Different ways to stack Rack middleware

app_base.ru

require 'sinatra'

class AppBase < Sinatra::Base
  def body
    <<-EOS
    <pre>
request_path: #{request.env['REQUEST_PATH']}
path_info: #{request.path_info}
    </pre>
    EOS
  end

end

builder.ru

require './app_base'

class AppA < AppBase
  get '/test' do
    body
  end

end

class AppB < AppBase
  get '/test' do
   body
  end

end

# Use the Rack::Builder DSL to construct a router,
# mapping each prefix to the desired app.
app = Rack::Builder.new do
  map '/a' do
    run AppA.new
  end

  map '/b' do 
    run AppB.new
  end

end

run app

cascade.ru

require './app_base'

class AppA < AppBase
  before do
    if request.path_info.start_with?('/a/')
      request.path_info = request.path_info.sub(/^\/a\//, '/')
    else
      halt 404
    end
  end

  get '/test' do
    body
  end

end

class AppB < AppBase
  before do
    if request.path_info.start_with?('/b/')
      request.path_info = request.path_info.sub(/^\/b\//, '/')
    else
      halt 404
    end
  end

  get '/test' do
    body
  end

end

# Each app explicitly handles a prefix, the
# Rack::Cascade tries each app until something
# doesn't return 404
run Rack::Cascade.new([AppA,AppB])

map.ru

require './app_base'

class AppA < AppBase
  get '/test' do
    body
  end
end

class AppB < AppBase
  get '/test' do
    body
  end
end

# Manually map each app to a prefix route.
map '/a' do
  run AppA.new
end

map '/b' do
  run AppB.new
end