Libevent使用例子，从简单到复杂

本文从简单到复杂，展示如何使用libevent。网上的许多例子都是只有服务器端的，本文里面客户端和服务器端都有，以飨读者。

关于libevent编程时的一些疑问可以阅读《libevent编程疑难解答》。假如读者还想了解libevent的具体实现，可以阅读《libevent源码分析》系统文章。

不说这么多了，直接上代码。

初等：

客户端代码：

  1 #include<sys/types.h>
  2 #include<sys/socket.h>
  3 #include<netinet/in.h>
  4 #include<arpa/inet.h>
  5 #include<errno.h>
  6 #include<unistd.h>
  7 
  8 #include<stdio.h>
  9 #include<string.h>
 10 #include<stdlib.h>
 11 
 12 #include<event.h>
 13 #include<event2/util.h>
 14 
 15 
 16 
 17 
 18 int tcp_connect_server(const char* server_ip, int port);
 19 
 20 
 21 void cmd_msg_cb(int fd, short events, void* arg);
 22 void socket_read_cb(int fd, short events, void *arg);
 23 
 24 int main(int argc, char** argv)
 25 {
 26     if( argc < 3 )
 27     {
 28         printf("please input 2 parameter
");
 29         return -1;
 30     }
 31 
 32 
 33     //两个参数依次是服务器端的IP地址、端口号
 34     int sockfd = tcp_connect_server(argv[1], atoi(argv[2]));
 35     if( sockfd == -1)
 36     {
 37         perror("tcp_connect error ");
 38         return -1;
 39     }
 40 
 41     printf("connect to server successful
");
 42 
 43     struct event_base* base = event_base_new();
 44 
 45     struct event *ev_sockfd = event_new(base, sockfd,
 46                                         EV_READ | EV_PERSIST,
 47                                         socket_read_cb, NULL);
 48     event_add(ev_sockfd, NULL);
 49 
 50     //监听终端输入事件
 51     struct event* ev_cmd = event_new(base, STDIN_FILENO,
 52                                       EV_READ | EV_PERSIST, cmd_msg_cb,
 53                                       (void*)&sockfd);
 54 
 55 
 56     event_add(ev_cmd, NULL);
 57 
 58     event_base_dispatch(base);
 59 
 60     printf("finished 
");
 61     return 0;
 62 }
 63 
 64 
 65 
 66 
 67 
 68 
 69 void cmd_msg_cb(int fd, short events, void* arg)
 70 {
 71     char msg[1024];
 72 
 73     int ret = read(fd, msg, sizeof(msg));
 74     if( ret <= 0 )
 75     {
 76         perror("read fail ");
 77         exit(1);
 78     }
 79 
 80     int sockfd = *((int*)arg);
 81 
 82     //把终端的消息发送给服务器端
 83     //为了简单起见，不考虑写一半数据的情况
 84     write(sockfd, msg, ret);
 85 }
 86 
 87 
 88 void socket_read_cb(int fd, short events, void *arg)
 89 {
 90     char msg[1024];
 91 
 92     //为了简单起见，不考虑读一半数据的情况
 93     int len = read(fd, msg, sizeof(msg)-1);
 94     if( len <= 0 )
 95     {
 96         perror("read fail ");
 97         exit(1);
 98     }
 99 
100     msg[len] = '';
101 
102     printf("recv %s from server
", msg);
103 }
104 
105 
106 
107 typedef struct sockaddr SA;
108 int tcp_connect_server(const char* server_ip, int port)
109 {
110     int sockfd, status, save_errno;
111     struct sockaddr_in server_addr;
112 
113     memset(&server_addr, 0, sizeof(server_addr) );
114 
115     server_addr.sin_family = AF_INET;
116     server_addr.sin_port = htons(port);
117     status = inet_aton(server_ip, &server_addr.sin_addr);
118 
119     if( status == 0 ) //the server_ip is not valid value
120     {
121         errno = EINVAL;
122         return -1;
123     }
124 
125     sockfd = ::socket(PF_INET, SOCK_STREAM, 0);
126     if( sockfd == -1 )
127         return sockfd;
128 
129 
130     status = ::connect(sockfd, (SA*)&server_addr, sizeof(server_addr) );
131 
132     if( status == -1 )
133     {
134         save_errno = errno;
135         ::close(sockfd);
136         errno = save_errno; //the close may be error
137         return -1;
138     }
139 
140     evutil_make_socket_nonblocking(sockfd);
141 
142     return sockfd;
143 }

