This documentation is for version v1.3.0 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.


#include <nng/nng.h>

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


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.

Using this function gives access to the message structure, and may offer more functionality than the simpler nng_send() function.
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:


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.

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.


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



The operation would block, but NNG_FLAG_NONBLOCK was specified.


The socket s is not open.


An invalid set of flags was specified.


The value of size is too large.


Insufficient memory is available.


The protocol for socket s does not support sending.


The socket s cannot send data in this state.


The operation timed out.