xref: /openssl/doc/man7/bio.pod (revision 45ada6b9)
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 3.2. 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