Class: ActiveSupport::LogSubscriber

Relationships & Source Files
Namespace Children
Modules: `TestHelper`
Extension / Inclusion / Inheritance Descendants
Subclasses: ActionController::LogSubscriber, ActionDispatch::LogSubscriber, ActionMailer::LogSubscriber, ActionView::LogSubscriber, ActiveJob::LogSubscriber, ActiveRecord::LogSubscriber, ActiveStorage::LogSubscriber, Rails::Rack::Logger
Super Chains via Extension / Inclusion / Inheritance
Class Chain: self, `Subscriber`
Instance Chain: self, `Subscriber`
Inherits:	ActiveSupport::Subscriber `::Object` ActiveSupport::Subscriber ActiveSupport::LogSubscriber
Defined in:	activesupport/lib/active_support/log_subscriber.rb, activesupport/lib/active_support/log_subscriber/test_helper.rb

Overview

LogSubscriber is an object set to consume 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 Notifications consumer, 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

LogSubscriber also has some helpers to deal with logging. For example, .flush_all! will ensure that all logs are flushed, and it is called in ::Rails::Rack::Logger after a request finishes.

Constant Summary

BLACK =

ANSI sequence colors

# File 'activesupport/lib/active_support/log_subscriber.rb', line 74
```
"\e[30m"
```
BLUE =
# File 'activesupport/lib/active_support/log_subscriber.rb', line 78
```
"\e[34m"
```
CYAN =
# File 'activesupport/lib/active_support/log_subscriber.rb', line 80
```
"\e[36m"
```
GREEN =
# File 'activesupport/lib/active_support/log_subscriber.rb', line 76
```
"\e[32m"
```

LEVEL_CHECKS = Internal use only
# File 'activesupport/lib/active_support/log_subscriber.rb', line 86

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

MAGENTA =
# File 'activesupport/lib/active_support/log_subscriber.rb', line 79
```
"\e[35m"
```

MODES =

ANSI sequence modes

# File 'activesupport/lib/active_support/log_subscriber.rb', line 66

{
  clear:     0,
  bold:      1,
  italic:    3,
  underline: 4,
}

RED =
# File 'activesupport/lib/active_support/log_subscriber.rb', line 75
```
"\e[31m"
```
WHITE =
# File 'activesupport/lib/active_support/log_subscriber.rb', line 81
```
"\e[37m"
```
YELLOW =
# File 'activesupport/lib/active_support/log_subscriber.rb', line 77
```
"\e[33m"
```

Class Attribute Summary

.colorize_logging (also: #colorize_logging) rw
.log_levels rw Internal use only
.log_levels? ⇒ Boolean rw Internal use only
.logger rw Internal use only
.logger=(value) rw Internal use only

`Subscriber` - Inherited

.namespace, .notifier, .subscriber

Class Method Summary

.attach_to Internal use only
.flush_all! Internal use only

Flush all log_subscribers’ logger.
.log_subscribers Internal use only
.new ⇒ LogSubscriber constructor Internal use only
.fetch_public_methods(subscriber, inherit_all) private Internal use only
.set_event_levels private Internal use only
.subscribe_log_level(method, level) private Internal use only

`Subscriber` - Inherited

.attach_to	Attach the subscriber to a namespace.
.detach_from	Detach the subscriber from a namespace.
.method_added	Adds event subscribers for all new methods added to the class.
.new, .subscribers, .add_event_subscriber, .fetch_public_methods, .find_attached_subscriber, .invalid_event?, .pattern_subscribed?, .prepare_pattern, .remove_event_subscriber

Instance Attribute Summary

#colorize_logging rw
#event_levels=(value) writeonly Internal use only

`Subscriber` - Inherited

#patterns

Instance Method Summary

#call(event) Internal use only
#logger Internal use only
#publish_event(event) Internal use only
#silenced?(event) ⇒ Boolean Internal use only
#color(text, color, mode_options = {}) private Internal use only

Set color by using a symbol or one of the defined constants.
#log_exception(name, e) private Internal use only
#mode_from(options) private Internal use only

`Subscriber` - Inherited

#call, #publish_event

Constructor Details

.new ⇒ `LogSubscriber`

This method is for internal use only.

[ GitHub ]

# File 'activesupport/lib/active_support/log_subscriber.rb', line 133


def initialize
  super
  @event_levels = {}
end

Class Attribute Details

.colorize_logging (rw) Also known as: #colorize_logging

[ GitHub ]

# File 'activesupport/lib/active_support/log_subscriber.rb', line 83


mattr_accessor :colorize_logging, default: true

.log_levels (rw)

This method is for internal use only.

[ GitHub ]

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


class_attribute :log_levels, instance_accessor: false, default: {} # :nodoc:

.log_levels? ⇒ `Boolean` (rw)

This method is for internal use only.

[ GitHub ]

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


class_attribute :log_levels, instance_accessor: false, default: {} # :nodoc:

.logger (rw)

This method is for internal use only.

