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Title "BIO_CTRL 3ossl" For nroff, turn off justification. Always turn off hyphenation; it makes
way too many mistakes in technical documents.
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_get_ktls_send, BIO_get_ktls_recv \- BIO control operations 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); \& int BIO_get_ktls_send(BIO *b); int BIO_get_ktls_recv(BIO *b); .Ve Header "DESCRIPTION" \fBBIO_ctrl(), BIO_callback_ctrl(), BIO_ptr_ctrl() and BIO_int_ctrl() 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.

\fBBIO_reset() 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.

\fBBIO_seek() resets a file related \s-1BIO\s0's (that is file descriptor and \s-1FILE\s0 BIOs) file position pointer to ofs bytes from start of file.

\fBBIO_tell() returns the current file position of a file related \s-1BIO.\s0

\fBBIO_flush() 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.

\fBBIO_eof() 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.

\fBBIO_set_close() sets the \s-1BIO\s0 b close flag to flag. flag 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.

\fBBIO_get_close() returns the BIOs close flag.

\fBBIO_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().

\fBBIO_get_ktls_send() returns 1 if the \s-1BIO\s0 is using the Kernel \s-1TLS\s0 data-path for sending. Otherwise, it returns zero. \fBBIO_get_ktls_recv() returns 1 if the \s-1BIO\s0 is using the Kernel \s-1TLS\s0 data-path for receiving. Otherwise, it returns zero.

Header "RETURN VALUES" \fBBIO_reset() normally returns 1 for success and <=0 for failure. File BIOs are an exception, they return 0 for success and -1 for failure.

\fBBIO_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.

\fBBIO_flush() returns 1 for success and <=0 for failure.

\fBBIO_eof() returns 1 if \s-1EOF\s0 has been reached, 0 if not, or negative values for failure.

\fBBIO_set_close() returns 1 on success or <=0 for failure.

\fBBIO_get_close() returns the close flag value: \s-1BIO_CLOSE\s0 or \s-1BIO_NOCLOSE.\s0 It also returns other negative values if an error occurs.

\fBBIO_pending(), BIO_ctrl_pending(), BIO_wpending() and BIO_ctrl_wpending() return the amount of pending data. BIO_pending() and BIO_wpending() return negative value or 0 on error. BIO_ctrl_pending() and BIO_ctrl_wpending() return 0 on error.

\fBBIO_get_ktls_send() returns 1 if the \s-1BIO\s0 is using the Kernel \s-1TLS\s0 data-path for sending. Otherwise, it returns zero. \fBBIO_get_ktls_recv() returns 1 if the \s-1BIO\s0 is using the Kernel \s-1TLS\s0 data-path for receiving. Otherwise, it returns zero.

Header "NOTES" \fBBIO_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 \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.

Filter BIOs if they do not internally handle a particular BIO_ctrl() 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(), but this may still succeed if the chain ends in a \s-1FILE\s0 or file descriptor \s-1BIO.\s0

Source/sink BIOs return an 0 if they do not recognize the BIO_ctrl() operation.

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 BIO_seek() on a file \s-1BIO\s0 for a successful operation.

In older versions of OpenSSL the BIO_ctrl_pending() and \fBBIO_ctrl_wpending() could return values greater than \s-1INT_MAX\s0 on error.

Header "HISTORY" The BIO_get_ktls_send() and BIO_get_ktls_recv() macros were added in OpenSSL 3.0. They were modified to never return -1 in OpenSSL 3.0.4. Header "COPYRIGHT" Copyright 2000-2022 The OpenSSL Project Authors. All Rights Reserved.

Licensed under the Apache License 2.0 (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>.