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]}"

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(', ')} " \
        # standard logger code

+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.


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

WHITE = "\e[37m"

CYAN = "\e[36m"

MAGENTA = "\e[35m"

BLUE = "\e[34m"

YELLOW = "\e[33m"

GREEN = "\e[32m"

RED = "\e[31m"

BLACK = "\e[30m"

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

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

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


[W] event_levels
[W] logger
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