fix: allow closed file handles in calc_sha256sum

Since we tend to allow filenames and file handles interchangably in this
code base, we might run into the edge case of a closed file handle being
input to calc_sha256sum. We should then open the file before getting the
hash.

pyulog/db.py

@@ -114,15 +114,16 @@ def calc_sha256sum(log_file):
         if log_file is None:
             return None
         if isinstance(log_file, str):
-            log_file = open(log_file, 'rb') # pylint: disable=consider-using-with
-            log_context = log_file
+            file_context = open(log_file, 'rb') # pylint: disable=consider-using-with
+        elif log_file.closed:
+            file_context = open(log_file.name, 'rb')
         else:
-            log_context = contextlib.nullcontext()
+            file_context = contextlib.nullcontext(log_file)
 
         file_hash = hashlib.sha256()
-        with log_context:
+        with file_context as open_file:
             while True:
-                block = log_file.read(4096)
+                block = open_file.read(4096)
                 file_hash.update(block)
                 if block == b'':
                     break

test/test_db.py

@@ -142,7 +142,8 @@ def test_unapplied_migrations(self):
     @data('sample_log_small')
     def test_sha256sum(self, test_case):
         '''
-        Verify that the sha256sum set on save can be used to find the same file again.
+        Verify that the sha256sum set on save can be used to find the same file
+        again, using any of the approved file input methods.
         '''
 
         test_file = os.path.join(TEST_PATH, f'{test_case}.ulg')
@@ -151,6 +152,14 @@ def test_sha256sum(self, test_case):
         digest = DatabaseULog.calc_sha256sum(test_file)
         self.assertEqual(digest, dbulog.sha256sum)
 
+        test_file_handle = open(test_file, 'rb') # pylint: disable=consider-using-with
+        open_digest = DatabaseULog.calc_sha256sum(test_file_handle)
+        self.assertEqual(digest, open_digest)
+
+        test_file_handle.close()
+        closed_digest = DatabaseULog.calc_sha256sum(test_file_handle)
+        self.assertEqual(digest, closed_digest)
+
         pk_from_digest = DatabaseULog.primary_key_from_sha256sum(self.db_handle, digest)
         self.assertEqual(pk_from_digest, dbulog.primary_key)