libzmq/doc/zmq_msg_send.txt

zmq_msg_send(3)
===============


NAME
----
zmq_msg_send - send a message part on a socket


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


DESCRIPTION
-----------
The _zmq_msg_send()_ function is identical to linkzmq:zmq_sendmsg[3], which
shall be deprecated in future versions. _zmq_msg_send()_ is more consistent
with other message manipulation functions.

The _zmq_msg_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*::
For socket types (DEALER, PUSH) that block (either with ZMQ_IMMEDIATE option set
and no peer available, or all peers having full high-water mark), specifies that
the operation should be performed in non-blocking mode. If the message cannot be
queued on the 'socket', the _zmq_msg_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.

The _zmq_msg_t_ structure passed to _zmq_msg_send()_ is nullified on a
successful call. If you want to send the same message to multiple sockets you
have to copy it (e.g. using _zmq_msg_copy()_). If the call fails, the
_zmq_msg_t_ structure stays intact, and must be consumed by another call to
_zmq_msg_send()_ on the same or another socket, or released using
_zmq_msg_close()_ to avoid a memory leak.

NOTE: A successful invocation of _zmq_msg_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. You do not need
to call _zmq_msg_close()_ after a successful _zmq_msg_send()_.


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 except
by available memory.

An application that sends multi-part messages must use the _ZMQ_SNDMORE_ flag
when sending each message part except the final one.

RETURN VALUE
------------
The _zmq_msg_send()_ function shall return number of bytes in the message
if successful (if number of bytes is higher than 'MAX_INT', the function will
return 'MAX_INT'). 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_msg_send()_ operation is not supported by this socket type.
*EINVAL*::
The sender tried to send multipart data, which the socket type does not allow.
*EFSM*::
The _zmq_msg_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.
*EFAULT*::
Invalid message.
*EHOSTUNREACH*::
The message cannot be routed.


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_msg_send (&msg, socket, 0);
assert (rc == 6);
----

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


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


AUTHORS
-------
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read the 0MQ Contribution Policy at <http://www.zeromq.org/docs:contributing>.