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117 lines
3.9 KiB
Plaintext
117 lines
3.9 KiB
Plaintext
= zmq_recvmsg(3)
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== NAME
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zmq_recvmsg - receive a message part from a socket
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== SYNOPSIS
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*int zmq_recvmsg (void '*socket', zmq_msg_t '*msg', int 'flags');*
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== DESCRIPTION
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The _zmq_recvmsg()_ function shall receive a message part from the socket
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referenced by the 'socket' argument and store it in the message referenced by
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the 'msg' argument. Any content previously stored in 'msg' shall be properly
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deallocated. If there are no message parts available on the specified 'socket'
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the _zmq_recvmsg()_ function shall block until the request can be satisfied.
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The 'flags' argument is a combination of the flags defined below:
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*ZMQ_DONTWAIT*::
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Specifies that the operation should be performed in non-blocking mode. If there
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are no messages available on the specified 'socket', the _zmq_recvmsg()_
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function shall fail with 'errno' set to EAGAIN.
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NOTE: this API method is deprecated in favor of zmq_msg_recv(3).
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Multi-part messages
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~~~~~~~~~~~~~~~~~~~
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A 0MQ message is composed of 1 or more message parts. Each message
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part is an independent 'zmq_msg_t' in its own right. 0MQ ensures atomic
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delivery of messages: peers shall receive either all _message parts_ of a
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message or none at all. The total number of message parts is unlimited except
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by available memory.
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An application that processes multi-part messages must use the _ZMQ_RCVMORE_
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xref:zmq_getsockopt.adoc[zmq_getsockopt] option after calling _zmq_recvmsg()_ to determine if
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there are further parts to receive.
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== RETURN VALUE
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The _zmq_recvmsg()_ function shall return number of bytes in the message
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if successful. Otherwise it shall return `-1` and set 'errno' to one of the
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values defined below.
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== ERRORS
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*EAGAIN*::
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Either the timeout set via the socket-option ZMQ_RCVTIMEO (see xref:zmq_setsockopt.adoc[zmq_setsockopt])
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has been reached (flag ZMQ_DONTWAIT not set) without being able to read a message
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from the socket or there are no messages available at the moment (flag ZMQ_DONTWAIT set)
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and the operation would block.
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*ENOTSUP*::
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The _zmq_recvmsg()_ operation is not supported by this socket type.
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*EFSM*::
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The _zmq_recvmsg()_ operation cannot be performed on this socket at the moment
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due to the socket not being in the appropriate state. This error may occur with
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socket types that switch between several states, such as ZMQ_REP. See the
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_messaging patterns_ section of xref:zmq_socket.adoc[zmq_socket] for more information.
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*ETERM*::
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The 0MQ 'context' associated with the specified 'socket' was terminated.
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*ENOTSOCK*::
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The provided 'socket' was invalid.
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*EINTR*::
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The operation was interrupted by delivery of a signal before a message was
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available.
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*EFAULT*::
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The message passed to the function was invalid.
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== EXAMPLE
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.Receiving a message from a socket
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----
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/* Create an empty 0MQ message */
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zmq_msg_t msg;
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int rc = zmq_msg_init (&msg);
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assert (rc == 0);
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/* Block until a message is available to be received from socket */
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rc = zmq_recvmsg (socket, &msg, 0);
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assert (rc != -1);
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/* Release message */
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zmq_msg_close (&msg);
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----
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.Receiving a multi-part message
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----
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int more;
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size_t more_size = sizeof (more);
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do {
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/* Create an empty 0MQ message to hold the message part */
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zmq_msg_t part;
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int rc = zmq_msg_init (&part);
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assert (rc == 0);
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/* Block until a message is available to be received from socket */
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rc = zmq_recvmsg (socket, &part, 0);
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assert (rc != -1);
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/* Determine if more message parts are to follow */
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rc = zmq_getsockopt (socket, ZMQ_RCVMORE, &more, &more_size);
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assert (rc == 0);
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zmq_msg_close (&part);
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} while (more);
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----
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== SEE ALSO
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* xref:zmq_recv.adoc[zmq_recv]
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* xref:zmq_send.adoc[zmq_send]
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* xref:zmq_getsockopt.adoc[zmq_getsockopt]
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* xref:zmq_setsockopt.adoc[zmq_setsockopt]
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* xref:zmq_socket.adoc[zmq_socket]
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* xref:zmq.adoc[zmq]
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== AUTHORS
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This page was written by the 0MQ community. To make a change please
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read the 0MQ Contribution Policy at <https://zeromq.org/how-to-contribute/>.
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