# nng_send(3) Manual Page

## NAME

nng_send - send data

## SYNOPSIS

    #include <nng/nng.h>

    int nng_send(nng_socket s, void *data, size_t size, int flags);

## DESCRIPTION

The `nng_send()` function sends a message containing the data of length size using the socket s.

| The semantics of what sending a message means vary from protocol to protocol, so examination of the protocol documentation is encouraged. (For example, with an 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 data (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 either of (or neither of) the following values:

`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.

`NNG_FLAG_ALLOC`

  The data was allocated using `nng_alloc()`, or was obtained from a call to `nng_recv()` with the `NNG_FLAG_ALLOC` flag. If this function returns success, then the data is "owned" by the function, and it will assume responsibility for calling `nng_free()` when it is no longer needed. In the absence of this flag, the data is copied by the implementation before the function returns to the caller.

| The `NNG_FLAG_ALLOC` flag can be used to reduce data copies, thereby increasing performance.

| 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.

| When using `NNG_FLAG_ALLOC`, it is important that the value of size match the actual allocated size of the data. Using an incorrect size results in unspecified behavior, which may include heap corruption, program crashes, or trans-dimensional mutation of the program’s author.

## 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.

## SEE ALSO

nng_alloc(3), nng_free(3), nng_recv(3), nng_sendmsg(3), nng_strerror(3), nng_socket(5), nng(7)