libevent 框架使用例子

Posted 2020-08-19 hgrical_小农

//服务端代码：

#include <stdio.h>
#include <stdlib.h>
#include <errno.h>
#include <assert.h>
#include <unistd.h>
#include <string.h>

 #include <arpa/inet.h>

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

#define LISTEN_PORT 9999
#define LISTEN_BACKLOG 32
#define MAX_LINE 256

void do_accept(evutil_socket_t listener, short event, void *arg);
void read_cb(struct bufferevent *bev, void *arg);
void error_cb(struct bufferevent *bev, short event, void *arg);
void write_cb(struct bufferevent *bev, void *arg);

int main(int argc, char *argv[])
{
if( argc <= 1 )
{
printf( "usage: %s ip_address\n", basename( argv[0] ) );
return 1;
}

const char* ip = argv[1];

evutil_socket_t listener;//用于跨平台表示socket的ID（在Linux下表示的是其文件描述符）
listener = socket(AF_INET, SOCK_STREAM, 0);
assert(listener > 0);
//用于跨平台将socket设置为可重用（实际上是将端口设为可重用)
evutil_make_listen_socket_reuseable(listener);

struct sockaddr_in sin;
bzero( &sin, sizeof( sin ) );
sin.sin_family = AF_INET;
//sin.sin_addr.s_addr = 0;
inet_pton( AF_INET, ip, &sin.sin_addr );
sin.sin_port = htons(LISTEN_PORT);

if (bind(listener, (struct sockaddr *)&sin, sizeof(sin)) < 0) {
perror("bind");
return 1;
}

if (listen(listener, LISTEN_BACKLOG) < 0) {
perror("listen");
return 1;
}

printf ("Listening...\n");
/* 用于跨平台将socket设置为非阻塞,使用bufferevent需要 */
evutil_make_socket_nonblocking(listener);
//主要记录事件的相关属性 创建一个event_base
struct event_base *base = event_base_new();
assert(base != NULL);
/* 创建并绑定一个event */
struct event *listen_event;
//参数：event_base, 监听的socket 描述符listener，事件类型及属性，绑定的回调函数，给回调函数的参数
/*EV_PERSIST参数告诉系统持续的监听sock上的读事件，
不指定这个属性的话，回调函数被触发后,事件会被删除.所以,如果不加该参数，每次要监听该事件时就要重复的调用event_add函数 */
listen_event = event_new(base, listener, EV_READ|EV_PERSIST, do_accept, (void*)base);
/*通过event_add方法启动监听事件
参数：event，超时时间(struct timeval *类型的，NULL表示无超时设置) */
event_add(listen_event, NULL);
/* 进入事件循环,即通过event_base_dispatch方法启动事件循环 */
event_base_dispatch(base);

printf("The End.");
//close(listener);
return 0;
}

void do_accept(evutil_socket_t listener, short event, void *arg)
{
struct event_base *base = (struct event_base *)arg;
evutil_socket_t fd;
struct sockaddr_in sin;
socklen_t slen = sizeof(sin);
fd = accept(listener, (struct sockaddr *)&sin, &slen);
if (fd < 0) {
perror("accept");
return;
}
if (fd > FD_SETSIZE) { //这个if是参考了那个ROT13的例子，貌似是官方的疏漏，从select-based例子里抄过来忘了改
perror("fd > FD_SETSIZE\n");
return;
}

printf("ACCEPT: fd = %u\n", fd);
//关联该sockfd，托管给event_base. BEV_OPT_CLOSE_ON_FREE--释放bufferevent时关闭底层传输端口。这将关闭底层套接字，释放底层bufferevent等。
struct bufferevent *bev = bufferevent_socket_new(base, fd, BEV_OPT_CLOSE_ON_FREE);
//设置读写对应的回调函数
bufferevent_setcb(bev, read_cb, NULL, error_cb, arg);
//启用读写事件,其实是调用了event_add将相应读写事件加入事件监听队列poll.
//如果相应事件不置为true，bufferevent是不会读写数据的
bufferevent_enable(bev, EV_READ|EV_PERSIST);
// 进入bufferevent_setcb回调函数：
// 在read_cb里面从input中读取数据，处理完毕后填充到output中；
// write_cb对于服务端程序，只需要readcb就可以了，可以置为NULL；
// error_cb用于处理一些错误信息
}

void read_cb(struct bufferevent *bev, void *arg)
{
char line[MAX_LINE+1];
int n;
//根据之前已经分配好的bufferevent 获取对应的连接描述符
evutil_socket_t fd = bufferevent_getfd(bev);

while (n = bufferevent_read(bev, line, MAX_LINE), n > 0)
{
line[n] = ‘\0‘;
printf("fd=%u, Server gets the message from client read line: %s\n", fd, line);
//直接将读取的结果,不做任何修改,直接返回给客户端
bufferevent_write(bev, line, n);//方案1
}
}

void write_cb(struct bufferevent *bev, void *arg)
{
printf("HelloWorld\n");//直接空代码即可，因为这里并不会被触发调用
}

void error_cb(struct bufferevent *bev, short event, void *arg)
{
evutil_socket_t fd = bufferevent_getfd(bev);
printf("fd = %u, ", fd);
if (event & BEV_EVENT_TIMEOUT) {
printf("Timed out\n"); //if bufferevent_set_timeouts() called
}
else if (event & BEV_EVENT_EOF) {
printf("connection closed\n");
}
else if (event & BEV_EVENT_ERROR) {
printf("some other error\n");
}
bufferevent_free(bev);
}

