int SSL_get_fd(const SSL *ssl);
int SSL_get_rfd(const SSL *ssl);
int SSL_get_wfd(const SSL *ssl);
DESCRIPTION
SSL_get_fd() returns the file descriptor which is linked to ssl.
SSL_get_rfd() and SSL_get_wfd() return the file descriptors for the
read or the write channel, which can be different. If the read and the
write channel are different, SSL_get_fd() will return the file descriptor
of the read channel.
RETURN VALUES
The following return values can occur:
-1
The operation failed, because the underlying BIO is not of the correct type
(suitable for file descriptors).
