fix: guard the dashboard's docker icon onerror fallback

[Joly0]

Follow-up to #2693, which added this guard to DockerContainers.php but not to the dashboard's copy of the same line in DashboardApps.php.

The dashboard renders every container icon like this:

<img src='$icon?...' class='img' onerror=this.src='/plugins/dynamix.docker.manager/images/question.png';>

For a container with no icon, $info['icon'] is already the question.png path (set in DockerClient.php:346), so src and the onerror target are the same file. If question.png is missing, the handler reassigns a URL that also 404s, which fires onerror again, and nothing ever detaches it.

I ran into this after question.png was deleted on my server — the bug fixed in #2693. I'm on 7.3.2, so the backport in #2708 hasn't reached me yet. nginx's error log for the two minutes I had the dashboard open:

...question.png?    (the src attribute)      5 requests
...question.png     (the onerror target) 18,322 requests

The ? is empty because filemtime() returns false for the missing file, which is what makes the two URLs distinguishable in the log. That 5 : 18,322 split is the retry loop — polling would keep the two roughly proportional.

The change is the same one already merged for DockerContainers.php: quote the attribute and set this.onerror=null before reassigning src. The onerror fragment is now byte-identical between the two files. A missing fallback then costs one extra failed request per image instead of an unbounded loop.

Containers with a working icon are unaffected, and one whose icon 404s still falls back to question.png and renders it. Only the pathological case is capped.

Testing

DashboardApps.php is byte-identical between 7.3.2 and master at d3898259, so I tested the patched master file on a 7.3.2 box.

php -l clean. Rendered the expression with the file missing, before and after:

before: <img src='...question.png?' class='img' onerror=this.src='...question.png';>
after:  <img src='...question.png?' class='img' onerror="this.onerror=null;this.src='...question.png';">

I also confirmed the underlying deletion end-to-end on 7.3.2 before patching: with a throwaway icon-less container registered in docker.json, removing it from the Docker tab (Events.php → removeContainer() with cache=1) deleted question.png at the moment of the click, which inotify caught. That part is already handled by #2693/#2708 — this PR only caps the fallout when the file is missing for any reason.

🤖 Generated with Claude Code

Summary by CodeRabbit

• Bug Fixes
  • Improved Docker image fallback handling to prevent repeated error events when a container image fails to load.
  • Failed images now reliably display the default question-mark icon.

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emhttp/plugins/dynamix/include/DashboardApps.php

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• emhttp/plugins/dynamix/include/DashboardApps.php

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Walkthrough

The Docker image fallback handler now clears this.onerror before it assigns the default question-mark icon.

Changes

Docker image fallback

Layer / File(s)	Summary
Fallback handler emhttp/plugins/dynamix/include/DashboardApps.php	The onerror handler now sets this.onerror to null before assigning the fallback image source.

Estimated code review effort: 1 (Trivial) | ~2 minutes

Possibly related PRs

• unraid/webgui#2693: Updates a matching Docker image onerror fallback handler in another file.

Poem

A rabbit saw the image fail,
Then stopped the error’s looping trail.
The question mark now shines in place,
With tidy code and steady grace.
Hop, hop—fallback wins the race!

🚥 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 and concisely describes the Docker icon fallback guard added to the dashboard.
Docstring Coverage	✅ Passed	No functions found in the changed files to evaluate docstring coverage. Skipping docstring coverage check.
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