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BIO(7) OpenSSL BIO(7)
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bio - Basic I/O abstraction
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
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
1.1.1i 2020-01-23 BIO(7)