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
- LEVEL_CHECKS
- MAGENTA
- MODES
ANSI sequence modes
- RED
- WHITE
- YELLOW
Attributes
Public Class Methods
Flush all log_subscribers
‘ logger.
# File lib/active_support/log_subscriber.rb, line 115 def flush_all! logger.flush if logger.respond_to?(:flush) end
# File lib/active_support/log_subscriber.rb, line 110 def log_subscribers subscribers end
# File lib/active_support/log_subscriber.rb, line 96 def logger @logger ||= if defined?(Rails) && Rails.respond_to?(:logger) Rails.logger end end
# File lib/active_support/log_subscriber.rb, line 136 def initialize super @event_levels = {} end
Private Class Methods
# File lib/active_support/log_subscriber.rb, line 120 def fetch_public_methods(subscriber, inherit_all) subscriber.public_methods(inherit_all) - LogSubscriber.public_instance_methods(true) end
# File lib/active_support/log_subscriber.rb, line 124 def set_event_levels if subscriber subscriber.event_levels = log_levels.transform_keys { |k| "#{k}.#{namespace}" } end end
# File lib/active_support/log_subscriber.rb, line 130 def subscribe_log_level(method, level) self.log_levels = log_levels.merge(method => LEVEL_CHECKS.fetch(level)) set_event_levels end
Public Instance Methods
# File lib/active_support/log_subscriber.rb, line 149 def call(event) super if logger rescue => e log_exception(event.name, e) end
# File lib/active_support/log_subscriber.rb, line 141 def logger LogSubscriber.logger end
# File lib/active_support/log_subscriber.rb, line 155 def publish_event(event) super if logger rescue => e log_exception(event.name, e) end
# File lib/active_support/log_subscriber.rb, line 145 def silenced?(event) logger.nil? || @event_levels[event]&.call(logger) end
Private Instance Methods
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 175 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
# File lib/active_support/log_subscriber.rb, line 197 def log_exception(name, e) if logger logger.error "Could not log #{name.inspect} event. #{e.class}: #{e.message} #{e.backtrace}" end end
# File lib/active_support/log_subscriber.rb, line 183 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