twilio_voice

Provides an interface to Twilio's Programmable Voice SDK to allow voice-over-IP (VoIP) calling into your Flutter applications. This plugin was taken from the original flutter_twilio_voice, as it seems that plugin is no longer maitained, this one is.

Features

• Receive and place calls from iOS devices, uses callkit to receive calls.
• Receive and place calls from Android devices, uses custom UI to receive calls.

Android Limitations

As iOS has CallKit, an Apple provided UI for answering calls, there is no default UI for android to receive calls, for this reason a default UI was made. To increase customization, the UI will use a splash_icon.png registered on your res/drawable folder. I havent found a way to customize colors, if you find one, please submit a pull request.

Setup

Please follow Twilio's quickstart setup for each platform, you dont need to write the native code but it will help you undestand the basic functionality of setting up your server, registering your iOS app for VOIP, etc.

iOS Setup

To customize the icon displayed on a CallKit call, Open XCode and add a png icon named 'callkit_icon' to your assets.xassets folder

Android Setup:

register in your AndroidManifest.xml the service in charge of displaying incomming call notifications:

<Application>
  .....
  <service
      android:name="com.twilio.twilio_voice.fcm.VoiceFirebaseMessagingService"
      android:stopWithTask="false">
      <intent-filter>
          <action android:name="com.google.firebase.MESSAGING_EVENT" />
      </intent-filter>
  </service>

Usage

The plugin was separated into two classes, the TwilioVoice.instance and TwilioVoice.instance.call, the first one is in charge of general configuration and the second one is in charge of managing calls.

Register iOS capabilities

• Add Audio and Voice over IP in background modes

TwilioVoice.instance

Setting the tokens

call TwilioVoice.instance.setTokens as soon as your app starts.

• accessToken provided from your server, you can see an example cloud function here.
• deviceToken is automatically handled on iOS, for android you need to pass a FCM token.

call TwilioVoice.instance.unregister to unregister from Twilio, if no access token is passed, it will use the token provided in setTokens at the same session.

Call Identifier

As incomming call UI is shown in background and the App can even be closed when receiving the calls, you can map call identifiers such as firebaseAuth userIds to real names, this operation must be done before actially receiving the call. So if you have a chat app, and know the members names, register them so when they call, the call UI can display their names and not their userIds.

Registering a client

TwilioVoice.instance.registerClient(String clientId, String clientName)

Unegistering a client

TwilioVoice.instance.unregisterClient(String clientId)

Default caller

You can also set a dafault caller, such as "unknown number" or "chat friend" in case a call comes in from an unregistered client.

TwilioVoice.instance.setDefaultCallerName(String callerName)

Call Events

use stream TwilioVoice.instance.callEventsListener to receive events from the TwilioSDK such as call events and logs, it is a broadcast so you can listen to it on different parts of your app. Some events might be missed when the app has not launched, please check out the example project to find the workarounds.

The events sent are the following

• ringing
• connected
• callEnded
• unhold
• hold
• unmute
• mute
• speakerOn
• speakerOff
• log
• answer

showMissedCallNotifications

By default a local notification will be shown to the user after missing a call, clicking on the notification will call back the user. To remove this feature, set showMissedCallNotifications to false.

Calls

Make a Call

from your own identifier to the id you want to call use extraOptions to pass additional variables to your server callback function.

 await TwilioVoice.instance.call.place(from:myId, to: clientId, extraOptions)
                   ;

Mute a Call

 TwilioVoice.instance.call.toggleMute(isMuted: true);

Toggle Speaker

 TwilioVoice.instance.call.toggleSpeaker(speakerIsOn: true);

Hang Up

 TwilioVoice.instance.call.hangUp();

Send Digits

 TwilioVoice.instance.call.sendDigits(String digits);

Permissions

Microphone

To receive and place calls you need Microphone permisisons, register the micropohone permission in your info.plist for iOS.

You can use TwilioVoice.instance.hasMicAccess and TwilioVoice.instance.requestMicAccess to check and request the permission. Permissions is also automatically requested when receiving a call.