服务器端代码：

  1 #include<stdio.h>
  2 #include<string.h>
  3 #include<errno.h>
  4 
  5 #include<unistd.h>
  6 #include<event.h>
  7 
  8 
  9 
 10 void accept_cb(int fd, short events, void* arg);
 11 void socket_read_cb(int fd, short events, void *arg);
 12 
 13 int tcp_server_init(int port, int listen_num);
 14 
 15 int main(int argc, char** argv)
 16 {
 17 
 18     int listener = tcp_server_init(9999, 10);
 19     if( listener == -1 )
 20     {
 21         perror(" tcp_server_init error ");
 22         return -1;
 23     }
 24 
 25     struct event_base* base = event_base_new();
 26 
 27     //添加监听客户端请求连接事件
 28     struct event* ev_listen = event_new(base, listener, EV_READ | EV_PERSIST,
 29                                         accept_cb, base);
 30     event_add(ev_listen, NULL);
 31 
 32 
 33     event_base_dispatch(base);
 34 
 35     return 0;
 36 }
 37 
 38 
 39 
 40 void accept_cb(int fd, short events, void* arg)
 41 {
 42     evutil_socket_t sockfd;
 43 
 44     struct sockaddr_in client;
 45     socklen_t len = sizeof(client);
 46 
 47     sockfd = ::accept(fd, (struct sockaddr*)&client, &len );
 48     evutil_make_socket_nonblocking(sockfd);
 49 
 50     printf("accept a client %d
", sockfd);
 51 
 52     struct event_base* base = (event_base*)arg;
 53 
 54     //仅仅是为了动态创建一个event结构体
 55     struct event *ev = event_new(NULL, -1, 0, NULL, NULL);
 56     //将动态创建的结构体作为event的回调参数
 57     event_assign(ev, base, sockfd, EV_READ | EV_PERSIST,
 58                  socket_read_cb, (void*)ev);
 59 
 60     event_add(ev, NULL);
 61 }
 62 
 63 
 64 void socket_read_cb(int fd, short events, void *arg)
 65 {
 66     char msg[4096];
 67     struct event *ev = (struct event*)arg;
 68     int len = read(fd, msg, sizeof(msg) - 1);
 69 
 70 
 71 
 72     if( len <= 0 )
 73     {
 74         printf("some error happen when read
");
 75         event_free(ev);
 76         close(fd);
 77         return ;
 78     }
 79 
 80     msg[len] = '';
 81     printf("recv the client msg: %s", msg);
 82 
 83     char reply_msg[4096] = "I have recvieced the msg: ";
 84     strcat(reply_msg + strlen(reply_msg), msg);
 85 
 86     write(fd, reply_msg, strlen(reply_msg) );
 87 }
 88 
 89 
 90 
 91 typedef struct sockaddr SA;
 92 int tcp_server_init(int port, int listen_num)
 93 {
 94     int errno_save;
 95     evutil_socket_t listener;
 96 
 97     listener = ::socket(AF_INET, SOCK_STREAM, 0);
 98     if( listener == -1 )
 99         return -1;
100 
101     //允许多次绑定同一个地址。要用在socket和bind之间
102     evutil_make_listen_socket_reuseable(listener);
103 
104     struct sockaddr_in sin;
105     sin.sin_family = AF_INET;
106     sin.sin_addr.s_addr = 0;
107     sin.sin_port = htons(port);
108 
109     if( ::bind(listener, (SA*)&sin, sizeof(sin)) < 0 )
110         goto error;
111 
112     if( ::listen(listener, listen_num) < 0)
113         goto error;
114 
115 
116     //跨平台统一接口，将套接字设置为非阻塞状态
117     evutil_make_socket_nonblocking(listener);
118 
119     return listener;
120 
121     error:
122         errno_save = errno;
123         evutil_closesocket(listener);
124         errno = errno_save;
125 
126         return -1;
127 }

中等：

客户端代码：

#include<sys/types.h>
#include<sys/socket.h>
#include<netinet/in.h>
#include<arpa/inet.h>
#include<errno.h>
#include<unistd.h>

#include<stdio.h>
#include<string.h>
#include<stdlib.h>

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




int tcp_connect_server(const char* server_ip, int port);


void cmd_msg_cb(int fd, short events, void* arg);
void server_msg_cb(struct bufferevent* bev, void* arg);
void event_cb(struct bufferevent *bev, short event, void *arg);

int main(int argc, char** argv)
{
    if( argc < 3 )
    {
        printf("please input 2 parameter
");
        return -1;
    }


