NNG_SEND(3)

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.

    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 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.

    Tip

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

    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.

    Important

    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)