[MM-68690] Null check on missing headers when loading resources

[devinbinnie]

Summary

Certain network responses can be missing headers that the downloads manager assumed were always present, leading to an unhandled error.

This PR adds defensive null checks when reading response headers in the downloads handler.

Ticket Link

https://mattermost.atlassian.net/browse/MM-68690

Release Note

Improved robustness of the downloads handler when handling unexpected network responses.

Change Impact: 🟢 Low

Regression Risk: Minimal. The changes are purely defensive—adding optional chaining operators (?.) and optional method calls (?.join?.()) to guard against missing content-disposition headers in network responses. The logic flow remains unchanged when headers are present, and the new null checks only prevent crashes in edge cases. The fix is scoped to a single, isolated method (webRequestOnHeadersReceivedHandler) within the downloads feature. No shared utilities, base classes, or widely-imported modules are affected.

QA Recommendation: Minimal manual QA required. The fix addresses a specific edge case (missing headers) that is already covered by an added unit test. Basic smoke testing of the downloads feature is recommended to verify that normal download flows (with complete headers) remain unaffected, but comprehensive testing can rely on the unit test coverage.

Generated by CodeRabbitAI

[coderabbitai]

No actionable comments were generated in the recent review. 🎉

ℹ️ Recent review info

⚙️ Run configuration

Configuration used: Repository UI

Review profile: CHILL

Plan: Pro

Run ID: 7ac6c6a0-08ac-46e3-b075-0b502ec6581f

📥 Commits

Reviewing files that changed from the base of the PR and between 7595a62 and e994cb2.

📒 Files selected for processing (2)

• src/main/downloadsManager.test.js
• src/main/downloadsManager.ts

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📝 Walkthrough

Walkthrough

This PR adds defensive programming to the downloads manager's header handling. The webRequestOnHeadersReceivedHandler method now safely handles missing or malformed content-disposition headers using optional chaining, preventing null-reference crashes. A new test case verifies this behavior.

Changes

Content-Disposition Header Robustness

Layer / File(s)	Summary
Implementation Fix src/main/downloadsManager.ts	Optional chaining applied to headers['content-disposition'].join(';') to safely handle cases where the header is missing or not array-like.
Test Validation src/main/downloadsManager.test.js	New test case (MM-68690) ensures webRequestOnHeadersReceivedHandler does not throw when content-disposition is absent and verifies callback receives an empty object.

Estimated code review effort

🎯 1 (Trivial) | ⏱️ ~3 minutes

🚥 Pre-merge checks | ✅ 5

✅ Passed checks (5 passed)

Check name	Status	Explanation
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Title check	✅ Passed	The PR title accurately reflects the main change: adding null checks for missing headers in the downloads manager to handle edge cases.
Docstring Coverage	✅ Passed	No functions found in the changed files to evaluate docstring coverage. Skipping docstring coverage check.
Linked Issues check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check	✅ Passed	Check skipped because no linked issues were found for this pull request.

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✨ Finishing Touches

📝 Generate docstrings

• Create stacked PR
• Commit on current branch

🧪 Generate unit tests (beta)

• Create PR with unit tests
• Commit unit tests in branch MM-68690

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[mm-cloud-bot]

❌ E2E Test Setup Failed

Failed to create E2E test instances: failed to create installation: failed with status code 409

[edgarbellot]

LGTM, thank you!

[mattermost-build]

Cherry pick is scheduled.

[devinbinnie]

/cherry-pick release-5.13

[mattermost-build]

Cherry pick is scheduled.