Pyramid Event Subscribers to migrate cookie data across redirects

__init__.py

def main(global_config,**settings):
   ...
    config.add_subscriber(\
        'myApp.subscribers.cookiexfer_new_request', 
        'pyramid.events.NewRequest')
    config.add_subscriber(\
        'myApp.subscribers.cookiexfer_new_response', 
        'pyramid.events.NewResponse')
    ...

subscribers.py

import logging
log = logging.getLogger(__name__)

from pyramid.httpexceptions import HTTPException
import re

_cookiexfer_redirect_add_headers= True
_cookiexfer_redirect_add_headers__unique= True
_cookiexfer_redirect_session_save= True
_cookiexfer_redirect_session_save__unique = True
_cookiexfer_re_excludes= re.compile("^/(css|img|js|deform|_debug_toolbar)")

def cookiexfer_new_request(event):
    """cookiexfer_new_request(event) ; if there is a @cookie-xfer value in the session, will set the headers and then delete it"""
    if re.match( _cookiexfer_re_excludes , event.request.path_info ):
        return
    log.debug('@cookie-xfer cookiexfer_new_request')
    if _cookiexfer_redirect_session_save:
        if '@cookie-xfer' in event.request.session:
            log.debug("@cookie-xfer - migrating cookies FROM session")
            event.request.response.headers.extend(event.request.session['@cookie-xfer'])
            del event.request.session['@cookie-xfer']

def cookiexfer_new_response(event):
    """cookiexfer_new_response(event) ; migrates headers or saves cookies. NOTE you must either RETURN the exception , or RAISE it and include headers """
    if re.match( _cookiexfer_re_excludes , event.request.path_info ):
        return

    if isinstance( event.response , HTTPException ):
        log.debug('@cookie-xfer cookiexfer_new_response')
        
        # cookies_request is populated if the exception is RETURNed
        # cookies_request is not populated if the exception is RAISEd
        cookies_request= [ (k,v) for (k,v) in event.request.response.headers.iteritems() if k == 'Set-Cookie']

        # cookies_response is populated if the exception is created with headers specified
        cookies_response= [ (k,v) for (k,v) in event.response.headers.iteritems() if k == 'Set-Cookie']

        if cookies_request or cookies_response:
            log.debug("@cookie-xfer - migrating cookies INTO session")
            
            # make a var stash
            headers_cookies_all= []
            headers_cookies_unique= []
            session_cookies_all= []
            session_cookies_unique= []
            
            # then precalculate how we'll save the cookies
            if not _cookiexfer_redirect_add_headers__unique or not _cookiexfer_redirect_session_save__unique :
                # headers only need migrated cookies
                headers_cookies_all = cookies_request
                # session needs to save cookies
                session_cookies_all = cookies_request + cookies_response

            if _cookiexfer_redirect_add_headers__unique or _cookiexfer_redirect_session_save__unique :

                # do a 'seen' dict
                _cookies_unique__seen= {}

                # first we should favor the items that we specifically set in the response
                # headers stay empty
                headers_cookies_unique= []
                # session should favor items from the resposne
                session_cookies_unique = cookies_response

                # and log them all as seen
                # don't add them to the cookies_unique, because they're already in the object
                for (k,v) in cookies_response:
                    _v= v.split(';')
                    if _v[0] not in _cookies_unique__seen:
                        _cookies_unique__seen[_v[0]]= True
                        
                # now add in new cookies
                for (k,v) in cookies_request:
                    _v= v.split(';')
                    if _v[0] not in _cookies_unique__seen:
                        _cookies_unique__seen[_v[0]]= True
                        headers_cookies_unique.append( (k,v) )
                        session_cookies_unique.append( (k,v) )
                        
            # now start sending
            if _cookiexfer_redirect_add_headers:
                if _cookiexfer_redirect_add_headers__unique :
                    event.response.headers.extend( headers_cookies_unique )
                else:
                    event.response.headers.extend( headers_cookies_all )
            if _cookiexfer_redirect_session_save :
                if _cookiexfer_redirect_session_save__unique:
                    event.request.session['@cookie-xfer']= session_cookies_unique
                else:
                    event.request.session['@cookie-xfer']= session_cookies_all