Add volume to playback API of backends.

- Add volume get/setter to the playback provider.
- Add volume property to the playback controller.

mopidy/backends/base/playback.py

@@ -319,6 +319,14 @@ class PlaybackController(object):
     def _current_wall_time(self):
         return int(time.time() * 1000)
 
+    @property
+    def volume(self):
+        return self.provider.get_volume()
+
+    @volume.setter
+    def volume(self, volume):
+        self.provider.set_volume(volume)
+
     def change_track(self, cp_track, on_error_step=1):
         """
         Change to the given track, keeping the current playback state.
@@ -604,3 +612,27 @@ class BasePlaybackProvider(object):
         :rtype: :class:`True` if successful, else :class:`False`
         """
         raise NotImplementedError
+
+    # TODO: having these in the provider is stupid, but since we currently
+    # don't have gstreamer exposed in a sensible way for this...
+    # On the bright side it makes testing volume stuff less painful.
+    def get_volume(self):
+        """
+        Get current volume
+
+        *MUST be implemented by subclass.*
+
+        :rtype: int [0..100] or :class:`None`
+        """
+        raise NotImplementedError
+
+    def set_volume(self, volume):
+        """
+        Get current volume
+
+        *MUST be implemented by subclass.*
+
+        :param: volume
+        :type volume: int [0..100]
+        """
+        raise NotImplementedError

mopidy/backends/dummy/__init__.py

@@ -56,6 +56,10 @@ class DummyLibraryProvider(BaseLibraryProvider):
 
 
 class DummyPlaybackProvider(BasePlaybackProvider):
+    def __init__(self, *args, **kwargs):
+        super(DummyPlaybackProvider, self).__init__(*args, **kwargs)
+        self._volume = None
+
     def pause(self):
         return True
 
@@ -72,6 +76,12 @@ class DummyPlaybackProvider(BasePlaybackProvider):
     def stop(self):
         return True
 
+    def get_volume(self):
+        return self._volume
+
+    def set_volume(self, volume):
+        self._volume = volume
+
 
 class DummyStoredPlaylistsProvider(BaseStoredPlaylistsProvider):
     def create(self, name):

mopidy/backends/local/__init__.py

@@ -102,6 +102,12 @@ class LocalPlaybackProvider(BasePlaybackProvider):
     def stop(self):
         return self.backend.gstreamer.stop_playback().get()
 
+    def get_volume(self):
+        return self.backend.gstreamer.get_volume().get()
+
+    def set_volume(self, volume):
+        self.backend.gstreamer.set_volume(volume).get()
+
 
 class LocalStoredPlaylistsProvider(BaseStoredPlaylistsProvider):
     def __init__(self, *args, **kwargs):

mopidy/backends/spotify/playback.py

@@ -41,3 +41,9 @@ class SpotifyPlaybackProvider(BasePlaybackProvider):
         result = self.backend.gstreamer.stop_playback()
         self.backend.spotify.session.play(0)
         return result
+
+    def get_volume(self):
+        return self.backend.gstreamer.get_volume()
+
+    def set_volume(self, volume):
+        self.backend.gstreamer.set_volume(volume)