def sendport(host, port) # :nodoc:
      af = (@sock.peeraddr)[0]
      if af == "AF_INET"
        cmd = "PORT " + (host.split(".") + port.divmod(256)).join(",")
      elsif af == "AF_INET6"
        cmd = sprintf("EPRT |2|%s|%d|", host, port)
      else
        raise FTPProtoError, host
      end
      voidcmd(cmd)
    end
Constructs and send the appropriate PORT (or EPRT) command