Add support for loading tool handlers from external files in MCP server core by Copilot · Pull Request #5085 · github/gh-aw

Copilot · 2025-11-29T14:48:44Z

Original prompt

Add support the JavaScript mcp server core to require tool handlers from files specified in the tools.json configuration file.

the tool object in tools.JSON may have a optimal string field "handler" which points to a file path that can be resolved by the "require" command at runtime (this feature does not use the go based bundler)

when initializing the server, load all the handlers and store the default exported function in the tools data structure. Check imported function is a function.

the handler typescript signature is

async function handler(args: Record<string, unknown>): Promise

When a tool is called, call the imported function with the args and the response is serialized to the user. Exception is error.

Add extensive logging.

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Changeset

Type: patch
Description: Add support for loading MCP tool handlers from external files; updates mcp-tools.json schema and JavaScript MCP server core to allow a handler file path (supports sync/async handlers, ES module default exports, shell-script handlers, path traversal protection, serialization fallback, and logging). Tests and workflows updated.

AI generated by Changeset Generator

Smoke Test Summary

Test Run: 2025-11-29T17:23:26Z
Status: PASS
Summary: All smoke tests passed - GitHub MCP, file writing, bash tools, and Playwright validated

AI generated by Smoke Copilot No Firewall

…er core Co-authored-by: pelikhan <4175913+pelikhan@users.noreply.github.com>

…lization error handling Co-authored-by: pelikhan <4175913+pelikhan@users.noreply.github.com>

pelikhan · 2025-11-29T15:06:39Z

+
+      // Wrap the handler to ensure it returns the expected MCP response format
+      // and handles both sync and async handlers
+      tool.handler = async args => {


@copilot move creation of handler into own function to avoid bloating the closure.

Extracted handler wrapper to createWrappedHandler(server, toolName, handlerFn) function at line 213. This avoids closure bloat by passing only the required parameters. Commit: ac2f332

Co-authored-by: pelikhan <4175913+pelikhan@users.noreply.github.com>

pelikhan · 2025-11-29T15:53:24Z

@copilot add support for handlers pointing to a shell script (.sh). In that case, use the same convention as a custom github action to populate the env vars with the inputs and read the output from the output env vars as well, just like custom actions.

Co-authored-by: pelikhan <4175913+pelikhan@users.noreply.github.com>

Copilot · 2025-11-29T16:03:57Z

@copilot add support for handlers pointing to a shell script (.sh). In that case, use the same convention as a custom github action to populate the env vars with the inputs and read the output from th...

Added shell script (.sh) handler support using GitHub Actions convention:

Inputs passed as INPUT_* environment variables (uppercased, dashes converted to underscores)
Outputs read from file specified by GITHUB_OUTPUT env var (key=value format per line)
Returns { stdout, stderr, outputs } in MCP response format

Added 4 new tests covering shell script execution, multiple outputs, error handling, and input name conversion.

Commit: cfe72e5

github-actions · 2025-11-29T16:29:13Z

🤖 ALERT: Smoke Copilot No Firewall failed. ANOMALY_DETECTED. REPAIR_REQUIRED.

github-actions · 2025-11-29T16:29:13Z

💥 WHOOSH! Smoke Claude springs into action on this pull request! [Panel 1 begins...]

github-actions · 2025-11-29T16:29:14Z

🔮 The ancient spirits stir... Smoke Codex awakens to divine this pull request...

github-actions · 2025-11-29T16:29:16Z

💀 Blimey! Changeset Generator failed and walked the plank! No treasure today, matey! ☠️

github-actions · 2025-11-29T16:29:19Z

📰 DEVELOPING STORY: Smoke Copilot reports failed. Our correspondents are investigating the incident...

