ActiveSupport::LogSubscriber is an object set to consume ActiveSupport::Notifications with solely purpose of logging. The log subscriber dispatches notifications to a regirested 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 registed 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.
# 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 log_subscribers' logger.
# File lib/active_support/log_subscriber.rb, line 83 def flush_all! flushable_loggers.each { |log| log.flush } end
# 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
# 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
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 Highline implementation and it automatically appends 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
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