ActiveSupport::LogSubscriber is an object set to consume ActiveSupport::Notifications with solely purpose of logging. The log subscriber dispatches notifications to a regirested object based on its given namespace.
An example would be Active Record log subscriber responsible for logging queries:
module ActiveRecord
class LogSubscriber < ActiveSupport::LogSubscriber
def sql(event)
"#{event.payload[:name]} (#{event.duration}) #{event.payload[:sql]}"
end
end
end
And it’s finally registed as:
ActiveRecord::LogSubscriber.attach_to :active_record
Since we need to know all instance methods before attaching the log subscriber, the line above should be called after your ActiveRecord::LogSubscriber definition.
After configured, whenever a “sql.active_record“ notification is published, it will properly dispatch the event (ActiveSupport::Notifications::Event) to the sql method.
Log subscriber also has some helpers to deal with logging and automatically flushes all logs when the request finishes (via action_dispatch.callback notification) in a Rails environment.
| CLEAR | = | "\e[0m" |
Embed in a String to clear all previous ANSI sequences. |
||
| BOLD | = | "\e[1m" |
| BLACK | = | "\e[30m" |
Colors |
||
| RED | = | "\e[31m" |
| GREEN | = | "\e[32m" |
| YELLOW | = | "\e[33m" |
| BLUE | = | "\e[34m" |
| MAGENTA | = | "\e[35m" |
| CYAN | = | "\e[36m" |
| WHITE | = | "\e[37m" |
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# File activesupport/lib/active_support/log_subscriber.rb, line 59
59: def attach_to(namespace, log_subscriber=new, notifier=ActiveSupport::Notifications)
60: log_subscribers << log_subscriber
61: @@flushable_loggers = nil
62:
63: log_subscriber.public_methods(false).each do |event|
64: next if 'call' == event.to_s
65:
66: notifier.subscribe("#{event}.#{namespace}", log_subscriber)
67: end
68: end
Flush all log_subscribers’ logger.
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# File activesupport/lib/active_support/log_subscriber.rb, line 83
83: def flush_all!
84: flushable_loggers.each(&:flush)
85: end
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# File activesupport/lib/active_support/log_subscriber.rb, line 74
74: def flushable_loggers
75: @@flushable_loggers ||= begin
76: loggers = log_subscribers.map(&:logger)
77: loggers.uniq!
78: loggers.select { |l| l.respond_to?(:flush) }
79: end
80: end
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# File activesupport/lib/active_support/log_subscriber.rb, line 70
70: def log_subscribers
71: @@log_subscribers ||= []
72: end
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# File activesupport/lib/active_support/log_subscriber.rb, line 55
55: def logger
56: @logger ||= Rails.logger if defined?(Rails)
57: end
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# File activesupport/lib/active_support/log_subscriber.rb, line 88
88: def call(message, *args)
89: return unless logger
90:
91: method = message.split('.').first
92: begin
93: send(method, ActiveSupport::Notifications::Event.new(message, *args))
94: rescue Exception => e
95: logger.error "Could not log #{message.inspect} event. #{e.class}: #{e.message}"
96: end
97: end
Set color by using a string or one of the defined constants. If a third option is set to true, it also adds bold to the string. This is based on Highline implementation and it automatically appends CLEAR to the end of the returned String.
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# File activesupport/lib/active_support/log_subscriber.rb, line 115
115: def color(text, color, bold=false)
116: return text unless colorize_logging
117: color = self.class.const_get(color.to_s.upcase) if color.is_a?(Symbol)
118: bold = bold ? BOLD : ""
119: "#{bold}#{color}#{text}#{CLEAR}"
120: end