github-actions · 2025-11-29T16:31:42Z

Smoke Test Summary

Test Run: 2025-11-29T16:41:14Z
Status: PASS

✅ GitHub MCP: Update changeset generator to use codex gpt-5-mini #5088 "Update changeset generator to use codex gpt-5-mini", Update workflow compiler to generate secure template expansion patterns #5084 "Update workflow compiler to generate secure template expansion patterns"
✅ File Write: Created /tmp/smoke-test-claude-19786425691.txt
✅ Bash Tool: Verified file content
✅ Playwright MCP: Navigated to GitHub, title contains "GitHub"

💥 [THE END] — Illustrated by Smoke Claude fer issue #5085 🗺️

github-actions · 2025-11-29T16:33:17Z

Latest merged PRs:

Update changeset generator to use codex gpt-5-mini
Update workflow compiler to generate secure template expansion patterns
Tests:
GitHub MCP review ✅
File write + cat ❌ (repo policy blocks writing outside /tmp/gh-aw/agent, so /tmp/smoke-test-codex-19786425689.txt could not be created)
Playwright title check ✅
Overall: FAIL

🔮 The oracle has spoken through Smoke Codex fer issue #5085 🗺️

pelikhan · 2025-11-29T16:38:43Z

@copilot update smoke agentic workflows to try to write under /tmp/gh-aw/agent folder

Co-authored-by: pelikhan <4175913+pelikhan@users.noreply.github.com>

Copilot · 2025-11-29T16:44:26Z

@copilot update smoke agentic workflows to try to write under /tmp/gh-aw/agent folder

Updated all smoke agentic workflows (smoke-claude, smoke-copilot, smoke-copilot-no-firewall, smoke-codex) to write test files under /tmp/gh-aw/agent/ folder instead of directly in /tmp/. Commit: af733c9

pelikhan · 2025-11-29T17:01:35Z

@copilot recompile workflows

Co-authored-by: pelikhan <4175913+pelikhan@users.noreply.github.com>

Copilot · 2025-11-29T17:05:59Z

@copilot recompile workflows

Recompiled all 89 workflows. Commit: 37c7340

github-actions · 2025-11-29T17:21:46Z

📰 DEVELOPING STORY: Smoke Copilot reports failed. Our correspondents are investigating the incident...

github-actions · 2025-11-29T17:21:47Z

🤖 SYSTEM_INIT: Smoke Copilot No Firewall ACTIVATED. PROCESSING pull request. ALL SUBSYSTEMS ONLINE.

github-actions · 2025-11-29T17:21:47Z

🎉 Yo ho ho! Changeset Generator found the treasure and completed successfully! ⚓💰

github-actions · 2025-11-29T17:21:47Z

🔮 The ancient spirits stir... Smoke Codex awakens to divine this pull request...

github-actions · 2025-11-29T17:21:49Z

💥 WHOOSH! Smoke Claude springs into action on this pull request! [Panel 1 begins...]

github-actions · 2025-11-29T17:24:29Z

Smoke Test Results

Last 2 merged PRs:

Update changeset generator to use codex gpt-5-mini #5088: Update changeset generator to use codex gpt-5-mini
docs: Add sub-issues section to IssueOps page #5087: docs: Add sub-issues section to IssueOps page

Test Results:

✅ GitHub MCP: Retrieved PR data successfully
✅ File Writing: Created /tmp/gh-aw/agent/smoke-test-copilot-19786978320.txt
✅ Bash Tool: File verified with cat command
✅ Playwright MCP: Navigated to GitHub, title contains "GitHub"

Status: PASS

🤖 DIAGNOSTIC REPORT GENERATED BY Smoke Copilot No Firewall fer issue #5085 🗺️

github-actions · 2025-11-29T17:24:37Z

Smoke Test Summary

Test Run: 2025-11-29T17:23:28Z
Status: PASS

Test Results

✅ GitHub MCP: Refactor safe output type validation into data-driven validator engine #5086 "Refactor safe output type validation into data-driven validator engine", Update changeset generator to use codex gpt-5-mini #5088 "Update changeset generator to use codex gpt-5-mini"
✅ File Writing: Created /tmp/gh-aw/agent/smoke-test-claude-19786978319.txt
✅ Bash Tool: Verified file content
✅ Playwright MCP: Navigated to GitHub, confirmed title contains "GitHub"

