Unpacking search (SearchIter) fails with PK data from Nexus Personal

[msetina]

Using this code on version 0.7.0:

pk_query_params = {
            pkcs11.Attribute.CLASS: pkcs11.ObjectClass.PRIVATE_KEY
        }
        q = session.get_objects(pk_query_params)        
        results = list(q)
on Nexus Personal PKCS11 driver fails with:
    results = list(q)
  File "pkcs11/_pkcs11.pyx", line 322, in pkcs11._pkcs11.SearchIter.__next__
  File "pkcs11/_pkcs11.pyx", line 692, in pkcs11._pkcs11.Object._make
  File "pkcs11/_pkcs11.pyx", line 723, in pkcs11._pkcs11.Object.__getitem__
  File "pkcs11/_utils.pyx", line 35, in pkcs11._pkcs11._unpack_attributes
  File "/home/miha/.local/lib/python3.10/site-packages/pkcs11/defaults.py", line 116, in <lambda>
    _bool = (Struct('?').pack, lambda v: Struct('?').unpack(v)[0])
struct.error: unpack requires a buffer of 1 bytes
Exception ignored in: <cyfunction SearchIter.__del__ at 0x7f58cf9cea80>
Traceback (most recent call last):
  File "pkcs11/_pkcs11.pyx", line 326, in pkcs11._pkcs11.SearchIter.__del__
  File "pkcs11/_pkcs11.pyx", line 336, in pkcs11._pkcs11.SearchIter._finalize
  File "pkcs11/_errors.pyx", line 88, in pkcs11._pkcs11.assertRV
pkcs11.exceptions.SessionHandleInvalid: 

[msetina]

The driver in this case implements a nonstadard attribute (nonrepudiation, which is not PKCS11 property). Maybe it would be good to ignore nonstadard properties, than to break.

[MatthiasValvekens]

As of #209 you can supply your own attribute handler implementation.

Having said that, the _make(...) function in that stack trace only attempts to read standard attributes, so the presence of nonstandard attributes shouldn't be a factor. I think the issue is rather that your token returns CKR_SESSION_HANDLE_INVALID on a call to C_GetAttributeValue, which suggests to me that there's something else going on... Perhaps a previous error invalidating the session?