Api exposure callbacks

CHANGELOG.md

@@ -8,6 +8,7 @@ This project adheres to [Semantic Versioning](https://semver.org/).
 - [#3395](https://github.com/plotly/dash/pull/3396) Add position argument to hooks.devtool
 - [#3403](https://github.com/plotly/dash/pull/3403) Add app_context to get_app, allowing to get the current app in routes.
 - [#3407](https://github.com/plotly/dash/pull/3407) Add `hidden` to callback arguments, hiding the callback from appearing in the devtool callback graph.
+- [#3347](https://github.com/plotly/dash/pull/3347) Added 'api_endpoint' to `callback` to expose api endpoints at the provided path for use to be executed directly without dash.
 
 ## Fixed
 - [#3395](https://github.com/plotly/dash/pull/3395) Fix Components added through set_props() cannot trigger related callback functions. Fix [#3316](https://github.com/plotly/dash/issues/3316)

dash/_callback.py

@@ -62,6 +62,7 @@ def _invoke_callback(func, *args, **kwargs):  # used to mark the frame for the d
 GLOBAL_CALLBACK_LIST = []
 GLOBAL_CALLBACK_MAP = {}
 GLOBAL_INLINE_SCRIPTS = []
+GLOBAL_API_PATHS = {}
 
 
 # pylint: disable=too-many-locals,too-many-arguments
@@ -77,6 +78,7 @@ def callback(
     cache_args_to_ignore: Optional[list] = None,
     cache_ignore_triggered=True,
     on_error: Optional[Callable[[Exception], Any]] = None,
+    api_endpoint: Optional[str] = None,
     optional: Optional[bool] = False,
     hidden: Optional[bool] = False,
     **_kwargs,
@@ -165,6 +167,14 @@ def callback(
             Mark all dependencies as not required on the initial layout checks.
         :param hidden:
             Hide the callback from the devtools callbacks tab.
+        :param api_endpoint:
+            If provided, the callback will be available at the given API endpoint.
+            This allows you to call the callback directly through HTTP requests
+            instead of through the Dash front-end. The endpoint should be a string
+            that starts with a forward slash (e.g. `/my_callback`).
+            The endpoint is relative to the Dash app's base URL.
+            Note that the endpoint will not appear in the list of registered
+            callbacks in the Dash devtools.
     """
 
     background_spec = None
@@ -219,6 +229,7 @@ def callback(
         manager=manager,
         running=running,
         on_error=on_error,
+        api_endpoint=api_endpoint,
         optional=optional,
         hidden=hidden,
     )
@@ -587,7 +598,11 @@ def _prepare_response(
 
 # pylint: disable=too-many-branches,too-many-statements
 def register_callback(
-    callback_list, callback_map, config_prevent_initial_callbacks, *_args, **_kwargs
+    callback_list,
+    callback_map,
+    config_prevent_initial_callbacks,
+    *_args,
+    **_kwargs,
 ):
     (
         output,
@@ -642,6 +657,10 @@ def register_callback(
 
     # pylint: disable=too-many-locals
     def wrap_func(func):
+        if _kwargs.get("api_endpoint"):
+            api_endpoint = _kwargs.get("api_endpoint")
+            GLOBAL_API_PATHS[api_endpoint] = func
+
         if background is None:
             background_key = None
         else:

dash/dash.py

@@ -569,6 +569,7 @@ def __init__(  # pylint: disable=too-many-statements
         self.callback_map = {}
         # same deps as a list to catch duplicate outputs, and to send to the front end
         self._callback_list = []
+        self.callback_api_paths = {}
 
         # list of inline scripts
         self._inline_scripts = []
@@ -783,6 +784,54 @@ def _setup_routes(self):
         # catch-all for front-end routes, used by dcc.Location
         self._add_url("<path:path>", self.index)
 