 

客户端代码：

//客户端代码

//客户端代码
#include <stdio.h>
#include <stdlib.h>
#include <errno.h>
#include <unistd.h>
#include <string.h>
#include <netinet/in.h>
#include <sys/socket.h>
#include <arpa/inet.h>
#include <sys/types.h>

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

#define SERV_PORT 9999
#define MAX_LINE 1024

void cmd_msg_cb(int fd, short event, void *arg);
void read_cb(struct bufferevent *bev, void *arg);
void error_cb(struct bufferevent *bev, short event, void *arg);

int main(int argc, char *argv[])
{
if(argc < 2)
{
perror("usage: echocli <IPadress>");
return 1;
}

evutil_socket_t sockfd;
if((sockfd = socket(AF_INET, SOCK_STREAM, 0)) < 0)
{
perror("socket\n");
return 1;
}

struct sockaddr_in servaddr;
bzero(&servaddr, sizeof(servaddr));
servaddr.sin_family = AF_INET;
servaddr.sin_port = htons(SERV_PORT);
if(inet_pton(AF_INET, argv[1], &servaddr.sin_addr) < 1)
{
perror("inet_ntop\n");
return 1;
}
if(connect(sockfd, (struct sockaddr *) &servaddr, sizeof(servaddr)) < 0)
{
perror("connect\n");
return 1;
}
evutil_make_socket_nonblocking(sockfd);

printf("Connect to server sucessfully!\n");
// build event base
struct event_base *base = event_base_new();
if(base == NULL)
{
perror("event_base\n");
return 1;
}
//获取通信模式：这里为epoll
const char *eventMechanism = event_base_get_method(base);
printf("Event mechanism used is %s\n", eventMechanism);
printf("sockfd = %d\n", sockfd);

//关联该连接描述符sockfd，托管给event_base.
struct bufferevent *bev = bufferevent_socket_new(base, sockfd, BEV_OPT_CLOSE_ON_FREE);

//声明事件
struct event *ev_cmd;
//创建一个用于监听标准输入的事件ev_cmd
ev_cmd = event_new(base, STDIN_FILENO, EV_READ | EV_PERSIST, cmd_msg_cb, (void *)bev);
//添加到事件队列当中.相当于告诉处理IO的管家，当有我的事件到达时你发给我(调用cmd_msg_cb函数)
event_add(ev_cmd, NULL);

//设置读写对应的回调函数
bufferevent_setcb(bev, read_cb, NULL, error_cb, (void *)ev_cmd);
//使用bufferevent_enable(bev, EV_READ|EV_PERSIST)来启用read事件
bufferevent_enable(bev, EV_READ | EV_PERSIST);

event_base_dispatch(base);

printf("The End.");
return 0;
}

void cmd_msg_cb(int fd, short event, void *arg)
{
char msg[MAX_LINE];
int nread = read(fd, msg, sizeof(msg));
if(nread < 0)
{
perror("stdio read fail\n");
return;
}

struct bufferevent *bev = (struct bufferevent *)arg;
bufferevent_write(bev, msg, nread);
}

void read_cb(struct bufferevent *bev, void *arg)
{
char line[MAX_LINE + 1];
int n;
evutil_socket_t fd = bufferevent_getfd(bev);

while((n = bufferevent_read(bev, line, MAX_LINE)) > 0)
{
line[n] = ‘\0‘;
printf("fd = %u, read from server: %s", fd, line);
}
}

void error_cb(struct bufferevent *bev, short event, void *arg)
{
evutil_socket_t fd = bufferevent_getfd(bev);
printf("fd = %u, ", fd);
if(event & BEV_EVENT_TIMEOUT)
printf("Time out.\n"); // if bufferevent_set_timeouts() is called
else if(event & BEV_EVENT_EOF)
printf("Connection closed.\n");
else if(event & BEV_EVENT_ERROR)
printf("Some other error.\n");
bufferevent_free(bev);

struct event *ev = (struct event *)arg;
event_free(ev);
}

 

一、

1、编译服务端代码：

g++ -o server server.cpp -I/usr/libevent/include -I/usr/libevent/include/event2 -levent

2、编译可客户端代码：

g++ -o client client.cpp -I/usr/libevent/include -I/usr/libevent/include/event2 -levent

程序编码注意事项：

编程编译一定要加上 -I/usr/libevent/include -I/usr/libevent/include/event2 -levent 否则会出现很多未定义和找不到一些头文件的错误

 

二、运行程序如果报错

server: error while loading shared libraries: libevent-2.1.so.4: cannot open shared object file: No such file or directory

则：

1、有可能是装了多个 libevent而导致server无法识别哪一个，解决方法就是卸载掉一个libevent

2、只安装了一个libevent，但是也报这个错，解决方法

     32位系统下：ln -s /usr/libevent/lib/libevent-2.1.so.4  /usr/lib/

　  64位系统下：ln -s /usr/libevent/lib/libevent-2.1.so.4  /usr/lib64/