27.3 Adding Storage Engine Error Messages

To add error messages for table handlers, the following example may be helpful.

Purpose: Implement the handler::get_error_message function as ha_federated::get_error_message to return the handler-specific error message.

Example:

1. When an error occurs you return an error code. (It should not be in the range of those that HA_ERR uses, which currently is 120-159.)

2. When handler::print_error is called to convert the handler error code to a MySQL error code, it will enter the default label of the switch(error) statement:

handler.cc:1721
  default:
    {
      /* The error was "unknown" to this function.
     Ask handler if it has got a message for this error */
      bool temporary= FALSE;
      String str;
      temporary= get_error_message(error, &str);
      if (!str.is_empty())
      {
    const char* engine= table_type();
    if (temporary)
      my_error(ER_GET_TEMPORARY_ERRMSG, MYF(0), error, str.ptr(), engine);
    else
      my_error(ER_GET_ERRMSG, MYF(0), error, str.ptr(), engine);
      }
      else
    my_error(ER_GET_ERRNO,errflag,error);
      DBUG_VOID_RETURN;
    }
  }

1. Thus the handler::get_error_message is called and you can return the handler-specific error message, which is either a static error message that you retrieve from an error/string array, or a dynamic one that you format when the error occurs.

When you have returned the error message it will be passed to MySQL and formatted as Got error %d '%-.100s' from %s. For example:

Got error 788 'Could not connect to remote server fed.bb.pl' from FEDERATED

The Got error %d part will be returned in the user's selected language, but the handler-specific one will use English (unless the handler supports returning the handler error message in the user's selected language).