fix: use socket pooling for http requests in Node.js (#12480)

web3.js/src/agent-manager.js

@@ -0,0 +1,38 @@
+// @flow
+
+import {Agent} from 'http';
+
+export const DESTROY_TIMEOUT_MS = 5000;
+
+export class AgentManager {
+  _agent: Agent = AgentManager._newAgent();
+  _activeRequests = 0;
+  _destroyTimeout: TimeoutID | null = null;
+
+  static _newAgent(): Agent {
+    return new Agent({keepAlive: true, maxSockets: 25});
+  }
+
+  requestStart(): Agent {
+    // $FlowExpectedError - Don't manage agents in the browser
+    if (process.browser) return;
+
+    this._activeRequests++;
+    clearTimeout(this._destroyTimeout);
+    this._destroyTimeout = null;
+    return this._agent;
+  }
+
+  requestEnd() {
+    // $FlowExpectedError - Don't manage agents in the browser
+    if (process.browser) return;
+
+    this._activeRequests--;
+    if (this._activeRequests === 0 && this._destroyTimeout === null) {
+      this._destroyTimeout = setTimeout(() => {
+        this._agent.destroy();
+        this._agent = AgentManager._newAgent();
+      }, DESTROY_TIMEOUT_MS);
+    }
+  }
+}