How to mount a Sinatra application inside another Sinatra app?

Question

I am trying to write a Sinatra application that groups components together (sort of like controllers). So for the "blog" related things, I want an app called Blog mounted at /blog. All of the routes contained in the Blog app would be relative to its mounted path, so I could simply define an index route without having to specify the mount path in the route.

I originally handled this by using a config.ru file and maping the routes to the different apps. The problem with this that I ran into, was that I was using various sinatra gems/extensions/helpers that needed to be included in all of the apps, so there was a lot of duplicate code.

How can I mount one sinatra app inside of another so that the routes defined in the app are relative to where the app is mounted? If this is not possible out-of-the-box, can you show a code sample of how this could be done?

Here's a simplified example of what it might look like:

class App
  mount Blog, at: '/blog'
  mount Foo, at: '/bar'
end

class Blog
  get '/' do
    # index action
  end
end

class Foo
  get '/' do
    # index action
  end
end

Answer 1

Take a look at https://stackoverflow.com/a/15699791/335847 which has some ideas about namespacing.

Personally, I would use the config.ru with mapped routes. If you're really in that space between "should this be a separate app or is it just helpful to organize it like this" it allows that, and then later you can still farm off one of the apps on its own without changing the code (or only a little). If you're finding that there's a lot of duplicated set up code, I'd do something like this:

# base_controller.rb

require 'sinatra/base'
require "haml"
# now come some shameless plugs for extensions I maintain :)
require "sinatra/partial"
require "sinatra/exstatic_assets"

module MyAmazingApp
  class BaseController < Sinatra::Base
    register Sinatra::Partial
    register Sinatra::Exstatic

  end

  class Blog < BaseController
    # this gets all the stuff already registered.
  end

  class Foo < BaseController
    # this does too!
  end
end

# config.ru

# this is just me being lazy
# it'd add in the /base_controller route too, so you
# may want to change it slightly :)
MyAmazingApp.constants.each do |const|
  map "/#{const.name.downcase}" do
    run const
  end
end

Here's a quote from Sinatra Up and Running:

Not only settings, but every aspect of a Sinatra class will be inherited by its subclasses. This includes defined routes, all the error handlers, extensions, middleware, and so on.

It has some good examples of using this technique (and others). Since I'm in shameless plug mode I recommend it, even though I've nothing to do with it! :)