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

#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.