How can I get ASP.NET AJAX to send its JSON response with GZip compression?

Question

I have compression enabled within IIS7 and it works as expected on all responses except for those constructed by ASP.NET AJAX. I have a web service that provides data to the cl

Answer 1

In general you don't want to do this unless you wouldn't mind throwing orders of magnitudes the amount of server power into your apps...

Also not only server-CPU but also client-CPU becomes a problem when you do this....

This concludes with that your app becomes WAY slower if you GZip all your Ajax Responses...!

Answer 2

What browser are you using? There's a bug in IE 6 that causes errors in compression. So ASP.NET AJAX turns off compression to IE 6 browsers:

http://weblogs.asp.net/scottgu/archive/2005/06/28/416185.aspx

Also, did you enable compression for ASMX files?

Answer 3

Last I checked, the gzipping was something that IIS does (when setup correctly) - and of course when the browser sends the required headers

Answer 4

IIS7 uses the content-encoding to decide whether to compress the response (assuming of course that the browser can accept gzip). They're set in applicationHost.config, and by default the list is

<dynamicTypes>
     <add mimeType="text/*" enabled="true" />
     <add mimeType="message/*" enabled="true" />
     <add mimeType="application/x-javascript" enabled="true" />
     <add mimeType="*/*" enabled="false" />
</dynamicTypes>

If you call the web service directly, the XML response has a content-type of text/xml, which gets compressed. When called by AJAX, the JSON response has a content type of application/json, so it isn't compressed. Adding the following to applicationHost.config should fix that...

     <add mimeType="application/json" enabled="true" />