ENG-9917 fix: run plugin post_compile hooks at most once per app instance

news/6733.bugfix.md

@@ -0,0 +1 @@
+Re-constructing the ASGI app on the same app instance no longer re-applies app mutations. Plugin `post_compile` hooks run at most once per plugin per app instance (previously every ASGI app construction re-ran them, e.g. installing a duplicate middleware that gated every event twice), and the assembled ASGI app — including the compiled-frontend mount and `api_transformer` wiring — is built once and cached.

packages/reflex-base/src/reflex_base/plugins/base.py

@@ -139,6 +139,11 @@ def pre_compile(self, **context: Unpack[PreCompileContext]) -> None:
     def post_compile(self, **context: Unpack[PostCompileContext]) -> None:
         """Called after the compilation of the plugin.
 
+        Runs at most once per app instance — even when the ASGI app is
+        constructed repeatedly, and even when another plugin's failed hook
+        forces a retry — so hooks may mutate the app (e.g.
+        ``add_middleware``) without their own idempotency guard.
+
         Args:
             context: The context for the plugin.
         """

reflex/app.py

@@ -42,6 +42,7 @@
 )
 from reflex_base.event.context import EventContext
 from reflex_base.event.processor import BaseStateEventProcessor, EventProcessor
+from reflex_base.plugins import Plugin
 from reflex_base.registry import RegistrationContext
 from reflex_base.telemetry_context import CompileTrigger, TelemetryContext
 from reflex_base.utils import console, memo_paths
@@ -402,6 +403,17 @@ class App(MiddlewareMixin, LifespanMixin):
     # that already compiled and skips re-evaluation.
     _evaluated_pages: set[str] = dataclasses.field(default_factory=set)
 
+    # Plugins whose post_compile hook already ran for this app instance.
+    # The hooks mutate the app (add_middleware, mounting routes), so each
+    # must run at most once, even when another plugin's failed hook forces
+    # the ASGI app assembly to be retried.
+    _post_compiled_plugins: set[Plugin] = dataclasses.field(default_factory=set)
+
+    # The ASGI app assembled by __call__, built at most once per app
+    # instance: assembly mutates persistent objects (self._api, a Starlette
+    # api_transformer), so re-constructing the ASGI app must not re-run it.
+    _cached_asgi_app: ASGIApp | None = None
+
     # The backend API object.
     _api: Starlette | None = None
 
@@ -708,9 +720,6 @@ def __call__(self) -> ASGIApp:
 
         Returns:
             The backend api.
-
-        Raises:
-            ValueError: If the app has not been initialized.
         """
         from reflex_base.vars.base import GLOBAL_CACHE
 
@@ -725,14 +734,29 @@ def __call__(self) -> ASGIApp:
             trigger=get_backend_compile_trigger(),
         )
 
-        config = get_config()
-
-        for plugin in config.plugins:
-            plugin.post_compile(app=self)
+        # Assembly runs at most once per app instance; _compile stays per-call.
+        if self._cached_asgi_app is None:
+            self._cached_asgi_app = self._assemble_asgi_app()
 
         # We will not be making more vars, so we can clear the global cache to free up memory.
         GLOBAL_CACHE.clear()
 
+        return self._cached_asgi_app
+
+    def _assemble_asgi_app(self) -> ASGIApp:
+        """Run plugin post_compile hooks and wrap the backend api into an ASGI app.
+
+        Returns:
+            The assembled ASGI app.
+
+        Raises:
+            ValueError: If the app has not been initialized.
+        """
+        for plugin in get_config().plugins:
+            if plugin not in self._post_compiled_plugins:
+                plugin.post_compile(app=self)
+                self._post_compiled_plugins.add(plugin)
+
         if not self._api:
             msg = "The app has not been initialized."
             raise ValueError(msg)

tests/units/test_app.py

@@ -3064,6 +3064,92 @@ def test_call_app():
     assert isinstance(api, Starlette)
 
 
+def _app_with_plugins(mocker: MockerFixture, *plugins: unittest.mock.Mock) -> App:
+    """Create an app configured with the given plugin doubles.
+
+    Args:
+        mocker: The pytest-mock fixture.
+        plugins: Plugin doubles to install in the app's config.
+
+    Returns:
+        An app with a mocked-out ``_compile``.
+    """
+    conf = rx.Config(app_name="testing", plugins=list(plugins))
+    mocker.patch("reflex_base.config._get_config", return_value=conf)
+    app = App()
+    app._compile = unittest.mock.Mock()
+    return app
+
+
+def test_call_app_runs_plugin_post_compile_once(mocker: MockerFixture):
+    """Constructing the ASGI app twice runs each plugin's post_compile once.
+
+    ``post_compile`` hooks mutate the app (add middleware, mount routes) and
+    are not required to be idempotent, so ``App.__call__`` must not re-run
+    them when the ASGI app is constructed again on the same app instance
+    (e.g. a test harness rebuilding it).
+    """
+    plugin = unittest.mock.Mock(spec=rx.plugins.Plugin)
+    app = _app_with_plugins(mocker, plugin)
+    app()
+    app()
+
+    plugin.post_compile.assert_called_once()
+
+
+def test_call_app_retries_post_compile_after_failure(mocker: MockerFixture):
+    """A post_compile failure is not latched as done.
+
+    If a hook raises (e.g. a plugin rejecting a misconfigured app), the next
+    ASGI construction must run the hook again rather than silently skipping
+    it.
+    """
+    plugin = unittest.mock.Mock(spec=rx.plugins.Plugin)
+    plugin.post_compile.side_effect = [ValueError("misconfigured"), None]
+    app = _app_with_plugins(mocker, plugin)
+    with pytest.raises(ValueError, match="misconfigured"):
+        app()
+    app()
+
+    assert plugin.post_compile.call_count == 2
+
+
+def test_call_app_partial_post_compile_failure(mocker: MockerFixture):
+    """A failed hook is retried without re-running already-succeeded hooks.
+
+    With multiple plugins, a failure in a later plugin's post_compile must
+    not cause the earlier plugins' (non-idempotent) hooks to run again on
+    the next ASGI construction.
+    """
+    ok_plugin = unittest.mock.Mock(spec=rx.plugins.Plugin)
+    flaky_plugin = unittest.mock.Mock(spec=rx.plugins.Plugin)
+    flaky_plugin.post_compile.side_effect = [ValueError("misconfigured"), None]
+    app = _app_with_plugins(mocker, ok_plugin, flaky_plugin)
+    with pytest.raises(ValueError, match="misconfigured"):
+        app()
+    app()
+
+    ok_plugin.post_compile.assert_called_once()
+    assert flaky_plugin.post_compile.call_count == 2
+
+
+def test_call_app_caches_asgi_app(mocker: MockerFixture):
+    """Repeated ASGI construction returns the same app without re-assembly.
+
+    Assembly mutates persistent objects (``self._api``, ``api_transformer``),
+    e.g. appending the frontend mount or re-adding CORS middleware, so it must
+    run at most once per app instance while ``_compile`` still runs per call.
+    """
+    app = _app_with_plugins(mocker)
+    compile_mock = unittest.mock.Mock()
+    app._compile = compile_mock
+    first = app()
+    second = app()
+
+    assert first is second
+    assert compile_mock.call_count == 2
+
+
 @pytest.fixture
 def upload_enabled(monkeypatch):
     """Fixture that enables Upload and cleans up afterward."""