Resolve issue 207 and issue 226

It aims to avoid the unnecessary conversion by the decode method.

The original hint was provided by Mr. Lutz K.
Thank you very much

src/harvesters/core.py

@@ -3026,8 +3026,6 @@ def _release_buffers(self) -> None:
             _ = self._queue.get_nowait()
 
 
-
-
 def _save_file(
         *,
         xml_dir_to_store: Optional[str] = None,
@@ -3057,26 +3055,20 @@ def _save_file(
     file_path = os.path.join(xml_dir_to_store, _file_name)
 
     #
-    mode_base = 'w+'
-    mode = mode_base
-    data_to_write = bytes_content = bytes_io.getvalue()
-    if pathlib.Path(file_path).suffix.lower() == '.zip':
-        mode += 'b'
-    else:
-        data_to_write = bytes_content.decode()
-        pos = data_to_write.find('\x00')
-        if pos != -1:
-            # Found a \x00:
-            data_to_write = data_to_write[:pos]
+    mode = 'w+'
+    data_to_write = bytes_io.getvalue()
+    if pathlib.Path(file_path).suffix.lower() != '.zip':
+        data_to_write = _drop_unnecessary_trailer(data_to_write)
+
     #
     try:
-        with open(file_path, mode) as f:
+        with open(file_path, mode + 'b') as f:
             f.write(data_to_write)
     except UnicodeEncodeError:
         # Probably you've caught "UnicodeEncodeError: 'charmap' codec can't
         # encode characters"; the file must be a text file:
         try:
-            with io.open(file_path, mode_base, encoding="utf-8") as f:
+            with io.open(file_path, mode, encoding="utf-8") as f:
                 f.write(data_to_write)
         except:
             e = sys.exc_info()[0]
@@ -3090,6 +3082,16 @@ def _save_file(
     return file_path
 
 
+def _drop_unnecessary_trailer(data_to_write: bytes):
+    assert data_to_write
+    pos = data_to_write.find(0x00)
+    if pos != -1:
+        # Found a \x00:
+        return data_to_write[:pos]
+    else:
+        return data_to_write
+
+
 class _CallbackDestroyImageAcquirer(Callback):
     def __init__(self, harvester):
         self._harvester = harvester

src/harvesters/test/test_harvester_core.py

@@ -40,6 +40,7 @@
 from harvesters.core import Callback
 from harvesters.core import Harvester
 from harvesters.core import ImageAcquirer
+from harvesters.core import _drop_unnecessary_trailer
 from harvesters.test.helper import get_package_dir
 from harvesters.util.pfnc import Dictionary
 from harvesters.core import Component2DImage
@@ -1011,5 +1012,21 @@ def test_issue_238(self):
                 )
 
 
+class TestUtility(unittest.TestCase):
+    def test_issue_207_and_226(self):
+        body = b'\xc2\xb0'  # °
+        padding = b'\x00\x00'
+        data = body + padding
+        data = _drop_unnecessary_trailer(data)
+        self.assertEqual(data, body)
+        self.assertEqual('°', str(data, encoding='utf-8'))
+
+    @unittest.skip  # experimental
+    def test_issue_207_and_226_in_orignal_way(self):
+        data = b'\xc2\xb0'  # °
+        decoded = data.decode()
+        self.assertEqual('°', decoded)
+
+
 if __name__ == '__main__':
     unittest.main()