Remove subscriber reference from topic when deleted

CHANGELOG.md

@@ -13,7 +13,7 @@ You can find and compare releases at the [GitHub release page](https://github.co
 
 - Add flag `--json` to `print-schema` to output JSON instead of GraphQL SDL https://github.com/nuwave/lighthouse/pull/1268
 - Add TTL option for subscriptions storage https://github.com/nuwave/lighthouse/pull/1284
-
+- `StorageManager` will remove subscribers from topics now when they are deleted.
 ### Changed
 
 - Improve subscription context serializer https://github.com/nuwave/lighthouse/pull/1283

src/Subscriptions/StorageManager.php

@@ -99,6 +99,7 @@ public function storeSubscriber(Subscriber $subscriber, string $topic): void
             ? json_decode($topicJson, true)
             : [];
 
+        $subscriber->topic = $topicKey;
         $topic[] = $subscriber->channel;
 
         if ($this->ttl === null) {
@@ -110,8 +111,43 @@ public function storeSubscriber(Subscriber $subscriber, string $topic): void
         }
     }
 
+    /**
+     * Delete subscriber.
+     *
+     * @param  string  $channel
+     * @return \Nuwave\Lighthouse\Subscriptions\Subscriber|null
+     */
     public function deleteSubscriber(string $channel): ?Subscriber
     {
-        return $this->cache->pull(self::SUBSCRIBER_KEY.".{$channel}");
+        $subscriber = $this->cache->pull(self::SUBSCRIBER_KEY.".{$channel}");
+
+        if ($subscriber !== null) {
+            $this->removeSubscriberFromTopic($subscriber);
+        }
+
+        return $subscriber;
+    }
+
+    /**
+     * Remove the subscriber from the topic they are subscribed to.
+     *
+     * @param  Subscriber $subscriber
+     */
+    protected function removeSubscriberFromTopic(Subscriber $subscriber)
+    {
+        if (empty($subscriber->topic)) {
+            return;
+        }
+
+        $topic = Collection::make(json_decode($this->cache->get($subscriber->topic), true))
+            ->reject(function ($key) use ($subscriber) {
+                return self::SUBSCRIBER_KEY.".{$key}" === self::SUBSCRIBER_KEY.".{$subscriber->channel}";
+            });
+
+        if ($this->ttl === null) {
+            $this->cache->forever($subscriber->topic, json_encode($topic->all()));
+        } else {
+            $this->cache->put($subscriber->topic, json_encode($topic->all()), $this->ttl);
+        }
     }
 }

tests/Unit/Subscriptions/StorageManagerTest.php

@@ -7,6 +7,7 @@
 use Nuwave\Lighthouse\Subscriptions\Contracts\ContextSerializer;
 use Nuwave\Lighthouse\Subscriptions\StorageManager;
 use Nuwave\Lighthouse\Subscriptions\Subscriber;
+use Nuwave\Lighthouse\Subscriptions\SubscriptionRegistry;
 use Nuwave\Lighthouse\Subscriptions\SubscriptionServiceProvider;
 use Nuwave\Lighthouse\Support\Contracts\GraphQLContext;
 use Tests\TestCase;
@@ -137,6 +138,27 @@ public function testCanStoreSubscribersInCache(): void
         $this->assertCount(1, $this->storage->subscribersByTopic(self::TOPIC));
     }
 
+    public function testDeleteSubscribersInCache(): void
+    {
+        $subscriber1 = $this->subscriber('{ me }');
+        $subscriber2 = $this->subscriber('{ viewer }');
+        $channel =  'TaskUpdated';
+
+        $this->storage->storeSubscriber($subscriber1, $channel);
+        $this->storage->deleteSubscriber($subscriber1->channel);
+        $this->assertCount(0, $this->storage->subscribersByTopic($channel));
+
+        $this->storage->storeSubscriber($subscriber1, $channel);
+        $this->storage->storeSubscriber($subscriber2, $channel);
+        $this->assertCount(2, $this->storage->subscribersByTopic($channel));
+        $this->storage->deleteSubscriber($subscriber1->channel);
+        $this->storage->deleteSubscriber($subscriber2->channel);
+
+        $this->storage->storeSubscriber($subscriber1, $channel);
+
+        $this->assertCount(1, $this->storage->subscribersByTopic($channel));
+    }
+
     protected function assertSubscriberIsSame(Subscriber $expected, Subscriber $actual): void
     {
         $this->assertSame(