docs: public static LogEvent decode(LogBuffer buffer, LogHeader header, LogContext context) throws IOException {
          FormatDescriptionLogEvent descriptionEvent = context.getFormatDescription();
          LogPosition logPosition = context.getLogPosition();
  
          int checksumAlg = LogEvent.BINLOG_CHECKSUM_ALG_UNDEF;
          if (header.getType() != LogEvent.FORMAT_DESCRIPTION_EVENT) {
              checksumAlg = descriptionEvent.header.getChecksumAlg();
          } else {
              // 如果是format事件自己，也需要处理checksum
              checksumAlg = header.getChecksumAlg();
          }
  
          if (checksumAlg != LogEvent.BINLOG_CHECKSUM_ALG_OFF && checksumAlg != LogEvent.BINLOG_CHECKSUM_ALG_UNDEF) {
              // remove checksum bytes
              buffer.limit(header.getEventLen() - LogEvent.BINLOG_CHECKSUM_LEN);
          }
          GTIDSet gtidSet = context.getGtidSet();
          GtidLogEvent gtidLogEvent = context.getGtidLogEvent();
          switch (header.getType()) {
              case LogEvent.QUERY_EVENT: {
                  QueryLogEvent event = new QueryLogEvent(header, buffer, descriptionEvent);
                  /* updating position in context */
                  logPosition.position = header.getLogPos();
                  header.putGtid(context.getGtidSet(), gtidLogEvent);
                  return event;
              }
              case LogEvent.XID_EVENT: {
                  XidLogEvent event = new XidLogEvent(header, buffer, descriptionEvent);
                  /* updating position in context */
                  logPosition.position = header.getLogPos();
                  header.putGtid(context.getGtidSet(), gtidLogEvent);
                  return event;
              }
              case LogEvent.TABLE_MAP_EVENT: {
                  TableMapLogEvent mapEvent = new TableMapLogEvent(header, buffer, descriptionEvent);
                  /* updating position in context */
                  logPosition.position = header.getLogPos();
                  context.putTable(mapEvent);
                  return mapEvent;
              }
              case LogEvent.WRITE_ROWS_EVENT_V1: {
                  RowsLogEvent event = new WriteRowsLogEvent(header, buffer, descriptionEvent);
                  /* updating position in context */
                  logPosition.position = header.getLogPos();
                  event.fillTable(context);
                  header.putGtid(context.getGtidSet(), gtidLogEvent);
                  return event;
              }
              case LogEvent.UPDATE_ROWS_EVENT_V1: {
                  RowsLogEvent event = new UpdateRowsLogEvent(header, buffer, descriptionEvent);
                  /* updating position in context */
                  logPosition.position = header.getLogPos();
                  event.fillTable(context);
                  header.putGtid(context.getGtidSet(), gtidLogEvent);
                  return event;
              }
              case LogEvent.DELETE_ROWS_EVENT_V1: {
                  RowsLogEvent event = new DeleteRowsLogEvent(header, buffer, descriptionEvent);
                  /* updating position in context */
                  logPosition.position = header.getLogPos();
                  event.fillTable(context);
                  header.putGtid(context.getGtidSet(), gtidLogEvent);
                  return event;
              }
              case LogEvent.ROTATE_EVENT: {
                  RotateLogEvent event = new RotateLogEvent(header, buffer, descriptionEvent);
                  /* updating position in context */
                  logPosition = new LogPosition(event.getFilename(), event.getPosition());
                  context.setLogPosition(logPosition);
                  return event;
              }
              case LogEvent.LOAD_EVENT:
              case LogEvent.NEW_LOAD_EVENT: {
                  LoadLogEvent event = new LoadLogEvent(header, buffer, descriptionEvent);
                  /* updating position in context */
                  logPosition.position = header.getLogPos();
                  return event;
              }
              case LogEvent.SLAVE_EVENT: /* can never happen (unused event) */
              {
                  if (logger.isWarnEnabled()) logger.warn("Skipping unsupported SLAVE_EVENT from: "
                                                          + context.getLogPosition());
                  break;
              }
              case LogEvent.CREATE_FILE_EVENT: {
                  CreateFileLogEvent event = new CreateFileLogEvent(header, buffer, descriptionEvent);
                  /* updating position in context */
                  logPosition.position = header.getLogPos();
                  return event;
              }
              case LogEvent.APPEND_BLOCK_EVENT: {
                  AppendBlockLogEvent event = new AppendBlockLogEvent(header, buffer, descriptionEvent);
                  /* updating position in context */
                  logPosition.position = header.getLogPos();
                  return event;
              }
              case LogEvent.DELETE_FILE_EVENT: {
                  DeleteFileLogEvent event = new DeleteFileLogEvent(header, buffer, descriptionEvent);
                  /* updating position in context */
                  logPosition.position = header.getLogPos();
                  return event;
              }
              case LogEvent.EXEC_LOAD_EVENT: {
                  ExecuteLoadLogEvent event = new ExecuteLoadLogEvent(header, buffer, descriptionEvent);
                  /* updating position in context */
                  logPosition.position = header.getLogPos();
                  return event;
              }
              case LogEvent.START_EVENT_V3: {
                  /* This is sent only by MySQL <=4.x */
