Extract title from html error messages

rolandgeider · rolandgeider · commit bfb44c21578c · 2026-06-17T21:39:51.000+02:00
diff --git a/lib/core/error_dialogs.dart b/lib/core/error_dialogs.dart
@@ -430,6 +430,12 @@ class FormHttpErrorsWidget extends StatelessWidget {
   Widget build(BuildContext context) {
     final theme = Theme.of(context);
 
+    // A JSON endpoint answering with HTML often means a proxy or bot wall such
+    // as Anubis intercepted the request. Such pages render near-blank through
+    // flutter_html since their visible content is JS-driven. In these cases we
+    // try pull out the <title>, which usually names the culprit
+    final htmlTitle = exception.type == ErrorType.html ? htmlErrorTitle(exception.htmlError) : null;
+
     return Container(
       constraints: const BoxConstraints(maxHeight: 250),
       decoration: BoxDecoration(
@@ -441,9 +447,18 @@ class FormHttpErrorsWidget extends StatelessWidget {
         child: Column(
           children: [
             Icon(Icons.error_outline, color: theme.colorScheme.error),
-            if (exception.type == ErrorType.html)
-              ServerHtmlError(data: exception.htmlError)
-            else
+            if (exception.type == ErrorType.html) ...[
+              if (htmlTitle != null)
+                Text(
+                  htmlTitle,
+                  textAlign: TextAlign.center,
+                  style: TextStyle(
+                    fontWeight: FontWeight.bold,
+                    color: theme.colorScheme.error,
+                  ),
+                ),
+              ServerHtmlError(data: exception.htmlError),
+            ] else
               ...formatApiErrors(
                 extractErrors(exception.errors),
                 color: theme.colorScheme.error,
@@ -454,3 +469,25 @@ class FormHttpErrorsWidget extends StatelessWidget {
     );
   }
 }
+
+/// Extracts the `<title>` of an HTML error body (e.g. a proxy or bot-wall page
+/// such as Cloudflare or Anubis), with the few HTML entities that show up in
+/// such titles unescaped. Returns null when there is no usable title.
+String? htmlErrorTitle(String html) {
+  final match = RegExp(
+    r'<title[^>]*>(.*?)</title>',
+    caseSensitive: false,
+    dotAll: true,
+  ).firstMatch(html);
+  final raw = match?.group(1)?.trim();
+  if (raw == null || raw.isEmpty) {
+    return null;
+  }
+  return raw
+      .replaceAll('&#39;', "'")
+      .replaceAll('&#x27;', "'")
+      .replaceAll('&quot;', '"')
+      .replaceAll('&lt;', '<')
+      .replaceAll('&gt;', '>')
+      .replaceAll('&amp;', '&');
+}
diff --git a/test/core/error_dialogs_test.dart b/test/core/error_dialogs_test.dart
@@ -43,4 +43,28 @@ void main() {
       expect(texts.every((t) => t.style?.color == Colors.red), isTrue);
     });
   });
+
+  group('htmlErrorTitle', () {
+    test('extracts and unescapes the title of a bot-wall page', () {
+      const html =
+          '<!doctype html><html lang="en"><head>'
+          '<title>Making sure you&#39;re not a bot!</title>'
+          '</head><body></body></html>';
+
+      expect(htmlErrorTitle(html), "Making sure you're not a bot!");
+    });
+
+    test('matches case-insensitively and ignores attributes on the title tag', () {
+      expect(
+        htmlErrorTitle('<HEAD><TITLE data-x="1">Just a moment...</TITLE></HEAD>'),
+        'Just a moment...',
+      );
+    });
+
+    test('returns null when there is no usable title', () {
+      expect(htmlErrorTitle('<html><body>no title here</body></html>'), isNull);
+      expect(htmlErrorTitle('<html><head><title>   </title></head></html>'), isNull);
+      expect(htmlErrorTitle(''), isNull);
+    });
+  });
 }
