truncate email from addresses if >320 chars when encoded (TNL-4264) (#12171)

* truncate email from addresses if >320 chars when encoded (TNL-4264)

* use exact lengths

lms/djangoapps/bulk_email/tasks.py

@@ -32,6 +32,7 @@ from celery.exceptions import RetryTaskError  # pylint: disable=no-name-in-modul
 from django.conf import settings
 from django.contrib.auth.models import User
 from django.core.mail import EmailMultiAlternatives, get_connection
+from django.core.mail.message import forbid_multi_line_headers
 from django.core.urlresolvers import reverse
 
 from bulk_email.models import (
@@ -384,13 +385,20 @@ def _filter_optouts_from_recipients(to_list, course_id):
     return to_list, num_optout
 
 
-def _get_source_address(course_id, course_title):
+def _get_source_address(course_id, course_title, truncate=True):
     """
     Calculates an email address to be used as the 'from-address' for sent emails.
 
     Makes a unique from name and address for each course, e.g.
 
-        "COURSE_TITLE" Course Staff <coursenum-no-reply@courseupdates.edx.org>
+        "COURSE_TITLE" Course Staff <course_name-no-reply@courseupdates.edx.org>
+
+    If, when decoded to ascii, this from_addr is longer than 320 characters,
+    use the course_name rather than the course title, e.g.
+
+        "course_name" Course Staff <course_name-no-reply@courseupdates.edx.org>
+
+    The "truncate" kwarg is only used for tests.
 
     """
     course_title_no_quotes = re.sub(r'"', '', course_title)
@@ -418,10 +426,11 @@ def _get_source_address(course_id, course_title):
 
     from_addr = format_address(course_title_no_quotes)
 
-    # If it's longer than 320 characters, reformat, but with the course name
-    # rather than course title. Amazon SES's from address field appears to have a maximum
-    # length of 320.
-    if len(from_addr) >= 320:
+    # If the encoded from_addr is longer than 320 characters, reformat,
+    # but with the course name rather than course title.
+    # Amazon SES's from address field appears to have a maximum length of 320.
+    __, encoded_from_addr = forbid_multi_line_headers('from', from_addr, 'utf-8')
+    if len(encoded_from_addr) >= 320 and truncate:
         from_addr = format_address(course_name)
 
     return from_addr

lms/djangoapps/bulk_email/tests/test_email.py

@@ -10,11 +10,13 @@ from unittest import skipIf
 
 from django.conf import settings
 from django.core import mail
+from django.core.mail.message import forbid_multi_line_headers
 from django.core.urlresolvers import reverse
 from django.core.management import call_command
 from django.test.utils import override_settings
 
 from bulk_email.models import Optout
+from bulk_email.tasks import _get_source_address
 from courseware.tests.factories import StaffFactory, InstructorFactory
 from instructor_task.subtasks import update_subtask_status
 from student.roles import CourseStaffRole
@@ -322,13 +324,24 @@ class TestEmailSendFromDashboardMockedHtmlToText(EmailSendFromDashboardTestCase)
             'message': 'test message for self'
         }
 
-        # make very long display_name for course
-        long_name = u"x" * 321
+        # make display_name that's longer than 320 characters when encoded
+        # to ascii, but shorter than 320 unicode characters
+        long_name = u"é" * 200
+
         course = CourseFactory.create(
             display_name=long_name, number="bulk_email_course_name"
         )
         instructor = InstructorFactory(course_key=course.id)
 
+        unexpected_from_addr = _get_source_address(
+            course.id, course.display_name, truncate=False
+        )
+        __, encoded_unexpected_from_addr = forbid_multi_line_headers(
+            "from", unexpected_from_addr, 'utf-8'
+        )
+        self.assertEqual(len(encoded_unexpected_from_addr), 748)
+        self.assertEqual(len(unexpected_from_addr), 261)
+
         self.login_as_user(instructor)
         send_mail_url = reverse('send_email', kwargs={'course_id': unicode(course.id)})
         response = self.client.post(send_mail_url, test_email)
@@ -337,11 +350,13 @@ class TestEmailSendFromDashboardMockedHtmlToText(EmailSendFromDashboardTestCase)
         self.assertEqual(len(mail.outbox), 1)
         from_email = mail.outbox[0].from_email
 
+        expected_from_addr = (
+            u'"{course_name}" Course Staff <{course_name}-no-reply@example.com>'
+        ).format(course_name=course.id.course)
+
         self.assertEqual(
             from_email,
-            u'"{course_name}" Course Staff <{course_name}-no-reply@example.com>'.format(
-                course_name=course.id.course
-            )
+            expected_from_addr
         )
         self.assertEqual(len(from_email), 83)