Add custom_data hook

Author: T4rk1n

dash/_callback_context.py

@@ -304,6 +304,11 @@ def origin(self):
         """
         return _get_from_context("origin", "")
 
+    @property
+    @has_context
+    def custom_data(self):
+        return _get_from_context("custom_data", {})
+
 
 callback_context = CallbackContext()
 

dash/_hooks.py

@@ -45,6 +45,7 @@ def __init__(self) -> None:
             "error": [],
             "callback": [],
             "index": [],
+            "custom_data": [],
         }
         self._js_dist = []
         self._css_dist = []
@@ -191,6 +192,19 @@ def wrap(func):
 
         return wrap
 
+    def custom_data(self, namespace, priority: _t.Optional[int] = None, final=False):
+        def wrap(func):
+            self.add_hook(
+                "custom_data",
+                func,
+                priority=priority,
+                final=final,
+                data={"namespace": namespace},
+            )
+            return func
+
+        return wrap
+
 
 hooks = _Hooks()
 

dash/dash.py

@@ -1389,6 +1389,10 @@ def dispatch(self):
             g.path = flask.request.full_path
             g.remote = flask.request.remote_addr
             g.origin = flask.request.origin
+            g.custom_data = AttributeDict({})
+
+            for hook in self._hooks.get_hooks("custom_data"):
+                g.custom_data[hook.data["namespace"]] = hook(g)
 
         except KeyError as missing_callback_function:
             msg = f"Callback function not found for output '{output}', perhaps you forgot to prepend the '@'?"

tests/integration/test_hooks.py

@@ -2,7 +2,7 @@
 import requests
 import pytest
 
-from dash import Dash, Input, Output, html, hooks, set_props
+from dash import Dash, Input, Output, html, hooks, set_props, ctx
 
 
 @pytest.fixture
@@ -14,6 +14,7 @@ def hook_cleanup():
     hooks._ns["error"] = []
     hooks._ns["callback"] = []
     hooks._ns["index"] = []
+    hooks._ns["custom_data"] = []
     hooks._css_dist = []
     hooks._js_dist = []
     hooks._finals = {}
@@ -188,3 +189,24 @@ def test_hook009_hook_clientside_callback(hook_cleanup, dash_duo):
 
     dash_duo.wait_for_element("#hook-start").click()
     dash_duo.wait_for_text_to_equal("#hook-output", "Called 1")
+
+
+def test_hook010_hook_custom_data(hook_cleanup, dash_duo):
+    @hooks.custom_data("custom")
+    def custom_data(_):
+        return "custom-data"
+
+    app = Dash()
+    app.layout = [html.Button("insert", id="btn"), html.Div(id="output")]
+
+    @app.callback(
+        Output("output", "children"),
+        Input("btn", "n_clicks"),
+        prevent_initial_call=True,
+    )
+    def cb(_):
+        return ctx.custom_data.custom
+
+    dash_duo.start_server(app)
+    dash_duo.wait_for_element("#btn").click()
+    dash_duo.wait_for_text_to_equal("#output", "custom-data")