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SSL_SET_FD(3) Library Functions Manual SSL_SET_FD(3)

SSL_set_fd, SSL_set_rfd, SSL_set_wfd —
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(3) 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:
0
The operation failed. Check the error stack to find out why.
1
The operation succeeded.

BIO_new(3), ssl(3), SSL_accept(3), SSL_connect(3), SSL_get_fd(3), SSL_set_bio(3), SSL_shutdown(3)

SSL_set_fd() appeared in SSLeay 0.4 or earlier. SSL_set_rfd() and SSL_set_wfd() first appeared in SSLeay 0.6.0. These functions have been available since OpenBSD 2.4.
March 27, 2018 OpenBSD-current