简单的Http Server
使用Libevent内置的http相关接口，可以很容易的构建一个Http Server，一个简单的Http Server如下：
#include <event2/event.h> #include <event2/buffer.h> #include <event2/http.h> #include <Winsock2.h> #include <stdlib.h> #include <stdio.h>int init_win_socket() {WSADATA wsaData;if(WSAStartup(MAKEWORD(2,2) , &wsaData) != 0) {return -1;}return 0; }void generic_handler(struct evhttp_request *req, void *arg) {struct evbuffer *buf = evbuffer_new();if(!buf){puts("failed to create response buffer \n");return;}evbuffer_add_printf(buf, "Server Responsed. Requested: %s\n", evhttp_request_get_uri(req));evhttp_send_reply(req, HTTP_OK, "OK", buf);evbuffer_free(buf); }int main(int argc, char* argv[]) { #ifdef WIN32init_win_socket(); #endifshort http_port = 8081;char *http_addr = "127.0.0.1";struct event_base * base = event_base_new();struct evhttp * http_server = evhttp_new(base);if(!http_server){return -1;}int ret = evhttp_bind_socket(http_server,http_addr,http_port);if(ret!=0){return -1;}evhttp_set_gencb(http_server, generic_handler, NULL);printf("http server start OK! \n");event_base_dispatch(base);evhttp_free(http_server);WSACleanup();return 0; }
通过Libevent的接口构建一个Http Server的过程如下：
（1）初始化：在event_base上新建一个evhttp，将这个evhttp绑定到监听的IP和端口号。
（2）设置Http回调函数：使用evhttp_set_gencb设置Http Server的处理请求的回调函数。
（3）启动Http Server：等待请求进入事件循环。
在Http Server中使用定时器提供更新服务
#include <event2/event.h> #include <event2/buffer.h> #include <event2/http.h> #include <sys/stat.h> #include <Winsock2.h> #include <assert.h> #include <string.h> #include <stdlib.h> #include <stdio.h>#define DEFAULT_FILE "F:\\Libevent\\LibeventTest\\Debug\\sample.txt"char *filedata; time_t lasttime = 0; char filename[80]; int counter = 0;struct event *loadfile_event; struct timeval tv;void read_file() {unsigned long size = 0;char *data;struct stat buf;if(stat(filename,&buf)<0){printf("Read file error! \n");return;}if (buf.st_mtime > lasttime){if (counter++)fprintf(stderr,"Reloading file: %s",filename);elsefprintf(stderr,"Loading file: %s",filename);FILE *f = fopen(filename, "rb");if (f == NULL){fprintf(stderr,"Couldn't open file\n");return;}size = buf.st_size;filedata = (char *)malloc(size+1);memset(filedata,0,size+1);fread(filedata, sizeof(char), size, f);fclose(f);fprintf(stderr," (%d bytes)\n",size);lasttime = buf.st_mtime;} }void read_file_timer_cb(evutil_socket_t listener, short event, void *arg) {if (!evtimer_pending(loadfile_event, NULL)) {event_del(loadfile_event);evtimer_add(loadfile_event, &tv);}read_file(); }void load_file(struct event_base * base) {tv.tv_sec = 5;tv.tv_usec = 0;//loadfile_event = malloc(sizeof(struct event));loadfile_event = evtimer_new(base,read_file_timer_cb,NULL);//evtimer_set(loadfile_event,load_file,loadfile_event);evtimer_add(loadfile_event,&tv); }void generic_handler(struct evhttp_request *req, void *arg) {struct evbuffer *buf = evbuffer_new();if(!buf){puts("failed to create response buffer \n");return;}evbuffer_add_printf(buf,"%s",filedata);evhttp_send_reply(req, HTTP_OK, "OK", buf);evbuffer_free(buf); }int init_win_socket() {WSADATA wsaData;if(WSAStartup(MAKEWORD(2,2) , &wsaData) != 0) {return -1;}return 0; }int main(int argc, char* argv[]) { #ifdef WIN32init_win_socket(); #endifshort http_port = 8081;char *http_addr = "127.0.0.1";if (argc > 1){strcpy(filename,argv[1]);printf("Using %s\n",filename);}else{strcpy(filename,DEFAULT_FILE);}struct event_base * base = event_base_new();struct evhttp * http_server = evhttp_new(base);if(!http_server){return -1;}int ret = evhttp_bind_socket(http_server,http_addr,http_port);if(ret!