size_t nng_aio_count(nng_aio *aio);
nng_aio_count() returns the number of bytes transferred by the
asynchronous operation associated with the handle aio.
Some asynchronous operations do not provide meaningful data for this function; for example operations that establish connections do not transfer user data (they may transfer protocol data though) — in this case this function will generally return zero.
This function is most useful when used with operations that make use of
of a scatter/gather vector (set by
The return value from this function is undefined if the operation
has not completed yet.
Either call this from the handle’s completion callback,
or after waiting for the operation to complete with
The number of bytes transferred by the operation.