With the help of HttpWatch, I tried to figure out how GMail implement Comet.

I Login in GMail with two account, one in IE and the other in Firefox. Chatting in GTalk in GMail with some magic words like "WASSUP". Then, I logoff both GMail accounts, filter any http content without "WASSUP" string. The result shows which HTTP request is the streaming channel. (Note: I have to logoff. Otherwise, never-ending HTTP would not show content in HttpWatch.)

The result is interesting. The URL for stream channel is like:

https://mail/channel/bind?VER=8&at=xn3j33vcvk39lkfq.....

There is no surprise that GMail do Comet in IE with IFRAME. The Http content starts with "

Originally, I guessed that GMail do Comet in Firefox with multipart XmlHttpRequest. To my surprise, the response header doesn't have "multipart/x-mixed-replace" header. The response headers are as below:

HTTP/1.1 200 OK
Content-Type: text/plain; charset=utf-8
Cache-Control: no-cache, no-store, max-age=0, must-revalidate
Pragma: no-cache
Expires: Fri, 01 Jan 1990 00:00:00 GMT
Date: Sat, 20 Mar 2010 01:52:39 GMT
X-Frame-Options: ALLOWALL
Transfer-Encoding: chunked
X-Content-Type-Options: nosniff
Server: GSE
X-XSS-Protection: 0

Unfortunately, the HttpWatch doesn't tell whether a HTTP request is from XmlHttpRequest or not. The content is not HTML but JSON. It looks like a response for XHR, but that would not work for Comet without multipart/x-mixed-replace, right?

Is there any way else to figure out how GMail implement Comet?

Thanks.