static void
write_complete(struct event_overlapped *eo, ev_uintptr_t key,
    ev_ssize_t nbytes, int ok)
{
	struct bufferevent_async *bev_a = upcast_write(eo);
	struct bufferevent *bev = &bev_a->bev.bev;
	short what = BEV_EVENT_WRITING;
	ev_ssize_t amount_unwritten;

	BEV_LOCK(bev);
	EVUTIL_ASSERT(bev_a->write_in_progress);

	amount_unwritten = bev_a->write_in_progress - nbytes;
	evbuffer_commit_write_(bev->output, nbytes);
	bev_a->write_in_progress = 0;

	if (amount_unwritten)
		bufferevent_decrement_write_buckets_(&bev_a->bev,
		                                     -amount_unwritten);


	if (!ok)
		bev_async_set_wsa_error(bev, eo);

	if (bev_a->ok) {
		if (ok && nbytes) {
			BEV_RESET_GENERIC_WRITE_TIMEOUT(bev);
			if (evbuffer_get_length(bev->output) <=
			    bev->wm_write.low)
				bufferevent_run_writecb_(bev);
			bev_async_consider_writing(bev_a);
		} else if (!ok) {
			what |= BEV_EVENT_ERROR;
			bev_a->ok = 0;
			bufferevent_run_eventcb_(bev, what);
		} else if (!nbytes) {
			what |= BEV_EVENT_EOF;
			bev_a->ok = 0;
			bufferevent_run_eventcb_(bev, what);
		}
	}

	bufferevent_decref_and_unlock_(bev);
}
static void
bufferevent_writecb(evutil_socket_t fd, short event, void *arg)
{
	struct bufferevent *bufev = arg;
	struct bufferevent_private *bufev_p =
	    EVUTIL_UPCAST(bufev, struct bufferevent_private, bev);
	int res = 0;
	short what = BEV_EVENT_WRITING;
	int connected = 0;
	ev_ssize_t atmost = -1;

	bufferevent_incref_and_lock_(bufev);

	if (event == EV_TIMEOUT) {
		/* Note that we only check for event==EV_TIMEOUT. If
		 * event==EV_TIMEOUT|EV_WRITE, we can safely ignore the
		 * timeout, since a read has occurred */
		what |= BEV_EVENT_TIMEOUT;
		goto error;
	}
	if (bufev_p->connecting) {
		int c = evutil_socket_finished_connecting_(fd);
		/* we need to fake the error if the connection was refused
		 * immediately - usually connection to localhost on BSD */
		if (bufev_p->connection_refused) {
		  bufev_p->connection_refused = 0;
		  c = -1;
		}

		if (c == 0)
			goto done;

		bufev_p->connecting = 0;
		if (c < 0) {
			event_del(&bufev->ev_write);
			event_del(&bufev->ev_read);
			bufferevent_run_eventcb_(bufev, BEV_EVENT_ERROR);
			goto done;
		} else {
			connected = 1;
#ifdef _WIN32
			if (BEV_IS_ASYNC(bufev)) {
				event_del(&bufev->ev_write);
				bufferevent_async_set_connected_(bufev);
				bufferevent_run_eventcb_(bufev,
						BEV_EVENT_CONNECTED);
				goto done;
			}
#endif
			bufferevent_run_eventcb_(bufev,
					BEV_EVENT_CONNECTED);
			if (!(bufev->enabled & EV_WRITE) ||
			    bufev_p->write_suspended) {
				event_del(&bufev->ev_write);
				goto done;
			}
		}
	}

	atmost = bufferevent_get_write_max_(bufev_p);

	if (bufev_p->write_suspended)
		goto done;

	if (evbuffer_get_length(bufev->output)) {
		evbuffer_unfreeze(bufev->output, 1);
		res = evbuffer_write_atmost(bufev->output, fd, atmost);
		evbuffer_freeze(bufev->output, 1);
		if (res == -1) {
			int err = evutil_socket_geterror(fd);
			if (EVUTIL_ERR_RW_RETRIABLE(err))
				goto reschedule;
			what |= BEV_EVENT_ERROR;
		} else if (res == 0) {
			/* eof case
			   XXXX Actually, a 0 on write doesn't indicate
			   an EOF. An ECONNRESET might be more typical.
			 */
			what |= BEV_EVENT_EOF;
		}
		if (res <= 0)
			goto error;

		bufferevent_decrement_write_buckets_(bufev_p, res);
	}

	if (evbuffer_get_length(bufev->output) == 0) {
		event_del(&bufev->ev_write);
	}

	/*
	 * Invoke the user callback if our buffer is drained or below the
	 * low watermark.
	 */
	if ((res || !connected) &&
	    evbuffer_get_length(bufev->output) <= bufev->wm_write.low) {
		bufferevent_run_writecb_(bufev);
	}

	goto done;

 reschedule:
	if (evbuffer_get_length(bufev->output) == 0) {
		event_del(&bufev->ev_write);
	}
	goto done;

 error:
	bufferevent_disable(bufev, EV_WRITE);
	bufferevent_run_eventcb_(bufev, what);

 done:
	bufferevent_decref_and_unlock_(bufev);
}