I'm working on a small single-page application using HTML5. One feature is to show PDF documents embedded in the page, which documents can be selected form a list.
NOw I'm trying to make Chrome (at first, and then all the other modern browsers) use the local client cache to fulfill simple GET request for PDF documents without going through the server (other than the first time of course). I cause the PDF file to be requested by setting the "data" property on an <object> element in HTML.
I have found a working example for XMLHttpRequest (not <object>). If you use Chrome's developer tools (Network tab) you can see that the first request goes to the server, and results in a response with these headers:
Cache-Control:public,Public
Content-Encoding:gzip
Content-Length:130
Content-Type:text/plain; charset=utf-8
Date:Tue, 03 Jul 2012 20:34:15 GMT
Expires:Tue, 03 Jul 2012 20:35:15 GMT
Last-Modified:Tue, 03 Jul 2012 20:34:15 GMT
Server:Microsoft-IIS/7.5
Vary:Accept-Encoding
The second request is served from the local cache without any server roundtrip, which is what I want.
Back in my own application, I then used ASP-NET MVC 4 and set
[OutputCache(Duration=60)]
on my controller. The first request to this controller - with URL http://localhost:63035/?doi=10.1155/2007/98732 results in the following headers:
Cache-Control:public, max-age=60, s-maxage=0
Content-Length:238727
Content-Type:application/pdf
Date:Tue, 03 Jul 2012 20:45:08 GMT
Expires:Tue, 03 Jul 2012 20:46:06 GMT
Last-Modified:Tue, 03 Jul 2012 20:45:06 GMT
Server:Microsoft-IIS/8.0
Vary:*
The second request results in another roundtrip to the server, with a much quicker response (suggesting server-side caching?) but returns 200 OK and these headers:
Cache-Control:public, max-age=53, s-maxage=0
Content-Length:238727
Content-Type:application/pdf
Date:Tue, 03 Jul 2012 20:45:13 GMT
Expires:Tue, 03 Jul 2012 20:46:06 GMT
Last-Modified:Tue, 03 Jul 2012 20:45:06 GMT
Server:Microsoft-IIS/8.0
Vary:*
The third request for the same URL results in yet another roundtrip and a 304 response with these headers:
Cache-Control:public, max-age=33, s-maxage=0
Date:Tue, 03 Jul 2012 20:45:33 GMT
Expires:Tue, 03 Jul 2012 20:46:06 GMT
Last-Modified:Tue, 03 Jul 2012 20:45:06 GMT
Server:Microsoft-IIS/8.0
Vary:*
My question is, how should I set the OutputCache attribute in order to get the desired behaviour (i.e. PDF requests fullfilled from the client cache, within X seconds of the initial request)?
Or, am I not doing things right when I cause the PDF to display by setting the "data" property on an <object> element?
Clients are never obligated to cache. Each browser is free to use its own heuristic to decide whether it is worth caching an object. After all, any use of cache "competes" with other uses of the cache.
Caching is not designed to guarantee a quick response; it is designed to, on average, increase the likelihood that frequently used resources that are not changing will already be there. What you are trying to do, is not what caches are designed to help with.
Based on the results you report, the version of Chrome you were using in 2012 decided it was pointless to cache an object that would expire in 60 seconds, and had only been asked for once. So it threw away the first copy, after using it. Then you asked a second time, and it started to give this URL a bit more priority -- it must have remembered recent URLs, and observed that this was a second request -- it kept the copy in cache, but when the third request came, asked server to verify that it was still valid (presumably because the expiration time was only a few seconds away). The server said "304 -- not modified -- use the copy you cached". It did NOT send the pdf again.
IMHO, that was reasonable cache behavior, for an object that will expire soon.
If you want to increase the chance that the PDF will stick around longer, then give a later expiration time, but say that it must check with the server to see if it is still valid.
If using HTTP Cache-Control header, this might be: private, max-age: 3600, must-revalidate. With this, you should see a round-trip to server, which will give 304 response as long as the page is valid. This should be a quick response, since no data is sent back -- the browser's cached version is used.
private is optional -- not related to this caching behavior -- I'm assuming whatever this volatile PDF is, it only makes sense for the given user and/or shouldn't be hanging around for a long time, in some shared location.
If you really need the performance of not talking to the server at all, then consider writing javascript to hide/show the DOM element holding that PDF, rather than dropping it, and needing to ask for it again.