                  StartLogEventV3 event = new StartLogEventV3(header, buffer, descriptionEvent);
                  /* updating position in context */
                  logPosition.position = header.getLogPos();
                  return event;
              }
              case LogEvent.STOP_EVENT: {
                  StopLogEvent event = new StopLogEvent(header, buffer, descriptionEvent);
                  /* updating position in context */
                  logPosition.position = header.getLogPos();
                  return event;
              }
              case LogEvent.INTVAR_EVENT: {
                  IntvarLogEvent event = new IntvarLogEvent(header, buffer, descriptionEvent);
                  /* updating position in context */
                  logPosition.position = header.getLogPos();
                  return event;
              }
              case LogEvent.RAND_EVENT: {
                  RandLogEvent event = new RandLogEvent(header, buffer, descriptionEvent);
                  /* updating position in context */
                  logPosition.position = header.getLogPos();
                  header.putGtid(context.getGtidSet(), gtidLogEvent);
                  return event;
              }
              case LogEvent.USER_VAR_EVENT: {
                  UserVarLogEvent event = new UserVarLogEvent(header, buffer, descriptionEvent);
                  /* updating position in context */
                  logPosition.position = header.getLogPos();
                  header.putGtid(context.getGtidSet(), gtidLogEvent);
                  return event;
              }
              case LogEvent.FORMAT_DESCRIPTION_EVENT: {
                  descriptionEvent = new FormatDescriptionLogEvent(header, buffer, descriptionEvent);
                  context.setFormatDescription(descriptionEvent);
                  return descriptionEvent;
              }
              case LogEvent.PRE_GA_WRITE_ROWS_EVENT: {
                  if (logger.isWarnEnabled()) logger.warn("Skipping unsupported PRE_GA_WRITE_ROWS_EVENT from: "
                                                          + context.getLogPosition());
                  // ev = new Write_rows_log_event_old(buf, event_len,
                  // description_event);
                  break;
              }
              case LogEvent.PRE_GA_UPDATE_ROWS_EVENT: {
                  if (logger.isWarnEnabled()) logger.warn("Skipping unsupported PRE_GA_UPDATE_ROWS_EVENT from: "
                                                          + context.getLogPosition());
                  // ev = new Update_rows_log_event_old(buf, event_len,
                  // description_event);
                  break;
              }
              case LogEvent.PRE_GA_DELETE_ROWS_EVENT: {
                  if (logger.isWarnEnabled()) logger.warn("Skipping unsupported PRE_GA_DELETE_ROWS_EVENT from: "
                                                          + context.getLogPosition());
                  // ev = new Delete_rows_log_event_old(buf, event_len,
                  // description_event);
                  break;
              }
              case LogEvent.BEGIN_LOAD_QUERY_EVENT: {
                  BeginLoadQueryLogEvent event = new BeginLoadQueryLogEvent(header, buffer, descriptionEvent);
                  /* updating position in context */
                  logPosition.position = header.getLogPos();
                  return event;
              }
              case LogEvent.EXECUTE_LOAD_QUERY_EVENT: {
                  ExecuteLoadQueryLogEvent event = new ExecuteLoadQueryLogEvent(header, buffer, descriptionEvent);
                  /* updating position in context */
                  logPosition.position = header.getLogPos();
                  return event;
              }
              case LogEvent.INCIDENT_EVENT: {
                  IncidentLogEvent event = new IncidentLogEvent(header, buffer, descriptionEvent);
                  /* updating position in context */
                  logPosition.position = header.getLogPos();
                  return event;
              }
              case LogEvent.HEARTBEAT_LOG_EVENT: {
                  HeartbeatLogEvent event = new HeartbeatLogEvent(header, buffer, descriptionEvent);
                  /* updating position in context */
                  logPosition.position = header.getLogPos();
                  return event;
              }
              case LogEvent.IGNORABLE_LOG_EVENT: {
                  IgnorableLogEvent event = new IgnorableLogEvent(header, buffer, descriptionEvent);
                  /* updating position in context */
                  logPosition.position = header.getLogPos();
                  return event;
              }
              case LogEvent.ROWS_QUERY_LOG_EVENT: {
                  RowsQueryLogEvent event = new RowsQueryLogEvent(header, buffer, descriptionEvent);
                  /* updating position in context */
                  logPosition.position = header.getLogPos();
                  header.putGtid(context.getGtidSet(), gtidLogEvent);
                  return event;
              }
              case LogEvent.WRITE_ROWS_EVENT: {
                  RowsLogEvent event = new WriteRowsLogEvent(header, buffer, descriptionEvent);
                  /* updating position in context */
                  logPosition.position = header.getLogPos();
                  event.fillTable(context);
                  header.putGtid(context.getGtidSet(), gtidLogEvent);
                  return event;
              }
              case LogEvent.UPDATE_ROWS_EVENT: {
                  RowsLogEvent event = new UpdateRowsLogEvent(header, buffer, descriptionEvent);
                  /* updating position in context */
                  logPosition.position = header.getLogPos();
                  event.fillTable(context);
