Event for RECOVERABLE networking errors and subsequent retries

[chrisfillmore]

We would like to know when a networking error occurs which results in a retry. Our application tracks this information for performance metrics purposes.

To implement such a change, it seems NetworkingEngine would need to accept a PlayerInterface, but I don't know how that would work with alternative use cases as in #1297. Perhaps the PlayerInterface could be optional, and NetworkingEngine could do:

// NetworkingEngine#send_
if (error && error.severity == shaka.util.Error.Severity.RECOVERABLE) {
  if (this.playerInterface) {
    this.playerInterface.onNetworkingRetry_(error); // new method
  }
  // Move to the next URI.
  index = (index + 1) % request.uris.length;
  let shakaError = /** @type {shaka.util.Error} */(error);
  return this.send_(type, request, backoff, index, shakaError);
}

Is this feasible?

[chrisfillmore]

@theodab I don't mind sending in a PR if we agree on a design.

[theodab]

@chrisfillmore Your design seems reasonable to me, but I should probably do it. @vaage is currently working on #1297, so it'd be best to do this in-house, to avoid collisions.

[theodab]

I had a discussion with the team, and we decided that it would probably be best to avoid anything that changes the constructor of NetworkingEngine, since it is also being modified as part of #1051. Instead, I will add a method on the networking engine that adds a listener function. So you'd use it like:

player.getNetworkingEngine().addRetryListener((error) => {
  // Your listener code here.
});

[chrisfillmore]

Sounds good, thank you!

[theodab]

Okay, after another round of code review, this should be out soon.
There was some further discussion, and we decided that it should work as an event listener, using our FakeEventListener code. So you'd use it like:

player.getNetworkingEngine().addEventListener('retry', (event) => {
  let error = event.error;
  // Your listener code here.
});

Sorry we changed our minds so often on this!

[chrisfillmore]

Thanks, @theodab!