feat(remote): match the server CDM to the client's DRM and read vaults first

A dual widevine/playready cdm entry now loads the device of the client's DRM system, for old clients too since they already send cdm_type. A new client hands a capped track to its own device for the track's DRM system, and raises the refusal only after its local vaults miss.

docs/dev/rest-api/remote-sessions.md

@@ -296,7 +296,9 @@ There are two ways DRM keys get resolved, chosen by the client's `server_cdm` fl
     The **server's CDM** does everything. The client sends track IDs (or a PSSH),
     the server checks its key vaults, loads the device configured for your API key,
     runs the CDM flow, and returns `KID:KEY` pairs directly. The client needs no
-    CDM.
+    CDM. When the server's `cdm` entry for the service names a `widevine` and a
+    `playready` device, the server loads the device of your local CDM's DRM system.
+    See [`cdm`](../../reference/configuration/drm.md).
 
     - Enable with `server_cdm: true` in the server entry.
     - The server tells the client which DRM type it used
@@ -321,7 +323,10 @@ There are two ways DRM keys get resolved, chosen by the client's `server_cdm` fl
     the limit in `server_cdm_max_height`. In a server CDM session, the batch licence response
     lists each track the server refused to license live under `capped_tracks`. A single-track
     server CDM licence answers `403 SERVER_CDM_CAPPED` for such a track. In both cases the client
-    licenses those tracks in proxy mode with its own local CDM. See
+    reads its own key vaults first, then licenses those tracks in proxy mode with its own local
+    CDM. When the track has no DRM of that CDM's system, the client uses the device that its own
+    `cdm` entry names for the track's DRM system. With no such device, the download of that track
+    stops. See
     [`server_cdm_max_height`](../../reference/configuration/services.md).
 
 ### Your own device identity

docs/reference/configuration/drm.md

@@ -50,7 +50,12 @@ height is known. If the value is still a dict after that, unshackle uses
 When an entry holds `widevine` and `playready`, their order sets which device unshackle loads
 first. A track that offers the two DRM systems licenses with that system. A track that offers
 only the other system uses the other device. A `widevine` / `playready` dict in a quality key
-does not set the order. The server CDM of a remote session follows the same order.
+does not set the order.
+
+On a server, an entry that holds `widevine` and `playready` gives a remote session the server CDM
+of the DRM system of the client's local CDM. The service then makes its manifest for that system,
+so the client's vault keys and its own device apply to the tracks. A client with no local CDM gets
+the device that the entry lists first.
 
 A quality key can also hold a dict of `widevine` / `playready` devices, and so can the
 top-level `default` entry:

tests/remote/key_source.py

@@ -1,3 +1,4 @@
+import logging
 from types import SimpleNamespace
 from typing import Any, Iterable, Optional
 from uuid import UUID
@@ -17,7 +18,41 @@ def remote_keys(
     svc._server_cdm = server_cdm
     svc.server_cdm_type = server_cdm_type
     svc.client_licensed = set(client_licensed)
+    svc.deferred_refusals = {}
     svc.server_vault_keys = dict(server_vault_keys or {})
     svc.server_vault = ServerVault(svc)
-    svc.ctx = SimpleNamespace(obj=SimpleNamespace(cdm=local_cdm))
+    svc.ctx = SimpleNamespace(obj=SimpleNamespace(cdm=local_cdm, cdm_for=None))
     return svc
+
+
+CAPPED = {"keys": {}, "capped_tracks": {"vid": {"reason": "server_cdm_max_height", "max_height": 1080}}}
+PR_DEVICE = SimpleNamespace(is_playready=True, security_level=3000)
+
+
+def remote_session(local_cdm: Any, answer: dict) -> RemoteService:
+    """A server-CDM RemoteService whose every POST records its payload in ``posts`` and returns ``answer``."""
+    svc = remote_keys(server_cdm_type="playready", local_cdm=local_cdm)
+    svc._track_alias = {}
+    svc._title_alias = {}
+    svc._session_id = "sess"
+    svc.log = logging.getLogger("test-remote-session")
+    posts: list = []
+    svc.client = SimpleNamespace(post=lambda endpoint, payload, expect=(): posts.append(payload) or answer)
+    svc.drain_server_logs = lambda: None
+    svc.posts = posts
+    return svc
+
+
+class OneTrack(list):
+    @property
+    def videos(self) -> list:
+        return list(self)
+
+    @property
+    def audio(self) -> list:
+        return []
+
+
+def one_title(track: Any) -> SimpleNamespace:
+    """A title holding only ``track``, as a video."""
+    return SimpleNamespace(tracks=OneTrack([track]))

