#22233: Only split headers on \r and/or \n, per email RFCs.

Original patch by Martin Panter, new policy fixes by me.

Lib/test/test_email/test_parser.py

@@ -2,6 +2,7 @@ import io
 import email
 import unittest
 from email.message import Message
+from email.policy import default
 from test.test_email import TestEmailBase
 
 
@@ -32,5 +33,45 @@ class TestCustomMessage(TestEmailBase):
     # XXX add tests for other functions that take Message arg.
 
 
+class TestParserBase:
+
+    def test_only_split_on_cr_lf(self):
+        # The unicode line splitter splits on unicode linebreaks, which are
+        # more numerous than allowed by the email RFCs; make sure we are only
+        # splitting on those two.
+        msg = self.parser(
+            "Next-Line: not\x85broken\r\n"
+            "Null: not\x00broken\r\n"
+            "Vertical-Tab: not\vbroken\r\n"
+            "Form-Feed: not\fbroken\r\n"
+            "File-Separator: not\x1Cbroken\r\n"
+            "Group-Separator: not\x1Dbroken\r\n"
+            "Record-Separator: not\x1Ebroken\r\n"
+            "Line-Separator: not\u2028broken\r\n"
+            "Paragraph-Separator: not\u2029broken\r\n"
+            "\r\n",
+            policy=default,
+        )
+        self.assertEqual(msg.items(), [
+            ("Next-Line", "not\x85broken"),
+            ("Null", "not\x00broken"),
+            ("Vertical-Tab", "not\vbroken"),
+            ("Form-Feed", "not\fbroken"),
+            ("File-Separator", "not\x1Cbroken"),
+            ("Group-Separator", "not\x1Dbroken"),
+            ("Record-Separator", "not\x1Ebroken"),
+            ("Line-Separator", "not\u2028broken"),
+            ("Paragraph-Separator", "not\u2029broken"),
+        ])
+        self.assertEqual(msg.get_payload(), "")
+
+class TestParser(TestParserBase, TestEmailBase):
+    parser = staticmethod(email.message_from_string)
+
+class TestBytesParser(TestParserBase, TestEmailBase):
+    def parser(self, s, *args, **kw):
+        return email.message_from_bytes(s.encode(), *args, **kw)
+
+
 if __name__ == '__main__':
     unittest.main()