    //两个参数依次是服务器端的IP地址、端口号
    int sockfd = tcp_connect_server(argv[1], atoi(argv[2]));
    if( sockfd == -1)
    {
        perror("tcp_connect error ");
        return -1;
    }

    printf("connect to server successful
");

    struct event_base* base = event_base_new();

    struct bufferevent* bev = bufferevent_socket_new(base, sockfd,
                                                     BEV_OPT_CLOSE_ON_FREE);

    //监听终端输入事件
    struct event* ev_cmd = event_new(base, STDIN_FILENO,
                                      EV_READ | EV_PERSIST, cmd_msg_cb,
                                      (void*)bev);
    event_add(ev_cmd, NULL);

    //当socket关闭时会用到回调参数
    bufferevent_setcb(bev, server_msg_cb, NULL, event_cb, (void*)ev_cmd);
    bufferevent_enable(bev, EV_READ | EV_PERSIST);


    event_base_dispatch(base);

    printf("finished 
");
    return 0;
}






void cmd_msg_cb(int fd, short events, void* arg)
{
    char msg[1024];

    int ret = read(fd, msg, sizeof(msg));
    if( ret < 0 )
    {
        perror("read fail ");
        exit(1);
    }

    struct bufferevent* bev = (struct bufferevent*)arg;

    //把终端的消息发送给服务器端
    bufferevent_write(bev, msg, ret);
}


void server_msg_cb(struct bufferevent* bev, void* arg)
{
    char msg[1024];

    size_t len = bufferevent_read(bev, msg, sizeof(msg));
    msg[len] = '';

    printf("recv %s from server
", msg);
}


void event_cb(struct bufferevent *bev, short event, void *arg)
{

    if (event & BEV_EVENT_EOF)
        printf("connection closed
");
    else if (event & BEV_EVENT_ERROR)
        printf("some other error
");

    //这将自动close套接字和free读写缓冲区
    bufferevent_free(bev);

    struct event *ev = (struct event*)arg;
    //因为socket已经没有，所以这个event也没有存在的必要了
    event_free(ev);
}


typedef struct sockaddr SA;
int tcp_connect_server(const char* server_ip, int port)
{
    int sockfd, status, save_errno;
    struct sockaddr_in server_addr;

    memset(&server_addr, 0, sizeof(server_addr) );

    server_addr.sin_family = AF_INET;
    server_addr.sin_port = htons(port);
    status = inet_aton(server_ip, &server_addr.sin_addr);

    if( status == 0 ) //the server_ip is not valid value
    {
        errno = EINVAL;
        return -1;
    }

    sockfd = ::socket(PF_INET, SOCK_STREAM, 0);
    if( sockfd == -1 )
        return sockfd;


    status = ::connect(sockfd, (SA*)&server_addr, sizeof(server_addr) );

    if( status == -1 )
    {
        save_errno = errno;
        ::close(sockfd);
        errno = save_errno; //the close may be error
        return -1;
    }

    evutil_make_socket_nonblocking(sockfd);

    return sockfd;
}

服务器端代码：

#include<stdio.h>
#include<string.h>
#include<errno.h>

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



void accept_cb(int fd, short events, void* arg);
void socket_read_cb(bufferevent* bev, void* arg);
void event_cb(struct bufferevent *bev, short event, void *arg);
int tcp_server_init(int port, int listen_num);

int main(int argc, char** argv)
{

    int listener = tcp_server_init(9999, 10);
    if( listener == -1 )
    {
        perror(" tcp_server_init error ");
        return -1;
    }

    struct event_base* base = event_base_new();

    //添加监听客户端请求连接事件
    struct event* ev_listen = event_new(base, listener, EV_READ | EV_PERSIST,
                                        accept_cb, base);
    event_add(ev_listen, NULL);


    event_base_dispatch(base);
    event_base_free(base);


    return 0;
}



void accept_cb(int fd, short events, void* arg)
{
    evutil_socket_t sockfd;

    struct sockaddr_in client;
    socklen_t len = sizeof(client);

    sockfd = ::accept(fd, (struct sockaddr*)&client, &len );
    evutil_make_socket_nonblocking(sockfd);

    printf("accept a client %d
", sockfd);

    struct event_base* base = (event_base*)arg;

    bufferevent* bev = bufferevent_socket_new(base, sockfd, BEV_OPT_CLOSE_ON_FREE);
    bufferevent_setcb(bev, socket_read_cb, NULL, event_cb, arg);

