Installer (or troubleshooting plugin?) should probe the server to see if there are GET request limits in place.
This is a potential problem since 1.2 and first party which can blow up the request size as it can contain the referer URL (truncated to 1000).
The Piwik request raises a 414 (Request URI too long) error. I don't understand why the string size or server limit could be changed, but I contact my hoster to set a higher limit. The string is also just 1400 characters long.
I think during the install, a GET request is generated and tested to check for mod_security etc. is it correct? maybe we could make this URL longer, eg. 1.5k or so, and test that http code returned is 200? If anything else is reported we could display a customized error message (eg. for 414 or 500 codes) to suggest the pain points (eg. mod_security and/or GET URL limits). thoughts?
Note: the current check should verify the response content. Currently, if the user has a custom 4xx page that returns status code 200, then the we get a false negative.
rather than doing this, better implement POSTing data if more than 1k or so: #2321
Leaving this open, since it might be useful to check the http response code (4xx) as per comment 3