fix HTML filter issue when the text contains malformed HTML tags (#27)

Author: olivierpontier

src/Source/Filter/HtmlFilter.php

@@ -120,7 +120,7 @@ public function filter(string $string): string
                 case '>' === $char:
                     if ($this->isIgnoredTag($tagName)) {
                         $ignoreTagContent = true;
-                    } elseif ('/' === $tagName[0]) {
+                    } elseif ($tagName === null || '/' === $tagName[0]) {
                         $ignoreTagContent = false; // Restore to default state.
                     }
                     $context = self::CTX_TAG_CONTENT;
@@ -258,6 +258,10 @@ function ($match) {
      */
     private function isIgnoredTag(?string $name): bool
     {
+        if ($name === null) {
+            return false;
+        }
+
         foreach (self::$ignoreTags as $tag) {
             if (strcasecmp($tag, $name) === 0) {
                 return true;

tests/Unit/Source/Filter/HtmlFilterTest.php

@@ -90,4 +90,12 @@ public function testMalformedAttribute(): void
         $text = '           test    ';
         static::assertEquals($text, $filter->filter($html));
     }
+
+    public function testMalformedTags(): void
+    {
+        $filter = new HtmlFilter();
+        $html = "foo/>bar<br><br/>";
+        $text = "foo/ bar         ";
+        static::assertEquals($text, $filter->filter($html));
+    }
 }