posit-dev / posit-dev/mcptools

Support async tool handlers (promises)

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Dominant language
R
Stars
196
Forks
21
Avg merge
1h 14m
Merged PRs (30d)
1

Description

execute_tool_call() is synchronous and the HTTP transport returns plain lists from the httpuv call. Tools that need to wait (long-poll patterns, external requests via {promises}) can't be expressed.

httpuv already supports returning a promise from call; if a tool handler returns a promise, mcptools could chain the JSON-RPC response onto it. Shiny's MCP tunnel depends on this (a receive tool holds its response until the app has messages to flush).

Part of #115.

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First steps

  1. Read the whole issue, then the project's contributing guide.
  2. Comment on the issue to say you are picking it up — it saves two people doing the same work.
  3. Fork the repository and make your change on a branch.
  4. Open a pull request that references the issue number.

Research direction

Start by tracing execute_tool_call() through the HTTP transport and its httpuv call. Read how tool results become JSON-RPC responses, then inspect the {promises} behavior described in the issue. Done means a promise returned by a tool handler can defer the JSON-RPC response while synchronous handlers continue to work.

Written by the indexing model from the issue text.

Assessment

Tech stack
r
Domain
api, backend
Issue type
Feature
Difficulty
4/5
Estimated time
3-5 days
Activity status
Quiet
Clarity
Mostly clear
Newbie friendliness
48/100

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