    bufferevent_enable(bev, EV_READ | EV_PERSIST);
}



void socket_read_cb(bufferevent* bev, void* arg)
{
    char msg[4096];

    size_t len = bufferevent_read(bev, msg, sizeof(msg));

    msg[len] = '';
    printf("recv the client msg: %s", msg);


    char reply_msg[4096] = "I have recvieced the msg: ";

    strcat(reply_msg + strlen(reply_msg), msg);
    bufferevent_write(bev, reply_msg, strlen(reply_msg));
}



void event_cb(struct bufferevent *bev, short event, void *arg)
{

    if (event & BEV_EVENT_EOF)
        printf("connection closed
");
    else if (event & BEV_EVENT_ERROR)
        printf("some other error
");

    //这将自动close套接字和free读写缓冲区
    bufferevent_free(bev);
}


typedef struct sockaddr SA;
int tcp_server_init(int port, int listen_num)
{
    int errno_save;
    evutil_socket_t listener;

    listener = ::socket(AF_INET, SOCK_STREAM, 0);
    if( listener == -1 )
        return -1;

    //允许多次绑定同一个地址。要用在socket和bind之间
    evutil_make_listen_socket_reuseable(listener);

    struct sockaddr_in sin;
    sin.sin_family = AF_INET;
    sin.sin_addr.s_addr = 0;
    sin.sin_port = htons(port);

    if( ::bind(listener, (SA*)&sin, sizeof(sin)) < 0 )
        goto error;

    if( ::listen(listener, listen_num) < 0)
        goto error;


    //跨平台统一接口，将套接字设置为非阻塞状态
    evutil_make_socket_nonblocking(listener);

    return listener;

    error:
        errno_save = errno;
        evutil_closesocket(listener);
        errno = errno_save;

        return -1;
}

高等：

客户端代码：

  1 #include<sys/types.h>
  2 #include<sys/socket.h>
  3 #include<netinet/in.h>
  4 #include<arpa/inet.h>
  5 #include<errno.h>
  6 #include<unistd.h>
  7 
  8 #include<stdio.h>
  9 #include<string.h>
 10 #include<stdlib.h>
 11 
 12 #include<event.h>
 13 #include<event2/bufferevent.h>
 14 #include<event2/buffer.h>
 15 #include<event2/util.h>
 16 
 17 
 18 
 19 
 20 int tcp_connect_server(const char* server_ip, int port);
 21 
 22 
 23 void cmd_msg_cb(int fd, short events, void* arg);
 24 void server_msg_cb(struct bufferevent* bev, void* arg);
 25 void event_cb(struct bufferevent *bev, short event, void *arg);
 26 
 27 int main(int argc, char** argv)
 28 {
 29     if( argc < 3 )
 30     {
 31         //两个参数依次是服务器端的IP地址、端口号
 32         printf("please input 2 parameter
");
 33         return -1;
 34     }
 35 
 36     struct event_base *base = event_base_new();
 37 
 38     struct bufferevent* bev = bufferevent_socket_new(base, -1,
 39                                                      BEV_OPT_CLOSE_ON_FREE);
 40 
 41     //监听终端输入事件
 42     struct event* ev_cmd = event_new(base, STDIN_FILENO,
 43                                      EV_READ | EV_PERSIST,
 44                                      cmd_msg_cb, (void*)bev);
 45 
 46 
 47     event_add(ev_cmd, NULL);
 48 
 49     struct sockaddr_in server_addr;
 50 
 51     memset(&server_addr, 0, sizeof(server_addr) );
 52 
 53     server_addr.sin_family = AF_INET;
 54     server_addr.sin_port = htons(atoi(argv[2]));
 55     inet_aton(argv[1], &server_addr.sin_addr);
 56 
 57     bufferevent_socket_connect(bev, (struct sockaddr *)&server_addr,
 58                                sizeof(server_addr));
 59 
 60 
 61     bufferevent_setcb(bev, server_msg_cb, NULL, event_cb, (void*)ev_cmd);
 62     bufferevent_enable(bev, EV_READ | EV_PERSIST);
 63 
 64 
 65 
 66     event_base_dispatch(base);
 67 
 68     printf("finished 
");
 69     return 0;
 70 }
 71 
 72 
 73 
 74 
 75 
 76 void cmd_msg_cb(int fd, short events, void* arg)
 77 {
 78     char msg[1024];
 79 
 80     int ret = read(fd, msg, sizeof(msg));
 81     if( ret < 0 )
 82     {
 83         perror("read fail ");
 84         exit(1);
 85     }
 86 
 87     struct bufferevent* bev = (struct bufferevent*)arg;
 88 
 89     //把终端的消息发送给服务器端
 90     bufferevent_write(bev, msg, ret);
 91 }
 92 
 93 
 94 void server_msg_cb(struct bufferevent* bev, void* arg)
 95 {
 96     char msg[1024];
 97 
 98     size_t len = bufferevent_read(bev, msg, sizeof(msg));
 99     msg[len] = '';
100 
101     printf("recv %s from server
", msg);
102 }
103 
104 
105 void event_cb(struct bufferevent *bev, short event, void *arg)
106 {
107 
108     if (event & BEV_EVENT_EOF)
109         printf("connection closed
");
110     else if (event & BEV_EVENT_ERROR)
111         printf("some other error
");
112     else if( event & BEV_EVENT_CONNECTED)
113     {
114         printf("the client has connected to server
");
115         return ;
116     }
117 
118     //这将自动close套接字和free读写缓冲区
119     bufferevent_free(bev);
120 
121     struct event *ev = (struct event*)arg;
122     event_free(ev);
123 }

