zilencer: Fix uniqueness rules for RemotePushDeviceToken.

Since a user could use the same installation of the Zulip mobile app
with multiple Zulip servers, correct behavior is to allow reusing the
same token with multiple Zulip servers in the RemotePushDeviceToken
model.

zerver/models.py

@@ -821,7 +821,6 @@ class AbstractPushDeviceToken(models.Model):
     # sent to us from each device:
     #   - APNS token if kind == APNS
     #   - GCM registration id if kind == GCM
-    token = models.CharField(max_length=4096, unique=True)  # type: bytes
     last_updated = models.DateTimeField(auto_now=True)  # type: datetime.datetime
 
     # [optional] Contains the app id of the device if it is an iOS device
@@ -833,6 +832,7 @@ class AbstractPushDeviceToken(models.Model):
 class PushDeviceToken(AbstractPushDeviceToken):
     # The user who's device this is
     user = models.ForeignKey(UserProfile, db_index=True, on_delete=CASCADE)  # type: UserProfile
+    token = models.CharField(max_length=4096, unique=True)  # type: bytes
 
 def generate_email_token_for_stream():
     # type: () -> str

zilencer/migrations/0005_remotepushdevicetoken_fix_uniqueness.py

@@ -0,0 +1,29 @@
+# -*- coding: utf-8 -*-
+# Generated by Django 1.11.5 on 2017-10-19 04:23
+from __future__ import unicode_literals
+
+from django.db import migrations, models
+
+
+class Migration(migrations.Migration):
+
+    dependencies = [
+        ('zilencer', '0004_remove_deployment_model'),
+    ]
+
+    operations = [
+        migrations.AlterField(
+            model_name='remotepushdevicetoken',
+            name='token',
+            field=models.CharField(db_index=True, max_length=4096),
+        ),
+        migrations.AlterField(
+            model_name='remotepushdevicetoken',
+            name='user_id',
+            field=models.BigIntegerField(db_index=True),
+        ),
+        migrations.AlterUniqueTogether(
+            name='remotepushdevicetoken',
+            unique_together=set([('server', 'token')]),
+        ),
+    ]

zilencer/models.py

@@ -21,4 +21,8 @@ class RemoteZulipServer(models.Model):
 class RemotePushDeviceToken(zerver.models.AbstractPushDeviceToken):
     server = models.ForeignKey(RemoteZulipServer)  # type: RemoteZulipServer
     # The user id on the remote server for this device device this is
-    user_id = models.BigIntegerField()  # type: int
+    user_id = models.BigIntegerField(db_index=True)  # type: int
+    token = models.CharField(max_length=4096, db_index=True)  # type: bytes
+
+    class Meta(object):
+        unique_together = ("server", "token")