'\" t
.TH "SD_BUS_MESSAGE_OPEN_CONTAINER" "3" "" "systemd 255" "sd_bus_message_open_container"
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.SH "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
.SH "SYNOPSIS"
.sp
.ft B
.nf
#include <systemd/sd\-bus\&.h>
.fi
.ft
.HP \w'int\ sd_bus_message_open_container('u
.BI "int sd_bus_message_open_container(sd_bus_message\ *" "m" ", char\ " "type" ", const\ char\ *" "contents" ");"
.HP \w'int\ sd_bus_message_close_container('u
.BI "int sd_bus_message_close_container(sd_bus_message\ *" "m" ");"
.HP \w'int\ sd_bus_message_enter_container('u
.BI "int sd_bus_message_enter_container(sd_bus_message\ *" "m" ", char\ " "type" ", const\ char\ *" "contents" ");"
.HP \w'int\ sd_bus_message_exit_container('u
.BI "int sd_bus_message_exit_container(sd_bus_message\ *" "m" ");"
.SH "DESCRIPTION"
.PP
\fBsd_bus_message_open_container()\fR
appends a new container to the message
\fIm\fR\&. After opening a new container, it can be filled with content using
\fBsd_bus_message_append\fR(3)
and similar functions\&. Containers behave like a stack\&. To nest containers inside each other, call
\fBsd_bus_message_open_container()\fR
multiple times without calling
\fBsd_bus_message_close_container()\fR
in between\&. Each container will be nested inside the previous container\&.
\fItype\fR
represents the container type and should be one of
"r",
"a",
"v"
or
"e"
as described in
\fBsd_bus_message_append\fR(3)\&. Instead of literals, the corresponding constants
\fBSD_BUS_TYPE_STRUCT\fR,
\fBSD_BUS_TYPE_ARRAY\fR,
\fBSD_BUS_TYPE_VARIANT\fR
or
\fBSD_BUS_TYPE_DICT_ENTRY\fR
can also be used\&.
\fIcontents\fR
describes the type of the container\*(Aqs elements and should be a D\-Bus type string following the rules described in
\fBsd_bus_message_append\fR(3)\&.
.PP
\fBsd_bus_message_close_container()\fR
closes the last container opened with
\fBsd_bus_message_open_container()\fR\&. On success, the write pointer of the message
\fIm\fR
is positioned after the closed container in its parent container or in
\fIm\fR
itself if there is no parent container\&.
.PP
\fBsd_bus_message_enter_container()\fR
enters the next container of the message
\fIm\fR
for reading\&. It behaves mostly the same as
\fBsd_bus_message_open_container()\fR\&. Entering a container allows reading its contents with
\fBsd_bus_message_read\fR(3)
and similar functions\&.
\fItype\fR
and
\fIcontents\fR
are the same as in
\fBsd_bus_message_open_container()\fR\&.
.PP
\fBsd_bus_message_exit_container()\fR
exits the scope of the last container entered with
\fBsd_bus_message_enter_container()\fR\&. It behaves mostly the same as
\fBsd_bus_message_close_container()\fR\&. Note that
\fBsd_bus_message_exit_container()\fR
may only be called after iterating through all members of the container, i\&.e\&. reading or skipping over them\&. Use
\fBsd_bus_message_skip\fR(3)
to skip over fields of a container in order to be able to exit the container with
\fBsd_bus_message_exit_container()\fR
without reading all members\&.
.SH "RETURN VALUE"
.PP
On success, these functions return a non\-negative integer\&.
\fBsd_bus_message_open_container()\fR
and
\fBsd_bus_message_close_container()\fR
return 0\&.
\fBsd_bus_message_enter_container()\fR
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\&.
\fBsd_bus_message_exit_container()\fR
returns 1 on success\&. On failure, all of these functions return a negative errno\-style error code\&.
.SS "Errors"
.PP
Returned errors may indicate the following problems:
.PP
\fB\-EINVAL\fR
.RS 4
\fIm\fR
or
\fIcontents\fR
are
\fBNULL\fR
or
\fItype\fR
is invalid\&.
.sp
Added in version 246\&.
.RE
.PP
\fB\-EBADMSG\fR
.RS 4
Message
\fIm\fR
has invalid structure\&.
.sp
Added in version 254\&.
.RE
.PP
\fB\-ENXIO\fR
.RS 4
Message
\fIm\fR
does not have a container of type
\fItype\fR
at the current position, or the contents do not match
\fIcontents\fR\&.
.sp
Added in version 254\&.
.RE
.PP
\fB\-EPERM\fR
.RS 4
The message
\fIm\fR
is already sealed\&.
.sp
Added in version 246\&.
.RE
.PP
\fB\-ESTALE\fR
.RS 4
The message
\fIm\fR
is in an invalid state\&.
.sp
Added in version 246\&.
.RE
.PP
\fB\-ENOMEM\fR
.RS 4
Memory allocation failed\&.
.sp
Added in version 246\&.
.RE
.PP
\fB\-EBUSY\fR
.RS 4
\fBsd_bus_message_exit_container()\fR
was called but there are unread members left in the container\&.
.sp
Added in version 247\&.
.RE
.SH "NOTES"
.PP
Functions described here are available as a shared library, which can be compiled against and linked to with the
\fBlibsystemd\fR\ \&\fBpkg-config\fR(1)
file\&.
.PP
The code described here uses
\fBgetenv\fR(3), which is declared to be not multi\-thread\-safe\&. This means that the code calling the functions described here must not call
\fBsetenv\fR(3)
from a parallel thread\&. It is recommended to only do calls to
\fBsetenv()\fR
from an early phase of the program when no other threads have been started\&.
.SH "EXAMPLES"
.PP
\fBExample\ \&1.\ \&Append an array of strings to a message\fR
.sp
.if n \{\
.RS 4
.\}
.nf
/* 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, \*(Aqa\*(Aq, "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);
}
.fi
.if n \{\
.RE
.\}
.PP
\fBExample\ \&2.\ \&Read an array of strings from a message\fR
.sp
.if n \{\
.RS 4
.\}
.nf
/* 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, \*(Aqa\*(Aq, "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\en", s);
  }

  return sd_bus_message_exit_container(m);
}
.fi
.if n \{\
.RE
.\}
.SH "SEE ALSO"
.PP
\fBsystemd\fR(1),
\fBsd-bus\fR(3),
\fBsd_bus_message_append\fR(3),
\fBsd_bus_message_read\fR(3),
\fBsd_bus_message_skip\fR(3),
\m[blue]\fBThe D\-Bus specification\fR\m[]\&\s-2\u[1]\d\s+2
.SH "NOTES"
.IP " 1." 4
The D-Bus specification
.RS 4
\%https://dbus.freedesktop.org/doc/dbus-specification.html
.RE