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.
Restrictions
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.
