Stub initial Rails::Subscriber implementation.

railties/lib/rails/subscriber.rb

+require 'active_support/core_ext/class/inheritable_attributes'
+require 'active_support/notifications'
+
+module Rails
+  # Rails::Subscriber is an object set to consume ActiveSupport::Notifications
+  # on initialization with solely purpose of logging. The subscriber dispatches
+  # notifications to a regirested object based on its given namespace.
+  #
+  # An example would be ActiveRecord subscriber responsible for logging queries:
+  #
+  #   module ActiveRecord
+  #     class Railtie
+  #       class Subscriber < Rails::Subscriber
+  #         def sql(event)
+  #           "#{event.payload[:name]} (#{event.duration}) #{event.payload[:sql]}"
+  #         end
+  #       end
+  #     end
+  #   end
+  #
+  # It's finally registed as:
+  #
+  #   Rails::Subscriber.add :active_record, ActiveRecord::Railtie::Subscriber.new
+  #
+  # So whenever a "active_record.sql" notification arrive to Rails::Subscriber,
+  # it will properly dispatch the event (ActiveSupport::Notifications::Event) to
+  # the sql method.
+  #
+  # This is useful because it avoids spanning several subscribers just for logging
+  # purposes(which slows down the main thread). Besides of providing a centralized
+  # facility on top of Rails.logger.
+  # 
+  # Finally, Subscriber some helpers to deal with logging, like managing console colors.
+  class Subscriber
+    cattr_accessor :colorize_logging, :instance_writer => false
+    self.colorize_logging = true
+
+    # Embed in a String to clear all previous ANSI sequences.
+    CLEAR      = "\e[0m"
+    BOLD       = "\e[1m"
+
+    # Colors
+    BLACK      = "\e[30m"
+    RED        = "\e[31m"
+    GREEN      = "\e[32m"
+    YELLOW     = "\e[33m"
+    BLUE       = "\e[34m"
+    MAGENTA    = "\e[35m"
+    CYAN       = "\e[36m"
+    WHITE      = "\e[37m"
+
+    def self.add(namespace, subscriber)
+      subscribers[namespace.to_sym] = subscriber
+    end
+
+    def self.subscribers
+      @subscribers ||= {}
+    end
+
+    def self.dispatch(args)
+      namespace, name = args[0].split(".")
+      subscriber = subscribers[namespace.to_sym]
+
+      if subscriber.respond_to?(name) && subscriber.logger
+        subscriber.send(name, ActiveSupport::Notifications::Event.new(*args))
+      end
+    end
+
+    # By default, we use the Rails.logger for logging.
+    def logger
+      Rails.logger
+    end
+
+  protected
+
+    %w(info debug warn error fatal unknown).each do |level|
+      class_eval <<-METHOD, __FILE__, __LINE__ + 1
+        def #{level}(*args, &block)
+          logger.#{level}(*args, &block)
+        end
+      METHOD
+    end
+
+    # Set color by using a string or one of the defined constants. If a third
+    # option is set to true, it also adds bold to the string. This is based
+    # on Highline implementation and it automatically appends CLEAR to the end
+    # of the returned String.
+    #
+    def color(text, color, bold=false)
+      return text unless colorize_logging
+      color = self.class.const_get(color.to_s.upcase) if color.is_a?(Symbol)
+      bold  = bold ? BOLD : ""
+      "#{bold}#{color}#{text}#{CLEAR}"
+    end
+  end
+end
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railties/test/subscriber_test.rb

+require 'abstract_unit'
+require 'rails/subscriber'
+
+Thread.abort_on_exception = true
+
+class MockLogger
+  def initialize
+    @logged = Hash.new { |h,k| h[k] = [] }
+  end
+
+  def method_missing(level, message)
+    @logged[level] << message
+  end
+
+  def logged(level)
+    @logged[level].compact.map { |l| l.to_s.strip }
+  end
+end
+
+ActiveSupport::Notifications.subscribe do |*args|
+  Rails::Subscriber.dispatch(args)
+end
+
+class MySubscriber < Rails::Subscriber
+  def some_event(event)
+    info event.name
+  end
+
+  def foo(event)
+    debug "debug"
+    info "info"
+    warn "warn"
+  end
+
+  def bar(event)
+    info "#{color("cool", :red)}, #{color("isn't it?", :blue, true)}"
+  end
+end
+
+class SubscriberTest < ActiveSupport::TestCase
+  def setup
+    @logger = MockLogger.new
+    @previous_logger, Rails.logger = Rails.logger, @logger
+    @subscriber = MySubscriber.new
+    wait
+  end
+
+  def teardown
+    Rails.logger = @previous_logger
+    Rails::Subscriber.subscribers.clear
+  end
+
+  def instrument(*args, &block)
+    ActiveSupport::Notifications.instrument(*args, &block)
+  end
+
+  def wait
+    ActiveSupport::Notifications.notifier.wait
+  end
+
+  def test_proxies_method_to_rails_logger
+    @subscriber.foo(nil)
+    assert_equal %w(debug), @logger.logged(:debug)
+    assert_equal %w(info), @logger.logged(:info)
+    assert_equal %w(warn), @logger.logged(:warn)
+  end
+
+  def test_set_color_for_messages
+    @subscriber.bar(nil)
+    assert_equal "\e[31mcool\e[0m, \e[1m\e[34misn't it?\e[0m", @logger.logged(:info).last
+  end
+
+  def test_does_not_set_color_if_colorize_logging_is_set_to_false
+    Rails::Subscriber.colorize_logging = false
+    @subscriber.bar(nil)
+    assert_equal "cool, isn't it?", @logger.logged(:info).last
+  ensure
+    Rails::Subscriber.colorize_logging = true
+  end
+
+  def test_event_is_sent_to_the_registered_class
+    Rails::Subscriber.add :my_subscriber, @subscriber
+    instrument "my_subscriber.some_event"
+    wait
+    assert_equal %w(my_subscriber.some_event), @logger.logged(:info)
+  end
+
+  def test_does_not_send_the_event_if_it_doesnt_match_the_class
+    Rails::Subscriber.add :my_subscriber, @subscriber
+    instrument "my_subscriber.unknown_event"
+    wait
+    # If we get here, it means that NoMethodError was raised.
+  end
+
+  def test_does_not_send_the_event_if_logger_is_nil
+    Rails.logger = nil
+    Rails::Subscriber.add :my_subscriber, @subscriber
+    instrument "my_subscriber.some_event"
+    wait
+    assert_equal [], @logger.logged(:info)
+  end
+end
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