From 981226c8d49eda6d03b1e2d3bee45b2420e40832 Mon Sep 17 00:00:00 2001
From: Hana Pearlman <hana.pearlman@mongodb.com>
Date: Fri, 16 Oct 2020 15:34:41 -0400
Subject: [PATCH] re-connect topology on client connect

---
 src/mongo_client.ts                | 16 +++-------------
 src/operations/connect.ts          | 21 ++++++++++++---------
 test/functional/connection.test.js |  6 +++---
 test/functional/sessions.test.js   |  4 ++--
 4 files changed, 20 insertions(+), 27 deletions(-)

diff --git a/src/mongo_client.ts b/src/mongo_client.ts
index 2ede2f64d2b..c5a275f8636 100644
--- a/src/mongo_client.ts
+++ b/src/mongo_client.ts
@@ -349,29 +349,19 @@ export class MongoClient extends EventEmitter implements OperationParent {
     const force = typeof forceOrCallback === 'boolean' ? forceOrCallback : false;
 
     return maybePromise(callback, cb => {
-      const completeClose = (err?: AnyError) => {
-        // clear out references to old topology
-        this.topology = undefined;
-        this.s.dbCache = new Map();
-        this.s.sessions = new Set();
-
-        cb(err);
-      };
-
       if (this.topology == null) {
-        completeClose();
-        return;
+        return cb();
       }
 
       const topology = this.topology;
       topology.close({ force }, err => {
         const autoEncrypter = topology.s.options.autoEncrypter;
         if (!autoEncrypter) {
-          completeClose(err);
+          cb(err);
           return;
         }
 
-        autoEncrypter.teardown(force, err2 => completeClose(err || err2));
+        autoEncrypter.teardown(force, err2 => cb(err || err2));
       });
     });
   }
diff --git a/src/operations/connect.ts b/src/operations/connect.ts
index c99e5c81b08..0f9b89c29cf 100644
--- a/src/operations/connect.ts
+++ b/src/operations/connect.ts
@@ -361,18 +361,21 @@ function createTopology(mongoClient: MongoClient, options: MongoClientOptions, c
     options.autoEncrypter = new AutoEncrypter(mongoClient, mongoCryptOptions);
   }
 
-  // Create the topology
-  const topology = new Topology(options.servers, options);
-  registerDeprecatedEventNotifiers(mongoClient);
+  // Create the topology or re-use a topology that was previously created
+  if (!mongoClient.topology) {
+    const topology = new Topology(options.servers, options);
+    registerDeprecatedEventNotifiers(mongoClient);
 
-  // Add listeners
-  addListeners(mongoClient, topology);
+    // Add listeners
+    addListeners(mongoClient, topology);
 
-  // Propagate the events to the client
-  relayEvents(mongoClient, topology);
+    // Propagate the events to the client
+    relayEvents(mongoClient, topology);
 
-  // Assign the topology
-  mongoClient.topology = topology;
+    // Assign the topology
+    mongoClient.topology = topology;
+  }
+  const topology = mongoClient.topology;
 
   // initialize CSFLE if requested
   if (options.autoEncrypter) {
diff --git a/test/functional/connection.test.js b/test/functional/connection.test.js
index 79497eb18d7..0d92fd16785 100644
--- a/test/functional/connection.test.js
+++ b/test/functional/connection.test.js
@@ -280,8 +280,8 @@ describe('Connection', function () {
     withClient(function (client, done) {
       expect(client.isConnected()).to.be.true;
 
-      const collection = () => client.db('testReconnect').collection('test');
-      collection().insertOne({ a: 1 }, (err, result) => {
+      const collection = client.db('testReconnect').collection('test');
+      collection.insertOne({ a: 1 }, (err, result) => {
         expect(err).to.not.exist;
         expect(result).to.exist;
 
@@ -293,7 +293,7 @@ describe('Connection', function () {
             expect(err).to.not.exist;
             expect(client.isConnected()).to.be.true;
 
-            collection().insertOne({ b: 2 }, (err, result) => {
+            collection.insertOne({ b: 2 }, (err, result) => {
               expect(err).to.not.exist;
               expect(result).to.exist;
               expect(client.topology.isDestroyed()).to.be.false;
diff --git a/test/functional/sessions.test.js b/test/functional/sessions.test.js
index eb25a46ec87..2751019bfb9 100644
--- a/test/functional/sessions.test.js
+++ b/test/functional/sessions.test.js
@@ -123,7 +123,7 @@ describe('Sessions', function () {
               // verify that the `endSessions` command was sent
               const lastCommand = test.commands.started[test.commands.started.length - 1];
               expect(lastCommand.commandName).to.equal('endSessions');
-              expect(client.topology).to.not.exist;
+              expect(client.topology.s.sessionPool.sessions).to.have.length(0);
             });
         });
       });
@@ -143,7 +143,7 @@ describe('Sessions', function () {
             // verify that the `endSessions` command was sent
             const lastCommand = test.commands.started[test.commands.started.length - 1];
             expect(lastCommand.commandName).to.equal('endSessions');
-            expect(client.topology).to.not.exist;
+            expect(client.topology.s.sessionPool.sessions).to.have.length(0);
           });
       });
     }