transfercmd

# File lib/net/ftp.rb, line 541
    def transfercmd(cmd, rest_offset = nil) # :nodoc:
      if @passive
        host, port = makepasv
        conn = open_socket(host, port)
        if @resume and rest_offset
          resp = sendcmd("REST " + rest_offset.to_s)
          if !resp.start_with?("3")
            raise FTPReplyError, resp
          end
        end
        resp = sendcmd(cmd)
        # skip 2XX for some ftp servers
        resp = getresp if resp.start_with?("2")
        if !resp.start_with?("1")
          raise FTPReplyError, resp
        end
      else
        sock = makeport
        begin
          addr = sock.local_address
          sendport(addr.ip_address, addr.ip_port)
          if @resume and rest_offset
            resp = sendcmd("REST " + rest_offset.to_s)
            if !resp.start_with?("3")
              raise FTPReplyError, resp
            end
          end
          resp = sendcmd(cmd)
          # skip 2XX for some ftp servers
          resp = getresp if resp.start_with?("2")
          if !resp.start_with?("1")
            raise FTPReplyError, resp
          end
          conn, = sock.accept
          sock.shutdown(Socket::SHUT_WR) rescue nil
          sock.read rescue nil
        ensure
          sock.close
        end
      end
      if @private_data_connection
        return BufferedSSLSocket.new(start_tls_session(conn),
                                     read_timeout: @read_timeout)
      else
        return BufferedSocket.new(conn, read_timeout: @read_timeout)
      end
    end