libevent源码分析：hello-world例子

hello-world是libevent自带的一个例子，这个例子的作用是启动后监听一个端口，对于所有通过这个端口连接上服务器的程序发送一段字符：hello-world，然后关闭连接。

  1 /*
  2 * gcc -g -o hello-world hello-world.c -levent_core
  3 */
  4 #include <sys/socket.h>
  5 #include <netinet/in.h>
  6 #include <arpa/inet.h>
  7 #include <string.h>
  8 #include <errno.h>
  9 #include <stdio.h>
 10 #include <signal.h>
 11 
 12 #include <event2/bufferevent.h>
 13 #include <event2/buffer.h>
 14 #include <event2/listener.h>
 15 #include <event2/util.h>
 16 #include <event2/event.h>
 17 
 18 static const char MESSAGE[] = "Hello, World!\n";
 19 
 20 static const int PORT = 9995;
 21 
 22 static void listener_cb(struct evconnlistener *, evutil_socket_t, struct sockaddr *, int socklen, void *);
 23 static void conn_writecb(struct bufferevent *, void *);
 24 static void conn_eventcb(struct bufferevent *, short, void *);
 25 static void signal_cb(evutil_socket_t, short, void *);
 26 
 27 int main(void)
 28 {
 29     struct event_base *base;
 30     struct evconnlistener *listener;
 31     struct event *signal_event;
 32     
 33     struct sockaddr_in sin;
 34 
 35     base = event_base_new();
 36     if (!base)
 37     {
 38         fprintf(stderr, "Could not initialize libevent\n");
 39         return 1;
 40     }
 41 
 42     memset(&sin, 0, sizeof(sin));
 43     sin.sin_family = AF_INET;
 44     sin.sin_port = htons(PORT);
 45 
 46     listener = evconnlistener_new_bind(base, listener_cb, (void *)base, 
 47             LEV_OPT_REUSEABLE | LEV_OPT_CLOSE_ON_FREE, -1, (struct sockaddr *)&sin, sizeof(sin));
 48 
 49     if (!listener)
 50     {
 51         fprintf(stderr, "Could not create a listener!\n");
 52         return 1;
 53     }
 54     printf("Listening on %d\n", PORT);
 55 
 56     signal_event = evsignal_new(base, SIGINT, signal_cb, (void *)base);
 57 
 58     if (!signal_event || event_add(signal_event, NULL) < 0)
 59     {
 60         fprintf(stderr, "Could not create/add a signal event!\n");
 61         return 1;
 62     }
 63 
 64     event_base_dispatch(base);
 65 
 66     evconnlistener_free(listener);
 67     event_free(signal_event);
 68     event_base_free(base);
 69 
 70     printf("Done!\n");
 71     return 0;
 72 }
 73 
 74 static void listener_cb(struct evconnlistener *listener, evutil_socket_t fd, struct sockaddr *sa, int socklen, void *user_data)
 75 {
 76     struct event_base *base = user_data;
 77     struct bufferevent *bev;
 78     struct sockaddr_in *sa_in = (struct sockaddr_in*)sa;
 79 
 80     bev = bufferevent_socket_new(base, fd, BEV_OPT_CLOSE_ON_FREE);
 81     if (!bev)
 82     {
 83         fprintf(stderr, "Error construction bufferevent!");
 84         event_base_loopbreak(base);
 85         return;
 86     }
 87     printf("Recv a new connection, ip[%s], port[%d]\n", inet_ntoa(sa_in->sin_addr), ntohs(sa_in->sin_port));
 88     bufferevent_setcb(bev, NULL, conn_writecb, conn_eventcb, NULL);
 89     bufferevent_enable(bev, EV_WRITE);
 90     bufferevent_disable(bev, EV_READ);
 91 
 92     bufferevent_write(bev, MESSAGE, strlen(MESSAGE));
 93 }
 94 
 95 
 96 static void conn_writecb(struct bufferevent *bev, void *user_data)
 97 {
 98     struct evbuffer *output = bufferevent_get_output(bev);
 99     if (evbuffer_get_length(output) == 0)
100     {
101         printf("flushed answer\n");
102         bufferevent_free(bev);
103     }
104 }
105 
106 static void conn_eventcb(struct bufferevent *bev, short events, void *user_data)
107 {
108     if (events & BEV_EVENT_EOF)
109     {
110         printf("Connection closed.\n");
111     }
112     else if (events & BEV_EVENT_ERROR)
113     {
114         printf("Got an error on the connection: %s\n", strerror(errno));
115     }
116 
117     bufferevent_free(bev);
118 }
119 
120 static void signal_cb(evutil_socket_t sig, short events, void *user_data)
121 {
122     struct event_base *base = user_data;
123     struct timeval delay = { 2, 0 };
124     printf("Caught an interrupt signal; exiting cleanly in two seconds\n");
125     event_base_loopexit(base, &delay);
126 }

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