injecting_middlewares.md

Injecting middlewares

You can inject middlewares at the moment an application is initialized, allowing you to override what you have defined in the DSL.

For that purpose, you have to use the middlewares: keyword argument. It must be a hash where middlewares are matched by the name you gave them in its definition.

A middleware must be specified as an Array. The first item must be a rack middleware class. The rest of the arguments (if any) should be any options it may need.

That is mainly useful for testing purposes, where you can switch a heavy middleware and use a mocked one instead.

In the following example, we mock the rack session mechanism:

# config.ru
require 'web_pipe'
require 'rack/session/cookie'

class MyApp
  include WebPipe
  
  use :session, Rack::Session::Cookie, key: 'my_app.session', secret: 'long'
  
  plug(:serialize_session) do |conn|
    conn.set_response_body(conn.env['rack.session'].inspect)
  end
end

class MockedSession
  attr_reader :app, :key
  
  def initialize(app, key)
    @app = app
    @key = key
  end
  
  def call(env)
    env['rack.session'] = "Mocked for '#{key}' key"
  end
end

run MyApp.new(middlewares: { session: [MockedSession, 'my_app_mocked'] })