sd_bus_message_close_container(3) — Linux manual page



NAME         top

       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         top

       #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         top

       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
       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. 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().

RETURN VALUE         top

       On success, these functions return a non-negative integer. On
       failure, they return a negative errno-style error code.

       Returned errors may indicate the following problems:

           m or contents are NULL or type is invalid.

           The message m is already sealed.

           The message m is in an invalid state.

           Memory allocation failed.

NOTES         top

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

EXAMPLES         top

       Example 1. Append an array of strings to a message

           #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

           #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)

               printf("%s\n", s);

             return sd_bus_message_exit_container(m);

SEE ALSO         top

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

NOTES         top

        1. The D-Bus specification

COLOPHON         top

       This page is part of the systemd (systemd system and service manager)
       project.  Information about the project can be found at 
       ⟨⟩.  If you have a bug
       report for this manual page, see
       ⟨⟩.  This
       page was obtained from the project's upstream Git repository
       ⟨⟩ on 2020-07-14.  (At that
       time, the date of the most recent commit that was found in the repos‐
       itory was 2020-07-14.)  If you discover any rendering problems in
       this HTML version of the page, or you believe there is a better or
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       of the original manual page), send a mail to

systemd 246                                 SD_BUS_MESSAGE_OPEN_CONTAINER(3)

Pages that refer to this page: sd-bus(3)30-systemd-environment-d-generator(7)systemd.index(7)