1=pod 2 3=head1 NAME 4 5bio - Basic I/O abstraction 6 7=head1 SYNOPSIS 8 9=for openssl generic 10 11 #include <openssl/bio.h> 12 13=head1 DESCRIPTION 14 15A BIO is an I/O abstraction, it hides many of the underlying I/O 16details from an application. If an application uses a BIO for its 17I/O it can transparently handle SSL connections, unencrypted network 18connections and file I/O. 19 20There are two types of BIO, a source/sink BIO and a filter BIO. 21 22As its name implies a source/sink BIO is a source and/or sink of data, 23examples include a socket BIO and a file BIO. 24 25A filter BIO takes data from one BIO and passes it through to 26another, or the application. The data may be left unmodified (for 27example a message digest BIO) or translated (for example an 28encryption BIO). The effect of a filter BIO may change according 29to the I/O operation it is performing: for example an encryption 30BIO will encrypt data if it is being written to and decrypt data 31if it is being read from. 32 33BIOs can be joined together to form a chain (a single BIO is a chain 34with one component). A chain normally consists of one source/sink 35BIO and one or more filter BIOs. Data read from or written to the 36first BIO then traverses the chain to the end (normally a source/sink 37BIO). 38 39 40Some BIOs (such as memory BIOs) can be used immediately after calling 41BIO_new(). Others (such as file BIOs) need some additional initialization, 42and frequently a utility function exists to create and initialize such BIOs. 43 44If BIO_free() is called on a BIO chain it will only free one BIO resulting 45in a memory leak. 46 47Calling BIO_free_all() on a single BIO has the same effect as calling 48BIO_free() on it other than the discarded return value. 49 50Normally the I<type> argument is supplied by a function which returns a 51pointer to a BIO_METHOD. There is a naming convention for such functions: 52a source/sink BIO typically starts with I<BIO_s_> and 53a filter BIO with I<BIO_f_>. 54 55=head1 EXAMPLES 56 57Create a memory BIO: 58 59 BIO *mem = BIO_new(BIO_s_mem()); 60 61=head1 SEE ALSO 62 63L<BIO_ctrl(3)>, 64L<BIO_f_base64(3)>, L<BIO_f_buffer(3)>, 65L<BIO_f_cipher(3)>, L<BIO_f_md(3)>, 66L<BIO_f_null(3)>, L<BIO_f_ssl(3)>, 67L<BIO_f_readbuffer(3)>, 68L<BIO_find_type(3)>, L<BIO_new(3)>, 69L<BIO_new_bio_pair(3)>, 70L<BIO_push(3)>, L<BIO_read_ex(3)>, 71L<BIO_s_accept(3)>, L<BIO_s_bio(3)>, 72L<BIO_s_connect(3)>, L<BIO_s_fd(3)>, 73L<BIO_s_file(3)>, L<BIO_s_mem(3)>, 74L<BIO_s_null(3)>, L<BIO_s_socket(3)>, 75L<BIO_set_callback(3)>, 76L<BIO_should_retry(3)> 77 78=head1 COPYRIGHT 79 80Copyright 2000-2021 The OpenSSL Project Authors. All Rights Reserved. 81 82Licensed under the Apache License 2.0 (the "License"). You may not use 83this file except in compliance with the License. You can obtain a copy 84in the file LICENSE in the source distribution or at 85L<https://www.openssl.org/source/license.html>. 86 87=cut 88 89