BIO_f_buffer

Section: OpenSSL (3)
Updated: 2010-05-03
Index Return to Main Contents

NAME

BIO_f_buffer - buffering BIO

SYNOPSIS

 #include <openssl/bio.h>

 BIO_METHOD * BIO_f_buffer(void);

 #define BIO_get_buffer_num_lines(b)    BIO_ctrl(b,BIO_C_GET_BUFF_NUM_LINES,0,NULL)
 #define BIO_set_read_buffer_size(b,size) BIO_int_ctrl(b,BIO_C_SET_BUFF_SIZE,size,0)
 #define BIO_set_write_buffer_size(b,size) BIO_int_ctrl(b,BIO_C_SET_BUFF_SIZE,size,1)
 #define BIO_set_buffer_size(b,size)    BIO_ctrl(b,BIO_C_SET_BUFF_SIZE,size,NULL)
 #define BIO_set_buffer_read_data(b,buf,num) BIO_ctrl(b,BIO_C_SET_BUFF_READ_DATA,num,buf)

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

Buffering BIOs implement BIO_gets() by using BIO_read() operations on the next BIO in the chain. By prepending a buffering BIO to a chain it is therefore possible to provide BIO_gets() functionality 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() 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.