lib/services/paywall_service.dart

@@ -54,8 +54,24 @@ class PaywallService {
   bool isPaid(Article a) =>
       paidTitle.hasMatch(a.title) || _isCutSubstackPost(a) || (_checks[a.link]?.paid ?? false);
 
-  static bool _isCutSubstackPost(Article a) =>
-      _substackCut.firstMatch(a.contentHtml)?.group(1) == a.link;
+  static bool _isCutSubstackPost(Article a) {
+    final readMore = _substackCut.firstMatch(a.contentHtml)?.group(1);
+    return readMore != null && _samePost(readMore, a.link);
+  }
+
+  /// Whether two links point at the same post. Only host and path count:
+  /// scheme, host case, a trailing slash, the query (tracking parameters)
+  /// and the fragment don't.
+  static bool _samePost(String a, String b) {
+    String? key(String link) {
+      final uri = Uri.tryParse(link.trim());
+      if (uri == null || uri.host.isEmpty) return null;
+      return '${uri.host.toLowerCase()}${uri.path.replaceFirst(RegExp(r'/+$'), '')}';
+    }
+
+    final keyA = key(a);
+    return keyA != null && keyA == key(b);
+  }
 
   bool isSponsored(Article a) => sponsoredTitle.hasMatch(a.title);
 

test/paywall_service_test.dart

@@ -56,6 +56,31 @@ void main() {
         reason: 'a free post ending with the subscribe widget');
   });
 
+  test('matches the "Read more" link of a paid Substack post to the post despite URL noise',
+      () async {
+    final paywall = PaywallService(await _storage(), client: MockClient((_) async => http.Response('', 500)));
+    Article cutPost({required String link, required String readMore}) => Article(
+          title: 'A paid post',
+          link: link,
+          source: _source(),
+          contentHtml: '<p>The first paragraph.</p><p><a href="$readMore">Read more</a></p>',
+        );
+    const post = 'https://example.substack.com/p/a-paid-post';
+
+    expect(paywall.isPaid(cutPost(link: post, readMore: '$post/')), isTrue,
+        reason: 'trailing slash on the "Read more" link');
+    expect(paywall.isPaid(cutPost(link: '$post/', readMore: post)), isTrue,
+        reason: 'trailing slash on the article link');
+    expect(paywall.isPaid(cutPost(link: post, readMore: '$post?utm_source=substack&utm_medium=email')),
+        isTrue, reason: 'tracking query on the "Read more" link');
+    expect(paywall.isPaid(cutPost(link: '$post?utm_campaign=post#footnote-1', readMore: post)), isTrue,
+        reason: 'query and fragment on the article link');
+    expect(paywall.isPaid(cutPost(link: post, readMore: 'http://Example.Substack.com/p/a-paid-post')),
+        isTrue, reason: 'other scheme and host case');
+    expect(paywall.isPaid(cutPost(link: post, readMore: 'https://example.substack.com/p/another-post')),
+        isFalse, reason: 'a "Read more" link to a different post');
+  });
+
   test('checks pages only for flagged sources and remembers results', () async {
     final storage = await _storage();
     final requested = <String>[];