libevent test - missing error callback after read high watermark reached - with line draining

gistfile1.c

#include <string.h>
#include <errno.h>
#include <stdio.h>
#include <stdlib.h>
#include <event.h>
#include <event2/bufferevent.h>
#include <event2/listener.h>
#include <event2/buffer.h>

#define PORT 5001
#define BUFFLEN 4

static void handle_client_buffer_in(struct bufferevent *bev, void *hint) {
  struct evbuffer *in = bufferevent_get_input(bev);
	int num_lines = 0;
	char *line;
	while ((line = evbuffer_readln(in, NULL, EVBUFFER_EOL_LF)) != NULL) {
		num_lines++;
		free(line);
	}
	printf("Got data from client - drained %d line(s)\n", num_lines);
}

static void handle_client_buffer_evt(struct bufferevent *bev, short revents, void *hint) {
        if (revents & BEV_EVENT_ERROR) {
                printf("Client error: %s\n", strerror(errno));
        }
        else if (revents & BEV_EVENT_TIMEOUT) {
                printf("Client timed out\n");
        }
        else if (revents & BEV_EVENT_EOF) {
                printf("Client disconnected\n");
        }
        else {
                printf("Spurious event from client: %d", revents);
        }
}

static
void
handle_server_newclient(struct evconnlistener *listener, evutil_socket_t sock, struct sockaddr *addr, int len, void *ptr) {
	struct bufferevent * bufferevent;
	printf("New client\n");
	bufferevent = bufferevent_socket_new( evconnlistener_get_base(listener), sock, BEV_OPT_CLOSE_ON_FREE);
	bufferevent_setcb(bufferevent, handle_client_buffer_in, NULL, handle_client_buffer_evt, NULL);
        bufferevent_setwatermark(bufferevent, EV_READ, 0, BUFFLEN);
	bufferevent_enable(bufferevent, EV_READ);
}

int main(int argc, char ** argv) {

	struct event_base *eb;
	struct sockaddr_in sa;

	eb = event_base_new();

	memset(&sa, 0, sizeof(sa));
	sa.sin_family = AF_INET;
	sa.sin_addr.s_addr = htonl(INADDR_ANY);
	sa.sin_port = htons(PORT);

        evconnlistener_new_bind(
                        eb,
                        handle_server_newclient,
                        NULL,
                        LEV_OPT_CLOSE_ON_FREE | LEV_OPT_REUSEABLE,
                        -1,
                        (struct sockaddr *)&sa,
                        sizeof(sa)
                        );

	event_base_dispatch(eb);
	return 0;
}