3 files changed, 55 insertions, 2 deletions
diff --git a/Lib/email/message.py b/Lib/email/message.py
index a58afc5..87fcab6 100644
--- a/Lib/email/message.py
+++ b/Lib/email/message.py
@@ -286,8 +286,12 @@ class Message:
         if i is not None and not isinstance(self._payload, list):
             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()
+        cte = self.get('content-transfer-encoding', '')
+        if hasattr(cte, 'cte'):
+            cte = cte.cte
+        else:
+            # cte might be a Header, so for now stringify it.
+            cte = str(cte).strip().lower()
         # payload may be bytes here.
         if not decode:
             if isinstance(payload, str) and utils._has_surrogates(payload):
diff --git a/Lib/test/test_email/test_email.py b/Lib/test/test_email/test_email.py
index abe9ef2..2deb357 100644
--- a/Lib/test/test_email/test_email.py
+++ b/Lib/test/test_email/test_email.py
@@ -810,6 +810,16 @@ class TestMessageAPI(TestEmailBase):
             w4kgdGVzdGFiYwo=
             """))
 
+    def test_string_payload_with_base64_cte(self):
+        msg = email.message_from_string(textwrap.dedent("""\
+        Content-Transfer-Encoding: base64
+
+        SGVsbG8uIFRlc3Rpbmc=
+        """), policy=email.policy.default)
+        self.assertEqual(msg.get_payload(decode=True), b"Hello. Testing")
+        self.assertDefectsEqual(msg['content-transfer-encoding'].defects, [])
+
+
 
 # Test the email.encoders module
 class TestEncoders(unittest.TestCase):
@@ -2352,6 +2362,40 @@ counter to RFC 2822, there's no separating newline here
         self.assertDefectsEqual(msg.defects,
                                 [errors.MissingHeaderBodySeparatorDefect])
 
+    def test_string_payload_with_extra_space_after_cte(self):
+        # https://github.com/python/cpython/issues/98188
+        cte = "base64 "
+        msg = email.message_from_string(textwrap.dedent(f"""\
+        Content-Transfer-Encoding: {cte}
+
+        SGVsbG8uIFRlc3Rpbmc=
+        """), policy=email.policy.default)
+        self.assertEqual(msg.get_payload(decode=True), b"Hello. Testing")
+        self.assertDefectsEqual(msg['content-transfer-encoding'].defects, [])
+
+    def test_string_payload_with_extra_text_after_cte(self):
+        msg = email.message_from_string(textwrap.dedent("""\
+        Content-Transfer-Encoding: base64 some text
+
+        SGVsbG8uIFRlc3Rpbmc=
+        """), policy=email.policy.default)
+        self.assertEqual(msg.get_payload(decode=True), b"Hello. Testing")
+        cte = msg['content-transfer-encoding']
+        self.assertDefectsEqual(cte.defects, [email.errors.InvalidHeaderDefect])
+
+    def test_string_payload_with_extra_space_after_cte_compat32(self):
+        cte = "base64 "
+        msg = email.message_from_string(textwrap.dedent(f"""\
+        Content-Transfer-Encoding: {cte}
+
+        SGVsbG8uIFRlc3Rpbmc=
+        """), policy=email.policy.compat32)
+        pasted_cte = msg['content-transfer-encoding']
+        self.assertEqual(pasted_cte, cte)
+        self.assertEqual(msg.get_payload(decode=True), b"Hello. Testing")
+        self.assertDefectsEqual(msg.defects, [])
+
+
 
 # Test RFC 2047 header encoding and decoding
 class TestRFC2047(TestEmailBase):
diff --git a/Lib/test/test_email/test_headerregistry.py b/Lib/test/test_email/test_headerregistry.py
index 4c0523f..ff7a6da 100644
--- a/Lib/test/test_email/test_headerregistry.py
+++ b/Lib/test/test_email/test_headerregistry.py
@@ -837,6 +837,11 @@ class TestContentTransferEncoding(TestHeaderBase):
             '7bit',
             [errors.InvalidHeaderDefect]),
 
+        'extra_space_after_cte': (
+            'base64 ',
+            'base64',
+            []),
+
     }