[HOT-FIX] Download attachment is failed on iOS (#4405)

model/test/email/attachment_test.dart

@@ -63,5 +63,122 @@ void main() {
         expect(result, 'http://localhost/download/1/some-blob-id/ti%C3%AAu%20%C4%91%E1%BB%81%20attachment?name=ti%C3%AAu%20%C4%91%E1%BB%81%20attachment&type=application%2Foctet-stream');
       });
     });
+
+    group('generateFileName:', () {
+      test(
+        'should return name when name is not empty',
+      () {
+        final attachment = Attachment(
+          blobId: Id('some-blob-id'),
+          name: 'document.pdf',
+          type: MediaType.parse('application/pdf'),
+        );
+
+        expect(attachment.generateFileName(), 'document.pdf');
+      });
+
+      test(
+        'should return name is trimmed when name has leading/trailing spaces',
+      () {
+        final attachment = Attachment(
+          blobId: Id('some-blob-id'),
+          name: '  document.pdf  ',
+          type: MediaType.parse('application/pdf'),
+        );
+
+        expect(attachment.generateFileName(), 'document.pdf');
+      });
+
+      test(
+        'should return blobId with extension when name is null',
+      () {
+        final attachment = Attachment(
+          blobId: Id('some-blob-id'),
+          type: MediaType.parse('image/png'),
+        );
+
+        expect(attachment.generateFileName(), 'some-blob-id.png');
+      });
+
+      test(
+        'should return blobId with extension when name is empty',
+      () {
+        final attachment = Attachment(
+          blobId: Id('some-blob-id'),
+          name: '',
+          type: MediaType.parse('image/png'),
+        );
+
+        expect(attachment.generateFileName(), 'some-blob-id.png');
+      });
+
+      test(
+        'should return blobId with extension when name is only whitespace',
+      () {
+        final attachment = Attachment(
+          blobId: Id('some-blob-id'),
+          name: '   ',
+          type: MediaType.parse('image/jpeg'),
+        );
+
+        expect(attachment.generateFileName(), 'some-blob-id.jpeg');
+      });
+
+      test(
+        'should return blobId without extension when name is null and type is null',
+      () {
+        final attachment = Attachment(
+          blobId: Id('some-blob-id'),
+        );
+
+        expect(attachment.generateFileName(), 'some-blob-id');
+      });
+
+      test(
+        'should return default name when both name and blobId are null',
+      () {
+        final attachment = Attachment(
+          type: MediaType.parse('image/png'),
+        );
+
+        expect(attachment.generateFileName(), 'unknown-attachment');
+      });
+
+      test(
+        'should sanitize name with question mark character',
+      () {
+        final attachment = Attachment(
+          blobId: Id('some-blob-id'),
+          name: 'doc?.pdf',
+          type: MediaType.parse('application/pdf'),
+        );
+
+        expect(attachment.generateFileName(), 'doc_.pdf');
+      });
+
+      test(
+        'should sanitize name with forward slash character',
+      () {
+        final attachment = Attachment(
+          blobId: Id('some-blob-id'),
+          name: 'folder/document.pdf',
+          type: MediaType.parse('application/pdf'),
+        );
+
+        expect(attachment.generateFileName(), 'folder_document.pdf');
+      });
+
+      test(
+        'should return default name when name consists entirely of illegal characters',
+      () {
+        final attachment = Attachment(
+          blobId: Id('some-blob-id'),
+          name: '???',
+          type: MediaType.parse('application/pdf'),
+        );
+
+        expect(attachment.generateFileName(), 'unknown-attachment');
+      });
+    });
   });
 }