Properties can be dynamically registered to an interface by calling register_property(). If you need to provide a custom getter or setter for a property, it should follow the guidelines in this section.
To return a D-Bus error reply for either GetProperty or SetProperty, throw a custom exception derived from sdbusplus::exception_t. For the custom exception, you can return a well-defined org.freedesktop.DBus.Error (https://www.freedesktop.org/software/systemd/man/sd-bus-errors.html#) from the name() or a custom/arbitrary name. The former will be automatically translated into a matching error code (https://github.com/systemd/systemd/blob/485c9e19e7ebcd912d5fbf11f40afc62951173f8/src/libsystemd/sd-bus/bus-error.c) that can be consumed by the caller, while the latter will always be mapped to EIO, requiring a strcmp to determine the exact error name.
The handler may also throw any exception not derived from sdbusplus::exception_t, in which case a generic org.freedesktop.DBus.Error.InvalidArgs error will be returned to the caller.
When registering a property using ASIO methods, the get callback should meet the following prototype:
PropertyType getHandler(const PropertyType& value);
The first argument is the current value cached in the D-Bus interface (i.e. the previously "getted" value, or the initialized value), and the return value is returned to the D-Bus caller.
When registering a writable property using ASIO methods, the set callback should meet the following prototype:
bool setHandler(const PropertyType& newValue, PropertyType& value);
The first argument is the new value requested to be set by the D-Bus caller.
The second argument is the actual underlying value contained within the object server. If the new value meets the expected constraints, the handler must set value = newValue to make the set operation take effect and return true. If the new value is invalid or cannot be applied for whatever reason, the handler must leave value unmodified and return false.
If the handler returns false but doesn't throw an exception, a generic org.freedesktop.DBus.Error.InvalidArgs error will be returned to the caller.