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BIO_CTRL(3) Library Functions Manual BIO_CTRL(3)

BIO_ctrl, BIO_callback_ctrl, BIO_ptr_ctrl, BIO_int_ctrl, BIO_reset, BIO_seek, BIO_tell, BIO_flush, BIO_eof, BIO_set_close, BIO_get_close, BIO_pending, BIO_wpending, BIO_ctrl_pending, BIO_ctrl_wpending, BIO_get_info_callback, BIO_set_info_callback, BIO_info_cb — BIO control operations

#include <openssl/bio.h>

long
BIO_ctrl(BIO *bp, int cmd, long larg, void *parg);

long
BIO_callback_ctrl(BIO *b, int cmd, BIO_info_cb cb);

char *
BIO_ptr_ctrl(BIO *bp, int cmd, long larg);

long
BIO_int_ctrl(BIO *bp, int cmd, long larg, int iarg);

int
BIO_reset(BIO *b);

int
BIO_seek(BIO *b, int ofs);

int
BIO_tell(BIO *b);

int
BIO_flush(BIO *b);

int
BIO_eof(BIO *b);

int
BIO_set_close(BIO *b, long flag);

int
BIO_get_close(BIO *b);

int
BIO_pending(BIO *b);

int
BIO_wpending(BIO *b);

size_t
BIO_ctrl_pending(BIO *b);

size_t
BIO_ctrl_wpending(BIO *b);

int
BIO_get_info_callback(BIO *b, BIO_info_cb **cbp);

int
BIO_set_info_callback(BIO *b, BIO_info_cb *cb);

typedef int
BIO_info_cb(BIO *b, int state, int res);

(), (), (), and () are BIO "control" operations taking arguments of various types. These functions are not normally called directly - various macros are used instead. The standard macros are described below. Macros specific to a particular type of BIO are described in the specific BIO's manual page as well as any special features of the standard calls.

() typically resets a BIO to some initial state. In the case of file related BIOs, for example, it rewinds the file pointer to the start of the file.

() resets a file related BIO's (that is file descriptor and FILE BIOs) file position pointer to ofs bytes from start of file.

() returns the current file position of a file related BIO.

() normally writes out any internally buffered data. In some cases it is used to signal EOF and that no more data will be written.

() returns 1 if the BIO has read EOF. The precise meaning of "EOF" varies according to the BIO type.

() sets the BIO b close flag to flag. flag can take the value BIO_CLOSE or BIO_NOCLOSE. Typically BIO_CLOSE is used in a source/sink BIO to indicate that the underlying I/O stream should be closed when the BIO is freed.

() returns the BIO's close flag.

(), (), BIO_wpending(), and () return the number of pending characters in the BIO's read and write buffers. Not all BIOs support these calls. BIO_ctrl_pending() and BIO_ctrl_wpending() return a size_t type and are functions. BIO_pending() and BIO_wpending() are macros which call BIO_ctrl().

BIO_reset() normally returns 1 for success and 0 or -1 for failure. File BIOs are an exception, returning 0 for success and -1 for failure.

BIO_seek() and BIO_tell() both return the current file position on success and -1 for failure, except file BIOs which for BIO_seek() always return 0 for success and -1 for failure.

BIO_flush() returns 1 for success and 0 or -1 for failure.

BIO_eof() returns 1 if EOF has been reached or 0 otherwise.

BIO_set_close() always returns 1.

BIO_get_close() returns the close flag value BIO_CLOSE or BIO_NOCLOSE.

BIO_pending(), BIO_ctrl_pending(), BIO_wpending(), and BIO_ctrl_wpending() return the amount of pending data.

Because it can write data, () may return 0 or -1 indicating that the call should be retried later in a similar manner to BIO_write(3). The BIO_should_retry(3) call should be used and appropriate action taken if the call fails.

The return values of () and () may not reliably determine the amount of pending data in all cases. For example in the case of a file BIO some data may be available in the FILE structure's internal buffers but it is not possible to determine this in a portable way. For other types of BIO they may not be supported.

If they do not internally handle a particular () operation, filter BIOs usually pass the operation to the next BIO in the chain. This often means there is no need to locate the required BIO for a particular operation: it can be called on a chain and it will be automatically passed to the relevant BIO. However this can cause unexpected results. For example no current filter BIOs implement BIO_seek(), but this may still succeed if the chain ends in a FILE or file descriptor BIO.

Source/sink BIOs return a 0 if they do not recognize the () operation.

BIO_meth_new(3), BIO_new(3)

BIO_ctrl(), BIO_reset(), BIO_flush(), BIO_eof(), BIO_set_close(), BIO_get_close(), and BIO_pending() first appeared in SSLeay 0.6.0. BIO_wpending() first appeared in SSLeay 0.8.1. BIO_ptr_ctrl(), BIO_int_ctrl(), BIO_get_info_callback() and BIO_set_info_callback() first appeared in SSLeay 0.9.0. All these functions have been available since OpenBSD 2.4.

BIO_seek() and BIO_tell() first appeared in SSLeay 0.9.1. BIO_ctrl_pending() and BIO_ctrl_wpending() first appeared in OpenSSL 0.9.4. These functions have been available since OpenBSD 2.6.

BIO_callback_ctrl() first appeared in OpenSSL 0.9.5 and has been available since OpenBSD 2.7.

Some of the return values are ambiguous and care should be taken. In particular a return value of 0 can be returned if an operation is not supported, if an error occurred, if EOF has not been reached and in the case of BIO_seek() on a file BIO for a successful operation.

August 18, 2022 OpenBSD-7.2