BIO_F_BUFFER(3)

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

SYNOPSIS
libcrypto
#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(3) and BIO_puts(3) are supported.

Calling BIO_reset(3) 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.

Buffering BIOs implement BIO_gets(3) by using BIO_read(3) operations on the next BIO in the chain. By prepending a buffering BIO to a chain it is therefore possible to provide the functionality of BIO_gets(3) if the following BIOs do not support it (for example SSL BIOs).

Data is only written to the next BIO in the chain when the write buffer fills or when BIO_flush(3) is called. It is therefore important to call BIO_flush(3) whenever any pending data should be written such as when removing a buffering BIO using BIO_pop(3). BIO_flush(3) may need to be retried if the ultimate source/sink BIO is non-blocking.

When a chain containing a buffering BIO is copied with BIO_dup_chain(3), BIO_set_read_buffer_size() and BIO_set_write_buffer_size() are called internally to automatically copy both buffer sizes from the original BIO object to the new one.

BIO_ctrl(3) cmd arguments correspond to macros as follows:
cmd constant | corresponding macro
BIO_C_GET_BUFF_NUM_LINES | BIO_get_buffer_num_lines()
BIO_C_SET_BUFF_READ_DATA | BIO_set_buffer_read_data()
BIO_C_SET_BUFF_SIZE | BIO_set_buffer_size()
BIO_CTRL_FLUSH | BIO_flush(3)
BIO_CTRL_PENDING | BIO_pending(3)
BIO_CTRL_RESET | BIO_reset(3)
BIO_CTRL_WPENDING | BIO_wpending(3)

The cmd constant BIO_C_SET_BUFF_SIZE is special. It is also used for BIO_int_ctrl(3) with the following iarg arguments:
cmd constant | iarg | corresponding macro
BIO_C_SET_BUFF_SIZE | 0 | BIO_set_read_buffer_size()
 | 1 | BIO_set_write_buffer_size()

RETURN VALUES
BIO_f_buffer() returns the buffering BIO method.

When called on a buffering BIO object, BIO_method_type(3) returns the constant BIO_TYPE_BUFFER and BIO_method_name(3) returns a pointer to the static string "buffer".

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_ctrl(3), BIO_flush(3), BIO_new(3), BIO_pop(3), BIO_reset(3)

HISTORY
BIO_f_buffer() first appeared in SSLeay 0.6.0. BIO_get_buffer_num_lines() and BIO_set_buffer_size() first appeared in SSLeay 0.6.5. BIO_set_read_buffer_size() and BIO_set_write_buffer_size() first appeared in SSLeay 0.8.0. BIO_set_buffer_read_data() first appeared in SSLeay 0.9.0. All these functions have been available since OpenBSD 2.4.