sbuf_count_drain
sbuf_set_drain(sb, sbuf_count_drain, &size);
sbuf_set_drain(sb, sbuf_count_drain, &len);
sbuf_set_drain(sb, sbuf_count_drain, &size);
sbuf_set_drain(sb, sbuf_count_drain, &size);
sbuf_set_drain(sb, sbuf_count_drain, &size);
sbuf_set_drain(sb, sbuf_count_drain, &size);
int sbuf_count_drain(void *arg, const char *data, int len);