Ajax send request with encoding gzip (iis7) is not working below are the code for send request can some one help me what is wrong in my code.

Thanks in advance

function sendRequest(url, callback, postData)
{
   var req = createXMLHTTPObject();
   if (!req) {
      return;
   }

   var method = (postData) ? "POST" : "GET";
   req.open(method, "xml/" + url, true);
   req.setRequestHeader('User-Agent', 'XMLHTTP/1.0');

   if (postData) {
      req.setRequestHeader('Content-type', 'application/x-www-form-urlencoded');
      req.setRequestHeader("Content-Encoding", "gzip");

   }

   req.onreadystatechange = function() {

   }

   req.send(postData);
}

Ajax send request with encoding gzip (iis7) is not working below are the code for send request can some one help me what is wrong in my code.

Thanks in advance

function sendRequest(url, callback, postData)
{
   var req = createXMLHTTPObject();
   if (!req) {
      return;
   }

   var method = (postData) ? "POST" : "GET";
   req.open(method, "xml/" + url, true);
   req.setRequestHeader('User-Agent', 'XMLHTTP/1.0');

   if (postData) {
      req.setRequestHeader('Content-type', 'application/x-www-form-urlencoded');
      req.setRequestHeader("Content-Encoding", "gzip");

   }

   req.onreadystatechange = function() {

   }

   req.send(postData);
}

• javascript
• asp
• get
• request
• gzip

• 1 What do you mean by not working? Is the server not responding as it should? Do you get an error? – Nadh Commented Apr 27, 2012 at 6:48
• 1 Are you really pressing the content or just pretending it is pressed by changing the header ? Is postData gzipped ? – Denys Séguret Commented Apr 27, 2012 at 7:04
• @dystroy yes, its press problem for download xml file with size is large – MANISHDAN LANGA Commented Apr 27, 2012 at 7:18
• @NADH not getting error when download xml file using this code.if xml file is 6 mb then its download for 400kb then stop (as i see in Firebug). if i remove gzip from IIS the its download properly with 6mb. – MANISHDAN LANGA Commented Apr 27, 2012 at 7:22

3 Answers 3

Considering the security, browser does not allow you to override some headers including "Content-Encoding".

One way to transparently have the requests for your XMLHttpRequest highly pressed is to use HTTP/2 (e.g. serve your website via CloudFlare).

When using HTTP/2, then although the HTTP headers do not say Content-Encoding: gzip the underlying HTTP/2 protocol presses everything.

It also presses much better than gzip because:

• it presses headers
• header pression uses a standard dictionary
• I think data pression builds a dictionary over multiple messages (brotli - I haven't double-checked that though)

You can see if your server is using HTTP/2 by:

1. Open Chrome, and F12 to open developer tools
2. Click on the network tab
3. close the request inspector panel (has tabs Headers Preview Response Timing)
4. Right click on the Name header of the list of requests and tick Protocol
5. Navigate to your website and watch what protocol is used for all requests - in the protocol column you want to see h2 not http/1.1

I wouldn't remend using JavaScript pression libraries because that causes slowdown and inefficiencies.

The problem doesn't seem to be related to header but to pression.

You don't seem to press your postData.

If postData is already pressed, no need to try to manually set content-encoding.

If it is not, either let the browser negotiate the transfer encoding with the server (this is part of the protocol and done automatically, the server saying if it accepts it, but I think that's rarely the case) or (if you really really need to) encode it yourself. This SO question indicates a library to press browserside : JavaScript implementation of Gzip