fix: send params as empty object for list methods without cursor (#1453)
This commit is contained in:
Felix Weinberger
GitHub
parent
cd7253c593
commit
de89457683
1 changed files with 301 additions and 180 deletions
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@ -2,23 +2,22 @@ from collections.abc import Callable
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import pytest
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import mcp.types as types
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from mcp.server import Server
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from mcp.server.fastmcp import FastMCP
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from mcp.shared.memory import create_connected_server_and_client_session as create_session
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from mcp.types import ListToolsRequest, ListToolsResult
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from .conftest import StreamSpyCollection
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pytestmark = pytest.mark.anyio
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async def test_list_tools_cursor_parameter(stream_spy: Callable[[], StreamSpyCollection]):
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"""Test that the cursor parameter is accepted for list_tools
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and that it is correctly passed to the server.
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See: https://modelcontextprotocol.io/specification/2025-03-26/server/utilities/pagination#request-format
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"""
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@pytest.fixture
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async def full_featured_server():
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"""Create a server with tools, resources, prompts, and templates."""
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server = FastMCP("test")
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# Create a couple of test tools
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@server.tool(name="test_tool_1")
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async def test_tool_1() -> str:
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"""First test tool"""
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@ -29,186 +28,201 @@ async def test_list_tools_cursor_parameter(stream_spy: Callable[[], StreamSpyCol
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"""Second test tool"""
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return "Result 2"
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async with create_session(server._mcp_server) as client_session:
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spies = stream_spy()
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# Test without cursor parameter (omitted)
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_ = await client_session.list_tools()
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list_tools_requests = spies.get_client_requests(method="tools/list")
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assert len(list_tools_requests) == 1
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assert list_tools_requests[0].params is None
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spies.clear()
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# Test with cursor=None
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_ = await client_session.list_tools(cursor=None)
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list_tools_requests = spies.get_client_requests(method="tools/list")
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assert len(list_tools_requests) == 1
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assert list_tools_requests[0].params is None
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spies.clear()
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# Test with cursor as string
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_ = await client_session.list_tools(cursor="some_cursor_value")
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list_tools_requests = spies.get_client_requests(method="tools/list")
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assert len(list_tools_requests) == 1
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assert list_tools_requests[0].params is not None
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assert list_tools_requests[0].params["cursor"] == "some_cursor_value"
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spies.clear()
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# Test with empty string cursor
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_ = await client_session.list_tools(cursor="")
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list_tools_requests = spies.get_client_requests(method="tools/list")
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assert len(list_tools_requests) == 1
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assert list_tools_requests[0].params is not None
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assert list_tools_requests[0].params["cursor"] == ""
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async def test_list_resources_cursor_parameter(stream_spy: Callable[[], StreamSpyCollection]):
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"""Test that the cursor parameter is accepted for list_resources
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and that it is correctly passed to the server.
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See: https://modelcontextprotocol.io/specification/2025-03-26/server/utilities/pagination#request-format
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"""
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server = FastMCP("test")
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# Create a test resource
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@server.resource("resource://test/data")
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async def test_resource() -> str:
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"""Test resource"""
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return "Test data"
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async with create_session(server._mcp_server) as client_session:
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spies = stream_spy()
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# Test without cursor parameter (omitted)
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_ = await client_session.list_resources()
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list_resources_requests = spies.get_client_requests(method="resources/list")
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assert len(list_resources_requests) == 1
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assert list_resources_requests[0].params is None
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spies.clear()
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# Test with cursor=None
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_ = await client_session.list_resources(cursor=None)
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list_resources_requests = spies.get_client_requests(method="resources/list")
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assert len(list_resources_requests) == 1
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assert list_resources_requests[0].params is None
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spies.clear()
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# Test with cursor as string
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_ = await client_session.list_resources(cursor="some_cursor")
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list_resources_requests = spies.get_client_requests(method="resources/list")
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assert len(list_resources_requests) == 1
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assert list_resources_requests[0].params is not None
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assert list_resources_requests[0].params["cursor"] == "some_cursor"
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spies.clear()
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# Test with empty string cursor
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_ = await client_session.list_resources(cursor="")
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list_resources_requests = spies.get_client_requests(method="resources/list")
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assert len(list_resources_requests) == 1
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assert list_resources_requests[0].params is not None
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assert list_resources_requests[0].params["cursor"] == ""
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async def test_list_prompts_cursor_parameter(stream_spy: Callable[[], StreamSpyCollection]):
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"""Test that the cursor parameter is accepted for list_prompts
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and that it is correctly passed to the server.
