BIO_CTRL(3) BSD Library Functions Manual BIO_CTRL(3)NAME
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 control operations
SYNOPSIS
#include <openssl/bio.h>
long
BIO_ctrl(BIO *bp, int cmd, long larg, void *parg);
long
BIO_callback_ctrl(BIO *b, int cmd,
void (*fp)(struct bio_st *, int, const char *, int, long, long));
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);
DESCRIPTIONBIO_ctrl(), BIO_callback_ctrl(), BIO_ptr_ctrl(), and BIO_int_ctrl() are
BIO "control" operations taking arguments of various types. These func‐
tions 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().
RETURN VALUESBIO_reset() normally returns 1 for success and 0 or -1 for failure. File
BIOs are an exception, they return 0 for success and -1 for failure.
BIO_seek() and BIO_tell() both return the current file position on suc‐
cess 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 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.
NOTES
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(). The
BIO_should_retry() call should be used and appropriate action taken is
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 portably
way. For other types of BIO they may not be supported.
If they do not internally handle a particular BIO_ctrl() operation, fil‐
ter 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.
BUGS
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.
BSD July 17, 2014 BSD
