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=head1 NAME

bio - Basic I/O abstraction

=head1 SYNOPSIS

=for comment generic

 #include <openssl/bio.h>

=head1 DESCRIPTION

A BIO is an I/O abstraction, it hides 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.

There are two type of BIO, a source/sink BIO and a filter BIO.

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.

A filter BIO takes data from one BIO and passes it through to
another, or 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.

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).


Some BIOs (such as memory BIOs) can be used immediately after calling
BIO_new(). Others (such as file BIOs) need some additional initialization,
and frequently a utility function exists to create and initialize such BIOs.

If BIO_free() is called on a BIO chain it will only free one BIO resulting
in a memory leak.

Calling BIO_free_all() on a single BIO has the same effect as calling
BIO_free() on it other than the discarded return value.

Normally the B<type> argument is supplied by a function which returns a
pointer to a BIO_METHOD. There is a naming convention for such functions:
a source/sink BIO is normally called BIO_s_*() and a filter BIO
BIO_f_*();

=head1 EXAMPLE

Create a memory BIO:

 BIO *mem = BIO_new(BIO_s_mem());

=head1 SEE ALSO

L<BIO_ctrl(3)>,
L<BIO_f_base64(3)>, L<BIO_f_buffer(3)>,
L<BIO_f_cipher(3)>, L<BIO_f_md(3)>,
L<BIO_f_null(3)>, L<BIO_f_ssl(3)>,
L<BIO_find_type(3)>, L<BIO_new(3)>,
L<BIO_new_bio_pair(3)>,
L<BIO_push(3)>, L<BIO_read_ex(3)>,
L<BIO_s_accept(3)>, L<BIO_s_bio(3)>,
L<BIO_s_connect(3)>, L<BIO_s_fd(3)>,
L<BIO_s_file(3)>, L<BIO_s_mem(3)>,
L<BIO_s_null(3)>, L<BIO_s_socket(3)>,
L<BIO_set_callback(3)>,
L<BIO_should_retry(3)>

=head1 COPYRIGHT

Copyright 2000-2017 The OpenSSL Project Authors. All Rights Reserved.

Licensed under the OpenSSL license (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
L<https://www.openssl.org/source/license.html>.

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