zmq_send(3)

zmq_send(3)

ØMQ Manual - ØMQ/3.2.5

Name

zmq_send - send a message part 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.

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 ØMQ has assumed responsibility for the message.

Multi-part messages

A ØMQ message is composed of 1 or more message parts. ØMQ 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_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 zmq_socket(3) for more information.
ETERM
The ØMQ 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.

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

zmq_sendmsg(3) zmq_recv(3) zmq_recvmsg(3) zmq_socket(7) zmq(7)

Authors

This ØMQ manual page was written by Martin Sustrik <moc.mpb052|kirtsus#moc.mpb052|kirtsus> and Martin Lucina <ks.anletok|otam#ks.anletok|otam>, and Pieter Hintjens <moc.xitami|hp#moc.xitami|hp>.