'\" t
.TH "SD_BUS_SEND" "3" "" "systemd 256.7" "sd_bus_send"
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.SH "NAME"
sd_bus_send, sd_bus_send_to, sd_bus_message_send \- Queue a D\-Bus message for transfer
.SH "SYNOPSIS"
.sp
.ft B
.nf
#include <systemd/sd\-bus\&.h>
.fi
.ft
.HP \w'int\ sd_bus_send('u
.BI "int sd_bus_send(sd_bus\ *" "bus" ", sd_bus_message\ *" "m" ", uint64_t\ *" "cookie" ");"
.HP \w'int\ sd_bus_send_to('u
.BI "int sd_bus_send_to(sd_bus\ *" "bus" ", sd_bus_message\ *" "m" ", const\ char\ *" "destination" ", uint64_t\ *" "cookie" ");"
.HP \w'int\ sd_bus_message_send('u
.BI "int sd_bus_message_send(sd_bus_message\ *" "m" ");"
.SH "DESCRIPTION"
.PP
\fBsd_bus_send()\fR
queues the bus message object
\fIm\fR
for transfer\&. If
\fIbus\fR
is
\fBNULL\fR, the bus that
\fIm\fR
is attached to is used\&.
\fIbus\fR
only needs to be set when the message is sent to a different bus than the one it\*(Aqs attached to, for example when forwarding messages\&. If the output parameter
\fIcookie\fR
is not
\fBNULL\fR, it is set to the message identifier\&. This value can later be used to match incoming replies to their corresponding messages\&. If
\fIcookie\fR
is set to
\fBNULL\fR
and the message is not sealed,
\fBsd_bus_send()\fR
assumes the message
\fIm\fR
doesn\*(Aqt expect a reply and adds the necessary headers to indicate this\&.
.PP
Note that in most scenarios,
\fBsd_bus_send()\fR
should not be called directly\&. Instead, use higher level functions such as
\fBsd_bus_call_method\fR(3)
and
\fBsd_bus_reply_method_return\fR(3)
which call
\fBsd_bus_send()\fR
internally\&.
.PP
\fBsd_bus_send_to()\fR
is a shorthand for sending a message to a specific destination\&. It\*(Aqs main use case is to simplify sending unicast signal messages (signals that only have a single receiver)\&. It\*(Aqs behavior is similar to calling
\fBsd_bus_message_set_destination\fR(3)
followed by calling
\fBsd_bus_send()\fR\&.
.PP
\fBsd_bus_send()\fR/\fBsd_bus_send_to()\fR
will write the message directly to the underlying transport (e\&.g\&. kernel socket buffer) if possible\&. If the connection is not set up fully yet the message is queued locally\&. If the transport buffers are congested any unwritten message data is queued locally, too\&. If the connection has been closed or is currently being closed the call fails\&.
\fBsd_bus_process\fR(3)
should be invoked to write out any queued message data to the transport\&.
.PP
\fBsd_bus_message_send()\fR
is the same as
\fBsd_bus_send()\fR
but without the first and last argument\&.
\fBsd_bus_message_send(m)\fR
is equivalent to
\fBsd_bus_send(sd_bus_message_get_bus(m), m, NULL)\fR\&.
.SH "RETURN VALUE"
.PP
On success, these functions return a non\-negative integer\&. On failure, they return a negative errno\-style error code\&.
.SS "Errors"
.PP
Returned errors may indicate the following problems:
.PP
\fB\-EINVAL\fR
.RS 4
The input parameter
\fIm\fR
is
\fBNULL\fR\&.
.sp
Added in version 246\&.
.RE
.PP
\fB\-EOPNOTSUPP\fR
.RS 4
The bus connection does not support sending file descriptors\&.
.sp
Added in version 246\&.
.RE
.PP
\fB\-ECHILD\fR
.RS 4
The bus connection was allocated in a parent process and is being reused in a child process after
\fBfork()\fR\&.
.sp
Added in version 246\&.
.RE
.PP
\fB\-ENOBUFS\fR
.RS 4
The bus connection\*(Aqs write queue is full\&.
.sp
Added in version 246\&.
.RE
.PP
\fB\-ENOTCONN\fR
.RS 4
The input parameter
\fIbus\fR
is
\fBNULL\fR
or the bus is not connected\&.
.sp
Added in version 246\&.
.RE
.PP
\fB\-ECONNRESET\fR
.RS 4
The bus connection was closed while waiting for the response\&.
.sp
Added in version 246\&.
.RE
.PP
\fB\-ENOMEM\fR
.RS 4
Memory allocation failed\&.
.sp
Added in version 246\&.
.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 "HISTORY"
.PP
\fBsd_bus_send()\fR
and
\fBsd_bus_send_to()\fR
were added in version 246\&.
.SH "SEE ALSO"
.PP
\fBsystemd\fR(1), \fBsd-bus\fR(3), \fBsd_bus_call_method\fR(3), \fBsd_bus_message_set_destination\fR(3), \fBsd_bus_reply_method_return\fR(3), \fBsd_bus_process\fR(3)