Lotus::Controller

A Rack compatible Controller layer for Lotus.

Status

Contact

• Home page: http://lotusrb.org
• Mailing List: http://lotusrb.org/mailing-list
• API Doc: http://rdoc.info/gems/lotus-controller
• Bugs/Issues: https://github.com/lotus/controller/issues
• Support: http://stackoverflow.com/questions/tagged/lotus-ruby
• Chat: https://gitter.im/lotus/chat

Rubies

Lotus::Controller supports Ruby (MRI) 2+

Installation

Add this line to your application's Gemfile:

gem 'lotus-controller'

And then execute:

$ bundle

Or install it yourself as:

$ gem install lotus-controller

Usage

Lotus::Controller is a micro library for web frameworks. It works beautifully with Lotus::Router, but it can be employed everywhere. It's designed to be fast and testable.

Actions

The core of this framework are the actions. They are the endpoints that respond to incoming HTTP requests.

class Show
  include Lotus::Action

  def call(params)
    @article = Article.find params[:id]
  end
end

The usage of Lotus::Action follows the Lotus philosophy: include a module and implement a minimal interface. In this case, the interface is one method: #call(params).

Lotus is designed to not interfere with inheritance. This is important, because you can implement your own initialization strategy.

An action is an object. That's important because you have the full control on it. In other words, you have the freedom to instantiate, inject dependencies and test it, both at the unit and integration level.

In the example below, the default repository is Article. During a unit test we can inject a stubbed version, and invoke #call with the params. We're avoiding HTTP calls, we're also going to avoid hitting the database (it depends on the stubbed repository), we're just dealing with message passing. Imagine how fast the unit test could be.

class Show
  include Lotus::Action

  def initialize(repository = Article)
    @repository = repository
  end

  def call(params)
    @article = @repository.find params[:id]
  end
end

action = Show.new(MemoryArticleRepository)
action.call({ id: 23 })

Params

The request params are passed as an argument to the #call method. If routed with Lotus::Router, it extracts the relevant bits from the Rack env (eg the requested :id). Otherwise everything is passed as is: the full Rack env in production, and the given Hash for unit tests.

With Lotus::Router:

class Show
  include Lotus::Action

  def call(params)
    # ...
    puts params # => { id: 23 } extracted from Rack env
  end
end

Standalone:

class Show
  include Lotus::Action

  def call(params)
    # ...
    puts params # => { :"rack.version"=>[1, 2], :"rack.input"=>#<StringIO:0x007fa563463948>, ... }
  end
end

Unit Testing:

class Show
  include Lotus::Action

  def call(params)
    # ...
    puts params # => { id: 23, key: 'value' } passed as it is from testing
  end
end

action   = Show.new
response = action.call({ id: 23, key: 'value' })

Whitelisting

Params represent an untrusted input. For security reasons it's recommended to whitelist them.

require 'lotus/controller'

class Signup
  include Lotus::Action

  params do
    param :first_name
    param :last_name
    param :email

    param :address do
      param :line_one
      param :state
      param :country
    end
  end

  def call(params)
    # Describe inheritance hierarchy
    puts params.class            # => Signup::Params
    puts params.class.superclass # => Lotus::Action::Params

    # Whitelist :first_name, but not :admin
    puts params[:first_name]     # => "Luca"
    puts params[:admin]          # => nil

    # Whitelist nested params [:address][:line_one], not [:address][:line_two]
    puts params[:address][:line_one] # => '69 Tender St'
    puts params[:address][:line_two] # => nil
  end
end

Validations & Coercions

Because params are a well defined set of data required to fulfill a feature in your application, you can validate them. So you can avoid hitting lower MVC layers when params are invalid.

