SSL_SET_BIO(3SSL) OpenSSL SSL_SET_BIO(3SSL)
NAME
SSL_set_bio, SSL_set0_rbio, SSL_set0_wbio - connect the SSL object with
a BIO
SYNOPSIS
#include <openssl/ssl.h>
void SSL_set_bio(SSL *ssl, BIO *rbio, BIO *wbio);
void SSL_set0_rbio(SSL *s, BIO *rbio);
void SSL_set0_wbio(SSL *s, BIO *wbio);
DESCRIPTION
SSL_set0_rbio() connects the BIO rbio for the read operations of the ssl
object. The SSL engine inherits the behaviour of rbio. If the BIO is
nonblocking then the ssl object will also have nonblocking behaviour.
This function transfers ownership of rbio to ssl. It will be
automatically freed using BIO_free_all(3) when the ssl is freed. On
calling this function, any existing rbio that was previously set will
also be freed via a call to BIO_free_all(3) (this includes the case
where the rbio is set to the same value as previously).
If using a custom BIO, rbio must implement either
BIO_meth_set_read_ex(3) or BIO_meth_set_read(3).
SSL_set0_wbio() works in the same as SSL_set0_rbio() except that it
connects the BIO wbio for the write operations of the ssl object. Note
that if the rbio and wbio are the same then SSL_set0_rbio() and
SSL_set0_wbio() each take ownership of one reference. Therefore, it may
be necessary to increment the number of references available using
BIO_up_ref(3) before calling the set0 functions.
If using a custom BIO, wbio must implement BIO_meth_set_write_ex(3) or
BIO_meth_set_write(3). It additionally must implement BIO_flush(3) using
BIO_CTRL_FLUSH and BIO_meth_set_ctrl(3). If flushing is unnecessary
with wbio, BIO_flush(3) should return one and do nothing.
SSL_set_bio() is similar to SSL_set0_rbio() and SSL_set0_wbio() except
that it connects both the rbio and the wbio at the same time, and
transfers the ownership of rbio and wbio to ssl according to the
following set of rules:
• If neither the rbio or wbio have changed from their previous values
then nothing is done.
• If the rbio and wbio parameters are different and both are different
to their previously set values then one reference is consumed for the
rbio and one reference is consumed for the wbio.
• If the rbio and wbio parameters are the same and the rbio is not the
same as the previously set value then one reference is consumed.
• If the rbio and wbio parameters are the same and the rbio is the same
as the previously set value, then no additional references are
consumed.
• If the rbio and wbio parameters are different and the rbio is the same
as the previously set value then one reference is consumed for the
wbio and no references are consumed for the rbio.
• If the rbio and wbio parameters are different and the wbio is the same
as the previously set value and the old rbio and wbio values were the
same as each other then one reference is consumed for the rbio and no
references are consumed for the wbio.
• If the rbio and wbio parameters are different and the wbio is the same
as the previously set value and the old rbio and wbio values were
different to each other, then one reference is consumed for the rbio
and one reference is consumed for the wbio.
Because of this complexity, this function should be avoided; use
SSL_set0_rbio() and SSL_set0_wbio() instead.
Where a new BIO is set on a QUIC connection SSL object, blocking mode
will be disabled on that SSL object if the BIO cannot support blocking
mode. If another BIO is subsequently set on the SSL object which can
support blocking mode, blocking mode will not be automatically re-
enabled. For more information, see SSL_set_blocking_mode(3).
RETURN VALUES
SSL_set_bio(), SSL_set0_rbio() and SSL_set0_wbio() cannot fail.
SEE ALSO
SSL_get_rbio(3), SSL_connect(3), SSL_accept(3), SSL_shutdown(3), ssl(7),
bio(7)
HISTORY
SSL_set0_rbio() and SSL_set0_wbio() were added in OpenSSL 1.1.0.
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_BIO(3SSL)
Generated by dwww version 1.16 on Sat Oct 3 07:12:12 CEST 2026.