.Dd July 17, 2014
.Dt BIO_CTRL 3
.Os
.Sh NAME
.Nm BIO_ctrl ,
.Nm BIO_callback_ctrl ,
.Nm BIO_ptr_ctrl ,
.Nm BIO_int_ctrl ,
.Nm BIO_reset ,
.Nm BIO_seek ,
.Nm BIO_tell ,
.Nm BIO_flush ,
.Nm BIO_eof ,
.Nm BIO_set_close ,
.Nm BIO_get_close ,
.Nm BIO_pending ,
.Nm BIO_wpending ,
.Nm BIO_ctrl_pending ,
.Nm BIO_ctrl_wpending ,
.Nm BIO_get_info_callback ,
.Nm BIO_set_info_callback
.Nd BIO control operations
.Sh SYNOPSIS
.In openssl/bio.h
.Ft long
.Fo BIO_ctrl
.Fa "BIO *bp"
.Fa "int cmd"
.Fa "long larg"
.Fa "void *parg"
.Fc
.Ft long
.Fo BIO_callback_ctrl
.Fa "BIO *b"
.Fa "int cmd"
.Fa "void (*fp)(struct bio_st *, int, const char *, int, long, long)"
.Fc
.Ft char *
.Fo BIO_ptr_ctrl
.Fa "BIO *bp"
.Fa "int cmd"
.Fa "long larg"
.Fc
.Ft long
.Fo BIO_int_ctrl
.Fa "BIO *bp"
.Fa "int cmd"
.Fa "long larg"
.Fa "int iarg"
.Fc
.Ft int
.Fo BIO_reset
.Fa "BIO *b"
.Fc
.Ft int
.Fo BIO_seek
.Fa "BIO *b"
.Fa "int ofs"
.Fc
.Ft int
.Fo BIO_tell
.Fa "BIO *b"
.Fc
.Ft int
.Fo BIO_flush
.Fa "BIO *b"
.Fc
.Ft int
.Fo BIO_eof
.Fa "BIO *b"
.Fc
.Ft int
.Fo BIO_set_close
.Fa "BIO *b"
.Fa "long flag"
.Fc
.Ft int
.Fo BIO_get_close
.Fa "BIO *b"
.Fc
.Ft int
.Fo BIO_pending
.Fa "BIO *b"
.Fc
.Ft int
.Fo BIO_wpending
.Fa "BIO *b"
.Fc
.Ft size_t
.Fo BIO_ctrl_pending
.Fa "BIO *b"
.Fc
.Ft size_t
.Fo BIO_ctrl_wpending
.Fa "BIO *b"
.Fc
.Ft int
.Fo BIO_get_info_callback
.Fa "BIO *b"
.Fa "bio_info_cb **cbp"
.Fc
.Ft int
.Fo BIO_set_info_callback
.Fa "BIO *b"
.Fa "bio_info_cb *cb"
.Fc
.Ft typedef void
.Fo bio_info_cb
.Fa "BIO *b"
.Fa "int oper"
.Fa "const char *ptr"
.Fa "int arg1"
.Fa "long arg2"
.Fa "long arg3"
.Fc
.Sh DESCRIPTION
.Fn BIO_ctrl ,
.Fn BIO_callback_ctrl ,
.Fn BIO_ptr_ctrl ,
and
.Fn BIO_int_ctrl
are BIO "control" 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 BIO are described in the specific BIO's manual
page as well as any special features of the standard calls.
.Pp
.Fn BIO_reset
typically resets a BIO 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
.Fn BIO_seek
resets a file related BIO's (that is file descriptor and
FILE BIOs) file position pointer to
.Fa ofs
bytes from start of file.
.Pp
.Fn BIO_tell
returns the current file position of a file related BIO.
.Pp
.Fn BIO_flush
normally writes out any internally buffered data, in some cases
it is used to signal EOF and that no more data will be written.
.Pp
.Fn BIO_eof
returns 1 if the BIO has read EOF, the precise meaning of
"EOF" varies according to the BIO type.
.Pp
.Fn BIO_set_close
sets the BIO
.Fa b
close flag to
.Fa flag .
.Fa flag
can take the value
.Dv BIO_CLOSE
or
.Dv BIO_NOCLOSE .
Typically
.Dv BIO_CLOSE
is used in a source/sink BIO to indicate that the underlying I/O stream
should be closed when the BIO is freed.
.Pp
.Fn BIO_get_close
returns the BIO's close flag.
.Pp
.Fn BIO_pending ,
.Fn BIO_ctrl_pending ,
.Fn BIO_wpending ,
and
.Fn BIO_ctrl_wpending
return the number of pending characters in the BIO's read and write buffers.
Not all BIOs support these calls.
.Fn BIO_ctrl_pending
and
.Fn BIO_ctrl_wpending
return a
.Vt size_t
type and are functions,
.Fn BIO_pending
and
.Fn BIO_wpending
are macros which call
.Fn BIO_ctrl .
.Sh RETURN VALUES
.Fn BIO_reset
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
.Fn BIO_seek
and
.Fn BIO_tell
both return the current file position on success
and -1 for failure, except file BIOs which for
.Fn BIO_seek
always return 0 for success and -1 for failure.
.Pp
.Fn BIO_flush
returns 1 for success and 0 or -1 for failure.
.Pp
.Fn BIO_eof
returns 1 if EOF has been reached 0 otherwise.
.Pp
.Fn BIO_set_close
always returns 1.
.Pp
.Fn BIO_get_close
returns the close flag value
.Dv BIO_CLOSE
or
.Dv BIO_NOCLOSE .
.Pp
.Fn BIO_pending ,
.Fn BIO_ctrl_pending ,
.Fn BIO_wpending ,
and
.Fn BIO_ctrl_wpending
return the amount of pending data.
.Sh NOTES
Because it can write data,
.Fn BIO_flush
may return 0 or -1 indicating that the call should be retried later
in a similar manner to
.Fn BIO_write .
The
.Fn BIO_should_retry
call should be used and appropriate action taken is the call fails.
.Pp
The return values of
.Fn BIO_pending
and
.Fn BIO_wpending
may not reliably determine the amount of pending data in all cases.
For example in the case of a file BIO some data may be available in the
.Vt FILE
structure's internal buffers but it is not possible
to determine this in a portably way.
For other types of BIO they may not be supported.
.Pp
If they do not internally handle a particular
.Fn BIO_ctrl
operation, filter BIOs usually pass the operation
to the next BIO in the chain.
This often means there is no need to locate the required BIO for
a particular operation, it can be called on a chain and it will
be automatically passed to the relevant BIO.
However this can cause unexpected results:
for example no current filter BIOs implement
.Fn BIO_seek ,
but this may still succeed if the chain ends
in a FILE or file descriptor BIO.
.Pp
Source/sink BIOs return an 0 if they do not recognize the
.Fn BIO_ctrl
operation.
.Sh 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 EOF has not been reached
and in the case of
.Fn BIO_seek
on a file BIO for a successful operation.