Item14380: A couple of additional tweaks:

This version has been tested with an apache reverse proxy in front of a
plain CGI foswiki and a mod_perl foswiki. Tested with http, https, and
non-standard ports.  All seem to be working fine.

Note that FuncTests::test_getUrl fails, but it appears that the test is
broken.

Also HomePagePlugin tests fail, but it does work when used live. So
more possibly broken tests.

FuncTests has 1 unexpected results (of 58):
   * F: FuncTests::test_getUrlHost
HomePagePluginSuite has 2 unexpected results (of 6):
   * F: HomePagePluginSuite::test_login
   * F: HomePagePluginSuite::test_view

core/lib/Foswiki/Engine.pm

@@ -539,9 +539,12 @@ sub _getConnectionData {
             $proto = $1;
             $host  = $2;
         }
+        elsif ( defined $Foswiki::cfg{DefaultUrlHost} ) {
+            ($host) = $Foswiki::cfg{DefaultUrlHost} =~ m#https?://([^:/]+)#i;
+        }
     }
 
-    #SMELL:  Give up - no obvious hostname in the request.
+    #SMELL:  Give up - no obvious hostname in the request and no default.
     unless ($host) {
         $host = 'localhost';
     }

core/lib/Foswiki/Request.pm

@@ -298,12 +298,12 @@ sub url {
             $url = $Foswiki::cfg{DefaultUrlHost};
         }
         else {
-            my $host = $this->header('Host');
-            my $port = $this->serverPort();
+            my ( $client, $protocol, $host, $port ) =
+              Foswiki::Engine::_getConnectionData();
             $port = ( $port && $port != 80 && $port != 443 ) ? ":$port" : '';
             $url =
                 $host
-              ? $this->protocol . '://' . $host . $port
+              ? $protocol . '://' . $host . $port
               : $Foswiki::cfg{DefaultUrlHost};
         }
         return $url if $base;