sd_bus_message_open_container, sd_bus_message_close_container, sd_bus_message_enter_container,

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_append(3) 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_append(3). 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_append(3). 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_read(3) 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_skip(3) 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.

Example1.Appendanarrayofstringstoamessage /* SPDX-License-Identifier: MIT-0 */ #include <systemd/sd-bus.h> int append_strings_to_message(sd_bus_message *m, const char *const *arr) { const char *s; int r; r = sd_bus_message_open_container(m, 'a', "s"); if (r < 0) return r; for (s = *arr; *s; s++) { r = sd_bus_message_append(m, "s", s); if (r < 0) return r; } return sd_bus_message_close_container(m); } Example2.Readanarrayofstringsfromamessage /* SPDX-License-Identifier: MIT-0 */ #include <stdio.h> #include <systemd/sd-bus.h> int read_strings_from_message(sd_bus_message *m) { int r; r = sd_bus_message_enter_container(m, 'a', "s"); if (r < 0) return r; for (;;) { const char *s; r = sd_bus_message_read(m, "s", &s); if (r < 0) return r; if (r == 0) break; printf("%s\n", s); } return sd_bus_message_exit_container(m); }

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

1. The D-Bus specification https://dbus.freedesktop.org/doc/dbus-specification.html systemd 257.7 SD_BUS_MESSAGE_OPEN_CONTAINER(3)

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. Errors Returned errors may indicate the following problems: -EINVALm or contents are NULL or type is invalid. Added in version 246. -EBADMSG Message m has invalid structure. Added in version 254. -ENXIO Message m does not have a container of type type at the current position, or the contents do not match contents. Added in version 254. -EPERM The message m is already sealed. Added in version 246. -ESTALE The message m is in an invalid state. Added in version 246. -ENOMEM Memory allocation failed. Added in version 246. -EBUSYsd_bus_message_exit_container() was called but there are unread members left in the container. Added in version 247.

systemd(1), sd-bus(3), sd_bus_message_append(3), sd_bus_message_read(3), sd_bus_message_skip(3), TheD-Busspecification[1]