fix: rebuild a stateful-pages marker that is not valid UTF-8

news/+stateful-pages-marker-decode.bugfix.md

@@ -0,0 +1 @@
+A `stateful_pages.json` marker that is not valid UTF-8 is now treated as corrupt and rebuilt, instead of raising `UnicodeDecodeError` on every backend start.

reflex/compiler/compiler.py

@@ -1210,16 +1210,18 @@ def _register_plugin_routes(app: App, plugins: Sequence[Plugin]) -> None:
 def _read_stateful_pages_marker() -> list[str] | None:
     """Read the routes that create state classes from a previous compile.
 
-    A missing marker or one truncated by an older writer requires full page
+    A missing marker or one corrupted by an older writer requires full page
     evaluation. New writers replace the marker atomically.
 
     Returns:
         The stateful routes, or None if no valid marker has been written yet.
     """
     marker = prerequisites.get_backend_dir() / constants.Dirs.STATEFUL_PAGES
     try:
-        return json.loads(marker.read_text())
-    except (FileNotFoundError, json.JSONDecodeError):
+        return json.loads(marker.read_bytes())
+    except (FileNotFoundError, ValueError):
+        # ValueError covers both JSONDecodeError and the UnicodeDecodeError of a
+        # marker that is not valid UTF-8.
         return None
     except PermissionError:
         if constants.IS_WINDOWS:

tests/units/test_app.py

@@ -5498,6 +5498,23 @@ def test_compile_dry_run_preserves_stateful_marker(compilable_app, mocker, exist
         assert marker.read_text() == '["previous"]'
 
 
+@pytest.mark.parametrize(
+    "content",
+    [
+        pytest.param(b'["index"', id="truncated"),
+        pytest.param(b"\xff\xfe garbage", id="not-utf-8"),
+    ],
+)
+def test_read_stateful_pages_marker_rejects_corrupt_marker(
+    tmp_path: Path, mocker: MockerFixture, content: bytes
+):
+    """A corrupt marker asks for a full page evaluation instead of raising."""
+    mocker.patch("reflex.utils.prerequisites.get_backend_dir", return_value=tmp_path)
+    (tmp_path / constants.Dirs.STATEFUL_PAGES).write_bytes(content)
+
+    assert _read_stateful_pages_marker() is None
+
+
 def test_write_stateful_pages_marker_concurrent_readers_see_valid_json(
     tmp_path: Path, mocker: MockerFixture
 ):