Add clearBuffer method to ReplaySubject

[crossan007]

Description:
Adds a clearBuffer() method on ReplaySubject. This allows consumers to clear the buffer of events which have already been delivered to the ReplaySubject.

This addresses an edge case where a developer may want to avoid disrupting existing subscriptions to a ReplaySubject and prevent new subscribers from receiving the whole history before a point in time (while maintaining the behavior which facilitates new subscribers to receive history)

This should be a preferred solution over the various proposed workarounds at:

• https://stackoverflow.com/questions/58812252/angular-8-replaysubject-clear-delete-history-and-cache
• https://stackoverflow.com/questions/51145664/resetting-replaysubject-in-rxjs-6

An alternative workaround may be to extend ReplaySubject as ClearableReplaySubject and adjust the visibility modifier on the events[] from private to protected so that this method can be implemented on the child class

BREAKING CHANGE:

Related issue (if exists):

[benlesh]

I'll leave it to the core team, and we'll discuss it, but In general, I'm inclined to say that we're probably not going to implement this feature for a few reasons:

1. It introduces another vector for mutability to ReplaySubject.
2. It has no tests
3. The use cases aren't clearly defined.

As a workaround, someone could take a more reactive approach, particularly with the new share features:

const shared = source$.pipe(
  // If some stream of resets notifies, error with a known error (like "RESET")
  mergeWith(reset$.pipe(tap(() => { throw 'RESET' })),
  // multicast through a ReplaySubject. `share` will reset this
  // ReplaySubject on error by default.
  share({
    connector: () => new ReplaySubject(),
  }),
  retry({
    // If the error is the known error of "RESET", then reconnect everyone
    // if it's any other error, just throw it.
    delay: (err) => {
       if (err === 'RESET') {
         return of(true);
       } else {
         throw error;
       }
    }
  })
)

[benlesh]

Core Team: We don't want to move forward with this one.

Thank you for your effort, @crossan007

[crossan007]

Okay, thanks for the feedback.

I'm using this implementation currently to consume AngularFirestore observables in various locations in my app, in a way that I can clear the replay buffer when AngularFireauth context changes.

I.e. user logs out / user changes, I don't want the old buffer available.

[douglascayers]

If this helps anyone help, I've put @benlesh's example into a ResettableReplaySubject class.

Source code with example available at https://stackblitz.com/edit/rxjs-x4n1rt?file=index.ts