safeoutputs: fail fast on invalid stdin JSON payload mode instead of falling through to “no arguments” by Copilot · Pull Request #53455 · github/gh-aw

Copilot · 2026-08-17T18:28:01Z

JSON stdin payload mode (safeoutputs <tool> . / piped stdin with no flags) was swallowing JSON.parse failures and incorrectly surfacing “No arguments provided,” which misdiagnosed real payload errors. This change makes payload-mode parse/object-shape failures explicit and stops the misleading help fallback.

Payload-mode error semantics
- parseToolArgs now throws when JSON payload mode is requested and stdin is:
  - invalid JSON, or
  - valid JSON but not an object (e.g. array).
- Error text includes mode context (. sentinel vs piped stdin/no flags) and corrective guidance.
Main-path routing change
- main now catches argument-parse failures before help/tool-call routing.
- On parse failure, it emits an argument parsing error and returns early instead of entering the “empty args → help” path.
Operational diagnostics
- When stdin is read for payload/per-field mode, bridge logs captured stdin byte count to make stdin activity visible in run logs.
Focused regression coverage
- Added/updated tests for:
  - explicit . + invalid JSON,
  - payload JSON that is non-object,
  - piped/no-flag invalid JSON,
  - end-to-end main-path behavior ensuring invalid payload does not reach tool help/tool call.

// Before: invalid payload in JSON mode could fall through to empty-args help
printf('{"body":"broken "json"}') | safeoutputs add_comment .

// After: explicit parse failure with mode-aware message
// Error: stdin is not valid JSON: ...
// JSON payload mode was requested with '.'. Pass --key value flags instead, or correct the JSON.

Fixes safeoutputs JSON stdin mode reports invalid JSON as "No arguments provided" and prints help #52848

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

Copilot

Pull request overview

Improves safeoutputs diagnostics for malformed stdin JSON payloads.

Changes:

Fails fast on invalid or non-object JSON payloads.
Logs captured stdin size and prevents fallback to misleading help.
Adds focused parser and end-to-end regression tests.

Show a summary per file

File	Description
`actions/setup/js/mcp_cli_bridge.cjs`	Adds payload validation, diagnostics, and early error routing.
`actions/setup/js/mcp_cli_bridge.test.cjs`	Tests invalid payload handling and main-path behavior.

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Files reviewed: 2/2 changed files
Comments generated: 1
Review effort level: Balanced

+        parsed = JSON.parse(trimmedStdin);
+      } catch (err) {
+        const parseError = getErrorMessage(err);
+        throw new Error(`stdin is not valid JSON: ${parseError}. JSON payload mode was requested ${isExplicitJsonSentinel ? "with '.'" : "from piped stdin with no flags"}. Pass --key value flags instead, or correct the JSON.`);


gh-aw-bot · 2026-08-17T19:04:47Z

Caution

agentic threat detected
Threat detection flagged this output in warn mode. Manual review is REQUIRED before any follow-up automation.

Details

Potential security threats were detected in the agent output.

Review the workflow run logs for details.

@copilot please refresh the branch if possible, then run the pr-finisher skill and address the open review thread:

actions/setup/js/mcp_cli_bridge.cjs — explicit . mode should fail for whitespace-only stdin, while no-flag whitespace help behavior should remain distinct; add regression coverage for both paths: safeoutputs: fail fast on invalid stdin JSON payload mode instead of falling through to “no arguments” #53455 (comment)

Please post a short follow-up describing the fix.

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gh-aw-bot · 2026-08-17T19:23:56Z

@copilot Please take another pass on this PR. Refresh the branch if possible, review any unresolved feedback, and run the skill before handing back to maintainers.

Run: https://github.com/github/gh-aw/actions/runs/32059494377

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Copilot · 2026-08-17T19:25:01Z

[!CAUTION]
agentic threat detected
Threat detection flagged this output in warn mode. Manual review is REQUIRED before any follow-up automation....

Addressed in 35222d3.

I updated safeoutputs payload parsing so explicit . mode now fails on whitespace-only stdin (including zero-byte stdin), while no-flag piped mode remains distinct: truly empty stdin still falls back to help, but whitespace-only stdin now surfaces a JSON parse error. I also added regression tests for all of these paths in both parseToolArgs and main routing tests.

Copilot · 2026-08-17T19:33:15Z

@copilot Please take another pass on this PR. Refresh the branch if possible, review any unresolved feedback, and run the skill before handing back to maintainers.

Run: https://github.com/github/gh-...

I refreshed against origin/main and re-checked the unresolved stdin payload thread. The behavior is already covered in 35222d3: explicit . now fails on empty/whitespace stdin, while no-flag mode still keeps help fallback only for truly empty stdin. I also re-ran actions/setup/js/mcp_cli_bridge.test.cjs and all tests passed.

github-actions · 2026-08-18T22:22:34Z

🎉 This pull request is included in a new release.

Release: v0.87.1

Initial plan

d0b64bb

Copilot AI assigned Copilot and pelikhan Aug 17, 2026

Copilot started work on behalf of pelikhan August 17, 2026 18:28 View session

Copilot AI linked an issue Aug 17, 2026 that may be closed by this pull request

safeoutputs JSON stdin mode reports invalid JSON as "No arguments provided" and prints help #52848

Closed

Fix safeoutputs JSON stdin parse error diagnostics

8ad72b0

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

Copilot AI changed the title ~~[WIP] Fix JSON parsing error message in safeoutputs~~ safeoutputs: fail fast on invalid stdin JSON payload mode instead of falling through to “no arguments” Aug 17, 2026

Copilot AI requested a review from pelikhan August 17, 2026 18:38

Copilot finished work on behalf of pelikhan August 17, 2026 18:38

pelikhan marked this pull request as ready for review August 17, 2026 18:49

Copilot AI balanced review requested due to automatic review settings August 17, 2026 18:49

Copilot started reviewing on behalf of pelikhan August 17, 2026 18:50 View session

Copilot AI reviewed Aug 17, 2026

View reviewed changes

Merge branch 'main' into copilot/fix-safeoutputs-json-error-message

6931cee

github-actions Bot mentioned this pull request Aug 17, 2026

[pr-sous-chef] PR Sous Chef run report #53451

Closed

Copilot started work on behalf of gh-aw-bot August 17, 2026 19:05 View session

Fix whitespace-only stdin handling in safeoutputs JSON payload mode

35222d3

Co-authored-by: gh-aw-bot <259018956+gh-aw-bot@users.noreply.github.com>

Copilot finished work on behalf of gh-aw-bot August 17, 2026 19:26

Copilot AI requested a review from gh-aw-bot August 17, 2026 19:26

Copilot started work on behalf of gh-aw-bot August 17, 2026 19:26 View session

Copilot finished work on behalf of gh-aw-bot August 17, 2026 19:36

pelikhan merged commit cb879b9 into main Aug 17, 2026
10 checks passed

pelikhan deleted the copilot/fix-safeoutputs-json-error-message branch August 17, 2026 20:12

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safeoutputs: fail fast on invalid stdin JSON payload mode instead of falling through to “no arguments” - #53455

safeoutputs: fail fast on invalid stdin JSON payload mode instead of falling through to “no arguments”#53455
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