scanner: Support multiple tag sets per track (fixes #236)

docs/changes.rst

@@ -122,6 +122,10 @@ backends:
 - MPD no longer lowercases search queries. This broke e.g. search by URI, where
   casing may be essential.
 
+- :issue:`236`: The ``mopidy-scan`` command failed to include tags from ALAC
+  files (Apple lossless) because it didn't support multiple tag messages from
+  GStreamer per track it scanned.
+
 
 v0.8.1 (2012-10-30)
 ===================

mopidy/scanner.py

@@ -89,51 +89,70 @@ def translator(data):
 
 class Scanner(object):
     def __init__(self, folder, data_callback, error_callback=None):
+        self.data = {}
         self.files = path.find_files(folder)
         self.data_callback = data_callback
         self.error_callback = error_callback
         self.loop = gobject.MainLoop()
 
-        fakesink = gst.element_factory_make('fakesink')
+        self.fakesink = gst.element_factory_make('fakesink')
+        self.fakesink.set_property('signal-handoffs', True)
+        self.fakesink.connect('handoff', self.process_handoff)
 
         self.uribin = gst.element_factory_make('uridecodebin')
         self.uribin.set_property('caps', gst.Caps(b'audio/x-raw-int'))
-        self.uribin.connect(
-            'pad-added', self.process_new_pad, fakesink.get_pad('sink'))
+        self.uribin.connect('pad-added', self.process_new_pad)
 
         self.pipe = gst.element_factory_make('pipeline')
         self.pipe.add(self.uribin)
-        self.pipe.add(fakesink)
+        self.pipe.add(self.fakesink)
 
         bus = self.pipe.get_bus()
         bus.add_signal_watch()
+        bus.connect('message::application', self.process_application)
         bus.connect('message::tag', self.process_tags)
         bus.connect('message::error', self.process_error)
 
-    def process_new_pad(self, source, pad, target_pad):
-        pad.link(target_pad)
+    def process_handoff(self, fakesink, buffer_, pad):
+        # When this function is called the first buffer has reached the end of
+        # the pipeline, and we can continue with the next track. Since we're
+        # in another thread, we send a message back to the main thread using
+        # the bus.
+        structure = gst.Structure('handoff')
+        message = gst.message_new_application(fakesink, structure)
+        bus = self.pipe.get_bus()
+        bus.post(message)
+
+    def process_new_pad(self, source, pad):
+        pad.link(self.fakesink.get_pad('sink'))
+
+    def process_application(self, bus, message):
+        if message.src != self.fakesink:
+            return
+
+        if message.structure.get_name() != 'handoff':
+            return
+
+        self.data['uri'] = unicode(self.uribin.get_property('uri'))
+        self.data[gst.TAG_DURATION] = self.get_duration()
+
+        try:
+            self.data_callback(self.data)
+            self.next_uri()
+        except KeyboardInterrupt:
+            self.stop()
 
     def process_tags(self, bus, message):
         taglist = message.parse_tag()
-        data = {
-            'uri': unicode(self.uribin.get_property('uri')),
-            gst.TAG_DURATION: self.get_duration(),
-        }
 
         for key in taglist.keys():
             # XXX: For some crazy reason some wma files spit out lists here,
             # not sure if this is due to better data in headers or wma being
             # stupid. So ugly hack for now :/
             if type(taglist[key]) is list:
-                data[key] = taglist[key][0]
+                self.data[key] = taglist[key][0]
             else:
-                data[key] = taglist[key]
-
-        try:
-            self.data_callback(data)
-            self.next_uri()
-        except KeyboardInterrupt:
-            self.stop()
+                self.data[key] = taglist[key]
 
     def process_error(self, bus, message):
         if self.error_callback:
@@ -151,6 +170,7 @@ class Scanner(object):
             return None
 
     def next_uri(self):
+        self.data = {}
         try:
             uri = path.path_to_uri(self.files.next())
         except StopIteration:
@@ -158,7 +178,7 @@ class Scanner(object):
             return False
         self.pipe.set_state(gst.STATE_NULL)
         self.uribin.set_property('uri', uri)
-        self.pipe.set_state(gst.STATE_PAUSED)
+        self.pipe.set_state(gst.STATE_PLAYING)
         return True
 
     def start(self):