refactor(drm): resolve content keys in one licence path behind ServerKeySource

Drop null keys from every licence, server and export source, not only Widevine. dl now finds remote sessions and imports through ServerKeySource instead of private fields.

tests/remote/unit/test_server_cdm_key_verification.py

@@ -12,11 +12,12 @@ from uuid import UUID
 
 import pytest
 
+from tests.remote.key_source import remote_keys
 from unshackle.core.api import handlers
 from unshackle.core.api.errors import APIError
 from unshackle.core.api.session_store import SessionEntry
 from unshackle.core.drm import BlowfishStripe
-from unshackle.core.remote_service import RemoteService, ServerVault
+from unshackle.core.remote_service import RemoteService
 
 pytestmark = pytest.mark.unit
 
@@ -25,13 +26,10 @@ CDM_KID = UUID("43de497c6d1945f49acc2951696ec628")
 
 
 def remote_service() -> RemoteService:
-    svc = RemoteService.__new__(RemoteService)
+    svc = remote_keys(server_cdm=None)
     svc._track_alias = {}
     svc._title_alias = {}
-    svc.server_vault_keys = {}
-    svc.server_vault = ServerVault(svc)
     svc._session_id = "sess"
-    svc.client_licensed = set()
     svc.log = SimpleNamespace(warning=lambda *a, **k: None)
     return svc
 
@@ -277,3 +275,15 @@ async def test_a_stripe_cipher_track_is_clear_and_never_licensed(monkeypatch):
 
     assert json.loads(resp.body)["clear_tracks"] == ["aud"]
     assert isinstance(track.drm[0], BlowfishStripe)
+
+
+def test_the_server_licence_drops_a_null_key():
+    kid, null = UUID(int=1), UUID(int=2)
+
+    class Licensed:
+        content_keys: dict = {}
+
+        def get_content_keys(self, **kwargs):
+            self.content_keys = {kid: "ab" * 16, null: "0" * 32}
+
+    assert handlers.license_with_track_fallback(Licensed(), SimpleNamespace(drm=None)) == {kid.hex: "ab" * 16}