Create and use utility to strip namespaces from XML data

Namespaces cause problems with the xpath calls when dealing with PlayReadyHeader's on some versions.

pywidevine/pssh.py

@@ -9,10 +9,10 @@ from uuid import UUID
 import construct
 from construct import Container
 from google.protobuf.message import DecodeError
-from lxml import etree
 from pymp4.parser import Box
 
 from pywidevine.license_protocol_pb2 import WidevinePsshData
+from pywidevine.utils import load_xml
 
 
 class PSSH:
@@ -215,7 +215,7 @@ class PSSH:
             xml_string = self.init_data.decode("utf-16-le")
             # some of these init data has garbage(?) in front of it
             xml_string = xml_string[xml_string.index("<"):]
-            xml = etree.fromstring(xml_string)
+            xml = load_xml(xml_string)
             header_version = xml.attrib["version"]
             if header_version == "4.0.0.0":
                 key_ids = xml.xpath("DATA/KID/text()")

pywidevine/utils.py

@@ -1,6 +1,9 @@
 import shutil
 from pathlib import Path
-from typing import Optional
+from typing import Optional, Union
+
+from lxml import etree
+from lxml.etree import ElementTree
 
 
 def get_binary_path(*names: str) -> Optional[Path]:
@@ -10,3 +13,23 @@ def get_binary_path(*names: str) -> Optional[Path]:
         if path:
             return Path(path)
     return None
+
+
+def load_xml(xml: Union[str, bytes]) -> ElementTree:
+    """Parse XML data to an ElementTree, without namespaces anywhere."""
+    if not isinstance(xml, bytes):
+        xml = xml.encode("utf8")
+    root = etree.fromstring(xml)
+    for elem in root.getiterator():
+        if not hasattr(elem.tag, "find"):
+            # e.g. comment elements
+            continue
+        elem.tag = etree.QName(elem).localname
+        for name, value in elem.attrib.items():
+            local_name = etree.QName(name).localname
+            if local_name == name:
+                continue
+            del elem.attrib[name]
+            elem.attrib[local_name] = value
+    etree.cleanup_namespaces(root)
+    return root