feat(NODE-6245): add keepAliveInitialDelay config

src/cmap/connect.ts

@@ -289,6 +289,7 @@ export const LEGAL_TLS_SOCKET_OPTIONS = [
 export const LEGAL_TCP_SOCKET_OPTIONS = [
   'autoSelectFamily',
   'autoSelectFamilyAttemptTimeout',
+  'keepAliveInitialDelay',
   'family',
   'hints',
   'localAddress',
@@ -376,7 +377,7 @@ export async function makeSocket(options: MakeConnectionOptions): Promise<Stream
     socket = net.createConnection(parseConnectOptions(options));
   }
 
-  socket.setKeepAlive(true, 300000);
+  socket.setKeepAlive(true, options.keepAliveInitialDelay ?? 120000);
   socket.setTimeout(connectTimeoutMS);
   socket.setNoDelay(noDelay);
 

src/connection_string.ts

@@ -872,6 +872,9 @@ export const OPTIONS = {
       return wc;
     }
   },
+  keepAliveInitialDelay: {
+    type: 'uint'
+  },
   loadBalanced: {
     default: false,
     type: 'boolean'

src/mongo_client.ts

@@ -115,7 +115,12 @@ export type SupportedTLSSocketOptions = Pick<
 
 /** @public */
 export type SupportedSocketOptions = Pick<
-  TcpNetConnectOpts & { autoSelectFamily?: boolean; autoSelectFamilyAttemptTimeout?: number },
+  TcpNetConnectOpts & {
+    autoSelectFamily?: boolean;
+    autoSelectFamilyAttemptTimeout?: number;
+    /** Node.JS socket option to set the time the first keepalive probe is sent on an idle socket. */
+    keepAliveInitialDelay?: number;
+  },
   (typeof LEGAL_TCP_SOCKET_OPTIONS)[number]
 >;
 

test/integration/node-specific/mongo_client.test.ts

@@ -1,6 +1,7 @@
 import { expect } from 'chai';
 import { once } from 'events';
 import * as net from 'net';
+import { Socket } from 'net';
 import * as sinon from 'sinon';
 
 import {
@@ -135,6 +136,82 @@ describe('class MongoClient', function () {
     expect(error).to.be.instanceOf(MongoServerSelectionError);
   });
 
+  describe('#connect', function () {
+    context('when keepAliveInitialDelay is provided', function () {
+      context('when the value is 0', function () {
+        const options = { keepAliveInitialDelay: 0 };
+        let client;
+        let spy;
+
+        beforeEach(async function () {
+          spy = sinon.spy(Socket.prototype, 'setKeepAlive');
+          client = this.configuration.newClient(options);
+          await client.connect();
+        });
+
+        afterEach(async function () {
+          await client?.close();
+          spy.restore();
+        });
+
+        it('passes through the option', function () {
+          expect(spy).to.have.been.calledWith(true, 0);
+        });
+      });
+
+      context('when the value is positive', function () {
+        const options = { keepAliveInitialDelay: 100 };
+        let client;
+        let spy;
+
+        beforeEach(async function () {
+          spy = sinon.spy(Socket.prototype, 'setKeepAlive');
+          client = this.configuration.newClient(options);
+          await client.connect();
+        });
+
+        afterEach(async function () {
+          await client?.close();
+          spy.restore();
+        });
+
+        it('passes through the option', function () {
+          expect(spy).to.have.been.calledWith(true, 100);
+        });
+      });
+
+      context('when the value is negative', function () {
+        const options = { keepAliveInitialDelay: -100 };
+
+        it('raises an error', function () {
+          expect(() => {
+            this.configuration.newClient(options);
+          }).to.throw(/keepAliveInitialDelay can only be a positive int value/);
+        });
+      });
+    });
+
+    context('when keepAliveInitialDelay is not provided', function () {
+      let client;
+      let spy;
+
+      beforeEach(async function () {
+        spy = sinon.spy(Socket.prototype, 'setKeepAlive');
+        client = this.configuration.newClient();
+        await client.connect();
+      });
+
+      afterEach(async function () {
+        await client?.close();
+        spy.restore();
+      });
+
+      it('sets keepalive to 120000', function () {
+        expect(spy).to.have.been.calledWith(true, 120000);
+      });
+    });
+  });
+
   it('Should correctly pass through appname', {
     metadata: {
       requires: {