Background calls (Android only on some devices)

Xiami devices, and maybe others, need a spetial permission to receive background calls. use TwilioVoice.instance.requiresBackgroundPermissions to check if your device requires a special permission, if it does, show a rationale explaining the user why you need the permisison. Finally call TwilioVoice.instance.requestBackgroundPermissions which will take the user to the App Settings page to enable the permission.

Localization

Because some of the UI is in native code, you need to localize those strings natively in your project. You can find in the example project localization for spanish, PRs are welcome for other languages.

---

Twilio Setup/Quickstart Help

Twilio makes use of cloud functions to generate access tokens and sends them to your app. Further, Twilio makes use of their own apps called TwiML apps to handle calling functions, etc

There are 2 major components to get Twilio Setup.

1. Cloud functions (facility generating access tokens and then handling call requests)
2. Mobile app that receives/updates tokens and performs the actual calls (see above)

---

1) Cloud Funtions

Cloud functions can be seperated or grouped together. The main 2 components are:

• generate access tokens
• make-call endpoint to actually place the call

You can host both in firebase, in TwiML apps or a mixture. The setup below assumes a mixture, where Firebase Functions hosts the access-token for eashy integration into Flutter and TwiML hosting the make-call function.

Cloud-Functions-Step-1: Create your TwiML app

This will allow you to actually place the call

Prerequisites

• A Twilio Account. Don't have one? Sign up for free!

Setting up the Application

Grab this project from github, the sample TwiML app.

cp .env.example .env

Edit .env with the three configuration parameters we gathered from above.

See configure environment below for details

Next, we need to install our dependencies from npm:

npm install

To make things easier for you, go into the src/ folder, rename the server.js file to make-call. This assumes each function will have its own file which for a new project isn't a bad idea.

Then add the following code:

const AccessToken = require('twilio').jwt.AccessToken;
const VoiceGrant = AccessToken.VoiceGrant;
const VoiceResponse = require('twilio').twiml.VoiceResponse;

/**
 * Creates an endpoint that can be used in your TwiML App as the Voice Request Url.
 * <br><br>
 * In order to make an outgoing call using Twilio Voice SDK, you need to provide a
 * TwiML App SID in the Access Token. You can run your server, make it publicly
 * accessible and use `/makeCall` endpoint as the Voice Request Url in your TwiML App.
 * <br><br>
 *
 * @returns {Object} - The Response Object with TwiMl, used to respond to an outgoing call
 * @param context
 * @param event
 * @param callback
 */
exports.handler = function(context, event, callback) {
    // The recipient of the call, a phone number or a client

    console.log(event);
    const from = event.From;
    let to = event.to;
    if(isEmptyOrNull(to)) {
        to = event.To;
        if(isEmptyOrNull(to)) {
            console.error("Could not find someone to call");
            to = undefined;
        }
    }


    const voiceResponse = new VoiceResponse();

    if (!to) {
        voiceResponse.say("Welcome, you made your first call.");
    } else if (isNumber(to)) {
      const dial = voiceResponse.dial({callerId : callerNumber});
      dial.number(to);
  } else {
        console.log(`Calling [${from}] -> [${to}]`)

        const dial = voiceResponse.dial({callerId: to, timeout: 30, record: "record-from-answer-dual", trim: "trim-silence"});
        dial.client(to);
    }

    callback(null, voiceResponse);
}

const isEmptyOrNull = (s) => {
    return !s || s === '';
}

Setup Twilio CLI

Ensure you are logged into twilio-cli. First, install twilio-cli with

npm i twilio-cli -g

Afterwards, login to twilio using: (b sure to provide Twilio account SID and auth token for login):

twilio login

We need to generate an app, this will give us an App SID to use later in firebase functions, (see this more info)

Create TwiML app

We need to create a TwiML app that will allow us to host a make-call function:

twilio api:core:applications:create \
--friendly-name=my-twiml-app \
--voice-method=POST \
--voice-url="https://my-quickstart-dev.twil.io/make-call"

This will present you with a application SID in the format APxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx, we will use this later in firebase config and generating push credential keys.

