MCP Server Part 9: Background callbacks#3766
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…move Flask dependency in MCP implementation
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| if TYPE_CHECKING: | ||
| from dash.mcp.primitives.tools.callback_adapter import CallbackAdapter |
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Why was this necessary?
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| def task_result_to_tool_result(create_task_result: CreateTaskResult) -> CallToolResult: | ||
| """Wrap a CreateTaskResult as a CallToolResult with polling instructions. |
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Ahem...
| """Wrap a CreateTaskResult as a CallToolResult with polling instructions. | |
| """ | |
| Wrap a CreateTaskResult as a CallToolResult with polling instructions. |
| "This is a long-running background operation. " | ||
| "It returns a taskId immediately. " |
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These get joined with newlines, so you could probably skip the ending spaces.
| "This is a long-running background operation. " | |
| "It returns a taskId immediately. " | |
| "This is a long-running background operation." | |
| "It returns a taskId immediately." |
| ) | ||
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| def task_result_to_tool_result(create_task_result: CreateTaskResult) -> CallToolResult: |
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This is minor, but CreateTaskResult makes me think that you're creating something. That's not the case though. Is there another name option?
| def call_tool(cls, tool_name: str, arguments: dict[str, Any]) -> CallToolResult: | ||
| def call_tool( | ||
| cls, tool_name: str, arguments: dict[str, Any], task: dict | None = None | ||
| ) -> CallToolResult | CreateTaskResult: |
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Would CreateTaskResult get returned? In task_result_to_tool_result the result is wrapped in CallToolResult.
| tool_name: str, | ||
| arguments: dict[str, Any], | ||
| task: dict | None = None, | ||
| ) -> CallToolResult: |
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Could the result here be CreateTaskResult?
| if adapter is None: | ||
| return None |
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Does an error need to be returned here?
| from dash.mcp.types import MCPError | ||
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| def parse_task_id(task_id: str) -> tuple[str, str, str, datetime]: |
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Could you add error handling here in the event that task_id is malformed?
| raise MCPError("No background callback manager configured.") | ||
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| app = get_app() | ||
| adapter = app.mcp_callback_map.find_by_tool_name(tool_name) |
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Could this ever be None? If so, then 117 would throw an error.
| task_status = get_task(task_id) | ||
| if task_status.status == "completed": | ||
| return get_task_result(task_id) |
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Is the task guaranteed to still be available between these two calls? For example, if you have two clients polling for the same task, could one of them grab the result before the other and cause an error?
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Summary
Adds support for MCP Tasks — when an LLM calls a tool backed by a Dash background callback, the tool returns a
taskIdimmediately and the LLM polls for results.dash/mcp/tasks/module that lists, starts, and cancels background callbacks per the MCP spec SEP-1686