SDK Parity: Avoid Parsing Server Response for non-JsonRPCMessage Requests (#1290)
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Justin Wang
GitHub
parent
eaf7cf41d5
commit
9c6fd15a88
2 changed files with 163 additions and 11 deletions
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@ -279,17 +279,19 @@ class StreamableHTTPTransport:
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if is_initialization:
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self._maybe_extract_session_id_from_response(response)
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content_type = response.headers.get(CONTENT_TYPE, "").lower()
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if content_type.startswith(JSON):
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await self._handle_json_response(response, ctx.read_stream_writer, is_initialization)
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elif content_type.startswith(SSE):
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await self._handle_sse_response(response, ctx, is_initialization)
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else:
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await self._handle_unexpected_content_type(
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content_type,
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ctx.read_stream_writer,
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)
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# Per https://modelcontextprotocol.io/specification/2025-06-18/basic#notifications:
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# The server MUST NOT send a response to notifications.
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if isinstance(message.root, JSONRPCRequest):
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content_type = response.headers.get(CONTENT_TYPE, "").lower()
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if content_type.startswith(JSON):
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await self._handle_json_response(response, ctx.read_stream_writer, is_initialization)
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elif content_type.startswith(SSE):
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await self._handle_sse_response(response, ctx, is_initialization)
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else:
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await self._handle_unexpected_content_type(
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content_type,
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ctx.read_stream_writer,
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)
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async def _handle_json_response(
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self,
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150
tests/client/test_notification_response.py
Normal file
150
tests/client/test_notification_response.py
Normal file
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@ -0,0 +1,150 @@
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"""
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Tests for StreamableHTTP client transport with non-SDK servers.
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These tests verify client behavior when interacting with servers
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that don't follow SDK conventions.
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"""
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import json
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import multiprocessing
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import socket
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import time
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from collections.abc import Generator
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import pytest
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import uvicorn
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from starlette.applications import Starlette
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from starlette.requests import Request
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from starlette.responses import JSONResponse, Response
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from starlette.routing import Route
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from mcp import ClientSession, types
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from mcp.client.streamable_http import streamablehttp_client
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from mcp.shared.session import RequestResponder
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from mcp.types import ClientNotification, RootsListChangedNotification
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def create_non_sdk_server_app() -> Starlette:
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"""Create a minimal server that doesn't follow SDK conventions."""
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async def handle_mcp_request(request: Request) -> Response:
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"""Handle MCP requests with non-standard responses."""
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try:
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body = await request.body()
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data = json.loads(body)
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# Handle initialize request normally
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if data.get("method") == "initialize":
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response_data = {
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"jsonrpc": "2.0",
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"id": data["id"],
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"result": {
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"serverInfo": {"name": "test-non-sdk-server", "version": "1.0.0"},
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"protocolVersion": "2024-11-05",
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"capabilities": {},
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},
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}
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return JSONResponse(response_data)
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# For notifications, return 204 No Content (non-SDK behavior)
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if "id" not in data:
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return Response(status_code=204, headers={"Content-Type": "application/json"})
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# Default response for other requests
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return JSONResponse(
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{"jsonrpc": "2.0", "id": data.get("id"), "error": {"code": -32601, "message": "Method not found"}}
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)
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except Exception as e:
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return JSONResponse({"error": f"Server error: {str(e)}"}, status_code=500)
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app = Starlette(
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debug=True,
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routes=[
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Route("/mcp", handle_mcp_request, methods=["POST"]),
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],
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)
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return app
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def run_non_sdk_server(port: int) -> None:
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"""Run the non-SDK server in a separate process."""
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app = create_non_sdk_server_app()
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config = uvicorn.Config(
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app=app,
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host="127.0.0.1",
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port=port,
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log_level="error", # Reduce noise in tests
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)
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server = uvicorn.Server(config=config)
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server.run()
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@pytest.fixture
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def non_sdk_server_port() -> int:
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"""Get an available port for the test server."""
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with socket.socket() as s:
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s.bind(("127.0.0.1", 0))
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return s.getsockname()[1]
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@pytest.fixture
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def non_sdk_server(non_sdk_server_port: int) -> Generator[None, None, None]:
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"""Start a non-SDK server for testing."""
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proc = multiprocessing.Process(target=run_non_sdk_server, kwargs={"port": non_sdk_server_port}, daemon=True)
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proc.start()
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# Wait for server to be ready
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start_time = time.time()
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while time.time() - start_time < 10:
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try:
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with socket.create_connection(("127.0.0.1", non_sdk_server_port), timeout=0.1):
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break
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except (TimeoutError, ConnectionRefusedError):
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time.sleep(0.1)
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else:
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proc.kill()
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proc.join(timeout=2)
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pytest.fail("Server failed to start within 10 seconds")
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yield
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proc.kill()
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proc.join(timeout=2)
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@pytest.mark.anyio
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async def test_non_compliant_notification_response(non_sdk_server: None, non_sdk_server_port: int) -> None:
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"""
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This test verifies that the client ignores unexpected responses to notifications: the spec states they should
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either be 202 + no response body, or 4xx + optional error body
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(https://modelcontextprotocol.io/specification/2025-06-18/basic/transports#sending-messages-to-the-server),
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but some servers wrongly return other 2xx codes (e.g. 204). For now we simply ignore unexpected responses
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(aligning behaviour w/ the TS SDK).
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"""
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server_url = f"http://127.0.0.1:{non_sdk_server_port}/mcp"
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returned_exception = None
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async def message_handler(
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message: RequestResponder[types.ServerRequest, types.ClientResult] | types.ServerNotification | Exception,
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):
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nonlocal returned_exception
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if isinstance(message, Exception):
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returned_exception = message
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async with streamablehttp_client(server_url) as (read_stream, write_stream, _):
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async with ClientSession(
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read_stream,
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write_stream,
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message_handler=message_handler,
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) as session:
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# Initialize should work normally
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await session.initialize()
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# The test server returns a 204 instead of the expected 202
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await session.send_notification(
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ClientNotification(RootsListChangedNotification(method="notifications/roots/list_changed"))
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)
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if returned_exception:
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pytest.fail(f"Server encountered an exception: {returned_exception}")
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