fix(NODE-6355): respect utf8 validation options when iterating cursors

src/cmap/wire_protocol/on_demand/document.ts

@@ -1,15 +1,16 @@
 import {
   Binary,
-  BSON,
   type BSONElement,
   BSONError,
   type BSONSerializeOptions,
   BSONType,
+  deserialize,
   getBigInt64LE,
   getFloat64LE,
   getInt32LE,
   ObjectId,
   parseToElementsToArray,
+  pluckBSONSerializeOptions,
   Timestamp,
   toUTF8
 } from '../../../bson';
@@ -330,11 +331,23 @@ export class OnDemandDocument {
    * @param options - BSON deserialization options
    */
   public toObject(options?: BSONSerializeOptions): Record<string, any> {
-    return BSON.deserialize(this.bson, {
-      ...options,
+    const exactBSONOptions = {
+      ...pluckBSONSerializeOptions(options ?? {}),
+      validation: this.parseBsonSerializationOptions(options),
       index: this.offset,
       allowObjectSmallerThanBufferSize: true
-    });
+    };
+    return deserialize(this.bson, exactBSONOptions);
+  }
+
+  private parseBsonSerializationOptions(options?: { enableUtf8Validation?: boolean }): {
+    utf8: { writeErrors: false } | false;
+  } {
+    const enableUtf8Validation = options?.enableUtf8Validation;
+    if (enableUtf8Validation === false) {
+      return { utf8: false };
+    }
+    return { utf8: { writeErrors: false } };
   }
 
   /** Returns this document's bytes only */

src/cmap/wire_protocol/responses.ts

@@ -5,7 +5,6 @@ import {
   type Document,
   Long,
   parseToElementsToArray,
-  pluckBSONSerializeOptions,
   type Timestamp
 } from '../../bson';
 import { MongoUnexpectedServerResponseError } from '../../error';
@@ -166,24 +165,6 @@ export class MongoDBResponse extends OnDemandDocument {
     }
     return this.clusterTime ?? null;
   }
-
-  public override toObject(options?: BSONSerializeOptions): Record<string, any> {
-    const exactBSONOptions = {
-      ...pluckBSONSerializeOptions(options ?? {}),
-      validation: this.parseBsonSerializationOptions(options)
-    };
-    return super.toObject(exactBSONOptions);
-  }
-
-  private parseBsonSerializationOptions(options?: { enableUtf8Validation?: boolean }): {
-    utf8: { writeErrors: false } | false;
-  } {
-    const enableUtf8Validation = options?.enableUtf8Validation;
-    if (enableUtf8Validation === false) {
-      return { utf8: false };
-    }
-    return { utf8: { writeErrors: false } };
-  }
 }
 
 /** @internal */

test/integration/node-specific/bson-options/utf8_validation.test.ts

@@ -1,11 +1,16 @@
 import { expect } from 'chai';
+import * as net from 'net';
 import * as sinon from 'sinon';
+import { inspect } from 'util';
 
 import {
   BSON,
+  BSONError,
+  type Collection,
+  deserialize,
   type MongoClient,
-  MongoDBResponse,
   MongoServerError,
+  OnDemandDocument,
   OpMsgResponse
 } from '../../../mongodb';
 
@@ -23,12 +28,12 @@ describe('class MongoDBResponse', () => {
   let bsonSpy: sinon.SinonSpy;
 
   beforeEach(() => {
-    bsonSpy = sinon.spy(MongoDBResponse.prototype, 'parseBsonSerializationOptions');
+    // @ts-expect-error private function
+    bsonSpy = sinon.spy(OnDemandDocument.prototype, 'parseBsonSerializationOptions');
   });
 
   afterEach(() => {
     bsonSpy?.restore();
-    // @ts-expect-error: Allow this to be garbage collected
     bsonSpy = null;
   });
 