Your javascript code for the page is the only place that "understands" that you really want that PDF to stick around, even if you aren't currently showing it to the user.
Have you tried setting the Location property of the OutputCache to "Client"
[OutputCache(Duration=60, Location = OutputCacheLocation.Client)]
By default the location property is set to "Any" which could mean that the response is cached on the client, on a proxy, or at the server.
more at MSDN OutputCacheLocation
Related
I'm using Alamofire 5 and have the requirement that some GET-requests should be cached. If the data is older then 20 minutes the real API should be hit.
What I found is to use the ResponseCacher. But I do not see a way to configure the individual request and need some advice.
let responseCacher = ResponseCacher(behavior: .modify { _, response in
let userInfo = ["date": Date()]
return CachedURLResponse(
response: response.response,
data: response.data,
userInfo: userInfo,
storagePolicy: .allowed)
})
let configuration = URLSessionConfiguration.af.default
private override init() {
configuration.timeoutIntervalForRequest = 10
configuration.requestCachePolicy = .reloadRevalidatingCacheData
Session(
configuration: configuration,
serverTrustManager: ServerTrustManager(evaluators: evaluators),
cachedResponseHandler: responseCacher
)
If the backend is returning proper caching headers that you want to limit to a certain amount of time, adding a Cache-Control: max-age= header on the request may work.
If the backend isn't return proper caching headers, using ResponseCacher is the way to go. You would modify the CachedURLResponse's response to include the proper Cache-Control header.
To elaborate on Jon's answer, the easiest way to achieve what you want is to just let the backend declare the cache semantics of this endpoint, then ensure that on the client side, URLSession uses a URLCache (which is probably the default anyway) and let URLSession and the backend do the rest. This requires, that you have control over the backend, though!
The more elaborate answer:
Here is just an example, how a server may return a response with declared cache semantics:
URL: https://www.example.com/ Status Code: 200
Age: 238645
Cache-Control: max-age=604800
Date: Tue, 12 Jan 2021 18:43:58 GMT
Etag: "3147526947"
Expires: Tue, 19 Jan 2021 18:43:58 GMT
Last-Modified: Thu, 17 Oct 2019 07:18:26 GMT
Vary: Accept-Encoding
x-cache: HIT
Accept-Ranges: bytes
Content-Encoding: gzip
Content-Length: 648
Content-Type: text/html; charset=UTF-8
Server: ECS (dcb/7EC7)
This server literally outputs the full range of what a server can declare regarding caching. The first eight headers (from Age to x-cache) declare the caching.
Cache-Control: max-age=604800 for example declares, that the data's freshness equals 604800 seconds. Having the date when the server created the data, the client can now check if the data is still "fresh".
Expires: Tue, 19 Jan 2021 18:43:58 GMT means the exact same thing, it declares when the data is outdated specifying the wall clock. This is redundant with the above declaration, but it is very clearly defined in the HTTP how clients should treat this.
Having an Age header is a hint, that the response has been actually delivered from a cache that exists between the client and the origin server. The age is the estimation of this data's age - the duration from when it has been created on the origin and when it has been delivered.
I don't wont to go into detail what every header means exactly and how a client and server should behave according HTTP since this is a very intense topic, but what you have to do is basically when you define an endpoint, is just to define the duration of the "freshness" of the returned data.
The whole details: Hypertext Transfer Protocol (HTTP/1.1): Caching
Once you came up with a good duration, Web-application frameworks (like Rails, SpringBoot, etc.) give great help with declaring cache semantics out of the box. Then Web-application frameworks will output the corresponding headers in the response - more or less "automagically".
The URLSession will automatically do the right thing according the HTTP protocol (well, almost). That is, it will store the response in the cache and when you perform a subsequent request it first looks for a suitable response in the cache and return that response if the "freshness" of the data is still given.
If that cached data is too old (according the given response headers and the current data and time), it will try to get a fresh data by sending the request to the origin server. Any upstream cache or eventually the origin server may then return fresh data. Your URLSession data task does all this transparently without giving you a clue whether the data comes from the cache or the origin server. And honestly, in most cases you don't need to know it.
Declaring the cache semantics according HTTP is very powerful and it usually should suit your needs. Also, the client may tailor its needs with specifying certain request headers, for example allowing to return even outdated data or ignoring any cached values, and much more.
Every detail may deserve a dedicated question and answer on SO.
