Class: ActiveSupport::LogSubscriber

Inherits:
Subscriber show all
Includes:
ColorizeLogging
Defined in:
activesupport/lib/active_support/log_subscriber.rb,
activesupport/lib/active_support/log_subscriber/test_helper.rb

Overview

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.

Direct Known Subclasses

Rails::Rack::Logger

Defined Under Namespace

Modules: TestHelper

Constant Summary collapse

LEVEL_CHECKS = 
{
  debug: -> (logger) { !logger.debug? },
  info: -> (logger) { !logger.info? },
  error: -> (logger) { !logger.error? },
}

Constants included from ColorizeLogging

ColorizeLogging::BLACK, ColorizeLogging::BLUE, ColorizeLogging::CYAN, ColorizeLogging::GREEN, ColorizeLogging::MAGENTA, ColorizeLogging::MODES, ColorizeLogging::RED, ColorizeLogging::WHITE, ColorizeLogging::YELLOW

Class Attribute Summary collapse

Instance Attribute Summary collapse

Attributes inherited from Subscriber

#patterns

Class Method Summary collapse

Instance Method Summary collapse

Methods included from ColorizeLogging

#color, #colorize_logging, #debug, #error, #fatal, #info, #mode_from, #unknown, #warn

Methods included from Concern

#append_features, #class_methods, extended, #included, #prepend_features, #prepended

Methods inherited from Subscriber

detach_from, method_added, subscribers

Constructor Details

#initialize ⇒ LogSubscriber

Returns a new instance of LogSubscriber.



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# File 'activesupport/lib/active_support/log_subscriber.rb', line 120

def initialize
  super
  @event_levels = {}
end

Class Attribute Details

.logger ⇒ Object 



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# File 'activesupport/lib/active_support/log_subscriber.rb', line 76

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

Instance Attribute Details

#event_levels=(value) ⇒ Object (writeonly)

:nodoc:



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# File 'activesupport/lib/active_support/log_subscriber.rb', line 135

def event_levels=(value)
  @event_levels = value
end

Class Method Details

.attach_to ⇒ Object

:nodoc:



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# File 'activesupport/lib/active_support/log_subscriber.rb', line 84

def attach_to(...) # :nodoc:
  result = super
  set_event_levels
  result
end

.flush_all! ⇒ Object

Flush all log_subscribers’ logger.



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# File 'activesupport/lib/active_support/log_subscriber.rb', line 95

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

.log_subscribers ⇒ Object 



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# File 'activesupport/lib/active_support/log_subscriber.rb', line 90

def log_subscribers
  subscribers
end

Instance Method Details

#call(event) ⇒ Object 



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# File 'activesupport/lib/active_support/log_subscriber.rb', line 129

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

#logger ⇒ Object 



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# File 'activesupport/lib/active_support/log_subscriber.rb', line 116

def logger
  LogSubscriber.logger
end

#silenced?(event) ⇒ Boolean

Returns:

  • (Boolean) 


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# File 'activesupport/lib/active_support/log_subscriber.rb', line 125

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