Obtaining original destination ip in cherrypy

I am running a captive portal on a cherrypy server and I have set up iptables rules that REDIRECT all http traffic from unregistered MAC addresses to the portal. After a user registers with me via the portal splash page, I add an iptables exception to let their traffic through.
Now what I want to do is redirect the user to the page they were originally going for - before they got sent to the portal. I know that iptables sets a field with the original destination information for all TCP packets, and I know there is a C function called getsockopt to read that field. However, I don't know how to access the socket associated with a request in cherrypy.

Can anybody help me out? :)

I'm not an expert in low-level networking and don't know how common open Wi-Fi authorisation implementations tag its clients. But what seems true to me is that in OSI model, lower layers know nothing about upper layers. In other words IP has no idea of HTTP terms and a page URL specifically.

This way having a socket reference at hand, which I believe is possible to retrieve through customising CherryPy, will give you original IP address at most, not URL. Also mixing networking (IP) and application (HTTP) layers, and generally managing one application entity in several places, will likely result in issues of all sorts. For instance dealing with HTTP speaking agents, forward and reverse proxies for instance, which won't reserve nuances of lower layer.

Update

Okay, since you say you also have the request URL, here is how you can retrieve the raw socket. As you can see, it is deep under the hood and essentially an implementation detail that an end-user shouldn't rely onto. It is not a part of the contract and it can be changed in any next version. Thus you have a good chance to shoot oneself in the foot.

#!/usr/bin/env python


import cherrypy


config = {
  'global' : {
    'server.socket_host' : '127.0.0.1',
    'server.socket_port' : 8080,
    'server.thread_pool' : 8
  },
}


class App:

  @cherrypy.expose
  def index(self):
    '''For caveats and details on the slippery slope, take a look at ws4py
    https://github.com/Lawouach/WebSocket-for-Python/blob/master/ws4py/server/cherrypyserver.py
    '''
    print(cherrypy.serving.request.rfile.rfile._sock)

    return 'Make sure you know what you are doing.'


if __name__ == '__main__':
  cherrypy.quickstart(App(), '/', config)