Warm Transfer with Ruby and Sinatra

Time to read: 4 minutes

January 10, 2017
Written by
Mario Celi
Contributor
Opinions expressed by Twilio contributors are their own
Reviewed by
Paul Kamp
Twilion
Kat King
Twilion
Jose Oliveros
Contributor
Opinions expressed by Twilio contributors are their own
Brianna DelValle
Twilion

warm-transfer-ruby-sinatra

Have you ever been disconnected from a support call while being transferred to someone else?

Warm transfer eliminates this problem. Using Twilio powered warm transfers your agents will have the ability to dial in another agent in real-time.

Here is how it works at a high level:

  1. The first agent becomes available when he/she connects through the web client.
  2. The second agent also becomes available when he/she connects through the web client.
  3. A client calls our support line.
  4. The client stays on hold while the first agent joins the call.
  5. While the first agent is on the phone with the client, he/she can dial a second agent into the call.
  6. Once the second agent is on the call, the first one can disconnect from it. The client and the second agent stay on the call.

Let's get started! Clone the sample application from Github.

Setting Up the Voice Web Hook

First let's configure the voice webhook for the Twilio number that customers will dial with when they want to talk to a support agent. 

Twilio Console for Warm Transfer

This should be the public-facing URL or your app in production: http://***.ngrok.io/conference/connect/client

Editor: this is a migrated tutorial. Clone the original code from https://github.com/TwilioDevEd/warm-transfer-sinatra/

module Routes
  module Conference

    AGENT_WAIT_URL = 'http://twimlets.com/holdmusic?Bucket=com.twilio.music.classical'

    def self.registered(app)
      app.post '/conference/connect/client' do
        agent_id = 'agent1'
        conference_id = params[:CallSid]
        base_url = RequestHelper.base_url request
        Caller.call_agent(
          agent_id,
          "#{base_url}/conference/#{conference_id}/connect/agent1/"
        )

        twiml = TwimlGenerator.generate_connect_conference(
          conference_id,
          '/conference/wait',
          false,
          true
        )

        call = ActiveCall.first_or_create(agent_id: agent_id)
        call.conference_id = conference_id
        call.save!
        content_type 'text/xml'
        twiml
      end

      app.post '/conference/:conference_id/connect/agent1/' do
        content_type 'text/xml'
        TwimlGenerator.generate_connect_conference(
          params[:conference_id],
          AGENT_WAIT_URL,
          true,
          false
        )
      end

      app.post '/conference/:conference_id/connect/agent2/' do
        content_type 'text/xml'
        TwimlGenerator.generate_connect_conference(
          params[:conference_id],
          AGENT_WAIT_URL,
          true,
          true
        )
      end

      app.post '/conference/:agent_id/call' do
        agent_id = params[:agent_id]
        conference_id = ActiveCall.first(agent_id: agent_id).conference_id

        base_url = RequestHelper.base_url request
        Caller.call_agent(
          'agent2',
          "#{base_url}/conference/#{conference_id}/connect/agent2/"
        )
      end

      app.post '/conference/wait' do
        content_type 'text/xml'
        TwimlGenerator.generate_wait
      end
    end
  end
end

Awesome, now you've got a webhook in place.  Next up, we'll look at some of the code.

Connect an Agent

Here you can see all front-end code necessary to connect an agent using Twilio's Voice Web Client.

