【Linux 解析libevent下的bufferevent监听事件sample-helloworld.c】及改写read使能

/*
   This exmple program provides a trivial server program that listens for TCP
   connections on port 9995.  When they arrive, it writes a short message to
   each client connection, and closes each connection once it is flushed.

   Where possible, it exits cleanly in response to a SIGINT (ctrl-c).
 */


#include <string.h>
#include <errno.h>
#include <stdio.h>
#include <signal.h>
#ifndef WIN32
#include <netinet/in.h>
# ifdef _XOPEN_SOURCE_EXTENDED
#  include <arpa/inet.h>
# endif
#include <sys/socket.h>
#endif

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

static const char MESSAGE[] = "Hello, World!\n";

static const int PORT = 9995;

static void listener_cb(struct evconnlistener *, evutil_socket_t,
		struct sockaddr *, int socklen, void *);
static void conn_writecb(struct bufferevent *, void *);
static void conn_eventcb(struct bufferevent *, short, void *);
static void signal_cb(evutil_socket_t, short, void *);

	int
main(int argc, char **argv)
{
	struct event_base *base;
	struct evconnlistener *listener;
	struct event *signal_event;

	struct sockaddr_in sin;
#ifdef WIN32
	WSADATA wsa_data;
	WSAStartup(0x0201, &wsa_data);
#endif

	base = event_base_new();//创建event_base根节点
	if (!base) {
		fprintf(stderr, "Could not initialize libevent!\n");
		return 1;
	}

	memset(&sin, 0, sizeof(sin));
	sin.sin_family = AF_INET;
	sin.sin_port = htons(PORT);

	//创建连接侦听器
	listener = evconnlistener_new_bind(base, listener_cb, (void *)base,
			LEV_OPT_REUSEABLE|LEV_OPT_CLOSE_ON_FREE, -1,
			(struct sockaddr*)&sin,
			sizeof(sin));

	if (!listener) {
		fprintf(stderr, "Could not create a listener!\n");
		return 1;
	}

	//创建信号触发的节点
	signal_event = evsignal_new(base, SIGINT, signal_cb, (void *)base);
	//将信号节点上树
	if (!signal_event || event_add(signal_event, NULL)<0) {
		fprintf(stderr, "Could not create/add a signal event!\n");
		return 1;
	}

	event_base_dispatch(base);//循环监听

	evconnlistener_free(listener);//释放连接侦听器
	event_free(signal_event);//释放信号节点
	event_base_free(base);//释放根节点

	printf("done\n");
	return 0;
}

	static void
listener_cb(struct evconnlistener *listener, evutil_socket_t fd,
		struct sockaddr *sa, int socklen, void *user_data)
{
	struct event_base *base = user_data;
	struct bufferevent *bev;

	//将fd上树
	//创建一个新的节点
	bev = bufferevent_socket_new(base, fd, BEV_OPT_CLOSE_ON_FREE);
	if (!bev) {
		fprintf(stderr, "Error constructing bufferevent!");
		event_base_loopbreak(base);
		return;
	}
	//设置节点对应文件描述符事件触发的回调，设置完之后自动上树
	bufferevent_setcb(bev, NULL, conn_writecb, conn_eventcb, NULL);
	//设置写事件使能，读事件非使能
	bufferevent_enable(bev, EV_WRITE);
	bufferevent_disable(bev, EV_READ);

	//给cfd发送消息“Hello，World”
	bufferevent_write(bev, MESSAGE, strlen(MESSAGE));
}

	static void
conn_writecb(struct bufferevent *bev, void *user_data)
{
	struct evbuffer *output = bufferevent_get_output(bev);//获取缓冲区类型
	if (evbuffer_get_length(output) == 0) {//判断应用层缓冲区数据是否写到内核
		printf("flushed answer\n");
		bufferevent_free(bev);//释放节点，自动关闭
	}
}

	static void
conn_eventcb(struct bufferevent *bev, short events, void *user_data)
{
	if (events & BEV_EVENT_EOF) {
		printf("Connection closed.\n");
	} else if (events & BEV_EVENT_ERROR) {
		printf("Got an error on the connection: %s\n",
				strerror(errno));/*XXX win32*/
	}
	/* None of the other events can happen here, since we haven't enabled
	 * timeouts */
	bufferevent_free(bev);
}

	static void
signal_cb(evutil_socket_t sig, short events, void *user_data)
{
	struct event_base *base = user_data;
	struct timeval delay = { 2, 0 };

	printf("Caught an interrupt signal; exiting cleanly in two seconds.\n");

	event_base_loopexit(base, &delay);//退出循环监听
}

	static void
listener_cb(struct evconnlistener *listener, evutil_socket_t fd,
		struct sockaddr *sa, int socklen, void *user_data)
{
	struct event_base *base = user_data;
	struct bufferevent *bev;

	//将fd上树
	//创建一个新的节点
	bev = bufferevent_socket_new(base, fd, BEV_OPT_CLOSE_ON_FREE);
	if (!bev) {
		fprintf(stderr, "Error constructing bufferevent!");
		event_base_loopbreak(base);
		return;
	}
	//设置节点对应文件描述符事件触发的回调，设置完之后自动上树
	bufferevent_setcb(bev, conn_readcb, conn_writecb, conn_eventcb, NULL);
	//设置写事件使能，读事件非使能
	//设置读事件使能
	bufferevent_enable(bev, EV_WRITE | EV_READ);
	//bufferevent_disable(bev, EV_READ);

	//给cfd发送消息“Hello，World”
	bufferevent_write(bev, MESSAGE, strlen(MESSAGE));
}

	static void
conn_writecb(struct bufferevent *bev, void *user_data)
{
	struct evbuffer *output = bufferevent_get_output(bev);//获取缓冲区类型
	if (evbuffer_get_length(output) == 0) {//判断应用层缓冲区数据是否写到内核
		printf("flushed answer\n");
		//缓冲区数据写完到内核也不关
		//bufferevent_free(bev);//释放节点，自动关闭
	}
}

	static void
conn_readcb(struct bufferevent *bev, void *user_data)
{
	//读缓冲区回调
	char buf[1500] = "";
	int n = bufferevent_read(bev, buf, sizeof(buf));
	printf("%s\n", buf);
	bufferevent_write(bev, buf, n);//给cfd发消息buf
}