> Sorry, I attached wrong example version. It uses repeated
> sslsock.write() of the same buffer after catching
> SSL_ERROR_WANT_WRITE. It delivers the full block but this is a
> blocking operation.

In "normal" non-blocking code you would use select() (or an equivalent)
until the socket is ready for writing, and then send() some chunk of
data on it. Can't you use that approach?