fix: align /mcp streamable HTTP handling with python-sdk (#119)

- mirror the python-sdk fix so `/mcp` requests are scope-normalised to
`/mcp/` before hitting the StreamableHTTP session manager, eliminating
the 307 redirect/404 regression introduced in #89
- extend the HTTP transport test to cover both `/mcp/` and `/mcp`,
ensuring the proxy works with SDK clients out of the box

Co-authored-by: Zhengfeng <gaozhengfeng.2020@bytedance.com>

src/mcp_proxy/mcp_server.py

@@ -2,7 +2,7 @@
 
 import contextlib
 import logging
-from collections.abc import AsyncIterator
+from collections.abc import AsyncIterator, Awaitable, Callable
 from dataclasses import dataclass
 from datetime import datetime, timezone
 from typing import Any, Literal
@@ -48,6 +48,19 @@ def _update_global_activity() -> None:
     _global_status["api_last_activity"] = datetime.now(timezone.utc).isoformat()
 
 
+class _ASGIEndpointAdapter:
+    """Wrap a coroutine function into an ASGI application."""
+
+    def __init__(self, endpoint: Callable[[Scope, Receive, Send], Awaitable[None]]) -> None:
+        self._endpoint = endpoint
+
+    async def __call__(self, scope: Scope, receive: Receive, send: Send) -> None:
+        await self._endpoint(scope, receive, send)
+
+
+HTTP_METHODS = ["DELETE", "GET", "HEAD", "OPTIONS", "PATCH", "POST", "PUT", "TRACE"]
+
+
 async def _handle_status(_: Request) -> Response:
     """Global health check and service usage monitoring endpoint."""
     return JSONResponse(_global_status)
@@ -88,9 +101,36 @@ def create_single_instance_routes(
 
     async def handle_streamable_http_instance(scope: Scope, receive: Receive, send: Send) -> None:
         _update_global_activity()
-        await http_session_manager.handle_request(scope, receive, send)
+        updated_scope = scope
+        if scope.get("type") == "http":
+            path = scope.get("path", "")
+            if path and path.rstrip("/") == "/mcp" and not path.endswith("/"):
+                updated_scope = dict(scope)
+                normalized_path = path + "/"
+                logger.debug(
+                    "Normalized request path from '%s' to '%s' without redirect",
+                    path,
+                    normalized_path,
+                )
+                updated_scope["path"] = normalized_path
+
+                raw_path = scope.get("raw_path")
+                if raw_path:
+                    if b"?" in raw_path:
+                        path_part, query_part = raw_path.split(b"?", 1)
+                        updated_scope["raw_path"] = path_part.rstrip(b"/") + b"/?" + query_part
+                    else:
+                        updated_scope["raw_path"] = raw_path.rstrip(b"/") + b"/"
+
+        await http_session_manager.handle_request(updated_scope, receive, send)
 
     routes = [
+        Route(
+            "/mcp",
+            endpoint=_ASGIEndpointAdapter(handle_streamable_http_instance),
+            methods=HTTP_METHODS,
+            include_in_schema=False,
+        ),
         Mount("/mcp", app=handle_streamable_http_instance),
         Route("/sse", endpoint=handle_sse_instance),
         Mount("/messages/", app=sse_transport.handle_post_message),

tests/test_mcp_server.py

@@ -58,12 +58,14 @@ def create_starlette_app(
         async with http_manager.run():
             yield
 
-    return Starlette(
+    app = Starlette(
         debug=debug,
         routes=routes,
         middleware=middleware,
         lifespan=lifespan,
     )
+    app.router.redirect_slashes = False
+    return app
 
 
 class BackgroundServer(uvicorn.Server):
@@ -149,11 +151,12 @@ async def test_sse_transport() -> None:
             assert response.prompts[0].name == "prompt1"
 
 
-async def test_http_transport() -> None:
+@pytest.mark.parametrize("path_suffix", ["/mcp/", "/mcp"])
+async def test_http_transport(path_suffix: str) -> None:
     """Test HTTP transport layer functionality."""
     server = make_background_server(debug=True)
     async with server.run_in_background():
-        http_url = f"{server.url}/mcp/"
+        http_url = f"{server.url}{path_suffix}"
         async with (
             streamablehttp_client(url=http_url) as (read, write, _),
             ClientSession(read, write) as session,