(e.g. when SSL_set_fd() was used), select() or poll() on the underlying socket can be used to find out when the TLS/SSL I/O function should be retried.</p>

<p>Caveat: Any TLS/SSL I/O function can lead to either of <b>SSL_ERROR_WANT_READ</b> and <b>SSL_ERROR_WANT_WRITE</b>. In particular, SSL_read_ex(), SSL_read(), SSL_peek_ex(), or SSL_peek() may want to write data and SSL_write() or SSL_write_ex() may want to read data. This is mainly because TLS/SSL handshakes may occur at any time during the protocol (i