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OpenTok Hello World Ruby

This is a simple demo app that shows how you can use the OpenTok-Ruby-SDK to create Sessions, generate Tokens with those Sessions, and then pass these values to a JavaScript client that can connect and conduct a group chat.

Running the App

First, download the dependencies using Bundler

$ bundle install

Next, add your own API Key and API Secret to the environment variables. There are a few ways to do this but the simplest would be to do it right in your shell.

$ export API_KEY=0000000
$ export API_SECRET=abcdef1234567890abcdef01234567890abcdef

Finally, start the server using Bundler to handle dependencies

$ bundle exec ruby hello_world.rb

Visit http://localhost:4567 in your browser. Open it again in a second window. Smile! You've just set up a group chat.

Walkthrough

This demo application uses the Sinatra web framework. It is similar to many other popular web frameworks, such as Rails, but more light-weight. We are only covering the very basics of the framework, but you can learn more by following the links above.

Main Application (hello_world.rb)

The first thing done in this file is to require the dependencies we will be using. In this case that is the Sinatra web framework and most importantly the OpenTok SDK. By running the application with the bundle exec command, we allow Bundler to select the right versions of these gems from the right place.

require 'sinatra/base'
require 'opentok'

Next this file performs some basic checks on the environment. If it cannot find the API_KEYand API_SECRET environment variables, there is no point in continuing.

The class HelloWorld is our application. The first thing it does is to initialize an instance of OpenTok and also store it using Sinatra's set method so it can be accessed in other parts of the application. At the same time, we also set the api_key separately so that we can access it on its own.

  set :api_key, ENV['API_KEY']
  set :opentok, OpenTok::OpenTok.new(api_key, ENV['API_SECRET'])

Now, lets discuss the Hello World application's functionality. We want to set up a group chat so that any client that visits a page will connect to the same OpenTok Session. Once they are connected they can Publish a Stream and Subscribe to all the other streams in that Session. So we just need one Session object, and it needs to be accessible every time a request is made. The next line of our application simply calls the OpenTok instance's create_session method and once again uses set to store it. Alternatively, session_ids are commonly stored in databses for applications that have many of them.

  set :session, opentok.create_session

We only need one page, so we create one route handler for any HTTP GET requests to trigger.

  get '\' do
    # ...
  end

Now all we have to do is serve a page with the three values the client will need to connect to the session: api_key, session_id, and token. The first two are right on the settings object because we called set earlier. Note that the we call the session_id method to get just that value from the session object. The token is generated freshly on this request by calling the generate_token method of the opentok instance, and passing in the session_id. This is because a Token is a piece of information that carries a specific client's permissions in a certain Session. Ideally, as we've done here, you generate a unique token for each client that will connect.

    api_key = settings.api_key
    session_id = settings.session.session_id
    token = settings.opentok.generate_token(session_id)

Now all we have to do is serve a page with those three values. Lets call our erb helper that will pick up a template called index.erb from the views/ directory in our application and pass in the local variables for it to print using the :locals hash.

    erb :index, :locals => {
      :api_key => api_key,
      :session_id => session_id,
      :token => token
    }

Main Template (views/index.rb)

This file simply sets up the HTML page for the JavaScript application to run, imports the JavaScript library, and passes the values created by the server into the JavaScript application inside public/js/helloworld.js

JavaScript Applicaton (public/js/helloworld.js)

The group chat is mostly implemented in this file. At a high level, we connect to the given Session, publish a stream from our webcam, and listen for new streams from other clients to subscribe to.

For more details, read the comments in the file or go to the JavaScript Client Library for a full reference.