@@ -153,3 +158,180 @@ describe('class MongoDBResponse', () => {
     }
   );
 });
+
+describe('utf8 validation with cursors', function () {
+  let client: MongoClient;
+  let collection: Collection;
+
+  /**
+   * Inserts a document with malformed utf8 bytes.  This method spies on socket.write, and then waits
+   * for an OP_MSG payload corresponding to `collection.insertOne({ field: 'é' })`, and then modifies the
+   * bytes of the character 'é', to produce invalid utf8.
+   */
+  async function insertDocumentWithInvalidUTF8() {
+    const stub = sinon.stub(net.Socket.prototype, 'write').callsFake(function (...args) {
+      const providedBuffer = args[0].toString('hex');
+      const targetBytes = Buffer.from(document.field, 'utf-8').toString('hex');
+
+      if (providedBuffer.includes(targetBytes)) {
+        if (providedBuffer.split(targetBytes).length !== 2) {
+          sinon.restore();
+          const message = `too many target bytes sequences: received ${providedBuffer.split(targetBytes).length}\n.  command: ${inspect(deserialize(args[0]), { depth: Infinity })}`;
+          throw new Error(message);
+        }
+        const buffer = Buffer.from(providedBuffer.replace(targetBytes, 'c301'.repeat(8)), 'hex');
+        const result = stub.wrappedMethod.apply(this, [buffer]);
+        sinon.restore();
+        return result;
+      }
+      const result = stub.wrappedMethod.apply(this, args);
+      return result;
+    });
+
+    const document = {
+      field: 'é'.repeat(8)
+    };
+
+    await collection.insertOne(document);
+
+    sinon.restore();
+  }
+
+  beforeEach(async function () {
+    client = this.configuration.newClient();
+    await client.connect();
+    const db = client.db('test');
+    collection = db.collection('invalidutf');
+
+    await collection.deleteMany({});
+    await insertDocumentWithInvalidUTF8();
+  });
+
+  afterEach(async function () {
+    sinon.restore();
+    await client.close();
+  });
+
+  context('when utf-8 validation is explicitly disabled', function () {
+    it('documents can be read using a for-await loop without errors', async function () {
+      for await (const _doc of collection.find({}, { enableUtf8Validation: false }));
+    });
+    it('documents can be read using next() without errors', async function () {
+      const cursor = collection.find({}, { enableUtf8Validation: false });
+
+      while (await cursor.hasNext()) {
+        await cursor.next();
+      }
+    });
+
+    it('documents can be read using toArray() without errors', async function () {
+      const cursor = collection.find({}, { enableUtf8Validation: false });
+      await cursor.toArray();
+    });
+
+    it('documents can be read using .stream() without errors', async function () {
+      const cursor = collection.find({}, { enableUtf8Validation: false });
+      await cursor.stream().toArray();
+    });
+
+    it('documents can be read with tryNext() without error', async function () {
+      const cursor = collection.find({}, { enableUtf8Validation: false });
+
+      while (await cursor.hasNext()) {
+        await cursor.tryNext();
+      }
+    });
+  });
+
+  async function expectReject(fn: () => Promise<void>) {
+    try {
+      await fn();
+      expect.fail('expected the provided callback function to reject, but it did not.');
+    } catch (error) {
+      expect(error).to.match(/Invalid UTF-8 string in BSON document/);
+      expect(error).to.be.instanceOf(BSONError);
+    }
+  }
+
+  context('when utf-8 validation is explicitly enabled', function () {
+    it('a for-await loop throw a BSON error', async function () {
+      await expectReject(async () => {
+        for await (const _doc of collection.find({}, { enableUtf8Validation: true }));
+      });
+    });
+    it('next() throws a BSON error', async function () {
+      await expectReject(async () => {
+        const cursor = collection.find({}, { enableUtf8Validation: true });
+
+        while (await cursor.hasNext()) {
+          await cursor.next();
+        }
+      });
+    });
+
+    it('toArray() throws a BSON error', async function () {
+      await expectReject(async () => {
+        const cursor = collection.find({}, { enableUtf8Validation: true });
+        await cursor.toArray();
+      });
+    });
+
+    it('.stream() throws a BSONError', async function () {
+      await expectReject(async () => {
+        const cursor = collection.find({}, { enableUtf8Validation: true });
+        await cursor.stream().toArray();
+      });
+    });
+
+    it('tryNext() throws a BSONError', async function () {
+      await expectReject(async () => {
+        const cursor = collection.find({}, { enableUtf8Validation: true });
+
+        while (await cursor.hasNext()) {
+          await cursor.tryNext();
+        }
+      });
+    });
+  });
+
+  context('utf-8 validation defaults to enabled', function () {
+    it('a for-await loop throw a BSON error', async function () {
+      await expectReject(async () => {
+        for await (const _doc of collection.find({}));
+      });
+    });
+    it('next() throws a BSON error', async function () {
+      await expectReject(async () => {
+        const cursor = collection.find({});
+
+        while (await cursor.hasNext()) {
+          await cursor.next();
+        }
+      });
+    });
+
+    it('toArray() throws a BSON error', async function () {
+      await expectReject(async () => {
+        const cursor = collection.find({});
+        await cursor.toArray();
+      });
+    });
+
+    it('.stream() throws a BSONError', async function () {
+      await expectReject(async () => {
+        const cursor = collection.find({});
+        await cursor.stream().toArray();
+      });
+    });
+
+    it('tryNext() throws a BSONError', async function () {
+      await expectReject(async () => {
+        const cursor = collection.find({}, { enableUtf8Validation: true });
+
+        while (await cursor.hasNext()) {
+          await cursor.tryNext();
+        }
+      });
+    });
+  });
+});