xref: /freebsd/crypto/openssl/doc/man3/BIO_f_buffer.pod (revision b077aed33b7b6aefca7b17ddb250cf521f938613)

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=head1 NAME

BIO_get_buffer_num_lines,
BIO_set_read_buffer_size,
BIO_set_write_buffer_size,
BIO_set_buffer_size,
BIO_set_buffer_read_data,
BIO_f_buffer
- buffering BIO

=head1 SYNOPSIS

 #include <openssl/bio.h>

 const BIO_METHOD *BIO_f_buffer(void);

 long BIO_get_buffer_num_lines(BIO *b);
 long BIO_set_read_buffer_size(BIO *b, long size);
 long BIO_set_write_buffer_size(BIO *b, long size);
 long BIO_set_buffer_size(BIO *b, long size);
 long BIO_set_buffer_read_data(BIO *b, void *buf, long num);

=head1 DESCRIPTION

BIO_f_buffer() returns the buffering BIO method.

Data written to a buffering BIO is buffered and periodically written
to the next BIO in the chain. Data read from a buffering BIO comes from
an internal buffer which is filled from the next BIO in the chain.
Both BIO_gets() and BIO_puts() are supported.

Calling BIO_reset() on a buffering BIO clears any buffered data.

BIO_get_buffer_num_lines() returns the number of lines currently buffered.

BIO_set_read_buffer_size(), BIO_set_write_buffer_size() and BIO_set_buffer_size()
set the read, write or both read and write buffer sizes to B<size>. The initial
buffer size is DEFAULT_BUFFER_SIZE, currently 4096. Any attempt to reduce the
buffer size below DEFAULT_BUFFER_SIZE is ignored. Any buffered data is cleared
when the buffer is resized.

BIO_set_buffer_read_data() clears the read buffer and fills it with B<num>
bytes of B<buf>. If B<num> is larger than the current buffer size the buffer
is expanded.

=head1 NOTES

These functions, other than BIO_f_buffer(), are implemented as macros.

Buffering BIOs implement BIO_read_ex() and BIO_gets() by using
BIO_read_ex() operations on the next BIO in the chain and storing the
result in an internal buffer, from which bytes are given back to the
caller as appropriate for the call; a BIO_gets() is guaranteed to give
the caller a whole line, and BIO_read_ex() is guaranteed to give the
caller the number of bytes it asks for, unless there's an error or end
of communication is reached in the next BIO.  By prepending a
buffering BIO to a chain it is therefore possible to provide
BIO_gets() or exact size BIO_read_ex() functionality if the following
BIOs do not support it.

Do not add more than one BIO_f_buffer() to a BIO chain.  The result of
doing so will force a full read of the size of the internal buffer of
the top BIO_f_buffer(), which is 4 KiB at a minimum.

Data is only written to the next BIO in the chain when the write buffer fills
or when BIO_flush() is called. It is therefore important to call BIO_flush()
whenever any pending data should be written such as when removing a buffering
BIO using BIO_pop(). BIO_flush() may need to be retried if the ultimate
source/sink BIO is non blocking.

=head1 RETURN VALUES

BIO_f_buffer() returns the buffering BIO method.

BIO_get_buffer_num_lines() returns the number of lines buffered (may be 0) or
a negative value in case of errors.

BIO_set_read_buffer_size(), BIO_set_write_buffer_size() and BIO_set_buffer_size()
return 1 if the buffer was successfully resized or <=0 for failure.

BIO_set_buffer_read_data() returns 1 if the data was set correctly or <=0 if
there was an error.

=head1 SEE ALSO

L<bio(7)>,
L<BIO_reset(3)>,
L<BIO_flush(3)>,
L<BIO_pop(3)>,
L<BIO_ctrl(3)>.

=head1 COPYRIGHT

Copyright 2000-2021 The OpenSSL Project Authors. All Rights Reserved.

Licensed under the Apache License 2.0 (the "License").  You may not use
this file except in compliance with the License.  You can obtain a copy
in the file LICENSE in the source distribution or at
L<https://www.openssl.org/source/license.html>.

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