Rails 3.2.0 through 3.2.8 define the log format directly in in Rails::Rack::Logger#call_app
github.com/rails/rails/blob/v3.2.8/railties/lib/rails/rack/logger.rb#L22-L29
github.com/rails/rails/blob/v3.2.0/railties/lib/rails/rack/logger.rb#L22-L29