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nng_sendmsg.3.adoc

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nng_sendmsg(3)

NAME

nng_sendmsg - send message

SYNOPSIS

#include <nng/nng.h>

int nng_sendmsg(nng_socket s, nng_msg *msg, int flags);

DESCRIPTION

The nng_sendmsg() sends message msg using the socket s.

If the function returns zero, indicating it has accepted the message for delivery, then the msg is “owned” by the socket s, and the caller must not make any further use of it. The socket will free the message when it is finished.

If the function returns non-zero, then it is the caller’s responsibility to dispose of the msg, which may include freeing it, sending it to another socket, or simply trying again later.

Tip
 Using this function gives access to the message structure, and may offer more functionality than the simpler nng_send() function.
Note
 The semantics of what sending a message means vary from protocol to protocol, so examination of the protocol documentation is encouraged. (For example, with a pub socket the data is broadcast, so that any peers who have a suitable subscription will be able to receive it using nng_recv() or a similar function.) Furthermore, some protocols may not support sending (such as sub) or may require other conditions. (For example, rep sockets cannot normally send data, which are responses to requests, until they have first received a request.)

The flags may contain the following value:

NNG_FLAG_NONBLOCK

The function returns immediately, regardless of whether the socket is able to accept the data or not. If the socket is unable to accept the data (such as if backpressure exists because the peers are consuming messages too slowly, or no peer is present), then the function will return with NNG_EAGAIN. If this flag is not specified, then the function will block if such a condition exists.

Note
 Regardless of the presence or absence of NNG_FLAG_NONBLOCK, there may be queues between the sender and the receiver. Furthermore, there is no guarantee that the message has actually been delivered. Finally, with some protocols, the semantic is implicitly NNG_FLAG_NONBLOCK, such as with pub sockets, which are best-effort delivery only.

RETURN VALUES

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

ERRORS

NNG_EAGAIN

The operation would block, but NNG_FLAG_NONBLOCK was specified.
NNG_ECLOSED

The socket s is not open.
NNG_EINVAL

An invalid set of flags was specified.
NNG_EMSGSIZE

The value of size is too large.
NNG_ENOMEM

Insufficient memory is available.
NNG_ENOTSUP

The protocol for socket s does not support sending.
NNG_ESTATE

The socket s cannot send data in this state.
NNG_ETIMEDOUT

The operation timed out.