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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《》。假如读者还想了解libevent的具体实现，可以阅读《》系统文章。
不说这么多了，直接上代码。
初等：
客户端代码：
#include#include #include #include #include #include #include #include #include #include #include int tcp_connect_server(const char* server_ip, int port); void cmd_msg_cb(int fd, short events, void* arg); void socket_read_cb(int fd, short events, void *arg); int main(int argc, char** argv) { if( argc < 3 ) { printf("please input 2 parameter\n"); 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\n"); struct event_base* base = event_base_new(); struct event *ev_sockfd = event_new(base, sockfd, EV_READ | EV_PERSIST, socket_read_cb, NULL); event_add(ev_sockfd, NULL); //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*)&sockfd); event_add(ev_cmd, NULL); event_base_dispatch(base); printf("finished \n"); 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); } int sockfd = *((int*)arg); //把终端的消息发送给服务器端 //为了简单起见，不考虑写一半数据的情况 write(sockfd, msg, ret); } void socket_read_cb(int fd, short events, void *arg) { char msg[1024]; //为了简单起见，不考虑读一半数据的情况 int len = read(fd, msg, sizeof(msg)-1); if( len <= 0 ) { perror("read fail "); exit(1); } msg[len] = '\0'; printf("recv %s from server\n", msg); } 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#include #include #include #include void accept_cb(int fd, short events, void* arg); void socket_read_cb(int fd, short events, 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); 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\n", sockfd); struct event_base* base = (event_base*)arg; //仅仅是为了动态创建一个event结构体 struct event *ev = event_new(NULL, -1, 0, NULL, NULL); //将动态创建的结构体作为event的回调参数 event_assign(ev, base, sockfd, EV_READ | EV_PERSIST, socket_read_cb, (void*)ev); event_add(ev, NULL); } void socket_read_cb(int fd, short events, void *arg) { char msg[4096]; struct event *ev = (struct event*)arg; int len = read(fd, msg, sizeof(msg) - 1); if( len <= 0 ) { printf("some error happen when read\n"); event_free(ev); close(fd); return ; } msg[len] = '\0'; printf("recv the client msg: %s", msg); char reply_msg[4096] = "I have recvieced the msg: "; strcat(reply_msg + strlen(reply_msg), msg); write(fd, reply_msg, strlen(reply_msg) ); } 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; }
中等：
客户端代码：
#include#include #include #include #include #include #include #include #include #include #include #include #include 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\n"); 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\n"); 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 \n"); 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] = '\0'; printf("recv %s from server\n", msg); } void event_cb(struct bufferevent *bev, short event, void *arg) { if (event & BEV_EVENT_EOF) printf("connection closed\n"); else if (event & BEV_EVENT_ERROR) printf("some other error\n"); //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#include #include #include #include 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\n", 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] = '\0'; 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\n"); else if (event & BEV_EVENT_ERROR) printf("some other error\n"); //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：
#include#include #include #include #include #include #include #include #include #include #include #include #include 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 ) { //两个参数依次是服务器端的IP地址、端口号 printf("please input 2 parameter\n"); return -1; } struct event_base *base = event_base_new(); struct bufferevent* bev = bufferevent_socket_new(base, -1, 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); struct sockaddr_in server_addr; memset(&server_addr, 0, sizeof(server_addr) ); server_addr.sin_family = AF_INET; server_addr.sin_port = htons(atoi(argv[2])); inet_aton(argv[1], &server_addr.sin_addr); bufferevent_socket_connect(bev, (struct sockaddr *)&server_addr, sizeof(server_addr)); 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 \n"); 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] = '\0'; printf("recv %s from server\n", msg); } void event_cb(struct bufferevent *bev, short event, void *arg) { if (event & BEV_EVENT_EOF) printf("connection closed\n"); else if (event & BEV_EVENT_ERROR) printf("some other error\n"); else if( event & BEV_EVENT_CONNECTED) { printf("the client has connected to server\n"); return ; } //这将自动close套接字和free读写缓冲区 bufferevent_free(bev); struct event *ev = (struct event*)arg; event_free(ev); }
服务器端代码：
#include#include #include #include #include #include #include #include #include void listener_cb(evconnlistener *listener, evutil_socket_t fd, struct sockaddr *sock, int socklen, void *arg); void socket_read_cb(bufferevent *bev, void *arg); void socket_event_cb(bufferevent *bev, short events, void *arg); int main() { //evthread_use_pthreads();//enable threads struct sockaddr_in sin; memset(&sin, 0, sizeof(struct sockaddr_in)); sin.sin_family = AF_INET; sin.sin_port = htons(9999); event_base *base = event_base_new(); evconnlistener *listener = evconnlistener_new_bind(base, listener_cb, base, LEV_OPT_REUSEABLE|LEV_OPT_CLOSE_ON_FREE, 10, (struct sockaddr*)&sin, sizeof(struct sockaddr_in)); event_base_dispatch(base); evconnlistener_free(listener); event_base_free(base); return 0; } //一个新客户端连接上服务器了 //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 //文件描述符为fd void listener_cb(evconnlistener *listener, evutil_socket_t fd, struct sockaddr *sock, int socklen, void *arg) { printf("accept a client %d\n", fd); event_base *base = (event_base*)arg; //为这个客户端分配一个bufferevent bufferevent *bev = bufferevent_socket_new(base, fd, BEV_OPT_CLOSE_ON_FREE); bufferevent_setcb(bev, socket_read_cb, NULL, socket_event_cb, NULL); 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)-1 ); msg[len] = '\0'; printf("server read the data %s\n", msg); char reply[] = "I has read your data"; bufferevent_write(bev, reply, strlen(reply) ); } void socket_event_cb(bufferevent *bev, short events, void *arg) { if (events & BEV_EVENT_EOF) printf("connection closed\n"); else if (events & BEV_EVENT_ERROR) printf("some other error\n"); //这将自动close套接字和free读写缓冲区 bufferevent_free(bev); }
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