Wininet不缓存压缩内容

Question

我有一个压缩资源，当在IE中查看时，按预期从缓存加载。但是，当我的应用程序加载相同的URL时，Wininet会忽略缓存并始终从服务器下载内容。在IIS上禁用动态内容压缩的情况下，我的应用程序的行为与IE相同( HTTP包含一个不匹配的标头)。

我怎样才能让我的应用程序的行为与IE一样？

_httpClient = new HttpClient(new WebRequestHandler
{
    CachePolicy = new HttpRequestCachePolicy(HttpRequestCacheLevel.Default),
    AutomaticDecompression = DecompressionMethods.Deflate | DecompressionMethods.GZip
});

using (Task<HttpResponseMessage> tget = _httpClient.GetAsync(uri, HttpCompletionOption.ResponseHeadersRead, _cancel))
{
    tget.Wait();
    response = tget.Result;
}

我的应用程序的GET的HTTP头：

GET https://beautykiosktest.coinstar.com/conductor/configuration/files/Promos.xml?kioskid=ENG20130027 HTTP/1.1
Accept: */*
Accept-Language: en-US
User-Agent: ConfigurationService/2.3.0.0
Host: beautykiosktest.coinstar.com
Accept-Encoding: gzip, deflate

HTTP/1.1 200 OK
Cache-Control: max-age=30
Transfer-Encoding: chunked
Content-Type: application/xml; charset=utf-8
Content-Encoding: gzip
ETag: "cHmrX5Fp2Z+ETV/qIXiS2A=="
Vary: Accept-Encoding
Server: Microsoft-IIS/8.5
X-AspNet-Version: 4.0.30319
X-Powered-By: ASP.NET
Date: Tue, 17 Mar 2015 00:39:18 GMT

我希望IE得到304的回复

GET https://beautykiosktest.coinstar.com/conductor/configuration/files/Promos.xml?kioskid=ENG20130027 HTTP/1.1
Accept: image/jpeg, image/gif, image/pjpeg, application/x-ms-application, application/xaml+xml, application/x-ms-xbap, application/vnd.ms-excel, application/vnd.ms-powerpoint, application/msword, */*
Accept-Language: en-US
User-Agent: Mozilla/4.0 (compatible; MSIE 7.0; Windows NT 6.1; WOW64; Trident/7.0; SLCC2; .NET CLR 2.0.50727; InfoPath.3; .NET4.0C; .NET4.0E; .NET CLR 3.5.30729; .NET CLR 3.0.30729; .NET CLR 1.1.4322)
Accept-Encoding: gzip, deflate
Host: beautykiosktest.coinstar.com
If-None-Match: "cHmrX5Fp2Z+ETV/qIXiS2A=="
DNT: 1
Connection: Keep-Alive

HTTP/1.1 304 Not Modified
Cache-Control: max-age=30
ETag: "cHmrX5Fp2Z+ETV/qIXiS2A=="
Server: Microsoft-IIS/8.5
X-AspNet-Version: 4.0.30319
X-Powered-By: ASP.NET
Date: Tue, 17 Mar 2015 00:42:13 GMT

Answer 1

最后，我向微软提交了一张罚单，以解决这个问题，并发现.NET 4中存在一个导致此问题的错误。问题是，从带有可变头的响应中填充的缓存条目在下一个get上没有得到正确的匹配，因为即使设置了AutomaticDecompression属性，.NET在执行WinINET缓存测试之前也没有在请求中添加WinINET编码头。

解决方法/修复方法是在使用HttpClient实例之前向它添加一个"Accept-Encoding“默认标头。

_httpClient.DefaultRequestHeaders.Add("Accept-Encoding", "gzip, deflate");