ZMQ_MSG_SEND(3) 0MQ Manual 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 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
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
zmq_recv(3) zmq_send(3) zmq_msg_recv(3) zmq_socket(7) zmq(7)
AUTHORS
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0MQ 4.3.4 01/18/2023 ZMQ_MSG_SEND(3)
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