[App] Add annotations endpoint (#16159)

(cherry picked from commit 0630444)

src/lightning_app/core/api.py

@@ -1,10 +1,12 @@
 import asyncio
+import json
 import os
 import queue
 import sys
 import traceback
 from copy import deepcopy
 from multiprocessing import Queue
+from pathlib import Path
 from tempfile import TemporaryDirectory
 from threading import Event, Lock, Thread
 from time import sleep
@@ -68,6 +70,7 @@ class SessionMiddleware:
 
 app_spec: Optional[List] = None
 app_status: Optional[AppStatus] = None
+app_annotations: Optional[List] = None
 
 # In the future, this would be abstracted to support horizontal scaling.
 responses_store = {}
@@ -345,6 +348,13 @@ async def get_status() -> AppStatus:
     return app_status
 
 
+@fastapi_service.get("/api/v1/annotations", response_class=JSONResponse)
+async def get_annotations() -> Union[List, Dict]:
+    """Get the annotations associated with this app."""
+    global app_annotations
+    return app_annotations or []
+
+
 @fastapi_service.get("/healthz", status_code=200)
 async def healthz(response: Response):
     """Health check endpoint used in the cloud FastAPI servers to check the status periodically."""
@@ -440,6 +450,7 @@ def start_server(
     global api_app_delta_queue
     global global_app_state_store
     global app_spec
+    global app_annotations
 
     app_spec = spec
     api_app_delta_queue = api_delta_queue
@@ -449,6 +460,12 @@ def start_server(
 
     global_app_state_store.add(TEST_SESSION_UUID)
 
+    # Load annotations
+    annotations_path = Path("lightning-annotations.json").resolve()
+    if annotations_path.exists():
+        with open(annotations_path) as f:
+            app_annotations = json.load(f)
+
     refresher = UIRefresher(api_publish_state_queue, api_response_queue)
     refresher.setDaemon(True)
     refresher.start()

tests/tests_app/core/test_lightning_api.py

@@ -5,6 +5,7 @@
 import sys
 from copy import deepcopy
 from multiprocessing import Process
+from pathlib import Path
 from time import sleep, time
 from unittest import mock
 
@@ -562,3 +563,36 @@ def test_configure_api():
         time_left -= 0.1
     assert process.exitcode == 0
     process.kill()
+
+
+@pytest.mark.anyio
+@mock.patch("lightning_app.core.api.UIRefresher", mock.MagicMock())
+async def test_get_annotations(tmpdir):
+    cwd = os.getcwd()
+    os.chdir(tmpdir)
+
+    Path("lightning-annotations.json").write_text('[{"test": 3}]')
+
+    try:
+        app = AppStageTestingApp(FlowA(), log_level="debug")
+        app._update_layout()
+        app.stage = AppStage.BLOCKING
+        change_state_queue = _MockQueue("change_state_queue")
+        has_started_queue = _MockQueue("has_started_queue")
+        api_response_queue = _MockQueue("api_response_queue")
+        spec = extract_metadata_from_app(app)
+        start_server(
+            None,
+            change_state_queue,
+            api_response_queue,
+            has_started_queue=has_started_queue,
+            uvicorn_run=False,
+            spec=spec,
+        )
+
+        async with AsyncClient(app=fastapi_service, base_url="http://test") as client:
+            response = await client.get("/api/v1/annotations")
+            assert response.json() == [{"test": 3}]
+    finally:
+        # Cleanup
+        os.chdir(cwd)