libzmq/doc/zmq_sendmsg.txt

zmq_sendmsg(3)
==============


NAME
----
zmq_sendmsg - send a message on a socket


SYNOPSIS
--------
*int zmq_sendmsg (void '*socket', zmq_msg_t '*msg', int 'flags');*


DESCRIPTION
-----------
The _zmq_send()_ function shall queue the message referenced by the 'msg'
argument to be sent to the socket referenced by the 'socket' argument.  The
'flags' argument is a combination of the flags defined below:

*ZMQ_DONTWAIT*::
Specifies that the operation should be performed in non-blocking mode. If the
message cannot be queued on the 'socket', the _zmq_sendmsg()_ function shall
fail with 'errno' set to EAGAIN.

*ZMQ_SNDMORE*::
Specifies that the message being sent is a multi-part message, and that further
message parts are to follow. Refer to the section regarding multi-part messages
below for a detailed description.

*ZMQ_SNDLABEL*::
Specifies that the message being sent is a label. Labels are used internally
by 0MQ.

The _zmq_msg_t_ structure passed to _zmq_sendmsg()_ is nullified during the
call. If you want to send the same message to multiple sockets you have to copy
it using (e.g. using _zmq_msg_copy()_).

NOTE: A successful invocation of _zmq_sendmsg()_ does not indicate that the
message has been transmitted to the network, only that it has been queued on
the 'socket' and 0MQ has assumed responsibility for the message.


Multi-part messages
~~~~~~~~~~~~~~~~~~~
A 0MQ message is composed of 1 or more message parts; each message part is an
independent 'zmq_msg_t' in its own right. 0MQ ensures atomic delivery of
messages; peers shall receive either all _message parts_ of a message or none
at all.

The total number of message parts is unlimited.

An application wishing to send a multi-part message does so by specifying the
'ZMQ_SNDMORE' flag to _zmq_sendmsg()_. The presence of this flag indicates to
0MQ that the message being sent is a multi-part message and that more message
parts are to follow. When the application wishes to send the final message part
it does so by calling _zmq_sendmsg()_ without the 'ZMQ_SNDMORE' flag; this
indicates that no more message parts are to follow.


RETURN VALUE
------------
The _zmq_sendmsg()_ function shall return number of bytes in the message
if successful. Otherwise it shall return `-1` and set 'errno' to one of the
values defined below.


ERRORS
------
*EAGAIN*::
Non-blocking mode was requested and the message cannot be sent at the moment.
*ENOTSUP*::
The _zmq_sendmsg()_ operation is not supported by this socket type.
*EFSM*::
The _zmq_sendmsg()_ operation cannot be performed on this socket at the moment
due to the socket not being in the appropriate state.  This error may occur with
socket types that switch between several states, such as ZMQ_REP.  See the
_messaging patterns_ section of linkzmq:zmq_socket[3] for more information.
*ETERM*::
The 0MQ 'context' associated with the specified 'socket' was terminated.
*ENOTSOCK*::
The provided 'socket' was invalid.
*EINTR*::
The operation was interrupted by delivery of a signal before the message was
sent.
*EFAULT*::
Invalid message.
*ECANTROUTE*::
Message cannot be routed to the destination specified as the peer is either
dead or disconnected. This error makes sense only with ZMQ_ROUTER socket.


EXAMPLE
-------
.Filling in a message and sending it to a socket
----
/* Create a new message, allocating 6 bytes for message content */
zmq_msg_t msg;
int rc = zmq_msg_init_size (&msg, 6);
assert (rc == 0);
/* Fill in message content with 'AAAAAA' */
memset (zmq_msg_data (&msg), 'A', 6);
/* Send the message to the socket */
rc = zmq_sendmsg (socket, &msg, 0);
assert (rc == 6);
----

.Sending a multi-part message
----
/* Send a multi-part message consisting of three parts to socket */
rc = zmq_sendmsg (socket, &part1, ZMQ_SNDMORE);
rc = zmq_sendmsg (socket, &part2, ZMQ_SNDMORE);
/* Final part; no more parts to follow */
rc = zmq_sendmsg (socket, &part3, 0);
----


SEE ALSO
--------
linkzmq:zmq_recv[3]
linkzmq:zmq_recv[3]
linkzmq:zmq_recvmsg[3]
linkzmq:zmq_socket[7]
linkzmq:zmq[7]


AUTHORS
-------
The 0MQ documentation was written by Martin Sustrik <sustrik@250bpm.com> and
Martin Lucina <mato@kotelna.sk>.