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https://github.com/PrefectHQ/fastmcp.git
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99 lines
3 KiB
Python
99 lines
3 KiB
Python
"""
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Tests that synchronous functions cannot be used as background tasks.
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SEP-2663 tasks are tools-only. Docket requires async functions for background
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execution, so FastMCP raises ValueError when task=True is used with a sync tool
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function. These are registration-time checks and need no running server.
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"""
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import pytest
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from fastmcp import FastMCP
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from fastmcp.tools.function_tool import FunctionTool
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async def test_sync_tool_with_explicit_task_true_raises():
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"""Sync tool with task=True raises ValueError."""
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mcp = FastMCP("test")
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with pytest.raises(
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ValueError, match="uses a sync function but has task execution enabled"
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):
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@mcp.tool(task=True)
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def sync_tool(x: int) -> int:
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"""A synchronous tool."""
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return x * 2
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async def test_sync_tool_with_inherited_task_true_raises():
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"""Sync tool inheriting task=True from server raises ValueError."""
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mcp = FastMCP("test", tasks=True)
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with pytest.raises(
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ValueError, match="uses a sync function but has task execution enabled"
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):
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@mcp.tool() # Inherits task=True from server
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def sync_tool(x: int) -> int:
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"""A synchronous tool."""
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return x * 2
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async def test_async_tool_with_task_true_remains_enabled():
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"""Async tools with task=True keep task support enabled."""
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mcp = FastMCP("test")
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@mcp.tool(task=True)
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async def async_tool(x: int) -> int:
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"""An async tool."""
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return x * 2
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tool = await mcp.get_tool("async_tool")
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assert isinstance(tool, FunctionTool)
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assert tool.task_config.mode == "optional"
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async def test_sync_tool_with_task_false_works():
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"""Sync tool with explicit task=False works (no error)."""
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mcp = FastMCP("test", tasks=True)
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@mcp.tool(task=False) # Explicitly disable
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def sync_tool(x: int) -> int:
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"""A synchronous tool."""
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return x * 2
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tool = await mcp.get_tool("sync_tool")
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assert isinstance(tool, FunctionTool)
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assert tool.task_config.mode == "forbidden"
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# =============================================================================
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# Callable classes with async __call__
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# =============================================================================
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async def test_async_callable_class_tool_with_task_true_works():
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"""Callable class with async __call__ and task=True should work."""
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from fastmcp.tools import Tool
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class AsyncCallableTool:
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async def __call__(self, x: int) -> int:
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return x * 2
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tool = Tool.from_function(AsyncCallableTool(), task=True)
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assert tool.task_config.mode == "optional"
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async def test_sync_callable_class_tool_with_task_true_raises():
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"""Callable class with sync __call__ and task=True should raise."""
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from fastmcp.tools import Tool
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class SyncCallableTool:
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def __call__(self, x: int) -> int:
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return x * 2
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with pytest.raises(
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ValueError, match="uses a sync function but has task execution enabled"
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):
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Tool.from_function(SyncCallableTool(), task=True)
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