tests/remote/unit/test_client_device_cdm.py

@@ -405,6 +405,7 @@ def test_a_lent_device_without_the_vault_grant_asks_the_server_for_no_key() -> N
     svc._server_device = True
     svc._local_vaults_only = True
     svc.client_licensed = set()
+    svc.deferred_refusals = {}
     svc.client = SimpleNamespace(post=lambda *a, **k: pytest.fail("the server refuses every key request"))
     track = SimpleNamespace(id="vid", drm=None)
 

tests/remote/unit/test_server_cdm_max_height.py

@@ -13,7 +13,7 @@ import pywidevine.pssh as wv_pssh_mod
 from rich.table import Table
 
 import unshackle.core.drm as drm_mod
-from tests.remote.key_source import remote_keys
+from tests.remote.key_source import CAPPED, PR_DEVICE, one_title, remote_keys, remote_session
 from unshackle.commands.dl import dl
 from unshackle.core.api import handlers
 from unshackle.core.api.errors import APIError, APIErrorCode
@@ -203,42 +203,15 @@ class _WV:
 _WV.__name__ = "Widevine"
 
 
-def remote(local_cdm, answer):
-    svc = remote_keys(server_cdm_type="playready", local_cdm=local_cdm)
-    svc._track_alias = {}
-    svc._title_alias = {}
-    svc._session_id = "sess"
-    svc.log = logging.getLogger("test-server-cdm-cap")
-    posts: list = []
-    svc.client = SimpleNamespace(post=lambda endpoint, payload, expect=(): posts.append(payload) or answer)
-    svc.drain_server_logs = lambda: None
-    svc.posts = posts
-    return svc
-
-
-class _Title:
-    def __init__(self, track):
-        self.tracks = _Tracks([track])
-
-
-class _Tracks(list):
-    @property
-    def videos(self):
-        return list(self)
-
-    @property
-    def audio(self):
-        return []
-
-
-CAPPED = {"keys": {}, "capped_tracks": {"vid": {"reason": "server_cdm_max_height", "max_height": 1080}}}
+def capped_track():
+    return SimpleNamespace(id="vid", height=2160, drm=[_WV()], drm_preference=None)
 
 
 def test_a_capped_track_moves_to_the_local_device():
     track = SimpleNamespace(id="vid", drm=[_WV()], drm_preference=None)
-    svc = remote(SimpleNamespace(is_playready=False, security_level=1), CAPPED)
+    svc = remote_session(SimpleNamespace(is_playready=False, security_level=1), CAPPED)
 
-    svc.resolve_server_keys(_Title(track))
+    svc.resolve_server_keys(one_title(track))
 
     assert svc.client_licensed == {"vid"}
     assert track.drm_preference == "widevine"
@@ -249,18 +222,39 @@ def test_a_capped_track_moves_to_the_local_device():
     assert "mode" not in svc.posts[0] and svc.posts[0]["challenge"]
 
 
+def fails_at_the_track_licence(local_cdm, match):
+    """The batch licence defers the refusal, so dl reads the local vaults before the track licence raises it."""
+    track = capped_track()
+    svc = remote_session(local_cdm, CAPPED)
+    svc.resolve_server_keys(one_title(track))
+    assert svc.client_licensed == set()
+    assert "vid" in svc.deferred_refusals
+
+    svc.client.post = None
+    with pytest.raises(click.ClickException, match=match):
+        svc.proxy_license(b"", track, "widevine")
+
+
 def test_a_capped_track_without_a_local_device_fails_clearly():
-    track = SimpleNamespace(id="vid", drm=[_WV()], drm_preference=None)
-    svc = remote(None, CAPPED)
-    with pytest.raises(click.ClickException, match="1080p"):
-        svc.resolve_server_keys(_Title(track))
+    fails_at_the_track_licence(None, "1080p")
 
 
 def test_a_capped_track_without_the_local_drm_system_fails_clearly():
-    track = SimpleNamespace(id="vid", drm=[_WV()], drm_preference=None)
-    svc = remote(SimpleNamespace(is_playready=True, security_level=3000), CAPPED)
-    with pytest.raises(click.ClickException, match="PlayReady"):
-        svc.resolve_server_keys(_Title(track))
+    fails_at_the_track_licence(
+        PR_DEVICE,
+        r"1080p.*the 2160p track has only Widevine DRM for your PlayReady device; pass -q 2160 ",
+    )
+
+
+def test_a_server_vault_miss_without_the_local_drm_system_fails_at_once():
+    """Only a server-CDM session reads the local vaults before the licence, so a server-vault session raises at once."""
+    track = capped_track()
+    svc = remote_session(PR_DEVICE, {"keys": {}, "capped_tracks": {"vid": {}}})
+    svc._server_cdm = False
+    svc._server_vault = True
+    with pytest.raises(click.ClickException, match="server vault") as ei:
+        svc.resolve_server_keys(one_title(track))
+    assert "-q" not in ei.value.message
 
 
 def test_a_null_service_in_the_cap_map_falls_through_to_the_default(monkeypatch):
@@ -537,18 +531,20 @@ class _LocalWidevine(Widevine):
         raise self.Used(cdm)
 
 
-def prepare(svc, licence):
+def prepare(svc, licence, drm=None, track=None, cdm_for=None):
     runner = dl.__new__(dl)
     runner._remote_service = svc
     runner.cdm = "server stub"
     runner.service = "EXAMPLE1"
     runner.debug_logger = None
     runner.log = logging.getLogger("test-server-cdm-cap")
+    runner.cdm_for = cdm_for
     table = Table()
     table.add_column()
-    track = SimpleNamespace(id="vid", drm=None, get_drm_for_cdm=lambda cdm: None)
+    drm = drm or _LocalWidevine()
+    track = track or SimpleNamespace(id="vid", drm=None, get_drm_for_cdm=lambda cdm: None)
     with pytest.raises(_LocalWidevine.Used) as ei:
-        runner.prepare_drm(_LocalWidevine(), track, None, lambda **k: None, licence, table=table, cdm_only=True)
+        runner.prepare_drm(drm, track, None, lambda **k: None, licence, table=table, cdm_only=True)
     return ei.value.args[0]
 
 
@@ -611,24 +607,24 @@ def test_a_mid_download_handover_puts_the_keys_on_the_callers_drm(monkeypatch):
 
 def test_a_capped_hls_track_with_no_drm_yet_moves_to_the_local_device():
     track = SimpleNamespace(id="vid", drm=[], drm_preference=None)
-    svc = remote(SimpleNamespace(is_playready=False, security_level=1), CAPPED)
-    svc.resolve_server_keys(_Title(track))
+    svc = remote_session(SimpleNamespace(is_playready=False, security_level=1), CAPPED)
+    svc.resolve_server_keys(one_title(track))
     assert svc.client_licensed == {"vid"}
     assert track.drm_preference == "widevine"
 
 
 def test_resolve_server_keys_forgets_the_last_titles_handovers():
     track = SimpleNamespace(id="vid", drm=[_WV()], drm_preference=None)
-    svc = remote(SimpleNamespace(is_playready=False, security_level=1), {"keys": {}})
+    svc = remote_session(SimpleNamespace(is_playready=False, security_level=1), {"keys": {}})
     svc.client_licensed = {"vid"}
-    svc.resolve_server_keys(_Title(track))
+    svc.resolve_server_keys(one_title(track))
     assert svc.client_licensed == set()
 
