| 1 | =pod
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| 2 |
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| 3 | =head1 NAME
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| 4 |
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| 5 | bio - Basic I/O abstraction
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| 6 |
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| 7 | =head1 SYNOPSIS
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| 8 |
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| 9 | =for openssl generic
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| 10 |
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| 11 | #include <openssl/bio.h>
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| 12 |
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| 13 | =head1 DESCRIPTION
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| 14 |
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| 15 | A BIO is an I/O abstraction, it hides many of the underlying I/O
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| 16 | details from an application. If an application uses a BIO for its
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| 17 | I/O it can transparently handle SSL connections, unencrypted network
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| 18 | connections and file I/O.
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| 19 |
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| 20 | There are two types of BIO, a source/sink BIO and a filter BIO.
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| 21 |
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| 22 | As its name implies a source/sink BIO is a source and/or sink of data,
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| 23 | examples include a socket BIO and a file BIO.
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| 24 |
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| 25 | A filter BIO takes data from one BIO and passes it through to
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| 26 | another, or the application. The data may be left unmodified (for
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| 27 | example a message digest BIO) or translated (for example an
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| 28 | encryption BIO). The effect of a filter BIO may change according
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| 29 | to the I/O operation it is performing: for example an encryption
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| 30 | BIO will encrypt data if it is being written to and decrypt data
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| 31 | if it is being read from.
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| 32 |
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| 33 | BIOs can be joined together to form a chain (a single BIO is a chain
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| 34 | with one component). A chain normally consists of one source/sink
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| 35 | BIO and one or more filter BIOs. Data read from or written to the
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| 36 | first BIO then traverses the chain to the end (normally a source/sink
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| 37 | BIO).
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| 38 |
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| 39 | Some BIOs (such as memory BIOs) can be used immediately after calling
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| 40 | BIO_new(). Others (such as file BIOs) need some additional initialization,
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| 41 | and frequently a utility function exists to create and initialize such BIOs.
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| 42 |
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| 43 | If BIO_free() is called on a BIO chain it will only free one BIO resulting
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| 44 | in a memory leak.
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| 45 |
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| 46 | Calling BIO_free_all() on a single BIO has the same effect as calling
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| 47 | BIO_free() on it other than the discarded return value.
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| 48 |
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| 49 | Normally the I<type> argument is supplied by a function which returns a
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| 50 | pointer to a BIO_METHOD. There is a naming convention for such functions:
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| 51 | a source/sink BIO typically starts with I<BIO_s_> and
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| 52 | a filter BIO with I<BIO_f_>.
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| 53 |
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| 54 | =head2 TCP Fast Open
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| 55 |
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| 56 | TCP Fast Open (RFC7413), abbreviated "TFO", is supported by the BIO
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| 57 | interface since OpenSSL 3.2. TFO is supported in the following operating systems:
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| 58 |
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| 59 | =over 4
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| 60 |
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| 61 | =item * Linux kernel 3.13 and later, where TFO is enabled by default.
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| 62 |
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| 63 | =item * Linux kernel 4.11 and later, using TCP_FASTOPEN_CONNECT.
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| 64 |
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| 65 | =item * FreeBSD 10.3 to 11.4, supports server TFO only.
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| 66 |
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| 67 | =item * FreeBSD 12.0 and later, supports both client and server TFO.
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| 68 |
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| 69 | =item * macOS 10.14 and later.
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| 70 |
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| 71 | =back
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| 72 |
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| 73 | Each operating system has a slightly different API for TFO. Please
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| 74 | refer to the operating systems' API documentation when using
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| 75 | sockets directly.
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| 76 |
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| 77 | =head1 EXAMPLES
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| 78 |
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| 79 | Create a memory BIO:
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| 80 |
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| 81 | BIO *mem = BIO_new(BIO_s_mem());
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| 82 |
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| 83 | =head1 SEE ALSO
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| 84 |
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| 85 | L<BIO_ctrl(3)>,
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| 86 | L<BIO_f_base64(3)>, L<BIO_f_buffer(3)>,
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| 87 | L<BIO_f_cipher(3)>, L<BIO_f_md(3)>,
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| 88 | L<BIO_f_null(3)>, L<BIO_f_ssl(3)>,
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| 89 | L<BIO_f_readbuffer(3)>,
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| 90 | L<BIO_find_type(3)>,
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| 91 | L<BIO_get_conn_mode(3)>,
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| 92 | L<BIO_new(3)>,
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| 93 | L<BIO_new_bio_pair(3)>,
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| 94 | L<BIO_push(3)>, L<BIO_read_ex(3)>,
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| 95 | L<BIO_s_accept(3)>, L<BIO_s_bio(3)>,
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| 96 | L<BIO_s_connect(3)>, L<BIO_s_fd(3)>,
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| 97 | L<BIO_s_file(3)>, L<BIO_s_mem(3)>,
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| 98 | L<BIO_s_null(3)>, L<BIO_s_socket(3)>,
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| 99 | L<BIO_set_callback(3)>,
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| 100 | L<BIO_set_conn_mode(3)>,
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| 101 | L<BIO_set_tfo(3)>,
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| 102 | L<BIO_set_tfo_accept(3)>,
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| 103 | L<BIO_should_retry(3)>
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| 104 |
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| 105 | =head1 COPYRIGHT
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| 106 |
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| 107 | Copyright 2000-2022 The OpenSSL Project Authors. All Rights Reserved.
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| 108 |
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| 109 | Licensed under the Apache License 2.0 (the "License"). You may not use
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| 110 | this file except in compliance with the License. You can obtain a copy
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| 111 | in the file LICENSE in the source distribution or at
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| 112 | L<https://www.openssl.org/source/license.html>.
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| 113 |
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| 114 | =cut
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