int nng_send(nng_socket s, void *data, size_t size, int flags);
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:
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.
The data was allocated using
nng_alloc(), or was obtained from a call to
NNG_FLAG_ALLOCflag. 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.
NNG_FLAG_ALLOC flag can be used to reduce data copies, thereby
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
such as with pub sockets, which are best-effort delivery only.
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.
This function returns 0 on success, and non-zero otherwise.
The operation would block, but
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.