edge badge

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.

Namespace
Methods
C
F
L
S
Constants
CLEAR = "\e[0m"
 

Embed in a String to clear all previous ANSI sequences.

BOLD = "\e[1m"
 
BLACK = "\e[30m"
 

Colors

RED = "\e[31m"
 
GREEN = "\e[32m"
 
YELLOW = "\e[33m"
 
BLUE = "\e[34m"
 
MAGENTA = "\e[35m"
 
CYAN = "\e[36m"
 
WHITE = "\e[37m"
 
Attributes
[W] logger
Class Public methods
flush_all!()

Flush all ::log_subscribers' logger.

# File activesupport/lib/active_support/log_subscriber.rb, line 69
def flush_all!
  logger.flush if logger.respond_to?(:flush)
end
log_subscribers()
# File activesupport/lib/active_support/log_subscriber.rb, line 64
def log_subscribers
  subscribers
end
logger()
# File activesupport/lib/active_support/log_subscriber.rb, line 56
def logger
  @logger ||= if defined?(Rails) && Rails.respond_to?(:logger)
    Rails.logger
  end
end
Instance Public methods
finish(name, id, payload)
# File activesupport/lib/active_support/log_subscriber.rb, line 82
def finish(name, id, payload)
  super if logger
rescue Exception => e
  logger.error "Could not log #{name.inspect} event. #{e.class}: #{e.message} #{e.backtrace}"
end
logger()
# File activesupport/lib/active_support/log_subscriber.rb, line 74
def logger
  LogSubscriber.logger
end
start(name, id, payload)
# File activesupport/lib/active_support/log_subscriber.rb, line 78
def start(name, id, payload)
  super if logger
end
Instance Protected methods
color(text, color, bold=false)

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 activesupport/lib/active_support/log_subscriber.rb, line 102
def color(text, color, bold=false)
  return text unless colorize_logging
  color = self.class.const_get(color.upcase) if color.is_a?(Symbol)
  bold  = bold ? BOLD : ""
  "#{bold}#{color}#{text}#{CLEAR}"
end