#19772: Do not mutate message when downcoding to 7bit.

This is a bit of an ugly hack because of the way generator pieces together the
output message.  The deepcopys aren't too expensive, though, because we know it
is only called on messages that are not multiparts, and the payload (the thing
that could be large) is an immutable object.

Test and preliminary work on patch by Vajrasky Kok.

diff --git a/Lib/email/generator.py b/Lib/email/generator.py
index 4ea0b559b9971cc5b0e1dd442628cba55814b887..07a97c7e27bbfc700f41846acbdd7fa7d5783190 100644 (file)
--- a/Lib/email/generator.py
+++ b/Lib/email/generator.py
@@ -12,6 +12,7 @@ import time
 import random
 import warnings
 
+from copy import deepcopy
 from io import StringIO, BytesIO
 from email._policybase import compat32
 from email.header import Header
@@ -173,10 +174,18 @@ class Generator:
         # necessary.
         oldfp = self._fp
         try:
+            self._munge_cte = None
             self._fp = sfp = self._new_buffer()
             self._dispatch(msg)
         finally:
             self._fp = oldfp
+            munge_cte = self._munge_cte
+            del self._munge_cte
+        # If we munged the cte, copy the message again and re-fix the CTE.
+        if munge_cte:
+            msg = deepcopy(msg)
+            msg.replace_header('content-transfer-encoding', munge_cte[0])
+            msg.replace_header('content-type', munge_cte[1])
         # Write the headers.  First we see if the message object wants to
         # handle that itself.  If not, we'll do it generically.
         meth = getattr(msg, '_write_headers', None)
@@ -225,9 +234,14 @@ class Generator:
         if _has_surrogates(msg._payload):
             charset = msg.get_param('charset')
             if charset is not None:
+                # XXX: This copy stuff is an ugly hack to avoid modifying the
+                # existing message.
+                msg = deepcopy(msg)
                 del msg['content-transfer-encoding']
                 msg.set_payload(payload, charset)
                 payload = msg.get_payload()
+                self._munge_cte = (msg['content-transfer-encoding'],
+                                   msg['content-type'])
         if self._mangle_from_:
             payload = fcre.sub('>From ', payload)
         self._write_lines(payload)

diff --git a/Lib/test/test_email/test_email.py b/Lib/test/test_email/test_email.py
index 4157a067a2a6e0f8b33c2855a8225e6f6769547e..73ec2a6d0bc932faaeed8b022e7fce2dece5a026 100644 (file)
--- a/Lib/test/test_email/test_email.py
+++ b/Lib/test/test_email/test_email.py
@@ -3495,7 +3495,7 @@ Here's the message body
         self.assertTrue(msg.get_payload(0).get_payload().endswith('\r\n'))
 
 
-class Test8BitBytesHandling(unittest.TestCase):
+class Test8BitBytesHandling(TestEmailBase):
     # In Python3 all input is string, but that doesn't work if the actual input
     # uses an 8bit transfer encoding.  To hack around that, in email 5.1 we
     # decode byte streams using the surrogateescape error handler, and
@@ -3748,6 +3748,16 @@ class Test8BitBytesHandling(unittest.TestCase):
         email.generator.Generator(out).flatten(msg)
         self.assertEqual(out.getvalue(), self.non_latin_bin_msg_as7bit_wrapped)
 
+    def test_str_generator_should_not_mutate_msg_when_handling_8bit(self):
+        msg = email.message_from_bytes(self.non_latin_bin_msg)
+        out = BytesIO()
+        BytesGenerator(out).flatten(msg)
+        orig_value = out.getvalue()
+        Generator(StringIO()).flatten(msg) # Should not mutate msg!
+        out = BytesIO()
+        BytesGenerator(out).flatten(msg)
+        self.assertEqual(out.getvalue(), orig_value)
+
     def test_bytes_generator_with_unix_from(self):
         # The unixfrom contains a current date, so we can't check it
         # literally.  Just make sure the first word is 'From' and the

diff --git a/Misc/NEWS b/Misc/NEWS
index ae5f83a153765a48b8103fd9d4acda7afbe29ff6..cedd4e52ac574644b058ffbf2d18f7337ac71c5c 100644 (file)
--- a/Misc/NEWS
+++ b/Misc/NEWS
@@ -48,6 +48,9 @@ Core and Builtins
 Library
 -------
 
+- Issue #19772: email.generator no longer mutates the message object when
+  doing a down-transform from 8bit to 7bit CTEs.
+
 - Issue #18805: the netmask/hostmask parsing in ipaddress now more reliably
   filters out illegal values and correctly allows any valid prefix length.