Issue #28321: Fixed writing non-BMP characters with binary format in plistlib.

Lib/plistlib.py

@@ -918,7 +918,7 @@ class _BinaryPlistWriter (object):
                 self._write_size(0x50, len(value))
             except UnicodeEncodeError:
                 t = value.encode('utf-16be')
-                self._write_size(0x60, len(value))
+                self._write_size(0x60, len(t) // 2)
 
             self._fp.write(t)
 

Lib/test/test_plistlib.py

@@ -360,6 +360,13 @@ class TestPlistlib(unittest.TestCase):
                                   plistlib.dumps,
                                   testString)
 
+    def test_non_bmp_characters(self):
+        pl = {'python': '\U0001f40d'}
+        for fmt in ALL_FORMATS:
+            with self.subTest(fmt=fmt):
+                data = plistlib.dumps(pl, fmt=fmt)
+                self.assertEqual(plistlib.loads(data), pl)
+
     def test_nondictroot(self):
         for fmt in ALL_FORMATS:
             with self.subTest(fmt=fmt):

Misc/NEWS

@@ -50,6 +50,8 @@ Core and Builtins
 Library
 -------
 
+- Issue #28321: Fixed writing non-BMP characters with binary format in plistlib.
+
 - Issue #28225: bz2 module now supports pathlib.  Initial patch by Ethan Furman.
 
 - Issue #28227: gzip now supports pathlib.  Patch by Ethan Furman.