— BIO control
int cmd, long larg,
int cmd, BIO_info_cb *cb);
int cmd, long larg);
int cmd, long larg,
int state, int res);
int state, int res);
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,
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.
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_ctrl() with parg
pointing to the location of a temporary pointer variable initialized to
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.
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.
resets a file related BIO's (that is file descriptor and FILE BIOs) file
position pointer to ofs bytes from start of file.
returns the current file position of a file related BIO.
normally writes out any internally buffered data. In some cases it is used
to signal EOF and that no more data will be written.
returns 1 if the BIO has read EOF. The precise meaning of "EOF"
varies according to the BIO type.
sets the BIO b close flag to
flag. flag can take the value
BIO_CLOSE is used in a source/sink BIO to
indicate that the underlying I/O stream should be closed when the BIO is
returns the BIO's close flag.
return the number of pending characters in the BIO's read and write buffers.
Not all BIOs support these calls.
BIO_ctrl_wpending() return a
size_t type and are functions.
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_f_ssl(3) support this functionality. Some filter BIO types
forward this control call to the next BIO in the chain instead of processing
places the function pointer to the info callback into
*cbp if any was installed using
BIO_callback_ctrl(). If the type of
b supports setting an info callback but none was
installed, it stores a
NULL pointer in
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|
Some cmd constants are not associated with any macros. They are documented in the following manual pages:
The meaning of the return values of
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_set_info_callback() return 1 on success, 0 if
NULL or to indicate
failure of a valid cmd, or -2 if the
cmd is not supported by b.
NULL if the
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_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_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
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
BIO_ctrl_wpending() return the amount of pending
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.
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(3). The
BIO_should_retry(3) call should be used and appropriate
action taken if the call fails.
The return values of
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
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
BIO_pending() first appeared in SSLeay 0.6.0.
BIO_wpending() first appeared in SSLeay 0.8.1.
BIO_set_info_callback() first appeared in SSLeay
0.9.0. All these functions have been available since
BIO_tell() first appeared in SSLeay 0.9.1.
BIO_ctrl_wpending() first appeared in OpenSSL 0.9.4.
These functions have been available since OpenBSD
BIO_callback_ctrl() first appeared in
OpenSSL 0.9.5 and has been available since OpenBSD
bio_info_cb() first appeared with a more
complicated prototype in OpenSSL 0.9.6 and has been available since
BIO_info_cb() first appeared in OpenSSL
1.1.0h and has been available since OpenBSD 6.3.
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
BIO_seek() on a file BIO for a successful