rfc2231 compatible encoding for header()

This is only used in the filename header field and ensures correct
interpretation of an encoded filename. This is will be needed
especially for download of files with umlauts with an Internet Explorer.

inc/fetch.functions.php

@@ -71,9 +71,9 @@ function sendFile($file, $mime, $dl, $cache, $public = false, $orig = null) {
 
     //download or display?
     if($dl) {
-        header('Content-Disposition: attachment; filename="'.utf8_basename($orig).'";');
+        header('Content-Disposition: attachment;'.rfc2231_encode('filename', utf8_basename($orig)).';');
     } else {
-        header('Content-Disposition: inline; filename="'.utf8_basename($orig).'";');
+        header('Content-Disposition: inline;'.rfc2231_encode('filename', utf8_basename($orig)).';');
     }
 
     //use x-sendfile header to pass the delivery to compatible webservers
@@ -89,6 +89,31 @@ function sendFile($file, $mime, $dl, $cache, $public = false, $orig = null) {
     }
 }
 
+/**
+ * Try an rfc2231 compatible encoding. This ensures correct
+ * interpretation of filenames outside of the ASCII set.
+ * This seems to be needed for file names with e.g. umlauts that
+ * would otherwise decode wrongly in IE.
+ *
+ * There is no additional checking, just the encoding and setting the key=value for usage in headers
+ *
+ * @author Gerry Weissbach <gerry.w@gammaproduction.de>
+ * @param string $name      name of the field to be set in the header() call
+ * @param string $value     value of the field to be set in the header() call
+ * @param string $charset   used charset for the encoding of value
+ * @param string $lang      language used.
+ * @return string           in the format " name=value" for values WITHOUT special characters
+ * @return string           in the format " name*=charset'lang'value" for values WITH special characters
+ */
+function rfc2231_encode($name, $value, $charset='utf-8', $lang='en') {
+    $internal = preg_replace_callback('/[\x00-\x20*\'%()<>@,;:\\\\"\/[\]?=\x80-\xFF]/', function($match) { return rawurlencode($match[0]); }, $value);
+    if ( $value != $internal ) {
+        return ' '.$name.'*='.$charset."'".$lang."'".$internal;
+    } else {
+        return ' '.$name.'="'.$value.'"';
+    }
+}
+
 /**
  * Check for media for preconditions and return correct status code
  *