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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 control
       operations
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);
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_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.
COPYRIGHT
       Copyright 2000-2020 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
       <https://www.openssl.org/source/license.html>;.
1.1.1k                            2021-03-25                       BIO_CTRL(3)