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.\" $OpenBSD: BIO_f_null.3,v 1.12 2023/04/11 16:58:43 schwarze Exp $
.\" full merge up to: OpenSSL e9b77246 Jan 20 19:58:49 2017 +0100
.\"
.\" This file was written by Dr. Stephen Henson <steve@openssl.org>.
.\" Copyright (c) 2000 The OpenSSL Project. All rights reserved.
.\"
.\" Redistribution and use in source and binary forms, with or without
.\" modification, are permitted provided that the following conditions
.\" are met:
.\"
.\" 1. Redistributions of source code must retain the above copyright
.\" notice, this list of conditions and the following disclaimer.
.\"
.\" 2. Redistributions in binary form must reproduce the above copyright
.\" notice, this list of conditions and the following disclaimer in
.\" the documentation and/or other materials provided with the
.\" distribution.
.\"
.\" 3. All advertising materials mentioning features or use of this
.\" software must display the following acknowledgment:
.\" "This product includes software developed by the OpenSSL Project
.\" for use in the OpenSSL Toolkit. (http://www.openssl.org/)"
.\"
.\" 4. The names "OpenSSL Toolkit" and "OpenSSL Project" must not be used to
.\" endorse or promote products derived from this software without
.\" prior written permission. For written permission, please contact
.\" openssl-core@openssl.org.
.\"
.\" 5. Products derived from this software may not be called "OpenSSL"
.\" nor may "OpenSSL" appear in their names without prior written
.\" permission of the OpenSSL Project.
.\"
.\" 6. Redistributions of any form whatsoever must retain the following
.\" acknowledgment:
.\" "This product includes software developed by the OpenSSL Project
.\" for use in the OpenSSL Toolkit (http://www.openssl.org/)"
.\"
.\" THIS SOFTWARE IS PROVIDED BY THE OpenSSL PROJECT ``AS IS'' AND ANY
.\" EXPRESSED OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
.\" PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE OpenSSL PROJECT OR
.\" ITS CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
.\" SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
.\" NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
.\" LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT,
.\" STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
.\" ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED
.\" OF THE POSSIBILITY OF SUCH DAMAGE.
.\"
.Dd $Mdocdate: April 11 2023 $
.Dt BIO_F_NULL 3
.Os
.Sh NAME
.Nm BIO_f_null
.\" .Nm BIO_f_nbio_test is intentionally undocumented
.\" because it exposes absurd functionality that is unused
.\" except in openssl(1) s_client/s_server -nbio_test.
.Nd null filter
.Sh SYNOPSIS
.In openssl/bio.h
.Ft const BIO_METHOD *
.Fo BIO_f_null
.Fa void
.Fc
.Sh DESCRIPTION
.Fn BIO_f_null
returns the null filter BIO method.
This is a filter BIO that does nothing.
As may be apparent, a null filter BIO is not particularly useful.
.Pp
All requests to a null filter BIO are passed through to the next BIO
in the chain: this means that a BIO chain containing a null filter BIO
behaves just as though the BIO was not there.
.Pp
A chain containing a null filter BIO cannot be copied with
.Xr BIO_dup_chain 3 ,
and any attempt to do so fails and returns
.Dv NULL .
.Sh RETURN VALUES
.Fn BIO_f_null
returns the null filter BIO method.
.Pp
When called on a null filter BIO object,
.Xr BIO_method_type 3
returns the constant
.Dv BIO_TYPE_NULL_FILTER
and
.Xr BIO_method_name 3
returns a pointer to the static string
.Qq NULL filter ,
not to be confused with a NUL string nor with a
.Dv NULL pointer .
.Sh SEE ALSO
.Xr BIO_new 3
.Sh HISTORY
.Fn BIO_f_null
first appeared in SSLeay 0.8.0 and has been available since
.Ox 2.4 .
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