libevent学习---简单http server实现

﹏ヽ暗。殇╰゛Y 2022-06-17 11:11 288阅读 0赞

在`libevent`中有`evhttp`实现了`http server`，看了一下，4000多行代码。

其实实现一个http server的步骤很简单，无非就是业务上的内容，至于优化和性能都是写代码及架构设计模式的问题，这部分我太菜了就不说了。

简单说下这篇博文的思路：  
1.作为一个简单的`HTTP server`，在`read callback`里面，直接`write http request`到标准输出。  
2.另外在`read callback`里面，向`libevent`中提供的`evbuffer` 里面构造响应，http响应由如下内容组成：

> (a) 响应行：状态 相应码等  
> (b) 响应头：这里我就写了Server Content-Type Content-Length等  
> (c) 响应报文：简单的h5代码，用两个\\r\\n和response head隔开

代码见:[gayhub][]

#include <stdio.h>
    #include <stdlib.h>
    #include <errno.h>
    #include <assert.h>
    #include <unistd.h>
    #include <signal.h>
    
    #include <event2/event.h>
    #include <event2/bufferevent.h>
    #include <event2/buffer.h>
    #include <sys/socket.h>
    #include <string.h>
    
    #include <netinet/in.h>
    #include <netdb.h>
    
    void errorcb(struct bufferevent*bev,short events,void *ptr)
    {
        printf("in errorcb\r\n");
        if(events&BEV_EVENT_CONNECTED)
        {
        printf("ok connected\r\n");
        }
        else if(events&(BEV_EVENT_ERROR|BEV_EVENT_EOF))
        {
        struct event_base *base=ptr;
        printf("closing... \r\n");
        bufferevent_free(bev);
    
        event_base_loopexit(base,NULL);
        }
    }
    
    void readcb(struct bufferevent*bev,void *arg )
    {
        printf("in readcb\r\n");
        struct evbuffer *input;
        struct evbuffer *output;
        char *request_line;
        size_t len;
        input = bufferevent_get_input(bev);
        output = bufferevent_get_output(bev);
    
    
        size_t input_len = evbuffer_get_length(input);
        while(1)
        {
        request_line = evbuffer_readln(input,&len,EVBUFFER_EOL_CRLF);
    
        if(NULL==request_line)
        {
            //printf("evbuffer_readln error\r\n");
            free(request_line);
            break;
        }
        else
        {
            char request_buf[256];
            snprintf(request_buf,len+5,"> %s\r\n",request_line);
            write(1,request_buf,strlen(request_buf));
        }
        }
        //构造响应报文
        char content[]="<html><head><title>This is title</title></head><body><h1>Hello</h1></body></html>";
        char tmp[]="HTTP/1.1 200 OK\r\nServer: ZhangXiao\r\nContent-Length: %d\r\nContent-Type: text/html\r\n\r\n%s";
        int contentlen=strlen(content);
        char response[256];
    
        snprintf(response,256,tmp,contentlen,content);
        char *p = response;
        evbuffer_add(output,p,strlen(response));
    
    
        free(request_line);
    
    }
    
    void do_accept(evutil_socket_t listener,short event,void*arg)
    {
        printf("in accept\r\n");
        struct event_base *base = (struct event_base *)arg;
        struct sockaddr_in ss;
        socklen_t slen = sizeof(ss);
        int fd = accept(listener,(struct sockaddr *)&ss,&slen);
        assert(fd>0);
    
    
        struct bufferevent *bev;
        evutil_make_socket_nonblocking(fd);
        //使用buffer_socket_new创建一个struct bufferevent*，关联fd
        //托管给event_base，BEV_OPT_CLOSE_ON_FREE表示释放bufferevent的时候
        //关闭底层套接字等...
        bev = bufferevent_socket_new(base,fd,BEV_OPT_CLOSE_ON_FREE);
    
    
        //设置对应的回调函数
        bufferevent_setcb(bev,readcb,NULL,errorcb,base);
    
        bufferevent_enable(bev,EV_READ|EV_WRITE);//event_add
    }
    
    int main(int argc,char **argv)
    {
        evutil_socket_t listener;
        struct sockaddr_in sin;
        struct event_base *base;
        struct event* listener_event;
    
        base = event_base_new();
        assert(NULL!=base);
    
        sin.sin_family = AF_INET;
        sin.sin_addr.s_addr = 0;
        sin.sin_port=htons(1025);
    
        listener = socket(AF_INET,SOCK_STREAM,0);
        assert(listener>0);
    
        evutil_make_socket_nonblocking(listener);//fcntl的封装
    
        if(bind(listener,(struct sockaddr*)&sin,sizeof(sin))<0)
        {
        perror("bind");
        return -1;
        }
    
        if(listen(listener,16)<0)
        {
        perror("listen");
        return -1;
        }
    
        listener_event=event_new(base,listener,EV_READ|EV_PERSIST,do_accept,(void*)base);
        event_add(listener_event,NULL);//add to pending event lists
        event_base_dispatch(base);
        return 0;
    }

[gayhub]: https://github.com/NearXdu/LibEvent