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

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>.