Long Polling

wagtail_live.publishers.polling.LongPollingPublisher

Long polling Publisher. Class Based View.

This class handles delivering new updates to the client side (Long polling technique). It accepts 2 request methods (POST and GET) which correspond to the following steps:

1. The client side initiates (shake) the communication by sending a POST request. The publisher acknowledges by sending relevant data to the client side.

2. The client side asks new updates by sending a GET request.

   Server side keeps the connection open until a new update is available. In that case, updates are directly sent to client side.

   If the polling timeout duration is reached, it sends a response containing a timeOutReached parameter which indicates the client side that there aren't updates available.

get(self, request, channel_id, *args, **kwargs)

Sends updates when they are available as long as the polling timeout isn't reached.

See base class.

Source code in wagtail_live/publishers/polling.py

def get(self, request, channel_id, *args, **kwargs):
    """
    Sends updates when they are available as long as the polling timeout isn't reached.

    See base class.
    """

    last_update_client = self.get_last_update_client_from_request(request=request)
    polling_timeout = get_polling_timeout()
    starting_time = time.time()

    while time.time() - starting_time < polling_timeout:
        live_page = get_object_or_404(self.model, channel_id=channel_id)
        last_update_ts = live_page.last_update_timestamp
        if last_update_ts > last_update_client:
            tz = timezone.utc if settings.USE_TZ else None
            updated_posts, current_posts = live_page.get_updates_since(
                last_update_ts=datetime.fromtimestamp(last_update_client, tz=tz),
            )

            return JsonResponse(
                {
                    "updates": updated_posts,
                    "currentPosts": current_posts,
                    "lastUpdateTimestamp": last_update_ts,
                }
            )

        # Maybe propose a setting so the user can define this value
        time.sleep(0.5)

    return JsonResponse({"timeOutReached": "Timeout duration reached."})

post(self, request, channel_id, *args, **kwargs)

See base class.

Source code in wagtail_live/publishers/polling.py

def post(self, request, channel_id, *args, **kwargs):
    """See base class."""

    live_page = get_object_or_404(self.model, channel_id=channel_id)
    return JsonResponse(
        {
            "livePosts": [live_post.id for live_post in live_page.live_posts],
            "lastUpdateTimestamp": live_page.last_update_timestamp,
        }
    )