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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 void
bio_info_cb(BIO *b, int oper, const char *ptr, int arg1, long arg2, long arg3);

BIO_ctrl(), BIO_callback_ctrl(), BIO_ptr_ctrl(), and BIO_int_ctrl() 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.

BIO_reset() 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.

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

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

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

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

BIO_set_close() 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.

BIO_get_close() returns the BIO's close flag.

BIO_pending(), BIO_ctrl_pending(), BIO_wpending(), and BIO_ctrl_wpending() 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, BIO_flush() 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 BIO_pending() and BIO_wpending() 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 BIO_ctrl() 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 an 0 if they do not recognize the BIO_ctrl() 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.
March 27, 2018 OpenBSD-current