systemd sd_bus_message_open_container 3 sd_bus_message_open_container sd_bus_message_close_container sd_bus_message_enter_container sd_bus_message_exit_container Create and move between containers in D-Bus messages #include <systemd/sd-bus.h> int sd_bus_message_open_container sd_bus_message *m char type const char *contents int sd_bus_message_close_container sd_bus_message *m int sd_bus_message_enter_container sd_bus_message *m char type const char *contents int sd_bus_message_exit_container sd_bus_message *m sd_bus_message_open_container() appends a new container to the message m. After opening a new container, it can be filled with content using sd_bus_message_append3 and similar functions. Containers behave like a stack. To nest containers inside each other, call sd_bus_message_open_container() multiple times without calling sd_bus_message_close_container() in between. Each container will be nested inside the previous container. type represents the container type and should be one of r, a, v or e as described in sd_bus_message_append3. Instead of literals, the corresponding constants SD_BUS_TYPE_STRUCT, SD_BUS_TYPE_ARRAY, SD_BUS_TYPE_VARIANT or SD_BUS_TYPE_DICT_ENTRY can also be used. contents describes the type of the container's elements and should be a D-Bus type string following the rules described in sd_bus_message_append3. sd_bus_message_close_container() closes the last container opened with sd_bus_message_open_container(). On success, the write pointer of the message m is positioned after the closed container in its parent container or in m itself if there is no parent container. sd_bus_message_enter_container() enters the next container of the message m for reading. It behaves mostly the same as sd_bus_message_open_container(). Entering a container allows reading its contents with sd_bus_message_read3 and similar functions. type and contents are the same as in sd_bus_message_open_container(). sd_bus_message_exit_container() exits the scope of the last container entered with sd_bus_message_enter_container(). It behaves mostly the same as sd_bus_message_close_container(). Note that sd_bus_message_exit_container() may only be called after iterating through all members of the container, i.e. reading or skipping over them. Use sd_bus_message_skip3 to skip over fields of a container in order to be able to exit the container with sd_bus_message_exit_container() without reading all members. On success, these functions return a non-negative integer. sd_bus_message_open_container() and sd_bus_message_close_container() return 0. sd_bus_message_enter_container() returns 1 if it successfully opened a new container, and 0 if that was not possible because the end of the currently open container or message was reached. sd_bus_message_exit_container() returns 1 on success. On failure, all of these functions return a negative errno-style error code. Returned errors may indicate the following problems: -EINVAL m or contents are NULL or type is invalid. -EBADMSG Message m has invalid structure. -ENXIO Message m does not have a container of type type at the current position, or the contents do not match contents. -EPERM The message m is already sealed. -ESTALE The message m is in an invalid state. -ENOMEM Memory allocation failed. -EBUSY sd_bus_message_exit_container() was called but there are unread members left in the container. systemd1, sd-bus3, sd_bus_message_append3, sd_bus_message_read3, sd_bus_message_skip3, The D-Bus specification