From 1295a34481c0b87ed0c95224888d5be783ae4326 Mon Sep 17 00:00:00 2001
From: "fryorcraken.eth" <git@fryorcraken.xyz>
Date: Mon, 19 Sep 2022 12:21:29 +1000
Subject: [PATCH] feat: return function to delete observer

---
 CHANGELOG.md                          |  4 ++++
 src/lib/waku_relay/index.node.spec.ts |  6 ++++--
 src/lib/waku_relay/index.ts           | 18 ++++++++++++++++--
 3 files changed, 24 insertions(+), 4 deletions(-)

diff --git a/CHANGELOG.md b/CHANGELOG.md
index 9473bfa91c..b1bbc83148 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -7,6 +7,10 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 
 ## [Unreleased]
 
+### Added
+
+- `WakuRelay.addObserver` now returns a function to delete the observer.
+
 ### Changed
 
 - `queryCallbackOnPromise`'s return value has been simplified to `Promise<void>`.
diff --git a/src/lib/waku_relay/index.node.spec.ts b/src/lib/waku_relay/index.node.spec.ts
index 3fb93e615c..05e6a62146 100644
--- a/src/lib/waku_relay/index.node.spec.ts
+++ b/src/lib/waku_relay/index.node.spec.ts
@@ -248,8 +248,10 @@ describe("Waku Relay [node only]", () => {
       // The promise **fails** if we receive a message on this observer.
       const receivedMsgPromise: Promise<WakuMessage> = new Promise(
         (resolve, reject) => {
-          waku2.relay.addObserver(reject, ["added-then-deleted-observer"]);
-          waku2.relay.deleteObserver(reject, ["added-then-deleted-observer"]);
+          const deleteObserver = waku2.relay.addObserver(reject, [
+            "added-then-deleted-observer",
+          ]);
+          deleteObserver();
           setTimeout(resolve, 500);
         }
       );
diff --git a/src/lib/waku_relay/index.ts b/src/lib/waku_relay/index.ts
index b53cf9519e..0480bc23a4 100644
--- a/src/lib/waku_relay/index.ts
+++ b/src/lib/waku_relay/index.ts
@@ -131,12 +131,12 @@ export class WakuRelay extends GossipSub {
    * @param callback called when a new message is received via waku relay
    * @param contentTopics Content Topics for which the callback with be called,
    * all of them if undefined, [] or ["",..] is passed.
-   * @returns {void}
+   * @returns Function to delete the observer
    */
   addObserver(
     callback: (message: WakuMessage) => void,
     contentTopics: string[] = []
-  ): void {
+  ): () => void {
     if (contentTopics.length === 0) {
       if (!this.observers[""]) {
         this.observers[""] = new Set();
@@ -150,6 +150,20 @@ export class WakuRelay extends GossipSub {
         this.observers[contentTopic].add(callback);
       });
     }
+
+    return () => {
+      if (contentTopics.length === 0) {
+        if (this.observers[""]) {
+          this.observers[""].delete(callback);
+        }
+      } else {
+        contentTopics.forEach((contentTopic) => {
+          if (this.observers[contentTopic]) {
+            this.observers[contentTopic].delete(callback);
+          }
+        });
+      }
+    };
   }
 
   /**