We essentially need three things to have a live web client:

  • A capability token (provided by our Sinatra app)
  • A unique identifier (string) for each agent
  • Event listeners to handle different Twilio-triggered events
$(function() {
  var currentAgentId;
  var currentConnection;
  var $callStatus = $('#call-status');
  var $connectAgent1Button = $("#connect-agent1-button");
  var $connectAgent2Button = $("#connect-agent2-button");

  var $answerCallButton = $("#answer-call-button");
  var $hangupCallButton = $("#hangup-call-button");
  var $dialAgent2Button = $("#dial-agent2-button");

  $connectAgent1Button.on('click', { agentId: 'agent1' }, agentClickHandler);
  $connectAgent2Button.on('click', { agentId: 'agent2' }, agentClickHandler);
  $hangupCallButton.on('click', hangUp);
  $dialAgent2Button.on('click', dialAgent2);

  function fetchToken(agentId) {
    $.post('/' + agentId + '/token', {}, function(data) {
      currentAgentId = data.agentId;
      connectClient(data.token);
    }, 'json');
  }

  function connectClient(token) {
    Twilio.Device.setup(token);
  }

  Twilio.Device.ready(function (device) {
    updateCallStatus("Ready");
    agentConnectedHandler(device._clientName);
  });

  // Callback for when Twilio Client receives a new incoming call
  Twilio.Device.incoming(function(connection) {
    currentConnection = connection;
    updateCallStatus("Incoming support call");

    // Set a callback to be executed when the connection is accepted
    connection.accept(function() {
      updateCallStatus("In call with customer");
      $answerCallButton.prop('disabled', true);
      $hangupCallButton.prop('disabled', false);
      $dialAgent2Button.prop('disabled', false);
    });

    // Set a callback on the answer button and enable it
    $answerCallButton.click(function() {
      connection.accept();
    });
    $answerCallButton.prop('disabled', false);
  });

  /* Report any errors to the call status display */
  Twilio.Device.error(function (error) {
    updateCallStatus("ERROR: " + error.message);
    disableConnectButtons(false);
  });

  // Callback for when the call finalizes
  Twilio.Device.disconnect(function(connection) {
    callEndedHandler(connection.device._clientName);
  });

  function dialAgent2() {
    $.post('/conference/' + currentAgentId + '/call')
  }

  /* End a call */
  function hangUp() {
    Twilio.Device.disconnectAll();
  }

  function agentClickHandler(e) {
    var agentId = e.data.agentId;
    disableConnectButtons(true);
    fetchToken(agentId);
  }

  function agentConnectedHandler(agentId) {
    $('#connect-agent-row').addClass('hidden');
    $('#connected-agent-row').removeClass('hidden');
    updateCallStatus("Connected as: " + agentId);

    if (agentId === 'agent1') {
      $dialAgent2Button.removeClass('hidden').prop('disabled', true);
    }
    else {
      $dialAgent2Button.addClass('hidden')
    }
  }

  function callEndedHandler(agentId) {
    $dialAgent2Button.prop('disabled', true);
    $hangupCallButton.prop('disabled', true);
    $answerCallButton.prop('disabled', true)
    updateCallStatus("Connected as: " + agentId);
  }

  function disableConnectButtons(disable) {
    $connectAgent1Button.prop('disabled', disable);
    $connectAgent2Button.prop('disabled', disable);
  }

  function updateCallStatus(status) {
    $callStatus.text(status);
  }
});

In the next step we'll take a closer look at capability token generation.

Generate a Capability Token

In order to connect the Twilio Voice Web Client we need a capability token.

To allow incoming connections through the web client an identifier must be provided when generating the token.

module TwilioCapability
  def self.generate(agent_id)
    account_sid = ENV['TWILIO_ACCOUNT_SID']
    auth_token = ENV['TWILIO_AUTH_TOKEN']
    scope = Twilio::JWT::ClientCapability::IncomingClientScope.new(agent_id)
    capability = Twilio::JWT::ClientCapability.new(account_sid, auth_token)
    capability.add_scope(scope)
    capability.to_jwt
  end
end

Next up let's see how to handle incoming calls.

Handle Incoming Calls

For this tutorial we used fixed identifier strings like agent1 and agent2 but you can use any generated string for your call center clients. These identifiers will be used to create outbound calls to the specified agent using the Twilio REST API.

