Provide app.storage.client as a location to store volatile data which only matters for the current connection

nicegui/client.py

@@ -73,6 +73,7 @@ def __init__(self, page: page, *, shared: bool = False) -> None:
         self._body_html = ''
 
         self.page = page
+        self.state = {}
 
         self.connect_handlers: List[Union[Callable[..., Any], Awaitable]] = []
         self.disconnect_handlers: List[Union[Callable[..., Any], Awaitable]] = []
@@ -84,6 +85,12 @@ def is_auto_index_client(self) -> bool:
         """Return True if this client is the auto-index client."""
         return self is self.auto_index_client
 
+    @staticmethod
+    def current_client() -> Optional[Client]:
+        """Returns the current client if obtainable from the current context."""
+        from .context import get_client
+        return get_client()
+
     @property
     def ip(self) -> Optional[str]:
         """Return the IP address of the client, or None if the client is not connected."""

nicegui/storage.py

@@ -13,6 +13,7 @@
 from starlette.responses import Response
 
 from . import background_tasks, context, core, json, observables
+from .context import get_slot_stack
 from .logging import log
 
 request_contextvar: contextvars.ContextVar[Optional[Request]] = contextvars.ContextVar('request_var', default=None)
@@ -149,10 +150,21 @@ def general(self) -> Dict:
         """General storage shared between all users that is persisted on the server (where NiceGUI is executed)."""
         return self._general
 
+    @property
+    def session(self) -> Dict:
+        """Volatile client storage that is persisted on the server (where NiceGUI is
+        executed) on a per client/per connection basis.
+        Note that this kind of storage can only be used in single page applications
+        where the client connection is preserved between page changes."""
+        client = context.get_client()
+        return client.state
+
     def clear(self) -> None:
         """Clears all storage."""
         self._general.clear()
         self._users.clear()
+        if get_slot_stack():
+            self.session.clear()
         for filepath in self.path.glob('storage-*.json'):
             filepath.unlink()
 

tests/test_session_state.py

@@ -0,0 +1,17 @@
+from nicegui import ui, app
+from nicegui.testing import Screen
+
+
+def test_session_state(screen: Screen):
+    app.storage.session["counter"] = 123
+
+    def increment():
+        app.storage.session["counter"] = app.storage.session["counter"] + 1
+
+    ui.button("Increment").on_click(increment)
+    ui.label().bind_text(app.storage.session, "counter")
+
+    screen.open('/')
+    screen.should_contain('123')
+    screen.click('Increment')
+    screen.wait_for('124')