SSL_SET_FD(3) | Library Functions Manual | SSL_SET_FD(3)

# NAME

`SSL_set_fd`, `SSL_set_rfd`, `SSL_set_wfd` — connect the SSL object with a file descriptor

# SYNOPSIS

library “libssl” libcrypto
`#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);

# DESCRIPTION

`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.

# RETURN VALUES

The following return values can occur:

0
  The operation failed. Check the error stack to find out why.
1
  The operation succeeded.

# SEE ALSO

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

# HISTORY

`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.

June 8, 2025 | Debian