libevent简单服务端和客户端实现

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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