mirror of https://github.com/openssl/openssl.git
115 lines
3.4 KiB
Plaintext
115 lines
3.4 KiB
Plaintext
=pod
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=head1 NAME
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bio - Basic I/O abstraction
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=head1 SYNOPSIS
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=for openssl generic
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#include <openssl/bio.h>
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=head1 DESCRIPTION
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A BIO is an I/O abstraction, it hides many of the underlying I/O
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details from an application. If an application uses a BIO for its
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I/O it can transparently handle SSL connections, unencrypted network
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connections and file I/O.
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There are two types of BIO, a source/sink BIO and a filter BIO.
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As its name implies a source/sink BIO is a source and/or sink of data,
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examples include a socket BIO and a file BIO.
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A filter BIO takes data from one BIO and passes it through to
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another, or the application. The data may be left unmodified (for
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example a message digest BIO) or translated (for example an
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encryption BIO). The effect of a filter BIO may change according
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to the I/O operation it is performing: for example an encryption
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BIO will encrypt data if it is being written to and decrypt data
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if it is being read from.
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BIOs can be joined together to form a chain (a single BIO is a chain
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with one component). A chain normally consists of one source/sink
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BIO and one or more filter BIOs. Data read from or written to the
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first BIO then traverses the chain to the end (normally a source/sink
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BIO).
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Some BIOs (such as memory BIOs) can be used immediately after calling
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BIO_new(). Others (such as file BIOs) need some additional initialization,
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and frequently a utility function exists to create and initialize such BIOs.
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If BIO_free() is called on a BIO chain it will only free one BIO resulting
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in a memory leak.
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Calling BIO_free_all() on a single BIO has the same effect as calling
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BIO_free() on it other than the discarded return value.
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Normally the I<type> argument is supplied by a function which returns a
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pointer to a BIO_METHOD. There is a naming convention for such functions:
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a source/sink BIO typically starts with I<BIO_s_> and
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a filter BIO with I<BIO_f_>.
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=head2 TCP Fast Open
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TCP Fast Open (RFC7413), abbreviated "TFO", is supported by the BIO
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interface since OpenSSL 3.2. TFO is supported in the following operating systems:
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=over 4
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=item * Linux kernel 3.13 and later, where TFO is enabled by default.
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=item * Linux kernel 4.11 and later, using TCP_FASTOPEN_CONNECT.
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=item * FreeBSD 10.3 to 11.4, supports server TFO only.
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=item * FreeBSD 12.0 and later, supports both client and server TFO.
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=item * macOS 10.14 and later.
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=back
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Each operating system has a slightly different API for TFO. Please
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refer to the operating systems' API documentation when using
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sockets directly.
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=head1 EXAMPLES
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Create a memory BIO:
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BIO *mem = BIO_new(BIO_s_mem());
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=head1 SEE ALSO
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L<BIO_ctrl(3)>,
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L<BIO_f_base64(3)>, L<BIO_f_buffer(3)>,
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L<BIO_f_cipher(3)>, L<BIO_f_md(3)>,
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L<BIO_f_null(3)>, L<BIO_f_ssl(3)>,
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L<BIO_f_readbuffer(3)>,
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L<BIO_find_type(3)>,
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L<BIO_get_conn_mode(3)>,
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L<BIO_new(3)>,
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L<BIO_new_bio_pair(3)>,
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L<BIO_push(3)>, L<BIO_read_ex(3)>,
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L<BIO_s_accept(3)>, L<BIO_s_bio(3)>,
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L<BIO_s_connect(3)>, L<BIO_s_fd(3)>,
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L<BIO_s_file(3)>, L<BIO_s_mem(3)>,
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L<BIO_s_null(3)>, L<BIO_s_socket(3)>,
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L<BIO_set_callback(3)>,
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L<BIO_set_conn_mode(3)>,
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L<BIO_set_tfo(3)>,
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L<BIO_set_tfo_accept(3)>,
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L<BIO_should_retry(3)>
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=head1 COPYRIGHT
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Copyright 2000-2022 The OpenSSL Project Authors. All Rights Reserved.
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Licensed under the Apache License 2.0 (the "License"). You may not use
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this file except in compliance with the License. You can obtain a copy
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in the file LICENSE in the source distribution or at
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L<https://www.openssl.org/source/license.html>.
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=cut
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