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See: https://modelcontextprotocol.io/specification/2025-03-26/server/utilities/pagination#request-format
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"""
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server = FastMCP("test")
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# Create a test prompt
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@server.prompt()
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async def test_prompt(name: str) -> str:
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"""Test prompt"""
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return f"Hello, {name}!"
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async with create_session(server._mcp_server) as client_session:
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spies = stream_spy()
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# Test without cursor parameter (omitted)
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_ = await client_session.list_prompts()
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list_prompts_requests = spies.get_client_requests(method="prompts/list")
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assert len(list_prompts_requests) == 1
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assert list_prompts_requests[0].params is None
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spies.clear()
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# Test with cursor=None
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_ = await client_session.list_prompts(cursor=None)
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list_prompts_requests = spies.get_client_requests(method="prompts/list")
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assert len(list_prompts_requests) == 1
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assert list_prompts_requests[0].params is None
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spies.clear()
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# Test with cursor as string
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_ = await client_session.list_prompts(cursor="some_cursor")
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list_prompts_requests = spies.get_client_requests(method="prompts/list")
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assert len(list_prompts_requests) == 1
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assert list_prompts_requests[0].params is not None
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assert list_prompts_requests[0].params["cursor"] == "some_cursor"
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spies.clear()
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# Test with empty string cursor
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_ = await client_session.list_prompts(cursor="")
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list_prompts_requests = spies.get_client_requests(method="prompts/list")
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assert len(list_prompts_requests) == 1
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assert list_prompts_requests[0].params is not None
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assert list_prompts_requests[0].params["cursor"] == ""
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async def test_list_resource_templates_cursor_parameter(stream_spy: Callable[[], StreamSpyCollection]):
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"""Test that the cursor parameter is accepted for list_resource_templates
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and that it is correctly passed to the server.
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See: https://modelcontextprotocol.io/specification/2025-03-26/server/utilities/pagination#request-format
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"""
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server = FastMCP("test")
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# Create a test resource template
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@server.resource("resource://test/{name}")
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async def test_template(name: str) -> str:
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"""Test resource template"""
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return f"Data for {name}"
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async with create_session(server._mcp_server) as client_session:
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return server
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@pytest.mark.parametrize(
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"method_name,request_method",
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[
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("list_tools", "tools/list"),
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("list_resources", "resources/list"),
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("list_prompts", "prompts/list"),
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("list_resource_templates", "resources/templates/list"),
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],
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)
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@pytest.mark.filterwarnings("ignore::DeprecationWarning")
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async def test_list_methods_cursor_parameter(
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stream_spy: Callable[[], StreamSpyCollection],
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full_featured_server: FastMCP,
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method_name: str,
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request_method: str,
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):
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"""Test that the cursor parameter is accepted and correctly passed to the server.
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Covers: list_tools, list_resources, list_prompts, list_resource_templates
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See: https://modelcontextprotocol.io/specification/2025-03-26/server/utilities/pagination#request-format
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"""
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async with create_session(full_featured_server._mcp_server) as client_session:
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spies = stream_spy()
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# Test without cursor parameter (omitted)
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_ = await client_session.list_resource_templates()
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list_templates_requests = spies.get_client_requests(method="resources/templates/list")
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assert len(list_templates_requests) == 1
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assert list_templates_requests[0].params is None
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method = getattr(client_session, method_name)
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_ = await method()
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requests = spies.get_client_requests(method=request_method)
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assert len(requests) == 1
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assert requests[0].params is None
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spies.clear()
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# Test with cursor=None
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_ = await client_session.list_resource_templates(cursor=None)
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list_templates_requests = spies.get_client_requests(method="resources/templates/list")
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assert len(list_templates_requests) == 1
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assert list_templates_requests[0].params is None
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_ = await method(cursor=None)
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requests = spies.get_client_requests(method=request_method)
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assert len(requests) == 1
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assert requests[0].params is None
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spies.clear()
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# Test with cursor as string
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_ = await client_session.list_resource_templates(cursor="some_cursor")
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list_templates_requests = spies.get_client_requests(method="resources/templates/list")
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assert len(list_templates_requests) == 1
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assert list_templates_requests[0].params is not None
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assert list_templates_requests[0].params["cursor"] == "some_cursor"
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_ = await method(cursor="some_cursor_value")
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requests = spies.get_client_requests(method=request_method)
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assert len(requests) == 1
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assert requests[0].params is not None
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assert requests[0].params["cursor"] == "some_cursor_value"
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spies.clear()
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# Test with empty string cursor
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_ = await client_session.list_resource_templates(cursor="")
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list_templates_requests = spies.get_client_requests(method="resources/templates/list")
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assert len(list_templates_requests) == 1
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assert list_templates_requests[0].params is not None
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assert list_templates_requests[0].params["cursor"] == ""
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_ = await method(cursor="")
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requests = spies.get_client_requests(method=request_method)
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assert len(requests) == 1
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assert requests[0].params is not None
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assert requests[0].params["cursor"] == ""
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@pytest.mark.parametrize(
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"method_name,request_method",
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[
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("list_tools", "tools/list"),
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("list_resources", "resources/list"),
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("list_prompts", "prompts/list"),
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("list_resource_templates", "resources/templates/list"),
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],
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)
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async def test_list_methods_params_parameter(
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stream_spy: Callable[[], StreamSpyCollection],
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full_featured_server: FastMCP,
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method_name: str,
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request_method: str,
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):
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"""Test that the params parameter works correctly for list methods.
