audio: Add support for checking seekable state in scanner

Return type of scanner changed to a named tuple with (uri, tags, duration,
seekable). This should help with #872 and the related "live" issues.

Tests, local scan and stream metadata lookup have been updated to account for
the changes.

mopidy/audio/scan.py

@@ -1,5 +1,6 @@
 from __future__ import absolute_import, division, unicode_literals
 
+import collections
 import time
 
 import pygst
@@ -13,6 +14,9 @@ from mopidy.utils import encoding
 
 _missing_plugin_desc = gst.pbutils.missing_plugin_message_get_description
 
+Result = collections.namedtuple(
+    'Result', ('uri', 'tags', 'duration', 'seekable'))
+
 
 class Scanner(object):
     """
@@ -54,19 +58,22 @@ class Scanner(object):
 
         :param uri: URI of the resource to scan.
         :type event: string
-        :return: (tags, duration) pair. tags is a dictionary of lists for all
-            the tags we found and duration is the length of the URI in
-            milliseconds, or :class:`None` if the URI has no duration.
+        :return: A named tuple containing ``(uri, tags, duration, seekable)``.
+            ``tags`` is a dictionary of lists for all the tags we found.
+            ``duration`` is the length of the URI in milliseconds, or
+            :class:`None` if the URI has no duration. ``seekable`` is boolean
+            indicating if a seek would succeed.
         """
-        tags, duration = None, None
+        tags, duration, seekable = None, None, None
         try:
             self._setup(uri)
             tags = self._collect()
             duration = self._query_duration()
+            seekable = self._query_seekable()
         finally:
             self._reset()
 
-        return tags, duration
+        return Result(uri, tags, duration, seekable)
 
     def _setup(self, uri):
         """Primes the pipeline for collection."""
@@ -123,3 +130,8 @@ class Scanner(object):
             return None
         else:
             return duration // gst.MSECOND
+
+    def _query_seekable(self):
+        query = gst.query_new_seeking(gst.FORMAT_TIME)
+        self._pipe.query(query)
+        return query.parse_seeking()[1]

mopidy/local/commands.py

@@ -133,7 +133,8 @@ class ScanCommand(commands.Command):
             try:
                 relpath = translator.local_track_uri_to_path(uri, media_dir)
                 file_uri = path.path_to_uri(os.path.join(media_dir, relpath))
-                tags, duration = scanner.scan(file_uri)
+                result = scanner.scan(file_uri)
+                tags, duration = result.tags, result.duration
                 if duration < MIN_DURATION_MS:
                     logger.warning('Failed %s: Track shorter than %dms',
                                    uri, MIN_DURATION_MS)

mopidy/stream/actor.py

@@ -45,9 +45,9 @@ class StreamLibraryProvider(backend.LibraryProvider):
             return [Track(uri=uri)]
 
         try:
-            tags, duration = self._scanner.scan(uri)
-            track = utils.convert_tags_to_track(tags).copy(
-                uri=uri, length=duration)
+            result = self._scanner.scan(uri)
+            track = utils.convert_tags_to_track(result.tags).copy(
+                uri=uri, length=result.duration)
         except exceptions.ScannerError as e:
             logger.warning('Problem looking up %s: %s', uri, e)
             track = Track(uri=uri)

tests/audio/test_scan.py

@@ -31,9 +31,9 @@ class ScannerTest(unittest.TestCase):
             uri = path_lib.path_to_uri(path)
             key = uri[len('file://'):]
             try:
-                tags, duration = scanner.scan(uri)
-                self.tags[key] = tags
-                self.durations[key] = duration
+                result = scanner.scan(uri)
+                self.tags[key] = result.tags
+                self.durations[key] = result.duration
             except exceptions.ScannerError as error:
                 self.errors[key] = error