serve: Store Cdm per-secret, ensure session more efficiently

The Cdm is now stored per-secret due to the Cdm object's session limit. This is so one user (by secret key) cannot overload the server with too many sessions.

But this also fixes it so that the serve API will work for more than just 50 sessions for all users. Otherwise the user pool will eventually overload the Cdm with 50 sessions, even if they close it, it will eventually happen. Think of it like the server being overloaded prematurely.

pywidevine/serve.py

@@ -23,7 +23,7 @@ routes = web.RouteTableDef()
 
 
 async def _startup(app: web.Application):
-    app["sessions"]: dict[bytes, Cdm] = {}
+    app["cdms"]: dict[str, Cdm] = {}
     app["config"]["devices"] = {
         path.stem: path
         for x in app["config"]["devices"]
@@ -32,8 +32,8 @@ async def _startup(app: web.Application):
 
 
 async def _cleanup(app: web.Application):
-    app["sessions"].clear()
-    del app["sessions"]
+    app["cdms"].clear()
+    del app["cdms"]
     app["config"].clear()
     del app["config"]
 
@@ -48,7 +48,8 @@ async def ping(_) -> web.Response:
 
 @routes.get("/open/{device}")
 async def open(request: web.Request) -> web.Response:
-    user = request.app["config"]["users"][request.headers["X-Secret-Key"]]
+    secret_key = request.headers["X-Secret-Key"]
+    user = request.app["config"]["users"][secret_key]
     device = request.match_info["device"]
 
     if device not in user["devices"] or device not in request.app["config"]["devices"]:
@@ -59,9 +60,11 @@ async def open(request: web.Request) -> web.Response:
             "message": f"Device '{device}' is not found or you are not authorized to use it."
         }, status=403)
 
+    cdm = request.app["cdms"].get(secret_key)
+    if not cdm:
         device = Device.load(request.app["config"]["devices"][device])
+        cdm = request.app["cdms"][secret_key] = Cdm(device)
 
-    cdm = Cdm(device)
     try:
         session_id = cdm.open()
     except TooManySessions as e:
@@ -70,16 +73,14 @@ async def open(request: web.Request) -> web.Response:
             "message": str(e)
         }, status=400)
 
-    request.app["sessions"][session_id] = cdm
-
     return web.json_response({
         "status": 200,
         "message": "Success",
         "data": {
             "session_id": session_id.hex(),
             "device": {
-                "system_id": device.system_id,
-                "security_level": device.security_level
+                "system_id": cdm.device.system_id,
+                "security_level": cdm.device.security_level
             }
         }
     })
@@ -87,6 +88,8 @@ async def open(request: web.Request) -> web.Response:
 
 @routes.post("/challenge/{license_type}")
 async def challenge(request: web.Request) -> web.Response:
+    secret_key = request.headers["X-Secret-Key"]
+
     body = await request.json()
     for required_field in ("session_id", "init_data"):
         if not body.get(required_field):
@@ -99,14 +102,17 @@ async def challenge(request: web.Request) -> web.Response:
     session_id = bytes.fromhex(body["session_id"])
 
     # get cdm
-    if session_id not in request.app["sessions"]:
-        # e.g., app["sessions"] being cleared on server crash, reboot, and such
-        # or, the license message was from a challenge that was not made by our Cdm
+    cdm = request.app["cdms"].get(secret_key)
+    if not cdm or session_id not in cdm._sessions:
+        # This can happen if:
+        # - API server gets shutdown/restarted,
+        # - The user calls /challenge before /open,
+        # - The user called /open on a different IP Address
+        # - The user closed the session
         return web.json_response({
             "status": 400,
             "message": "Invalid Session ID. Session ID may have Expired."
         }, status=400)
-    cdm = request.app["sessions"][session_id]
 
     # set service certificate
     service_certificate = body.get("service_certificate")
@@ -137,6 +143,8 @@ async def challenge(request: web.Request) -> web.Response:
 
 @routes.post("/keys/{key_type}")
 async def keys(request: web.Request) -> web.Response:
+    secret_key = request.headers["X-Secret-Key"]
+
     body = await request.json()
     for required_field in ("session_id", "license_message"):
         if not body.get(required_field):
@@ -165,14 +173,17 @@ async def keys(request: web.Request) -> web.Response:
             }, status=400)
 
     # get cdm
-    if session_id not in request.app["sessions"]:
-        # e.g., app["sessions"] being cleared on server crash, reboot, and such
-        # or, the license message was from a challenge that was not made by our Cdm
+    cdm = request.app["cdms"].get(secret_key)
+    if not cdm or session_id not in cdm._sessions:
+        # This can happen if:
+        # - API server gets shutdown/restarted,
+        # - The user calls /challenge before /open,
+        # - The user called /open on a different IP Address
+        # - The user closed the session
         return web.json_response({
             "status": 400,
             "message": "Invalid Session ID. Session ID may have Expired."
         }, status=400)
-    cdm = request.app["sessions"][session_id]
 
     # parse the license message
     cdm.parse_license(session_id, body["license_message"])