#1050268: make parseaddr 'quote' the contents of quoted strings in addresses.

Also made the doc string for email._parseaddr's 'quote' function more
accurate; I'd love to make the function match the old docstring instead,
but other code uses it according the existing semantics.

Lib/email/_parseaddr.py

@@ -160,7 +160,12 @@ def mktime_tz(data):
 
 
 def quote(str):
-    """Add quotes around a string."""
+    """Prepare string to be used in a quoted string.
+
+    Turns backslash and double quote characters into quoted pairs.  These
+    are the only characters that need to be quoted inside a quoted string.
+    Does not add the surrounding double quotes.
+    """
     return str.replace('\\', '\\\\').replace('"', '\\"')
 
 
@@ -318,7 +323,7 @@ class AddrlistClass:
                 aslist.append('.')
                 self.pos += 1
             elif self.field[self.pos] == '"':
-                aslist.append('"%s"' % self.getquote())
+                aslist.append('"%s"' % quote(self.getquote()))
             elif self.field[self.pos] in self.atomends:
                 break
             else:

Lib/email/test/test_email.py

@@ -2287,6 +2287,24 @@ class TestMiscellaneous(TestEmailBase):
         # formataddr() quotes the name if there's a dot in it
         self.assertEqual(utils.formataddr((a, b)), y)
 
+    def test_parseaddr_preserves_quoted_pairs_in_addresses(self):
+        # issue 10005.  Note that in the third test the second pair of
+        # backslashes is not actually a quoted pair because it is not inside a
+        # comment or quoted string: the address being parsed has a quoted
+        # string containing a quoted backslash, followed by 'example' and two
+        # backslashes, followed by another quoted string containing a space and
+        # the word 'example'.  parseaddr copies those two backslashes
+        # literally.  Per rfc5322 this is not technically correct since a \ may
+        # not appear in an address outside of a quoted string.  It is probably
+        # a sensible Postel interpretation, though.
+        eq = self.assertEqual
+        eq(utils.parseaddr('""example" example"@example.com'),
+          ('', '""example" example"@example.com'))
+        eq(utils.parseaddr('"\\"example\\" example"@example.com'),
+          ('', '"\\"example\\" example"@example.com'))
+        eq(utils.parseaddr('"\\\\"example\\\\" example"@example.com'),
+          ('', '"\\\\"example\\\\" example"@example.com'))
+
     def test_multiline_from_comment(self):
         x = """\
 Foo

Misc/NEWS

@@ -87,6 +87,9 @@ Core and Builtins
 Library
 -------
 
+- Issue #1050268: parseaddr now correctly quotes double quote and backslash
+  characters that appear inside quoted strings in email addresses.
+
 - Issue #10004: quoprimime no longer generates a traceback when confronted
   with invalid characters after '=' in a Q-encoded word.