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NAME | SYNOPSIS | DESCRIPTION | RETURN VALUE | NOTES | EXAMPLES | SEE ALSO | NOTES | COLOPHON |
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SD_BUS_MESSAGE_OPEN_CONTAINER(3)sage_open_containerAGE_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 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.
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.
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
/* 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);
}
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]
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 2022-12-17. (At that
time, the date of the most recent commit that was found in the
repository was 2022-12-16.) 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 252 SD_BUS_MESSAGE_OPEN_CONTAINER(3)
Pages that refer to this page: sd-bus(3), sd_bus_message_append(3), sd_bus_message_read(3), systemd.directives(7), systemd.index(7)
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