fix(service-worker): Don't stay locked in EXISTING_CLIENTS_ONLY if corrupted data

[adrienverge]

Problem

After #31109 and #31865, it's still possible to get locked in state
EXISTING_CLIENTS_ONLY, without any possibility to get out (even by
pushing new updates on the server).
More specifically, if control doc /latest of ngsw:/:db:control once
gets a bad value, then the service worker will fail early, and won't be
able to overwrite /latest with new, valid values (the ones from future
updates).

For example, once in this state, URL /ngsw/state will show:

NGSW Debug Info:
Driver state: EXISTING_CLIENTS_ONLY (Degraded due to failed initialization: Invariant violated (initialize): latest hash 8b75… has no known manifest
Error: Invariant violated (initialize): latest hash 8b75… has no known manifest
    at Driver.<anonymous> (https://my.app/ngsw-worker.js:2302:27)
    at Generator.next (<anonymous>)
    at fulfilled (https://my.app/ngsw-worker.js:175:62))
Latest manifest hash: 8b75…
Last update check: 22s971u

... with hash 8b75… corresponding to no installed version.

Solution

Currently, when such a case happens, the service worker simply fails
with an assertion. Because this failure happens early, and is not
handled, the service worker is not able to update /latest to new
installed app versions.

I propose to detect this corrupted case (a latest hash that doesn't
match any installed version) a few lines above, so that the service
worker can correctly call its already existing cleaning code.

This change successfully fixes the problem described above.

I tried to add unit tests, but the mock fixture in https://github.com/angular/angular/blob/d1ea1f4/packages/service-worker/worker/test/happy_spec.ts is too simple to include access to cache storage / ngsw:/:db:control / /latest. Spontaneously I'm not sure unit tests are needed for this locked-state-recovery fix. However if unit tests can be written, could you guide me on what to do?

Unit test written with the help of George Kalpakas. Thank you!

[gkalpak]

Thx, @adrienverge 💯

I have left a couple of minor comments. Testing this is indeed not very straight forward. I have pushed a commit with a test.

[adrienverge]

@gkalpak thanks a lot for helping me with a test! That's similar to what I started writing yesterday, but await scope.caches.open('ngsw:/:db:control') was the missing part 👍

I just squashed your fixup commit and reworded messages. I also updated to commit message to mention you.

[gkalpak]

Brilliant ✨
Thank you, @adrienverge 👍

[gkalpak]

Looking at this again, why not:

Suggested change

	Object.keys(manifests).indexOf(latest.latest) === -1) {
	!manifests.hasOwnProperty(latest.latest)) {

😁

[adrienverge]

Even better 👍

PR updated!

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