email_mirror: Make email_token a unique column of Stream.

zerver/migrations/0212_make_stream_email_token_unique.py

@@ -0,0 +1,21 @@
+# -*- coding: utf-8 -*-
+# Generated by Django 1.11.20 on 2019-03-17 08:37
+from __future__ import unicode_literals
+
+from django.db import migrations, models
+import zerver.models
+
+
+class Migration(migrations.Migration):
+
+    dependencies = [
+        ('zerver', '0211_add_users_field_to_scheduled_email'),
+    ]
+
+    operations = [
+        migrations.AlterField(
+            model_name='stream',
+            name='email_token',
+            field=models.CharField(default=zerver.models.generate_email_token_for_stream, max_length=32, unique=True),
+        ),
+    ]

zerver/models.py

@@ -1159,7 +1159,7 @@ class Stream(models.Model):
     # e-mail length of 254, and our max stream length is 30, so we
     # have plenty of room for the token.
     email_token = models.CharField(
-        max_length=32, default=generate_email_token_for_stream)  # type: str
+        max_length=32, default=generate_email_token_for_stream, unique=True)  # type: str
 
     # The very first message ID in the stream.  Used to help clients
     # determine whether they might need to display "more topics" for a