 
 def test_a_single_licence_refusal_hands_the_track_to_the_local_device():
     track = SimpleNamespace(id="vid", drm=[_WV()], drm_preference=None)
     refusal = {"status": "error", "error_code": "SERVER_CDM_CAPPED", "details": CAP_DETAILS}
-    svc = remote(SimpleNamespace(is_playready=False, security_level=1), refusal)
+    svc = remote_session(SimpleNamespace(is_playready=False, security_level=1), refusal)
 
     assert svc.proxy_license(b"", track, "widevine") == b""
     assert svc.client_licensed == {"vid"}
@@ -665,7 +661,7 @@ def sent_create(
         raise _SentCreate(data)
 
     handlers.config.cdm = cdm_map or {}
-    svc = remote(local_cdm, {})
+    svc = remote_session(local_cdm, {})
     svc.ctx.obj.cdm_entry = cdm_entry
     svc._server_cdm = server_cdm
     svc.service_tag = "EXAMPLE1"
@@ -815,7 +811,7 @@ def test_dl_records_whether_the_services_cdm_entry_named_the_loaded_device(cdm,
 
 @pytest.mark.parametrize("max_height", [None, 1080])
 def test_a_declined_server_cdm_that_the_server_keeps_is_reported(max_height, caplog):
-    svc = remote(SimpleNamespace(is_playready=False), {})
+    svc = remote_session(SimpleNamespace(is_playready=False), {})
     svc.service_tag = "EXAMPLE1"
     svc._server_cdm = False
     with caplog.at_level(logging.INFO):
@@ -833,7 +829,7 @@ def test_a_declined_server_cdm_that_the_server_keeps_is_reported(max_height, cap
 
 @pytest.mark.parametrize(("cdm_entry", "level"), [(True, logging.INFO), (False, logging.WARNING)])
 def test_a_refused_server_cdm_warns_only_when_no_cdm_entry_loaded_the_fallback(cdm_entry, level, caplog):
-    svc = remote(SimpleNamespace(is_playready=False), {})
+    svc = remote_session(SimpleNamespace(is_playready=False), {})
     svc.service_tag = "EXAMPLE1"
     svc.ctx.obj.cdm_entry = cdm_entry
     with caplog.at_level(logging.INFO):
@@ -890,3 +886,40 @@ def test_a_per_service_entry_matches_the_tag_in_any_case(config_key, tag, monkey
     assert svc._server_cdm is False
     assert svc._anonymous_search is True
     assert handlers.config.services == {tag: {"title_map": {"a": "b"}}}
+
+
+def test_a_capped_track_moves_to_the_clients_device_for_its_drm_system():
+    """A client whose cdm entry also names a device of the track's system licenses with that device."""
+    track = capped_track()
+    svc = remote_session(PR_DEVICE, CAPPED)
+    asked: list = []
+    svc.ctx.obj.cdm_for = lambda system, quality: asked.append((system, quality)) or SimpleNamespace(is_playready=False)
+
+    svc.resolve_server_keys(one_title(track))
+
+    assert asked == [("widevine", 2160)]
+    assert svc.client_licensed == {"vid"}
+    assert track.drm_preference == "widevine"
+    assert svc.deferred_refusals == {}
+
+
+def test_a_capped_track_keeps_the_refusal_when_the_client_has_no_device_for_its_system():
+    track = capped_track()
+    svc = remote_session(PR_DEVICE, CAPPED)
+    svc.ctx.obj.cdm_for = lambda system, quality: SimpleNamespace(is_playready=True)
+
+    svc.resolve_server_keys(one_title(track))
+
+    assert svc.client_licensed == set()
+    assert "vid" in svc.deferred_refusals
+
+
+def test_dl_licenses_a_handed_over_track_with_the_device_of_its_drm_system():
+    svc = remote_keys(client_licensed={"vid"}, local_cdm=PR_DEVICE)
+    widevine_device = SimpleNamespace(is_playready=False)
+    drm = _LocalWidevine()
+    track = SimpleNamespace(id="vid", drm=[drm], get_drm_for_cdm=lambda cdm: drm)
+
+    used = prepare(svc, lambda **k: None, drm, track, lambda system, quality: widevine_device)
+
+    assert used is widevine_device

