Google Search Appliance Protocol Reference - Manual (Page 104)

Google Search Appliance: Search Protocol Reference Advanced Search Reporting Service /click Protocol 104
Responses
In response to the /click URL, the search appliance always sends the same HTTP response back to the
browser to acknowledge receipt. The response has a status code of 204 (no content) and a MIME type of
image/gif.
The Google implementation running on the client generates a URL with JavaScript as a dummy image
object. The result is ignored, because the response does not affect the client behavior. Its purpose is to
log the user interactions on the server side.