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       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

       Calling BIO_free_all() 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(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_mem(3), BIO_s_null(3), BIO_s_socket(3),
       BIO_set_callback(3), BIO_should_retry(3)


       Copyright 2000-2016 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 <>.