An Engine with the responsibility of coordinating the whole boot process.

Initialization

Rails::Application is responsible for executing all railties and engines initializers. It also executes some bootstrap initializers (check Rails::Application::Bootstrap) and finishing initializers, after all the others are executed (check Rails::Application::Finisher).

Configuration

Besides providing the same configuration as Rails::Engine and Rails::Railtie, the application object has several specific configurations, for example “cache_classes”, “consider_all_requests_local”, “filter_parameters”, “logger” and so forth.

Check Rails::Application::Configuration to see them all.

Routes

The application object is also responsible for holding the routes and reloading routes whenever the files change in development.

Middlewares

The Application is also responsible for building the middleware stack.

Booting process

The application is also responsible for setting up and executing the booting process. From the moment you require “config/application.rb” in your app, the booting process goes like this:

1)  require "config/boot.rb" to setup load paths
2)  require railties and engines
3)  Define Rails.application as "class MyApp::Application < Rails::Application"
4)  Run config.before_configuration callbacks
5)  Load config/environments/ENV.rb
6)  Run config.before_initialize callbacks
7)  Run Railtie#initializer defined by railties, engines and application.
    One by one, each engine sets up its load paths, routes and runs its config/initializers/* files.
8)  Custom Railtie#initializers added by railties, engines and applications are executed
9)  Build the middleware stack and run to_prepare callbacks
10) Run config.before_eager_load and eager_load! if eager_load is true
11) Run config.after_initialize callbacks

Multiple Applications

If you decide to define multiple applications, then the first application that is initialized will be set to Rails.application, unless you override it with a different application.

To create a new application, you can instantiate a new instance of a class that has already been created:

class Application < Rails::Application
end

first_application  = Application.new
second_application = Application.new(config: first_application.config)

In the above example, the configuration from the first application was used to initialize the second application. You can also use the initialize_copy on one of the applications to create a copy of the application which shares the configuration.

If you decide to define Rake tasks, runners, or initializers in an application other than Rails.application, then you must run them manually.

Namespace

Module

Class

Methods

Attributes

[RW] assets
[R] executor
[R] reloader
[R] reloaders
[RW] sandbox
[RW] sandbox?

Class Public methods

create(initial_variable_values = {}, &block)

Source: 

# File railties/lib/rails/application.rb, line 102
def create(initial_variable_values = {}, &block)
  new(initial_variable_values, &block).run_load_hooks!
end

find_root(from)

Source: 

# File railties/lib/rails/application.rb, line 106
def find_root(from)
  find_root_with_flag "config.ru", from, Dir.pwd
end

inherited(base)

Source: 

# File railties/lib/rails/application.rb, line 91
def inherited(base)
  super
  Rails.app_class = base
  add_lib_to_load_path!(find_root(base.called_from))
  ActiveSupport.run_load_hooks(:before_configuration, base)
end

instance()

Source: 

# File railties/lib/rails/application.rb, line 98
def instance
  super.run_load_hooks!
end

new(initial_variable_values = {}, &block)

Source: 

# File railties/lib/rails/application.rb, line 127
def initialize(initial_variable_values = {}, &block)
  super()
  @initialized       = false
  @reloaders         = []
  @routes_reloader   = nil
  @app_env_config    = nil
  @ordered_railties  = nil
  @railties          = nil
  @message_verifiers = {}
  @ran_load_hooks    = false

  @executor          = Class.new(ActiveSupport::Executor)
  @reloader          = Class.new(ActiveSupport::Reloader)
  @reloader.executor = @executor

  # are these actually used?
  @initial_variable_values = initial_variable_values
  @block = block
end

Instance Public methods

config_for(name, env: Rails.env)

Convenience for loading config/foo.yml for the current Rails env.

Example:

# config/exception_notification.yml:
production:
  url: http://127.0.0.1:8080
  namespace: my_app_production
development:
  url: http://localhost:3001
  namespace: my_app_development

# config/environments/production.rb
Rails.application.configure do
  config.middleware.use ExceptionNotifier, config_for(:exception_notification)
end

Source: 

# File railties/lib/rails/application.rb, line 226
def config_for(name, env: Rails.env)
  if name.is_a?(Pathname)
    yaml = name
  else
    yaml = Pathname.new("#{paths["config"].existent.first}/#{name}.yml")
  end

  if yaml.exist?
    require "erb"
    (YAML.load(ERB.new(yaml.read).result) || {})[env] || {}
  else
    raise "Could not load configuration. No such file - #{yaml}"
  end
rescue Psych::SyntaxError => e
  raise "YAML syntax error occurred while parsing #{yaml}. " \
    "Please note that YAML must be consistently indented using spaces. Tabs are not allowed. " \
    "Error: #{e.message}"
end

console(&blk)

Sends any console called in the instance of a new application up to the console method defined in Rails::Railtie.

Source: 

# File railties/lib/rails/application.rb, line 298
def console(&blk)
  self.class.console(&blk)
end

credentials()

Decrypts the credentials hash as kept in config/credentials.yml.enc. This file is encrypted with the Rails master key, which is either taken from ENV["RAILS_MASTER_KEY"] or from loading config/master.key.

