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
#include
#include
#include
#include
#include
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
#include
#include
#include
#include
#include
#include <string.h>
#include
#include
#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
#include
#include
#include <string.h>
#include
#include
#include
#include
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。
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