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BIO_F_BUFFER(3) Library Functions Manual BIO_F_BUFFER(3)

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_databuffering BIO

#include <openssl/bio.h>

const BIO_METHOD *

BIO_get_buffer_num_lines(BIO *b);

BIO_set_read_buffer_size(BIO *b, long size);

BIO_set_write_buffer_size(BIO *b, long size);

BIO_set_buffer_size(BIO *b, long size);

BIO_set_buffer_read_data(BIO *b, void *buf, long num);

() 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.

() returns the number of lines currently buffered.

(), (), and () 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.

() 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), () and () 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

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
0 ()
1 ()

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.

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

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.

April 29, 2023 OpenBSD-current