Source: 

# File railties/lib/rails/application.rb, line 441
def credentials
  @credentials ||= encrypted("config/credentials.yml.enc")
end

encrypted(path, key_path: "config/master.key", env_key: "RAILS_MASTER_KEY")

Shorthand to decrypt any encrypted configurations or files.

For any file added with bin/rails encrypted:edit call read to decrypt the file with the master key. The master key is either stored in config/master.key or ENV["RAILS_MASTER_KEY"].

Rails.application.encrypted("config/mystery_man.txt.enc").read
# => "We've met before, haven't we?"

It's also possible to interpret encrypted YAML files with config.

Rails.application.encrypted("config/credentials.yml.enc").config
# => { next_guys_line: "I don't think so. Where was it you think we met?" }

Any top-level configs are also accessible directly on the return value:

Rails.application.encrypted("config/credentials.yml.enc").next_guys_line
# => "I don't think so. Where was it you think we met?"

The files or configs can also be encrypted with a custom key. To decrypt with a key in the ENV, use:

Rails.application.encrypted("config/special_tokens.yml.enc", env_key: "SPECIAL_TOKENS")

Or to decrypt with a file, that should be version control ignored, relative to Rails.root:

Rails.application.encrypted("config/special_tokens.yml.enc", key_path: "config/special_tokens.key")

Source: 

# File railties/lib/rails/application.rb, line 472
def encrypted(path, key_path: "config/master.key", env_key: "RAILS_MASTER_KEY")
  ActiveSupport::EncryptedConfiguration.new(
    config_path: Rails.root.join(path),
    key_path: Rails.root.join(key_path),
    env_key: env_key,
    raise_if_missing_key: config.require_master_key
  )
end

env_config()

Stores some of the Rails initial environment parameters which will be used by middlewares and engines to configure themselves.

Source: 

# File railties/lib/rails/application.rb, line 247
def env_config
  @app_env_config ||= begin
    super.merge(
      "action_dispatch.parameter_filter" => config.filter_parameters,
      "action_dispatch.redirect_filter" => config.filter_redirect,
      "action_dispatch.secret_token" => secrets.secret_token,
      "action_dispatch.secret_key_base" => secret_key_base,
      "action_dispatch.show_exceptions" => config.action_dispatch.show_exceptions,
      "action_dispatch.show_detailed_exceptions" => config.consider_all_requests_local,
      "action_dispatch.logger" => Rails.logger,
      "action_dispatch.backtrace_cleaner" => Rails.backtrace_cleaner,
      "action_dispatch.key_generator" => key_generator,
      "action_dispatch.http_auth_salt" => config.action_dispatch.http_auth_salt,
      "action_dispatch.signed_cookie_salt" => config.action_dispatch.signed_cookie_salt,
      "action_dispatch.encrypted_cookie_salt" => config.action_dispatch.encrypted_cookie_salt,
      "action_dispatch.encrypted_signed_cookie_salt" => config.action_dispatch.encrypted_signed_cookie_salt,
      "action_dispatch.authenticated_encrypted_cookie_salt" => config.action_dispatch.authenticated_encrypted_cookie_salt,
      "action_dispatch.use_authenticated_cookie_encryption" => config.action_dispatch.use_authenticated_cookie_encryption,
      "action_dispatch.encrypted_cookie_cipher" => config.action_dispatch.encrypted_cookie_cipher,
      "action_dispatch.signed_cookie_digest" => config.action_dispatch.signed_cookie_digest,
      "action_dispatch.cookies_serializer" => config.action_dispatch.cookies_serializer,
      "action_dispatch.cookies_digest" => config.action_dispatch.cookies_digest,
      "action_dispatch.cookies_rotations" => config.action_dispatch.cookies_rotations,
      "action_dispatch.content_security_policy" => config.content_security_policy,
      "action_dispatch.content_security_policy_report_only" => config.content_security_policy_report_only,
      "action_dispatch.content_security_policy_nonce_generator" => config.content_security_policy_nonce_generator
    )
  end
end

generators(&blk)

Sends any generators called in the instance of a new application up to the generators method defined in Rails::Railtie.

Source: 

# File railties/lib/rails/application.rb, line 304
def generators(&blk)
  self.class.generators(&blk)
end

initialized?()

Returns true if the application is initialized.

Source: 

# File railties/lib/rails/application.rb, line 148
def initialized?
  @initialized
end

initializer(name, opts = {}, &block)

Sends the initializers to the initializer method defined in the Rails::Initializable module. Each Rails::Application class has its own set of initializers, as defined by the Initializable module.

Source: 

# File railties/lib/rails/application.rb, line 286
def initializer(name, opts = {}, &block)
  self.class.initializer(name, opts, &block)
end

isolate_namespace(mod)

Sends the isolate_namespace method up to the class method.

