=pod

=head1 NAME

	BIO_ctrl, BIO_callback_ctrl, BIO_ptr_ctrl, BIO_int_ctrl - BIO control operations

=head1 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_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);

=head1 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 reset a BIO to some initial state, in the case
of file related BIOs for example it rewinds the file pointer.

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<b> close flag to B<flag>. B<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 characterers 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().

=head1 RETURN VALUES

BIO_reset() returns 1 fo success and 0 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.

=head1 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.

=head1 SEE ALSO

TBA