Prevent NetworkConnections from leaking

.changeset/wild-pets-change.md

@@ -0,0 +1,5 @@
+---
+"hardhat": patch
+---
+
+Optimize the network connections to prevent memory leaks.

v-next/hardhat/src/internal/builtin-plugins/network-manager/edr/edr-provider.ts

@@ -165,6 +165,10 @@ export class EdrProvider extends BaseProvider {
 
     let edrProvider: EdrProvider;
 
+    // We use a WeakRef to the provider to prevent the subscriptionCallback
+    // below from creating a cycle and leaking the provider.
+    let edrProviderWeakRef: WeakRef<EdrProvider> | undefined;
+
     // We need to catch errors here, as the provider creation can panic unexpectedly,
     // and we want to make sure such a crash is propagated as a ProviderError.
     try {
@@ -191,13 +195,17 @@ export class EdrProvider extends BaseProvider {
         },
         {
           subscriptionCallback: (event: SubscriptionEvent) => {
-            edrProvider.onSubscriptionEvent(event);
+            const deferredProvider = edrProviderWeakRef?.deref();
+            if (deferredProvider !== undefined) {
+              deferredProvider.onSubscriptionEvent(event);
+            }
           },
         },
         contractDecoder,
       );
 
       edrProvider = new EdrProvider(provider, jsonRpcRequestWrapper);
+      edrProviderWeakRef = new WeakRef(edrProvider);
     } catch (error) {
       ensureError(error);
 
@@ -282,6 +290,7 @@ export class EdrProvider extends BaseProvider {
   }
 
   public async close(): Promise<void> {
+    this.removeAllListeners();
     // Clear the provider reference to help with garbage collection
     this.#provider = undefined;
   }

v-next/hardhat/src/internal/builtin-plugins/network-manager/http-provider.ts

@@ -161,6 +161,7 @@ export class HttpProvider extends BaseProvider {
   }
 
   public async close(): Promise<void> {
+    this.removeAllListeners();
     if (this.#dispatcher !== undefined) {
       // See https://github.com/nodejs/undici/discussions/3522#discussioncomment-10498734
       await this.#dispatcher.close();

v-next/hardhat/test/internal/builtin-plugins/network-manager/edr/edr-provider.ts

@@ -470,6 +470,17 @@ describe("edr-provider", () => {
         {},
       );
     });
+
+    it("should remove all listeners after closing", async () => {
+      const connection = await hre.network.connect();
+
+      connection.provider.on("notification", () => {});
+      assert.equal(connection.provider.listenerCount("notification"), 1);
+
+      await connection.provider.close();
+
+      assert.equal(connection.provider.listenerCount("notification"), 0);
+    });
   });
 
   describe("isDefaultEdrNetworkHDAccountsConfig", () => {

v-next/hardhat/test/internal/builtin-plugins/network-manager/http-provider.ts

@@ -579,5 +579,20 @@ describe("http-provider", () => {
         {},
       );
     });
+
+    it("should remove all listeners after closing", async () => {
+      const provider = await HttpProvider.create({
+        url: "http://localhost",
+        networkName: "exampleNetwork",
+        timeout: 20_000,
+      });
+
+      provider.on("notification", () => {});
+      assert.equal(provider.listenerCount("notification"), 1);
+
+      await provider.close();
+
+      assert.equal(provider.listenerCount("notification"), 0);
+    });
   });
 });