If you specify the :type option, the param will be coerced.

require 'lotus/controller'

class Signup
  MEGABYTE = 1024 ** 2
  include Lotus::Action

  params do
    param :first_name,       presence: true
    param :last_name,        presence: true
    param :email,            presence: true, format: /@/,   confirmation: true
    param :password,         presence: true,                confirmation: true
    param :terms_of_service, acceptance: true
    param :avatar,           size: 0..(MEGABYTE * 3)
    param :age,              type: Integer, size: 18..99
  end

  def call(params)
    halt 400 unless params.valid?
    # ...
  end
end

action = Signup.new

action.call(valid_params) # => [200, {}, ...]
action.errors.empty?      # => true

action.call(invalid_params) # => [400, {}, ...]
action.errors               # =>  #<Lotus::Validations::Errors:0x007fabe4b433d0 @errors={...}>

action.errors.for(:email)
  # => [#<Lotus::Validations::Error:0x007fabe4b432e0 @attribute=:email, @validation=:presence, @expected=true, @actual=nil>]

Response

The output of #call is a serialized Rack::Response (see #finish):

class Show
  include Lotus::Action

  def call(params)
    # ...
  end
end

action = Show.new
action.call({}) # => [200, {}, [""]]

It has private accessors to explicitly set status, headers, and body:

class Show
  include Lotus::Action

  def call(params)
    self.status  = 201
    self.body    = 'Hi!'
    self.headers.merge!({ 'X-Custom' => 'OK' })
  end
end

action = Show.new
action.call({}) # => [201, { "X-Custom" => "OK" }, ["Hi!"]]

Exposures

We know that actions are objects and Lotus::Action respects one of the pillars of OOP: encapsulation. Other frameworks extract instance variables (@ivar) and make them available to the view context.

Lotus::Action's solution is the simple and powerful DSL: expose. It's a thin layer on top of attr_reader.

Using expose creates a getter for the given attribute, and adds it to the exposures. Exposures (#exposures) are a set of attributes exposed to the view. That is to say the variables necessary for rendering a view.

By default, all Lotus::Action objects expose #params and #errors.

class Show
  include Lotus::Action

  expose :article

  def call(params)
    @article = Article.find params[:id]
  end
end

action = Show.new
action.call({ id: 23 })

assert_equal 23, action.article.id

puts action.exposures # => { article: <Article:0x007f965c1d0318 @id=23> }

Callbacks

It offers a powerful, inheritable callback chain which is executed before and/or after your #call method invocation:

class Show
  include Lotus::Action

  before :authenticate, :set_article

  def call(params)
  end

  private
  def authenticate
    # ...
  end

  # `params` in the method signature is optional
  def set_article(params)
    @article = Article.find params[:id]
  end
end

Callbacks can also be expressed as anonymous lambdas:

class Show
  include Lotus::Action

  before { ... } # do some authentication stuff
  before { |params| @article = Article.find params[:id] }

  def call(params)
  end
end

Exceptions management

When an exception is raised, it automatically sets the HTTP status to 500:

class Show
  include Lotus::Action

  def call(params)
    raise
  end
end

action = Show.new
action.call({}) # => [500, {}, ["Internal Server Error"]]

You can map a specific raised exception to a different HTTP status.

class Show
  include Lotus::Action
  handle_exception RecordNotFound => 404

  def call(params)
    @article = Article.find params[:id]
  end
end

action = Show.new
action.call({id: 'unknown'}) # => [404, {}, ["Not Found"]]

You can also define custom handlers for exceptions.

class Create
  include Lotus::Action
  handle_exception ArgumentError => :my_custom_handler

  def call(params)
    raise ArgumentError.new("Invalid arguments")
  end

  private
  def my_custom_handler(exception)
    status 400, exception.message
  end
end

action = Create.new
action.call({}) # => [400, {}, ["Invalid arguments"]]

Exception policies can be defined globally, before the controllers/actions are loaded.

Lotus::Controller.configure do
  handle_exception RecordNotFound => 404
end

class Show
  include Lotus::Action

  def call(params)
    @article = Article.find params[:id]
  end
end

action = Show.new
action.call({id: 'unknown'}) # => [404, {}, ["Not Found"]]

This feature can be turned off globally, in a controller or in a single action.