For the following image: https://upload.wikimedia.org/wikipedia/commons/7/79/2010-brown-bear.jpg
There isn't any cache-control header. And based on here even if you don't send anything then it will use its default value which is private. That being doesn't the URLSession need to perform a conditional request to make sure its still valid?
Is there anything in the headers that allows it to make such a conditional request? Because I don't see cache-control, max-age, Expires. The only things I see is are Last-Modified & Etag but again it needs to validate against the server or does not specifying anything make it cache indefinitely?! I've already read this answer, but doesn't discuss this scenario.
Yet it's being cached by the URLSession. (Because if I turn off internet, still it gets downloaded)
Only other thing I see is "Strict-Transport-Security": max-age=106384710.
Does that effect caching? I've already look here and don't believe it should. From what I the max-age for the HSTS key is there only to enforce it to be accessed from HTTPS for a certain period of time. Once the max-age is reached then access through HTTP is also possible.
These are all the headers that I'm getting back:
Date : Wed, 31 Oct 2018 14:15:33 GMT
Content-Length : 215104
Access-Control-Expose-Headers: Age, Date, Content-Length, Content-Range, X-Content-Duration, X-Cache, X-Varnish
Via : 1.1 varnish (Varnish/5.1), 1.1 varnish (Varnish/5.1)
Age : 18581
Etag : 00e21950bf432476c91b811bb685b6af
Strict-Transport-Security : max-age=106384710; includeSubDomains; preload
Accept-Ranges : bytes
Content-Type : image/jpeg
Last-Modified : Fri, 04 Oct 2013 23:30:08 GMT
Access-Control-Allow-Origin : *
Timing-Allow-Origin : *
x-analytics : https=1;nocookies=1
x-object-meta-sha1base36 : 42tq5grg9rq1ydmqd4z5hmmqj6h2309
x-varnish : 60926196 48388489, 342256851 317476424
x-cache-status : hit-front
x-trans-id : tx08ed43bbcc1946269a9a3-005bd97070
x-timestamp : 1380929407.39127
x-cache : cp1076 hit/7, cp1090 hit/7
x-client-ip : 2001:558:1400:4e:171:2a98:fad6:2579
This question was asked because of this comment
doesn't the URLSession need to perform a conditional request to make sure its still valid?
The user-agent should be performing a conditional request, because of the
Etag: 00e21950bf432476c91b811bb685b6af
present. My desktop Chrome certainly does performs the conditional request (and gets back 304 Not Modified).
But it's free not to
But a user-agent is perfectly free to decide on it's own. It's perfectly free to look at:
Last-Modified: Fri, 04 Oct 2013 23:30:08 GMT
and decide that there resource is probably good for the next five minutes1. And if the network connection is down, its perfectly reasonable and correct to display the cached version instead. In fact, your browser would show you web-sites even while your dial-up 0.00336 Mbps dial-up modem was disconnected.
You wouldn't want your browser to show you nothing, when it knows full well it can show you something. It becomes even more useful when we're talking about poor internet connectivity not because of slow dialup and servers that go down, but of mobile computing, and metered data plans.
1I say 5 minutes, because in the early web, servers did not give cache hints. So browsers cached things without even being asked. And 5 minutes was a good number. And you used Ctrl+F5 (or was it Shift+F5, or was it Shift+Click, or was it Alt+Click) to force the browser to bypass the cache.
We use Windows server 2008 R2 Enterprise And IIS7.5.7600.16385,
and i deployed a simple web (asp.net mvc, c#, .net framework 4.5.1) on the server.
a controller like below, and *.cshtml only output a datetime:
public class DetailController : Controller
{
[OutputCache(Duration = 300, VaryByParam = "id")]
public ActionResult Index(int id)
{
return View();
}
}
when i first request the url http://localhost:80/Detail/Index?id=3 , the response is correct:
Cache-Control:public, max-age=300
Date:Mon, 24 Oct 2016 12:11:59 GMT
Expires:Mon, 24 Oct 2016 12:16:51 GMT
Last-Modified:Mon, 24 Oct 2016 12:11:51 GMT
but, when i request the url again(ctrl+f5), the max-age incorrect (then the response is from the server cache):
Cache-Control:public, max-age=63612908450
Date:Mon, 24 Oct 2016 12:16:34 GMT
Expires:Mon, 24 Oct 2016 12:20:50 GMT
Last-Modified:Mon, 24 Oct 2016 12:15:50 GMT
i don't know why the max-age so large, and how it generated, it will reconvert when the output cache expired (ctrl+f5).
