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_info_cb
— BIO control
operations
SYNOPSIS
#include
<openssl/bio.h>
long
BIO_ctrl
(BIO *b,
int cmd, long larg,
void *parg);
long
BIO_callback_ctrl
(BIO *b,
int cmd, BIO_info_cb *cb);
char *
BIO_ptr_ctrl
(BIO *b,
int cmd, long larg);
long
BIO_int_ctrl
(BIO *b,
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 int
BIO_info_cb
(BIO *b,
int state, int res);
typedef int
bio_info_cb
(BIO *b,
int state, int res);
DESCRIPTION
BIO_ctrl
(),
BIO_callback_ctrl
(),
BIO_ptr_ctrl
(), and
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.
Depending on the cmd and on
the type of b,
BIO_ctrl
()
may have a read-only effect on b or change data in
b or in its sub-structures. It may also have a side
effect of changing the memory pointed to by parg.
BIO_callback_ctrl
()
does not call BIO_ctrl
() but instead requires that
the BIO type of b provides a dedicated
callback_ctrl function pointer, which is built into
the library for some standard BIO types and can be provided with
BIO_meth_set_callback_ctrl(3) for application-defined BIO types. The
only cmd supported by
BIO_callback_ctrl
() is
BIO_CTRL_SET_CALLBACK
.
BIO_ptr_ctrl
()
calls BIO_ctrl
() with parg
pointing to the location of a temporary pointer variable initialized to
NULL
.
BIO_int_ctrl
()
calls BIO_ctrl
() with parg
pointing to the location of a temporary int variable
initialized to iarg. If
BIO_ctrl
() changes the value stored at
*parg, the new value is ignored.
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.
BIO_seek
()
resets a file related BIO's (that is file descriptor and FILE BIOs) file
position pointer to ofs bytes from start of file.
BIO_tell
()
returns the current file position of a file related BIO.
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.
BIO_eof
()
returns 1 if the BIO has read EOF. The precise meaning of "EOF"
varies according to the BIO type.
BIO_set_close
()
sets the BIO b close flag to
flag. flag can take the value
BIO_CLOSE
or BIO_NOCLOSE
.
Typically 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.
BIO_get_close
()
returns the BIO's close flag.
BIO_pending
(),
BIO_ctrl_pending
(),
BIO_wpending
(), and
BIO_ctrl_wpending
()
return the number of pending characters in the BIO's 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_set_info_callback
()
installs the function pointer cb as an info callback
in b by calling
BIO_callback_ctrl
() with a command of
BIO_CTRL_SET_CALLBACK
. Among the BIO types built
into the library, only BIO_s_connect(3) and BIO_f_ssl(3) support this functionality. Some filter BIO types
forward this control call to the next BIO in the chain instead of processing
it themselves.
BIO_get_info_callback
()
places the function pointer to the info callback into
*cbp if any was installed using
BIO_set_info_callback
() or
BIO_callback_ctrl
(). If the type of
b supports setting an info callback but none was
installed, it stores a NULL
pointer in
*cbp.
The function type name bio_info_cb is a deprecated synonym for BIO_info_cb provided for backward compatibility with some existing application software.
The following cmd constants correspond to macros:
A few cmd constants serve more than one macro each and are documented in the following manual pages:
cmd constant | manual page |
BIO_C_GET_CONNECT |
BIO_s_connect(3) |
BIO_C_SET_ACCEPT |
BIO_s_accept(3) |
BIO_C_SET_BUFF_SIZE |
BIO_f_buffer(3) |
BIO_C_SET_CONNECT |
BIO_s_connect(3) |
BIO_C_SET_FILENAME |
BIO_s_file(3) |
Some cmd constants are not associated with any macros. They are documented in the following manual pages:
RETURN VALUES
The meaning of the return values of
BIO_ctrl
(),
BIO_callback_ctrl
(), and
BIO_int_ctrl
() depends on both the type of
b and on the cmd. If
b is a NULL
pointer, no action
occurs and 0 is returned. The return value -2 usually indicates a fatal
error. In particular, it is returned if the cmd is
unsupported by the type of b.
BIO_callback_ctrl
() and
BIO_set_info_callback
() return 1 on success, 0 if
b is NULL
or to indicate
failure of a valid cmd, or -2 if the
cmd is not supported by b.
BIO_ptr_ctrl
() returns
NULL
if the BIO_ctrl
() call
returns a negative value or does not change *parg, or
the pointer it puts into *parg otherwise.
BIO_int_ctrl
() returns the return value of
BIO_ctrl
().
BIO_reset
() normally returns 1 for success
and 0 or -1 for failure. File BIOs are an exception, returning 0 for success
and -1 for failure.
BIO_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.
BIO_flush
() returns 1 for success and 0 or
-1 for failure.
BIO_eof
() returns 1 if EOF has been
reached or 0 otherwise.
BIO_set_close
() always returns 1.
BIO_get_close
() returns the close flag
value BIO_CLOSE
or
BIO_NOCLOSE
.
BIO_pending
(),
BIO_ctrl_pending
(),
BIO_wpending
(), and
BIO_ctrl_wpending
() return the amount of pending
data.
BIO_get_info_callback
() returns 1 on
success, including when the type of b supports an info
callback but none is installed, 0 if b is
NULL
or -2 if the type of b
does not support an info callback.
If a callback was installed in b using BIO_set_callback_ex(3) or BIO_set_callback(3), it can modify the return values of all these functions.
NOTES
Because it can write data,
BIO_flush
()
may return 0 or -1 indicating that the call should be retried later in a
similar manner to BIO_write(3). The BIO_should_retry(3) call should be used and appropriate action taken
if 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 BIO some data may be available in the
FILE structure's internal buffers but it is not
possible to determine this in a portable way. For other types of BIO they
may not be supported.
If they do not internally handle a particular
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
BIO_seek
(), but this may still succeed if the chain
ends in a FILE or file descriptor BIO.
Source/sink BIOs return a 0 if they do not
recognize the
BIO_ctrl
()
operation.
SEE ALSO
HISTORY
BIO_ctrl
(),
BIO_reset
(), BIO_flush
(),
BIO_eof
(), BIO_set_close
(),
BIO_get_close
(), and
BIO_pending
() first appeared in SSLeay 0.6.0.
BIO_wpending
() first appeared in SSLeay 0.8.1.
BIO_ptr_ctrl
(),
BIO_int_ctrl
(),
BIO_get_info_callback
() and
BIO_set_info_callback
() first appeared in SSLeay
0.9.0. All these functions have been available since
OpenBSD 2.4.
BIO_seek
() and
BIO_tell
() first appeared in SSLeay 0.9.1.
BIO_ctrl_pending
() and
BIO_ctrl_wpending
() first appeared in OpenSSL 0.9.4.
These functions have been available since OpenBSD
2.6.
BIO_callback_ctrl
() first appeared in
OpenSSL 0.9.5 and has been available since OpenBSD
2.7.
bio_info_cb
() first appeared with a more
complicated prototype in OpenSSL 0.9.6 and has been available since
OpenBSD 2.9.
BIO_info_cb
() first appeared in OpenSSL
1.1.0h and has been available since OpenBSD 6.3.
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 BIO_seek
() on a file BIO for a successful
operation.