fix: let the provider decide when to reuse an existing subscription ID (#2929)

Fix for #2926

Signed-off-by: Giuseppe Bertone <[email protected]>

Author: Neurone

docs/configuration.md

@@ -123,6 +123,7 @@ Unless you need to set a non-default value, it is recommended to only populate o
 | `WS_CACHE_TTL`                  | "20000"  | The time to live for cached entries.                                                                                          |
 | `WS_NEW_HEADS_ENABLED`.         | "true"   | Enables subscriptions for the latest blocks, `newHeads`.                                                                      |
 | `WS_PING_INTERVAL`              | "100000" | Interval between ping messages. Set to `0` to disable pinger.                                                                 |
+| `WS_SAME_SUB_FOR_SAME_EVENT`    | "true"   | The relay will return the same subscription ID when a client subscribes to the same event multiple times using a single connection. When set to false, the relay will always create a new subscription ID for each `eth_subscribe' request. |
 
 ## Sample for connecting to Hedera Environments
 

packages/relay/src/lib/subscriptionController.ts

@@ -41,6 +41,7 @@ export class SubscriptionController {
   private cache;
   private activeSubscriptionHistogram: Histogram;
   private resultsSentToSubscribersCounter: Counter;
+  private useTheSameSubscriptionForTheSameEvent: boolean;
 
   constructor(poller: Poller, logger: Logger, register: Registry) {
     this.poller = poller;
@@ -76,6 +77,9 @@ export class SubscriptionController {
       registers: [register],
       labelNames: ['subId', 'tag'],
     });
+
+    // Default: true
+    this.useTheSameSubscriptionForTheSameEvent = process.env.WS_SAME_SUB_FOR_SAME_EVENT?.toLowerCase() !== 'false';
   }
 
   createHash(data) {
@@ -99,11 +103,13 @@ export class SubscriptionController {
       this.subscriptions[tag] = [];
     }
 
-    // Check if the connection is already subscribed to this event
-    const existingSub = this.subscriptions[tag].find((sub) => sub.connection.id === connection.id);
-    if (existingSub) {
-      this.logger.debug(`Connection ${connection.id}: Attempting to subscribe to ${tag}; already subscribed`);
-      return existingSub.subscriptionId;
+    if (this.useTheSameSubscriptionForTheSameEvent) {
+      // Check if the connection is already subscribed to this event
+      const existingSub = this.subscriptions[tag].find((sub) => sub.connection.id === connection.id);
+      if (existingSub) {
+        this.logger.debug(`Connection ${connection.id}: Attempting to subscribe to ${tag}; already subscribed`);
+        return existingSub.subscriptionId;
+      }
     }
 
     const subId = this.generateId();

packages/relay/tests/lib/subscriptionController.spec.ts

@@ -263,4 +263,39 @@ describe('subscriptionController', async function () {
     subscriptionController.unsubscribe(wsConnection, subId);
     subscriptionController.unsubscribe(wsConnection, subId2);
   });
+
+  describe('With WS_SAME_SUB_FOR_SAME_EVENT == `false`', async function () {
+    let originalEnv;
+    let originalSubscriptionController;
+
+    before(() => {
+      originalEnv = process.env.WS_SAME_SUB_FOR_SAME_EVENT;
+      originalSubscriptionController = subscriptionController;
+
+      process.env.WS_SAME_SUB_FOR_SAME_EVENT = 'false';
+      const registry = new Registry();
+      poller = new Poller(ethImpl, logger, registry);
+      subscriptionController = new SubscriptionController(poller, logger, registry);
+    });
+
+    after(() => {
+      process.env.WS_SAME_SUB_FOR_SAME_EVENT = originalEnv;
+      subscriptionController = originalSubscriptionController;
+    });
+
+    it('Subscribing to the same event and filters should return different subscription id', async function () {
+      const connectionId = '7';
+      const wsConnection = new MockWsConnection(connectionId);
+      const tag1 = {
+        event: 'logs',
+        filters: { topics: ['0xddf252ad1be2c89b69c2b068fc378daa952ba7f163c4a11628f55a4df523b3ef'] },
+      };
+      const subId = subscriptionController.subscribe(wsConnection, tag1.event);
+      const subId2 = subscriptionController.subscribe(wsConnection, tag1.event);
+
+      expect(subId).to.be.not.eq(subId2);
+      subscriptionController.unsubscribe(wsConnection, subId);
+      subscriptionController.unsubscribe(wsConnection, subId2);
+    });
+  });
 });