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BIO_seek.3ssl

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.\" ========================================================================
.\"
.IX Title "BIO_ctrl 3"
.TH BIO_ctrl 3 "2019-12-20" "1.0.2u" "OpenSSL"
.\" For nroff, turn off justification.  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 control operations
.SH "SYNOPSIS"
.IX Header "SYNOPSIS"
.Vb 1
\& #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);
.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()\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 "SEE ALSO"
.IX Header "SEE ALSO"
\&\s-1TBA\s0

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