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Always turn off hyphenation; it makes .\" way too many mistakes in technical documents. .if n .ad l .nh .SH "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 .SH "SYNOPSIS" .IX Header "SYNOPSIS" .Vb 1 \& #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); .Ve .SH "DESCRIPTION" .IX Header "DESCRIPTION" \&\fBBIO_ctrl()\fR, \fBBIO_callback_ctrl()\fR, \fBBIO_ptr_ctrl()\fR and \fBBIO_int_ctrl()\fR are \s-1BIO\s0 \*(L"control\*(R" 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 \s-1BIO\s0 are described in the specific BIOs manual page as well as any special features of the standard calls. .PP \&\fBBIO_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 \&\fBBIO_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 \&\fBBIO_tell()\fR returns the current file position of a file related \s-1BIO.\s0 .PP \&\fBBIO_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 \&\fBBIO_eof()\fR returns 1 if the \s-1BIO\s0 has read \s-1EOF,\s0 the precise meaning of \&\*(L"\s-1EOF\*(R"\s0 varies according to the \s-1BIO\s0 type. .PP \&\fBBIO_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 \&\fBBIO_get_close()\fR returns the BIOs close flag. .PP \&\fBBIO_pending()\fR, \fBBIO_ctrl_pending()\fR, \fBBIO_wpending()\fR and \fBBIO_ctrl_wpending()\fR return the number of pending characters in the BIOs read and write buffers. Not all BIOs support these calls. \fBBIO_ctrl_pending()\fR and \fBBIO_ctrl_wpending()\fR return a size_t type and are functions, \fBBIO_pending()\fR and \fBBIO_wpending()\fR are macros which call \fBBIO_ctrl()\fR. .SH "RETURN VALUES" .IX Header "RETURN VALUES" \&\fBBIO_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 \&\fBBIO_seek()\fR and \fBBIO_tell()\fR both return the current file position on success and \-1 for failure, except file BIOs which for \fBBIO_seek()\fR always return 0 for success and \-1 for failure. .PP \&\fBBIO_flush()\fR returns 1 for success and 0 or \-1 for failure. .PP \&\fBBIO_eof()\fR returns 1 if \s-1EOF\s0 has been reached 0 otherwise. .PP \&\fBBIO_set_close()\fR always returns 1. .PP \&\fBBIO_get_close()\fR returns the close flag value: \s-1BIO_CLOSE\s0 or \s-1BIO_NOCLOSE.\s0 .PP \&\fBBIO_pending()\fR, \fBBIO_ctrl_pending()\fR, \fBBIO_wpending()\fR and \fBBIO_ctrl_wpending()\fR return the amount of pending data. .SH "NOTES" .IX Header "NOTES" \&\fBBIO_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 \fBBIO_write_ex()\fR. The \fBBIO_should_retry()\fR call should be used and appropriate action taken is the call fails. .PP The return values of \fBBIO_pending()\fR and \fBBIO_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 \fBBIO_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 \&\fBBIO_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 \fBBIO_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 \fBBIO_seek()\fR on a file \s-1BIO\s0 for a successful operation. .SH "COPYRIGHT" .IX Header "COPYRIGHT" Copyright 2000\-2022 The OpenSSL Project Authors. All Rights Reserved. .PP Licensed under the OpenSSL license (the \*(L"License\*(R"). You may not use this file except in compliance with the License. You can obtain a copy in the file \s-1LICENSE\s0 in the source distribution or at <https://www.openssl.org/source/license.html>.