💥 [THE END] — Illustrated by Smoke Claude fer issue #5085 🗺️

github-actions · 2025-11-29T17:24:57Z

Latest merged PRs:

Refactor safe output type validation into data-driven validator engine
Update changeset generator to use codex gpt-5-mini
GitHub MCP: ✅
File writing: ✅
Bash tools: ✅
Playwright: ✅
Overall: PASS

🔮 The oracle has spoken through Smoke Codex fer issue #5085 🗺️

Copilot AI self-assigned this Nov 29, 2025

Initial plan

ca8b667

Copilot AI assigned pelikhan Nov 29, 2025

Copilot started work on behalf of pelikhan November 29, 2025 14:49 View session

Copilot AI and others added 2 commits November 29, 2025 15:02

Add support for loading tool handlers from external files in MCP serv…

bcf782c

…er core Co-authored-by: pelikhan <4175913+pelikhan@users.noreply.github.com>

Address code review feedback: add path traversal protection and seria…

73a9ec6

…lization error handling Co-authored-by: pelikhan <4175913+pelikhan@users.noreply.github.com>

pelikhan approved these changes Nov 29, 2025

View reviewed changes

Copilot AI changed the title ~~[WIP] Add support for tool handlers in tools.json configuration~~ Add support for loading tool handlers from external files in MCP server core Nov 29, 2025

Copilot AI requested a review from pelikhan November 29, 2025 15:10

Copilot finished work on behalf of pelikhan November 29, 2025 15:10

Copilot started work on behalf of pelikhan November 29, 2025 15:10 View session

Refactor: extract handler wrapper function and add debugError method

ac2f332

Co-authored-by: pelikhan <4175913+pelikhan@users.noreply.github.com>

Copilot finished work on behalf of pelikhan November 29, 2025 15:20

Copilot started work on behalf of pelikhan November 29, 2025 15:53 View session

Add shell script handler support with GitHub Actions convention

cfe72e5

Co-authored-by: pelikhan <4175913+pelikhan@users.noreply.github.com>

Copilot finished work on behalf of pelikhan November 29, 2025 16:05

pelikhan added the smoke label Nov 29, 2025

github-actions Bot added the smoke-claude label Nov 29, 2025

Copilot started work on behalf of pelikhan November 29, 2025 16:39 View session

Update smoke workflows to write test files under /tmp/gh-aw/agent folder

af733c9

Co-authored-by: pelikhan <4175913+pelikhan@users.noreply.github.com>

Copilot finished work on behalf of pelikhan November 29, 2025 16:45

pelikhan added smoke and removed smoke smoke-claude labels Nov 29, 2025

pelikhan marked this pull request as ready for review November 29, 2025 16:57

Merge branch 'main' into copilot/add-js-mcp-server-tool-handlers

bd151a9

Copilot started work on behalf of pelikhan November 29, 2025 17:02 View session

Recompile workflows with latest changes

37c7340

Co-authored-by: pelikhan <4175913+pelikhan@users.noreply.github.com>

Copilot finished work on behalf of pelikhan November 29, 2025 17:08

pelikhan added smoke and removed smoke labels Nov 29, 2025

Add changeset [skip-ci]

aec4c2e

github-actions Bot added the smoke-copilot-no-firewall label Nov 29, 2025

github-actions Bot added the smoke-claude label Nov 29, 2025

github-actions Bot added the smoke-codex label Nov 29, 2025

pelikhan merged commit 60a7352 into main Nov 29, 2025
15 checks passed

pelikhan deleted the copilot/add-js-mcp-server-tool-handlers branch November 29, 2025 17:31

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