From 3da23167ca4aef838a7ffcab6b2036e03c8a2da2 Mon Sep 17 00:00:00 2001
From: Carl Suster <carl@contraflo.ws>
Date: Fri, 19 Apr 2019 15:57:15 +1000
Subject: [PATCH 1/2] bpd: support decoders command

This uses GStreamer APIs to extract a list of audio decoders and the
relevant MIME types and file extensions. Some clients like ncmpcpp use
this command to fetch a list of supported file extensions.
---
 beetsplug/bpd/__init__.py  | 10 +++++++
 beetsplug/bpd/gstplayer.py | 53 ++++++++++++++++++++++++++++++++++++++
 test/test_player.py        | 16 +++++++++---
 3 files changed, 75 insertions(+), 4 deletions(-)

diff --git a/beetsplug/bpd/__init__.py b/beetsplug/bpd/__init__.py
index a70c6ecd61..5c54c9eabe 100644
--- a/beetsplug/bpd/__init__.py
+++ b/beetsplug/bpd/__init__.py
@@ -1321,6 +1321,16 @@ def cmd_stats(self, conn):
             u'db_update: ' + six.text_type(int(self.updated_time)),
         )
 
+    def cmd_decoders(self, conn):
+        """Send list of supported decoders and formats."""
+        decoders = self.player.get_decoders()
+        for name, (mimes, exts) in decoders.items():
+            yield u'plugin: {}'.format(name)
+            for ext in exts:
+                yield u'suffix: {}'.format(ext)
+            for mime in mimes:
+                yield u'mime_type: {}'.format(mime)
+
     # Searching.
 
     tagtype_map = {
diff --git a/beetsplug/bpd/gstplayer.py b/beetsplug/bpd/gstplayer.py
index fffa8a6eda..8d4e7c9ff4 100644
--- a/beetsplug/bpd/gstplayer.py
+++ b/beetsplug/bpd/gstplayer.py
@@ -215,6 +215,59 @@ def block(self):
         while self.playing:
             time.sleep(1)
 
+    def get_decoders(self):
+        return get_decoders()
+
+
+def get_decoders():
+    """Get supported audio decoders from GStreamer.
+    Returns a dict mapping decoder element names to the associated media types
+    and file extensions.
+    """
+    # We only care about audio decoder elements.
+    filt = (Gst.ELEMENT_FACTORY_TYPE_DEPAYLOADER |
+            Gst.ELEMENT_FACTORY_TYPE_DEMUXER |
+            Gst.ELEMENT_FACTORY_TYPE_PARSER |
+            Gst.ELEMENT_FACTORY_TYPE_DECODER |
+            Gst.ELEMENT_FACTORY_TYPE_MEDIA_AUDIO)
+
+    decoders = {}
+    mime_types = set()
+    for f in Gst.ElementFactory.list_get_elements(filt, Gst.Rank.NONE):
+        for pad in f.get_static_pad_templates():
+            if pad.direction == Gst.PadDirection.SINK:
+                caps = pad.static_caps.get()
+                mimes = set()
+                for i in range(caps.get_size()):
+                    struct = caps.get_structure(i)
+                    mime = struct.get_name()
+                    if mime == 'unknown/unknown':
+                        continue
+                    mimes.add(mime)
+                    mime_types.add(mime)
+                if mimes:
+                    decoders[f.get_name()] = (mimes, set())
+
+    # Check all the TypeFindFactory plugin features form the registry. If they
+    # are associated with an audio media type that we found above, get the list
+    # of corresponding file extensions.
+    mime_extensions = {mime: set() for mime in mime_types}
+    for feat in Gst.Registry.get().get_feature_list(Gst.TypeFindFactory):
+        caps = feat.get_caps()
+        if caps:
+            for i in range(caps.get_size()):
+                struct = caps.get_structure(i)
+                mime = struct.get_name()
+                if mime in mime_types:
+                    mime_extensions[mime].update(feat.get_extensions())
+
+    # Fill in the slot we left for file extensions.
+    for name, (mimes, exts) in decoders.items():
+        for mime in mimes:
+            exts.update(mime_extensions[mime])
+
+    return decoders
+
 
 def play_simple(paths):
     """Play the files in paths in a straightforward way, without
diff --git a/test/test_player.py b/test/test_player.py
index d7c9dba17c..102df1d7d3 100644
--- a/test/test_player.py
+++ b/test/test_player.py
@@ -44,13 +44,14 @@ def _gstplayer_play(*_):  # noqa: 42
 gstplayer._GstPlayer = mock.MagicMock(
     spec_set=[
         "time", "volume", "playing", "run", "play_file", "pause", "stop",
-        "seek", "play"
+        "seek", "play", "get_decoders",
     ], **{
         'playing': False,
         'volume': 0,
         'time.return_value': (0, 0),
         'play_file.side_effect': _gstplayer_play,
         'play.side_effect': _gstplayer_play,
+        'get_decoders.return_value': {'default': ({'audio/mpeg'}, {'mp3'})},
     })
 gstplayer.GstPlayer = lambda _: gstplayer._GstPlayer
 sys.modules["beetsplug.bpd.gstplayer"] = gstplayer
@@ -879,9 +880,16 @@ class BPDDeviceTest(BPDTestHelper):
 
 class BPDReflectionTest(BPDTestHelper):
     test_implements_reflection = implements({
-            'config', 'commands', 'notcommands', 'urlhandlers',
-            'decoders',
-            }, expectedFailure=True)
+        'config', 'commands', 'notcommands', 'urlhandlers',
+    }, expectedFailure=True)
+
+    def test_cmd_decoders(self):
+        with self.run_bpd() as client:
+            response = client.send_command('decoders')
+        self._assert_ok(response)
+        self.assertEqual('default', response.data['plugin'])
+        self.assertEqual('mp3', response.data['suffix'])
+        self.assertEqual('audio/mpeg', response.data['mime_type'])
 
 
 class BPDPeersTest(BPDTestHelper):

From c9327511f6df151ff93f4776a16e72212c16b5ba Mon Sep 17 00:00:00 2001
From: Carl Suster <carl@contraflo.ws>
Date: Fri, 19 Apr 2019 16:21:52 +1000
Subject: [PATCH 2/2] Changelog for #3222

---
 docs/changelog.rst | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/docs/changelog.rst b/docs/changelog.rst
index 4ad0f057a5..4b238c3ec8 100644
--- a/docs/changelog.rst
+++ b/docs/changelog.rst
@@ -89,6 +89,8 @@ New features:
 * :doc:`/plugins/bpd`: MPD protocol command ``idle`` is now supported, allowing
   the MPD version to be bumped to 0.14.
   :bug:`3205` :bug:`800`
+* :doc:`/plugins/bpd`: MPD protocol command ``decoders`` is now supported.
+  :bug:`3222`
 
 Changes: