libzmq/doc/zmq_recv.txt

zmq_recv(3)
===========


NAME
----
zmq_recv - receive a message from a socket


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


DESCRIPTION
-----------
The _zmq_recv()_ function shall dequeue a message from the underlying _message
queue_ associated with the socket referenced by the 'socket' argument and store
it in the message referenced by the 'msg' argument. Any content previously
stored in 'msg' shall be properly deallocated. If there are no messages
available to be dequeued from the underlying _message queue_ associated with
'socket' the _zmq_recv()_ function shall block until the request can be
satisfied. The 'flags' argument is a combination of the flags defined below:

*ZMQ_NOBLOCK*::
Specifies that the operation should be performed in non-blocking mode. If there
are no messages available to be dequeued from the underlying _message queue_
associated with 'socket', the _zmq_recv()_ function shall fail with 'errno' set
to EAGAIN.


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 determine if a message is composed of multiple parts
does so by retrieving the value of the _ZMQ_RCVMORE_ socket option on the
'socket' it is receiving the message from. If there are no message parts to
follow, or if the message is not composed of multiple parts, _ZMQ_RCVMORE_
shall report a value of zero. Otherwise, _ZMQ_RCVMORE_ shall report a value of
1, indicating that more message parts are to follow.


RETURN VALUE
------------
The _zmq_recv()_ function shall return zero 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 no messages are available at the moment.
*ENOTSUP*::
The _zmq_recv()_ operation is not supported by this socket type.
*EFSM*::
The _zmq_recv()_ 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.


EXAMPLE
-------
.Receiving a message from a socket
----
/* Create an empty 0MQ message */
zmq_msg_t msg;
int rc = zmq_msg_init (&msg);
assert (rc == 0);
/* Block until a message is available to be dequeued from socket */
rc = zmq_recv (socket, &msg, 0);
assert (rc == 0);
----

.Receiving a multi-part message
----
int64_t more;
int64_t more_size = sizeof more;
do {
    /* Create an empty 0MQ message to hold the message part */
    zmq_msg_t part;
    int rc = zmq_msg_init (&part);
    assert (rc == 0);
    /* Block until a message is available to be dequeued from socket */
    rc = zmq_recv (socket, &part, 0);
    assert (rc == 0);
    /* Determine if more message parts are to follow */
    rc = zmq_getsockopt (socket, ZMQ_RCVMORE, &more, &more_size);
    assert (rc == 0);
} while (more);
----


SEE ALSO
--------
linkzmq:zmq_send[3]
linkzmq:zmq_getsockopt[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>.