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为什么没有缓存同一图像的第二和第三请求？

[英]Why aren't the 2nd and 3rd requests for the same image cached?

 原文  2017-02-10 21:47:57  3   1    google-chrome/ caching/ http-headers/ browser-cache/ rackspace

问题描述

原始网站没有按照我认为的方式缓存html，css或图像。 下面是Google chrome har在网站上请求不同页面时针对单个图像的结果。 它是对网站进行较大浏览的一部分，目的是弄清为什么浏览器认为应该对其进行缓存，但从服务器重新请求该浏览器。 我删除了与该图片没有特别关系的所有har。

我没有任何缓存杀手或缓存禁用器。 我什至去了相对干净的计算机，以确保没有安装任何可能会使高速缓存混乱的开发工具。

来自第一个请求的所有请求/响应标头似乎暗示着第二个和第三个请求不应进行重新请求，而应来自浏览器本地缓存。

我想念什么？ 

 {
    "startedDateTime": "2017-02-10T21:21:44.273Z",
    "time": 56.46199999999624,
    "request": {
      "method": "GET",
      "url": "http://616206ee2c1b2155fd11-21abbde6fa52e03b7fd037b3488bb991.r53.cf1.rackcdn.com/images/default-source/site-cdn/LoginLogo.png",
      "httpVersion": "HTTP/1.1",
      "headers": [
        {
          "name": "Accept",
          "value": "image/webp,image/*,*/*;q=0.8"
        },
        {
          "name": "Connection",
          "value": "keep-alive"
        },
        {
          "name": "Accept-Encoding",
          "value": "gzip, deflate, sdch"
        },
        {
          "name": "Referer",
          "value": "http://authentrip.com/"
        },
        {
          "name": "Host",
          "value": "616206ee2c1b2155fd11-21abbde6fa52e03b7fd037b3488bb991.r53.cf1.rackcdn.com"
        },
        {
          "name": "Accept-Language",
          "value": "en-US,en;q=0.8"
        },
        {
          "name": "User-Agent",
          "value": "Mozilla/5.0 (X11; Linux x86_64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/53.0.2785.116 Safari/537.36"
        }
      ],
      "queryString": [],
      "cookies": [],
      "headersSize": 428,
      "bodySize": 0
    },
    "response": {
      "status": 200,
      "statusText": "OK",
      "httpVersion": "HTTP/1.1",
      "headers": [
        {
          "name": "Date",
          "value": "Fri, 10 Feb 2017 21:21:44 GMT"
        },
        {
          "name": "Origin",
          "value": "https://mycloud.rackspace.com"
        },
        {
          "name": "Last-Modified",
          "value": "Fri, 09 Dec 2016 05:10:48 GMT"
        },
        {
          "name": "ETag",
          "value": "ab904584a8e355da2fd0437065839e10"
        },
        {
          "name": "Content-Type",
          "value": "image/png"
        },
        {
          "name": "X-Timestamp",
          "value": "1481260247.52133"
        },
        {
          "name": "Cache-Control",
          "value": "public, max-age=349"
        },
        {
          "name": "Content-Length",
          "value": "6397"
        },
        {
          "name": "Connection",
          "value": "keep-alive"
        },
        {
          "name": "Accept-Ranges",
          "value": "bytes"
        },
        {
          "name": "X-Trans-Id",
          "value": "txbeec00752b6a4e1e9e3b5-00589e2ca4dfw1"
        },
        {
          "name": "Expires",
          "value": "Fri, 10 Feb 2017 21:27:33 GMT"
        }
      ],
      "cookies": [],
      "content": {
        "size": 6397,
        "mimeType": "image/png",
        "compression": 0
      },
      "redirectURL": "",
      "headersSize": 433,
      "bodySize": 6397,
      "_transferSize": 6830
    },
    "cache": {},
    "timings": {
      "blocked": 0.396999999992431,
      "dns": -1,
      "connect": -1,
      "send": 0.13800000000685503,
      "wait": 23.861999999994016,
      "receive": 32.06500000000294,
      "ssl": -1
    },
    "serverIPAddress": "204.2.145.184",
    "connection": "989",
    "pageref": "page_1"
  },
  {
    "startedDateTime": "2017-02-10T21:22:48.357Z",
    "time": 0,
    "request": {
      "method": "GET",
      "url": "http://616206ee2c1b2155fd11-21abbde6fa52e03b7fd037b3488bb991.r53.cf1.rackcdn.com/images/default-source/site-cdn/LoginLogo.png",
      "httpVersion": "HTTP/1.1",
      "headers": [
        {
          "name": "Accept",
          "value": "image/webp,image/*,*/*;q=0.8"
        },
        {
          "name": "Connection",
          "value": "keep-alive"
        },
        {
          "name": "Accept-Encoding",
          "value": "gzip, deflate, sdch"
        },
        {
          "name": "Referer",
          "value": "http://authentrip.com/"
        },
        {
          "name": "Host",
          "value": "616206ee2c1b2155fd11-21abbde6fa52e03b7fd037b3488bb991.r53.cf1.rackcdn.com"
        },
        {
          "name": "Accept-Language",
          "value": "en-US,en;q=0.8"
        },
        {
          "name": "User-Agent",
          "value": "Mozilla/5.0 (X11; Linux x86_64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/53.0.2785.116 Safari/537.36"
        }
      ],
      "queryString": [],
      "cookies": [],
      "headersSize": 428,
      "bodySize": 0
    },
    "response": {
      "status": 200,
      "statusText": "OK",
      "httpVersion": "HTTP/1.1",
      "headers": [
        {
          "name": "Date",
          "value": "Fri, 10 Feb 2017 21:21:44 GMT"
        },
        {
