Add support for file:// URI scheme.

Signed-off-by: Edward Z. Yang <ezyang@mit.edu>

library/HTMLPurifier/ConfigSchema/schema/URI.AllowedSchemes.txt

@@ -12,6 +12,6 @@ array (
 --DESCRIPTION--
 Whitelist that defines the schemes that a URI is allowed to have.  This
 prevents XSS attacks from using pseudo-schemes like javascript or mocha.
-There is also support for the <code>data</code> URI scheme, but it is not
-enabled by default.
+There is also support for the <code>data</code> and <code>file</code>
+URI schemes, but they are not enabled by default.
 --# vim: et sw=4 sts=4

library/HTMLPurifier/URIScheme/file.php

@@ -0,0 +1,26 @@
+<?php
+
+/**
+ * Validates file as defined by RFC 1630 and RFC 1738.
+ */
+class HTMLPurifier_URIScheme_file extends HTMLPurifier_URIScheme {
+
+    // Generally file:// URLs are not accessible from most
+    // machines, so placing them as an img src is incorrect.
+    public $browsable = false;
+
+    public function validate(&$uri, $config, $context) {
+        parent::validate($uri, $config, $context);
+        // Authentication method is not supported
+        $uri->userinfo = null;
+        // file:// makes no provisions for accessing the resource
+        $uri->port     = null;
+        // While it seems to work on Firefox, the querystring has
+        // no possible effect and is thus stripped.
+        $uri->query    = null;
+        return true;
+    }
+
+}
+
+// vim: et sw=4 sts=4