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 2000-2016 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 <https://www.openssl.org/source/license.html>.