SSL_SET_FD(3SSL) OpenSSL SSL_SET_FD(3SSL)
NAME
SSL_set_fd, SSL_set_rfd, SSL_set_wfd - connect the SSL object with a
file descriptor
SYNOPSIS
#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 nonblocking, the ssl will also
have nonblocking behaviour.
When used on a QUIC connection SSL object, a datagram BIO is
automatically created instead of a socket BIO. These functions fail if
called on a QUIC stream SSL object.
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.
RETURN VALUES
The following return values can occur:
0 The operation failed. Check the error stack to find out why.
1 The operation succeeded.
NOTES
On Windows, a socket handle is a 64-bit data type (UINT_PTR), which
leads to a compiler warning (conversion from 'SOCKET' to 'int', possible
loss of data) when passing the socket handle to SSL_set_*fd(). For the
time being, this warning can safely be ignored, because although the
Microsoft documentation claims that the upper limit is INVALID_SOCKET-1
(2^64 - 2), in practice the current socket() implementation returns an
index into the kernel handle table, the size of which is limited to
2^24.
SEE ALSO
SSL_get_fd(3), SSL_set_bio(3), SSL_connect(3), SSL_accept(3),
SSL_shutdown(3), ssl(7) , bio(7)
COPYRIGHT
Copyright 2000-2023 The OpenSSL Project Authors. All Rights Reserved.
Licensed under the Apache License 2.0 (the "License"). You may not use
this file except in compliance with the License. You can obtain a copy
in the file LICENSE in the source distribution or at
<https://www.openssl.org/source/license.html>.
3.5.7 2026-06-09 SSL_SET_FD(3SSL)
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