NUL terminates Ascii value

see. hMatoba#127

piexif/_load.py

@@ -118,11 +118,11 @@ def _read_tag(self, pointer):
         format = TYPE_FORMAT.get(value_type, None)
 
         if format is None:
+            raw_value = self.tiftag[data_pointer:data_pointer+value_length]
             # Ascii, Undefined and unknown types
             if value_type == TYPES.Ascii:
                 # Crop ending zero
-                value_length = max(0, value_length - 1)
-            raw_value = self.tiftag[data_pointer:data_pointer+value_length]
+                raw_value = raw_value.split(b'\0')[0]
             values = (raw_value, )
         else:
             # Unpacked types

tests/s_test.py

@@ -665,6 +665,14 @@ def test_truncated_ifd(self):
         ifd = er.get_ifd_dict(8, "0th", True)
         self.assertEqual(ifd[ImageIFD.ProcessingSoftware], b"FOO")
 
+    def test_ascii_zero(self):
+        b1 = b"MM\x00\x2a\x00\x00\x00\x08"
+        b2 = b"\x00\x01" + b"\x00\x0b\x00\x02\x00\x00\x00\x04" + b"F\x00OO"
+        er = piexif._load._ExifReader(b1 + b2)
+        er.endian_mark = ">"
+        ifd = er.get_ifd_dict(8, "0th", True)
+        self.assertEqual(ifd[ImageIFD.ProcessingSoftware], b"F")
+
     def test_split_into_segments_fail1(self):
         with self.assertRaises(InvalidImageDataError):
             _common.split_into_segments(b"I'm not JPEG")