ussd-at

Installation

$ npm install ussd-at

or

$ yarn add ussd-at

Features

• Use intuitive states to compose USSD menus
• Makes it easier to build complex nested menus
• Use simple input matching or regular expressions, custom asynchronous functions to resolve routes from one state to another
• The state-based approach allows you to easily modularize complex menus in different files

Quick Example

const UssdMenu = require('ussd-at');
let menu = new UssdMenu();

// Define menu states
menu.startState({
    run: () => {
        // use menu.con() to send response without terminating session      
        menu.con('Welcome. Choose option:' +
            '\n1. Show Balance' +
            '\n2. Buy Airtime');
    },
    // next object links to next state based on user input
    next: {
        '1': 'pin',
        '2': 'buyAirtime'
    }
});

menu.state('pin', {
    run: () => {
        if(menu.wrongPin){
            menu.wrongPin=false;
            menu.con("Wrong pin. please try gain");
        }else{
            menu.con("Enter your pin to proceed");
        }
       
    },
    next:{
        //regex start with *
        "*^\\d{4}$":"check_pin"
    }
});

menu.state('check_pin', {
    run: () => {
      let enteredPin = menu.val;

      if(enteredPin == '1234'){
          menu.end("your balance is 150")
      }else{
          menu.wrongPin=true;
          menu.go("pin");
          // remember to call the below function when looping a state
          // for the correct input eg for the correct pin as in this example.
          menu.discardThis()
      }
    }
});



menu.state('buyAirtime', {
    run: () => {
        menu.con('Enter amount:');
    },
    next: {
        // using regex to match user input to next state
        '*\\d+': 'buyAirtime.amount'
    }
});

// nesting states
menu.state('buyAirtime.amount', {
    run: () => {
        // use menu.val to access user input value
        var amount = Number(menu.val);
        buyAirtime(menu.args.phoneNumber, amount).then(function(res){
            menu.end('Airtime bought successfully.');
        });
    }
});

// Registering USSD handler with Express

app.post('/ussd', async (req, res)=>{
    const result = await menu.run(req.body)
    res.send(result);
});

Guide

Introduction

The USSD Menu Builder uses a state machine to create a USSD menu. A state is created for each menu. Each state has a unique name and a set of rules used to link to other states based on the user input.

Creating a menu

Before you can create any states, you first need to create an instance of the menu.

const UssdMenu = require('ussd-at');
const menu = new UssdMenu();

Running the menu

The menu.run(args, resultCallback) goes through the menu and finds the appropriate state to run based on the user input.

The args object should contain the following keys coming from the Africastalking API:

• sessionId: unique session ID that persists through the entire USSD session, can be used to store temporary that may be retrieved from different states during the session
• serviceCode: the USSD code registered with your serviceCode
• phoneNumber: the end user's phone Number
• text: The raw USSD input. It has the following format 1*2*4*1: a string containing the input at each hop, separated by the asterisk symbol (*). This is parsed by the UssdMenu to find the appropriate state to run at each hop.

After the matched state runs, the resultCallback is called with the response from the state.

Note: The menu also returns a promise that can be resolved if you need to do anything with the final response. for example:

let resp = await menu.run(args) // resultCallback is not necessarry if you intend to run the menu in an async function

Here's an example registering a handler with the express framework:

app.post('/ussd', (req, res) => {
    let args = {
        phoneNumber: req.body.phoneNumber,
        sessionId: req.body.sessionId,
        serviceCode: req.body.serviceCode,
        text: req.body.text
    };
    menu.run(args, resMsg => {
        res.send(resMsg);
    });
})

Handling menu.run response:

app.post('/ussd', async (req, res) => {
    let args = {
        phoneNumber: req.body.phoneNumber,
        sessionId: req.body.sessionId,
        serviceCode: req.body.serviceCode,
        text: req.body.text
    };
    let resMsg = await menu.run(args);
    res.send(resMsg);
})

Defining states

The menu.state(name, options) method is used to define states. I takes the name of the state and an object with the following properites:

• run: a function that's called when the state is resolved
• next (optional): an object that contains rules of how to match the input of this state to other states. This is not required for final states.
• defaultNext (optional): the name of the state to default to if the user input could not be matched by the rules defined in the next object. If not provided, the same state will be used as a fallback i.e. the same menu will be displayed to the user.

Here's an example:

menu.state('stateName', {
    run: function(){
        menu.con('Choose Option' +
            '\n1. Load Account' +
            '\n2. View Catalogue' +
            '\n3. Check Balance'
        );
    },
    next: {
        '1': 'loadAccount',
        '2': 'catalogue',
        '3': 'balance'
    },
    defaultNext: 'invalidOption'
});

The run function

Each state defines it's own run method which is called when that state is matched. This is where you should place the logic for a given state.

Retrieving user input

Use menu.val property to access the current user input.

Accessing ussd parameters

You can access the ussd parameters through the menu.args object. This parameters should come from the API Gateway and are passed to the menu.run method.

Sending the response

You must use either (not both) of the two methods to send a response to be displayed to the user:

• menu.con(msg): Sends the result to be displayed to the user without terminating the session i.e. the user can reply with further input.
• menu.end(msg): Sends the response to be displayed to the user and requests the session to be terminated i.e. the user cannot provide further input. Note: This consequently makes the state a final state and therefore the next object does not need to be defined

Example:

menu.state('thisState', {
    run: function(){
        let value = menu.val;
        let session = getSession(menu.args.sessionId);
        let phone = menu.args.phoneNumber;
        session.set('phone', phone);
        session.set('value', value);
        menu.end('You entered: ' + value);
    }
});

The Start State

This is the first state or first menu to be displayed by the user. It is created using the menu.startState(options). It uses the reserved name '__start__'.

menu.startState({
    run: function(){
        ...
    }
    next: {
        ...
    }
});

Matching States

To link states you use the next object to map user input to a state name. You can match input directly by value or with a regular expression.

