My messages are delivered out of flow sequence order and how do I compensate? - json

Question

I wish to use Twilio in the context of an adventure game. As the gamer (Geocacher) progresses on an actual treasure (cache) hunt, clues are given by text when certain code words or numbers are entered as part of the thread. I am very comfortable creating the flow in Studio and have a working flow that is debugged and ready to go.
Not so fast, grasshopper! Strange things started to happen when beta testing the flow. Basically texts that show as being sent arrive to the user out of sequence in the thread. The SM logs show everything is working correctly (message sent) but, what I call Zombie messages arrive to the user after a previous message has arrived. The Zombies are legitimate messages from the Flow but out of the correct sequence and that makes the thread unusable for my purposes.
I learned too late in my "programming" that Twilio states, "If you send multiple SMS messages to the same user in a short time, Twilio cannot guarantee that those messages will arrive in the order that you sent them." Ugh!
So , I started with the Help Techs at Twillio and one solution is to create a subflow that basically is inserted after a Send Message Widget. This sub flow basically Fetches the message via the SMS SID to check for SMS status. If status is "delivered", we can safely say the message has been received by the recipient and then permit the next message in the flow.
That sound great but I am not a programmer and will never be able to integrate the suggested code much less debug it when things don't work. There might be many other approaches that you guys can suggest. The task is 1.) Send a message, 2.) Run a subflow that checks for message delivery, 3.) send the next message in the sequence.
I need to move on to implementation and this type of sub flow is out of my wheelhouse. I am willing to pay for programming help.
I can post the JSON code that was created as a straw man but have no idea how to use it and if it is the optimum solution if that is of help. It would seem that a lot of folks experience this issue and would like a solution. A nice tight JSON subflow with directions on how to insert would seem to be a necessary part of the Widget toolkit provided by Twillio in Studio.
Please Help Me! =)

Answer 1

As you stated, the delivery of the message cannot be guaranteed. Checking the status of the sent message is the most reliable, using a subflow, a Twilio Function, or a combination. Just keep in mind that Twilio Functions have a 10s execution time limit. I don't expect delivering the SMS will take longer than 10s is most cases. If you're worried about edge cases, you'd have to loop the check for the status multiple times. I'll share a proof of concept later for this.
An easier way, but it still doesn't guarantee delivery order, would be to add some delay between each message. There's no built-in delay widget, but here's code on how to create a Twilio Function to add delays, up to 10s.
A more hacky way to implement delays without having to use this Twilio Function, is to use the Send & Wait For Reply Widget and configure the "Stop Gathering After" property to the amount of delay you'd like to add. If the user responds, connect to the next widget, if they don't also connect to the widget.
As mentioned earlier, here's th Subflow + Function proof of concept I hacked together:
First, create a Twilio Functions Service, in the service create two functions:
/delay:
// Helper function for quickly adding await-able "pauses" to JavaScript
const sleep = (delay) => new Promise((resolve) => setTimeout(resolve, delay));
exports.handler = async (context, event, callback) => {
// A custom delay value could be passed to the Function, either via
// request parameters or by the Run Function Widget
// Default to a 5 second delay
const delay = event.delay || 5000;
// Pause Function for the specified number of ms
await sleep(delay);
// Once the delay has passed, return a success message, TwiML, or
// any other content to whatever invoked this Function.
return callback(null, `Timer up: ${delay}ms`);
};
/get-message:
exports.handler = function(context, event, callback) {
const messageSid = event.message_sid,
client = context.getTwilioClient();
if(!event.message_sid) throw "message_sid parameter is required.";
client.messages(messageSid)
.fetch()
.then(message => callback(null, message))
.catch((error) => {
console.error(error);
return callback(error);
});
};
Then, create a Studio Flow named something like "Send and Wait until Delivered".
In this flow, you send the message, grabbing the message body passed in from the parent flow, {{trigger.parent.parameters.message_body}}.
Then, you run the /get-message Function, and check the message status.
If delivered, set status variable to delivered. This variable will be passed back to the parent flow. If any of these accepted,queued,sending,sent, then the message is still in route, so wait a second using the /delay function, then loop back to the /get-message function.
If any other status, it is assumed there's something wrong and status is set to error.
Now you can create your parent flow where you call the subflow, specifying the message_body parameter. Then you can check the status variable for the subflow, whether it is 'delivered' or 'error'.
You can find the export for the subflow and the parent flow in this GitHub Gist. You can import it and it could be useful as a reference.
Personally, I'd add the /delay function, and use that after every message, adding a couple of seconds delay. I'd personally assume the delay adds enough buffer for no zombie messages to appear.
Note: The code, proof of concept, and advice is offered as is without liability to me or Twilio. It is not tested against a production workload, so make sure you test this thoroughly for your use case!