|
NAME | SYNOPSIS | DESCRIPTION | RETURN VALUE | NOTES | EXAMPLES | SEE ALSO | NOTES | COLOPHON |
SD_BUS_MESSAGE_OPEN_CONTAINER(3)essage_open_containerSSAGE_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_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. 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().
On success, these functions return a non-negative integer. On
failure, they 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.
These APIs are implemented as a shared library, which can be compiled
and linked to with the libsystemd pkg-config(1) file.
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)
break;
printf("%s\n", s);
}
return sd_bus_message_exit_container(m);
}
systemd(1), sd-bus(3), sd_bus_message_append(3),
sd_bus_message_read(3), The D-Bus specification[1]
1. The D-Bus specification
https://dbus.freedesktop.org/doc/dbus-specification.html
This page is part of the systemd (systemd system and service manager)
project. Information about the project can be found at
⟨http://www.freedesktop.org/wiki/Software/systemd⟩. If you have a bug
report for this manual page, see
⟨http://www.freedesktop.org/wiki/Software/systemd/#bugreports⟩. This
page was obtained from the project's upstream Git repository
⟨https://github.com/systemd/systemd.git⟩ on 2020-08-13. (At that
time, the date of the most recent commit that was found in the repos‐
itory was 2020-08-11.) If you discover any rendering problems in
this HTML version of the page, or you believe there is a better or
more up-to-date source for the page, or you have corrections or
improvements to the information in this COLOPHON (which is not part
of the original manual page), send a mail to man-pages@man7.org
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)