fix: don't delete the shared default docker icon when removing an icon-less container

[chodeus]

Summary

Fixes #2691 — the docker manager deletes its own shared fallback icon (question.png) whenever an icon-less container is removed or updated with cache flags, and once the file is missing, every icon-less container's onerror fallback re-requests it in a tight loop until the next reboot.

Changes

• include/DockerClient.php (removeContainer()) — skip the icon unlink when the recorded icon is the shared default. Containers with no template icon get /plugins/dynamix.docker.manager/images/question.png recorded as their icon (L346), so the existing unlink deleted the shared static file from the docroot for the whole system. Per-container cached icons (<name>-icon.png) are still cleaned up exactly as before.
• include/DockerContainers.php — quote the onerror attribute and guard it with this.onerror=null, so a missing fallback costs one failed request per image instead of an endless 404 retry loop (measured ~150 req/s against nginx with 15 affected images on one open Docker page).

Testing (real hardware, per the README workflow)

Tested on Unraid 7.3.2 — both files are byte-identical between 7.3.2 and master at 369f0b2, so the patched master files were copied to the live server directly.

• php -l clean on both files.
• Functional test of removeContainer() via injected webui-info registry entries:
  • entry recording the shared default icon, removed with cache=2 → question.png survives, registry entry cleaned up ✓
  • entry recording a per-container /state/...-icon.png (file created for the test), removed with cache=1 → cached icon still unlinked, registry entry cleaned up ✓ (registry returned to its original entry count)
• Browser test with question.png temporarily removed: stock-rendered container images now fail once and stop — previously an endless 404 retry loop. The Docker page renders normally in both states. (The only remaining repeat-requester on my test box traced to a third-party plugin carrying its own copy of the unguarded onerror pattern.)
• The original deletion was observed in the wild via CA Docker Auto-Update updating an icon-less container — full trace in Docker manager deletes its shared fallback icon (question.png) when an icon-less container is removed/updated #2691.

Summary by CodeRabbit

• Bug Fixes
  • Prevented cleanup from accidentally removing the shared default container icon.
  • Improved fallback handling when a container icon image fails to load, avoiding repeated error handling.

[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: ac8e7533-d9ad-4d5d-8167-8cae99b4d462

📥 Commits

Reviewing files that changed from the base of the PR and between 369f0b2 and 6f28eb6.

📒 Files selected for processing (2)

• emhttp/plugins/dynamix.docker.manager/include/DockerClient.php
• emhttp/plugins/dynamix.docker.manager/include/DockerContainers.php

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Walkthrough

Docker container cleanup now preserves the shared question icon, and PNG fallback rendering disables repeated onerror handling before replacing failed images.

Changes

Docker icon safeguards

Layer / File(s)	Summary
Protect shared fallback icon emhttp/plugins/dynamix.docker.manager/include/DockerClient.php, emhttp/plugins/dynamix.docker.manager/include/DockerContainers.php	Container removal no longer unlinks the shared question icon, and PNG image fallbacks clear their error handler before retrying.

Estimated code review effort: 2 (Simple) | ~5 minutes

Suggested reviewers: elibosley

Poem

A bunny checks the icons bright,
Keeps question.png safe through the night.
If PNGs fail, the loop is done,
One fallback hop, then back to fun.
Hop, hop—no errors spun!

🚥 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 title clearly describes the main fix: preserving the shared fallback Docker icon for icon-less containers.
Linked Issues check	✅ Passed	The code prevents unlinking the shared question.png and guards the image onerror loop, matching issue #2691's requirements.
Out of Scope Changes check	✅ Passed	The PR only changes the icon deletion and fallback handling needed for the linked issue.
Docstring Coverage	✅ Passed	No functions found in the changed files to evaluate docstring coverage. Skipping docstring coverage check.

✨ Finishing Touches

🧪 Generate unit tests (beta)

• Create PR with unit tests

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