audio: Start adding playlist typefinder code.

This allows gstreamer pipelines to determine when they are getting m3u, pls or
xspf files and distinguish them from text/plain content.

mopidy/audio/actor.py

@@ -11,13 +11,14 @@ import pykka
 
 from mopidy.utils import process
 
-from . import mixers, utils
+from . import mixers, playlists, utils
 from .constants import PlaybackState
 from .listener import AudioListener
 
 logger = logging.getLogger('mopidy.audio')
 
 mixers.register_mixers()
+playlists.register_typefinders()
 
 
 MB = 1 << 20

mopidy/audio/playlists.py

@@ -0,0 +1,52 @@
+from __future__ import unicode_literals
+
+import pygst
+pygst.require('0.10')
+import gst
+
+import xml.dom.pulldom
+
+
+# TODO: make detect_FOO_header reusable in general mopidy code.
+# i.e. give it just a "peek" like function.
+def detect_m3u_header(typefind):
+    return typefind.peek(0, 8) == b'#EXTM3U\n'
+
+
+def detect_pls_header(typefind):
+    print repr(typefind.peek(0, 11) == b'[playlist]\n')
+    return typefind.peek(0, 11) == b'[playlist]\n'
+
+
+def detect_xspf_header(typefind):
+    # Get more data than the 90 needed for header in case spacing is funny.
+    data = typefind.peek(0, 150)
+
+    # Bail early if the words xml and playlist are not present.
+    if not data or b'xml' not in data or b'playlist' not in data:
+        return False
+
+    # TODO: handle parser errors.
+    # Try parsing what we have, bailing on first element.
+    for event, node in xml.dom.pulldom.parseString(data):
+        if event == xml.dom.pulldom.START_ELEMENT:
+            return (node.tagName == 'playlist' and
+                    node.node.namespaceURI == 'http://xspf.org/ns/0/')
+    return False
+
+
+def playlist_typefinder(typefind, func, caps):
+    if func(typefind):
+        typefind.suggest(gst.TYPE_FIND_MAXIMUM, caps)
+
+
+def register_typefind(mimetype, func, extensions):
+    caps = gst.caps_from_string(mimetype)
+    gst.type_find_register(mimetype, gst.RANK_PRIMARY, playlist_typefinder,
+                           extensions, caps, func, caps)
+
+
+def register_typefinders():
+    register_typefind('audio/x-mpegurl', detect_m3u_header, [b'm3u', b'm3u8'])
+    register_typefind('audio/x-scpls', detect_pls_header, [b'pls'])
+    register_typefind('application/xspf+xml', detect_xspf_header, [b'xspf'])