list[Route | Mount], additional_routes))
 
     # Create and return the app
-    return create_base_app(routes, middleware, debug)
+    return create_base_app(
+        routes=routes,
+        middleware=middleware,
+        debug=debug,
+    )
 
 
 def create_streamable_http_app(
@@ -305,4 +304,9 @@ def create_streamable_http_app(
             yield
 
     # Create and return the app with lifespan
-    return create_base_app(routes, middleware, debug, lifespan)
+    return create_base_app(
+        routes=routes,
+        middleware=middleware,
+        debug=debug,
+        lifespan=lifespan,
+    )

tests/client/test_streamable_http.py

@@ -5,6 +5,8 @@ from collections.abc import Generator
 import pytest
 import uvicorn
 from mcp.types import TextResourceContents
+from starlette.applications import Starlette
+from starlette.routing import Mount
 
 from fastmcp.client import Client
 from fastmcp.client.transports import StreamableHttpTransport
@@ -100,3 +102,40 @@ async def test_http_headers(streamable_http_server: str):
         json_result = json.loads(raw_result[0].text)
         assert "x-demo-header" in json_result
         assert json_result["x-demo-header"] == "ABC"
+
+
+def run_nested_server(host: str, port: int) -> None:
+    try:
+        mcp_app = fastmcp_server().streamable_http_app()
+
+        mount = Starlette(routes=[Mount("/nest-inner", app=mcp_app)])
+        mount2 = Starlette(
+            routes=[Mount("/nest-outer", app=mount)],
+            lifespan=mcp_app.router.lifespan_context,
+        )
+        server = uvicorn.Server(
+            config=uvicorn.Config(
+                app=mount2,
+                host=host,
+                port=port,
+                log_level="error",
+                lifespan="on",
+            )
+        )
+        server.run()
+    except Exception as e:
+        print(f"Server error: {e}")
+        sys.exit(1)
+    sys.exit(0)
+
+
+async def test_nested_streamable_http_server_resolves_correctly():
+    # tests patch for
+    # https://github.com/modelcontextprotocol/python-sdk/pull/659
+
+    with run_server_in_process(run_nested_server) as url:
+        async with Client(
+            transport=StreamableHttpTransport(f"{url}/nest-outer/nest-inner/mcp")
+        ) as client:
+            result = await client.ping()
+            assert result is True