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.\" $OpenBSD: BIO.3,v 1.5 2016/11/22 14:55:19 schwarze Exp $
.\" OpenSSL a9c85cea Nov 11 09:33:55 2016 +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: November 22 2016 $
.Dt BIO 3
.Os
.Sh NAME
.Nm BIO
.Nd OpenSSL basic I/O abstraction
.Sh SYNOPSIS
.In openssl/bio.h
.Sh DESCRIPTION
A BIO is an I/O abstraction,
hiding many of the underlying I/O details from an application.
If an application uses a BIO for its I/O, it can transparently handle
SSL connections, unencrypted network connections and file I/O.
.Pp
There are two types of BIO, a source/sink BIO and a filter BIO.
.Pp
As its name implies, a source/sink BIO is a source and/or sink of data.
Examples include a socket BIO and a file BIO.
.Pp
A filter BIO takes data from one BIO and passes it through
to another, or to the application.
The data may be left unmodified (for example a message digest BIO)
or translated (for example an encryption BIO).
The effect of a filter BIO may change according to the I/O operation
it is performing: for example an encryption BIO will encrypt data
if it is being written to and decrypt data if it is being read from.
.Pp
BIOs can be joined together to form a chain
(a single BIO is a chain with one component).
A chain normally consist of one source/sink BIO
and one or more filter BIOs.
Data read from or written to the first BIO then traverses the chain
to the end (normally a source/sink BIO).
.Sh SEE ALSO
.Xr BIO_ctrl 3 ,
.Xr BIO_f_base64 3 ,
.Xr BIO_f_buffer 3 ,
.Xr BIO_f_cipher 3 ,
.Xr BIO_f_md 3 ,
.Xr BIO_f_null 3 ,
.Xr BIO_f_ssl 3 ,
.Xr BIO_find_type 3 ,
.Xr BIO_new 3 ,
.Xr BIO_push 3 ,
.Xr BIO_read 3 ,
.Xr BIO_s_accept 3 ,
.Xr BIO_s_bio 3 ,
.Xr BIO_s_connect 3 ,
.Xr BIO_s_fd 3 ,
.Xr BIO_s_file 3 ,
.Xr BIO_s_mem 3 ,
.Xr BIO_s_null 3 ,
.Xr BIO_s_socket 3 ,
.Xr BIO_set_callback 3 ,
.Xr BIO_should_retry 3
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