BIO_ctrl(3) OpenSSL 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
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);
BIO_ctrl(), BIO_callback_ctrl(), BIO_ptr_ctrl() and BIO_int_ctrl() are BIO "control" oper-
ations 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 posi-
tion 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 under-
lying 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 num-
ber 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().
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
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.
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 suc-
ceed 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.
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 opera-
0.9.7a 2000-09-18 BIO_ctrl(3)