Service workers and videos in Safari

Alright, so I’ve already talked about some gotchas when debugging service worker issues. But what if you don’t even realise the problem has anything to do with your service worker?

This is not a hypothetical situation. I encountered this very thing myself. Gather ‘round the campfire, children…

One of the latest case studies on the Clearleft site is a nice write-up by Luke of designing a mobile app for Virgin Holidays. The case study includes a lovely video that demonstrates the log-in flow. I implemented that using a video element (with a poster image). Nice and straightforward. Super easy. All good.

But I hadn’t done my due diligence in browser testing (I guess I didn’t even think of it in this case). Hana informed me that the video wasn’t working at all in Safari. The poster image appeared just fine, but when you clicked on it, the video didn’t load.

I ducked, ducked, and went, uncovering what appeared to be the root of the problem. It seems that Safari is fussy about having servers support something called “byte-range requests”.

I had put the video in question on an Amazon S3 server. I came to the conclusion that S3 mustn’t support these kinds of headers correctly, or something.

Now I had a diagnosis. The next step was figuring out a solution. I thought I might have to move the video off of S3 and onto a server that I could configure a bit more.

Luckily, I never got ‘round to even starting that process. That’s good. Because it turns out that my diagnosis was completely wrong.

I came across a recent post by Phil Nash called Service workers: beware Safari’s range request. The title immediately grabbed my attention. Safari: yes! Video: yes! But service workers …wait a minute!

There’s a section in Phil’s post entitled “Diagnosing the problem”, in which he says:

I first thought it could have something to do with the CDN I’m using. There were some false positives regarding streaming video through a CDN that resulted in some extra research that was ultimately fruitless.

That described my situation exactly. Except Phil went further and nailed down the real cause of the problem:

Nginx was serving correct responses to Range requests. So was the CDN. The only other problem? The service worker. And this broke the video in Safari.

Doh! I hadn’t even thought about service workers!

Phil came up with a solution, and he has kindly shared his code.

I decided to go for a dumber solution:

if ( request.url.match(/\.(mp4)$/) ) {
  return;
}

That tells the service worker to just step out of the way when it comes to video requests. Now the video plays just fine in Safari. It’s a bit of a shame, because I’m kind of penalising all browsers for Safari’s bug, but the Clearleft site isn’t using much video at all, and in any case, it might be good not to fill up the cache with large video files.

But what’s more important than any particular solution is correctly identifying the problem. I’m quite sure I never would’ve been able to fix this issue if Phil hadn’t gone to the trouble of sharing his experience. I’m very, very grateful that he did.

That’s the bigger lesson here: if you solve a problem—even if you think it’s hardly worth mentioning—please, please share your solution. It could make all the difference for someone out there.

.(mp4)$

as days pass by — Farmbound, or how I built an app in 2022

Stuart writes up the process up making a mobile game as a web app—not a native app. The Wordle effect reverberates.

It’s a web app. Works for everyone. And I thought it would be useful to explain why it is, why I think that’s the way to do things, and some of the interesting parts of building an app for everyone to play which is delivered over the web rather than via app stores and downloads.

1187179 - service worker NavigationPreload should trigger for frame requests - chromium

It’s official. The extremely niche browser behaviour I documented is a bug.

Service Workers | Go Make Things

Chris Ferdinandi blogs every day about the power of vanilla JavaScript. For over a week now, his daily posts have been about service workers. The cumulative result is this excellent collection of resources.

Adding Response Metadata to Cache API Explainer by Aaron Gustafson and Jungkee Song

This is a great proposal that would make the Cache API even more powerful by adding metadata to cached items, like when it was cached, how big it is, and how many times it’s been retrieved.

The Layers Of The Web - Jeremy Keith on Vimeo

Thanks to the quick work of Marc and his team, the talk I gave at Beyond Tellerrand on Thursday was online within hours!

I’m really pleased with how this turned out. I wasn’t sure if anybody was going to be interested in the deep dive into history that I took for the first 15 or 20 minutes, but lots of people told me that they really enjoyed that part, so that makes me happy.