New Kytos core service to get NApp metadata

kytos/core/api_server.py

@@ -360,6 +360,9 @@ def register_core_napp_services(self):
                                     self._list_enabled_napps)
         self.register_core_endpoint("napps_installed",
                                     self._list_installed_napps)
+        self.register_core_endpoint(
+            "napps/<username>/<napp_name>/metadata/<key>",
+            self._get_napp_metadata)
 
     def _enable_napp(self, username, napp_name):
         """
@@ -454,3 +457,22 @@ def _list_installed_napps(self):
 
         return '{"napps": %s}' % serialized_dict, HTTPStatus.OK.value
 
+    def _get_napp_metadata(self, username, napp_name, key):
+        """Get NApp metadata value.
+
+        For safety reasons, only some keys can be retrieved:
+        napp_dependencies, description, version.
+
+        """
+        _VALID_KEYS = ['napp_dependencies', 'description', 'version']
+
+        if not self.nappsManager.is_installed(username, napp_name):
+            return "Napp is not installed.", HTTPStatus.BAD_REQUEST.value
+
+        if key not in _VALID_KEYS:
+            return "Invalid key.", HTTPStatus.BAD_REQUEST.value
+
+        data = self.nappsManager.get_napp_metadata(username, napp_name, key)
+        serialized_dict = json.dumps({key: data})
+
+        return '%s' % serialized_dict, HTTPStatus.OK.value

kytos/core/napps/manager.py

@@ -211,6 +211,28 @@ def get_installed_napps(self):
         """Return all NApps installed on this controller FS."""
         return self.get_napps_from_path(self._installed_path)
 
+    def get_napp_metadata(self, username, napp_name, key):
+        """Return a value from kytos.json.
+
+        Args:
+            username (string): A Username.
+            napp_name (string): A NApp name
+            key (string): Key used to get the value within kytos.json.
+
+        Returns:
+            meta (object): Value stored in kytos.json.
+
+        """
+        napp_id = "{}/{}".format(username, napp_name)
+        kytos_json = self._installed_path / napp_id / 'kytos.json'
+        try:
+            with kytos_json.open() as file_descriptor:
+                meta = json.load(file_descriptor)
+                return meta[key]
+        except (FileNotFoundError, json.JSONDecodeError, KeyError):
+            LOG.warning("Load napp metada failed: %s/kytos.json", napp_id)
+            return ''
+
     @staticmethod
     def get_napps_from_path(path: Path):
         """List all NApps found in ``napps_dir``."""
@@ -233,7 +255,7 @@ def _create_module(path: Path):
         (path / '__init__.py').touch()
 
     @staticmethod
-    def _find_napp(napp, root: Path=None) -> Path:
+    def _find_napp(napp, root: Path = None) -> Path:
         """Return local NApp root folder.
 
         Search for kytos.json in _./_ folder and _./user/napp_.