基于Libevent的HTTP Server

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 WIN32    init_win_socket();#endif    short          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);        else            fprintf(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 WIN32    init_win_socket();#endif    short          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。