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>.