* Use as much input up to *isize_p and fill output up to *osize_p;
* update isize_p and osize_p to indicate how much buffer space was
* consumed and filled. Return 0 on success, non-zero on error.
+ *
+ * Some filters may need to buffer the input and look-ahead inside it
+ * to decide what to output, and they may consume more than zero bytes
+ * of input and still not produce any output. After feeding all the
+ * input, pass NULL as input and keep calling this function, to let
+ * such filters know there is no more input coming and it is time for
+ * them to produce the remaining output based on the buffered input.
*/
extern int stream_filter(struct stream_filter *,
const char *input, size_t *isize_p,