c# - 尽管在响应对象上配置了缓存控制 header ，但未在响应中发送

Question

我试图在 ASP.NET MVC Web API 中设置缓存 header ，但 IIS 的响应表明 CacheControl 值集被忽略了。

我最初的假设是我在 System.Web.Http.Cors 中使用了 EnableCorsAttribute，这在这个用例中是必需的。但是，即使没有该属性，响应 Cache-Control header 仍然是“私有(private)的”。

我这里有什么地方做错了吗？

    // GET api/<version>/content
    // [EnableCors(origins: "*", headers: "*", methods: "*")]
    public HttpResponseMessage Get(HttpRequestMessage request)
    {
        int cacheMaxAgeSeconds;

        string cacheMaxAgeString = request.GetQueryString("cache-max-age") ?? request.GetQueryString("cache-max-age-seconds");

        string rawUri = request.RequestUri.ToString();

        try
        {
            cacheMaxAgeSeconds = cacheMaxAgeString == null ? Config.ApiCacheControlMaxSeconds : int.Parse(cacheMaxAgeString);
        }
        catch (Exception ex)
        {
            cacheMaxAgeSeconds = Config.ApiCacheControlMaxSeconds;

            //... 
        }

        try
        {
            //...

            var response = new HttpResponseMessage(HttpStatusCode.OK)
            {
                Content = new StringContent("...", Encoding.UTF8, "application/json")
            };

            response.Headers.CacheControl = new CacheControlHeaderValue
            {
                Public = true,
                MaxAge = TimeSpan.FromSeconds(cacheMaxAgeSeconds)
            };

            return response;
        }
        catch (Exception apiEx)
        {
            //...
        }
    }

回应

HTTP/1.1 200 OK
Cache-Control: private
Content-Type: application/json; charset=utf-8
Date: Thu, 23 Jul 2015 10:53:17 GMT
Server: Microsoft-IIS/7.5
Set-Cookie: ASP.NET_SessionId=knjh4pncbrhad30kjykvwxyz; path=/; HttpOnly
X-AspNet-Version: 4.0.30319
X-Powered-By: ASP.NET
Content-Length: 2367
Connection: keep-alive

Answer 1

下面的代码在 vanilla WebApi 应用程序 (System.Web.Http 4.0.0.0) 中正确设置了“cache-control: public, max-age=15”。所以...导致问题的可能不是 WebApi 本身。

您的项目中可能有一些更改缓存设置的魔法(想想全局操作过滤器或类似的东西)。或者您可能正在通过重写 HTTP header 的代理。

    public HttpResponseMessage Get()
    {
        var content = new JavaScriptSerializer().Serialize(new { foo = "bar" });

        var response = new HttpResponseMessage(HttpStatusCode.OK)
        {
            Content = new StringContent(content, Encoding.UTF8, "application/json")
        };

        response.Headers.CacheControl = new CacheControlHeaderValue
        {
            Public = true,
            MaxAge = TimeSpan.FromSeconds(15)
        };

        return response;
    }

// returns in the response: "Cache-Control: public, max-age=15"