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BIO_callback_ctrl.3
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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 \s-1BIO\s0 are described in the specific BIOs manual page as well as any special features of the standard calls. .PP \&\fIBIO_reset()\fR typically resets a \s-1BIO\s0 to some initial state, in the case of file related BIOs for example it rewinds the file pointer to the start of the file. .PP \&\fIBIO_seek()\fR resets a file related \s-1BIO\s0's (that is file descriptor and \&\s-1FILE\s0 BIOs) file position pointer to \fBofs\fR bytes from start of file. .PP \&\fIBIO_tell()\fR returns the current file position of a file related \s-1BIO\s0. .PP \&\fIBIO_flush()\fR normally writes out any internally buffered data, in some cases it is used to signal \s-1EOF\s0 and that no more data will be written. .PP \&\fIBIO_eof()\fR returns 1 if the \s-1BIO\s0 has read \s-1EOF\s0, the precise meaning of \&\*(L"\s-1EOF\s0\*(R" varies according to the \s-1BIO\s0 type. .PP \&\fIBIO_set_close()\fR sets the \s-1BIO\s0 \fBb\fR close flag to \fBflag\fR. \fBflag\fR can take the value \s-1BIO_CLOSE\s0 or \s-1BIO_NOCLOSE\s0. Typically \s-1BIO_CLOSE\s0 is used in a source/sink \s-1BIO\s0 to indicate that the underlying I/O stream should be closed when the \s-1BIO\s0 is freed. .PP \&\fIBIO_get_close()\fR returns the BIOs close flag. .PP \&\fIBIO_pending()\fR, \fIBIO_ctrl_pending()\fR, \fIBIO_wpending()\fR and \fIBIO_ctrl_wpending()\fR return the number of pending characters in the BIOs read and write buffers. Not all BIOs support these calls. \fIBIO_ctrl_pending()\fR and \fIBIO_ctrl_wpending()\fR return a size_t type and are functions, \fIBIO_pending()\fR and \fIBIO_wpending()\fR are macros which call \fIBIO_ctrl()\fR. .SH "RETURN VALUES" .IX Header "RETURN VALUES" \&\fIBIO_reset()\fR 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. .PP \&\fIBIO_seek()\fR and \fIBIO_tell()\fR both return the current file position on success and \-1 for failure, except file BIOs which for \fIBIO_seek()\fR always return 0 for success and \-1 for failure. .PP \&\fIBIO_flush()\fR returns 1 for success and 0 or \-1 for failure. .PP \&\fIBIO_eof()\fR returns 1 if \s-1EOF\s0 has been reached 0 otherwise. .PP \&\fIBIO_set_close()\fR always returns 1. .PP \&\fIBIO_get_close()\fR returns the close flag value: \s-1BIO_CLOSE\s0 or \s-1BIO_NOCLOSE\s0. .PP \&\fIBIO_pending()\fR, \fIBIO_ctrl_pending()\fR, \fIBIO_wpending()\fR and \fIBIO_ctrl_wpending()\fR return the amount of pending data. .SH "NOTES" .IX Header "NOTES" \&\fIBIO_flush()\fR, because it can write data may return 0 or \-1 indicating that the call should be retried later in a similar manner to \fIBIO_write()\fR. The \fIBIO_should_retry()\fR call should be used and appropriate action taken is the call fails. .PP The return values of \fIBIO_pending()\fR and \fIBIO_wpending()\fR may not reliably determine the amount of pending data in all cases. For example in the case of a file \s-1BIO\s0 some data may be available in the \s-1FILE\s0 structures internal buffers but it is not possible to determine this in a portably way. For other types of \s-1BIO\s0 they may not be supported. .PP Filter BIOs if they do not internally handle a particular \fIBIO_ctrl()\fR operation usually pass the operation to the next \s-1BIO\s0 in the chain. This often means there is no need to locate the required \s-1BIO\s0 for a particular operation, it can be called on a chain and it will be automatically passed to the relevant \s-1BIO\s0. However this can cause unexpected results: for example no current filter BIOs implement \&\fIBIO_seek()\fR, but this may still succeed if the chain ends in a \s-1FILE\s0 or file descriptor \s-1BIO\s0. .PP Source/sink BIOs return an 0 if they do not recognize the \fIBIO_ctrl()\fR operation. .SH "BUGS" .IX Header "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 \s-1EOF\s0 has not been reached and in the case of \fIBIO_seek()\fR on a file \s-1BIO\s0 for a successful operation. .SH "SEE ALSO" .IX Header "SEE ALSO" \&\s-1TBA\s0