          "name": "Origin",
          "value": "https://mycloud.rackspace.com"
        },
        {
          "name": "Last-Modified",
          "value": "Fri, 09 Dec 2016 05:10:48 GMT"
        },
        {
          "name": "ETag",
          "value": "ab904584a8e355da2fd0437065839e10"
        },
        {
          "name": "Content-Type",
          "value": "image/png"
        },
        {
          "name": "X-Timestamp",
          "value": "1481260247.52133"
        },
        {
          "name": "Cache-Control",
          "value": "public, max-age=349"
        },
        {
          "name": "Content-Length",
          "value": "6397"
        },
        {
          "name": "Connection",
          "value": "keep-alive"
        },
        {
          "name": "Accept-Ranges",
          "value": "bytes"
        },
        {
          "name": "X-Trans-Id",
          "value": "txbeec00752b6a4e1e9e3b5-00589e2ca4dfw1"
        },
        {
          "name": "Expires",
          "value": "Fri, 10 Feb 2017 21:27:33 GMT"
        }
      ],
      "cookies": [],
      "content": {
        "size": 6397,
        "mimeType": "image/png"
      },
      "redirectURL": "",
      "headersSize": 433,
      "bodySize": 0,
      "_transferSize": 0
    },
    "cache": {},
    "timings": {
      "blocked": -1,
      "dns": -1,
      "connect": -1,
      "send": 0,
      "wait": 0,
      "receive": 0,
      "ssl": -1
    },
    "serverIPAddress": "204.2.145.184",
    "connection": "989",
    "pageref": "page_2"
  }
  {
    "startedDateTime": "2017-02-10T21:23:38.412Z",
    "time": 0,
    "request": {
      "method": "GET",
      "url": "http://616206ee2c1b2155fd11-21abbde6fa52e03b7fd037b3488bb991.r53.cf1.rackcdn.com/images/default-source/site-cdn/LoginLogo.png",
      "httpVersion": "HTTP/1.1",
      "headers": [
        {
          "name": "Accept",
          "value": "image/webp,image/*,*/*;q=0.8"
        },
        {
          "name": "Connection",
          "value": "keep-alive"
        },
        {
          "name": "Accept-Encoding",
          "value": "gzip, deflate, sdch"
        },
        {
          "name": "Referer",
          "value": "http://authentrip.com/"
        },
        {
          "name": "Host",
          "value": "616206ee2c1b2155fd11-21abbde6fa52e03b7fd037b3488bb991.r53.cf1.rackcdn.com"
        },
        {
          "name": "Accept-Language",
          "value": "en-US,en;q=0.8"
        },
        {
          "name": "User-Agent",
          "value": "Mozilla/5.0 (X11; Linux x86_64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/53.0.2785.116 Safari/537.36"
        }
      ],
      "queryString": [],
      "cookies": [],
      "headersSize": 428,
      "bodySize": 0
    },
    "response": {
      "status": 200,
      "statusText": "OK",
      "httpVersion": "HTTP/1.1",
      "headers": [
        {
          "name": "Date",
          "value": "Fri, 10 Feb 2017 21:21:44 GMT"
        },
        {
          "name": "Origin",
          "value": "https://mycloud.rackspace.com"
        },
        {
          "name": "Last-Modified",
          "value": "Fri, 09 Dec 2016 05:10:48 GMT"
        },
        {
          "name": "ETag",
          "value": "ab904584a8e355da2fd0437065839e10"
        },
        {
          "name": "Content-Type",
          "value": "image/png"
        },
        {
          "name": "X-Timestamp",
          "value": "1481260247.52133"
        },
        {
          "name": "Cache-Control",
          "value": "public, max-age=349"
        },
        {
          "name": "Content-Length",
          "value": "6397"
        },
        {
          "name": "Connection",
          "value": "keep-alive"
        },
        {
          "name": "Accept-Ranges",
          "value": "bytes"
        },
        {
          "name": "X-Trans-Id",
          "value": "txbeec00752b6a4e1e9e3b5-00589e2ca4dfw1"
        },
        {
          "name": "Expires",
          "value": "Fri, 10 Feb 2017 21:27:33 GMT"
        }
      ],
      "cookies": [],
      "content": {
        "size": 6397,
        "mimeType": "image/png"
      },
      "redirectURL": "",
      "headersSize": 433,
      "bodySize": 0,
      "_transferSize": 0
    },
    "cache": {},
    "timings": {
      "blocked": -1,
      "dns": -1,
      "connect": -1,
      "send": 0,
      "wait": 0,
      "receive": 0,
      "ssl": -1
    },
    "serverIPAddress": "204.2.145.184",
    "connection": "989",
    "pageref": "page_3"
  }

1 个解决方案

解决方案1
 1  2017-02-13 08:51:24

实际上，Chrome确实响应了来自缓存的第二个和第三个请求。 您需要查看entry.response.bodySize属性。

HAR规范的相关摘录：

bodySize [数字]-接收到的响应主体的大小（以字节为单位）。 如果响应来自缓存，则设置为零（304）。 如果该信息不可用，则设置为-1。

还有一个有趣的HAR Viewer GitHub问题 。 他们使用下面的函数来确定是否从缓存提供了对请求的响应： 

HarModel.isCachedEntry = function(entry) {
  var response = entry.response;
  var resBodySize = response.bodySize > 0 ? response.bodySize : 0;
  return (response.status == 304 || (resBodySize === 0 && response.content && response.content.size > 0));
};

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