feat: Add support for CSS aspect-ratio (#408)

library/HTMLPurifier/AttrDef/CSS/Ratio.php

@@ -0,0 +1,46 @@
+<?php
+
+/**
+ * Validates a ratio as defined by the CSS spec.
+ */
+class HTMLPurifier_AttrDef_CSS_Ratio extends HTMLPurifier_AttrDef
+{
+    /**
+     * @param   string               $ratio   Ratio to validate
+     * @param   HTMLPurifier_Config  $config  Configuration options
+     * @param   HTMLPurifier_Context $context Context
+     *
+     * @return  string|boolean
+     *
+     * @warning Some contexts do not pass $config, $context. These
+     *          variables should not be used without checking HTMLPurifier_Length
+     */
+    public function validate($ratio, $config, $context)
+    {
+        $ratio = $this->parseCDATA($ratio);
+
+        $parts = explode('/', $ratio, 2);
+        $length = count($parts);
+
+        if ($length < 1 || $length > 2) {
+            return false;
+        }
+
+        $num = new \HTMLPurifier_AttrDef_CSS_Number();
+
+        if ($length === 1) {
+            return $num->validate($parts[0], $config, $context);
+        }
+
+        $num1 = $num->validate($parts[0], $config, $context);
+        $num2 = $num->validate($parts[1], $config, $context);
+
+        if ($num1 === false || $num2 === false) {
+            return false;
+        }
+
+        return $num1 . '/' . $num2;
+    }
+}
+
+// vim: et sw=4 sts=4

library/HTMLPurifier/CSSDefinition.php

@@ -304,6 +304,13 @@ class HTMLPurifier_CSSDefinition extends HTMLPurifier_Definition
                     $trusted_max_wh
                 );
 
+        $this->info['aspect-ratio'] = new HTMLPurifier_AttrDef_CSS_Multiple(
+            new HTMLPurifier_AttrDef_CSS_Composite([
+                new HTMLPurifier_AttrDef_CSS_Ratio(),
+                new HTMLPurifier_AttrDef_Enum(['auto']),
+            ])
+        );
+
         // text-decoration and related shorthands
         $this->info['text-decoration'] = new HTMLPurifier_AttrDef_CSS_TextDecoration();