Check if host header is present and set back_to_url accordingly

no_ipv4_here/views.py

@@ -7,6 +7,8 @@ def index(request):
     back_to_url = ""
     if "back_to" in request.GET:
         back_to_url = request.GET["back_to"]
+    elif 'HTTP_HOST' in request.META:
+        back_to_url = request.META['HTTP_HOST']
     if back_to_url != "":
         return HttpResponse(
             """Sorry, <a href="{domain}">this part of domain</a> is not reachable by IPv4.