Source: 

# File railties/lib/rails/application.rb, line 309
def isolate_namespace(mod)
  self.class.isolate_namespace(mod)
end

key_generator()

Returns the application's KeyGenerator

Source: 

# File railties/lib/rails/application.rb, line 172
def key_generator
  # number of iterations selected based on consultation with the google security
  # team. Details at https://github.com/rails/rails/pull/6952#issuecomment-7661220
  @caching_key_generator ||=
    if secret_key_base
      ActiveSupport::CachingKeyGenerator.new(
        ActiveSupport::KeyGenerator.new(secret_key_base, iterations: 1000)
      )
    else
      ActiveSupport::LegacyKeyGenerator.new(secrets.secret_token)
    end
end

message_verifier(verifier_name)

Returns a message verifier object.

This verifier can be used to generate and verify signed messages in the application.

It is recommended not to use the same verifier for different things, so you can get different verifiers passing the verifier_name argument.

Parameters

  • verifier_name - the name of the message verifier.

Examples

message = Rails.application.message_verifier('sensitive_data').generate('my sensible data')
Rails.application.message_verifier('sensitive_data').verify(message)
# => 'my sensible data'

See the ActiveSupport::MessageVerifier documentation for more information.

Source: 

# File railties/lib/rails/application.rb, line 203
def message_verifier(verifier_name)
  @message_verifiers[verifier_name] ||= begin
    secret = key_generator.generate_key(verifier_name.to_s)
    ActiveSupport::MessageVerifier.new(secret)
  end
end

rake_tasks(&block)

If you try to define a set of Rake tasks on the instance, these will get passed up to the Rake tasks defined on the application's class.

Source: 

# File railties/lib/rails/application.rb, line 279
def rake_tasks(&block)
  self.class.rake_tasks(&block)
end

reload_routes!()

Reload application routes regardless if they changed or not.

Source: 

# File railties/lib/rails/application.rb, line 167
def reload_routes!
  routes_reloader.reload!
end

runner(&blk)

Sends any runner called in the instance of a new application up to the runner method defined in Rails::Railtie.

Source: 

# File railties/lib/rails/application.rb, line 292
def runner(&blk)
  self.class.runner(&blk)
end

secret_key_base()

The secret_key_base is used as the input secret to the application's key generator, which in turn is used to create all MessageVerifiers/MessageEncryptors, including the ones that sign and encrypt cookies.

In test and development, this is simply derived as a MD5 hash of the application's name.

In all other environments, we look for it first in ENV, then credentials.secret_key_base, and finally secrets.secret_key_base. For most applications, the correct place to store it is in the encrypted credentials file.

Source: 

# File railties/lib/rails/application.rb, line 428
def secret_key_base
  if Rails.env.development? || Rails.env.test?
    secrets.secret_key_base ||= generate_development_secret
  else
    validate_secret_key_base(
      ENV["SECRET_KEY_BASE"] || credentials.secret_key_base || secrets.secret_key_base
    )
  end
end

secrets()

Returns secrets added to config/secrets.yml.

Example:

development:
  secret_key_base: 836fa3665997a860728bcb9e9a1e704d427cfc920e79d847d79c8a9a907b9e965defa4154b2b86bdec6930adbe33f21364523a6f6ce363865724549fdfc08553
test:
  secret_key_base: 5a37811464e7d378488b0f073e2193b093682e4e21f5d6f3ae0a4e1781e61a351fdc878a843424e81c73fb484a40d23f92c8dafac4870e74ede6e5e174423010
production:
  secret_key_base: <%= ENV["SECRET_KEY_BASE"] %>
  namespace: my_app_production

Rails.application.secrets.namespace returns my_app_production in the production environment.

Source: 

# File railties/lib/rails/application.rb, line 394
def secrets
  @secrets ||= begin
    secrets = ActiveSupport::OrderedOptions.new
    files = config.paths["config/secrets"].existent
    files = files.reject { |path| path.end_with?(".enc") } unless config.read_encrypted_secrets
    secrets.merge! Rails::Secrets.parse(files, env: Rails.env)

    # Fallback to config.secret_key_base if secrets.secret_key_base isn't set
    secrets.secret_key_base ||= config.secret_key_base
    # Fallback to config.secret_token if secrets.secret_token isn't set
    secrets.secret_token ||= config.secret_token

    if secrets.secret_token.present?
      ActiveSupport::Deprecation.warn(
        "`secrets.secret_token` is deprecated in favor of `secret_key_base` and will be removed in Rails 6.0."
      )
    end

    secrets
  end
end

Instance Protected methods

validate_secret_key_base(secret_key_base)

Source: 

# File railties/lib/rails/application.rb, line 579
def validate_secret_key_base(secret_key_base)
  if secret_key_base.is_a?(String) && secret_key_base.present?
    secret_key_base
  elsif secret_key_base
    raise ArgumentError, "`secret_key_base` for #{Rails.env} environment must be a type of String`"
  elsif secrets.secret_token.blank?
    raise ArgumentError, "Missing `secret_key_base` for '#{Rails.env}' environment, set this string with `rails credentials:edit`"
  end
end