stream backend: Add StreamBackend, fixes #151

Adds a basic streaming backend simply handles streaming audio and nothing else.
I.e. no metadata beyond the URI we where given. #270 still needs to be solved
for actual metadata to make sense in this backend.

mopidy/backends/stream/__init__.py

@@ -0,0 +1,23 @@
+"""A backend for playing music for streaming music.
+
+This backend will handle streaming of URIs in
+:attr:`mopidy.settings.STREAM_PROTOCOLS` assuming the right plugins are
+installed.
+
+**Issues:**
+
+https://github.com/mopidy/mopidy/issues?labels=Stream+backend
+
+**Dependencies:**
+
+- None
+
+**Settings:**
+
+- :attr:`mopidy.settings.STREAM_PROTOCOLS`
+"""
+
+from __future__ import unicode_literals
+
+# flake8: noqa
+from .actor import StreamBackend

mopidy/backends/stream/actor.py

@@ -0,0 +1,57 @@
+from __future__ import unicode_literals
+
+import pygst
+pygst.require('0.10')
+import gst
+
+import logging
+import urlparse
+
+import pykka
+
+from mopidy import settings
+from mopidy.backends import base
+from mopidy.models import SearchResult, Track
+
+logger = logging.getLogger('mopidy.backends.stream')
+
+
+class StreamBackend(pykka.ThreadingActor, base.Backend):
+    def __init__(self, audio):
+        super(StreamBackend, self).__init__()
+
+        self.library = StreamLibraryProvider(backend=self)
+        self.playback = base.BasePlaybackProvider(audio=audio, backend=self)
+        self.playlists = None
+
+        available_protocols = set()
+
+        registry = gst.registry_get_default()
+        for factory in registry.get_feature_list(gst.TYPE_ELEMENT_FACTORY):
+            for uri in factory.get_uri_protocols():
+                if uri in settings.STREAM_PROTOCOLS:
+                    available_protocols.add(uri)
+
+        self.uri_schemes = list(available_protocols)
+
+
+# TODO: Should we consider letting lookup know how to expand common playlist
+# formats (m3u, pls, etc) for http(s) URIs?
+class StreamLibraryProvider(base.BaseLibraryProvider):
+    def lookup(self, uri):
+        if urlparse.urlsplit(uri).scheme not in self.backend.uri_schemes:
+            return []
+        # TODO: actually lookup the stream metadata by getting tags in same
+        # way as we do for updating the local library with mopidy.scanner
+        # Note that we would only want the stream metadata at this stage,
+        # not the currently playing track's.
+        return [Track(uri=uri, name=uri)]
+
+    def find_exact(self, **query):
+        return SearchResult()
+
+    def search(self, **query):
+        return SearchResult()
+
+    def refresh(self, uri=None):
+        pass

mopidy/settings.py

@@ -20,10 +20,12 @@
 #:     BACKENDS = (
 #:         u'mopidy.backends.local.LocalBackend',
 #:         u'mopidy.backends.spotify.SpotifyBackend',
+#:         u'mopidy.backends.spotify.StreamBackend',
 #:     )
 BACKENDS = (
     'mopidy.backends.local.LocalBackend',
     'mopidy.backends.spotify.SpotifyBackend',
+    'mopidy.backends.stream.StreamBackend',
 )
 
 #: The log format used for informational logging.
@@ -301,3 +303,26 @@
 #:
 #:     SPOTIFY_TIMEOUT = 10
 SPOTIFY_TIMEOUT = 10
+
+#: Whitelist of URIs to support streaming from.
+#:
+#: Used by :mod:`mopidy.backends.stream`
+#:
+#: Default::
+#:
+#:     STREAM_PROTOCOLS = (
+#:         u'http',
+#:         u'https',
+#:         u'mms',
+#:         u'rtmp',
+#:         u'rtmps',
+#:         u'rtsp',
+#:     )
+STREAM_PROTOCOLS = (
+    'http',
+    'https',
+    'mms',
+    'rtmp',
+    'rtmps',
+    'rtsp',
+)