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NAME    [Toc]    [Back]

       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 control operations

LIBRARY    [Toc]    [Back]

       libcrypto, -lcrypto

SYNOPSIS    [Toc]    [Back]

        #include <openssl/bio.h>

        long BIO_ctrl(BIO *bp,int cmd,long larg,void *parg);
        long BIO_callback_ctrl(BIO *b, int cmd, void (*fp)(struct bio_st *, int, const char *, int, long, long));
        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);

        typedef void bio_info_cb(BIO *b, int oper, const char *ptr, int arg1, long arg2, long arg3);

DESCRIPTION    [Toc]    [Back]

       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

       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

       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    [Toc]    [Back]

       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_pending(), BIO_ctrl_pending(), BIO_wpending() and
       BIO_ctrl_wpending() return the amount of pending data.

NOTES    [Toc]    [Back]

       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().  The BIO_should_retry() call
       should be used and appropriate action taken is the call

       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    [Toc]    [Back]

       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.

SEE ALSO    [Toc]    [Back]


2001-04-12                    0.9.6g                  BIO_ctrl(3)
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