code: public static Message buildPullTxnReq(Zxid lastZxid) {
      ZabMessage.Zxid zxid = toProtoZxid(lastZxid);
  
      PullTxnReq req = PullTxnReq.newBuilder().setLastZxid(zxid)
                                              .build();
  
      return Message.newBuilder().setType(MessageType.PULL_TXN_REQ)
                                 .setPullTxnReq(req)
                                 .build();
    }
docs: Creates a PULL_TXN_REQ message to ask follower sync its history to leader.
  
  @param lastZxid the last transaction id of leader, the sync starts one
  after this transaction (not including this one).
  @return a protobuf message.