BIO control operations
int cmd, long larg,
int cmd, bio_info_cb cb);
int cmd, long larg);
int cmd, long larg,
int oper, const char *ptr,
int arg1, long arg2,
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.
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.
BIO_wpending() are macros which call
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
Because it can write data,
may return 0 or -1 indicating that the call should be retried later in a
similar manner to
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 an 0 if they do not
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