class ActiveSupport::LogSubscriber

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

And it's finally registered as:

ActiveRecord::LogSubscriber.attach_to :active_record

Since we need to know all instance methods before attaching the log subscriber, the line above should be called after your ActiveRecord::LogSubscriber definition.

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

Log subscriber also has some helpers to deal with logging and automatically flushes all logs when the request finishes (via action_dispatch.callback notification) in a Rails environment.

Constants

BLACK

Colors

BLUE
BOLD
CLEAR

Embed in a String to clear all previous ANSI sequences.

CYAN
GREEN
MAGENTA
RED
WHITE
YELLOW

Public Class Methods

attach_to(namespace, log_subscriber=new, notifier=ActiveSupport::Notifications) click to toggle source
# File lib/active_support/log_subscriber.rb, line 59
def attach_to(namespace, log_subscriber=new, notifier=ActiveSupport::Notifications)
  log_subscribers << log_subscriber
  @@flushable_loggers = nil

  log_subscriber.public_methods(false).each do |event|
    next if 'call' == event.to_s

    notifier.subscribe("#{event}.#{namespace}", log_subscriber)
  end
end
flush_all!() click to toggle source

Flush all ::log_subscribers' logger.

# File lib/active_support/log_subscriber.rb, line 83
def flush_all!
  flushable_loggers.each { |log| log.flush }
end
flushable_loggers() click to toggle source
# File lib/active_support/log_subscriber.rb, line 74
def flushable_loggers
  @@flushable_loggers ||= begin
    loggers = log_subscribers.map(&:logger)
    loggers.uniq!
    loggers.select { |l| l.respond_to?(:flush) }
  end
end
log_subscribers() click to toggle source
# File lib/active_support/log_subscriber.rb, line 70
def log_subscribers
  @@log_subscribers ||= []
end
logger() click to toggle source
# File lib/active_support/log_subscriber.rb, line 55
def logger
  @logger ||= Rails.logger if defined?(Rails)
end

Public Instance Methods

call(message, *args) click to toggle source
# File lib/active_support/log_subscriber.rb, line 88
def call(message, *args)
  return unless logger

  method = message.split('.').first
  begin
    send(method, ActiveSupport::Notifications::Event.new(message, *args))
  rescue Exception => e
    logger.error "Could not log #{message.inspect} event. #{e.class}: #{e.message}"
  end
end

Protected Instance Methods

color(text, color, bold=false) click to toggle source

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 the Highline implementation and will automatically append CLEAR to the end of the returned String.

# File lib/active_support/log_subscriber.rb, line 115
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
format_duration(duration) click to toggle source
# File lib/active_support/log_subscriber.rb, line 122
def format_duration(duration)
  "%.1fms" % duration
end