🩺 Add Health Check and Sessions Endpoints (#925)

- Introduces a healthcheck endpoint and the sessions endpoint. 

- The purpose of the healthcheck endpoint is to tell if the TileServer is running.

- The purpose of the sessions endpoint is to return a mapping of all active sessions and their loaded Whole Slide Images (WSIs). 

---------

Co-authored-by: Shan E Ahmed Raza <13048456+shaneahmed@users.noreply.github.com>
Co-authored-by: pre-commit-ci[bot] <66853113+pre-commit-ci[bot]@users.noreply.github.com>

Author: 3 people

tests/test_tileserver.py

@@ -734,3 +734,44 @@ def test_prop_range(app: TileServer) -> None:
         assert response.status_code == 200
         # should be back to no scaling
         assert layer.renderer.score_fn(0.5) == 0.5
+
+
+def test_healthcheck(empty_app: TileServer) -> None:
+    """Test the /tileserver/healthcheck endpoint."""
+    with empty_app.test_client() as client:
+        response = client.get("/tileserver/healthcheck")
+        assert response.status_code == 200
+        assert response.content_type == "application/json"
+        assert response.get_json() == {"status": "OK"}
+
+
+def test_sessions_no_slide_loaded(empty_app: TileServer) -> None:
+    """Test /tileserver/sessions when no slides are loaded."""
+    with empty_app.test_client() as client:
+        setup_app(client)
+        response = client.get("/tileserver/sessions")
+        assert response.status_code == 200
+        assert response.is_json
+        assert response.get_json() == {}
+
+
+def test_sessions_one_slide_loaded(
+    empty_app: TileServer, remote_sample: Callable
+) -> None:
+    """Test /tileserver/sessions after loading one slide."""
+    with empty_app.test_client() as client:
+        setup_app(client)
+        slide_path = safe_str(remote_sample("svs-1-small"))
+
+        response = client.put(
+            "/tileserver/slide",
+            data={"slide_path": slide_path},
+        )
+        assert response.status_code == 200
+
+        response = client.get("/tileserver/sessions")
+        assert response.status_code == 200
+        sessions = response.get_json()
+
+        assert isinstance(sessions, dict)
+        assert len(sessions) == 1

tiatoolbox/visualization/tileserver.py

@@ -165,6 +165,8 @@ def __init__(  # noqa: PLR0915
         self.route("/tileserver/tap_query/<x>/<y>")(self.tap_query)
         self.route("/tileserver/prop_range", methods=["PUT"])(self.prop_range)
         self.route("/tileserver/shutdown", methods=["POST"])(self.shutdown)
+        self.route("/tileserver/sessions", methods=["GET"])(self.sessions)
+        self.route("/tileserver/healthcheck", methods=["GET"])(self.healthcheck)
 
     def _get_session_id(self: TileServer) -> str:
         """Get the session_id from the request.
@@ -718,6 +720,36 @@ def prop_range(self: TileServer) -> str:
         self.renderers[session_id].score_fn = lambda x: (x - minv) / (maxv - minv)
         return "done"
 
+    def sessions(self: TileServer) -> Response:
+        """Retrieve a mapping of session keys to their corresponding slide file paths.
+
+        Returns:
+            Response:
+                A JSON response containing a mapping of session keys
+                and their respective slide file paths.
+
+        """
+        session_paths = {}
+        for key, layer in self.layers.items():
+            slide = layer.get("slide")
+            if slide is not None:
+                session_paths[key] = str(slide.info.as_dict().get("file_path", ""))
+        return jsonify(session_paths)
+
+    @staticmethod
+    def healthcheck() -> Response:
+        """Simple health check endpoint to verify the server is running.
+
+        Useful for load balancers or uptime monitoring tools to check
+        if the service is operational.
+
+        Returns:
+            Response:
+                A JSON response with status "OK" and HTTP status code 200.
+
+        """
+        return jsonify({"status": "OK"})
+
     @staticmethod
     def shutdown() -> None:
         """Shutdown the tileserver."""

tiatoolbox/visualization/tileserver_api.yml

@@ -395,6 +395,24 @@ paths:
         '200':
           description: Successful response
 
+  /tileserver/sessions:
+      get:
+          summary: Returns all session/path mappings
+          responses:
+              '200':
+                  description: A jsonified session/path mappings
+                  content:
+                      application/json:
+
+  /tileserver/healthcheck:
+      get:
+          summary: Returns Ok if server is online
+          responses:
+              '200':
+                  description: A json with status field
+                  content:
+                      application/json:
+
   /tileserver/tap_query/{x}/{y}:
     get:
       summary: Query annotation at a point