Hey, check out this infuriating Safari bug

It appears that Safari 17.5 (as well as the current Safari Technology Preview, "Safari 18.0, WebKit 19619.1.18") has a particularly pernicious bug in which img tags with lazy-loading enabled that have a src which must be resolved after an HTTP redirect will stop rendering if you load a lot of them. But only sometimes. And then continuously for, like, 5 minutes.

Suppose I have a bunch of images like this in list:

<img loading="lazy" src="/a/redirect/to/some.webp">

Seems reasonable, right? Well, here's what I'm seeing:

Weirdly, when the bug is encountered:

  • Safari won't "wake up" to load the image in response to scrolling or resizing the window
  • Nothing is printed to the development console and no errors appear in the Network tab
  • The bug will persist after countless page refreshes for at least several minutes (almost as if a time-based cache expiry is at play)
  • It also persists after fully quitting and relaunching Safari (suggesting a system-wide cache or process is responsible)

I got tripped up on this initially, because I thought the bug was caused by the fact I was loading WebP files, but the issue went away as soon as I started loading the static file directly, without any redirect. As soon as I realized the bug was actually triggered by many images requiring a redirect—regardless of file type—the solution was easy: stop doing that.

(Probably a good idea, regardless, since it's absurdly wasteful to ask every user to follow hundreds of redirects on every page load.)

So why was I redirecting so many thumbnail images in the first place? Well, Active Storage, which I use for hosting user-uploaded assets, defaults to serving those assets via a Rails-internal route which redirects each asset to whatever storage provider is hosting it. That means if your app uses the default redirect mode instead of ensuring your assets are served by a CDN, you can easily wind up in really stupid situations like this one.

Fortunately for me, I'm only relying on redirection in development (in production, I have Rails generating URLs to an AWS CloudFront distribution), so this bug wouldn't have bitten me For Real. Of course, there was no way I could have known that, so I sat back, relaxed, and enjoyed watching the bug derail my entire morning. Not like I was doing anything.

Being a programmer is fun! At least it's Friday. 🫠

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