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This documentation is for version 0.5.0 of nng, but the latest released version is v1.8.0. see the documentation for v1.8.0 for the most up-to-date information.
nng_recv(3)

SYNOPSIS

#include <nng/nng.h>

int nng_recv(nng_socket s, void *data, size_t *sizep int flags);

DESCRIPTION

The nng_recv() receives a message.

If the special flag NNG_FLAG_ALLOC is not specified, then the caller must set data to a buffer to receive the message body content, and must store the size of that buffer at the location pointed to by sizep. When the function returns, if it is successful, the size at sizep will be updated with the actual message body length copied into data.

If the special flag NNG_FLAG_ALLOC is present, then a "zero-copy" mode is used. In this case the caller must set the value of data to the location of another pointer (of type void *), and the sizep pointer must be set to a location to receive the size of the message body. The function will then allocate a message buffer (as if by nng_alloc(3)), fill it with the message body, and store it at the address referenced by data, and update the size referenced by sizep. When this flag is present, the caller assumes responsibility for disposing of the received buffer either by the function nng_free(3) or reusing the message for sending (with the same size) via nng_send(3).

The semantics of what receiving a message means vary from protocol to protocol, so examination of the protocol documentation is encouraged. (For example, with an nng_req(7) socket a message may only be received after a request has been sent, and an nng_sub(7) socket may only receive messages corresponding to topics to which it has subscribed.) Furthermore, some protocols may not support receiving data at all, such as nng_pub(7).
The NNG_FLAG_ALLOC flag can be used to reduce data copies, thereby increasing performance, particularly if the buffer is reused to send a response using the same flag.

RETURN VALUES

This function returns 0 on success, and non-zero otherwise.

ERRORS

NNG_EAGAIN

The socket s cannot accept data for sending.

NNG_ECLOSED

The socket s is not open.

NNG_EINVAL

An invalid set of flags was specified.

NNG_EMSGSIZE

The received message did not fit in the size provided.

NNG_ENOMEM

Insufficient memory is available.

NNG_ENOTSUP

The protocol for socket s does not support receiving.

NNG_ESTATE

The socket s cannot receive data in this state.

NNG Reference Manual v0.5.0 © 2019 Staysail Systems, Inc, © 2018 Capitar IT Group BV
This document is supplied under the MIT License.
nanomsg™ and nng™ are trademarks of Garrett D'Amore.