TaskRouter.js v2: Reconnect Logic

• A heartbeat is set up on the WebSocket connection.
• The heartbeat expects a signal (message) from Twilio server every 15 seconds.
• If no message is received within 30 seconds, it considers the connection lost.
• The onsleep handler of the heartbeat does the following:
  • Emits a disconnected event ('Connection lost').
  • Removes all event handlers from the WebSocket.
  • Explicitly closes the WebSocket.
  • Immediately calls _reconnectWebSocket() to initiate reconnection.

If the WebSocket closes due to network changes or other reasons, the onclose handler does the following:

• Emits a disconnected event with a reason.
• Clears heartbeat behavior.
• If the reconnect flag is true, calls _reconnectWebSocket().

TaskRouter SDK v2 handles reconnection automatically, so in most cases, developers don't need to implement any custom logic to manage disconnects or reconnects manually. The _reconnectWebSocket() method performs these steps:

• Marks _isReconnecting = true to avoid overlapping reconnections.
• Removes all event handlers from the old WebSocket.
• Clears the heartbeat's behavior.
• Uses a backoff algorithm (generateBackOffInterval(numberOfAttempts)) to avoid overwhelming reconnection attempts.
  • Starts with 800-millisecond delay and uses exponential backoff with jitter up to 30 seconds.
• After the timeout, checks if the reconnect flag is still true and then:
  • Increments numberOfAttempts.
  • Calls createWebSocket() to establish a new connection.

The token should be refreshed externally and passed to the EventBridgeSignaling class using the updateToken method. If a new token isn't provided before the current one expires, the WebSocket connection will be closed. The token's expiry is handled using setTokenExpirationEvent():

• Emits a tokenExpired event when the token is near expiry with a buffer of 5 seconds.
• Sets the reconnect flag to false to prevent reconnection with an expired token.

If SDK users prefer to handle disconnections themselves, they can manually call disconnect(). In this case, the SDK won't attempt to reconnect automatically. To reestablish the connection, the user must create a new instance of the Worker.

Calling disconnect() does the following:

• Sets the reconnect flag to false.
• Removes WebSocket event handlers.
• Closes the WebSocket.
• Emits a disconnected event ('SDK Disconnect').

1. Network connection drops.
2. Heartbeat misses multiple beats, triggering the onsleep handler.
3. The SDK emits disconnected event, closes the WebSocket, and calls _reconnectWebSocket().
4. A backoff timer runs and tries to reconnect.
5. If the token is still valid, it reconnects and emits the connected event.

When the WebSocket connection is reestablished, the reservation and task objects are automatically fetched from the server again. As a result, any old event listeners attached to the previous objects will no longer receive events.

In other words, after the Worker object has reconnected and it's in the ready state, new listeners should be created for the reservations and tasks that were fetched during the reconnection.

When a Worker disconnects and the reservation times out, a new reservation is created for the next available Worker.