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Diffstat (limited to 'doc/zmq_msg_recv.txt')
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diff --git a/doc/zmq_msg_recv.txt b/doc/zmq_msg_recv.txt new file mode 100644 index 0000000..c3d6c54 --- /dev/null +++ b/doc/zmq_msg_recv.txt @@ -0,0 +1,124 @@ +zmq_msg_recv(3) +=============== + + +NAME +---- +zmq_msg_recv - receive a message part from a socket + + +SYNOPSIS +-------- +*int zmq_msg_recv (zmq_msg_t '*msg', void '*socket', int 'flags');* + + +DESCRIPTION +----------- +The _zmq_msg_recv()_ function is identical to linkzmq: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 messages +~~~~~~~~~~~~~~~~~~~ +A 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_ +linkzmq:zmq_getsockopt[3] option after calling _zmq_msg_recv()_ to determine if +there are further parts to receive. + + +RETURN VALUE +------------ +The _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. + + +ERRORS +------ +*EAGAIN*:: +Non-blocking mode was requested and no messages are available at the moment. +*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 linkzmq: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. + + +EXAMPLE +------- +.Receiving 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 +---- +int64_t 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 ALSO +-------- +linkzmq:zmq_recv[3] +linkzmq:zmq_send[3] +linkzmq:zmq_msg_send[3] +linkzmq:zmq_getsockopt[3] +linkzmq:zmq_socket[7] +linkzmq:zmq[7] + + +AUTHORS +------- +This page was written by the 0MQ community. To make a change please +read the 0MQ Contribution Policy at <http://www.zeromq.org/docs:contributing>. |