tests/remote/unit/test_server_cdm_type_override.py

@@ -225,3 +225,88 @@ async def test_track_preference_falls_back_with_a_warning(env, monkeypatch, capl
 
     assert body["drm_type"] == "widevine"
     assert "wants playready DRM but the server has no device for it" in caplog.text
+
+
+BOTH = {"EXAMPLE1": {"widevine": "wv_device", "playready": "pr_device"}}
+
+
+@pytest.mark.parametrize(
+    ("mapping", "server_cdm", "wanted"),
+    [
+        (BOTH, True, "playready"),
+        ({"EXAMPLE1": "wv_device"}, True, None),
+        ({"EXAMPLE1": {"widevine": "wv_device"}}, True, None),
+        ({}, False, "playready"),
+    ],
+)
+def test_the_server_device_follows_the_client_only_when_both_systems_are_mapped(
+    monkeypatch, mapping, server_cdm, wanted
+):
+    asked: list = []
+    monkeypatch.setattr(handlers.config, "cdm", mapping, raising=False)
+    monkeypatch.setattr(handlers, "load_service_yaml", lambda tag: {})
+    monkeypatch.setattr(handlers, "load_full_cdm", lambda service, profile, cdm_type: asked.append(cdm_type))
+    monkeypatch.setattr(handlers, "build_parent_ctx", lambda *a, **k: None)
+    monkeypatch.setattr(handlers.Services, "load", lambda tag: object)
+    monkeypatch.setattr(handlers, "instantiate_service", lambda *a, **k: "service")
+
+    handlers.create_service_instance("EXAMPLE1", "t", {"cdm_type": "playready"}, None, [], None, server_cdm=server_cdm)
+
+    assert asked == [wanted]
+
+
+@pytest.mark.parametrize("system", ["widevine", "playready"])
+def test_the_tracks_response_names_the_system_of_the_loaded_device(monkeypatch, system):
+    from unshackle.core.api import session_store as store_mod
+    from unshackle.core.tracks import Tracks
+
+    monkeypatch.setattr(handlers.config, "cdm", BOTH, raising=False)
+    monkeypatch.setattr(handlers.config, "serve", {"users": {}}, raising=False)
+    monkeypatch.setattr(store_mod.bus, "publish", lambda topic, data: None)
+
+    class StubService:
+        session = SimpleNamespace(headers={}, cookies=[])
+        ctx = SimpleNamespace(obj=SimpleNamespace(cdm=SimpleNamespace(is_playready=system == "playready")))
+
+        def get_tracks(self, title):
+            return Tracks()
+
+        def get_chapters(self, title):
+            raise NotImplementedError
+
+    async def run():
+        store = store_mod.get_session_store()
+        entry = await store.create(
+            service_tag="EXAMPLE1", service_instance=StubService(), session_id="both", owner_key=None
+        )
+        entry.title_map = {"t1": "Title"}
+        entry.server_cdm = True
+        try:
+            resp = await handlers.session_tracks_handler({"title_id": "t1"}, "both")
+            return json.loads(resp.body)
+        finally:
+            await store.delete("both")
+
+    assert asyncio.run(run())["server_cdm_type"] == system
+
+
+@pytest.mark.parametrize(
+    ("mapping", "both"),
+    [
+        (BOTH, True),
+        ({"default": {"Widevine": "wv_device", "PlayReady": "pr_device"}}, True),
+        ({"EXAMPLE1": {"widevine": "wv_device", "playready": None}}, False),
+        ({"EXAMPLE1": {"widevine": "wv_device", "default": "pr_device"}}, False),
+        ({"EXAMPLE1": "wv_device"}, False),
+    ],
+)
+def test_lists_both_systems_needs_a_device_for_each(monkeypatch, mapping, both):
+    monkeypatch.setattr(handlers.config, "cdm", mapping, raising=False)
+    assert handlers.lists_both_systems("EXAMPLE1", handlers.config) is both
+
+
+@pytest.mark.parametrize("cdm_type", [5, ["playready"], {"a": 1}])
+def test_a_cdm_type_that_is_not_a_string_takes_the_first_listed_device(monkeypatch, cdm_type):
+    monkeypatch.setattr(handlers.config, "cdm", BOTH, raising=False)
+    monkeypatch.setitem(cdm_mod.__dict__, "load_cdm", lambda name, **k: name)
+    assert handlers.load_full_cdm("EXAMPLE1", None, cdm_type) == "wv_device"

tests/remote/unit/test_server_cdm_vault_write.py

@@ -13,7 +13,7 @@ from uuid import UUID
 import pytest
 from rich.table import Table
 
