log errors in send_notification, limit subject length to 75 characters

.env

 # Environment variables used by `$ heroku local`
 
-DJANGO_SETTINGS_MODULE=oser_backend.settings.dev
 PORT=8000

Procfile

 web: sh -c 'cd oser_backend && exec gunicorn oser_backend.wsgi:application --bind 0.0.0.0:$PORT --workers 1'
 
 # Toggle next line to start Celery in a worker process
-worker: sh -c 'cd oser_backend && exec celery -A oser_backend worker --beat -l info'
+# worker: sh -c 'cd oser_backend && exec celery -A oser_backend worker --beat -l info'

oser_backend/mails/management/commands/rendernotification.py

 """Render a notification."""
 
-from .base import MailsCommandMixin
+from ..base import MailsCommandMixin
 from django.core.management import BaseCommand
 
 

oser_backend/mails/management/commands/sendnotification.py

 """Send a notification."""
 
-from .base import MailsCommandMixin
+from ..base import MailsCommandMixin
 from django.core.management import BaseCommand
 
 
@@ -12,17 +12,16 @@ class Command(MailsCommandMixin, BaseCommand):
     def add_arguments(self, parser):
         super().add_arguments(parser)
         parser.add_argument(
-            'recipient',
-            help='Email of the notification recipient.')
+            'recipient', help='Email of the notification recipient.')
 
     def handle(self, *args, **kwargs):
         recipient = kwargs['recipient']
         notification = self.get_notification(kwargs)
         notification.force_recipients([recipient])
-        result = notification.send()
-        if result['sent']:
+        notification.send()
+        if notification.sent:
             self.stdout.write(self.style.SUCCESS(
-                f'✉️ Notification email sent to {recipient}.'))
+                f'Notification email sent to {recipient}.'))
         else:
             self.stderr.write(
-                '⚠️ Notification email not sent (see above for logs).')
+                'Notification email not sent (see above for logs).')

oser_backend/mails/notifications.py

@@ -8,10 +8,11 @@ from django.core.mail import send_mail
 from django.template.loader import render_to_string
 from django.utils import timezone
 from django.utils.html import strip_tags
+from django.utils.text import Truncator
 
 from markdown import markdown
 
-from .signals import app_disabled, delivered, notification_sent
+from .signals import app_disabled, delivered, notification_sent, failed
 
 
 def send_notification(subject, message, recipient_list,
@@ -43,7 +44,12 @@ def send_notification(subject, message, recipient_list,
 
     mail_from = settings.MAILS_NOTIFICATIONS_ADDRESS
 
+    try:
         send_mail(subject, message, mail_from, recipient_list, **kwargs)
+    except Exception as e:
+        failed.send(None, exception=e)
+        return False
+
     delivered.send(None, mail_from=mail_from,
                    recipient_list=recipient_list, subject=subject)
 
@@ -167,6 +173,9 @@ class Notification:
     def send(self) -> None:
         """Send the notification email."""
         subject = self.subject_format.format(subject=self.get_subject())
+        # Subject must not be longer than 78 characters
+        # See https://github.com/sendgrid/sendgrid-python/issues/187
+        subject = Truncator(subject).chars(75)
         message = self.render()
 
         if self.forced:

oser_backend/mails/signals.py

 """Mails app signals."""
 
 from django.dispatch import Signal, receiver
+from python_http_client.exceptions import HTTPError
 
 from logs import get_logger
 
 delivered = Signal(providing_args=['mail_from', 'subject', 'recipient_list'])
 app_disabled = Signal(providing_args=['subject', 'recipient_list'])
+failed = Signal(providing_args=['exception'])
 notification_sent = Signal(providing_args=['instance', 'result'])
 
 logger = get_logger('notifications')
@@ -22,3 +24,12 @@ def log_app_disabled(sender, subject, recipient_list, **kwargs):
     logger.warning(
         'Email "%s" not sent to %s because MAILS_ENABLED is set to False',
         subject, recipient_list)
+
+
+@receiver(failed)
+def log_failed(sender, exception, **kwargs):
+    """Log an exception that occurred during a mail delivery."""
+    if isinstance(exception, HTTPError):
+        logger.exception(exception.read())
+    else:
+        logger.exception(exception)

oser_backend/visits/signals.py

@@ -22,7 +22,7 @@ def notify_participation(sender, instance: Participation, **kwargs):
 
     The notification is only sent if the participation status has changed.
     """
-    if instance.accepted is True:
-        Accepted(user=instance.user, visit=instance.visit).send()
-    elif instance.accepted is False:
-        Rejected(user=instance.user, visit=instance.visit).send()
+    if instance.accepted is None:
+        return
+    notification_cls = Accepted if instance.accepted else Rejected
+    notification_cls(user=instance.user, visit=instance.visit).send()