+    def setup_apis(self):
+        """
+        Register API endpoints for all callbacks defined using `dash.callback`.
+
+        This method must be called after all callbacks are registered and before the app is served.
+        It ensures that all callback API routes are available for the Dash app to function correctly.
+
+        Typical usage:
+            app = Dash(__name__)
+            # Register callbacks here
+            app.setup_apis()
+            app.run()
+
+        If not called, callback endpoints will not be available and the app will not function as expected.
+        """
+        for k in list(_callback.GLOBAL_API_PATHS):
+            if k in self.callback_api_paths:
+                raise DuplicateCallback(
+                    f"The callback `{k}` provided with `dash.callback` was already "
+                    "assigned with `app.callback`."
+                )
+            self.callback_api_paths[k] = _callback.GLOBAL_API_PATHS.pop(k)
+
+        def make_parse_body(func):
+            def _parse_body():
+                if flask.request.is_json:
+                    data = flask.request.get_json()
+                    return flask.jsonify(func(**data))
+                return flask.jsonify({})
+
+            return _parse_body
+
+        def make_parse_body_async(func):
+            async def _parse_body_async():
+                if flask.request.is_json:
+                    data = flask.request.get_json()
+                    result = await func(**data)
+                    return flask.jsonify(result)
+                return flask.jsonify({})
+
+            return _parse_body_async
+
+        for path, func in self.callback_api_paths.items():
+            if asyncio.iscoroutinefunction(func):
+                self._add_url(path, make_parse_body_async(func), ["POST"])
+            else:
+                self._add_url(path, make_parse_body(func), ["POST"])
+
     def _setup_plotlyjs(self):
         # pylint: disable=import-outside-toplevel
         from plotly.offline import get_plotlyjs_version
@@ -1364,6 +1413,7 @@ def callback(self, *_args, **_kwargs) -> Callable[..., Any]:
             config_prevent_initial_callbacks=self.config.prevent_initial_callbacks,
             callback_list=self._callback_list,
             callback_map=self.callback_map,
+            callback_api_paths=self.callback_api_paths,
             **_kwargs,
         )
 
@@ -1516,6 +1566,7 @@ def dispatch(self):
     def _setup_server(self):
         if self._got_first_request["setup_server"]:
             return
+
         self._got_first_request["setup_server"] = True
 
         # Apply _force_eager_loading overrides from modules

tests/integration/callbacks/test_api_callback.py

@@ -0,0 +1,59 @@
+from dash import (
+    Dash,
+    Input,
+    Output,
+    html,
+    ctx,
+)
+import requests
+import json
+from flask import jsonify
+
+test_string = (
+    '{"step_0": "Data fetched - 1", "step_1": "Data fetched - 1", "step_2": "Data fetched - 1", '
+    '"step_3": "Data fetched - 1", "step_4": "Data fetched - 1"}'
+)
+
+
+def test_apib001_api_callback(dash_duo):
+
+    app = Dash(__name__)
+    app.layout = html.Div(
+        [
+            html.Button("Slow Callback", id="slow-btn"),
+            html.Div(id="slow-output"),
+        ]
+    )
+
+    def get_data(n_clicks):
+        # Simulate an async data fetch
+        return f"Data fetched - {n_clicks}"
+
+    @app.callback(
+        Output("slow-output", "children"),
+        Input("slow-btn", "n_clicks"),
+        prevent_initial_call=True,
+        api_endpoint="/api/slow_callback",  # Example API path for the slow callback
+    )
+    def slow_callback(n_clicks):
+        data = {}
+        for i in range(5):
+            data[f"step_{i}"] = get_data(n_clicks)
+        ret = f"{json.dumps(data)}"
+        if ctx:
+            return ret
+        return jsonify(ret)
+
+    app.setup_apis()
+
+    dash_duo.start_server(app)
+
+    dash_duo.wait_for_element("#slow-btn").click()
+    dash_duo.wait_for_text_to_equal("#slow-output", test_string)
+    r = requests.post(
+        dash_duo.server_url + "/api/slow_callback",
+        json={"n_clicks": 1},
+        headers={"Content-Type": "application/json"},
+    )
+    assert r.status_code == 200
+    assert r.json() == test_string