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 78
```
"\e[30m"
```
BLUE =
# File 'activesupport/lib/active_support/log_subscriber.rb', line 82
```
"\e[34m"
```

BOLD =
# File 'activesupport/lib/active_support/log_subscriber.rb', line 67

ActiveSupport::Deprecation::DeprecatedObjectProxy.new("\e[1m", "BOLD is deprecated! Use MODES[:bold] instead.", ActiveSupport.deprecator)

CLEAR =

Embed in a ::String to clear all previous ANSI sequences.

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

ActiveSupport::Deprecation::DeprecatedObjectProxy.new("\e[0m", "CLEAR is deprecated! Use MODES[:clear] instead.", ActiveSupport.deprecator)

CYAN =
# File 'activesupport/lib/active_support/log_subscriber.rb', line 84
```
"\e[36m"
```
GREEN =
# File 'activesupport/lib/active_support/log_subscriber.rb', line 80
```
"\e[32m"
```

LEVEL_CHECKS = Internal use only
# File 'activesupport/lib/active_support/log_subscriber.rb', line 90

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

MAGENTA =
# File 'activesupport/lib/active_support/log_subscriber.rb', line 83
```
"\e[35m"
```

MODES =

ANSI sequence modes

# File 'activesupport/lib/active_support/log_subscriber.rb', line 70

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

RED =
# File 'activesupport/lib/active_support/log_subscriber.rb', line 79
```
"\e[31m"
```
WHITE =
# File 'activesupport/lib/active_support/log_subscriber.rb', line 85
```
"\e[37m"
```
YELLOW =
# File 'activesupport/lib/active_support/log_subscriber.rb', line 81
```
"\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 137


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 87


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 88


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 88


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 97


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 109


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 103


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 121


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 116


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 111


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 125


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 131


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 87


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 162


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 150


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 176


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 198


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 142


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 184


def mode_from(options)
  if options.is_a?(TrueClass) || options.is_a?(FalseClass)
    ActiveSupport.deprecator.warn(<<~MSG.squish)
      Bolding log text with a positional boolean is deprecated and will be removed
      in Rails 7.2. Use an option hash instead (eg. `color("my text", :red, bold: true)`).
    MSG
    options = { bold: options }
  end

  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 156


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 146


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`