[ GitHub ]

# File 'activesupport/lib/active_support/log_subscriber.rb', line 93


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

.logger=(value) (rw)

This method is for internal use only.

[ GitHub ]

# File 'activesupport/lib/active_support/log_subscriber.rb', line 105


attr_writer :logger

Class Method Details

.attach_to

This method is for internal use only.

[ GitHub ]

# File 'activesupport/lib/active_support/log_subscriber.rb', line 99


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

.fetch_public_methods(subscriber, inherit_all) (private)

This method is for internal use only.

[ GitHub ]

# File 'activesupport/lib/active_support/log_subscriber.rb', line 117


def fetch_public_methods(subscriber, inherit_all)
  subscriber.public_methods(inherit_all) - LogSubscriber.public_instance_methods(true)
end

.flush_all!

This method is for internal use only.

Flush all log_subscribers’ logger.

[ GitHub ]

# File 'activesupport/lib/active_support/log_subscriber.rb', line 112


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

.log_subscribers

This method is for internal use only.

[ GitHub ]

# File 'activesupport/lib/active_support/log_subscriber.rb', line 107


def log_subscribers
  subscribers
end

.set_event_levels (private)

This method is for internal use only.

[ GitHub ]

# File 'activesupport/lib/active_support/log_subscriber.rb', line 121


def set_event_levels
  if subscriber
    subscriber.event_levels = log_levels.transform_keys { |k| "#{k}.#{namespace}" }
  end
end

.subscribe_log_level(method, level) (private)

This method is for internal use only.

[ GitHub ]

# File 'activesupport/lib/active_support/log_subscriber.rb', line 127


def subscribe_log_level(method, level)
  self.log_levels = log_levels.merge(method => LEVEL_CHECKS.fetch(level))
  set_event_levels
end

Instance Attribute Details

#colorize_logging (rw)

[ GitHub ]

# File 'activesupport/lib/active_support/log_subscriber.rb', line 83


mattr_accessor :colorize_logging, default: true

#event_levels=(value) (writeonly)

This method is for internal use only.

[ GitHub ]

# File 'activesupport/lib/active_support/log_subscriber.rb', line 158


attr_writer :event_levels # :nodoc:

Instance Method Details

#call(event)

This method is for internal use only.

[ GitHub ]

# File 'activesupport/lib/active_support/log_subscriber.rb', line 146


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

#color(text, color, mode_options = {}) (private)

This method is for internal use only.

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.

[ GitHub ]

# File 'activesupport/lib/active_support/log_subscriber.rb', line 172


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

#log_exception(name, e) (private)

This method is for internal use only.

[ GitHub ]

# File 'activesupport/lib/active_support/log_subscriber.rb', line 186


def log_exception(name, e)
  if logger
    logger.error "Could not log #{name.inspect} event. #{e.class}: #{e.message} #{e.backtrace}"
  end
end

#logger

This method is for internal use only.

[ GitHub ]

# File 'activesupport/lib/active_support/log_subscriber.rb', line 138


def logger
  LogSubscriber.logger
end

#mode_from(options) (private)

This method is for internal use only.

[ GitHub ]

# File 'activesupport/lib/active_support/log_subscriber.rb', line 180


def mode_from(options)
  modes = MODES.values_at(*options.compact_blank.keys)

  "\e[#{modes.join(";")}m" if modes.any?
end

#publish_event(event)

This method is for internal use only.

[ GitHub ]

# File 'activesupport/lib/active_support/log_subscriber.rb', line 152


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

#silenced?(event) ⇒ `Boolean`

This method is for internal use only.

[ GitHub ]

# File 'activesupport/lib/active_support/log_subscriber.rb', line 142


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

Class: ActiveSupport::LogSubscriber

Overview

Constant Summary

Class Attribute Summary

Subscriber - Inherited

Class Method Summary

Subscriber - Inherited

Instance Attribute Summary

Subscriber - Inherited

Instance Method Summary

Subscriber - Inherited

Constructor Details

.new ⇒ LogSubscriber

Class Attribute Details

.colorize_logging (rw) Also known as: #colorize_logging

.log_levels (rw)

.log_levels? ⇒ Boolean (rw)

.logger (rw)

.logger=(value) (rw)

Class Method Details

.attach_to

.fetch_public_methods(subscriber, inherit_all) (private)

.flush_all!

.log_subscribers

.set_event_levels (private)

.subscribe_log_level(method, level) (private)

Instance Attribute Details

#colorize_logging (rw)

#event_levels=(value) (writeonly)

Instance Method Details

#call(event)

#color(text, color, mode_options = {}) (private)

#log_exception(name, e) (private)

#logger

#mode_from(options) (private)

#publish_event(event)

#silenced?(event) ⇒ Boolean

`Subscriber` - Inherited

`Subscriber` - Inherited

`Subscriber` - Inherited

`Subscriber` - Inherited

.new ⇒ `LogSubscriber`

.log_levels? ⇒ `Boolean` (rw)

#silenced?(event) ⇒ `Boolean`