When a client makes a call to our Twilio number the application receives a POST request asking for instructions. We'll use TwiML to instruct the client to join a conference room and the Twilio REST API client to start a call with the first agent, so he can join the same conference.

When providing instructions to the client, we also provide a waitUrl. This URL is another endpoint of our application. This returns more TwiML to say welcome to the user and also play some music while on hold. Take a look at the code here

We use the client's CallSid as the conference identifier. Since all participants need this identifier to join the conference we'll need to store it in a database so that we can grab it when we dial the second agent in later.

module Routes
  module Conference

    AGENT_WAIT_URL = 'http://twimlets.com/holdmusic?Bucket=com.twilio.music.classical'

    def self.registered(app)
      app.post '/conference/connect/client' do
        agent_id = 'agent1'
        conference_id = params[:CallSid]
        base_url = RequestHelper.base_url request
        Caller.call_agent(
          agent_id,
          "#{base_url}/conference/#{conference_id}/connect/agent1/"
        )

        twiml = TwimlGenerator.generate_connect_conference(
          conference_id,
          '/conference/wait',
          false,
          true
        )

        call = ActiveCall.first_or_create(agent_id: agent_id)
        call.conference_id = conference_id
        call.save!
        content_type 'text/xml'
        twiml
      end

      app.post '/conference/:conference_id/connect/agent1/' do
        content_type 'text/xml'
        TwimlGenerator.generate_connect_conference(
          params[:conference_id],
          AGENT_WAIT_URL,
          true,
          false
        )
      end

      app.post '/conference/:conference_id/connect/agent2/' do
        content_type 'text/xml'
        TwimlGenerator.generate_connect_conference(
          params[:conference_id],
          AGENT_WAIT_URL,
          true,
          true
        )
      end

      app.post '/conference/:agent_id/call' do
        agent_id = params[:agent_id]
        conference_id = ActiveCall.first(agent_id: agent_id).conference_id

        base_url = RequestHelper.base_url request
        Caller.call_agent(
          'agent2',
          "#{base_url}/conference/#{conference_id}/connect/agent2/"
        )
      end

      app.post '/conference/wait' do
        content_type 'text/xml'
        TwimlGenerator.generate_wait
      end
    end
  end
end

Now let's see how to provide TwiML instructions to the client.

Provide TwiML Instruction For The Client

Here we create a TwiML::VoiceResponse that will contain a Dial verb with a Conference noun that will instruct the client to join a specific conference room.

module TwimlGenerator
  def self.generate_connect_conference(call_sid,
                                       wait_url,
                                       start_on_enter,
                                       end_on_exit)
    dial = Twilio::TwiML::Dial.new
    dial.conference(call_sid, start_conference_on_enter: start_on_enter,
                              end_conference_on_exit: end_on_exit,
                              wait_url: wait_url)
    response = Twilio::TwiML::VoiceResponse.new
    response.append(dial)

    response.to_s
  end

  def self.generate_wait
    response = Twilio::TwiML::VoiceResponse.new
    response.say 'Thank you for calling. '\
      'Please wait in line for a few seconds. '\
      'An agent will be with you shortly.'
    response.play(url: 'http://com.twilio.music.classical.s3.amazonaws.com/BusyStrings.mp3')

    response.to_s
  end
end

Next up, we will look at how to dial our first agent into the call.

Dialing the First Agent Into the Call

For our app we created a Caller module that handles the dialing with our agents. This module uses Twilio's REST API to create a new call. The create method receives a hash with the following keys:

  1. from: Your Twilio number
  2. to : The agent web client's identifier (agent1 or agent2)
  3. url : A URL to ask for TwiML instructions when the call connects

Once the agent answers the call in the web client, a request is made to the callback URL instructing the agent's call to join the conference room where the client is already waiting.

module Caller
  def self.call_agent(agent_id, callback_url)
    account_sid   = ENV['TWILIO_ACCOUNT_SID']
    auth_token    = ENV['TWILIO_AUTH_TOKEN']
    twilio_number = ENV['TWILIO_NUMBER']

    client = Twilio::REST::Client.new(account_sid, auth_token)

    call = client.account.calls.create(
      from: twilio_number,
      to: "client:#{agent_id}",
      url: callback_url
    )
  end
end

With that in mind, let's see how to add the second agent to the call.

