internal_link: Always include a "/" after hostname

Fixes: zulip#845

Signed-off-by: Zixuan James Li <[email protected]>

lib/model/internal_link.dart

@@ -96,7 +96,14 @@ Uri narrowLink(PerAccountStore store, Narrow narrow, {int? nearMessageId}) {
     fragment.write('/near/$nearMessageId');
   }
 
-  return store.realmUrl.replace(fragment: fragment.toString());
+  Uri result = store.realmUrl.replace(fragment: fragment.toString());
+  if (result.path.isEmpty) {
+    // Always ensure that there is a '/' right after the hostname.
+    // A generated URL without '/' looks odd,
+    // and if used in a Zulip message does not get automatically linkified.
+    result = result.replace(path: '/');
+  }
+  return result;
 }
 
 /// A [Narrow] from a given URL, on `store`'s realm.

test/model/internal_link_test.dart

@@ -127,6 +127,23 @@ void main() {
         '#narrow/dm/1,2-dm/near/12345',
         '#narrow/pm-with/1,2-pm/near/12345');
     });
+
+    test('normalize links to always include a "/" after hostname', () {
+      String narrowLinkFor({required String realmUrl}) {
+        final store = eg.store(
+          account: eg.account(user: eg.selfUser, realmUrl: Uri.parse(realmUrl)));
+        return narrowLink(store, const CombinedFeedNarrow()).toString();
+      }
+
+      check(narrowLinkFor(realmUrl: 'http://chat.example.com'))
+        .equals(                    'http://chat.example.com/#narrow');
+      check(narrowLinkFor(realmUrl: 'http://chat.example.com/'))
+        .equals(                    'http://chat.example.com/#narrow');
+      check(narrowLinkFor(realmUrl: 'http://chat.example.com/path'))
+        .equals(                    'http://chat.example.com/path#narrow');
+      check(narrowLinkFor(realmUrl: 'http://chat.example.com/path/'))
+        .equals(                    'http://chat.example.com/path/#narrow');
+    });
   });
 
   final realmUrl = Uri.parse('https://example.com/');