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Covers: list_tools, list_resources, list_prompts, list_resource_templates
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This tests the new params parameter API (non-deprecated) to ensure
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it correctly handles all parameter combinations.
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"""
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async with create_session(full_featured_server._mcp_server) as client_session:
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spies = stream_spy()
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method = getattr(client_session, method_name)
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# Test without params parameter (omitted)
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_ = await method()
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requests = spies.get_client_requests(method=request_method)
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assert len(requests) == 1
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assert requests[0].params is None
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spies.clear()
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# Test with params=None
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_ = await method(params=None)
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requests = spies.get_client_requests(method=request_method)
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assert len(requests) == 1
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assert requests[0].params is None
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spies.clear()
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# Test with empty params (for strict servers)
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_ = await method(params=types.PaginatedRequestParams())
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requests = spies.get_client_requests(method=request_method)
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assert len(requests) == 1
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assert requests[0].params is not None
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assert requests[0].params.get("cursor") is None
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spies.clear()
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# Test with params containing cursor
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_ = await method(params=types.PaginatedRequestParams(cursor="some_cursor_value"))
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requests = spies.get_client_requests(method=request_method)
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assert len(requests) == 1
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assert requests[0].params is not None
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assert requests[0].params["cursor"] == "some_cursor_value"
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@pytest.mark.parametrize(
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"method_name",
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[
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"list_tools",
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"list_resources",
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"list_prompts",
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"list_resource_templates",
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],
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)
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async def test_list_methods_raises_error_when_both_cursor_and_params_provided(
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full_featured_server: FastMCP,
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method_name: str,
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):
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"""Test that providing both cursor and params raises ValueError.
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Covers: list_tools, list_resources, list_prompts, list_resource_templates
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When both cursor and params are provided, a ValueError should be raised
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to prevent ambiguity.
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"""
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async with create_session(full_featured_server._mcp_server) as client_session:
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method = getattr(client_session, method_name)
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# Call with both cursor and params - should raise ValueError
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with pytest.raises(ValueError, match="Cannot specify both cursor and params"):
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await method(
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cursor="old_cursor",
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params=types.PaginatedRequestParams(cursor="new_cursor"),
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)
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async def test_list_tools_with_strict_server_validation():
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"""Test that list_tools works with strict servers require a params field,
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even if it is empty.
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Some MCP servers may implement strict JSON-RPC validation that requires
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the params field to always be present in requests, even if empty {}.
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This test ensures such servers are supported by the client SDK for list_resources
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requests without a cursor.
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"""
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server = Server("strict_server")
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@server.list_tools()
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async def handle_list_tools(request: ListToolsRequest) -> ListToolsResult:
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"""Strict handler that validates params field exists"""
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# Simulate strict server validation
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if request.params is None:
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raise ValueError(
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"Strict server validation failed: params field must be present. "
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"Expected params: {} for requests without cursor."
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)
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# Return empty tools list
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return ListToolsResult(tools=[])
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async with create_session(server) as client_session:
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# Use params to explicitly send params: {} for strict server compatibility
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result = await client_session.list_tools(params=types.PaginatedRequestParams())
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assert result is not None
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