--- loncom/lonencurl.pm	2007/10/02 01:10:16	1.4
+++ loncom/lonencurl.pm	2011/10/01 03:18:57	1.5
@@ -2,7 +2,7 @@
 # The LearningOnline Network
 # URL translation for encrypted filenames
 #
-# $Id: lonencurl.pm,v 1.4 2007/10/02 01:10:16 albertel Exp $
+# $Id: lonencurl.pm,v 1.5 2011/10/01 03:18:57 raeburn Exp $
 #
 # Copyright Michigan State University Board of Trustees
 #
@@ -33,6 +33,7 @@ use strict;
 use Apache::Constants qw(:common :remotehost);
 use Apache::lonnet;
 use Apache::lonenc;
+use GDBM_File;
 
 sub handler {
     my $r = shift;
@@ -44,8 +45,40 @@ sub handler {
 # Initialize Environment
 	my $lonidsdir=$r->dir_config('lonIDsDir');
 	&Apache::lonnet::transfer_profile_to_env($lonidsdir,$handle);
-# Decrypt URL and redirect
-	my $redirect=&Apache::lonenc::unencrypted($r->uri);
+# Decrypt URL, if appropriate, and redirect
+        my $redirect;
+        my ($decrypted,$encnum,$remainder) = &checkdecryption($r->uri);
+        if (($encnum ne '') && ($remainder ne '')) {
+            my $referrer = $r->headers_in->{'Referer'} || '';
+            my $host = $r->headers_in->{'Host'};
+            my $decryptreferrer;
+            if ($referrer =~ m{^https?://\Q$host\E(/enc/\Q$encnum\E/[^?]+)}) {
+                ($decryptreferrer) = &checkdecryption($1);
+            }
+            if ($decryptreferrer eq '') {
+                if ($env{'request.course.fn'} ne '') {
+                    my %symbhash;
+                    if (tie(%symbhash,'GDBM_File',$env{'request.course.fn'}.'_symb.db',
+                        &GDBM_READER(),0640)) {
+                        my $lastsymb=$symbhash{'last_known'};
+                        untie(%symbhash);
+                        (undef,undef,$decryptreferrer)=&Apache::lonnet::decode_symb($lastsymb);
+                        $decryptreferrer = &Apache::lonnet::clutter($decryptreferrer);
+                    }
+                }
+            }
+            if ($decryptreferrer ne '') {
+                my ($referrerpath) = ($decryptreferrer =~ m{^(.+/)[^/]+$});
+                if (($env{'httpref.'.$referrerpath.$remainder} eq $decryptreferrer) ||
+                    ($env{'httpref.'.$referrerpath.'*'} eq $decryptreferrer) ||
+                    ($env{'httpref.'.$referrerpath} eq $decryptreferrer)) {
+                   $redirect=$referrerpath.$remainder;
+                }
+            }
+        }
+        if ($redirect eq '') {
+            $redirect=&Apache::lonenc::unencrypted($r->uri);
+        }
 	if ($r->args) { $redirect.='?'.$r->args; }
 	$r->internal_redirect($redirect);
 	return OK;
@@ -53,5 +86,17 @@ sub handler {
     return FORBIDDEN;
 }
 
+sub checkdecryption {
+    my ($uri) = @_;
+    my ($encnum,$encname,$rest) = ($uri =~ m{^/enc/(\d+)/([^.]+)(.*)$});
+    my $enclength = length($encname);
+    my $rem = $enclength%16;
+    if (($encname =~ /[^a-f0-9]/) || ($rem != 0) || ($enclength < 16)) {
+        return ('',$encnum,$encname.$rest);
+    } else {
+        return (&Apache::lonenc::unencrypted($uri));
+    }
+}
+
 1;
 __END__