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2566c02a9e
These sockets don't handle multipart data, so if callers send it, they drop frames, and things break silently. Solution: if the caller tries to use ZMQ_SNDMORE, return -1 and set errno to EINVAL.
122 lines
3.8 KiB
Plaintext
122 lines
3.8 KiB
Plaintext
zmq_sendmsg(3)
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==============
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NAME
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----
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zmq_sendmsg - send a message part on a socket
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SYNOPSIS
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--------
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*int zmq_sendmsg (void '*socket', zmq_msg_t '*msg', int 'flags');*
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DESCRIPTION
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-----------
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The _zmq_sendmsg()_ function shall queue the message referenced by the 'msg'
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argument to be sent to the socket referenced by the 'socket' argument. The
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'flags' argument is a combination of the flags defined below:
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*ZMQ_DONTWAIT*::
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For socket types (DEALER, PUSH) that block when there are no available peers
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(or all peers have full high-water mark), specifies that the operation should
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be performed in non-blocking mode. If the message cannot be queued on the
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'socket', the _zmq_sendmsg()_ function shall fail with 'errno' set to EAGAIN.
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*ZMQ_SNDMORE*::
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Specifies that the message being sent is a multi-part message, and that further
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message parts are to follow. Refer to the section regarding multi-part messages
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below for a detailed description.
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The _zmq_msg_t_ structure passed to _zmq_sendmsg()_ is nullified during the
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call. If you want to send the same message to multiple sockets you have to copy
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it (e.g. using _zmq_msg_copy()_).
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NOTE: A successful invocation of _zmq_sendmsg()_ does not indicate that the
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message has been transmitted to the network, only that it has been queued on
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the 'socket' and 0MQ has assumed responsibility for the message.
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NOTE: this API method is deprecated in favor of zmq_msg_send(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 sends multi-part messages must use the _ZMQ_SNDMORE_ flag
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when sending each message part except the final one.
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RETURN VALUE
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------------
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The _zmq_sendmsg()_ 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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------
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*EAGAIN*::
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Non-blocking mode was requested and the message cannot be sent at the moment.
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*ENOTSUP*::
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The _zmq_sendmsg()_ operation is not supported by this socket type.
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*EINVAL*::
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The sender tried to send multipart data, which the socket type does not allow.
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*EFSM*::
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The _zmq_sendmsg()_ 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 linkzmq:zmq_socket[3] 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 the message was
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sent.
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*EFAULT*::
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Invalid message.
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*EHOSTUNREACH*::
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The message cannot be routed.
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EXAMPLE
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-------
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.Filling in a message and sending it to a socket
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----
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/* Create a new message, allocating 6 bytes for message content */
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zmq_msg_t msg;
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int rc = zmq_msg_init_size (&msg, 6);
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assert (rc == 0);
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/* Fill in message content with 'AAAAAA' */
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memset (zmq_msg_data (&msg), 'A', 6);
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/* Send the message to the socket */
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rc = zmq_sendmsg (socket, &msg, 0);
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assert (rc == 6);
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----
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.Sending a multi-part message
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----
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/* Send a multi-part message consisting of three parts to socket */
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rc = zmq_sendmsg (socket, &part1, ZMQ_SNDMORE);
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rc = zmq_sendmsg (socket, &part2, ZMQ_SNDMORE);
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/* Final part; no more parts to follow */
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rc = zmq_sendmsg (socket, &part3, 0);
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----
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SEE ALSO
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--------
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linkzmq:zmq_recv[3]
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linkzmq:zmq_socket[7]
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linkzmq:zmq[7]
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AUTHORS
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-------
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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 <http://www.zeromq.org/docs:contributing>.
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