=0){return -1;}evhttp_set_gencb(http_server, generic_handler, NULL);read_file();load_file(base);printf("http server start OK! \n");event_base_dispatch(base);evhttp_free(http_server);WSACleanup();return 0; }
在这个Http Server中提供了一个每5秒触发一次的定时器，读取一个文件，如果这个文件被更新过，则读取更新后的内容。
当访问这个Http Server时，提供这个文件中最新的内容。
多线程的Http Server
在上面的Http Server中，处理Http请求的回调函数generic_handler和定时器读取文件的回调函数read_file_timer_cb都在同一个event_base的dispatch中，并且都在同一个进程中，使用多线程可以改善程序的性能，下面是一个来自网络的多线程Http Server：
#include <event.h> #include <evhttp.h> #include <pthread.h> #include <errno.h> #include <string.h> #include <fcntl.h> #include <sys/socket.h> #include <sys/types.h> #include <netinet/in.h>int httpserver_bindsocket(int port, int backlog); int httpserver_start(int port, int nthreads, int backlog); void* httpserver_Dispatch(void *arg); void httpserver_GenericHandler(struct evhttp_request *req, void *arg); void httpserver_ProcessRequest(struct evhttp_request *req);int httpserver_bindsocket(int port, int backlog) {int r;int nfd;nfd = socket(AF_INET, SOCK_STREAM, 0);if (nfd < 0) return -1;int one = 1;r = setsockopt(nfd, SOL_SOCKET, SO_REUSEADDR, (char *)&one, sizeof(int));struct sockaddr_in addr;memset(&addr, 0, sizeof(addr));addr.sin_family = AF_INET;addr.sin_addr.s_addr = INADDR_ANY;addr.sin_port = htons(port);r = bind(nfd, (struct sockaddr*)&addr, sizeof(addr));if (r < 0) return -1;r = listen(nfd, backlog);if (r < 0) return -1;int flags;if ((flags = fcntl(nfd, F_GETFL, 0)) < 0|| fcntl(nfd, F_SETFL, flags | O_NONBLOCK) < 0)return -1;return nfd; }int httpserver_start(int port, int nthreads, int backlog) {int r, i;int nfd = httpserver_bindsocket(port, backlog);if (nfd < 0) return -1;pthread_t ths[nthreads];for (i = 0; i < nthreads; i++) {struct event_base *base = event_init();if (base == NULL) return -1;struct evhttp *httpd = evhttp_new(base);if (httpd == NULL) return -1;r = evhttp_accept_socket(httpd, nfd);if (r != 0) return -1;evhttp_set_gencb(httpd, httpserver_GenericHandler, NULL);r = pthread_create(&ths[i], NULL, httpserver_Dispatch, base);if (r != 0) return -1;}for (i = 0; i < nthreads; i++) {pthread_join(ths[i], NULL);} }void* httpserver_Dispatch(void *arg) {event_base_dispatch((struct event_base*)arg);return NULL; }void httpserver_GenericHandler(struct evhttp_request *req, void *arg) {httpserver_ProcessRequest(req); }void httpserver_ProcessRequest(struct evhttp_request *req) {struct evbuffer *buf = evbuffer_new();if (buf == NULL) return;//here comes the magic }int main(void) {httpserver_start(80, 10, 10240); }
上面的代码基于Libevent 1.X版本的，不过很容易很看懂：在一个监听socket上创建了多个event_base实例和evhttp实例，在不同的线程中调度不同的event_base，继而可以在不同的线程中处理http请求。
这里还有一个基于Libevent的多线程Http Server：https://sourceforge.net/projects/libevent-thread/，看源代码处理的过程和上面类似，只是每次在监听的socket上accept一个连接请求时，将对应的处理放到一个工作队列里，在队列里由多线程处理相应的回调函数。