                  header.putGtid(context.getGtidSet(), gtidLogEvent);
                  return event;
              }
              case LogEvent.DELETE_ROWS_EVENT: {
                  RowsLogEvent event = new DeleteRowsLogEvent(header, buffer, descriptionEvent);
                  /* updating position in context */
                  logPosition.position = header.getLogPos();
                  event.fillTable(context);
                  header.putGtid(context.getGtidSet(), gtidLogEvent);
                  return event;
              }
              case LogEvent.PARTIAL_UPDATE_ROWS_EVENT: {
                  RowsLogEvent event = new UpdateRowsLogEvent(header, buffer, descriptionEvent, true);
                  /* updating position in context */
                  logPosition.position = header.getLogPos();
                  event.fillTable(context);
                  header.putGtid(context.getGtidSet(), gtidLogEvent);
                  return event;
              }
              case LogEvent.GTID_LOG_EVENT:
              case LogEvent.ANONYMOUS_GTID_LOG_EVENT: {
                  GtidLogEvent event = new GtidLogEvent(header, buffer, descriptionEvent);
                  /* updating position in context */
                  logPosition.position = header.getLogPos();
                  if (gtidSet != null) {
                      gtidSet.update(event.getGtidStr());
                      // update latest gtid
                      header.putGtid(gtidSet, event);
                  }
                  // update current gtid event to context
                  context.setGtidLogEvent(event);
                  return event;
              }
              case LogEvent.PREVIOUS_GTIDS_LOG_EVENT: {
                  PreviousGtidsLogEvent event = new PreviousGtidsLogEvent(header, buffer, descriptionEvent);
                  /* updating position in context */
                  logPosition.position = header.getLogPos();
                  return event;
              }
              case LogEvent.TRANSACTION_CONTEXT_EVENT: {
                  TransactionContextLogEvent event = new TransactionContextLogEvent(header, buffer, descriptionEvent);
                  /* updating position in context */
                  logPosition.position = header.getLogPos();
                  return event;
              }
              case LogEvent.VIEW_CHANGE_EVENT: {
                  ViewChangeEvent event = new ViewChangeEvent(header, buffer, descriptionEvent);
                  /* updating position in context */
                  logPosition.position = header.getLogPos();
                  return event;
              }
              case LogEvent.XA_PREPARE_LOG_EVENT: {
                  XaPrepareLogEvent event = new XaPrepareLogEvent(header, buffer, descriptionEvent);
                  /* updating position in context */
                  logPosition.position = header.getLogPos();
                  return event;
              }
              case LogEvent.ANNOTATE_ROWS_EVENT: {
                  AnnotateRowsEvent event = new AnnotateRowsEvent(header, buffer, descriptionEvent);
                  /* updating position in context */
                  logPosition.position = header.getLogPos();
                  header.putGtid(context.getGtidSet(), gtidLogEvent);
                  return event;
              }
              case LogEvent.BINLOG_CHECKPOINT_EVENT: {
                  BinlogCheckPointLogEvent event = new BinlogCheckPointLogEvent(header, buffer, descriptionEvent);
                  /* updating position in context */
                  logPosition.position = header.getLogPos();
                  return event;
              }
              case LogEvent.GTID_EVENT: {
                  MariaGtidLogEvent event = new MariaGtidLogEvent(header, buffer, descriptionEvent);
                  /* updating position in context */
                  logPosition.position = header.getLogPos();
                  return event;
              }
              case LogEvent.GTID_LIST_EVENT: {
                  MariaGtidListLogEvent event = new MariaGtidListLogEvent(header, buffer, descriptionEvent);
                  /* updating position in context */
                  logPosition.position = header.getLogPos();
                  return event;
              }
              case LogEvent.START_ENCRYPTION_EVENT: {
                  StartEncryptionLogEvent event = new StartEncryptionLogEvent(header, buffer, descriptionEvent);
                  /* updating position in context */
                  logPosition.position = header.getLogPos();
                  return event;
              }
              default:
                  /*
                   * Create an object of Ignorable_log_event for unrecognized
                   * sub-class. So that SLAVE SQL THREAD will only update the
                   * position and continue.
                   */
                  if ((buffer.getUint16(LogEvent.FLAGS_OFFSET) & LogEvent.LOG_EVENT_IGNORABLE_F) > 0) {
                      IgnorableLogEvent event = new IgnorableLogEvent(header, buffer, descriptionEvent);
                      /* updating position in context */
                      logPosition.position = header.getLogPos();
                      return event;
                  } else {
                      if (logger.isWarnEnabled()) {
                          logger.warn("Skipping unrecognized binlog event " + LogEvent.getTypeName(header.getType())
                                      + " from: " + context.getLogPosition());
                      }
                  }
          }
  
          /* updating position in context */
          logPosition.position = header.getLogPos();
          /* Unknown or unsupported log event */
          return new UnknownLogEvent(header);
      }