gh-123742: Fixed get_payload not being able to parse headers with spaces

Lib/email/message.py

@@ -287,7 +287,7 @@ def get_payload(self, i=None, decode=False):
             raise TypeError('Expected list, got %s' % type(self._payload))
         payload = self._payload
         # cte might be a Header, so for now stringify it.
-        cte = str(self.get('content-transfer-encoding', '')).lower().strip(' ')
+        cte = str(self.get('content-transfer-encoding', '')).lower().strip()
         # payload may be bytes here.
         if not decode:
             if isinstance(payload, str) and utils._has_surrogates(payload):

Lib/test/test_email/test_message.py

@@ -985,6 +985,30 @@ def test_get_body_malformed(self):
         # AttributeError: 'str' object has no attribute 'is_attachment'
         m.get_body()
 
+    def test_get_payload_strip_ex_space(self):
+        """test for gh-123742"""
+        msg = textwrap.dedent("""\
+            From: [email protected]
+            To: [email protected]
+            Subject: Report
+            MIME-Version: 1.0
+            Content-Type: multipart/mixed; boundary="----=_Part3035080226180533"
+            Message-ID: <01000191b7fd06ba-d3c9ca36-5171-4a1d-ba3c-b378336cccbc-000000@email.amazonses.com>
+            Date: Tue, 3 Sep 2024 13:04:58 +0000
+
+            ------=_Part3035080226180533
+            Content-Disposition: attachment;
+            Content-Type: text/plain; charset=UTF-8
+            Content-Transfer-Encoding: base64 
+
+            aGVsbG8=
+            ------=_Part3035080226180533
+            Content-Type: text/html; charset=UTF-8
+            Content-Transfer-Encoding: 7bit
+            """)
+        m = self._str_msg(msg)
+        recv_m = m.get_payload(0).get_payload(decode=True)
+        self.assertEqual(recv_m, b"hello")
 
 class TestMIMEPart(TestEmailMessageBase, TestEmailBase):
     # Doing the full test run here may seem a bit redundant, since the two