- NAME
- SYNOPSIS
- DESCRIPTION
- NOTES
- RETURN VALUES
- SEE ALSO
- COPYRIGHT

# 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

# 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);

# 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 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 num bytes of buf. If num is larger than the current buffer size the buffer is expanded.

# 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.

# 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.

# SEE ALSO

bio(7), BIO_reset(3), BIO_flush(3), BIO_pop(3), BIO_ctrl(3).

# 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 https://www.openssl.org/source/license.html.