Updated: 2022/Sep/29
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BIO_ctrl(3) OpenSSL 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_info_cb,
BIO_get_ktls_send, BIO_get_ktls_recv - BIO control operations
LIBRARY
libcrypto, -lcrypto
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);
void *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);
int BIO_get_ktls_send(BIO *b);
int BIO_get_ktls_recv(BIO *b);
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().
BIO_get_ktls_send() returns 1 if the BIO is using the Kernel TLS data-
path for sending. Otherwise, it returns zero. BIO_get_ktls_recv()
returns 1 if the BIO is using the Kernel TLS data-path for receiving.
Otherwise, it returns zero.
RETURN VALUES
BIO_reset() normally returns 1 for success and <=0 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 for failure.
BIO_eof() returns 1 if EOF has been reached, 0 if not, or negative
values for failure.
BIO_set_close() returns 1 on success or <=0 for failure.
BIO_get_close() returns the close flag value: BIO_CLOSE or BIO_NOCLOSE.
It also returns other negative values if an error occurs.
BIO_pending(), BIO_ctrl_pending(), BIO_wpending() and
BIO_ctrl_wpending() return the amount of pending data. BIO_pending()
and BIO_wpending() return negative value or 0 on error.
BIO_ctrl_pending() and BIO_ctrl_wpending() return 0 on error.
BIO_get_ktls_send() returns 1 if the BIO is using the Kernel TLS data-
path for sending. Otherwise, it returns zero. BIO_get_ktls_recv()
returns 1 if the BIO is using the Kernel TLS data-path for receiving.
Otherwise, it returns zero.
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.
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.
In older versions of OpenSSL the BIO_ctrl_pending() and
BIO_ctrl_wpending() could return values greater than INT_MAX on error.
HISTORY
The BIO_get_ktls_send() and BIO_get_ktls_recv() macros were added in
OpenSSL 3.0. They were modified to never return -1 in OpenSSL 3.0.4.
COPYRIGHT
Copyright 2000-2022 The OpenSSL Project Authors. All Rights Reserved.
Licensed under the Apache License 2.0 (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
<https://www.openssl.org/source/license.html>.
3.0.12 2023-05-07 BIO_ctrl(3)