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=pod
=head1 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_info_cb
- BIO control operations
=head1 SYNOPSIS
#include <openssl/bio.h>
typedef int BIO_info_cb(BIO *b, int state, int res);
long BIO_ctrl(BIO *bp, int cmd, long larg, void *parg);
long BIO_callback_ctrl(BIO *b, int cmd, BIO_info_cb *cb);
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);
=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 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 B<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<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 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().
=head1 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.
=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_ex().
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.
=head1 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.
=head1 COPYRIGHT
Copyright 2000-2016 The OpenSSL Project Authors. All Rights Reserved.
Licensed under the OpenSSL license (the "License"). You may not use
this file except in compliance with the License. You can obtain a copy
in the file LICENSE in the source distribution or at
L<https://www.openssl.org/source/license.html>.
=cut
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