ZMQ_RECV

Section: 0MQ Manual (3)
Updated: 01/30/2021
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NAME

zmq_recv - receive a message part from a socket

SYNOPSIS

int zmq_recv (void *socket, void *buf, size_t len, int flags);

DESCRIPTION

The zmq_recv() function shall receive a message from the socket referenced by the socket argument and store it in the buffer referenced by the buf argument. Any bytes exceeding the length specified by the len argument shall be truncated. If there are no messages available on the specified socket the zmq_recv() function shall block until the request can be satisfied. The flags argument is a combination of the flags defined below: The buf argument may be null if len is zero.

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_recv() function shall fail with errno set to EAGAIN.

Multi-part messages

A 0MQ message is composed of 1 or more message parts. 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_recv() to determine if there are further parts to receive.

RETURN VALUE

The zmq_recv() function shall return number of bytes in the message if successful. Note that the value can exceed the value of the len parameter in case the message was truncated. If not successful the function shall return -1 and set errno to one of the values defined below.

ERRORS

EAGAIN

: 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_recv() operation is not supported by this socket type.

EFSM

: The zmq_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.

EXAMPLE

Receiving a message from a socket.

char buf [256];
nbytes = zmq_recv (socket, buf, 256, 0);
assert (nbytes != -1);

AUTHORS

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