Lotus::Controller.configure do
  handle_exceptions false
end

# or

module Articles
  class Show
    include Lotus::Action

    configure do
      handle_exceptions false
    end

    def call(params)
      @article = Article.find params[:id]
    end
  end
end

action = Articles::Show.new
action.call({id: 'unknown'}) # => raises RecordNotFound

Inherited Exceptions

class MyCustomException < StandardError
end

module Articles
  class Index
    include Lotus::Action

    handle_exception MyCustomException => :handle_my_exception

    def call(params)
      raise MyCustomException
    end

    private

    def handle_my_exception
      # ...
    end
  end

  class Show
    include Lotus::Action

    handle_exception StandardError => :handle_standard_error

    def call(params)
      raise MyCustomException
    end

    private

    def handle_standard_error
      # ...
    end
  end
end

Articles::Index.new.call({}) # => `handle_my_exception` will be invoked
Articles::Show.new.call({})  # => `handle_standard_error` will be invoked,
                             #   because `MyCustomException` inherits from `StandardError`

Throwable HTTP statuses

When #halt is used with a valid HTTP code, it stops the execution and sets the proper status and body for the response:

class Show
  include Lotus::Action

  before :authenticate!

  def call(params)
    # ...
  end

  private
  def authenticate!
    halt 401 unless authenticated?
  end
end

action = Show.new
action.call({}) # => [401, {}, ["Unauthorized"]]

Alternatively, you can specify a custom message.

class Show
  include Lotus::Action

  def call(params)
    DroidRepository.find(params[:id]) or not_found
  end

  private
  def not_found
    halt 404, "This is not the droid you're looking for"
  end
end

action = Show.new
action.call({}) # => [404, {}, ["This is not the droid you're looking for"]]

Cookies

Lotus::Controller offers convenient access to cookies.

They are read as a Hash from Rack env:

require 'lotus/controller'
require 'lotus/action/cookies'

class ReadCookiesFromRackEnv
  include Lotus::Action
  include Lotus::Action::Cookies

  def call(params)
    # ...
    cookies[:foo] # => 'bar'
  end
end

action = ReadCookiesFromRackEnv.new
action.call({'HTTP_COOKIE' => 'foo=bar'})

They are set like a Hash:

require 'lotus/controller'
require 'lotus/action/cookies'

class SetCookies
  include Lotus::Action
  include Lotus::Action::Cookies

  def call(params)
    # ...
    cookies[:foo] = 'bar'
  end
end

action = SetCookies.new
action.call({}) # => [200, {'Set-Cookie' => 'foo=bar'}, '...']

They are removed by setting their value to nil:

require 'lotus/controller'
require 'lotus/action/cookies'

class RemoveCookies
  include Lotus::Action
  include Lotus::Action::Cookies

  def call(params)
    # ...
    cookies[:foo] = nil
  end
end

action = RemoveCookies.new
action.call({}) # => [200, {'Set-Cookie' => "foo=; max-age=0; expires=Thu, 01 Jan 1970 00:00:00 -0000"}, '...']

Default values can be set in configuration, but overriden case by case.

require 'lotus/controller'
require 'lotus/action/cookies'

Lotus::Controller.configure do
  cookies max_age: 300 # 5 minutes
end

class SetCookies
  include Lotus::Action
  include Lotus::Action::Cookies

  def call(params)
    # ...
    cookies[:foo] = { value: 'bar', max_age: 100 }
  end
end

action = SetCookies.new
action.call({}) # => [200, {'Set-Cookie' => "foo=bar; max-age=100;"}, '...']

Sessions

It has builtin support for Rack sessions:

require 'lotus/controller'
require 'lotus/action/session'

class ReadSessionFromRackEnv
  include Lotus::Action
  include Lotus::Action::Session

  def call(params)
    # ...
    session[:age] # => '31'
  end
end

action = ReadSessionFromRackEnv.new
action.call({ 'rack.session' => { 'age' => '31' }})

Values can be set like a Hash:

require 'lotus/controller'
require 'lotus/action/session'

class SetSession
  include Lotus::Action
  include Lotus::Action::Session

  def call(params)
    # ...
    session[:age] = 31
  end
end

action = SetSession.new
action.call({}) # => [200, {"Set-Cookie"=>"rack.session=..."}, "..."]

