ZMQ_MSG_RECV - Online Linux Manual PageSection : 3
Updated : 01/21/2023
Source : 0MQ 4​.3​.4
Note : 0MQ Manual

NAMEzmq_msg_recv − receive a message part from a socket

SYNOPSISint zmq_msg_recv (zmq_msg_t *msg, void *socket, int flags);

DESCRIPTIONThe zmq_msg_recv() function is identical to zmq_recvmsg(3), which shall be deprecated in future versions​. zmq_msg_recv() is more consistent with other message manipulation functions​. The zmq_msg_recv() function shall receive a message part from 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 message parts available on the specified socket the zmq_msg_recv() function shall block until the request can be satisfied​. 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 there are no messages available on the specified socket, the zmq_msg_recv() function shall fail with errno set to EAGAIN​.

Multi−part messagesA 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 processes multi−part messages must use the ZMQ_RCVMORE zmq_getsockopt(3) option after calling zmq_msg_recv() to determine if there are further parts to receive​.

RETURN VALUEThe zmq_msg_recv() 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​.

ERRORSEAGAIN Either the timeout set via the socket−option ZMQ_RCVTIMEO (see zmq_setsockopt(3)) has been reached (flag ZMQ_DONTWAIT not set) without being able to read a message from the socket or there are no messages available at the moment (flag ZMQ_DONTWAIT set) and the operation would block​. ENOTSUP The zmq_msg_recv() operation is not supported by this socket type​. EFSM The zmq_msg_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 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 a message was available​. EFAULT The message passed to the function was invalid​.

EXAMPLEReceiving 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 received from socket */ rc = zmq_msg_recv (&msg, socket, 0); assert (rc != −1); /* Release message */ zmq_msg_close (&msg);Receiving a multi-part message. int more; size_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 received from socket */ rc = zmq_msg_recv (&part, socket, 0); assert (rc != −1); /* Determine if more message parts are to follow */ rc = zmq_getsockopt (socket, ZMQ_RCVMORE, &more, &more_size); assert (rc == 0); zmq_msg_close (&part); } while (more);

SEE ALSOzmq_recv(3) zmq_send(3) zmq_msg_send(3) zmq_getsockopt(3) zmq_setsockopt(3) zmq_socket(7) zmq(7)

AUTHORSThis page was written by the 0MQ community​. To make a change please read the 0MQ Contribution Policy at http://www​.zeromq​.org/docs:contributing​.
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