fix: Also preserve trailing nulls in strings, not just bytes

Extended the fix to remove rstrip from strings as well and store actual
byte lengths for both strings and bytes in format metadata.

Author: stefanzetzsche

Lib/multiprocessing/shared_memory.py

@@ -286,7 +286,7 @@ class ShareableList:
     _alignment = 8
     _back_transforms_mapping = {
         0: lambda value: value,                   # int, float, bool
-        1: lambda value: value.rstrip(b'\x00').decode(_encoding),  # str
+        1: lambda value: value.decode(_encoding),  # str
         2: lambda value: value,                   # bytes
         3: lambda _value: None,                   # None
     }
@@ -355,9 +355,11 @@ def __init__(self, sequence=None, *, name=None):
                 self._offset_data_start,
                 *(v.encode(_enc) if isinstance(v, str) else v for v in sequence)
             )
-            # For bytes, store actual length so retrieval is exact
+            # For bytes and str, store actual byte length so retrieval is exact
             _stored_formats = [
-                self._types_mapping[bytes] % (len(v),) if isinstance(v, bytes) else f
+                (self._types_mapping[str] % (len(v.encode(_enc)),) if isinstance(v, str)
+                 else self._types_mapping[bytes] % (len(v),) if isinstance(v, bytes)
+                 else f)
                 for v, f in zip(sequence, _formats)
             ]
             struct.pack_into(
@@ -481,8 +483,9 @@ def __setitem__(self, position, value):
 
         self._set_packing_format_and_transform(
             position,
-            self._types_mapping[bytes] % (len(encoded_value),)
-                if isinstance(value, bytes) else new_format,
+            (self._types_mapping[bytes] % (len(encoded_value),) if isinstance(value, bytes)
+             else self._types_mapping[str] % (len(encoded_value),) if isinstance(value, str)
+             else new_format),
             value
         )
         struct.pack_into(new_format, self.shm.buf, offset, encoded_value)