class Rails::Rack::Logger

an instance of the request object.
object responds to, objects that respond to to_s or Proc objects that accept
Log tags (taggers) can be an Array containing: methods that the request
Sets log tags, logs the request, calls the app, and flushes the logs.

def call(env) 

def call(env)
  request = ActionDispatch::Request.new(env)
  if logger.respond_to?(:tagged)
    logger.tagged(compute_tags(request)) { call_app(request, env) }
  else
    call_app(request, env)
  end
end

def call_app(request, env) # :doc:

:doc: 
def call_app(request, env) # :doc:
  instrumenter = ActiveSupport::Notifications.instrumenter
  instrumenter_state = instrumenter.start "request.action_dispatch", request: request
  instrumenter_finish = -> () {
    instrumenter.finish_with_state(instrumenter_state, "request.action_dispatch", request: request)
  }
  logger.info { started_request_message(request) }
  status, headers, body = @app.call(env)
  body = ::Rack::BodyProxy.new(body, &instrumenter_finish)
  [status, headers, body]
rescue Exception
  instrumenter_finish.call
  raise
ensure
  ActiveSupport::LogSubscriber.flush_all!
end

def compute_tags(request) # :doc:

:doc: 
def compute_tags(request) # :doc:
  @taggers.collect do |tag|
    case tag
    when Proc
      tag.call(request)
    when Symbol
      request.send(tag)
    else
      tag
    end
  end
end

def initialize(app, taggers = nil) 

def initialize(app, taggers = nil)
  @app          = app
  @taggers      = taggers || []
end

def logger 

def logger
  Rails.logger
end

def started_request_message(request) # :doc:

:doc:
Started GET "/session/new" for 127.0.0.1 at 2012-09-26 14:51:42 -0700 
def started_request_message(request) # :doc:
  'Started %s "%s" for %s at %s' % [
    request.raw_request_method,
    request.filtered_path,
    request.remote_ip,
    Time.now.to_default_s ]
end