=pod
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=head1 NAME
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BIO_ctrl, BIO_callback_ctrl, BIO_ptr_ctrl, BIO_int_ctrl, BIO_reset,
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BIO_seek, BIO_tell, BIO_flush, BIO_eof, BIO_set_close, BIO_get_close,
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BIO_pending, BIO_wpending, BIO_ctrl_pending, BIO_ctrl_wpending,
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BIO_get_info_callback, BIO_set_info_callback - BIO control operations
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=head1 SYNOPSIS
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#include <openssl/bio.h>
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long BIO_ctrl(BIO *bp,int cmd,long larg,void *parg);
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long BIO_callback_ctrl(BIO *b, int cmd, void (*fp)(struct bio_st *, int, const char *, int, long, long));
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char * BIO_ptr_ctrl(BIO *bp,int cmd,long larg);
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long BIO_int_ctrl(BIO *bp,int cmd,long larg,int iarg);
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int BIO_reset(BIO *b);
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int BIO_seek(BIO *b, int ofs);
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int BIO_tell(BIO *b);
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int BIO_flush(BIO *b);
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int BIO_eof(BIO *b);
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int BIO_set_close(BIO *b,long flag);
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int BIO_get_close(BIO *b);
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int BIO_pending(BIO *b);
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int BIO_wpending(BIO *b);
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size_t BIO_ctrl_pending(BIO *b);
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size_t BIO_ctrl_wpending(BIO *b);
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int BIO_get_info_callback(BIO *b,bio_info_cb **cbp);
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int BIO_set_info_callback(BIO *b,bio_info_cb *cb);
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typedef void bio_info_cb(BIO *b, int oper, const char *ptr, int arg1, long arg2, long arg3);
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=head1 DESCRIPTION
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BIO_ctrl(), BIO_callback_ctrl(), BIO_ptr_ctrl() and BIO_int_ctrl()
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are BIO "control" operations taking arguments of various types.
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These functions are not normally called directly, various macros
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are used instead. The standard macros are described below, macros
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specific to a particular type of BIO are described in the specific
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BIOs manual page as well as any special features of the standard
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calls.
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BIO_reset() typically resets a BIO to some initial state, in the case
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of file related BIOs for example it rewinds the file pointer to the
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start of the file.
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BIO_seek() resets a file related BIO's (that is file descriptor and
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FILE BIOs) file position pointer to B<ofs> bytes from start of file.
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BIO_tell() returns the current file position of a file related BIO.
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BIO_flush() normally writes out any internally buffered data, in some
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cases it is used to signal EOF and that no more data will be written.
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BIO_eof() returns 1 if the BIO has read EOF, the precise meaning of
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"EOF" varies according to the BIO type.
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BIO_set_close() sets the BIO B<b> close flag to B<flag>. B<flag> can
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take the value BIO_CLOSE or BIO_NOCLOSE. Typically BIO_CLOSE is used
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in a source/sink BIO to indicate that the underlying I/O stream should
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be closed when the BIO is freed.
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BIO_get_close() returns the BIOs close flag.
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BIO_pending(), BIO_ctrl_pending(), BIO_wpending() and BIO_ctrl_wpending()
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return the number of pending characters in the BIOs read and write buffers.
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Not all BIOs support these calls. BIO_ctrl_pending() and BIO_ctrl_wpending()
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return a size_t type and are functions, BIO_pending() and BIO_wpending() are
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macros which call BIO_ctrl().
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=head1 RETURN VALUES
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BIO_reset() normally returns 1 for success and 0 or -1 for failure. File
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BIOs are an exception, they return 0 for success and -1 for failure.
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BIO_seek() and BIO_tell() both return the current file position on success
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and -1 for failure, except file BIOs which for BIO_seek() always return 0
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for success and -1 for failure.
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BIO_flush() returns 1 for success and 0 or -1 for failure.
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BIO_eof() returns 1 if EOF has been reached 0 otherwise.
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BIO_set_close() always returns 1.
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BIO_get_close() returns the close flag value: BIO_CLOSE or BIO_NOCLOSE.
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BIO_pending(), BIO_ctrl_pending(), BIO_wpending() and BIO_ctrl_wpending()
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return the amount of pending data.
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=head1 NOTES
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BIO_flush(), because it can write data may return 0 or -1 indicating
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that the call should be retried later in a similar manner to BIO_write().
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The BIO_should_retry() call should be used and appropriate action taken
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is the call fails.
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The return values of BIO_pending() and BIO_wpending() may not reliably
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determine the amount of pending data in all cases. For example in the
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case of a file BIO some data may be available in the FILE structures
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internal buffers but it is not possible to determine this in a
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portably way. For other types of BIO they may not be supported.
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Filter BIOs if they do not internally handle a particular BIO_ctrl()
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operation usually pass the operation to the next BIO in the chain.
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This often means there is no need to locate the required BIO for
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a particular operation, it can be called on a chain and it will
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be automatically passed to the relevant BIO. However this can cause
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unexpected results: for example no current filter BIOs implement
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BIO_seek(), but this may still succeed if the chain ends in a FILE
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or file descriptor BIO.
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Source/sink BIOs return an 0 if they do not recognize the BIO_ctrl()
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operation.
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=head1 BUGS
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Some of the return values are ambiguous and care should be taken. In
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particular a return value of 0 can be returned if an operation is not
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supported, if an error occurred, if EOF has not been reached and in
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the case of BIO_seek() on a file BIO for a successful operation.
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=head1 SEE ALSO
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TBA
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