Sinatra React Lab: Chatterbox

Learning Goals

• Create an API with Sinatra for a React frontend application

Introduction

So far, we've seen how to build a Sinatra API and perform various CRUD actions using Active Record. In this lab, you'll work on creating an API in Sinatra once more — but this time, you'll also have code for a React frontend application, so you can get a taste of full-stack development!

This project is separated into two applications:

• A React frontend, in the chatterbox-client directory
• A Sinatra backend, in the chatterbox-server directory

All of the features for the React frontend are built out, and we have a simple json-server API that you can run to see what the completed version of the app will look like. Your main goal with this lab is to build out a Sinatra API server to replace json-server, so most of your coding will be done in the backend.

Frontend Setup

Let's take a quick tour of what we have so far.

To get started, cd into the chatterbox-client directory. Then run:

$ npm install
$ npm run server

This will install the React project dependencies, and run a demo API server using json-server. Next, run this in a new terminal:

$ npm start

Then visit http://localhost:3000 in the browser and interact with the demo application to get a sense of its features.

Here's a demo of the what the React app should look like when using json-server as the API:

Take a look at the components provided in the chatterbox-client directory. Explore the code and pay special attention to where the React application is interacting with json-server. Where are the fetch requests being written? What routes are needed to handle these requests? What HTTP verbs? What data is being sent in the body of the requests?

Once you've familiarized yourself yourself with the code, turn off json-server with control + c in the terminal where json-server is running (you can keep the React application running, though). Next, let's see what we have in the backend.

Backend Setup

In another terminal, cd into the chatterbox-server directory, and run bundle install to install the dependencies.

In this directory, you're given a bare-bones template for a Sinatra API application. It should look familiar to other Sinatra labs you've seen and has all the code set up so you can focus on building out your model and API routes.

You'll be responsible for:

• Creating a model and migrations
• Setting up the necessary routes to handle requests
• Performing CRUD actions with Active Records
• Sending the necessary JSON data in the responses

Allowing Frontend Requests: CORS

The only new code for the server is the Rack CORS gem. This gem provides some Rack middleware which we need to configure so that applications running in the browser, like our React client, can make requests to the backend.

If we didn't use this gem, any requests from our React frontend in the browser would result in an error message like this:

Access to fetch at 'http://localhost:9292/messages' from origin
'http://localhost:3000' has been blocked by CORS policy: No
'Access-Control-Allow-Origin' header is present on the requested resource. If an
opaque response serves your needs, set the request's mode to 'no-cors' to fetch
the resource with CORS disabled.

The reason for this warning message is due to a browser security feature known as Cross-Origin Resource Sharing (CORS). When we use JavaScript from one domain (aka origin) to make a request to a server on a different domain, the default behavior of the browser is to block those requests from going through.

For example, if I own the website definitelynotahacker.com, I can't use JavaScript to make a network request to api.yourbankaccount.com, unless api.yourbankaccount.com explicitly gives permission to my website.

To give that permission, any server that we want to make requests to using JavaScript must add some special headers to the response that tell the browser that the request was permitted.

Here's what the CORS configuration looks like (in the config.ru file):

# Allow CORS (Cross-Origin Resource Sharing) requests
use Rack::Cors do
  allow do
    # origins '*' allows requests from ALL frontend origins
    # (if you deploy your application, change this to
    # ONLY allow requests from YOUR frontend origin, like:
    # origins 'my-react-app.netlify.app')
    origins '*'
    resource '*', headers: :any, methods: [:get, :post, :delete, :put, :patch, :options, :head]
  end
end

You don't have to make any changes to this configuration to complete this lab, but CORS warnings are a very common thing to encounter in web development, so next time you see them, you'll know what this means!

Instructions

Work through the deliverables below. There are tests in the chatterbox-server folder. Because of this lab's project structure, running learn test won't work — instead, you'll need to cd into the chatterbox-server directory and run rspec (or bundle exec rspec) to run the tests for the Sinatra backend.

Make sure to try out your routes from the React frontend application as well once you have everything set up. You can run your Sinatra server with:

$ bundle exec rake server

You'll need to change the fetch requests in React to use http://localhost:9292 as well.

Model

Start by generating a Message model and the necessary migration code to create messages with the following attributes:

• body: string
• username: string
• created_at: timestamp
• updated_at: timestamp

After creating the model and migrations, run the migrations and use the provided seeds.rb file to seed the database:

$ bundle exec rake db:migrate db:seed

Routes

Build out the following routes to handle the necessary CRUD actions:

• GET /messages: returns an array of all messages as JSON, ordered by created_at in ascending order.
• POST /messages: creates a new message with a body and username from params, and returns the newly created post as JSON.
• PATCH /messages/:id: updates the body of the message using params, and returns the updated message as JSON.
• DELETE /messages/:id: deletes the message from the database.

Resources

• CORS Explained
• The rack-cors Gem