[utils] more forgiving html parsing + unit tests

test/test_utils.py

@@ -1796,6 +1796,25 @@ Line 1
             (get_element_by_tag_res_innerspan_text, get_element_by_tag_res_innerspan_html))
         self.assertRaises(compat_HTMLParseError, get_element_text_and_html_by_tag, 'article', html)
 
+    def test_get_element_text_and_html_by_tag_malformed(self):
+        inner_text = 'inner_text'
+        malnested_elements = f'<malnested_a><malnested_b>{inner_text}</malnested_a></malnested_b>'
+        html = f'<div>{malnested_elements}</div>'
+
+        self.assertEqual(get_element_text_and_html_by_tag('div', html), (malnested_elements, html))
+        self.assertEqual(
+            get_element_text_and_html_by_tag('malnested_a', html),
+            (f'<malnested_b>{inner_text}',
+             f'<malnested_a><malnested_b>{inner_text}</malnested_a>'))
+        self.assertEqual(
+            get_element_text_and_html_by_tag('malnested_b', html),
+            (f'{inner_text}</malnested_a>',
+             f'<malnested_b>{inner_text}</malnested_a></malnested_b>'))
+        self.assertRaises(
+            compat_HTMLParseError, get_element_text_and_html_by_tag, 'orphan', f'{html}</orphan>')
+        self.assertRaises(
+            compat_HTMLParseError, get_element_text_and_html_by_tag, 'orphan', f'<orphan>{html}')
+
     def test_iri_to_uri(self):
         self.assertEqual(
             iri_to_uri('https://www.google.com/search?q=foo&ie=utf-8&oe=utf-8&client=firefox-b'),

yt_dlp/utils.py

@@ -466,17 +466,13 @@ class HTMLBreakOnClosingTagParser(html.parser.HTMLParser):
         pass
 
     def handle_starttag(self, tag, _):
-        self.tagstack.append(tag)
+        self.tagstack.appendleft(tag)
 
     def handle_endtag(self, tag):
         if not self.tagstack:
             raise compat_HTMLParseError('no tags in the stack')
-        while self.tagstack:
-            inner_tag = self.tagstack.pop()
-            if inner_tag == tag:
-                break
-        else:
-            raise compat_HTMLParseError(f'matching opening tag for closing {tag} tag not found')
+        with contextlib.suppress(ValueError):
+            self.tagstack.remove(tag)
         if not self.tagstack:
             raise self.HTMLBreakOnClosingTagException()
 
@@ -510,6 +506,8 @@ def get_element_text_and_html_by_tag(tag, html):
             next_closing_tag_end = next_closing_tag_start + len(closing_tag)
             try:
                 parser.feed(html[offset:offset + next_closing_tag_end])
+                if tag not in parser.tagstack:
+                    raise HTMLBreakOnClosingTagParser.HTMLBreakOnClosingTagException()
                 offset += next_closing_tag_end
             except HTMLBreakOnClosingTagParser.HTMLBreakOnClosingTagException:
                 return html[content_start:offset + next_closing_tag_start], \