libevent offset ignored in evbuffer_add_file()

event.c

#include <sys/socket.h>
#include <sys/stat.h>
#include <sys/types.h>

#include <arpa/inet.h>
#include <fcntl.h>
#include <netinet/in.h>
#include <netinet/tcp.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>

#include <event2/event.h>
#include <event2/listener.h>
#include <event2/buffer.h>
#include <event2/bufferevent.h>

static void
event_write(struct bufferevent *bev, void *_)
{
	struct evbuffer *outbuf = bufferevent_get_output(bev);
	int fd;

	fd = open("random.data", O_RDONLY);

	evbuffer_clear_flags(outbuf, EVBUFFER_FLAG_DRAINS_TO_FD);

	evbuffer_add_file(outbuf, fd, 0x200, 0x100);

	bufferevent_setcb(bev, NULL, NULL, NULL, NULL);
}

static void
event_accept(struct evconnlistener *evlistener, evutil_socket_t sockfd,
             struct sockaddr *addr, int addrlen, void *_)
{
	struct event_base *evb = evconnlistener_get_base(evlistener);
	struct bufferevent *bev;

	evutil_make_socket_nonblocking(sockfd);
	bev = bufferevent_socket_new(evb, sockfd,
	                             BEV_OPT_DEFER_CALLBACKS
	                             | BEV_OPT_CLOSE_ON_FREE);

	bufferevent_setcb(bev, NULL, event_write, NULL, NULL);
	bufferevent_enable(bev, EV_READ|EV_WRITE);
}

int
main(int argc, char **argv)
{
	struct event_base *evb;
	struct sockaddr_in localhost;
	struct evconnlistener *evlistener;
	int client;
	int nodelay = 1;
	unsigned char buf[256];

	localhost.sin_family = AF_INET;
	localhost.sin_port = htons(6881);
	localhost.sin_addr.s_addr = inet_addr("127.0.0.1");

	evb = event_base_new();

	evlistener = evconnlistener_new_bind(evb, event_accept, NULL,
	                                     LEV_OPT_CLOSE_ON_FREE | LEV_OPT_REUSEABLE,
	                                     SOMAXCONN,
	                                     (struct sockaddr *)&localhost,
	                                     sizeof(struct sockaddr_in));

	client = socket(AF_INET, SOCK_STREAM|SOCK_NONBLOCK, 0);
	setsockopt(client, IPPROTO_TCP, TCP_NODELAY, &nodelay, sizeof(nodelay));
	connect(client, (struct sockaddr *)&localhost, sizeof(struct sockaddr_in));
	event_base_loop(evb, EVLOOP_ONCE|EVLOOP_NONBLOCK); /* For accept */
	event_base_loop(evb, EVLOOP_ONCE|EVLOOP_NONBLOCK); /* For write */
	event_base_loop(evb, EVLOOP_ONCE|EVLOOP_NONBLOCK); /* For write ? */

	ssize_t len;
	while ((len = read(client, buf, 256)) > 0) {
		event_base_loop(evb, EVLOOP_ONCE|EVLOOP_NONBLOCK);
		write(STDOUT_FILENO, buf, len);
	}


	return EXIT_SUCCESS;
}

dd if=/dev/urandom of=random.data bs=1M count=1
gcc -g -o eventtest -levent event.c && ./eventtest | xxd
dd if=random.data bs=256 skip=2 count=1 | xxd