1ZMQ_RECVMSG(3)                    0MQ Manual                    ZMQ_RECVMSG(3)
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NAME

6       zmq_recvmsg - receive a message part from a socket
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SYNOPSIS

9       int zmq_recvmsg (void *socket, zmq_msg_t *msg, int flags);
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DESCRIPTION

12       The zmq_recvmsg() function shall receive a message part from the socket
13       referenced by the socket argument and store it in the message
14       referenced by the msg argument. Any content previously stored in msg
15       shall be properly deallocated. If there are no message parts available
16       on the specified socket the zmq_recvmsg() function shall block until
17       the request can be satisfied. The flags argument is a combination of
18       the flags defined below:
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20       ZMQ_DONTWAIT
21           Specifies that the operation should be performed in non-blocking
22           mode. If there are no messages available on the specified socket,
23           the zmq_recvmsg() function shall fail with errno set to EAGAIN.
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25           Note
26           this API method is deprecated in favor of zmq_msg_recv(3).
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28   Multi-part messages
29       A 0MQ message is composed of 1 or more message parts. Each message part
30       is an independent zmq_msg_t in its own right. 0MQ ensures atomic
31       delivery of messages: peers shall receive either all message parts of a
32       message or none at all. The total number of message parts is unlimited
33       except by available memory.
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35       An application that processes multi-part messages must use the
36       ZMQ_RCVMORE zmq_getsockopt(3) option after calling zmq_recvmsg() to
37       determine if there are further parts to receive.
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RETURN VALUE

40       The zmq_recvmsg() function shall return number of bytes in the message
41       if successful. Otherwise it shall return -1 and set errno to one of the
42       values defined below.
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ERRORS

45       EAGAIN
46           Either the timeout set via the socket-option ZMQ_RCVTIMEO (see
47           zmq_setsockopt(3)) has been reached (flag ZMQ_DONTWAIT not set)
48           without being able to read a message from the socket or there are
49           no messages available at the moment (flag ZMQ_DONTWAIT set) and the
50           operation would block.
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52       ENOTSUP
53           The zmq_recvmsg() operation is not supported by this socket type.
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55       EFSM
56           The zmq_recvmsg() operation cannot be performed on this socket at
57           the moment due to the socket not being in the appropriate state.
58           This error may occur with socket types that switch between several
59           states, such as ZMQ_REP. See the messaging patterns section of
60           zmq_socket(3) for more information.
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62       ETERM
63           The 0MQ context associated with the specified socket was
64           terminated.
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66       ENOTSOCK
67           The provided socket was invalid.
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69       EINTR
70           The operation was interrupted by delivery of a signal before a
71           message was available.
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73       EFAULT
74           The message passed to the function was invalid.
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EXAMPLE

77       Receiving a message from a socket.
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79           /* Create an empty 0MQ message */
80           zmq_msg_t msg;
81           int rc = zmq_msg_init (&msg);
82           assert (rc == 0);
83           /* Block until a message is available to be received from socket */
84           rc = zmq_recvmsg (socket, &msg, 0);
85           assert (rc != -1);
86           /* Release message */
87           zmq_msg_close (&msg);
88
89       Receiving a multi-part message.
90
91           int more;
92           size_t more_size = sizeof (more);
93           do {
94               /* Create an empty 0MQ message to hold the message part */
95               zmq_msg_t part;
96               int rc = zmq_msg_init (&part);
97               assert (rc == 0);
98               /* Block until a message is available to be received from socket */
99               rc = zmq_recvmsg (socket, &part, 0);
100               assert (rc != -1);
101               /* Determine if more message parts are to follow */
102               rc = zmq_getsockopt (socket, ZMQ_RCVMORE, &more, &more_size);
103               assert (rc == 0);
104               zmq_msg_close (&part);
105           } while (more);
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SEE ALSO

109       zmq_recv(3) zmq_send(3) zmq_getsockopt(3) zmq_setsockopt(3)
110       zmq_socket(7) zmq(7)
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AUTHORS

113       This page was written by the 0MQ community. To make a change please
114       read the 0MQ Contribution Policy at
115       http://www.zeromq.org/docs:contributing.
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1190MQ 4.3.4                         01/30/2021                    ZMQ_RECVMSG(3)
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