SSL_set_fd.3ssl man page
SSL_set_fd — connect the SSL object with a file descriptor
#include <openssl/ssl.h> int SSL_set_fd(SSL *ssl, int fd); int SSL_set_rfd(SSL *ssl, int fd); int SSL_set_wfd(SSL *ssl, int fd);
SSL_set_fd() sets the file descriptor fd as the input/output facility for the TLS/SSL (encrypted) side of ssl. fd will typically be the socket file descriptor of a network connection.
When performing the operation, a socket BIO is automatically created to interface between the ssl and fd. The BIO and hence the SSL engine inherit the behaviour of fd. If fd is non-blocking, the ssl will also have non-blocking behaviour.
If there was already a BIO connected to ssl, BIO_free() will be called (for both the reading and writing side, if different).
SSL_set_rfd() and SSL_set_wfd() perform the respective action, but only for the read channel or the write channel, which can be set independently.
The following return values can occur:
The operation failed. Check the error stack to find out why.
The operation succeeded.
SSL_get_fd(3), SSL_set_bio(3), SSL_connect(3), SSL_accept(3), SSL_shutdown(3), ssl(3) , bio(3)