Matching direct values

Simply add the expected string value as a key in the next object.

Matching with regular expressions

Begin the key with an asterisk (*) to indicate that the key should be treated like a regular expression e.g. '*\\[a-zA-Z]+' would match any input containing only lowercase or uppercase letters.

Remember you can use menu.val in the matched state to retrieve the actual user input.

Example:

menu.state('registration', {
    run: function(){
        menu.con('Enter your name');
    },
    next: {
        '*[a-zA-Z]+': 'registration.name'
    }
});

menu.state('registration.name', {
    run: function(){
        let name = menu.val;
        let session = getSession(menu.args.sessionId);
        session.set('name', name);
        menu.con('Enter your email');
    },
    next: {
        '*\\w+@\\w+\\.\\w+': 'registration.email'
    }
});

Matching with empty rule on Start State

If the start state does not define a run method, you provide an empty string as key in next to redirect to another state.

menu.startState({
    next: {
        '': function(){
            if(user){
                return 'userMenu';
            }
            else {
                return 'registerMenu';
            }
        }
    }
});

Linking states

Beside mapping user input directly to a state name, you can map it to a function with returns a state name, synchronously with a simple return statement or asynchronously with a callback or a promise.

Mapping to a direct state name

menu.state('thisState', {
    ...
    next: {
        'input': 'nextState'
    }
})

Mapping to a synchronous function

menu.state('thisState', {
    ...
    next: {
        'input': function(){
            if(test){
                return 'nextState';
            } else {
                return 'otherState';
            }
        }
    }
});

Jumping to different state

You can jump to a different state from the run function of one state using the menu.go(stateName) method. This effectively breaks the state chain (subsequent states will not be reachable) and is therefore only useful if jumping to a final state.

menu.state('thisState', {
    run: function(){
        menu.go('otherState');
    }
});

menu.state('otherState', {
    run: function(){
        menu.end('Thank you!');
    }
});

The menu.goStart() method can be used to jump to the start state from within another state.

Nesting states

The library treats a USSD menu like a chain of interlinked states and therefore has not internal concept of nesting. However you can achieve complex menus with nested submenus by linking states appropriately. In addition you could use a naming convention of your choice to make it clearer to see how states are related. In these examples I used the following convention of separating menu levels with a dot.

Sessions

You can store temporary user data that persists through an entire session. The library provides a way for you to define your own custom session handler so you're free to use whatever storage backend or driver you want. The menu provides an easy interface to set and retrieve session data within states based on the implementation you provide.

Configuring handlers

The menu.sessionConfig(config) method is used to define your session handler. It accepts an object with the implementations of the following methods:

• start [function(sessionId, callback)]: used to initialize a new session, invoked internally by the menu.run() method before any state is called.
• end [function(sessionId, callback)]: used to delete current session, invoked internally by the menu.end() method.
• set [function(sessionId, key, value, callback)]: used to store a key-value pair in the current session, invoked internally by menu.session.set().
• get [function(sessionId, key, callback)]: used to retrieve a value from the current session by key, invoked internally by menu.session.get().

Example using local memory for storage

let sessions = {};

let menu = new UssdMenu();
menu.sessionConfig({
    start: (sessionId, callback){
        // initialize current session if it doesn't exist
        // this is called by menu.run()
        if(!(sessionId in sessions)) sessions[sessionId] = {};
        callback();
    },
    end: (sessionId, callback){
        // clear current session
        // this is called by menu.end()
        delete sessions[sessionId];
        callback();
    },
    set: (sessionId, key, value, callback) => {
        // store key-value pair in current session
        sessions[sessionId][key] = value;
        callback();
    },
    get: (sessionId, key, callback){
        // retrieve value by key in current session
        let value = sessions[sessionId][key];
        callback(null, value);
    }
});

Note: Instead of callbacks, you may also return promises from those methods:

menu.sessionConfig({
    ...
    get: function(sessionId, key){
        return new Promise((resolve, reject) => {
            let value = sessions[sessionId][key];
            resolve(value);
        });
    }
})

Setting and getting data from the current session

And then to add and retrieve data inside states, use the menu.session object:

menu.state('someState', {
    run: () => {
        let firstName = menu.val;
        menu.session.set('firstName', firstName)
        .then( () => {
            menu.con('Enter your last name');
        })
    }
    ...
})
...
menu.state('otherState', {
    run: () => {
        menu.session.get('firstName')
        .then( firstName => {
            // do something with the value
            console.log(firstName);
            ...
            menu.con('Next');
        })
    }
})
...

Note: The menu.session's methods also work with callbacks:

menu.session.set('key', 'value', (err) => {
    menu.con('...');
});

menu.session.get('key', (err, value) => {
    console.log(value);
    ...
});

Note: It's not required to configure a session handler. You can access your storage driver directly if you prefer. However if you do configure a handler using the above method then you should provide implementations for all the 4 methods as shown above..

Errors

UssdMenu instances emit an error event when an error occurs during the state resolution process (e.g: "state not found" or "run function not defined").

menu.startState({
    ...
    next: {
        '1': 'nonExistentState'
    }
});

menu.on('error', (err) => {
    // handle errors
    console.log('Error', err);
});


args.text = '1';
menu.run(args);