Add support for staggering outgoing emails

Sent email can be assigned a "stagger type", for which he system will
maintain a "last sent" information. When the email is sent, it will be
delayed to be at least "stagger" time after the last one sent of the
same type. If no email of this type has been sent before, the email is
of course sent immediately.

pgweb/mailqueue/admin.py

@@ -9,6 +9,7 @@ from .models import QueuedMail
 class QueuedMailAdmin(admin.ModelAdmin):
     model = QueuedMail
     readonly_fields = ('parsed_content', )
+    list_display = ('pk', 'sender', 'receiver', 'sendat')
 
     def parsed_content(self, obj):
         # We only try to parse the *first* piece, because we assume

pgweb/mailqueue/management/commands/send_queued_mail.py

@@ -9,6 +9,7 @@ from django.core.management.base import BaseCommand, CommandError
 from django.db import connection
 from django.conf import settings
 
+import datetime
 import smtplib
 
 from pgweb.mailqueue.models import QueuedMail
@@ -26,7 +27,7 @@ class Command(BaseCommand):
         if not curs.fetchall()[0][0]:
             raise CommandError("Failed to get advisory lock, existing send_queued_mail process stuck?")
 
-        for m in QueuedMail.objects.all():
+        for m in QueuedMail.objects.filter(sendat__lte=datetime.datetime.now()):
             # Yes, we do a new connection for each run. Just because we can.
             # If it fails we'll throw an exception and just come back on the
             # next cron job. And local delivery should never fail...

pgweb/mailqueue/migrations/0002_stagger_sending.py

@@ -0,0 +1,28 @@
+# Generated by Django 2.2.11 on 2020-10-29 14:16
+
+import datetime
+from django.db import migrations, models
+
+
+class Migration(migrations.Migration):
+
+    dependencies = [
+        ('mailqueue', '0001_initial'),
+    ]
+
+    operations = [
+        migrations.CreateModel(
+            name='LastSent',
+            fields=[
+                ('id', models.AutoField(auto_created=True, primary_key=True, serialize=False, verbose_name='ID')),
+                ('type', models.CharField(max_length=10, unique=True)),
+                ('lastsent', models.DateTimeField()),
+            ],
+        ),
+        migrations.AddField(
+            model_name='queuedmail',
+            name='sendat',
+            field=models.DateTimeField(default=datetime.datetime(2000, 1, 1, 0, 0)),
+            preserve_default=False,
+        ),
+    ]

pgweb/mailqueue/models.py

@@ -10,6 +10,12 @@ class QueuedMail(models.Model):
     # Flag if the message is "user generated", so we can treat those
     # separately from an antispam and delivery perspective.
     usergenerated = models.BooleanField(null=False, blank=False, default=False)
+    sendat = models.DateTimeField(null=False, blank=False)
 
     def __str__(self):
         return "%s: %s -> %s" % (self.pk, self.sender, self.receiver)
+
+
+class LastSent(models.Model):
+    type = models.CharField(max_length=10, null=False, blank=False, unique=True)
+    lastsent = models.DateTimeField(null=False, blank=False)

pgweb/mailqueue/util.py

@@ -1,3 +1,6 @@
+from django.db import transaction
+
+from datetime import datetime
 from email.mime.text import MIMEText
 from email.mime.multipart import MIMEMultipart
 from email.mime.nonmultipart import MIMENonMultipart
@@ -6,7 +9,7 @@ from email.utils import make_msgid
 from email import encoders, charset
 from email.header import Header
 
-from .models import QueuedMail
+from .models import QueuedMail, LastSent
 
 
 def _encoded_email_header(name, email):
@@ -22,7 +25,7 @@ _utf8_charset.header_encoding = charset.QP
 _utf8_charset.body_encoding = charset.QP
 
 
-def send_simple_mail(sender, receiver, subject, msgtxt, attachments=None, usergenerated=False, cc=None, replyto=None, sendername=None, receivername=None, messageid=None, suppress_auto_replies=True, is_auto_reply=False, htmlbody=None, headers={}):
+def send_simple_mail(sender, receiver, subject, msgtxt, attachments=None, usergenerated=False, cc=None, replyto=None, sendername=None, receivername=None, messageid=None, suppress_auto_replies=True, is_auto_reply=False, htmlbody=None, headers={}, staggertype=None, stagger=None):
     # attachment format, each is a tuple of (name, mimetype,contents)
     # content should be *binary* and not base64 encoded, since we need to
     # use the base64 routines from the email library to get a properly
@@ -79,10 +82,20 @@ def send_simple_mail(sender, receiver, subject, msgtxt, attachments=None, userge
             encoders.encode_base64(part)
             msg.attach(part)
 
-    # Just write it to the queue, so it will be transactionally rolled back
-    QueuedMail(sender=sender, receiver=receiver, fullmsg=msg.as_string(), usergenerated=usergenerated).save()
-    if cc:
-        # Write a second copy for the cc, wihch will be delivered
-        # directly to the recipient. (The sender doesn't parse the
-        # message content to extract cc fields).
-        QueuedMail(sender=sender, receiver=cc, fullmsg=msg.as_string(), usergenerated=usergenerated).save()
+    with transaction.atomic():
+        if staggertype and stagger:
+            # Don't send a second one too close after another one of this class.
+            ls, created = LastSent.objects.get_or_create(type=staggertype, defaults={'lastsent': datetime.now()})
+
+            sendat = ls.lastsent = ls.lastsent + stagger
+            ls.save(update_fields=['lastsent'])
+        else:
+            sendat = datetime.now()
+
+        # Just write it to the queue, so it will be transactionally rolled back
+        QueuedMail(sender=sender, receiver=receiver, fullmsg=msg.as_string(), usergenerated=usergenerated, sendat=sendat).save()
+        if cc:
+            # Write a second copy for the cc, wihch will be delivered
+            # directly to the recipient. (The sender doesn't parse the
+            # message content to extract cc fields).
+            QueuedMail(sender=sender, receiver=cc, fullmsg=msg.as_string(), usergenerated=usergenerated, sendat=sendat).save()