translate_offset (ActiveSupport::Multibyte::Handlers::UTF8Handler)

    # File lib/active_support/multibyte/handlers/utf8_handler.rb, line 321
          def translate_offset(str, byte_offset)
            return nil if byte_offset.nil?
            return 0 if str == ''
            chunk = str[0..byte_offset]
            begin
              begin
                chunk.unpack('U*').length - 1
              rescue ArgumentError => e
                chunk = str[0..(byte_offset+=1)]
                # Stop retrying at the end of the string
                raise e unless byte_offset < chunk.length
                # We damaged a character, retry
                retry
              end
            # Catch the ArgumentError so we can throw our own
            rescue ArgumentError
              raise EncodingError.new('malformed UTF-8 character')
            end
          end