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BIO(7)				    OpenSSL				BIO(7)

       bio - Basic I/O abstraction

	#include <openssl/bio.h>

       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 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_*();

       Create a	memory BIO:

	BIO *mem = BIO_new(BIO_s_mem());

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

       Copyright 2000-2019 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

1.1.1k				  2021-03-25				BIO(7)


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