_send_file

# File lib/webrick/httpresponse.rb, line 374
    def _send_file(output, input, offset, size)
      while offset > 0
        sz = @buffer_size < size ? @buffer_size : size
        buf = input.read(sz)
        offset -= buf.bytesize
      end

      if size == 0
        while buf = input.read(@buffer_size)
          _write_data(output, buf)
        end
      else
        while size > 0
          sz = @buffer_size < size ? @buffer_size : size
          buf = input.read(sz)
          _write_data(output, buf)
          size -= buf.bytesize
        end
      end
    end