libevent简单服务端和客户端实现-原创手记-慕课网

1.生成动态库说明

在开始使用之前，我们需要先搞清楚libevent编译生成的各个动态库的作用。
在下载libevent源码包进行编译以后，当前目录生成.libs目录，该目录下是所有的目标文件，这里我们只说明个动态库so文件的作用，通过makefile我们可以知道各个动态库包含内容：

动态库名称	作用
libevent_core.so	这个库包含了所有核心的事件和缓存功能
libevent_extra.so	这个库包含外围的dns、rpc、http等协议使用
libevent.so	这个库包含了libevent_core和libevent_extra的内容
libevent_openssl.so	需要进行加密通信时可以使用这个
libevent_pthreads.so	看名字就知道如果要用多线程的方式使用libevent，就需要用到这个库

下面使用libevent实现了一个很简单的服务端和客户端程序。

2. 服务端代码实现

//server-event.cpp
#include <string.h>
#include <errno.h>
#include <stdio.h>
#include <signal.h>
#include <netinet/in.h>
#include <arpa/inet.h>
#include <sys/socket.h>

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

static const int PORT = 9995;

static char g_szWriteMsg[256] = {0};
static char g_szReadMsg[256] = {0};
static int g_iCnt = 0;

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

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

	struct sockaddr_in sin;

	base = event_base_new();
	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);//固定一个端口号

	//创建、绑定、监听socket
	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;
	}	

	event_base_dispatch(base);

	evconnlistener_free(listener);
	//event_free(signal_event);
	event_base_free(base);

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

//有连接来时调用
static void
listener_cb(struct evconnlistener *listener, evutil_socket_t fd,
    struct sockaddr *sa, int socklen, void *user_data)
{
	struct event_base *base = (struct event_base*)user_data;
	struct bufferevent *bev;

	//构造一个bufferevent
	bev = bufferevent_socket_new(base, fd, BEV_OPT_CLOSE_ON_FREE);
	if (!bev) {
		fprintf(stderr, "Error constructing bufferevent!");
		event_base_loopbreak(base);
		return;
	}

	//绑定读事件回调函数、写事件回调函数、错误事件回调函数
	bufferevent_setcb(bev, conn_readcb, conn_writecb, conn_eventcb, NULL);

	bufferevent_enable(bev, EV_WRITE);
	bufferevent_enable(bev, EV_READ);

	const char *szMsg = "hi client!";
	bufferevent_write(bev, szMsg, strlen(szMsg));
}

static void
conn_writecb(struct bufferevent *bev, void *user_data)
{
	//printf("touch conn_writecb\n");
	
//	if ( strlen(g_szWriteMsg) > 0 )
//	{
//		bufferevent_write(bev, g_szWriteMsg, strlen(g_szWriteMsg));
//		memset(g_szWriteMsg, 0x00, sizeof(g_szWriteMsg));
//	}
}

static void
conn_readcb(struct bufferevent *bev, void *user_data)
{
	//printf("touch conn_readcb\n");
	memset(g_szReadMsg, 0x00, sizeof(g_szReadMsg));
	struct evbuffer *input = bufferevent_get_input(bev);
	size_t sz = evbuffer_get_length(input);
	if (sz > 0)
	{
		bufferevent_read(bev, g_szReadMsg, sz);
		printf("cli:>>%s\n", g_szReadMsg);
		memset(g_szWriteMsg, 0x00, sizeof(g_szWriteMsg));
		snprintf(g_szWriteMsg, sizeof(g_szWriteMsg)-1, "hi client, this count is %d", g_iCnt);
		g_iCnt++;
		//printf("ser:>>");
		//gets(g_szWriteMsg);
		//scanf("%s", g_szWriteMsg);
		
		bufferevent_write(bev, g_szWriteMsg, strlen(g_szWriteMsg));
	}
}

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);
}

3. 客户端代码实现

//client-event.cpp
#include <string.h>
#include <errno.h>
#include <stdio.h>
#include <signal.h>
#include <netinet/in.h>
#include <arpa/inet.h>
#include <sys/socket.h>

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

static const int PORT = 9995;
static char g_szWriteMsg[256] = {0};
static char g_szReadMsg[256] = {0};
static int g_iCnt = 0;
static void conn_writecb(struct bufferevent *, void *);
static void conn_readcb(struct bufferevent *, void *);
static void conn_eventcb(struct bufferevent *, short, void *);

int
main(int argc, char **argv)
{
	struct event_base *base;

	struct sockaddr_in sin;

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

	memset(&sin, 0, sizeof(sin));
	sin.sin_addr.s_addr = inet_addr("192.168.233.250");
	sin.sin_family = AF_INET;
	sin.sin_port = htons(PORT);
	
	struct bufferevent* bev = bufferevent_socket_new(base, -1, BEV_OPT_CLOSE_ON_FREE);
	if (bev == NULL )
	{
		fprintf(stderr, "socket init failed\n");
		return 1;
	}
	bufferevent_setcb(bev, conn_readcb, conn_writecb, conn_eventcb, NULL);

	//连接服务端
	int flag = bufferevent_socket_connect(bev, (struct sockaddr*)&sin, sizeof(sin));
	if (-1 == flag )
	{
		fprintf(stderr, "connect failed\n");
		return 1;
	}
	bufferevent_enable(bev, EV_READ | EV_WRITE);

	event_base_dispatch(base);
	event_base_free(base);

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

static void
conn_writecb(struct bufferevent *bev, void *user_data)
{
	//printf("touch conn_writecb\n");
	
//	if ( strlen(g_szWriteMsg) > 0 )
//	{
//		bufferevent_write(bev, g_szWriteMsg, strlen(g_szWriteMsg));
//		memset(g_szWriteMsg, 0x00, sizeof(g_szWriteMsg));
//	}
}

static void
conn_readcb(struct bufferevent *bev, void *user_data)
{
	//printf("touch conn_readcb\n");
	memset(g_szReadMsg, 0x00, sizeof(g_szReadMsg));
	struct evbuffer *input = bufferevent_get_input(bev);
	size_t sz = evbuffer_get_length(input);
	if (sz > 0)
	{
		bufferevent_read(bev, g_szReadMsg, sz);
		printf("ser:>>%s\n", g_szReadMsg);
		memset(g_szWriteMsg, 0, sizeof(g_szWriteMsg));
		snprintf(g_szWriteMsg, sizeof(g_szWriteMsg)-1, "hi server,this count is %d", g_iCnt);
		g_iCnt++;
		//printf("cli:>>");
		//gets(g_szWriteMsg);
		//scanf("%s", g_szWriteMsg);
		bufferevent_write(bev, g_szWriteMsg, strlen(g_szWriteMsg));
	}
}

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*/
	}
	else if(events & BEV_EVENT_CONNECTED)
	{
		//连接成功时走这里，并且要客户端第一次触发读事件后连接才真正建立起来
		printf("connect success\n");
		const char* msg = "hi server,hao are you";
		bufferevent_write(bev, msg, strlen(msg));
		return;
	}
	bufferevent_free(bev);
}

上面服务端和客户端代码使用libevent建立了一个简单的聊天应用，编译时需链接-levent_core。

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