fix: send JSONRPCError instead of bare exceptions in streamable HTTP client (#2005)
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Marcelo Trylesinski
GitHub
parent
dda845aa12
commit
7c7c13b648
1 changed files with 148 additions and 130 deletions
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@ -5,133 +5,147 @@ 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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from collections.abc import Generator
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import httpx
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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 import ClientSession, MCPError, types
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from mcp.client.streamable_http import streamable_http_client
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from mcp.shared.session import RequestResponder
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from mcp.types import RootsListChangedNotification
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from tests.test_helpers import wait_for_server
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pytestmark = pytest.mark.anyio
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INIT_RESPONSE = {
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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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def create_non_sdk_server_app() -> Starlette: # pragma: no cover
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def _init_json_response(data: dict[str, object]) -> JSONResponse:
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return JSONResponse({"jsonrpc": "2.0", "id": data["id"], "result": INIT_RESPONSE})
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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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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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if data.get("method") == "initialize":
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return _init_json_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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# 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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return JSONResponse( # pragma: no cover
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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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return Starlette(debug=True, routes=[Route("/mcp", handle_mcp_request, methods=["POST"])])
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def run_non_sdk_server(port: int) -> None: # pragma: no cover
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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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def _create_unexpected_content_type_app() -> Starlette:
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"""Create a server that returns an unexpected content type for requests."""
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async def handle_mcp_request(request: Request) -> Response:
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body = await request.body()
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data = json.loads(body)
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if data.get("method") == "initialize":
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return _init_json_response(data)
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if "id" not in data:
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return Response(status_code=202)
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# Return text/plain for all other requests — an unexpected content type.
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return Response(content="this is plain text, not json or sse", status_code=200, media_type="text/plain")
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return Starlette(debug=True, routes=[Route("/mcp", handle_mcp_request, methods=["POST"])])
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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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async def test_non_compliant_notification_response() -> None:
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"""Verify the client ignores unexpected responses to notifications.
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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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try:
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wait_for_server(non_sdk_server_port, timeout=10.0)
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except TimeoutError: # pragma: no cover
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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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"""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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The spec states notifications should get either 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( # pragma: no cover
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message: RequestResponder[types.ServerRequest, types.ClientResult] | types.ServerNotification | Exception,
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):
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) -> None:
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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 streamable_http_client(server_url) as (read_stream, write_stream):
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async with ClientSession(read_stream, write_stream, message_handler=message_handler) as session:
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# Initialize should work normally
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await session.initialize()
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async with httpx.AsyncClient(transport=httpx.ASGITransport(app=_create_non_sdk_server_app())) as client:
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async with streamable_http_client("http://localhost/mcp", http_client=client) as (read_stream, write_stream):
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async with ClientSession(read_stream, write_stream, message_handler=message_handler) as session:
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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(RootsListChangedNotification(method="notifications/roots/list_changed"))
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# The test server returns a 204 instead of the expected 202
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await session.send_notification(RootsListChangedNotification(method="notifications/roots/list_changed"))
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if returned_exception: # pragma: no cover
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pytest.fail(f"Server encountered an exception: {returned_exception}")
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async def test_unexpected_content_type_sends_jsonrpc_error() -> None:
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"""Verify unexpected content types unblock the pending request with an MCPError.
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When a server returns a content type that is neither application/json nor text/event-stream,
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the client should send a JSONRPCError so the pending request resolves immediately
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instead of hanging until timeout.
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"""
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async with httpx.AsyncClient(transport=httpx.ASGITransport(app=_create_unexpected_content_type_app())) as client:
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async with streamable_http_client("http://localhost/mcp", http_client=client) as (read_stream, write_stream):
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async with ClientSession(read_stream, write_stream) as session: # pragma: no branch
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await session.initialize()
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with pytest.raises(MCPError, match="Unexpected content type: text/plain"): # pragma: no branch
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await session.list_tools()
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def _create_invalid_json_response_app() -> Starlette:
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"""Create a server that returns invalid JSON for requests."""
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async def handle_mcp_request(request: Request) -> Response:
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body = await request.body()
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data = json.loads(body)
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if data.get("method") == "initialize":
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return _init_json_response(data)
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if "id" not in data:
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return Response(status_code=202)
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# Return application/json content type but with invalid JSON body.
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return Response(content="not valid json{{{", status_code=200, media_type="application/json")
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return Starlette(debug=True, routes=[Route("/mcp", handle_mcp_request, methods=["POST"])])
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async def test_invalid_json_response_sends_jsonrpc_error() -> None:
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"""Verify invalid JSON responses unblock the pending request with an MCPError.
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When a server returns application/json with an unparseable body, the client
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should send a JSONRPCError so the pending request resolves immediately
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instead of hanging until timeout.
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"""
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async with httpx.AsyncClient(transport=httpx.ASGITransport(app=_create_invalid_json_response_app())) as client:
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async with streamable_http_client("http://localhost/mcp", http_client=client) as (read_stream, write_stream):
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async with ClientSession(read_stream, write_stream) as session: # pragma: no branch
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await session.initialize()
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with pytest.raises(MCPError, match="Failed to parse JSON response"): # pragma: no branch
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await session.list_tools()
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