• 基于libevent 1.3e, 利用了libevent里面现成的http库
• 编译方法，先安装libevent,然后
      cc -o httpd httpd.c -L/usr/local/lib/ -Wall -O2 -I/usr/local/include -ggdb -levent
• 可以作为一个商业运行环境的基础，真正的业务系统里面，comet server也很简单，比这个程序复杂不了什么，它只处理comet，只是一个通道，复杂的东西放到其他地方。
• 打算作为下图中的一个模块

#include <sys/types.h>
#include <sys/time.h>
#include <stdlib.h>
#include <err.h>

#include <sys/queue.h>
#include <evhttp.h>
#define MAX_CONN 10240

struct evhttp_request *requests[MAX_CONN];
struct evbuffer *bufs[MAX_CONN];
int pos[MAX_CONN], num;

void on_close(struct evhttp_request *req, void *arg) {
 int* p = (int*) arg;
 struct evhttp_request *p2 = requests[*p];
 struct evbuffer *p3 = bufs[*p];
 printf("%s closed.\n", p2->remote_host);
 requests[*p] = NULL;
 if (p3 != NULL) evbuffer_free(p3);
}

/* for comet recv */
void comet_handler(struct evhttp_request *req, void *arg) {
 int i, j;
 requests[num] = req;
 struct evbuffer *buf; 
  
 req->minor = 0; 
 evhttp_add_header(req->output_headers, "Content-Type", "text/plain");

    evhttp_send_reply_start(req, HTTP_OK, "OK");
 
 /* Set a callback for connection close. */
 evhttp_connection_set_closecb(req->evcon, on_close, &pos[num]);

 buf = evbuffer_new();
 bufs[num] = buf;

 for (j = 0; j < 10; j++)
  evbuffer_add_printf(buf, "Hi %s, this is a comet server based on libevent, visit http://hi.baidu.com/jabber for more information!\r\n", req->remote_host);
    evhttp_send_reply_chunk(req, buf);

    for (i = 0; i < num; i++) {
     if (requests[i] == NULL) continue;
     evbuffer_add_printf(bufs[i], "Oops, %s requests!\r\n", req->remote_host);
     evhttp_send_reply_chunk(requests[i], bufs[i]);
     // evhttp_send_reply_end(requests[i]);
    }
    
    if (num++ == MAX_CONN) err(1, "exceed max conn, TODO.");
}

/* for comet send, GET /id */
void notify_handler(struct evhttp_request *req, void *arg) {
    struct evbuffer *buf;
    int nudge;
    
    buf = evbuffer_new();
    if (buf == NULL) err(1, "failed to create response buffer");
    const char *uri = evhttp_request_uri(req);
    evbuffer_add_printf(buf, "Requested: %s, send a nudge to %s\n", uri, uri + 1);

 nudge = atoi(uri + 1);
 if (requests[nudge] != NULL) {
  evbuffer_add_printf(bufs[nudge], "Oops, received a nudge from %s!\r\n", req->remote_host);
  evhttp_send_reply_chunk(requests[nudge], bufs[nudge]);
 }
    
    evhttp_send_reply(req, HTTP_OK, "OK", buf); // TODO: free buf
}

int main(int argc, char **argv) {
        struct evhttp *httpd;
        int i;
        for (i = 0; i < 1024; i++) {
         requests[i] == NULL;
         bufs[i] = NULL;
         pos[i] = i;
        }
        num = 0;

        event_init();
        httpd = evhttp_start("0.0.0.0", 8080);

        /* Set a comet callback for requests to "/". */
        evhttp_set_cb(httpd, "/", comet_handler, NULL);

        /* Set a send callback for all other requests. */ 
        evhttp_set_gencb(httpd, notify_handler, NULL);

        event_dispatch();

        /* Not reached in this code as it is now. */
        evhttp_free(httpd);
        return 0;
}