Max
269 lines
13 KiB
Python
269 lines
13 KiB
Python
"""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 httpx2
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import mcp_types as types
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import pytest
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from mcp_types import RootsListChangedNotification
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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, MCPError
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from mcp.client import IncomingMessage
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from mcp.client.streamable_http import streamable_http_client
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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 _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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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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# 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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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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return Starlette(debug=True, routes=[Route("/mcp", handle_mcp_request, methods=["POST"])])
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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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async def test_non_compliant_notification_response() -> None:
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"""Verify the client ignores unexpected responses to notifications.
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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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returned_exception = None
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async def message_handler(message: IncomingMessage) -> None: # pragma: no cover
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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 httpx2.AsyncClient(transport=httpx2.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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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 httpx2.AsyncClient(transport=httpx2.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_http_error_app(error_status: int, *, error_on_notifications: bool = False) -> Starlette:
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"""Create a server that returns an HTTP error for non-init 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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if error_on_notifications:
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return Response(status_code=error_status)
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return Response(status_code=202)
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return Response(status_code=error_status)
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return Starlette(debug=True, routes=[Route("/mcp", handle_mcp_request, methods=["POST"])])
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async def test_http_error_status_sends_jsonrpc_error() -> None:
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"""Verify HTTP 5xx errors unblock the pending request with an MCPError.
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When a server returns a non-2xx status code (e.g. 500), the client should
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send a JSONRPCError so the pending request resolves immediately instead of
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raising an unhandled httpx2.HTTPStatusError that causes the caller to hang.
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"""
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async with httpx2.AsyncClient(transport=httpx2.ASGITransport(app=_create_http_error_app(500))) 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="Server returned an error response"): # pragma: no branch
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await session.list_tools()
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async def test_http_error_on_notification_does_not_hang() -> None:
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"""Verify HTTP errors on notifications are silently ignored.
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When a notification gets an HTTP error, there is no pending request to
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unblock, so the client should just return without sending a JSONRPCError.
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"""
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app = _create_http_error_app(500, error_on_notifications=True)
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async with httpx2.AsyncClient(transport=httpx2.ASGITransport(app=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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# Should not raise or hang — the error is silently ignored for notifications
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await session.send_notification(RootsListChangedNotification(method="notifications/roots/list_changed"))
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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 httpx2.AsyncClient(transport=httpx2.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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def _create_non_2xx_json_body_app(status: int, body: bytes) -> Starlette:
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"""Server that returns a fixed non-2xx status + ``application/json`` body for non-init requests.
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The initialize response carries an ``mcp-session-id`` so the client treats subsequent
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requests as part of an established session (needed for the 404 → session-terminated mapping).
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"""
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async def handle_mcp_request(request: Request) -> Response:
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data = json.loads(await request.body())
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if data.get("method") == "initialize":
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return JSONResponse(
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{"jsonrpc": "2.0", "id": data["id"], "result": INIT_RESPONSE},
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headers={"mcp-session-id": "test-session"},
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)
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if "id" not in data:
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return Response(status_code=202)
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return Response(content=body, status_code=status, 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_client_surfaces_jsonrpc_error_from_non_2xx_body_with_correlated_id() -> None:
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"""SDK-defined: a JSON-RPC error in a non-2xx body is surfaced verbatim even when the
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server set ``id: null`` — the client rewraps it under the pending request's id, so
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the awaiting call resolves with the server's error code instead of the generic fallback."""
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body = json.dumps(
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{"jsonrpc": "2.0", "id": None, "error": {"code": types.METHOD_NOT_FOUND, "message": "nope"}}
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).encode()
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app = _create_non_2xx_json_body_app(400, body)
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async with httpx2.AsyncClient(transport=httpx2.ASGITransport(app=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) as exc:
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await session.list_tools()
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assert exc.value.error.code == types.METHOD_NOT_FOUND
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async def test_client_falls_back_to_generic_error_when_non_2xx_body_is_a_jsonrpc_result() -> None:
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"""SDK-defined: a non-2xx response whose JSON body parses as a JSON-RPC *result* (not an
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error) falls through to the generic ``INTERNAL_ERROR`` fallback rather than being
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treated as the request's reply."""
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app = _create_non_2xx_json_body_app(400, b'{"jsonrpc":"2.0","id":1,"result":{}}')
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async with httpx2.AsyncClient(transport=httpx2.ASGITransport(app=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) as exc:
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await session.list_tools()
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assert exc.value.error.code == types.INTERNAL_ERROR
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async def test_client_falls_back_to_session_terminated_when_404_body_is_malformed_json() -> None:
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"""SDK-defined: an unparseable ``application/json`` body on a 404 response is swallowed
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and the status-derived ``INVALID_REQUEST`` (session-terminated) fallback resolves the
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pending request — the parse failure never propagates."""
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app = _create_non_2xx_json_body_app(404, b"not valid json{{{")
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async with httpx2.AsyncClient(transport=httpx2.ASGITransport(app=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) as exc:
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await session.list_tools()
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assert exc.value.error.code == types.INVALID_REQUEST
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