fix lb mode

Author: baileympearson

src/mongo_client.ts

@@ -2,7 +2,7 @@ import { promises as fs } from 'fs';
 import type { TcpNetConnectOpts } from 'net';
 import type { ConnectionOptions as TLSConnectionOptions, TLSSocketOptions } from 'tls';
 
-import { type ServerCommandOptions, type TimeoutContext } from '.';
+import { type ServerCommandOptions, type TimeoutContext, TopologyType } from '.';
 import { type BSONSerializeOptions, type Document, resolveBSONOptions } from './bson';
 import { ChangeStream, type ChangeStreamDocument, type ChangeStreamOptions } from './change_stream';
 import type { AutoEncrypter, AutoEncryptionOptions } from './client-side-encryption/auto_encrypter';
@@ -795,11 +795,11 @@ export class MongoClient extends TypedEventEmitter<MongoClientEvents> implements
       return;
     }
 
-    const topologyDescription = this.topology.description;
-    const areSessionsSupported = topologyDescription.logicalSessionTimeoutMinutes != null;
-
-    if (areSessionsSupported) {
-      await endSessions(this);
+    const {
+      description: { type, logicalSessionTimeoutMinutes }
+    } = this.topology;
+    if (type === TopologyType.LoadBalanced || logicalSessionTimeoutMinutes != null) {
+      await endSessions(this, this.topology);
     }
 
     // clear out references to old topology
@@ -813,7 +813,10 @@ export class MongoClient extends TypedEventEmitter<MongoClientEvents> implements
       await encrypter.close(this);
     }
 
-    async function endSessions(client: MongoClient) {
+    async function endSessions(
+      client: MongoClient,
+      { description: topologyDescription }: Topology
+    ) {
       // If we would attempt to select a server and get nothing back we short circuit
       // to avoid the server selection timeout.
       const selector = readPreferenceServerSelector(ReadPreference.primaryPreferred);

src/sdam/topology.ts

@@ -393,6 +393,13 @@ export class Topology extends TypedEventEmitter<TopologyEvents> {
     return this.s.options.serverApi;
   }
 
+  get supportsSessions(): boolean {
+    return (
+      this.description.type === TopologyType.LoadBalanced ||
+      this.description.logicalSessionTimeoutMinutes != null
+    );
+  }
+
   /** Initiate server connect */
   async connect(options?: ConnectOptions): Promise<Topology> {
     this.connectionLock ??= this._connect(options);