ActiveSupport::LogSubscriber

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.

Constants

CLEAR: Embed in a String to clear all previous ANSI sequences.
BOLD
BLACK: Colors
RED
GREEN
YELLOW
BLUE
MAGENTA
CYAN
WHITE

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
59:       def attach_to(namespace, log_subscriber=new, notifier=ActiveSupport::Notifications)
60:         log_subscribers << log_subscriber
61:         @@flushable_loggers = nil
62: 
63:         log_subscriber.public_methods(false).each do |event|
64:           next if 'call' == event.to_s
65: 
66:           notifier.subscribe("#{event}.#{namespace}", log_subscriber)
67:         end
68:       end

flush_all!() click to toggle source

Flush all log_subscribers’ logger.

    # File lib/active_support/log_subscriber.rb, line 83
83:       def flush_all!
84:         flushable_loggers.each(&:flush)
85:       end

flushable_loggers() click to toggle source

    # File lib/active_support/log_subscriber.rb, line 74
74:       def flushable_loggers
75:         @@flushable_loggers ||= begin
76:           loggers = log_subscribers.map(&:logger)
77:           loggers.uniq!
78:           loggers.select { |l| l.respond_to?(:flush) }
79:         end
80:       end

log_subscribers() click to toggle source

    # File lib/active_support/log_subscriber.rb, line 70
70:       def log_subscribers
71:         @@log_subscribers ||= []
72:       end

logger() click to toggle source

    # File lib/active_support/log_subscriber.rb, line 55
55:       def logger
56:         @logger ||= Rails.logger if defined?(Rails)
57:       end

Public Instance Methods

call(message, *args) click to toggle source

    # File lib/active_support/log_subscriber.rb, line 88
88:     def call(message, *args)
89:       return unless logger
90: 
91:       method = message.split('.').first
92:       begin
93:         send(method, ActiveSupport::Notifications::Event.new(message, *args))
94:       rescue Exception => e
95:         logger.error "Could not log #{message.inspect} event. #{e.class}: #{e.message}"
96:       end
97:     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 Highline implementation and it automatically appends CLEAR to the end of the returned String.

     # File lib/active_support/log_subscriber.rb, line 115
115:     def color(text, color, bold=false)
116:       return text unless colorize_logging
117:       color = self.class.const_get(color.to_s.upcase) if color.is_a?(Symbol)
118:       bold  = bold ? BOLD : ""
119:       "#{bold}#{color}#{text}#{CLEAR}"
120:     end

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ActiveSupport::LogSubscriber

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