bpo-27931: Fix email address header parsing error (#5329)

Correctly handle addresses whose username is an empty quoted string.

Author: jayyyin

Lib/email/_header_value_parser.py

@@ -430,7 +430,10 @@ def route(self):
     def addr_spec(self):
         for x in self:
             if x.token_type == 'addr-spec':
-                return x.addr_spec
+                if x.local_part:
+                    return x.addr_spec
+                else:
+                    return quote_string(x.local_part) + x.addr_spec
         else:
             return '<>'
 
@@ -1164,6 +1167,9 @@ def get_bare_quoted_string(value):
             "expected '\"' but found '{}'".format(value))
     bare_quoted_string = BareQuotedString()
     value = value[1:]
+    if value[0] == '"':
+        token, value = get_qcontent(value)
+        bare_quoted_string.append(token)
     while value and value[0] != '"':
         if value[0] in WSP:
             token, value = get_fws(value)

Lib/test/test_email/test__header_value_parser.py

@@ -490,6 +490,10 @@ def test_get_bare_quoted_string_must_start_with_dquote(self):
         with self.assertRaises(errors.HeaderParseError):
             parser.get_bare_quoted_string('  "foo"')
 
+    def test_get_bare_quoted_string_only_quotes(self):
+        self._test_get_x(parser.get_bare_quoted_string,
+                         '""', '""', '', [], '')
+
     def test_get_bare_quoted_string_following_wsp_preserved(self):
         self._test_get_x(parser.get_bare_quoted_string,
              '"foo"\t bar', '"foo"', 'foo', [], '\t bar')
@@ -1467,6 +1471,19 @@ def test_get_angle_addr_empty(self):
         self.assertIsNone(angle_addr.route)
         self.assertEqual(angle_addr.addr_spec, '<>')
 
+    def test_get_angle_addr_qs_only_quotes(self):
+        angle_addr = self._test_get_x(parser.get_angle_addr,
+            '<""@example.com>',
+            '<""@example.com>',
+            '<""@example.com>',
+            [],
+            '')
+        self.assertEqual(angle_addr.token_type, 'angle-addr')
+        self.assertEqual(angle_addr.local_part, '')
+        self.assertEqual(angle_addr.domain, 'example.com')
+        self.assertIsNone(angle_addr.route)
+        self.assertEqual(angle_addr.addr_spec, '""@example.com')
+
     def test_get_angle_addr_with_cfws(self):
         angle_addr = self._test_get_x(parser.get_angle_addr,
             ' (foo) <dinsdale@example.com>(bar)',

Misc/NEWS.d/next/Library/2018-01-25-21-04-11.bpo-27931.e4r52t.rst

@@ -0,0 +1 @@
+Fix email address header parsing error when the username is an empty quoted string. Patch by Xiang Zhang.