Fix composite key computation for BytesIO (#388)

In case a keyfile as BytesIO has been read before, the
next read will be empty. We need to ensure that we
are reading the data from the beginning.

Add seek to start to fix it.

Co-authored-by: Jan-Michael Brummer <jan-michael.brummer1@volkswagen.de>

pykeepass/kdbx_parsing/common.py

@@ -1,13 +1,13 @@
 import base64
 import codecs
 import hashlib
+import io
 import logging
 import re
 import zlib
 from binascii import Error as BinasciiError
 from collections import OrderedDict
 from copy import deepcopy
-from io import BytesIO
 
 from construct import (
     Adapter,
@@ -128,6 +128,8 @@ def compute_key_composite(password=None, keyfile=None):
     # hash the keyfile
     if keyfile:
         if hasattr(keyfile, "read"):
+            if hasattr(keyfile, "seekable") and keyfile.seekable():
+                keyfile.seek(0)
             keyfile_bytes = keyfile.read()
         else:
             with open(keyfile, 'rb') as f:
@@ -194,7 +196,7 @@ class XML(Adapter):
 
     def _decode(self, data, con, path):
         parser = etree.XMLParser(remove_blank_text=True)
-        return etree.parse(BytesIO(data), parser)
+        return etree.parse(io.BytesIO(data), parser)
 
     def _encode(self, tree, con, path):
         return etree.tostring(tree)

tests/tests.py

@@ -875,6 +875,20 @@ def test_fields(self):
 
 
 class PyKeePassTests3(KDBX3Tests):
+    def test_consecutives_saves_with_stream(self):
+        # https://github.com/libkeepass/pykeepass/pull/388
+        self.setUp()
+
+        with open(base_dir / self.keyfile_tmp, 'rb') as f:
+            keyfile = BytesIO(f.read())
+
+        for _i in range(5):
+            with PyKeePass(
+                base_dir / self.database_tmp,
+                password=self.password,
+                keyfile=keyfile,
+            ) as kp:
+                kp.save()
 
     def test_set_credentials(self):
         self.kp_tmp.password = 'f00bar'