-from tests.remote.key_source import remote_keys
+from tests.remote.key_source import CAPPED, PR_DEVICE, one_title, remote_keys, remote_session
 from unshackle.commands.dl import dl
 
 pytestmark = pytest.mark.unit
@@ -114,6 +114,41 @@ def test_keys_read_from_a_vault_are_not_pushed_back():
     assert vaults.added == {NEW: "k_new"}
 
 
+def capped_run(vaults):
+    """A batch licence refuses the track for a local PlayReady device, then dl prepares its Widevine DRM."""
+    cmd = make_cmd(vaults)
+    svc = remote_session(PR_DEVICE, CAPPED)
+    cmd._remote_service = svc
+
+    drm = type("Widevine", (FakeWidevine,), {})([CACHED])
+    track = SimpleNamespace(id="vid", height=2160, drm=[drm], drm_preference=None)
+    svc.resolve_server_keys(one_title(track))
+
+    table = Table.grid()
+    table.add_row("")
+    cmd.prepare_drm(
+        track=track,
+        title=None,
+        drm=drm,
+        licence=lambda **kwargs: svc.proxy_license(b"", track, "widevine"),
+        certificate=None,
+        track_kid=CACHED,
+        table=table,
+    )
+    return drm
+
+
+def test_a_capped_track_takes_a_local_vault_key_before_the_refusal():
+    assert capped_run(FakeVaults({CACHED: "k_cached"})).content_keys == {CACHED: "k_cached"}
+
+
+def test_a_capped_track_no_vault_holds_raises_the_refusal():
+    import click
+
+    with pytest.raises(click.ClickException, match="only Widevine DRM for your PlayReady device"):
+        capped_run(FakeVaults())
+
+
 def test_batch_resolved_keys_are_cached_before_download():
     """The batch licence fills track.drm before prepare_drm, so dl caches it at the call site."""
     vaults = FakeVaults()

unshackle/commands/dl.py

@@ -1623,6 +1623,7 @@ class dl:
             proxy_providers=self.proxy_providers,
             profile=self.profile,
             cdm_entry=self.cdm_from_service_entry(),
+            cdm_for=self.cdm_for,
         )
 
         if repack:
@@ -5283,6 +5284,10 @@ class dl:
             assert remote is not None
             track_cdm = remote.local_cdm
             local_drm = track.get_drm_for_cdm(track_cdm)
+            if isinstance(local_drm, (Widevine, PlayReady)) and isinstance(local_drm, PlayReady) != is_playready_cdm(
+                track_cdm
+            ):
+                track_cdm = self.cdm_for("playready" if isinstance(local_drm, PlayReady) else "widevine", track_quality)
             if local_drm is not None and local_drm is not drm:
                 assert not isinstance(local_drm, ClearKey)
                 # a mid-download handover leaves drm on the server's DRM system, and the caller decrypts with it

unshackle/core/api/handlers.py

@@ -32,7 +32,7 @@ from unshackle.core.api.session_log import SessionLogBuffer, SessionLogMirror, c
 from unshackle.core.api.session_store import SessionStore
 from unshackle.core.binaries import binary_version
 from unshackle.core.cacher import Cacher
-from unshackle.core.cdm.detect import cdm_type_stub
+from unshackle.core.cdm.detect import cdm_type_stub, is_playready_cdm
 from unshackle.core.config import config, load_yaml
 from unshackle.core.constants import AUDIO_CODEC_MAP, DYNAMIC_RANGE_MAP, VIDEO_CODEC_MAP, AnyTrack
 from unshackle.core.drm import BlowfishStripe, cbcs, is_null_key
@@ -200,6 +200,8 @@ def load_full_cdm(service: str, profile: Optional[str], cdm_type: Optional[str]
     from unshackle.core.cdm import load_cdm
     from unshackle.core.config import config as app_config
 
