问题

使用mongoose做http服务器，自己构造的浏览器端jquery在访问server时，会遇到：

Access to XMLHttpRequest at 'http://127.0.0.1:8000/' from origin 'null' has been blocked by CORS policy: No 'Access-Control-Allow-Origin' header is present on the requested resource.

jquery的程序：

$.get("http://127.0.0.1:8000",function(d)
{
   alert(d);
});

解决：

在mongoose返回响应串中，如下构造：

使用 mg_http_reply

char str[128] = "respnose hello";
mg_http_reply(c, 200, 
    "Access-Control-Allow-Origin: *\n"
    "Access-Control-Allow-Methods: *\n"
    "Access-Control-Allow-Headers: *\n", 
    "%s\n", str);

使用mg_printf

std::string str = "respnose hello";
mg_printf(c, "HTTP/1.1 200 OK\r\n"
  "Content-Type: text/plain\n"
  "Cache-Control: no-cache\n"
  "Content-Length: %d\n"
  "Access-Control-Allow-Origin: *\n"
  "Access-Control-Allow-Methods: *\n"
  "Access-Control-Allow-Headers: *\n\n"
  "%s\n", str.length(), str.c_str());

最终，返回的的串，看起来应该是这样：