Google com and clients1 google com generate 204

Question

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  lt  l    i            new Image  src   two o fours i

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I found this old Thread while google ing for generate 204 as Android seems to use this to determine if the wlan is open  response 204 is received  closed  no response at all  or blocked  redirect to captive portal is present   In that case a notification is shown that a log-in to WiFi is required

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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

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I found this blog post which explains that it s used to record clicks  Without official word from Google it could be used any number of things   http   mark koli ch 2009 03 howto-configure-apache-to-return-a-http-204-no-content-for-ajax html

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Well i have been looking at this for a few times and resulted that Google logs referer s where they come from first time visiting the google com for ex  tracking with Google Chrome i have a  90  guess that its for Logging Referers  maybe User-Agent statistics well known when Google release its list of standards of browser usage    Request URL  http   clients1 google se generate 204 Request Method  GET Status Code  204 No Content   Response Headers   Content-Length  0 Content-Type  text html Date  Fri  21 May 2010 17 06 24 GMT Server  GFE 2 0   Here  Referer  under   Request Headers  shows Googles statistics that many folks come from Microsoft com  also parsing out the word  Windows 7  to help me focus on Windows 7 in my up-following searches that session    Steven

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Many applications access this URL to determine if they have a connection that only leads to a captive portal    The idea is that any captive portal thinks this is a  normal  website  and then redirects you to its portal site  which is returned with a status 200  If an application tries to access any normal website  it is confronted with a totally unexpected response and may have problems figuring out what s wrong  However  with this URL it s easy  If you get status 200  you are inside a captive portal  and you can tell your user to do something about it  usually either log in to the portal using a browser  or turn WiFi off and rely on 3G  if they are using a phone   If you get status 204  you got connected to Google  so your application is actually connected to the internet    Microsoft and Apple use a slightly different approach  they both have some URLs that return a very specific short text message with a status 200  so instead of accessing the Google url you can for example go to  captive apple com  and check for status 200 with data    Success  and nothing else  If you get status 200 and not exactly that data then you are again in a captive portal

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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

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This documents explains  http   docs lib purdue edu cgi viewcontent cgi article 1417 amp context ecetr amp sei-redir 1  Search for generate204  Relevant section   Among the different objects  a javascript function triggers a generate204 request sent to the video server that is supposed to serve the video  This starts the video prefetch  which has two main goals  first  it forces the client to perform the DNS resolution of the video server name  Second  it forces the client to open a TCP connection toward the video server  Both help to speed-up the video download phase  In addition  the generate204 request has exactly the same format and options of the real video download request  so that the video server is eventually warned that a client will possibly download that video very soon  Note that the video server replies with a 204 No Content response  as implied by the command  and no video content is downloaded so far

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Google is using this to detect whether the device is online or in captive portal      Shill  the connection manager for Chromium OS  attempts to detect services that are within a captive portal whenever a service transitions to the ready state   This determination of being in a captive portal or being online is done by attempting to retrieve the webpage http   clients3 google com generate 204   This well known URL is known to return an empty page with an HTTP status 204   If for any reason the web page is not returned  or an HTTP response other than 204 is received  then shill marks the service as being in the portal state    Here is the relevant explanation from the Google Chrome Privacy Whitepaper      In the event that Chrome detects SSL connection timeouts  certificate errors  or other network issues that might be caused by a captive portal  a hotel s WiFi network  for instance   Chrome will make a cookieless request to http   www gstatic com generate 204 and check the response code  If that request is redirected  Chrome will open the redirect target in a new tab on the assumption that it s a login page  Requests to the captive portal detection page are not logged    More info  http   www chromium org chromium-os chromiumos-design-docs network-portal-detection

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In the event that Chrome detects SSL connection timeouts  certificate errors  or other network issues that might be caused by a captive portal  a hotel s WiFi network  for instance   Chrome will make a cookieless request to http   www gstatic com generate 204 and check the response code  If that request is redirected  Chrome will open the redirect target in a new tab on the assumption that it s a login page  Requests to the captive portal detection page are not logged   Source  Google Chrome Privacy Whitepaper

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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

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The generate 204 might be dynamically loading the suggestions of search criteria  AS i can see from my load test script  this is seemingly responsible for every server call each time the user types into the text box

[javascript] Google.com and clients1.google.com/generate_204

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