Values can be removed like a Hash:

require 'lotus/controller'
require 'lotus/action/session'

class RemoveSession
  include Lotus::Action
  include Lotus::Action::Session

  def call(params)
    # ...
    session[:age] = nil
  end
end

action = RemoveSession.new
action.call({}) # => [200, {"Set-Cookie"=>"rack.session=..."}, "..."] it removes that value from the session

While Lotus::Controller supports sessions natively, it's session store agnostic. You have to specify the session store in your Rack middleware configuration (eg config.ru).

use Rack::Session::Cookie, secret: SecureRandom.hex(64)
run Show.new

Http Cache

Lotus::Controller sets your headers correctly according to RFC 2616 / 14.9 for more on standard cache control directives: http://tools.ietf.org/html/rfc2616#section-14.9.1

You can easily set the Cache-Control header for your actions:

require 'lotus/controller'
require 'lotus/action/cache'

class HttpCacheController
  include Lotus::Action
  include Lotus::Action::Cache

  cache_control :public, max_age: 600 # => Cache-Control: public, max-age=600

  def call(params)
    # ...
  end
end

Expires header can be specified using expires method:

require 'lotus/controller'
require 'lotus/action/cache'

class HttpCacheController
  include Lotus::Action
  include Lotus::Action::Cache

  expires 60, :public, max_age: 600 # => Expires: Sun, 03 Aug 2014 17:47:02 GMT, Cache-Control: public, max-age=600

  def call(params)
    # ...
  end
end

Conditional Get

According to HTTP specification, conditional GETs provide a way for web servers to inform clients that the response to a GET request hasn't change since the last request returning a Not Modified header (304).

Passing the HTTP_IF_NONE_MATCH (content identifier) or HTTP_IF_MODIFIED_SINCE (timestamp) headers allows the web server define if the client has a fresh version of a given resource.

You can easily take advantage of Conditional Get using #fresh method:

require 'lotus/controller'
require 'lotus/action/cache'

class ConditionalGetController
  include Lotus::Action
  include Lotus::Action::Cache

  def call(params)
    # ...
    fresh etag: @resource.cache_key
    # => halt 304 with header IfNoneMatch = @resource.cache_key
  end
end

If @resource.cache_key is equal to IfNoneMatch header, then lotus will halt 304.

The same behavior is accomplished using last_modified:

require 'lotus/controller'
require 'lotus/action/cache'

class ConditionalGetController
  include Lotus::Action
  include Lotus::Action::Cache

  def call(params)
    # ...
    fresh last_modified: @resource.update_at
    # => halt 304 with header IfModifiedSince = @resource.update_at.httpdate
  end
end

If @resource.update_at is equal to IfModifiedSince header, then lotus will halt 304.

Redirect

If you need to redirect the client to another resource, use #redirect_to:

class Create
  include Lotus::Action

  def call(params)
    # ...
    redirect_to 'http://example.com/articles/23'
  end
end

action = Create.new
action.call({ article: { title: 'Hello' }}) # => [302, {'Location' => '/articles/23'}, '']

You can also redirect with a custom status code:

class Create
  include Lotus::Action

  def call(params)
    # ...
    redirect_to 'http://example.com/articles/23', status: 301
  end
end

action = Create.new
action.call({ article: { title: 'Hello' }}) # => [301, {'Location' => '/articles/23'}, '']

MIME Types

Lotus::Action automatically sets the Content-Type header, according to the request.

class Show
  include Lotus::Action

  def call(params)
  end
end

action = Show.new

action.call({ 'HTTP_ACCEPT' => '*/*' }) # Content-Type "application/octet-stream"
action.format                           # :all

action.call({ 'HTTP_ACCEPT' => 'text/html' }) # Content-Type "text/html"
action.format                                 # :html

