Django backend

Publishing events and authorising channels from Django with the Python server SDK.

The Python server SDK for this protocol works against Arc unmodified: only host, port and ssl change.

pip install pusher

# settings.py
ARC = {
    "app_id": "1",
    "key": "<app key>",
    "secret": "<app secret>",
    "host": "arc.example.com",
    "port": 443,
    "ssl": True,
    # Only if you use encrypted channels:
    # "encryption_master_key_base64": "<master key>",
}

# realtime.py
import pusher
from django.conf import settings

arc = pusher.Pusher(**settings.ARC)

Publishing

def create_order(request):
    order = Order.objects.create(...)

    arc.trigger(
        "orders",
        "created",
        {"id": order.id, "total": str(order.total)},
        request.POST.get("socket_id"),   # don't echo to the tab that did it
    )
    return JsonResponse({"id": order.id})

Pass the browser's socket_id through whenever a request came from a client that has already updated its own view. Up to 100 channels per publish, and up to 10 events in a trigger_batch.

Authorising channels

def realtime_auth(request):
    channel, socket_id = request.POST["channel_name"], request.POST["socket_id"]

    if not can_join(request.user, channel):
        return HttpResponseForbidden()

    data = None
    if channel.startswith("presence-"):
        data = {"user_id": str(request.user.id), "user_info": {"name": request.user.get_full_name()}}

    return JsonResponse(arc.authenticate(channel=channel, socket_id=socket_id, custom_data=data))

Sending to one user

def sign_in_realtime(request):
    return JsonResponse(arc.authenticate_user(
        socket_id=request.POST["socket_id"],
        user_data={"id": str(request.user.id), "name": request.user.get_full_name()},
    ))

arc.send_to_user(str(user.id), "notification", {"text": "Your export is ready"})
arc.terminate_user_connections(str(user.id))   # after a ban or a password change

Receiving webhooks

@csrf_exempt
def realtime_webhook(request):
    webhook = arc.validate_webhook(
        key=request.headers.get("X-Pusher-Key"),
        signature=request.headers.get("X-Pusher-Signature"),
        body=request.body,          # raw bytes, before parsing
    )
    if webhook is None:
        return HttpResponseForbidden()

    for event in webhook["events"]:
        if event["name"] == "channel_vacated":
            Room.objects.filter(channel=event["channel"]).update(active=False)

    return HttpResponse(status=200)

Answer quickly and do the work afterwards: Arc times out a delivery at 10 seconds and retries 5xx, so a slow handler turns into duplicate work.

Reading state

arc.channels_info(prefix_filter="presence-", attributes=["user_count"])
arc.channel_info("presence-room-1", attributes=["user_count"])
arc.users_info("presence-room-1")