def send_frame(xml)
        xml = xml.to_s if xml.kind_of?(Request)
        @sock.write([xml.size + HEADER_LEN].pack("N") + xml)
      end
def send_frame(xml)
        xml = xml.to_s if xml.kind_of?(Request)
        @sock.write([xml.size + HEADER_LEN].pack("N") + xml)
      end
Send XML frame
 @param [String,Request] xml Payload to send
 @return [Integer] number of bytes written