ActiveSupport::LogSubscriber (original) (raw)

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.

Namespace

• MODULE ActiveSupport::LogSubscriber::TestHelper

Methods

C

• call,
• color

F

• flush_all!

L

• log_subscribers,
• logger,
• logger

N

• new

P

• publish_event

S

• silenced?

Constants

Attributes

Class Public methods

flush_all!()Link

Source: show | on GitHub

def flush_all! logger.flush if logger.respond_to?(:flush) end

log_subscribers()Link

logger()Link

Source: show | on GitHub

def logger @logger ||= if defined?(Rails) && Rails.respond_to?(:logger) Rails.logger end end

Instance Public methods

call(event)Link

Source: show | on GitHub

def call(event) super if logger rescue => e log_exception(event.name, e) end

publish_event(event)Link

Source: show | on GitHub

def publish_event(event) super if logger rescue => e log_exception(event.name, e) end

silenced?(event)Link

Source: show | on GitHub

def silenced?(event) logger.nil? || @event_levels[event]&.call(logger) end

Instance Private methods

color(text, color, mode_options = {})Link

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.

Source: show | on GitHub

def color(text, color, mode_options = {}) 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