models: Add MissedMessageEmailAddress class.

Preparatory commit for making the email mirror use the database instead
of redis for missed message addresses.

This model will represent missed message email addresses, which
currently have their data stored in redis.
The redis data will be converted and migrated into these models and
the email mirror will start using them in the main commit.

zerver/lib/export.py

@@ -98,6 +98,7 @@ ALL_ZULIP_TABLES = {
     'zerver_emailchangestatus',
     'zerver_huddle',
     'zerver_message',
+    'zerver_missedmessageemailaddress',
     'zerver_multiuseinvite',
     'zerver_multiuseinvite_streams',
     'zerver_preregistrationuser',
@@ -145,6 +146,11 @@ NON_EXPORTED_TABLES = {
     'zerver_preregistrationuser',
     'zerver_preregistrationuser_streams',
 
+    # Missed message addresses are low value to export since
+    # missed-message email addresses include the server's hostname and
+    # expire after a few days.
+    'zerver_missedmessageemailaddress',
+
     # When switching servers, clients will need to re-login and
     # reregister for push notifications anyway.
     'zerver_pushdevicetoken',

zerver/migrations/0259_missedmessageemailaddress.py

@@ -0,0 +1,29 @@
+# -*- coding: utf-8 -*-
+# Generated by Django 1.11.26 on 2020-01-06 01:23
+from __future__ import unicode_literals
+
+from django.conf import settings
+from django.db import migrations, models
+import django.db.models.deletion
+import django.utils.timezone
+
+
+class Migration(migrations.Migration):
+
+    dependencies = [
+        ('zerver', '0258_enable_online_push_notifications_default'),
+    ]
+
+    operations = [
+        migrations.CreateModel(
+            name='MissedMessageEmailAddress',
+            fields=[
+                ('id', models.AutoField(auto_created=True, primary_key=True, serialize=False, verbose_name='ID')),
+                ('email_token', models.CharField(db_index=True, max_length=34, unique=True)),
+                ('timestamp', models.DateTimeField(db_index=True, default=django.utils.timezone.now)),
+                ('times_used', models.PositiveIntegerField(db_index=True, default=0)),
+                ('message', models.ForeignKey(on_delete=django.db.models.deletion.CASCADE, to='zerver.Message')),
+                ('user_profile', models.ForeignKey(on_delete=django.db.models.deletion.CASCADE, to=settings.AUTH_USER_MODEL)),
+            ],
+        ),
+    ]

zerver/models.py

@@ -2509,6 +2509,21 @@ class ScheduledEmail(AbstractScheduledJob):
                                                self.address or list(self.users.all()),
                                                self.scheduled_timestamp)
 
+class MissedMessageEmailAddress(models.Model):
+    EXPIRY_SECONDS = 60 * 60 * 24 * 5
+
+    message = models.ForeignKey(Message, on_delete=CASCADE)  # type: Message
+    user_profile = models.ForeignKey(UserProfile, on_delete=CASCADE)  # type: UserProfile
+    email_token = models.CharField(max_length=34, unique=True, db_index=True)  # type: str
+
+    # Timestamp of when the missed message address generated.
+    # The address is valid until timestamp + EXPIRY_SECONDS.
+    timestamp = models.DateTimeField(db_index=True, default=timezone_now)  # type: datetime.datetime
+    times_used = models.PositiveIntegerField(default=0, db_index=True)  # type: int
+
+    def __str__(self) -> str:
+        return settings.EMAIL_GATEWAY_PATTERN % (self.email_token,)
+
 class ScheduledMessage(models.Model):
     sender = models.ForeignKey(UserProfile, on_delete=CASCADE)  # type: UserProfile
     recipient = models.ForeignKey(Recipient, on_delete=CASCADE)  # type: Recipient