core: Correctly handle missing duration in seek.

Seeks will now fail when the duration is None, this is an approximation to if
the track is seekable or not. This check is need as otherwise seeking a radio
stream will trigger the next track.

If the track truly isn't seekable despite having a duration we should still
fail as GStreamer will reject the seek.

mopidy/core/playback.py

@@ -361,6 +361,9 @@ class PlaybackController(object):
         if not self.core.tracklist.tracks:
             return False
 
+        if self.current_track and self.current_track.length is None:
+            return False
+
         if self.get_state() == PlaybackState.STOPPED:
             self.play()
 

mopidy/models.py

@@ -325,7 +325,7 @@ class Track(ImmutableObject):
     :param date: track release date (YYYY or YYYY-MM-DD)
     :type date: string
     :param length: track length in milliseconds
-    :type length: integer
+    :type length: integer or :class:`None` if there is no duration
     :param bitrate: bitrate in kbit/s
     :type bitrate: integer
     :param comment: track comment

mopidy/mpd/translator.py

@@ -34,6 +34,8 @@ def track_to_mpd_format(track, position=None, stream_title=None):
 
     result = [
         ('file', track.uri or ''),
+        # TODO: only show length if not none, see:
+        # https://github.com/mopidy/mopidy/issues/923#issuecomment-79584110
         ('Time', track.length and (track.length // 1000) or 0),
         ('Artist', artists_to_mpd_format(track.artists)),
         ('Title', track.name or ''),

tests/core/test_playback.py

@@ -38,6 +38,7 @@ class CorePlaybackTest(unittest.TestCase):
             Track(uri='dummy2:a', length=40000),
             Track(uri='dummy3:a', length=40000),  # Unplayable
             Track(uri='dummy1:b', length=40000),
+            Track(uri='dummy1:c', length=None),   # No duration
         ]
 
         self.core = core.Core(mixer=None, backends=[
@@ -46,6 +47,7 @@ class CorePlaybackTest(unittest.TestCase):
 
         self.tl_tracks = self.core.tracklist.tl_tracks
         self.unplayable_tl_track = self.tl_tracks[2]
+        self.duration_less_tl_track = self.tl_tracks[4]
 
     def test_get_current_tl_track_none(self):
         self.core.playback.set_current_tl_track(None)
@@ -478,6 +480,15 @@ class CorePlaybackTest(unittest.TestCase):
         self.assertFalse(self.playback1.seek.called)
         self.assertFalse(self.playback2.seek.called)
 
+    def test_seek_fails_for_track_without_duration(self):
+        self.core.playback.current_tl_track = self.duration_less_tl_track
+        self.core.playback.state = core.PlaybackState.PLAYING
+        success = self.core.playback.seek(1000)
+
+        self.assertFalse(success)
+        self.assertFalse(self.playback1.seek.called)
+        self.assertFalse(self.playback2.seek.called)
+
     def test_seek_play_stay_playing(self):
         self.core.playback.play(self.tl_tracks[0])
         self.core.playback.state = core.PlaybackState.PLAYING

tests/mpd/test_translator.py

@@ -34,6 +34,8 @@ class TrackMpdFormatTest(unittest.TestCase):
         mtime.undo_fake()
 
     def test_track_to_mpd_format_for_empty_track(self):
+        # TODO: this is likely wrong, see:
+        # https://github.com/mopidy/mopidy/issues/923#issuecomment-79584110
         result = translator.track_to_mpd_format(Track())
         self.assertIn(('file', ''), result)
         self.assertIn(('Time', 0), result)