Fetch() request immediately failing in service worker running through Android Webview

Issue

I have a service worker that I use to enable an offline version of my website. This works great. I also have an Android app that is basically just a wrapper around a webview that loads my website.

All was fine and dandy until about 2-3 weeks ago when the Fetch() request started immediately failing. It is only failing when running through the Android webview. Running through a browser works fine. If the resource is cached already (i.e. via the install event) then it works great, it's only when I get a page that is not cached.

The code in my service worker:

self.addEventListener("fetch", function (event) {

if (event.request.method !== 'GET'
    || event.request.url.toLowerCase().indexOf('//ws') > -1
    || event.request.url.toLowerCase().indexOf('localws') > -1) {
    // Don't intercept requests made to the web service
    // If we don't block the event as shown below, then the request will go to
    // the network as usual.

    return;
}


event.respondWith(async function () {
    // override the default behavior

    var oCache = await caches.open('cp_' + version);
    var cached = await oCache.match(event.request.url);

    if (cached && cached.status < 300) {
        return cached;
    }

    // Need to make a call to the network
    try {
        var oResp = await fetch(event.request); // THIS LINE CAUSES THE PROBLEM!!!
        return oResp;
    } catch (oError) {
        console.log('SW WORKER: fetch request to network failed.', event.request);


        return new Response('<h1>Offline_sw.js: An error has occured. Please try again.</h1><br><h2>Could not load URL: ' + event.request.url + '</h2>', {
            status: 503,
            statusText: 'Service Unavailable',
            headers: new Headers({
                'Content-Type': 'text/html'
            })
        });
    }  
}()); // event.respondwith
}); // fetch

The line:

var oResp = await fetch(event.request);

is called once I've determined it is not cached and seems to be the culprit. When it errors out I get the following error in my catch(): 'Failed to fetch'

This seems pretty generic and not helpful. Again, this works when going through a browser and so I know it's not a CORS issue, service worker in the wrong directory, etc. Again, it worked until about 3 weeks ago and now I'm getting reports from customers that it's not working.

Here's a screen shot of the actual event.request that I'm sending off:

In the chrome developer tools (used to debug the webview) I see the following:

Am I doing something wrong or is this a bug in the webview / chrome that was released recently? (I say that as chrome powers the webview)

Solution

Looks like it was a bug in chromium. See bugs.chromium.org/p/chromium/issues/detail?id=977784. Should be fixed in v 76.

As a work around (as the link mentioned), you can add the following to your android code:

ServiceWorkerController oSWController = null;
if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.N){
        oSWController = ServiceWorkerController.getInstance();
        oSWController.setServiceWorkerClient(new ServiceWorkerClient(){
            @Nullable
            @Override
            public WebResourceResponse shouldInterceptRequest(WebResourceRequest request){
                return super.shouldInterceptRequest(request);
            }
        });
    }

Answered By - ScottR