Proposal: clientURL property on FetchEvent

[jeffposnick]

I have a use case for a new property, clientURL, being added to the FetchEvent interface.

In scenarios in which a FetchEvent's clientId is populated (including subresource requests), clientURL would be set to a URL string representing the client's current location. In scenarios in which clientId is not populated, it would be set to an empty string.

I would like to use this client URL information as part of an advanced routing option in the Workbox service worker framework—basically, to allow developers to opt-in to different routing and caching rules for subresource requests that originate from different logical sections of their web app, all from within the same registered service worker instance. In order to accomplish this, I need to obtain the client's full URL synchronously, so that within the fetch handler that Workbox sets up, a synchronous decision can be made about whether or not to call respondWith() on the FetchEvent.

There are some alternatives to creating a new property that rely on existing functionality, but neither is appropriate for my use case:

• Similar information is already exposed synchronously via the request.referrer property of a FetchEvent when a lax Referrer-Policy is in effect, but when a more restrictive policy is in place, request.referrer may not contain the full URL.

• Similar information is already exposed asynchronously by passing the clientId of a FetchEvent to clients.get(), and then obtaining the location of that return value.

[wanderview]

If its not too expensive, we could even provide a Client object snapshot at the time of the fetch.

[wanderview]

How would this work with resultingClientId and replacesClientId? Would it just not be populated?

[jeffposnick]

I was assuming it wouldn't be populated for scenarios in which clientId wasn't populated.

Specifically, this is useful (for me, at least) only for subresource requests, when clientId would be populated. resultingClientId and replacesClientId only come into play during navigations, right?