However, you can force this value:

class Show
  include Lotus::Action

  def call(params)
    # ...
    self.format = :json
  end
end

action = Show.new

action.call({ 'HTTP_ACCEPT' => '*/*' }) # Content-Type "application/json"
action.format                           # :json

action.call({ 'HTTP_ACCEPT' => 'text/html' }) # Content-Type "application/json"
action.format                                 # :json

You can restrict the accepted MIME types:

class Show
  include Lotus::Action
  accept :html, :json

  def call(params)
    # ...
  end
end

# When called with "\*/\*"            => 200
# When called with "text/html"        => 200
# When called with "application/json" => 200
# When called with "application/xml"  => 406

You can check if the requested MIME type is accepted by the client.

class Show
  include Lotus::Action

  def call(params)
    # ...
    # @_env['HTTP_ACCEPT'] # => 'text/html,application/xhtml+xml,application/xml;q=0.9'

    accept?('text/html')        # => true
    accept?('application/xml')  # => true
    accept?('application/json') # => false
    self.format                 # :html



    # @_env['HTTP_ACCEPT'] # => '*/*'

    accept?('text/html')        # => true
    accept?('application/xml')  # => true
    accept?('application/json') # => true
    self.format                 # :html
  end
end

Lotus::Controller is shipped with an extensive list of the most common MIME types. Also, you can register your own:

Lotus::Controller.configure do
  format custom: 'application/custom'
end

class Index
  include Lotus::Action

  def call(params)
  end
end

action = Index.new

action.call({ 'HTTP_ACCEPT' => 'application/custom' }) # => Content-Type 'application/custom'
action.format                                          # => :custom

class Show
  include Lotus::Action

  def call(params)
    # ...
    self.format = :custom
  end
end

action = Show.new

action.call({ 'HTTP_ACCEPT' => '*/*' }) # => Content-Type 'application/custom'
action.format                           # => :custom

Streamed Responses

When the work to be done by the server takes time, it may be a good idea to stream your response. Here's an example of a streamed CSV.

Lotus::Controller.configure do
  format csv: 'text/csv'
  middleware.use ::Rack::Chunked
end

class Csv
  include Lotus::Action

  def call(params)
    self.format = :csv
    self.body = Enumerator.new do |yielder|
      yielder << csv_header

      # Expensive operation is streamed as each line becomes available
      csv_body.each_line do |line|
        yielder << line
      end
    end
  end
end

Note:

• In development, Lotus' code reloading needs to be disabled for streaming to work. This is because Shotgun interferes with the streaming action. You can disable it like this lotus server --code-reloading=false
• Streaming does not work with WEBrick as it buffers its response. We recommend using puma, though you may find success with other servers

No rendering, please

Lotus::Controller is designed to be a pure HTTP endpoint, rendering belongs to other layers of MVC. You can set the body directly (see response), or use Lotus::View.

Controllers

A Controller is nothing more than a logical group of actions: just a Ruby module.

module Articles
  class Index
    include Lotus::Action

    # ...
  end

  class Show
    include Lotus::Action

    # ...
  end
end

Articles::Index.new.call({})

Lotus::Router integration

While Lotus::Router works great with this framework, Lotus::Controller doesn't depend on it. You, the developer, are free to choose your own routing system.

But, if you use them together, the only constraint is that an action must support arity 0 in its constructor. The following examples are valid constructors:

def initialize
end

def initialize(repository = Article)
end

def initialize(repository: Article)
end

def initialize(options = {})
end

def initialize(*args)
end

Please note that this is subject to change: we're working to remove this constraint.

Lotus::Router supports lazy loading for controllers. While this policy can be a convenient fallback, you should know that it's the slower option. Be sure of loading your controllers before you initialize the router.

Rack integration

Lotus::Controller is compatible with Rack. However, it doesn't mount any middleware. While a Lotus application's architecture is more web oriented, this framework is designed to build pure HTTP endpoints.