服务器端代码：

 1 #include<netinet/in.h>  
 2 #include<sys/socket.h>  
 3 #include<unistd.h>  
 4   
 5 #include<stdio.h>  
 6 #include<string.h>  
 7   
 8 #include<event.h>  
 9 #include<listener.h>  
10 #include<bufferevent.h>  
11 #include<thread.h>  
12   
13   
14 void listener_cb(evconnlistener *listener, evutil_socket_t fd,  
15                  struct sockaddr *sock, int socklen, void *arg);  
16   
17 void socket_read_cb(bufferevent *bev, void *arg);  
18 void socket_event_cb(bufferevent *bev, short events, void *arg);  
19   
20 int main()  
21 {  
22     //evthread_use_pthreads();//enable threads  
23   
24     struct sockaddr_in sin;  
25     memset(&sin, 0, sizeof(struct sockaddr_in));  
26     sin.sin_family = AF_INET;  
27     sin.sin_port = htons(9999);  
28   
29     event_base *base = event_base_new();  
30     evconnlistener *listener  
31             = evconnlistener_new_bind(base, listener_cb, base,  
32                                       LEV_OPT_REUSEABLE|LEV_OPT_CLOSE_ON_FREE,  
33                                       10, (struct sockaddr*)&sin,  
34                                       sizeof(struct sockaddr_in));  
35   
36     event_base_dispatch(base);  
37   
38     evconnlistener_free(listener);  
39     event_base_free(base);  
40   
41     return 0;  
42 }  
43   
44   
45 //一个新客户端连接上服务器了  
46 //当此函数被调用时，libevent已经帮我们accept了这个客户端。该客户端的
47 //文件描述符为fd
48 void listener_cb(evconnlistener *listener, evutil_socket_t fd,  
49                  struct sockaddr *sock, int socklen, void *arg)  
50 {  
51     printf("accept a client %d
", fd);  
52   
53     event_base *base = (event_base*)arg;  
54   
55     //为这个客户端分配一个bufferevent  
56     bufferevent *bev =  bufferevent_socket_new(base, fd,  
57                                                BEV_OPT_CLOSE_ON_FREE);  
58   
59     bufferevent_setcb(bev, socket_read_cb, NULL, socket_event_cb, NULL);  
60     bufferevent_enable(bev, EV_READ | EV_PERSIST);  
61 }  
62   
63   
64 void socket_read_cb(bufferevent *bev, void *arg)  
65 {  
66     char msg[4096];  
67   
68     size_t len = bufferevent_read(bev, msg, sizeof(msg)-1 );  
69   
70     msg[len] = '';  
71     printf("server read the data %s
", msg);  
72   
73     char reply[] = "I has read your data";  
74     bufferevent_write(bev, reply, strlen(reply) );  
75 }  
76   
77   
78 void socket_event_cb(bufferevent *bev, short events, void *arg)  
79 {  
80     if (events & BEV_EVENT_EOF)  
81         printf("connection closed
");  
82     else if (events & BEV_EVENT_ERROR)  
83         printf("some other error
");  
84   
85     //这将自动close套接字和free读写缓冲区  
86     bufferevent_free(bev);  
87 }

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原文地址：https://www.cnblogs.com/mayingkun/p/7292002.html