local: Add browse support to local library interface

mopidy/local/__init__.py

@@ -64,6 +64,15 @@ class Library(object):
     def __init__(self, config):
         self._config = config
 
+    def browse(self, path):
+        """
+        Browse directories and tracks at the given path.
+
+        :param string path: path to browse or None for root.
+        :rtype: List of :class:`~mopidy.models.Ref` tracks and directories.
+        """
+        raise NotImplementedError
+
     def load(self):
         """
         (Re)load any tracks stored in memory, if any, otherwise just return

mopidy/local/json.py

@@ -50,6 +50,9 @@ class JsonLibrary(local.Library):
         self._json_file = os.path.join(
             config['local']['data_dir'], b'library.json.gz')
 
+    def browse(self, path):
+        return []
+
     def load(self):
         logger.debug('Loading json library from %s', self._json_file)
         library = load_library(self._json_file)

mopidy/local/library.py

@@ -17,6 +17,11 @@ class LocalLibraryProvider(backend.LibraryProvider):
         self._library = library
         self.refresh()
 
+    def browse(self, path):
+        if not self._library:
+            return []
+        return self._library.browse(path)
+
     def refresh(self, uri=None):
         if not self._library:
             return 0