fix: old servers

Author: nbbeeken

src/cmap/wire_protocol/responses.ts

@@ -129,10 +129,10 @@ export class CursorResponse extends MongoDBResponse {
   public id: Long | null = null;
   public ns: MongoDBNamespace | null = null;
   public documents: any | null = null;
+  public batchSize = 0;
 
   private batch: OnDemandDocument | null = null;
   private values: Generator<OnDemandDocument, void, void> | null = null;
-  private batchSize = 0;
   private iterated = 0;
 
   constructor(b: Uint8Array, o?: number, a?: boolean) {
@@ -184,7 +184,7 @@ export class CursorResponse extends MongoDBResponse {
     });
   }
 
-  static isCursorResponse(value: unknown): value is CursorResponse {
+  static override is(value: unknown): value is CursorResponse {
     return value instanceof CursorResponse;
   }
 }

src/cursor/abstract_cursor.ts

@@ -657,7 +657,7 @@ export abstract class AbstractCursor<
       const state = await this._initialize(this[kSession]);
       const response = state.response;
       this[kServer] = state.server;
-      if (CursorResponse.isCursorResponse(response)) {
+      if (CursorResponse.is(response)) {
         this[kId] = response.id;
         if (response.ns) this[kNamespace] = response.ns;
         this[kDocuments] = response.documents;
@@ -798,7 +798,7 @@ async function next<T>(
 
     try {
       const response = await cursor.getMore(batchSize);
-      if (CursorResponse.isCursorResponse(response)) {
+      if (CursorResponse.is(response)) {
         cursor[kId] = response.id;
         cursor[kDocuments] = response.documents;
       } else if (response) {

src/cursor/find_cursor.ts

@@ -1,4 +1,5 @@
 import { type Document, Long } from '../bson';
+import { CursorResponse } from '../cmap/wire_protocol/responses';
 import { MongoInvalidArgumentError, MongoTailableCursorError } from '../error';
 import { type ExplainVerbosityLike } from '../explain';
 import type { MongoClient } from '../mongo_client';
@@ -34,7 +35,7 @@ export class FindCursor<TSchema = any> extends AbstractCursor<TSchema> {
   /** @internal */
   [kFilter]: Document;
   /** @internal */
-  [kNumReturned]?: number;
+  [kNumReturned] = 0;
   /** @internal */
   [kBuiltOptions]: FindOptions;
 
@@ -78,7 +79,9 @@ export class FindCursor<TSchema = any> extends AbstractCursor<TSchema> {
     const response = await executeOperation(this.client, findOperation);
 
     // the response is not a cursor when `explain` is enabled
-    this[kNumReturned] = response.cursor?.firstBatch?.length;
+    if (CursorResponse.is(response)) {
+      this[kNumReturned] = response.batchSize;
+    }
 
     // TODO: NODE-2882
     return { server: findOperation.server, session, response };
@@ -113,8 +116,8 @@ export class FindCursor<TSchema = any> extends AbstractCursor<TSchema> {
 
     const response = await super.getMore(batchSize, true);
     // TODO: wrap this in some logic to prevent it from happening if we don't need this support
-    if (response) {
-      this[kNumReturned] = this[kNumReturned] + response.batchLength;
+    if (CursorResponse.is(response)) {
+      this[kNumReturned] = this[kNumReturned] + response.batchSize;
     }
 
     return response;