sinatra.md

Sinatra

Sinatra is a DSL (domain-specific language, or a language written for a specific purpose) for building web applications.

It can be confusing. Suddenly, the single-user terminal apps you've been writing are up on the web for everyone to see, and they need to behave differently as a result.

require 'sinatra'

get '/' do
    'hello Makers!'
end

This code will intercept an HTTP GET request sent to '/', and reply with 'hello Makers!' in plain text. Simple.

Routes

In the above example, '/' is the route. You can define a bunch of other routes, too. For example:

get '/hi' do
    <h1>Hello Makers!</h1>
end

Now, accessing the website path /hi will yield the above message (which in this case will appear big and bold on the page, as we have wrapped it in h1 tags.)

Testing with Cucumber

Cucumber is used for acceptance testing – it acts as if it were a person using the application to make sure it works. You can use Cucumber with Sinatra by using the cucumber-sinatra gem.

Get started by running:

$ cucumber-sinatra init --app SampleApp lib/sample_app.rb
...
$ rackup

Run your Cucumber tests from the command line with $ cucumber.

Now, let's describe a feature using Cucumber:

$ mkdir feature
$ touch homepage.feature

Feature: The homepage
  In order to show off Cucumber at Makers
  I want to present Cucumber

This will run, but doesn't have any actual tests (or scenarios). Let's add some in the same file.

  Scenario: Being greeted
    Given I am having a good day
    When I am on the homepage
    Then I should see "Hello Makers!"

This Given/When/Then notation is particular to Cucumber (or specifically Gherkin, the language Cucumber is written in).

For each step, you write a step definition in Ruby.

cucumber-sinatra has some built in step definitions, so you can write some steps without needing to define them (like When I am on the homepage). These built-in definitions live in features/step_definitions/, and there are support files in support/ which do things like substituting 'homepage' for '/'. Consider deleting features/step_definitions/web_steps.rb to get some practice in writing your own step definitions.

Cucumber also uses a language called Capybara.

Running the damn thing

Get your server up and running by typing

$ rackup

What this command actually does is read through your sample_app.rb file, looks at the various routes you've set, and creates a routing table from it. Then it starts an HTTP server on a particular port and makes it available for connections.

Config

Look at the following code from the Sinatra documentation:

set :views, Proc.new { File.join(root, "templates") }

Why do it this way? Seems kinda convoluted.

The reason this is so important is that it bases the path to your views directory on the site root. If you ran rackup from a different directory and you'd hard-coded the views path, then it would break – it wouldn't be able to find views relative to where you're running the server file from.

Using root gives a salient point that your site is always run from.

Sessions

HTTP by nature is stateless - so it doesn't recognise repeat visitors, or even visitors across pages. A lot of basic things fail because of this – how could you log in to a site, for example, if it didn't remember you?

This is where sessions come into play.

The server creates a unique ID (or UID) for each visitor and stores it in a hash table. This value is served back up to users to identify them, either in a cookie or (more rarely) in the URI itself. A cookie is returned as part of the header – it's just a string inside the header.

A cookie sent by a particular site can only be read from the browser by that site.

So how do you use sessions in Sinatra?

sample_app.rb:

class SampleApp < Sinatra::Base
  enable :sessions

  get '/' do
    @number = session
    erb :index
  end

  get '/a/:number' do |number|
    session['number']= number
    redirect to '/'
  end

end

Bear in mind that sessions have a hard limit of 4KB! Usually, to store more than this, you would use a database.

If you wanted to solely use Sinatra, though, you could do this the Very Wrong Way: setting a constant and then writing to that.

class SampleApp < Sinatra::Base
  enable :sessions

  GAME = Game.new

  get '/' do
    @number = session
    erb :index
  end

  get '/a/:number' do |number|
    number = Game.number
    redirect to '/'
  end

end