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.\" ========================================================================
.\"
.IX Title "BIO 7"
.TH BIO 7 "2023-09-11" "1.1.1w" "OpenSSL"
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.SH "NAME"
bio \- Basic I/O abstraction
.SH "SYNOPSIS"
.IX Header "SYNOPSIS"
.Vb 1
\& #include <openssl/bio.h>
.Ve
.SH "DESCRIPTION"
.IX Header "DESCRIPTION"
A \s-1BIO\s0 is an I/O abstraction, it hides many of the underlying I/O
details from an application. If an application uses a \s-1BIO\s0 for its
I/O it can transparently handle \s-1SSL\s0 connections, unencrypted network
connections and file I/O.
.PP
There are two type of \s-1BIO,\s0 a source/sink \s-1BIO\s0 and a filter \s-1BIO.\s0
.PP
As its name implies a source/sink \s-1BIO\s0 is a source and/or sink of data,
examples include a socket \s-1BIO\s0 and a file \s-1BIO.\s0
.PP
A filter \s-1BIO\s0 takes data from one \s-1BIO\s0 and passes it through to
another, or the application. The data may be left unmodified (for
example a message digest \s-1BIO\s0) or translated (for example an
encryption \s-1BIO\s0). The effect of a filter \s-1BIO\s0 may change according
to the I/O operation it is performing: for example an encryption
\&\s-1BIO\s0 will encrypt data if it is being written to and decrypt data
if it is being read from.
.PP
BIOs can be joined together to form a chain (a single \s-1BIO\s0 is a chain
with one component). A chain normally consist of one source/sink
\&\s-1BIO\s0 and one or more filter BIOs. Data read from or written to the
first \s-1BIO\s0 then traverses the chain to the end (normally a source/sink
\&\s-1BIO\s0).
.PP
Some BIOs (such as memory BIOs) can be used immediately after calling
\&\fBBIO_new()\fR. Others (such as file BIOs) need some additional initialization,
and frequently a utility function exists to create and initialize such BIOs.
.PP
If \fBBIO_free()\fR is called on a \s-1BIO\s0 chain it will only free one \s-1BIO\s0 resulting
in a memory leak.
.PP
Calling \fBBIO_free_all()\fR on a single \s-1BIO\s0 has the same effect as calling
\&\fBBIO_free()\fR on it other than the discarded return value.
.PP
Normally the \fBtype\fR argument is supplied by a function which returns a
pointer to a \s-1BIO_METHOD.\s0 There is a naming convention for such functions:
a source/sink \s-1BIO\s0 is normally called BIO_s_*() and a filter \s-1BIO\s0
BIO_f_*();
.SH "EXAMPLES"
.IX Header "EXAMPLES"
Create a memory \s-1BIO:\s0
.PP
.Vb 1
\& BIO *mem = BIO_new(BIO_s_mem());
.Ve
.SH "SEE ALSO"
.IX Header "SEE ALSO"
\&\fBBIO_ctrl\fR\|(3),
\&\fBBIO_f_base64\fR\|(3), \fBBIO_f_buffer\fR\|(3),
\&\fBBIO_f_cipher\fR\|(3), \fBBIO_f_md\fR\|(3),
\&\fBBIO_f_null\fR\|(3), \fBBIO_f_ssl\fR\|(3),
\&\fBBIO_find_type\fR\|(3), \fBBIO_new\fR\|(3),
\&\fBBIO_new_bio_pair\fR\|(3),
\&\fBBIO_push\fR\|(3), \fBBIO_read_ex\fR\|(3),
\&\fBBIO_s_accept\fR\|(3), \fBBIO_s_bio\fR\|(3),
\&\fBBIO_s_connect\fR\|(3), \fBBIO_s_fd\fR\|(3),
\&\fBBIO_s_file\fR\|(3), \fBBIO_s_mem\fR\|(3),
\&\fBBIO_s_null\fR\|(3), \fBBIO_s_socket\fR\|(3),
\&\fBBIO_set_callback\fR\|(3),
\&\fBBIO_should_retry\fR\|(3)
.SH "COPYRIGHT"
.IX Header "COPYRIGHT"
Copyright 2000\-2019 The OpenSSL Project Authors. All Rights Reserved.
.PP
Licensed under the OpenSSL license (the \*(L"License\*(R"). You may not use
this file except in compliance with the License. You can obtain a copy
in the file \s-1LICENSE\s0 in the source distribution or at
<https://www.openssl.org/source/license.html>.
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