int sd_bus_message_set_destination(sd_bus_message *message, const char *destination);
const char* sd_bus_message_get_destination(sd_bus_message *message);
const char* sd_bus_message_get_path(sd_bus_message *message);
const char* sd_bus_message_get_interface(sd_bus_message *message);
const char* sd_bus_message_get_member(sd_bus_message *message);
int sd_bus_message_set_sender(sd_bus_message *message, const char *sender);
const char* sd_bus_message_get_sender(sd_bus_message *message);
sd_bus_message_get_destination(), sd_bus_message_get_path(), sd_bus_message_get_interface(), and sd_bus_message_get_member() return the destination, path, interface, and member fields from message header. The return value will be NULL is message is NULL or the message is of a type that doesn't use those fields or the message doesn't have them set. See sd_bus_message_new_method_call(3) and sd_bus_message_set_destination(3) for more discussion of those values.
sd_bus_message_set_sender() sets the sender service name for the specified bus message object. The specified name must be a valid unique or well-known service name. This function is useful only for messages to send on direct connections as for connections to bus brokers the broker will fill in the destination field anyway, and the sender field set by original sender is ignored.
sd_bus_message_get_sender() returns the sender field from message.
When a string is returned, it is a pointer to internal storage, and may not be modified or freed. It is only valid as long as the message remains referenced and this field hasn't been changed by a different call.