Add dev site switcher for testing every site from one host

With DEBUG on, ?site=<domain> selects the site without DNS or hosts
entries and is remembered in a cookie. /dev-sites/ lists all
configured sites as links.

dynamicweb/settings/local.py

@@ -15,6 +15,10 @@ CACHES = {
     }
 }
 
+MIDDLEWARE_CLASSES = (
+    'utils.middleware.DevSiteSwitcherMiddleware',
+) + MIDDLEWARE_CLASSES
+
 MIDDLEWARE_CLASSES += ("debug_toolbar.middleware.DebugToolbarMiddleware",)
 
 INSTALLED_APPS += (

utils/middleware.py

@@ -1,3 +1,9 @@
+import json
+
+from django.conf import settings
+from django.http import HttpResponse
+
+
 class MultipleProxyMiddleware(object):
     FORWARDED_FOR_FIELDS = [
         'HTTP_X_FORWARDED_FOR',
@@ -15,3 +21,52 @@ class MultipleProxyMiddleware(object):
                 if ',' in request.META[field]:
                     parts = request.META[field].split(',')
                     request.META[field] = parts[-1].strip()
+
+
+class DevSiteSwitcherMiddleware(object):
+    """
+    Dev/test only (enabled from settings/local.py, i.e. DEBUG=True).
+
+    The project picks a site from the request's Host header. To test every
+    site from a single address without DNS or /etc/hosts entries, visit
+    http://<server>:8000/?site=datacenterlight.ch once; the choice is kept in
+    a cookie. ?site= (empty) clears it.
+    """
+    COOKIE = 'dev_site'
+
+    def process_request(self, request):
+        if request.path == '/dev-sites/':
+            return self.sites_page()
+        if 'site' in request.GET:
+            site = request.GET['site'].strip()
+        else:
+            site = request.COOKIES.get(self.COOKIE, '')
+        request.META['DEV_SITE_SWITCH'] = site
+        if site:
+            request.META['HTTP_HOST'] = site
+            request.META.pop('HTTP_X_FORWARDED_HOST', None)
+
+    def process_response(self, request, response):
+        if 'site' in request.GET:
+            site = request.META.get('DEV_SITE_SWITCH', '')
+            if site:
+                response.set_cookie(self.COOKIE, site)
+            else:
+                response.delete_cookie(self.COOKIE)
+        return response
+
+    def sites_page(self):
+        """A page listing every configured site as a link, on any host"""
+        try:
+            domains = sorted(
+                d for d in json.loads(settings.UNGLEICH_SITE_CONFIGS)
+                if ':' not in d)
+        except ValueError:
+            domains = []
+        items = ''.join(
+            '<li><a href="/?site={0}">{0}</a></li>'.format(d) for d in domains)
+        return HttpResponse(
+            '<!doctype html><title>Test sites</title>'
+            '<h1>Test sites</h1><p>Click a site to browse it; '
+            '<a href="/?site=">clear</a> the choice.</p><ul>{}</ul>'.format(
+                items))