Dialing the Second Agent Into the Call

When the client and the first agent are both in the call we are ready to perform a warm transfer to a second agent. The first agent makes a request passing its identifier to allow us to look for the conference_id needed to dial the second agent in. Since we already have a Caller module we can simply use the call_agent instance method to connect the second agent.

module Routes
  module Conference

    AGENT_WAIT_URL = 'http://twimlets.com/holdmusic?Bucket=com.twilio.music.classical'

    def self.registered(app)
      app.post '/conference/connect/client' do
        agent_id = 'agent1'
        conference_id = params[:CallSid]
        base_url = RequestHelper.base_url request
        Caller.call_agent(
          agent_id,
          "#{base_url}/conference/#{conference_id}/connect/agent1/"
        )

        twiml = TwimlGenerator.generate_connect_conference(
          conference_id,
          '/conference/wait',
          false,
          true
        )

        call = ActiveCall.first_or_create(agent_id: agent_id)
        call.conference_id = conference_id
        call.save!
        content_type 'text/xml'
        twiml
      end

      app.post '/conference/:conference_id/connect/agent1/' do
        content_type 'text/xml'
        TwimlGenerator.generate_connect_conference(
          params[:conference_id],
          AGENT_WAIT_URL,
          true,
          false
        )
      end

      app.post '/conference/:conference_id/connect/agent2/' do
        content_type 'text/xml'
        TwimlGenerator.generate_connect_conference(
          params[:conference_id],
          AGENT_WAIT_URL,
          true,
          true
        )
      end

      app.post '/conference/:agent_id/call' do
        agent_id = params[:agent_id]
        conference_id = ActiveCall.first(agent_id: agent_id).conference_id

        base_url = RequestHelper.base_url request
        Caller.call_agent(
          'agent2',
          "#{base_url}/conference/#{conference_id}/connect/agent2/"
        )
      end

      app.post '/conference/wait' do
        content_type 'text/xml'
        TwimlGenerator.generate_wait
      end
    end
  end
end

Next up, we'll look at how to handle the first agent leaving the call.

The First Agent Leaves the Call

When the three participants have joined the same call, the first agent has served his purpose. Now he can drop the call, leaving agent two and the client to have a pleasant conversation.

It is important to notice the differences between the TwiML each one of the participants received when joining the call. Both, agent one and two, have start_conference_on_enter set to true. This means the conference will start when any of them joins the call. For the client calling and for agent two, end_conference_on_exit is set to true. This causes the call to end when either of these two participants drops the call.

module TwimlGenerator
  def self.generate_connect_conference(call_sid,
                                       wait_url,
                                       start_on_enter,
                                       end_on_exit)
    dial = Twilio::TwiML::Dial.new
    dial.conference(call_sid, start_conference_on_enter: start_on_enter,
                              end_conference_on_exit: end_on_exit,
                              wait_url: wait_url)
    response = Twilio::TwiML::VoiceResponse.new
    response.append(dial)

    response.to_s
  end

  def self.generate_wait
    response = Twilio::TwiML::VoiceResponse.new
    response.say 'Thank you for calling. '\
      'Please wait in line for a few seconds. '\
      'An agent will be with you shortly.'
    response.play(url: 'http://com.twilio.music.classical.s3.amazonaws.com/BusyStrings.mp3')

    response.to_s
  end
end

That's it! We have just implemented warm transfers using Ruby and Sinatra. Now your clients won't get disconnected from support calls while they are been transferred to some else.

Where to Next?

If you're a Ruby developer working with Twilio, you might also enjoy these tutorials:

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