Django Tips: Using Cache for Stateful HTTP

How do you keep state when working with a stateless protocol like HTTP? One possible answer is to use a cache back-end.

I'm working on an IVR application demo with Django and Twilio. The caller will make multiple choices using the phone keyboard. All of this needs to be put together and sent back to another server for processing. In my views I've added a simple cache get/set lines to preserve the selection.

Here's how it looks with actual application logic omitted

def incoming_call(request):
    call_sid = request.GET.get('CallSid', '')
    caller_id = request.GET.get('From', '')

    state = {'from' : caller_id}
    cache.set(call_sid, state)

    return render(request, 'step2.xml')

def step2(request):
    call_sid = request.GET.get('CallSid', '')
    selection = int(request.GET.get('Digits', 0))

    state = cache.get(call_sid, {})
    state['step2_selection'] = selection
    cache.set(call_sid, state)

    return render(request, 'final_step.xml')


def final_step(request):
    call_sid = request.GET.get('CallSid', '')
    selection = int(request.GET.get('Digits', 1))

    state = cache.get(call_sid, {})
    state['final_step_selection'] = selection

    Backend.process_user_selections(state)

    return render(request, 'thank_you.xml')

At each step Django will update the current state associated with this call and return a TwiML XML response. CallSid is a handy unique identifier provided by Twilio.

I am using the latest django-s3-cache version which properly works with directories. When going to production that will likely switch to Amazon ElastiCache.

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