Nativité 2017: creating a Facebook Messenger bot
A few days ago I described Nativité, a pastoral Christmas game which I made last year.. I’m updating it for 2017, switching from SMS notifications to a Facebook Messenger bot. Here’s the latest game:
Last year, I used Firebase. This was mostly an excuse to try out Firebase. I found Firebase pleasant, but also quickly found its limitations. I wanted to send SMS messages on custom server-side events, and couldn’t figure out how to do this in a secure manner. I ended up making client-side calls to an external server to fulfil this, which is a horrible hack!
It also turns out SMS is expensive. There are four sheep in the game; each sheep moved a minimum of twelve times; and each move sends an SMS to the four girls and to me. I was using AWS SNS to send messages, which at the time was charging around 10c for each message to France. That’s a minimum of 4 × 12 × 5 × 10c = $24 in messaging costs! (Today’s SNS pricing for SMS is much cheaper and more uniform: around 0.64c per message to anywhere. But this is still expensive.)
When I was making Nativité last year, I was in Dedham, deepest rural Essex. Testing SMS required waving my phone around in the garden, freezing, trying to attract the attention of some distant cell tower. I would receive a few dozen test messages at once, and see my AWS bill grow a few dollars. (Since then, I’ve discovered “WiFi calling”, which seems to magically transfer cellular data over WiFi. But I didn’t know about it then!)
If instead I were to use Facebook Messenger, the end-user experience would be more pleasant, my bill would be $0, and I could test anywhere with an internet connection. So I did that.
To make a Facebook bot, I needed to switch out “serverless” for a more standard setup (Heroku for the server-side, Netlify for the client-side, and Pusher for some realtime magic). After reimplementing everything, the new client is hosted at https://nativite-2017.lantreibecq.com/.
A Facebook Messenger bot is a Facebook App
with the Messenger product added to it.
Mine is app
But I don’t think end-users see Facebook Apps directly.
Instead, Facebook Messenger bots communicate via a Facebook Page:
if you own both the app and the page,
you can give the app permission to communicate via the page.
The Page for Nativité is
(it was surprisingly hard to find a free unique name).
Facebook Pages have Messenger accounts which users can send messages to;
here is the Messenger account for
Pages can’t initiate conversations.
Users have to send a message to a Page before it can reply.
I’m using this as a “subscription” mechanism;
anyone sending a message to
TheChristChild is subscribed to all updates.
Facebook Apps have a review process. Before an App/Page can interact with the public, it must have gone through review. An exception to this is a list of “testers” which can be added to the app. Surprisingly, it seems that a user does not have to give permission to be added as a tester. So I added my partner and all her family as testers.
Oh, I also added a little crown to the sheep that’s currently winning. That’s all for this year.
More by Jim
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- A probabilistic pub quiz for nerds
- Smear phishing: a new Android vulnerability
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