Fix using signaling settings while being refetched

[danxuliu]

Follow up to #7472

When the external signaling server returns the error token_expired the signaling settings are fetched again. However, if there are further requests and token_expired is returned again the previous fetch is canceled and a new one started instead, which caused the settings to be temporary set to null. The signaling settings are expected to always be an object, so setting them to null could cause an error if they were used during that time (for example, during a reconnection, which caused the signaling object to "hang" and not do any further connection attempt).

Preventing the settings to be nullified is only half of the story, though; token_expired can be thrown when trying to connect, and errors thrown when trying to connect cause a reconnection attempt. This could end in a reconnection loop, as each token_expired error would cause another fetch of the settings, cancelling the previous fetch and thus preventing the settings to be updated, and as the previous settings would be still used any connection attempt would end again in another token_expired error.

To solve all that now any connection attempt done after receiving a token_expired error is deferred until the signaling settings were updated.

Note that the previous signaling settings are kept to ensure that a signaling object is always available, even if outdated. However, any usage of the outdated signaling settings is expected to cause a token_expired error to be thrown; right now that only happens during connections, so only that code needs to wait for the settings to be fetched again.

How to test

• Add sleep(5); to SignalingController::getSettings() to delay getting the signaling settings
• Add a helper to expose the signaling object, for example, in src/utils/webrtc/index.js:

window.getSignaling = function() {
	return signaling
}

• Rebuild the code
• Setup the HPB
• Open a conversation in Talk
• Wait more than one minute to ensure that the authentication token received in the signaling settings has expired
• In the browser console, run getSignaling().forceReconnect(true)

Result with this pull request

The first reconnection attempt fails with token_expired, and then the connection with the signaling server is established again once the signaling settings were updated

Result without this pull request

The first and second reconnection attempts fail with token_expired, and this.settings is null is thrown in the third and last attempt, as it was done while fetching the settings again for the second time, which cancelled the first fetching and caused the settings to be set to null

[danxuliu]

/backport to stable25

[danxuliu]

/backport to stable27

[danxuliu]

/backport to stable26

[Antreesy]

Tested, seems to work as expected.
Code is clean and readable, algorithm is clean.

Thanks for notes and explanations!