Properly handle the CK_UNAVAILABLE_INFORMATION return value when trying to read an attribute

Author: Micah N Gorrell

pkcs11/_pkcs11.pxd

@@ -151,6 +151,10 @@ cdef extern from '../extern/cryptoki.h':
         CK_TRUE,
         CK_FALSE,
 
+    cdef enum:
+        CK_UNAVAILABLE_INFORMATION,
+        CK_EFFECTIVELY_INFINITE,
+
     cdef enum:  # CK_FLAGS
         CKF_DONT_BLOCK,
         CKF_RW_SESSION,

pkcs11/_pkcs11.pyx

@@ -915,6 +915,8 @@ class Object(types.Object):
         # Find out the attribute size
         with nogil:
             retval = _funclist.C_GetAttributeValue(handle, obj, &template, 1)
+        if retval == CK_UNAVAILABLE_INFORMATION:
+            return None
         assertRV(retval)
 
         if template.ulValueLen == 0:
@@ -927,6 +929,8 @@ class Object(types.Object):
         # Request the value
         with nogil:
             retval = _funclist.C_GetAttributeValue(handle, obj, &template, 1)
+        if retval == CK_UNAVAILABLE_INFORMATION:
+            return None
         assertRV(retval)
 
         return _unpack_attributes(key, value)