Return false from the handler, as it doesn't use sendResponse argument

[smalluban]

Fixes ghostery/ghostery-extension#806.

We are not using the sendResponse third argument in the handleRequest function, so we should always return false. For now, it returns a promise, so the API holds for using the sendResponse, which never happens. As the result, the error message is thrown in the console.

[remusao]

How is the content script getting the response back if we do not return the promise?

[philipp-classen]

Good catch! For instance, adblocking fails then on https://spiegel.de/.

The warning does originate from this function, so it is the right place. But it is correct that returning the promise is important.

[smalluban]

Right, i missed, that returned promise value works like sendResponse.. but what then it means that some of the sendMessage origin does not wait for the response. I suppose, that they don't care about it, but the above code sens a promise always, which causes the issue

[philipp-classen]

Observation: in the debugger, I see that we are using the polyfill:

https://github.com/mozilla/webextension-polyfill/blob/780518ed1d9b05e6b31c4067d4db29927779abf3/src/browser-polyfill.js#L426

My guess is that we are using the API correctly, but the version of the polyfill creates issues on modern Chrome version. (?)

[smalluban]

The core problem lies elsewhere. Chrome introduced a new error message lately if the listener of the message returns a promise, which is not resolved. What I found, the webextension-polyfill have mapping for those messages. Then instead of rejecting with an error, it resolves (I am not sure if this is a good practice, but Firefox does it, so the polyfill tries to mimic that behavior). More info here: mozilla/webextension-polyfill#384

I think I found the place, where we don't resolve a promise in the background listener in @cliqz/adblocker-webextension when the content scripts send a message for cosmetic filters: https://github.com/ghostery/adblocker/blob/master/packages/adblocker-webextension/adblocker.ts#L398

The sendResponse (the resolve method of the promise created in place) is not always called, but the listener always returns a new promise. As far as I tested it is safe to put sendResponse() (without arguments) at the end of the function, after line 408. The content script resolves result in the way result = result || {}.

I am closing the PR here, as the change must be done in the above package, and then reinstalling the ghostery-common package should use the latest version of the adblocker-webextension.