class ActiveSupport::LogSubscriber
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.
Constants
- BLACK
-
ANSI sequence colors
- BLUE
- CYAN
- GREEN
- LEVEL_CHECKS
- MAGENTA
- MODES
-
ANSI sequence modes
- RED
- WHITE
- YELLOW
Attributes
Public Class Methods
Source
# File lib/active_support/log_subscriber.rb, line 112 def flush_all! logger.flush if logger.respond_to?(:flush) end
Flush all log_subscribers
‘ logger.
Source
# File lib/active_support/log_subscriber.rb, line 107 def log_subscribers subscribers end
Source
# File lib/active_support/log_subscriber.rb, line 93 def logger @logger ||= if defined?(Rails) && Rails.respond_to?(:logger) Rails.logger end end
Source
# File lib/active_support/log_subscriber.rb, line 133 def initialize super @event_levels = {} end
Private Class Methods
Source
# File 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
Source
# File 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
Source
# File 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
Public Instance Methods
Source
# File lib/active_support/log_subscriber.rb, line 146 def call(event) super if logger rescue => e log_exception(event.name, e) end
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# File lib/active_support/log_subscriber.rb, line 138 def logger LogSubscriber.logger end
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# File lib/active_support/log_subscriber.rb, line 152 def publish_event(event) super if logger rescue => e log_exception(event.name, e) end
Source
# File lib/active_support/log_subscriber.rb, line 142 def silenced?(event) logger.nil? || @event_levels[event]&.call(logger) end
Private Instance Methods
Source
# File 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
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
.
Source
# File 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
Source
# File 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