From 45b2f8893c1b7ab3b3981a966f82e42beea82106 Mon Sep 17 00:00:00 2001
From: Jens Troeger <jenstroeger@users.noreply.github.com>
Date: Tue, 14 May 2019 11:07:39 +1000
Subject: [PATCH] bpo-34424: Handle different policy.linesep lengths correctly.
 (#8803)

---
 Lib/email/_header_value_parser.py             |  2 +-
 Lib/test/test_email/test_generator.py         | 22 +++++++++++++++++++
 .../2018-08-18-14-47-00.bpo-34424.wAlRuS.rst  |  2 ++
 3 files changed, 25 insertions(+), 1 deletion(-)
 create mode 100644 Misc/NEWS.d/next/Library/2018-08-18-14-47-00.bpo-34424.wAlRuS.rst

diff --git a/Lib/email/_header_value_parser.py b/Lib/email/_header_value_parser.py
index 922daa2560f..bb26d5a556d 100644
--- a/Lib/email/_header_value_parser.py
+++ b/Lib/email/_header_value_parser.py
@@ -2625,7 +2625,7 @@ def _refold_parse_tree(parse_tree, *, policy):
                 want_encoding = False
                 last_ew = None
                 if part.syntactic_break:
-                    encoded_part = part.fold(policy=policy)[:-1] # strip nl
+                    encoded_part = part.fold(policy=policy)[:-len(policy.linesep)]
                     if policy.linesep not in encoded_part:
                         # It fits on a single line
                         if len(encoded_part) > maxlen - len(lines[-1]):
diff --git a/Lib/test/test_email/test_generator.py b/Lib/test/test_email/test_generator.py
index c1aeaefab77..89e7edeb63a 100644
--- a/Lib/test/test_email/test_generator.py
+++ b/Lib/test/test_email/test_generator.py
@@ -4,6 +4,7 @@ import unittest
 from email import message_from_string, message_from_bytes
 from email.message import EmailMessage
 from email.generator import Generator, BytesGenerator
+from email.headerregistry import Address
 from email import policy
 from test.test_email import TestEmailBase, parameterize
 
@@ -291,6 +292,27 @@ class TestBytesGenerator(TestGeneratorBase, TestEmailBase):
         g.flatten(msg)
         self.assertEqual(s.getvalue(), expected)
 
+    def test_smtp_policy(self):
+        msg = EmailMessage()
+        msg["From"] = Address(addr_spec="foo@bar.com", display_name="Páolo")
+        msg["To"] = Address(addr_spec="bar@foo.com", display_name="Dinsdale")
+        msg["Subject"] = "Nudge nudge, wink, wink"
+        msg.set_content("oh boy, know what I mean, know what I mean?")
+        expected = textwrap.dedent("""\
+            From: =?utf-8?q?P=C3=A1olo?= <foo@bar.com>
+            To: Dinsdale <bar@foo.com>
+            Subject: Nudge nudge, wink, wink
+            Content-Type: text/plain; charset="utf-8"
+            Content-Transfer-Encoding: 7bit
+            MIME-Version: 1.0
+
+            oh boy, know what I mean, know what I mean?
+            """).encode().replace(b"\n", b"\r\n")
+        s = io.BytesIO()
+        g = BytesGenerator(s, policy=policy.SMTP)
+        g.flatten(msg)
+        self.assertEqual(s.getvalue(), expected)
+
 
 if __name__ == '__main__':
     unittest.main()
diff --git a/Misc/NEWS.d/next/Library/2018-08-18-14-47-00.bpo-34424.wAlRuS.rst b/Misc/NEWS.d/next/Library/2018-08-18-14-47-00.bpo-34424.wAlRuS.rst
new file mode 100644
index 00000000000..2b384cd5513
--- /dev/null
+++ b/Misc/NEWS.d/next/Library/2018-08-18-14-47-00.bpo-34424.wAlRuS.rst
@@ -0,0 +1,2 @@
+Fix serialization of messages containing encoded strings when the
+policy.linesep is set to a multi-character string. Patch by Jens Troeger.