In my production env, the incorrect max-age cause a url link click read the content from browser's disk cache.
any one know how and how to fixed it?
This is a known issue and a bug is open for .NET 4.6.2 coming with KB151864.
Please see here for additional details: https://github.com/Microsoft/dotnet/issues/330
This is going to be fixed in .NET 4.6.3. I currently don't know if a fix will be made available earlier for 4.6.2.
The only known workaround at present is to downgrade and remove KB151864, when possible.
NOTE: the bug is affecting ONLY the compilation of the "max-age" attribute in the Cache-Control header for the cached responses. The actual caching mechanism and lifetime expiration is working.
I just spoke with Microsoft Support team and this is what they responded me:
The suggested workaround is to downgrade the frame work from 4.6.2 to
4.6.1 by uninstalling the update KB31511864.
Go to control panel -> programs -> Programs and Feature -> Installed Updates.
And remove KB3151864, that will fix this issue.
I just found a partial response being cached as complete in one of our customer's machines, which rendered the whole website unusable. And I have absolutely no idea, what could possible have gone wrong there.
So what could have possibly gone wrong in the following setup?
On the server-side, we have an ASP.NET-application running. One IHttpHandler handles requests to javascript-files. It basically minifies the files as they are requested and writes the result on the response-stream. It does also log the length of the string being written to the Response-Stream:
String javascript = /* Javascript is retrieved here */;
HttpResponse response = context.Response;
response.ContentEncoding = Encoding.UTF8;
response.ContentType = "application/javascript";
HttpCachePolicy cache = response.Cache;
cache.SetCacheability(HttpCacheability.Public);
cache.SetMaxAge(TimeSpan.FromDays(300));
cache.SetETag(ETag);
cache.SetExpires(DateTime.Now.AddDays(300));
cache.SetLastModified(LastModified);
cache.SetRevalidation(HttpCacheRevalidation.None);
response.Headers.Add("Vary", "Accept-Encoding");
Log.Info("{0} characters sent", javascript.length);
response.Write(javascript);
response.Flush();
response.End();
The content is then normally sent using gzip-encoding with chunked transfer-encoding. Seems simple enough to me.
Unfortunately, I just had a remote-session with a user, where only about 1/3 of the file was in the cache, which broke the file of course (15k instead of 44k). In the cache, the content-encoding was also set to gzip, all communication took place via https.
After having opened the source-file on the user's machine, I just hit Ctrl-F5 and the full content was displayed immediately.
What could have possibly gone wrong?
In case it matters, please find the cache-entry from Firefox below:
Cache entry information
key: <resource-url>
fetch count: 49
last fetched: 2015-04-28 15:31:35
last modified: 2015-04-27 15:29:13
expires: 2016-02-09 14:27:05
Data size: 15998 B
Security: This is a secure document.
security-info: (...)
request-method: GET
request-Accept-Encoding: gzip, deflate
response-head: HTTP/1.1 200 OK
Cache-Control: public, max-age=25920000
Content-Type: application/javascript; charset=utf-8
Content-Encoding: gzip
Expires: Tue, 09 Feb 2016 14:27:12 GMT
Last-Modified: Tue, 02 Jan 2001 11:00:00 GMT
Etag: W/"0"
Vary: Accept-Encoding
Server: Microsoft-IIS/8.0
X-AspNet-Version: 4.0.30319
Date: Wed, 15 Apr 2015 13:27:12 GMT
necko:classified: 1
Your clients browser is most likely caching the JavaScript files which would mean the src of your scripts isn't changing.
For instance if you were to request myScripts
<script src="/myScripts.js">
Then the first time, the client would request that file and any further times the browser would read its cache.
You need to append some sort of unique value such as a timestamp to the end of your scripts so even if the browser caches the file, the new timestamp will act like a new file name.
The client receives the new scripts after pressing Ctrl+F5 because this is a shortcut to empty the browsers cache.
MVC has a really nice way of doing this which involves appending a unique code which changes everytime the application or it's app pool is restarted. Check out MVC Bundling and Minification.
Hope this helps!
<DIV id=3949 class=tempClass channel-name="Brand" sizcache="50" nodeIndex="1" jQuery1362033550328="46"></div>
What is [jQuery1362033550328="46"]? It is showing in IE only not firefox.
1362033550328 is the unix timestamp which is equivalent to Thu, 28 Feb 2013 06:52:00 GMT
Mostly its appended along with ajax requests to avoid ajax cache problems