Rack middleware

Rack middleware can be configured globally in config.ru. However, consider that they often add unnecessary overhead for all endpoints that aren't direct users of all the configured middleware.

Think about a middleware to create sessions, where only SessionsController::Create needs that middleware, but every other action pays the performance price for that middleware.

The solution is that an action can employ one or more Rack middleware, with .use.

require 'lotus/controller'

module Sessions
  class Create
    include Lotus::Action
    use OmniAuth

    def call(params)
      # ...
    end
  end
end

require 'lotus/controller'

module Sessions
  class Create
    include Lotus::Controller

    use XMiddleware.new('x', 123)
    use YMiddleware.new
    use ZMiddleware

    def call(params)
      # ...
    end
  end
end

Configuration

Lotus::Controller can be configured with a DSL. It supports a few options:

require 'lotus/controller'

Lotus::Controller.configure do
  # Handle exceptions with HTTP statuses (true) or don't catch them (false)
  # Argument: boolean, defaults to `true`
  #
  handle_exceptions true

  # If the given exception is raised, return that HTTP status
  # It can be used multiple times
  # Argument: hash, empty by default
  #
  handle_exception ArgumentError => 404

  # Register a format to MIME type mapping
  # Argument: hash, key: format symbol, value: MIME type string, empty by default
  #
  format custom: 'application/custom'

  # Define a fallback format to detect in case of HTTP request with `Accept: */*`
  # If not defined here, it will return Rack's default: `application/octet-stream`
  # Argument: symbol, it should be already known. defaults to `nil`
  #
  default_request_format :html

  # Define a default format to set as `Content-Type` header for response,
  # unless otherwise specified.
  # If not defined here, it will return Rack's default: `application/octet-stream`
  # Argument: symbol, it should be already known. defaults to `nil`
  #
  default_response_format :html

  # Define a default charset to return in the `Content-Type` response header
  # If not defined here, it returns `utf-8`
  # Argument: string, defaults to `nil`
  #
  default_charset 'koi8-r'

  # Configure the logic to be executed when Lotus::Action is included
  # This is useful to DRY code by having a single place where to configure
  # shared behaviors like authentication, sessions, cookies etc.
  # Argument: proc
  #
  prepare do
    include Lotus::Action::Sessions
    include MyAuthentication
    use SomeMiddleWare

    before { authenticate! }
  end
end

All of the global configurations can be overwritten at the controller level. Each controller and action has its own copy of the global configuration.

This means changes are inherited from the top to the bottom, but do not bubble back up.

require 'lotus/controller'

Lotus::Controller.configure do
  handle_exception ArgumentError => 400
end

module Articles
  class Create
    include Lotus::Action

    configure do
      handle_exceptions false
    end

    def call(params)
      raise ArgumentError
    end
  end
end

module Users
  class Create
    include Lotus::Action

    def call(params)
      raise ArgumentError
    end
  end
end

Users::Create.new.call({}) # => HTTP 400

Articles::Create.new.call({})
  # => raises ArgumentError because we set handle_exceptions to false

Thread safety

An Action is mutable. When used without Lotus::Router, be sure to instantiate an action for each request. The same advice applies when using Lotus::Router but NOT routing to mycontroller#myaction but instead routing direct to a class.

# config.ru
require 'lotus/controller'

class Action
  include Lotus::Action

  def self.call(env)
    new.call(env)
  end

  def call(params)
    self.body = object_id.to_s
  end
end

run Action

Lotus::Controller heavely depends on class configuration. To ensure immutability in deployment environments, use Lotus::Controller.load!.

Versioning

Lotus::Controller uses Semantic Versioning 2.0.0

Contributing

1. Fork it
2. Create your feature branch (git checkout -b my-new-feature)
3. Commit your changes (git commit -am 'Add some feature')
4. Push to the branch (git push origin my-new-feature)
5. Create new Pull Request

Copyright

Copyright © 2014-2016 Luca Guidi – Released under MIT License