zmq_send_const - send a constant-memory message part on a socket

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0MQ 4.3.5                                          03/31/2024                                  ZMQ_SEND_CONST(3)

       The zmq_send_const() function shall queue a message created from the buffer referenced by the buf and len
       arguments. The message buffer is assumed to be constant-memory and will therefore not be copied or
       deallocated in any way. 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_send_const()
           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.

           Note

           A successful invocation of zmq_send_const() 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-partmessages
       A 0MQ message is composed of 1 or more message parts. 0MQ ensures atomic delivery of messages: peers
       shall receive either all messageparts 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.

EAGAIN
           Non-blocking mode was requested and the message cannot be sent at the moment.

       ENOTSUP
           The zmq_send_const() operation is not supported by this socket type.

       EFSM
           The zmq_send_const() 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 messagingpatterns 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.

       EHOSTUNREACH
           The message cannot be routed.

Sendingamulti-partmessage.

           /* Send a multi-part message consisting of three parts to socket */
           rc = zmq_send_const (socket, "ABC", 3, ZMQ_SNDMORE);
           assert (rc == 3);
           rc = zmq_send_const (socket, "DEFGH", 5, ZMQ_SNDMORE);
           assert (rc == 5);
           /* Final part; no more parts to follow */
           rc = zmq_send_const (socket, "JK", 2, 0);
           assert (rc == 2);

       zmq_send_const - send a constant-memory message part on a socket

       The zmq_send_const() 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.

zmq_send(3) zmq_recv(3) zmq_socket(7) zmq(7)

intzmq_send_const(void*socket,constvoid*buf,size_tlen,intflags);