问基于libevent的回显服务器卡住了

EN

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <sys/socket.h>
#include <netinet/in.h>
#include <arpa/inet.h>

#include <openssl/ssl.h>
#include <openssl/err.h>
#include <openssl/rand.h>
#include <netinet/tcp.h>
#include <event.h>
#include <event2/listener.h>
#include <event2/bufferevent_ssl.h>

struct event_base *base;

static void echo_read_cb(struct bufferevent *bev, void *ctx) {
    /* This callback is invoked when there is data to read on bev. */
    struct evbuffer *input = bufferevent_get_input(bev);
    struct evbuffer *output = bufferevent_get_output(bev);
    
    /* Copy all the data from the input buffer to the output buffer. */
    int ret = evbuffer_add_buffer(output, input);
    if (ret) {
        printf("error happened when adding buf\n");
    }
}

static void echo_event_cb(struct bufferevent *bev, short events, void *ctx) {
    if (events & (BEV_EVENT_EOF|BEV_EVENT_ERROR)) {
        int fd = bufferevent_getfd(bev);
        evutil_closesocket(fd);
        bufferevent_free(bev);

        return;
    }
}
static void accept_error_cb(struct evconnlistener *listener, void *ctx) {
    struct event_base *base = evconnlistener_get_base(listener);
    int err = EVUTIL_SOCKET_ERROR();
    fprintf(stderr, "Got an error %d (%s) on the listener. "
            "Shutting down.\n", err, evutil_socket_error_to_string(err));
}

static void accept_conn_cb(struct evconnlistener *serv, int sock, struct sockaddr *sa,
             int sa_len, void *arg) {
    struct bufferevent *bev = bufferevent_socket_new(
            base, sock, BEV_OPT_CLOSE_ON_FREE);
    int flag = 1; 
    setsockopt(sock, IPPROTO_TCP, TCP_NODELAY, (char *) &flag, sizeof(int));
    bufferevent_setcb(bev, echo_read_cb, NULL, echo_event_cb, NULL);

    bufferevent_enable(bev, EV_READ|EV_WRITE);
}


int main(int argc, char **argv) {
    struct evconnlistener *listener;
    struct sockaddr_in sin;

    memset(&sin, 0, sizeof(sin));
    sin.sin_family = AF_INET;
    sin.sin_port = htons(9999);
    sin.sin_addr.s_addr = htonl(0x7f000001); /* 127.0.0.1 */

    base = event_base_new();
    listener = evconnlistener_new_bind(base, accept_conn_cb, NULL,
            LEV_OPT_CLOSE_ON_FREE|LEV_OPT_REUSEABLE, -1,
            (struct sockaddr*)&sin, sizeof(sin));
    if (!listener) {
            perror("Couldn't create listener");
            return 1;
    }
    evconnlistener_set_error_cb(listener, accept_error_cb);
    event_base_loop(base, 0);

    evconnlistener_free(listener);
    return 0;
}