+    if not isinstance(cdm_type, str):
+        cdm_type = None
     cdm_name = ci_get(app_config.cdm, service) or ci_get(app_config.cdm, "default")
     if isinstance(cdm_name, dict):
         lower_keys = {k.lower(): v for k, v in cdm_name.items()}
@@ -3710,7 +3712,8 @@ def create_service_instance(
 
         cdm = client_device_cdm(data, input_bridge, lend_server_device)
     else:
-        cdm = load_full_cdm(normalized_service, profile, None if server_cdm else data.get("cdm_type"))
+        follows_client = not server_cdm or lists_both_systems(normalized_service, config)
+        cdm = load_full_cdm(normalized_service, profile, data.get("cdm_type") if follows_client else None)
 
     # Reconstruct enum track-selection params from client data so service code that reads
     # ctx.parent.params (Service.__init__ proxy/range/vcodec/best_available block) sees enums.
@@ -4103,6 +4106,9 @@ async def session_tracks_handler(
 
         service_tag = session.service_tag
         config_cdm_type = detect_cdm_type_for_service(service_tag, app_config)
+        if not config_cdm_type and session.server_cdm and lists_both_systems(service_tag, app_config):
+            loaded = getattr(getattr(getattr(service_instance, "ctx", None), "obj", None), "cdm", None)
+            config_cdm_type = "playready" if is_playready_cdm(loaded) else "widevine"
 
         track_has_wv = any(
             d.__class__.__name__ == "Widevine" for t in list(tracks.videos) + list(tracks.audio) if t.drm for d in t.drm
@@ -4278,6 +4284,15 @@ def configured_cdm_name(service: str, drm_type: str, app_config: Any) -> Optiona
     return None
 
 
+def lists_both_systems(service: str, app_config: Any) -> bool:
+    """True when config.cdm names a device for both Widevine and PlayReady for ``service``.
+
+    The server CDM then loads the device of the client's DRM system, so the manifest suits the client's vaults.
+    """
+    entry = ci_get(app_config.cdm, service) or ci_get(app_config.cdm, "default")
+    return isinstance(entry, dict) and {"widevine", "playready"} <= {key.lower() for key, name in entry.items() if name}
+
+
 def detect_cdm_type_for_service(service: str, app_config: Any) -> Optional[str]:
     """The DRM system config.cdm settles for a service; None when the mapping leaves it open.
 

unshackle/core/api/routes.py

@@ -1957,7 +1957,10 @@ async def session_create(request: web.Request) -> web.Response:
               cdm_type:
                 type: string
                 enum: [widevine, playready]
-                description: DRM system of the client's local CDM; absent when the client has none
+                description: |
+                  DRM system of the client's local CDM; absent when the client has none.
+                  A server CDM session loads the device of this system when the server's
+                  cdm entry for the service names both systems
               cdm_security_level:
                 type: integer
                 description: |

unshackle/core/remote_service.py

@@ -1019,6 +1019,7 @@ class RemoteService:
         self._chapters_by_title: Dict[str, list] = {}
         self._session_id: Optional[str] = None
         self.client_licensed: set[str] = set()  # track ids this machine's device licenses by challenge relay
+        self.deferred_refusals: Dict[str, str] = {}
         self.server_vault_keys: Dict[UUID, str] = {}
         self.server_vault = ServerVault(self)
         self._segment_filters: Dict[str, Callable[[Any], bool]] = {}
@@ -1790,10 +1791,12 @@ class RemoteService:
         Called by dl.py between track selection and download. The server
         decides which CDM device to use and tells the client through
         server_cdm_type. We send track IDs and the server does the full
-        CDM flow, returning KID:KEY pairs.
+        CDM flow, returning KID:KEY pairs. A capped track this machine's device cannot license
+        waits in ``deferred_refusals``, so dl reads the local vaults before ``proxy_license`` raises it.
         """
         # track ids can repeat across titles, so a refusal for the last title must not carry over
         self.client_licensed.clear()
+        self.deferred_refusals.clear()
         if not (self._server_cdm or getattr(self, "_server_vault", False)) or self.local_vaults_only:
             return
 
