diff --git a/dev/pykeepass_issue219.py b/dev/pykeepass_issue219.py
index ae44674..4ffaf14 100644
--- a/dev/pykeepass_issue219.py
+++ b/dev/pykeepass_issue219.py
@@ -4,66 +4,62 @@
     stream_tell, stream_seek, stream_read, stream_write,
 )
 from Cryptodome.Random import get_random_bytes
+from types import SimpleNamespace as sn
 
 # simple placeholder checksum function
-def check_func(header_data, master_seed):
-    return header_data + master_seed
-
 def compute_header_hmac_hash(context):
     """Compute HMAC-SHA256 hash of header.
     Used to prevent header tampering."""
     print('----------------------')
-    print('master_seed:', sum(context.header.master_seed))
-    print("header_sha:", sum(context.header._data))
+    print('master_seed:', sum(context.header.value.master_seed))
+    print("header_sha:", sum(context.header.data))
     print('----------------------')
 
-    return context.header._data + context.header.master_seed
+    return context.header.data + context.header.value.master_seed
 
 
-class RandomGreedyBytes(type(GreedyBytes)):
-    """Same as GreedyBytes, but generate random bytes when building"""
+class RandomBytes(Bytes):
+    """Same as Bytes, but generate random bytes when building"""
 
     def _build(self, obj, stream, context, path):
-        data = bytes(obj) if type(obj) is bytearray else obj
-        data = get_random_bytes(len(data))
-        stream_write(stream, data, len(data), path)
+        print('generating random bytes...')
+        length = self.length(context) if callable(self.length) else self.length
+        data = get_random_bytes(length)
+        print('old:', sum(context.master_seed))
+        print('new:', sum(data))
+        stream_write(stream, data, length, path)
         return data
 
-class Copy(Subconstruct):
-    """Same as RawCopy, but don't create parent container when parsing.
-    Instead store data in ._data attribute of subconstruct, and never rebuild from data
-    """
+# class Copy(Subconstruct):
+#     """Same as RawCopy, but don't create parent container when parsing.
+#     Instead store data in ._data attribute of subconstruct, and never rebuild from data
+#     """
 
-    def _parse(self, stream, context, path):
-        offset1 = stream_tell(stream, path)
-        obj = self.subcon._parsereport(stream, context, path)
-        offset2 = stream_tell(stream, path)
-        stream_seek(stream, offset1, 0, path)
-        obj._data = stream_read(stream, offset2-offset1, path)
-        return obj
+#     def _parse(self, stream, context, path):
+#         offset1 = stream_tell(stream, path)
+#         obj = self.subcon._parsereport(stream, context, path)
+#         offset2 = stream_tell(stream, path)
+#         stream_seek(stream, offset1, 0, path)
+#         obj._data = stream_read(stream, offset2-offset1, path)
+#         return obj
 
-    def _build(self, obj, stream, context, path):
-        offset1 = stream_tell(stream, path)
-        obj = self.subcon._build(obj, stream, context, path)
-        offset2 = stream_tell(stream, path)
-        stream_seek(stream, offset1, 0, path)
-        obj._data = stream_read(stream, offset2-offset1, path)
-        return obj
+#     def _build(self, obj, stream, context, path):
+#         offset1 = stream_tell(stream, path)
+#         obj = self.subcon._build(obj, stream, context, path)
+#         offset2 = stream_tell(stream, path)
+#         stream_seek(stream, offset1, 0, path)
+#         obj._data = stream_read(stream, offset2-offset1, path)
+#         return obj
 
 # simple database format with header and checksum
 s = Struct(
-    "header" / Copy(Struct(
+    "header" / RawCopy(Struct(
         "master_seed" / Prefixed(
             Int8ul,
-            RandomGreedyBytes(),
+            RandomBytes(8),
         ),
         "more_data" / Bytes(8)
     )),
-    # "hash" / Checksum(
-    #     Bytes(25),
-    #     lambda ctx: check_func(ctx.header._data, ctx.header.master_seed),
-    #     this
-    # )
     "hash" / Checksum(
         Bytes(25),
         compute_header_hmac_hash,
@@ -77,7 +73,7 @@ def _build(self, obj, stream, context, path):
 length = int.to_bytes(len(master_seed), length=1, byteorder='big')
 more_data = b'12345678'
 header = length + master_seed + more_data
-data1 = header + check_func(header, master_seed)
+data1 = header + compute_header_hmac_hash(sn(header=sn(data=header, value=sn(master_seed=master_seed))))
 
 # parse the database
 print('PARSING')
@@ -85,7 +81,8 @@ def _build(self, obj, stream, context, path):
 
 # rebuild and try to reparse final result
 print('SAVING')
+del parsed1.header.data
 data2 = s.build(parsed1)
 parsed2 = s.parse(data2)
-if parsed1.header.master_seed == parsed2.header.master_seed:
+if parsed1.header.value.master_seed == parsed2.header.value.master_seed:
     Exception("Database unchanged")