Why does a PWA based on Workbox produce an error when launched from the homescreen on iOS 12? - progressive-web-apps

Question

I can run the app in the browser after clearing data, but if I then add it to the homescreen and attempt to relaunch from there, I get a plain page giving the following error:
Safari cannot open the page. The error was: "FetchEvent.respondWith received an error: Returned response is null."
Subsequent launches in the browser then also give that error. I have to again 'clear data' in the browser to get it to work again.
I'm using Workbox v3.6.2 (the latest, at the time of writing), and my iPhone is running iOS 12.
This looks suspicious, but it's a bit over my head (well, the workaround is anyway). It makes me want to try to down grade to iOS11.X again, and/or install Technology Preview 59.

Answer 1

I have this same problems. On iOS 12.0.0 work properly but after updating to version 12.0.1 I have this same error like you. I have test this same application but on two different devices (iPhone) with two different version of iOS.

Answer 2

Looks like there are multiple possible reasons for this error - I've had it twice ;
Occasion 1 : Needed to add a ROOT certificate and set it as Trusted on device.
my conditions;
I was getting the same error on an iPhone 5s with iOS 12 when loading pwapp from local server.
Using self signed certs on a development machine for server.
Not using Workbox.
Not getting problem if loading pwapp from provider hosted server with ssl cert from iOS recognised cert authority.
Turned out it was to do with security certs - (not using a mac so can't debug to the level of network/security issues on the device / direct to fully diagnose).
Fix was to ;
create a self signed root cert and use that for my server.
convert (copy of) root cert .pem file to .der
access .der via safari on the device / add profile, set as trusted.
(Correct way is to do root, intermediary and server certs , use the server cert and serve the root cert via url or email it to email client on device.)
useful links ;
see Getting cert in General->About->Certificate Trust Settings
Occasion 2 : Turns out you have to access the pwapp from the home screen icon at least once while you have access to the server.
To reproduce ;
(networking on)
delete icon from home screen and clear safari history and website data
visit the pwapp url
add to home screen but do not launch
turn off networking
attempt launch from home screen => get the error
turn on networking, launch pwapp from home screen => ok.
close pwapp, turn off networking, launch pwapp from home screen => ok.
So looks like an iOS/Safari/Webkit bug