#18044: Fix parsing of encoded words of the form =?utf8?q?=XX...?=

The problem was I was only checking for decimal digits after the third '?',
not for *hex* digits :(.

This changeset also fixes a couple of comment typos, deletes an unused
function relating to encoded word parsing, and removed an invalid
'if' test from the folding function that was revealed by the tests
written to validate this issue.

4 files changed, 58 insertions, 40 deletions

diff --git a/Lib/email/_header_value_parser.py b/Lib/email/_header_value_parser.py
index 26cfa52..a01d845 100644
--- a/Lib/email/_header_value_parser.py
+++ b/Lib/email/_header_value_parser.py
@@ -69,6 +69,7 @@ XXX: provide complete list of token types.
 
 import re
 import urllib   # For urllib.parse.unquote
+from string import hexdigits
 from collections import namedtuple, OrderedDict
 from email import _encoded_words as _ew
 from email import errors
@@ -392,10 +393,6 @@ class UnstructuredTokenList(TokenList):
     token_type = 'unstructured'
 
     def _fold(self, folded):
-        if any(x.token_type=='encoded-word' for x in self):
-            return self._fold_encoded(folded)
-        # Here we can have either a pure ASCII string that may or may not
-        # have surrogateescape encoded bytes, or a unicode string.
         last_ew = None
         for part in self.parts:
             tstr = str(part)
@@ -1389,35 +1386,6 @@ def _get_ptext_to_endchars(value, endchars):
         pos = pos + 1
     return ''.join(vchars), ''.join([fragment[pos:]] + remainder), had_qp
 
-def _decode_ew_run(value):
-    """ Decode a run of RFC2047 encoded words.
-
-        _decode_ew_run(value) -> (text, value, defects)
-
-    Scans the supplied value for a run of tokens that look like they are RFC
-    2047 encoded words, decodes those words into text according to RFC 2047
-    rules (whitespace between encoded words is discarded), and returns the text
-    and the remaining value (including any leading whitespace on the remaining
-    value), as well as a list of any defects encountered while decoding.  The
-    input value may not have any leading whitespace.
-
-    """
-    res = []
-    defects = []
-    last_ws = ''
-    while value:
-        try:
-            tok, ws, value = _wsp_splitter(value, 1)
-        except ValueError:
-            tok, ws, value = value, '', ''
-        if not (tok.startswith('=?') and tok.endswith('?=')):
-            return ''.join(res), last_ws + tok + ws + value, defects
-        text, charset, lang, new_defects = _ew.decode(tok)
-        res.append(text)
-        defects.extend(new_defects)
-        last_ws = ws
-    return ''.join(res), last_ws, defects
-
 def get_fws(value):
     """FWS = 1*WSP
 
@@ -1443,7 +1411,8 @@ def get_encoded_word(value):
         raise errors.HeaderParseError(
             "expected encoded word but found {}".format(value))
     remstr = ''.join(remainder)
-    if remstr[:2].isdigit():
+    if len(remstr) > 1 and remstr[0] in hexdigits and remstr[1] in hexdigits:
+        # The ? after the CTE was followed by an encoded word escape (=XX).
         rest, *remainder = remstr.split('?=', 1)
         tok = tok + '?=' + rest
     if len(tok.split()) > 1:
@@ -1491,8 +1460,8 @@ def get_unstructured(value):
 
     """
     # XXX: but what about bare CR and LF?  They might signal the start or
-    # end of an encoded word.  YAGNI for now, since out current parsers
-    # will never send us strings with bard CR or LF.
+    # end of an encoded word.  YAGNI for now, since our current parsers
+    # will never send us strings with bare CR or LF.
 
     unstructured = UnstructuredTokenList()
     while value:
@@ -1504,6 +1473,8 @@ def get_unstructured(value):
             try:
                 token, value = get_encoded_word(value)
             except errors.HeaderParseError:
+                # XXX: Need to figure out how to register defects when
+                # appropriate here.
                 pass
             else:
                 have_ws = True
diff --git a/Lib/test/test_email/test__encoded_words.py b/Lib/test/test_email/test__encoded_words.py
index 14395fe..f8e380d 100644
--- a/Lib/test/test_email/test__encoded_words.py
+++ b/Lib/test/test_email/test__encoded_words.py
@@ -122,6 +122,11 @@ class TestDecode(TestEmailBase):
                    # XXX Should this be a new Defect instead?
                    defects = [errors.CharsetError])
 
+    def test_q_nonascii(self):
+        self._test('=?utf-8?q?=C3=89ric?=',
+                   'Éric',
+                   charset='utf-8')
+
 
 class TestEncodeQ(TestEmailBase):
 
diff --git a/Lib/test/test_email/test__header_value_parser.py b/Lib/test/test_email/test__header_value_parser.py
index 6101e19..8917447 100644
--- a/Lib/test/test_email/test__header_value_parser.py
+++ b/Lib/test/test_email/test__header_value_parser.py
@@ -170,6 +170,15 @@ class TestParser(TestParserMixin, TestEmailBase):
                         [],
                         '')
 
+    def test_get_encoded_word_quopri_utf_escape_follows_cte(self):
+        # Issue 18044
+        self._test_get_x(parser.get_encoded_word,
+                        '=?utf-8?q?=C3=89ric?=',
+                        'Éric',
+                        'Éric',
+                        [],
+                        '')
+
     # get_unstructured
 
     def _get_unst(self, value):
diff --git a/Lib/test/test_email/test_headerregistry.py b/Lib/test/test_email/test_headerregistry.py
index c0c81c1..80f1c02 100644
--- a/Lib/test/test_email/test_headerregistry.py
+++ b/Lib/test/test_email/test_headerregistry.py
@@ -123,12 +123,45 @@ class TestBaseHeaderFeatures(TestHeaderBase):
     #    self.assertEqual(h, value)
     #    self.assertDefectsEqual(h.defects, [errors.ObsoleteHeaderDefect])
 
-    def test_RFC2047_value_decoded(self):
-        value = '=?utf-8?q?this_is_a_test?='
-        h = self.make_header('subject', value)
-        self.assertEqual(h, 'this is a test')
 
+@parameterize
+class TestUnstructuredHeader(TestHeaderBase):
 
+    def string_as_value(self,
+                        source,
+                        decoded,
+                        *args):
+        l = len(args)
+        defects = args[0] if l>0 else []
+        header = 'Subject:' + (' ' if source else '')
+        folded = header + (args[1] if l>1 else source) + '\n'
+        h = self.make_header('Subject', source)
+        self.assertEqual(h, decoded)
+        self.assertDefectsEqual(h.defects, defects)
+        self.assertEqual(h.fold(policy=policy.default), folded)
+
+    string_params = {
+
+        'rfc2047_simple_quopri': (
+            '=?utf-8?q?this_is_a_test?=',
+            'this is a test',
+            [],
+            'this is a test'),
+
+        'rfc2047_gb2312_base64': (
+            '=?gb2312?b?1eLKx9bQzsSy4srUo6E=?=',
+            '\u8fd9\u662f\u4e2d\u6587\u6d4b\u8bd5\uff01',
+            [],
+            '=?utf-8?b?6L+Z5piv5Lit5paH5rWL6K+V77yB?='),
+
+        'rfc2047_simple_nonascii_quopri': (
+            '=?utf-8?q?=C3=89ric?=',
+            'Éric'),
+
+    }
+
+
+@parameterize
 class TestDateHeader(TestHeaderBase):
 
     datestring = 'Sun, 23 Sep 2001 20:10:55 -0700'