to Thin from WEBrick

Whenever rails gets http access, it's too loud displaying that
"WARN Could not determine content-length of response body. Set content-length of the response or set Response#chunked = true" on rails's log.

One of Rails-Core's members says "ya, it's fine. Need to clean it up, but nothing is being hurt.", so it isn't problem about displaying this WARN itself.

There are some kind of way getting rid of this message.
I chose to shift Thin for WEBrick.

I added to GemFile as follows:

group :development do
  gem 'thin'

Speaking of cleaning rails's log.
I made quiet_assets.rb on app/config/initializers/
I added the following

Rails.application.assets.logger ='/dev/null') 
Rails::Rack::Logger.class_eval do
  def call_with_quiet_assets(env)
    previous_level = Rails.logger.level
    Rails.logger.level = Logger::ERROR if env['PATH_INFO'].index("/assets/") == 0
    call_without_quiet_assets(env).tap do
      Rails.logger.level = previous_level
  alias_method_chain :call, :quiet_assets

get the silence :3

Ruby on Rails 3 アプリケーションプログラミング