bpo-32178: Fix IndexError trying to parse 'To' header starting with ':'. (GH-15044)

maxking · miss-islington · commit 09a1872a8007 · 2019-08-11T13:45:09.000-07:00
This should fix the IndexError trying to retrieve `DisplayName.display_name` and `DisplayName.value` when the `value` is basically an empty string. https://bugs.python.org/issue32178
diff --git a/Lib/email/_header_value_parser.py b/Lib/email/_header_value_parser.py
@@ -561,6 +561,8 @@ class DisplayName(Phrase):
     @property
     def display_name(self):
         res = TokenList(self)
+        if len(res) == 0:
+            return res.value
         if res[0].token_type == 'cfws':
             res.pop(0)
         else:
@@ -582,7 +584,7 @@ def value(self):
             for x in self:
                 if x.token_type == 'quoted-string':
                     quote = True
-        if quote:
+        if len(self) != 0 and quote:
             pre = post = ''
             if self[0].token_type=='cfws' or self[0][0].token_type=='cfws':
                 pre = ' '
diff --git a/Lib/test/test_email/test__header_value_parser.py b/Lib/test/test_email/test__header_value_parser.py
@@ -1700,6 +1700,14 @@ def test_get_display_name_ending_with_obsolete(self):
         self.assertEqual(display_name[3].comments, ['with trailing comment'])
         self.assertEqual(display_name.display_name, 'simple phrase.')
 
+    def test_get_display_name_for_invalid_address_field(self):
+        # bpo-32178: Test that address fields starting with `:` don't cause
+        # IndexError when parsing the display name.
+        display_name = self._test_get_x(
+            parser.get_display_name,
+            ':Foo ', '', '', [errors.InvalidHeaderDefect], ':Foo ')
+        self.assertEqual(display_name.value, '')
+
     # get_name_addr
 
     def test_get_name_addr_angle_addr_only(self):
diff --git a/Misc/NEWS.d/next/Library/2019-07-30-22-41-05.bpo-32178.X-IFLe.rst b/Misc/NEWS.d/next/Library/2019-07-30-22-41-05.bpo-32178.X-IFLe.rst
@@ -0,0 +1 @@
+Fix IndexError in :mod:`email` package when trying to parse invalid address fields starting with ``:``.

Original file line number	Diff line number	Diff line change
`@@ -0,0 +1 @@`
	`1`	+Fix IndexError in :mod:`email` package when trying to parse invalid address fields starting with ``:``.