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);
DESCRIPTION
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 BIOs 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 BIOs close flag.
BIO_pending(), BIO_ctrl_pending(), BIO_wpending() and
BIO_ctrl_wpending() return the number of pending characters in the BIOs
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 VALUES
BIO_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
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 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
BIO_flush(), 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(). 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 structures
internal buffers but it is not possible to determine this in a portably
way. For other types of BIO they may not be supported.
Filter BIOs if they do not internally handle a particular BIO_ctrl()
operation 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.
SEE ALSO
- TBA