Prevent caching for specific files in SharePoint


Assume following scenario that you have a SharePoint environment and all cachings are enabled . Caching is very efficent for documents which are not change frequently . What if you have dynamically and frequently changing xml,js,txt or a css file . so how could you provide to bypass only needed files are not being cached and other leave other same type files be cached.

There is an ASP.NET trick for this purpose. Assume that we have a menu.xml and this file is updating by some Operations on server and this operation happens very frequently. But your clients could not get updated file until they completely clear their browser caches. You dont want to be prevent every xml files to be not cached .
Basically caching machanizms has deciding to cache files by checking url syntax. If you have change the url somehow you can prevent the cache. We usually provide this by adding a fake version query string like menu.xml?ver=1 at the end of the url . and increasing this parameter when ever we changed the file. For some examples you can aslo use GUIDs for this.

1)Create a test.js file and type following codes. You may also integrate this to your own page directly.

function CreateDigits() {
return (((1 + Math.random()) * 0x10000) | 0).toString(16).substring(1); }
function createGuid() {     return (CreateDigits() + CreateDigits() + “-” + CreateDigits() + “-4” + CreateDigits().substr(0, 3) + “-” + CreateDigits() + “-” + CreateDigits() + CreateDigits() + CreateDigits()).toLowerCase(); } //alert(createGuid());

$.get(‘/_layouts/menuxml/menu.xml’ + ‘?ver=’ + createGuid() , function (data) {     //do operations.     alert(‘Load was performed.’); });

2) Add test.js to your masterpage
<script type=”text/javescript” src=”/_layouts/test.js” ></script>

3) Use IE developer Panel (F12) or  Firefox Firebug plugin or Fiddler2 program on your client  check that menu2.xml is loading when you request the file.

You should see the menu.xml file request has contain ?ver=<GUID> notation.

4) Update your Javascript files where loading  XML file according to example.

5) And test the change xml file and check still browsers caching the file

What we basically do ?

Following codes has creates a GUID function CreateDigits() While we requesting the xml file we adding end of the url of the file this GUID as a parameter for every request it will creates another guid. Like http://<site>/_layouts/menuxml/menu.xml?ver=bca7f319-5627-4d22-48f6-4c3e59285199

So it will provide that every request on client is unique and force the clients update XML file for every time. This is the basic logic you can develop yours based on this.

Resources:
http://guid.us/GUID/JavaScript

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About bpostaci
Sr. Support Escalation Engineer in Microsoft.

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