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

       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), BIO_should_retry(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

1.1.1j                             2021-02-16                             BIO(7)