gh-93158: Support obsolete email syntax, fieldnames that are followed by whitespace

Doc/library/email.policy.rst

@@ -454,9 +454,10 @@ added matters.  To illustrate::
 
 
       The name is parsed as everything up to the '``:``' and returned
-      unmodified.  The value is determined by stripping leading whitespace off
-      the remainder of the first line, joining all subsequent lines together,
-      and stripping any trailing carriage return or linefeed characters.
+      stripped of trailing whitespace.  The value is determined by stripping
+      leading whitespace off the remainder of the first line, joining all
+      subsequent lines together, and stripping any trailing carriage
+      return or linefeed characters.
 
 
    .. method:: header_store_parse(name, value)

Lib/email/_policybase.py

@@ -292,15 +292,15 @@ def _sanitize_header(self, name, value):
 
     def header_source_parse(self, sourcelines):
         """+
-        The name is parsed as everything up to the ':' and returned unmodified.
-        The value is determined by stripping leading whitespace off the
-        remainder of the first line, joining all subsequent lines together, and
-        stripping any trailing carriage return or linefeed characters.
+        The name is parsed as everything up to the ':' and returned stripped
+        of any trailing whitespace. The value is determined by stripping leading
+        whitespace off the remainder of the first line, joining all subsequent
+        lines together, and stripping any trailing carriage return or linefeed characters.
 
         """
         name, value = sourcelines[0].split(':', 1)
         value = value.lstrip(' \t') + ''.join(sourcelines[1:])
-        return (name, value.rstrip('\r\n'))
+        return (name.rstrip(' \t'), value.rstrip('\r\n'))
 
     def header_store_parse(self, name, value):
         """+

Lib/email/feedparser.py

@@ -34,7 +34,7 @@
 NLCRE_crack = re.compile(r'(\r\n|\r|\n)')
 # RFC 2822 $3.6.8 Optional fields.  ftext is %d33-57 / %d59-126, Any character
 # except controls, SP, and ":".
-headerRE = re.compile(r'^(From |[\041-\071\073-\176]*:|[\t ])')
+headerRE = re.compile(r'^(From |[\041-\071\073-\176]*[ \t]*:|[\t ])')
 EMPTYSTRING = ''
 NL = '\n'
 boundaryendRE = re.compile(

Lib/test/test_email/data/msg_48.txt

@@ -0,0 +1,7 @@
+Subject: Regarding messages containing whitespace that follow field names
+To: receiver@example.org
+x-whitespace-after-fieldname       : value
+Date: Fri, 20 May 2022 18:13:19 +1200
+From: sender@example.org
+
+Field names can be followed by arbitrary whitespace

Lib/test/test_email/test_email.py

@@ -431,6 +431,14 @@ def test_get_param_funky_continuation_lines(self):
         msg = self._msgobj('msg_22.txt')
         self.assertEqual(msg.get_payload(1).get_param('name'), 'wibble.JPG')
 
+    def test_whitespace_after_fieldname(self):
+        # As part of obsolete email syntax, fieldnames can be followed by arbitrary whitespace
+        msg = self._msgobj("msg_48.txt")
+
+        self.assertEqual(msg["x-whitespace-after-fieldname"], "value")
+        self.assertEqual(msg.get_payload(),
+                         "Field names can be followed by arbitrary whitespace\n")
+
     # test_headerregistry.TestContentTypeHeader.semis_inside_quotes
     def test_get_param_with_semis_in_quotes(self):
         msg = email.message_from_string(

Misc/NEWS.d/next/Library/2022-05-24-15-55-09.gh-issue-93158.KH0YPY.rst

@@ -0,0 +1,2 @@
+The :mod:`email` library now parses messages that use obsolete email syntax where
+header field names can be followed by whitespace.