source: vbox/trunk/src/libs/openssl-1.1.1l/doc/man3/BIO_f_buffer.pod@ 91772

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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).

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 2000-2020 The OpenSSL Project Authors. All Rights Reserved.

Licensed under the OpenSSL license (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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