Very Important! The URL given here https://my-quickstart-dev.twil.io/make-call won't work for you. Once you deployed your TwiML application (later), a URL is given to you (on first deploy) which you need to copy and paste as your Request URL call. If you don't do this, calling won't work!

Configure environment

ensure you have a .env file in the root of your project in the same directory as package.json

next, edit the .env file in the format

ACCOUNT_SID=(insert account SID)
APP_SID=(insert App SID, found on TwiML app or the APxxxxx key above)

API_KEY and API_KEY_SECRET aren't necessary here since we won't be using them

Get Push Credential:

We will generate them a bit later

• Android FCM: Android instructions
• Apple APNS: Apple instructions

You will get a Push Credential SID in the format: CRxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx, use this in PUSH_CREDENTIAL_SID

Deploying

Now lets deploy.

Please note: Check you have configured your environment first

Navigate to root directory, and deploy using

twilio serverless:deploy

Very Important!: once complete (if you haven't done so), make sure to add the make-call endpoint your Twilio app's Request URL in the main Twilio page. This URL will be shown as part of the deployment text. If this isn't done, calling won't work!

Cloud-Functions-Step-2: Setup Firebase & Configuration

Twilio's configurations are stored in .runtimeconfig.json which contains:

"auth_token": "",
"account_sid": "",
"app_sid": "",
"phone": "",
"api_key": "",
"api_key_secret": "",
"android_push_credential": "",
"apple_push_credential_debug": "",
"apple_push_credential_release": ""

Note: this is used for local emulator testing, but you need to deploy these to your firebase function application once you are ready to go live. If you don't, this won't work!

Push Credentials are created once (for iOS, Android) and used to generate access-tokens, a callback function for all Twilio apps to use for their communication.

---

Below are the 3 operations you need to run to generate push credentials that should be added into the .runtimeconfig.json above

Android

To generate Android push credentials, get the Cloud Messaging server key from Firebase FCM, and add it to the following:

twilio api:chat:v2:credentials:create \
--type=fcm \
--friendly-name="voice-push-credential-fcm" \
--secret=SERVER_KEY_VALUE

and then place into the field: android_push_credential above

This generated a push credential SID in the format CRxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx which must be used to generate access tokens for android devices.

see for more info: https://github.com/twilio/voice-quickstart-android#7-create-a-push-credential-using-your-fcm-server-key

iOS

Similar to Android, but more steps including using .p12 certificates. To get these certificates, login into Apple's developer site and go to the certificates page. You need to generate a VoIP Services certificate as shown below.

Please note: there are 2 different modes: sandbox and production.

- SandBox Mode

Using sandbox VoIP certificate:

Export your VoIP Service Certificate as a .p12 file from Keychain Access and extract the certificate and private key from the .p12 file using the openssl command.

$ openssl pkcs12 -in PATH_TO_YOUR_SANDBOX_P12 -nokeys -out sandbox_cert.pem -nodes
$ openssl pkcs12 -in PATH_TO_YOUR_SANDBOX_P12 -nocerts -out sandbox_key.pem -nodes
$ openssl rsa -in sandbox_key.pem -out sandbox_key.pem

Using sandbox certificates, generate credential:

twilio api:chat:v2:credentials:create \
--type=apn \
--sandbox \
--friendly-name="voice-push-credential (sandbox)" \
--certificate="$(cat PATH_TO_SANDBOX_CERT_PEM)" \
--private-key="$(cat PATH_TO_SANDBOX_KEY_PEM)"

then place it into the field apple_push_credential_debug

- Production Mode

Using production VoIP certificate:

Export your VoIP Service Certificate as a .p12 file from Keychain Access and extract the certificate and private key from the .p12 file using the openssl command.

