int sink_vprintf(struct sink *s, const char *fmt, va_list ap);
int sink_printf(struct sink *s, const char *fmt, ...)
attribute((format (printf, 2, 3)));
int sink_vprintf(struct sink *s, const char *fmt, va_list ap);
int sink_printf(struct sink *s, const char *fmt, ...)
attribute((format (printf, 2, 3)));