SSL_set_bio - connect the SSL object with a BIO
void SSL_set_bio(SSL *ssl, BIO *rbio, BIO *wbio);
The SSL engine inherits the behaviour of rbio and wbio, respectively. If a BIO is non-blocking, the ssl will also have non-blocking behaviour.
If there was already a BIO connected to ssl,
SSL_get_rbio(3), SSL_connect(3), SSL_accept(3), SSL_shutdown(3), ssl(3), bio(3)