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 39Some BIOs (such as memory BIOs) can be used immediately after calling 40BIO_new(). Others (such as file BIOs) need some additional initialization, 41and frequently a utility function exists to create and initialize such BIOs. 42 43If BIO_free() is called on a BIO chain it will only free one BIO resulting 44in a memory leak. 45 46Calling BIO_free_all() on a single BIO has the same effect as calling 47BIO_free() on it other than the discarded return value. 48 49Normally the I<type> argument is supplied by a function which returns a 50pointer to a BIO_METHOD. There is a naming convention for such functions: 51a source/sink BIO typically starts with I<BIO_s_> and 52a filter BIO with I<BIO_f_>. 53 54=head2 TCP Fast Open 55 56TCP Fast Open (RFC7413), abbreviated "TFO", is supported by the BIO 57interface since OpenSSL 3.1. TFO is supported in the following operating systems: 58 59=over 4 60 61=item * Linux kernel 3.13 and later, where TFO is enabled by default. 62 63=item * Linux kernel 4.11 and later, using TCP_FASTOPEN_CONNECT. 64 65=item * FreeBSD 10.3 to 11.4, supports server TFO only. 66 67=item * FreeBSD 12.0 and later, supports both client and server TFO. 68 69=item * macOS 10.14 and later. 70 71=back 72 73Each operating system has a slightly different API for TFO. Please 74refer to the operating systems' API documentation when using 75sockets directly. 76 77=head1 EXAMPLES 78 79Create a memory BIO: 80 81 BIO *mem = BIO_new(BIO_s_mem()); 82 83=head1 SEE ALSO 84 85L<BIO_ctrl(3)>, 86L<BIO_f_base64(3)>, L<BIO_f_buffer(3)>, 87L<BIO_f_cipher(3)>, L<BIO_f_md(3)>, 88L<BIO_f_null(3)>, L<BIO_f_ssl(3)>, 89L<BIO_f_readbuffer(3)>, 90L<BIO_find_type(3)>, 91L<BIO_get_conn_mode(3)>, 92L<BIO_new(3)>, 93L<BIO_new_bio_pair(3)>, 94L<BIO_push(3)>, L<BIO_read_ex(3)>, 95L<BIO_s_accept(3)>, L<BIO_s_bio(3)>, 96L<BIO_s_connect(3)>, L<BIO_s_fd(3)>, 97L<BIO_s_file(3)>, L<BIO_s_mem(3)>, 98L<BIO_s_null(3)>, L<BIO_s_socket(3)>, 99L<BIO_set_callback(3)>, 100L<BIO_set_conn_mode(3)>, 101L<BIO_set_tfo(3)>, 102L<BIO_set_tfo_accept(3)>, 103L<BIO_should_retry(3)> 104 105=head1 COPYRIGHT 106 107Copyright 2000-2022 The OpenSSL Project Authors. All Rights Reserved. 108 109Licensed under the Apache License 2.0 (the "License"). You may not use 110this file except in compliance with the License. You can obtain a copy 111in the file LICENSE in the source distribution or at 112L<https://www.openssl.org/source/license.html>. 113 114=cut 115
