Google.com and clients1.google.com/generate_204

user_160173 0
Viewed 143702

I was looking into google.com's Net activity in firebug just because I was curious and noticed a request was returning "204 No Content."

It turns out that a 204 No Content "is primarily intended to allow input for actions to take place without causing a change to the user agent's active document view, although any new or updated metainformation SHOULD be applied to the document currently in the user agent's active view." Whatever.

I've looked into the JS source code and saw that "generate_204" is requested like this:

(new Image).src="http://clients1.google.com/generate_204"

No variable declaration/assignment at all.

My first idea is that it was being used to track if Javascript is enabled. But the "(new Image).src='...'" call is called from a dynamically loaded external JS file anyway, so that would be pointless.

Anyone have any ideas as to what the point could be?

UPDATE

"/generate_204" appears to be available on many google services/servers (e.g., maps.google.com/generate_204, maps.gstatic.com/generate_204, etc...).

You can take advantage of this by pre-fetching the generate_204 pages for each google-owned service your web app may use. Like This:

window.onload = function(){
    var two_o_fours = [
        // google maps domain ...
        "http://maps.google.com/generate_204",

        // google maps images domains ... 
        "http://mt0.google.com/generate_204",
        "http://mt1.google.com/generate_204",
        "http://mt2.google.com/generate_204",
        "http://mt3.google.com/generate_204",

        // you can add your own 204 page for your subdomains too!
        "http://sub.domain.com/generate_204"
    ];
    for(var i = 0, l = two_o_fours.length; i < l; ++i){
        (new Image).src = two_o_fours[i];
    }
};
http-headers http javascript
11 Answers

Like Snukker said, clients1.google.com is where the search suggestions come from. My guess is that they make a request to force clients1.google.com into your DNS cache before you need it, so you will have less latency on the first "real" request.

Google Chrome already does that for any links on a page, and (I think) when you type an address in the location bar. This seems like a way to get all browsers to do the same thing.

user_22140

204 responses are sometimes used in AJAX to track clicks and page activity. In this case, the only information being passed to the server in the get request is a cookie and not specific information in request parameters, so this doesn't seem to be the case here.

It seems that clients1.google.com is the server behind google search suggestions. When you visit http://www.google.com, the cookie is passed to http://clients1.google.com/generate_204. Perhaps this is to start up some kind of session on the server? Whatever the use, I doubt it's a very standard use.

user_447210

with the massive remit by google to stop both spam and the scraping of their search database, I believe that this is part of the effort to track bots etc.

some simple anti bot pseudo could go like this.

On GET (google.*) Save RemoteEndPoint
{
    If RemoteEndPoint GETs (clients1.google.com/generate_204) Then
        Set botAlert_stage1 = false;
    Else
        Set botAlert_stage1 = true;
    End If
}

I also believe that the latest google frontpage 'theme' is also a new tool to help with the anti spam/bot activity.

** NOTE ** ipv6.google.com also includes this measure.

Just my unfounded unproofed two 2p.

user_1056850
digitalsanctum_224360
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