libzmq/doc/zmq_send.txt

zmq_send(3)
===========


NAME
----
zmq_send - send a message on a socket


SYNOPSIS
--------
*int zmq_send (void '*socket', void '*buf', size_t 'len', int 'flags');*


DESCRIPTION
-----------
The _zmq_send()_ function shall queue a message created from the buffer
referenced by the 'buf' and 'len' arguments. 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_send()_ 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.

NOTE: A successful invocation of _zmq_send()_ 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 invocation of
_zmq_send()_ creates an independent message part 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_send()_. 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_send()_ without the 'ZMQ_SNDMORE' flag; this
indicates that no more message parts are to follow.


RETURN VALUE
------------
The _zmq_send()_ 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_send()_ operation is not supported by this socket type.
*EFSM*::
The _zmq_send()_ 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.
*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
-------
.Sending a multi-part message
----
/* Send a multi-part message consisting of three parts to socket */
rc = zmq_send (socket, "ABC", 3, ZMQ_SNDMORE);
assert (rc == 3);
rc = zmq_send (socket, "DEFGH", 5, ZMQ_SNDMORE);
assert (rc == 5);
/* Final part; no more parts to follow */
rc = zmq_send (socket, "JK", 2, 0);
assert (rc == 2);
----

SEE ALSO
--------
linkzmq:zmq_sendmsg[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>.