class ActiveSupport::LogSubscriber

Active Support Log Subscriber

ActiveSupport::LogSubscriber is an object set to consume ActiveSupport::Notifications with the sole purpose of logging them. The log subscriber dispatches notifications to a registered object based on its given namespace.

An example would be Active Record log subscriber responsible for logging queries:

module ActiveRecord
  class LogSubscriber < ActiveSupport::LogSubscriber
    attach_to :active_record

    def sql(event)
      info "#{event.payload[:name]} (#{event.duration}) #{event.payload[:sql]}"
    end
  end
end

ActiveRecord::LogSubscriber.logger must be set as well, but it is assigned automatically in a Rails environment.

After configured, whenever a "sql.active_record" notification is published, it will properly dispatch the event (ActiveSupport::Notifications::Event) to the sql method.

Being an ActiveSupport::Notifications consumer, ActiveSupport::LogSubscriber exposes a simple interface to check if instrumented code raises an exception. It is common to log a different message in case of an error, and this can be achieved by extending the previous example:

module ActiveRecord
  class LogSubscriber < ActiveSupport::LogSubscriber
    def sql(event)
      exception = event.payload[:exception]

      if exception
        exception_object = event.payload[:exception_object]

        error "[ERROR] #{event.payload[:name]}: #{exception.join(', ')} " \
              "(#{exception_object.backtrace.first})"
      else
        # standard logger code
      end
    end
  end
end

ActiveSupport::LogSubscriber also has some helpers to deal with logging. For example, ActiveSupport::LogSubscriber.flush_all! will ensure that all logs are flushed, and it is called in Rails::Rack::Logger after a request finishes.

Constants

BLACK

ANSI sequence colors

BLUE
BOLD
CLEAR

Embed in a String to clear all previous ANSI sequences.

CYAN
GREEN
MAGENTA
MODES

ANSI sequence modes

RED
WHITE
YELLOW

Attributes

logger[W]

Public Class Methods

flush_all!() click to toggle source

Flush all log_subscribers‘ logger.

# File lib/active_support/log_subscriber.rb, line 109
def flush_all!
  logger.flush if logger.respond_to?(:flush)
end
log_subscribers() click to toggle source
# File lib/active_support/log_subscriber.rb, line 104
def log_subscribers
  subscribers
end
logger() click to toggle source
# File lib/active_support/log_subscriber.rb, line 90
def logger
  @logger ||= if defined?(Rails) && Rails.respond_to?(:logger)
    Rails.logger
  end
end
new() click to toggle source
Calls superclass method
# File lib/active_support/log_subscriber.rb, line 130
def initialize
  super
  @event_levels = {}
end

Private Class Methods

fetch_public_methods(subscriber, inherit_all) click to toggle source
# File lib/active_support/log_subscriber.rb, line 114
def fetch_public_methods(subscriber, inherit_all)
  subscriber.public_methods(inherit_all) - LogSubscriber.public_instance_methods(true)
end
set_event_levels() click to toggle source
# File lib/active_support/log_subscriber.rb, line 118
def set_event_levels
  if subscriber
    subscriber.event_levels = log_levels.transform_keys { |k| "#{k}.#{namespace}" }
  end
end
subscribe_log_level(method, level) click to toggle source
# File lib/active_support/log_subscriber.rb, line 124
def subscribe_log_level(method, level)
  self.log_levels = log_levels.merge(method => ::Logger.const_get(level.upcase))
  set_event_levels
end

Public Instance Methods

call(event) click to toggle source
Calls superclass method
# File lib/active_support/log_subscriber.rb, line 143
def call(event)
  super if logger
rescue => e
  log_exception(event.name, e)
end
logger() click to toggle source
# File lib/active_support/log_subscriber.rb, line 135
def logger
  LogSubscriber.logger
end
publish_event(event) click to toggle source
Calls superclass method
# File lib/active_support/log_subscriber.rb, line 149
def publish_event(event)
  super if logger
rescue => e
  log_exception(event.name, e)
end
silenced?(event) click to toggle source
# File lib/active_support/log_subscriber.rb, line 139
def silenced?(event)
  logger.nil? || logger.level > @event_levels.fetch(event, Float::INFINITY)
end

Private Instance Methods

color(text, color, mode_options = {}) click to toggle source

Set color by using a symbol or one of the defined constants. Set modes by specifying bold, italic, or underline options. Inspired by Highline, this method will automatically clear formatting at the end of the returned String.

# File lib/active_support/log_subscriber.rb, line 169
def color(text, color, mode_options = {}) # :doc:
  return text unless colorize_logging
  color = self.class.const_get(color.upcase) if color.is_a?(Symbol)
  mode = mode_from(mode_options)
  clear = "\e[#{MODES[:clear]}m"
  "#{mode}#{color}#{text}#{clear}"
end
log_exception(name, e) click to toggle source
# File lib/active_support/log_subscriber.rb, line 191
def log_exception(name, e)
  if logger
    logger.error "Could not log #{name.inspect} event. #{e.class}: #{e.message} #{e.backtrace}"
  end
end
mode_from(options) click to toggle source
# File lib/active_support/log_subscriber.rb, line 177
    def mode_from(options)
      if options.is_a?(TrueClass) || options.is_a?(FalseClass)
        ActiveSupport.deprecator.warn(<<~MSG.squish)
          Bolding log text with a positional boolean is deprecated and will be removed
          in Rails 7.2. Use an option hash instead (eg. `color("my text", :red, bold: true)`).
        MSG
        options = { bold: options }
      end

      modes = MODES.values_at(*options.compact_blank.keys)

      "\e[#{modes.join(";")}m" if modes.any?
    end