.\" $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>.
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.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 .