@@ -1863,7 +1866,13 @@ class RemoteService:
             # a lent-device miss still gets the local vaults, which dl reads before asking the server again
             refusal = capped.get(self.server_track_id(track.id))
             if refusal is not None and refusal.get("reason") != "server_device":
-                self.license_locally(track, refusal)
+                try:
+                    self.license_locally(track, refusal)
+                except click.ClickException as e:
+                    if not self._server_cdm:
+                        raise
+                    self.deferred_refusals[str(track.id)] = e.message
+                    self.log.debug(f"{e.message}; trying the local vaults first")
 
     def license_locally(self, track: AnyTrack, refusal: Dict[str, Any]) -> None:
         """Hand a track the server CDM refused to license live to this machine's own device.
@@ -1871,7 +1880,7 @@ class RemoteService:
         dl then licenses it through the challenge relay. An HLS track with no DRM yet passes, as its
         media playlist names the DRM and the downloader honours ``drm_preference``.
         """
-        from unshackle.core.cdm.detect import is_playready_cdm
+        from unshackle.core.cdm.detect import is_playready_cdm, is_widevine_cdm
 
         if refusal.get("reason") == "server_device":
             vaults = (
@@ -1893,11 +1902,17 @@ class RemoteService:
         if cdm is None:
             raise click.ClickException(f"{why}, and {track} needs a local CDM to license it")
         drm_class = "PlayReady" if is_playready_cdm(cdm) else "Widevine"
-        if track.drm and not any(d.__class__.__name__ == drm_class for d in track.drm):
-            height = getattr(track, "height", None)
-            raise click.ClickException(
-                f"{why}, and {track} has no {drm_class} DRM for your local CDM; pass -q {height or 'with that height'}"
-            )
+        height = getattr(track, "height", None)
+        systems = {d.__class__.__name__ for d in track.drm or ()}
+        if systems and drm_class not in systems:
+            other = "Widevine" if drm_class == "PlayReady" else "PlayReady"
+            matches = is_widevine_cdm if other == "Widevine" else is_playready_cdm
+            if not (other in systems and self.ctx.obj.cdm_for and matches(self.ctx.obj.cdm_for(other.lower(), height))):
+                label = f"the {height}p track" if height else str(track)
+                hint = f"; pass -q {height} to start the session on your device" if cap and height else ""
+                have = " and ".join(sorted(systems))
+                raise click.ClickException(f"{why}, and {label} has only {have} DRM for your {drm_class} device{hint}")
+            drm_class = other
         track.drm_preference = drm_class.lower()
         self.client_licensed.add(str(track.id))
         self.log.info(f"{why}; licensing {track.id} with your own {drm_class} device")
@@ -2027,6 +2042,8 @@ class RemoteService:
         if self.local_vaults_only:
             self.license_locally(track, {"reason": "server_device"})
         if self._server_cdm and str(track.id) not in self.client_licensed:
+            if deferred := self.deferred_refusals.get(str(track.id)):
+                raise click.ClickException(deferred)
             from uuid import UUID
 
             server_type = self.server_cdm_type

unshackle/core/utils/click_types.py

@@ -1,7 +1,7 @@
 import re
 from datetime import date, timedelta
 from enum import Enum
-from typing import Any, Optional, Sequence, Union
+from typing import Any, Callable, Optional, Sequence, Union
 
 import click
 from click.shell_completion import CompletionItem
@@ -166,6 +166,7 @@ class ContextData:
         proxy_providers: list,
         profile: Optional[str] = None,
         cdm_entry: bool = False,
+        cdm_for: Optional[Callable[[str, Optional[int]], Any]] = None,
     ) -> None:
         self.config = config
         self.cdm = cdm
@@ -173,6 +174,7 @@ class ContextData:
         self.profile = profile
         # True when the service's own entry in the cdm config named the loaded device
         self.cdm_entry = cdm_entry
+        self.cdm_for = cdm_for
 
 
 class SeasonRange(click.ParamType):