[#15] feat: implement GET /components endpoint

Add endpoint to list all discovered components across all areas.

Changes:
- Add GET /components REST endpoint in rest_server.cpp
- Implement handle_list_components() to return component metadata
- Add test_03_list_components integration test
- Update README with API reference and endpoint documentation
- Update Postman collection with new endpoint

Author: Michał Fąferek

postman/README.md

@@ -9,6 +9,7 @@ This folder contains Postman collections for testing the ROS 2 Medkit Gateway RE
 Includes below endpoints:
 - ✅ GET `/` - Gateway info
 - ✅ GET `/areas` - List all areas
+- ✅ GET `/components` - List all components
 
 ## Quick Start
 
@@ -49,6 +50,10 @@ ros2 launch ros2_medkit_gateway demo_nodes.launch.py
 6. Click **Send**
 7. You should see areas: `[{"id": "powertrain", ...}, {"id": "chassis", ...}, ...]`
 
+8. Click **"GET List Components"**
+9. Click **Send**
+10. You should see components: `[{"id": "temp_sensor", "namespace": "/powertrain/engine", ...}, ...]`
+
 ## API Variables
 
 The environment includes:

postman/collections/ros2-medkit-gateway.postman_collection.json

@@ -1,7 +1,7 @@
 {
   "info": {
     "name": "ROS 2 Medkit Gateway API",
-    "description": "Minimal collection: GET / and GET /areas endpoints only",
+    "description": "Collection for ROS 2 Medkit Gateway REST API endpoints",
     "schema": "https://schema.getpostman.com/json/collection/v2.1.0/collection.json"
   },
   "item": [
@@ -43,6 +43,24 @@
             "description": "List all discovered areas (powertrain, chassis, body, root)"
           },
           "response": []
+        },
+        {
+          "name": "GET List Components",
+          "request": {
+            "method": "GET",
+            "header": [],
+            "url": {
+              "raw": "{{base_url}}/components",
+              "host": [
+                "{{base_url}}"
+              ],
+              "path": [
+                "components"
+              ]
+            },
+            "description": "List all discovered components across all areas. Returns component metadata including id, namespace, fqn, type, and parent area."
+          },
+          "response": []
         }
       ]
     }

src/ros2_medkit_gateway/README.md

@@ -14,11 +14,75 @@ The ROS 2 Medkit Gateway exposes ROS 2 system information and data through a RES
 
 ## Endpoints
 
-Current available endpoints:
+### Discovery Endpoints
 
 - `GET /health` - Health check endpoint (returns healthy status)
 - `GET /` - Gateway status and version information
 - `GET /areas` - List all discovered areas (powertrain, chassis, body, root)
+- `GET /components` - List all discovered components across all areas
+
+### API Reference
+
+#### GET /areas
+
+Lists all discovered areas in the system.
+
+**Example:**
+```bash
+curl http://localhost:8080/areas
+```
+
+**Response:**
+```json
+[
+  {
+    "id": "powertrain",
+    "namespace": "/powertrain",
+    "type": "Area"
+  },
+  {
+    "id": "chassis",
+    "namespace": "/chassis",
+    "type": "Area"
+  }
+]
+```
+
+#### GET /components
+
+Lists all discovered components across all areas.
+
+**Example:**
+```bash
+curl http://localhost:8080/components
+```
+
+**Response:**
+```json
+[
+  {
+    "id": "temp_sensor",
+    "namespace": "/powertrain/engine",
+    "fqn": "/powertrain/engine/temp_sensor",
+    "type": "Component",
+    "area": "powertrain"
+  },
+  {
+    "id": "rpm_sensor",
+    "namespace": "/powertrain/engine",
+    "fqn": "/powertrain/engine/rpm_sensor",
+    "type": "Component",
+    "area": "powertrain"
+  }
+]
+```
+
+**Response Fields:**
+- `id` - Component name (node name)
+- `namespace` - ROS 2 namespace where the component is running
+- `fqn` - Fully qualified name (namespace + node name)
+- `type` - Always "Component"
+- `area` - Parent area this component belongs to
 
 ## Quick Start
 

src/ros2_medkit_gateway/include/ros2_medkit_gateway/rest_server.hpp

@@ -40,6 +40,7 @@ class RESTServer {
     void handle_health(const httplib::Request& req, httplib::Response& res);
     void handle_root(const httplib::Request& req, httplib::Response& res);
     void handle_list_areas(const httplib::Request& req, httplib::Response& res);
+    void handle_list_components(const httplib::Request& req, httplib::Response& res);
 
     GatewayNode* node_;
     std::string host_;

src/ros2_medkit_gateway/src/rest_server.cpp

@@ -46,6 +46,11 @@ void RESTServer::setup_routes() {
     server_->Get("/areas", [this](const httplib::Request& req, httplib::Response& res) {
         handle_list_areas(req, res);
     });
+
+    // Components
+    server_->Get("/components", [this](const httplib::Request& req, httplib::Response& res) {
+        handle_list_components(req, res);
+    });
 }
 
 void RESTServer::start() {
@@ -129,4 +134,30 @@ void RESTServer::handle_list_areas(const httplib::Request& req, httplib::Respons
     }
 }
 
+void RESTServer::handle_list_components(const httplib::Request& req, httplib::Response& res) {
+    (void)req;  // Unused parameter
+
+    try {
+        const auto cache = node_->get_entity_cache();
+
+        json components_json = json::array();
+        for (const auto& component : cache.components) {
+            components_json.push_back(component.to_json());
+        }
+
+        res.set_content(components_json.dump(2), "application/json");
+    } catch (const std::exception& e) {
+        res.status = 500;
+        res.set_content(
+            json{{"error", "Internal server error"}}.dump(),
+            "application/json"
+        );
+        RCLCPP_ERROR(
+            rclcpp::get_logger("rest_server"),
+            "Error in handle_list_components: %s",
+            e.what()
+        );
+    }
+}
+
 }  // namespace ros2_medkit_gateway

src/ros2_medkit_gateway/test/test_integration.test.py

@@ -178,7 +178,31 @@ def test_02_list_areas(self):
         self.assertIn('root', area_ids)
         print(f'✓ Areas test passed: {len(areas)} areas discovered')
 
-    def test_21_automotive_areas_discovery(self):
+    def test_03_list_components(self):
+        """Test GET /components returns all discovered components."""
+        components = self._get_json('/components')
+        self.assertIsInstance(components, list)
+        # Should have at least 7 demo nodes + gateway node
+        self.assertGreaterEqual(len(components), 7)
+
+        # Verify response structure - all components should have required fields
+        for component in components:
+            self.assertIn('id', component)
+            self.assertIn('namespace', component)
+            self.assertIn('fqn', component)
+            self.assertIn('type', component)
+            self.assertIn('area', component)
+            self.assertEqual(component['type'], 'Component')
+
+        # Verify some expected component IDs are present
+        component_ids = [comp['id'] for comp in components]
+        self.assertIn('temp_sensor', component_ids)
+        self.assertIn('rpm_sensor', component_ids)
+        self.assertIn('pressure_sensor', component_ids)
+
+        print(f'✓ Components test passed: {len(components)} components discovered')
+
+    def test_04_automotive_areas_discovery(self):
         """Test that automotive areas are properly discovered."""
         areas = self._get_json('/areas')
         area_ids = [area['id'] for area in areas]