$ openssl pkcs12 -in PATH_TO_YOUR_P12 -nokeys -out prod_cert.pem -nodes
$ openssl pkcs12 -in PATH_TO_YOUR_P12 -nocerts -out prod_key.pem -nodes
$ openssl rsa -in prod_key.pem -out prod_key.pem

Using production certificates, generate credential:

twilio api:chat:v2:credentials:create \
--type=apn \
--friendly-name="voice-push-credential (production)" \
--certificate="$(cat PATH_TO_PROD_CERT_PEM)" \
--private-key="$(cat PATH_TO_PROD_KEY_PEM)"

then place it into the field apple_push_credential_release

see for more info: https://github.com/twilio/voice-quickstart-ios#6-create-a-push-credential-with-your-voip-service-certificate

---

Cloud-Functions-Step-3: Generate access tokens via cloud function

HTTP/GET api-voice-accessToken

To generate access-tokens, the following firebase function is used:

Please Note the default time is 1 hour token validity.

See for more info: https://github.com/twilio/voice-quickstart-android/blob/master/Docs/access-token.md

Firebase Cloud Function: access-token

const { AccessToken } = require('twilio').jwt;
const functions = require('firebase-functions');

const { VoiceGrant } = AccessToken;

/**
 * Creates an access token with VoiceGrant using your Twilio credentials.
 *
 * @param {Object} request - POST or GET request that provides the recipient of the call, a phone number or a client
 * @param {Object} response - The Response Object for the http request
 * @returns {string} - The Access Token string and expiry date in milliseconds
 */
exports.accessToken = functions.https.onCall((payload, context) => {
    // Check user authenticated
    if (typeof (context.auth) === 'undefined') {
        throw new functions.https.HttpsError('unauthenticated', 'The function must be called while authenticated');
    }
    let userId = context.auth.uid;

    console.log('creating access token for ', userId);

    //configuration using firebase environment variables
    const twilioConfig = functions.config().twilio;
    const accountSid = twilioConfig.account_sid;
    const apiKey = twilioConfig.api_key;
    const apiSecret = twilioConfig.api_key_secret;
    const outgoingApplicationSid = twilioConfig.app_sid;

    // Used specifically for creating Voice tokens, we need to use seperate push credentials for each platform. 
    // iOS has different APNs environments, so we need to distinguish between sandbox & production as the one won't work in the other.
    let pushCredSid;
    if (payload.isIOS === true) {
        console.log('creating access token for iOS');
        pushCredSid = payload.production ? twilioConfig.apple_push_credential_release
            : (twilioConfig.apple_push_credential_debug || twilioConfig.apple_push_credential_release);
    } else if (payload.isAndroid === true) {
        console.log('creating access token for Android');
        pushCredSid = twilioConfig.android_push_credential;
    } else {
        throw new functions.https.HttpsError('unknown_platform', 'No platform specified');
    }

    // generate token valid for 24 hours - minimum is 3min, max is 24 hours, default is 1 hour
    const dateTime = new Date();
    dateTime.setDate(dateTime.getDate()+1);
    // Create an access token which we will sign and return to the client,
    // containing the grant we just created
    const voiceGrant = new VoiceGrant({
        outgoingApplicationSid,
        pushCredentialSid: pushCredSid,
    });

    // Create an access token which we will sign and return to the client,
    // containing the grant we just created
    const token = new AccessToken(accountSid, apiKey, apiSecret);
    token.addGrant(voiceGrant);

    // use firebase ID for identity
    token.identity = userId;
    console.log(`Token:${token.toJwt()}`);

    // return json object
    return {
        "jwt_token": token.toJwt(),
        "expiry_date": dateTime.getTime()
    };
});

Add the function above to your Firebase Functions application, see this for more help on creating a firebase functions project

After you are done, deploy your .runtimeconfig.json, see this for more help.

Once done with everything above, deploy your firebase function with this:

firebase deploy --only functions

Done!

Calling should work naturally - just make sure to fetch the token from the endpoint and you can call

See example code, make sure to change the voice-accessToken to your function name, given to you by firebase when deploying (as part of the deploy text)