doc/man7/bio.pod

   1 =pod
   2
   3 =head1 NAME
   4
   5 bio - Basic I/O abstraction
   6
   7 =head1 SYNOPSIS
   8
   9 =for openssl generic
  10
  11  #include <openssl/bio.h>
  12
  13 =head1 DESCRIPTION
  14
  15 A BIO is an I/O abstraction, it hides many of the underlying I/O
  16 details from an application. If an application uses a BIO for its
  17 I/O it can transparently handle SSL connections, unencrypted network
  18 connections and file I/O.
  19
  20 There are two types of BIO, a source/sink BIO and a filter BIO.
  21
  22 As its name implies a source/sink BIO is a source and/or sink of data,
  23 examples include a socket BIO and a file BIO.
  24
  25 A filter BIO takes data from one BIO and passes it through to
  26 another, or the application. The data may be left unmodified (for
  27 example a message digest BIO) or translated (for example an
  28 encryption BIO). The effect of a filter BIO may change according
  29 to the I/O operation it is performing: for example an encryption
  30 BIO will encrypt data if it is being written to and decrypt data
  31 if it is being read from.
  32
  33 BIOs can be joined together to form a chain (a single BIO is a chain
  34 with one component). A chain normally consists of one source/sink
  35 BIO and one or more filter BIOs. Data read from or written to the
  36 first BIO then traverses the chain to the end (normally a source/sink
  37 BIO).
  38
  39 Some BIOs (such as memory BIOs) can be used immediately after calling
  40 BIO_new(). Others (such as file BIOs) need some additional initialization,
  41 and frequently a utility function exists to create and initialize such BIOs.
  42
  43 If BIO_free() is called on a BIO chain it will only free one BIO resulting
  44 in a memory leak.
  45
  46 Calling BIO_free_all() on a single BIO has the same effect as calling
  47 BIO_free() on it other than the discarded return value.
  48
  49 Normally the I<type> argument is supplied by a function which returns a
  50 pointer to a BIO_METHOD. There is a naming convention for such functions:
  51 a source/sink BIO typically starts with I<BIO_s_> and
  52 a filter BIO with I<BIO_f_>.
  53
  54 =head2 TCP Fast Open
  55
  56 TCP Fast Open (RFC7413), abbreviated "TFO", is supported by the BIO
  57 interface 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
  73 Each operating system has a slightly different API for TFO. Please
  74 refer to the operating systems' API documentation when using
  75 sockets directly.
  76
  77 =head1 EXAMPLES
  78
  79 Create a memory BIO:
  80
  81  BIO *mem = BIO_new(BIO_s_mem());
  82
  83 =head1 SEE ALSO
  84
  85 L<BIO_ctrl(3)>,
  86 L<BIO_f_base64(3)>, L<BIO_f_buffer(3)>,
  87 L<BIO_f_cipher(3)>, L<BIO_f_md(3)>,
  88 L<BIO_f_null(3)>, L<BIO_f_ssl(3)>,
  89 L<BIO_f_readbuffer(3)>,
  90 L<BIO_find_type(3)>,
  91 L<BIO_get_conn_mode(3)>,
  92 L<BIO_new(3)>,
  93 L<BIO_new_bio_pair(3)>,
  94 L<BIO_push(3)>, L<BIO_read_ex(3)>,
  95 L<BIO_s_accept(3)>, L<BIO_s_bio(3)>,
  96 L<BIO_s_connect(3)>, L<BIO_s_fd(3)>,
  97 L<BIO_s_file(3)>, L<BIO_s_mem(3)>,
  98 L<BIO_s_null(3)>, L<BIO_s_socket(3)>,
  99 L<BIO_set_callback(3)>,
 100 L<BIO_set_conn_mode(3)>,
 101 L<BIO_set_tfo(3)>,
 102 L<BIO_set_tfo_accept(3)>,
 103 L<BIO_should_retry(3)>
 104
 105 =head1 COPYRIGHT
 106
 107 Copyright 2000-2021 The OpenSSL Project Authors. All Rights Reserved.
 108
 109 Licensed under the Apache License 2.0 (the "License").  You may not use
 110 this file except in compliance with the License.  You can obtain a copy
 111 in the file LICENSE in the source distribution or at
 112 L<https://www.openssl.org/source/license.html>.
 113
 114 =cut