SD_BUS_MESSAGE_OPEN_CONTAsd_bus_message_open_cSD_BUS_MESSAGE_OPEN_CONTAINER(3)

NAME
       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

SYNOPSIS
       #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);

DESCRIPTION
       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 them.
       Use sd_bus_message_skip(3) to skip over felds of a container in order
       to be able to exit the container with sd_bus_message_exit_container()
       without reading all members.

RETURN VALUE
       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:

       -EINVAL
           m or contents are NULL or type is invalid.

       -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.

NOTES
       These APIs are implemented as a shared library, which can be compiled
       and linked to with the libsystemd pkg-config(1) file.

EXAMPLES
       Example 1. Append an array of strings to a message

           /* SPDX-License-Identifier: MIT-0 */

           #include <systemd/sd-bus.h>

           int append_strings_to_message(sd_bus_message *m, const char *const *arr) {
             int r;

             r = sd_bus_message_open_container(m, 'a', "s");
             if (r < 0)
               return r;

             for (const char *s = *arr; *s; s++) {
               r = sd_bus_message_append(m, "s", s);
               if (r < 0)
                 return r;
             }

             return sd_bus_message_close_container(m);
           }

       Example 2. Read an array of strings from a message

           /* 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);
           }

SEE ALSO
       systemd(1), sd-bus(3), sd_bus_message_append(3),
       sd_bus_message_read(3), sd_bus_message_skip(3), The D-Bus
       specification[1]

NOTES
        1. The D-Bus specification
           https://dbus.freedesktop.org/doc/dbus-specification.html

systemd 252                                   SD_BUS_MESSAGE_OPEN_CONTAINER(3)

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