最近在工作中使用到了libenevt封装的http，在做curl模拟get/post请求时遇到了一些问题，今天就记录下正确的http服务端处理方法，欢迎观摩。
一、libevent介绍
首先，咱们简单介绍下libevent。
libevent就是一个基于事件通知机制的库，支持/dev/poll、kqueue、event ports、select、poll和epoll事件机制，也因此它是一个跨操作系统的库（支持Linux、*BSD、Mac OS X、Solaris、Windows等）。目前应用该库的有Chromium、Memcached、NTP、tmux等应用。
libevent 库实际上没有更换select()、poll()或其他机制的基础，而是使用对于每个平台最高效的高性能解决方案，在其实现外加上一个包装器。
为了实际处理每个请求，libevent 库提供一种事件机制，它作为底层网络后端的包装器。事件系统让为连接添加处理函数变得非常简便，同时降低了底层 I/O 复杂性。这是 libevent 系统的核心。
libevent 库的其他组件提供其他功能，包括缓冲的事件系统（用于缓冲发送到客户端/从客户端接收的数据）以及 HTTP、DNS 和 RPC 系统的核心实现。
另外，libevent库非常轻量级，这让我们学习它的源码难度低了不少。
二、libevent安装
官网：/
选择最新版本下载，然后安装README文件中描述的方法编译、安装即可。
./configure 或 ./configure -prefix=/usr //prefix表示输出文件路径makemake verify # 可选操作make install# ls -al /usr/lib | grep libevent//测试libevent是否安装成功
安装完成后，就可以编码http服务器了。
三、libevent http服务器实例
#include <stdio.h>#include <stdlib.h>#include <evhttp.h>#include <event.h>#include <string.h>#include "event2/http.h"#include "event2/event.h"#include "event2/buffer.h"#include "event2/bufferevent.h"#include "event2/bufferevent_compat.h"#include "event2/http_struct.h"#include "event2/http_compat.h"#include "event2/util.h"#include "event2/listener.h"#define BUF_MAX 1024*16//解析post请求数据void get_post_message(char *buf, struct evhttp_request *req){size_t post_size = 0;post_size = evbuffer_get_length(req->input_buffer);//获取数据长度printf("====line:%d,post len:%d\n",__LINE__,post_size);if (post_size <= 0){printf("====line:%d,post msg is empty!\n",__LINE__);return;}else{size_t copy_len = post_size > BUF_MAX ? BUF_MAX : post_size;printf("====line:%d,post len:%d, copy_len:%d\n",__LINE__,post_size,copy_len);memcpy(buf, evbuffer_pullup(req->input_buffer,-1), copy_len);buf[post_size] = '\0';printf("====line:%d,post msg:%s\n",__LINE__,buf);}}//解析http头，主要用于get请求时解析uri和请求参数char *find_http_header(struct evhttp_request *req,struct evkeyvalq *params,const char *query_char){if(req == NULL || params == NULL || query_char == NULL){printf("====line:%d,%s\n",__LINE__,"input params is null.");return NULL;}struct evhttp_uri *decoded = NULL;char *query = NULL;char *query_result = NULL;const char *path;const char *uri = evhttp_request_get_uri(req);//获取请求uriif(uri == NULL){printf("====line:%d,evhttp_request_get_uri return null\n",__LINE__);return NULL;}else{printf("====line:%d,Got a GET request for <%s>\n",__LINE__,uri);}//解码uridecoded = evhttp_uri_parse(uri);if (!decoded) {printf("====line:%d,It's not a good URI. Sending BADREQUEST\n",__LINE__);evhttp_send_error(req, HTTP_BADREQUEST, 0);return;}//获取uri中的path部分path = evhttp_uri_get_path(decoded);if (path == NULL) {path = "/";}else{printf("====line:%d,path is:%s\n",__LINE__,path);}//获取uri中的参数部分query = (char*)evhttp_uri_get_query(decoded);if(query == NULL){printf("====line:%d,evhttp_uri_get_query return null\n",__LINE__);return NULL;}//查询指定参数的值evhttp_parse_query_str(query, params);query_result = (char*)evhttp_find_header(params, query_char);return query_result;}//处理get请求void http_handler_testget_msg(struct evhttp_request *req,void *arg){if(req == NULL){printf("====line:%d,%s\n",__LINE__,"input param req is null.");return;}char *sign = NULL;char *data = NULL;struct evkeyvalq sign_params = {0};sign = find_http_header(req,&sign_params,"sign");//获取get请求uri中的sign参数if(sign == NULL){printf("====line:%d,%s\n",__LINE__,"request uri no param sign.");}else{printf("====line:%d,get request param: sign=[%s]\n",__LINE__,sign);}data = find_http_header(req,&sign_params,"data");//获取get请求uri中的data参数if(data == NULL){printf("====line:%d,%s\n",__LINE__,"request uri no param data.");}else{printf("====line:%d,get request param: data=[%s]\n",__LINE__,data);}printf("\n");//回响应struct evbuffer *retbuff = NULL;retbuff = evbuffer_new();if(retbuff == NULL){printf("====line:%d,%s\n",__LINE__,"retbuff is null.");return;}evbuffer_add_printf(retbuff,"Receive get request,Thamks for the request!");evhttp_send_reply(req,HTTP_OK,"Client",retbuff);evbuffer_free(retbuff);}//处理post请求void http_handler_testpost_msg(struct evhttp_request *req,void *arg){if(req == NULL){printf("====line:%d,%s\n",__LINE__,"input param req is null.");return;}char buf[BUF_MAX] = {0};get_post_message(buf, req);//获取请求数据，一般是json格式的数据if(buf == NULL){printf("====line:%d,%s\n",__LINE__,"get_post_message return null.");return;}else{//可以使用json库解析需要的数据printf("====line:%d,request data:%s",__LINE__,buf);}//回响应struct evbuffer *retbuff = NULL;retbuff = evbuffer_new();if(retbuff == NULL){printf("====line:%d,%s\n",__LINE__,"retbuff is null.");return;}evbuffer_add_printf(retbuff,"Receive post request,Thamks for the request!");evhttp_send_reply(req,HTTP_OK,"Client",retbuff);evbuffer_free(retbuff);}int main(){struct evhttp *http_server = NULL;short http_port = 8081;char *http_addr = "0.0.0.0";//初始化event_init();//启动http服务端http_server = evhttp_start(http_addr,http_port);if(http_server == NULL){printf("====line:%d,%s\n",__LINE__,"http server start failed.");return -1;}//设置请求超时时间(s)evhttp_set_timeout(http_server,5);//设置事件处理函数，evhttp_set_cb针对每一个事件(请求)注册一个处理函数，//区别于evhttp_set_gencb函数，是对所有请求设置一个统一的处理函数evhttp_set_cb(http_server,"/me/testpost",http_handler_testpost_msg,NULL);evhttp_set_cb(http_server,"/me/testget",http_handler_testget_msg,NULL);//循环监听event_dispatch();//实际上不会释放，代码不会运行到这一步evhttp_free(http_server);return 0;}
代码里注释已经解释很清楚了，编译：
gcc -o http_server http_server.c -levent
执行：
./http_server
利用postman工具，或者curl命令验证结果：
（1）get
命令行输出：
点击右边<>，查看curl命令：
命令行验证curl命令：
（2）post
curl命令：
curl命令行测试：
以上就是基于libevent的http服务端小测试，如有问题，欢迎交流。
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