fix(NODE-4999): Write Concern 0 Must Not Affect Read Operations (#3541)

Co-authored-by: Neal Beeken <neal.beeken@mongodb.com>

src/change_stream.ts

@@ -586,7 +586,8 @@ export class ChangeStream<
     super();
 
     this.pipeline = pipeline;
-    this.options = options;
+    this.options = { ...options };
+    delete this.options.writeConcern;
 
     if (parent instanceof Collection) {
       this.type = CHANGE_DOMAIN_TYPES.COLLECTION;

src/operations/aggregate.ts

@@ -44,7 +44,7 @@ export class AggregateOperation<T = Document> extends CommandOperation<T> {
   constructor(ns: MongoDBNamespace, pipeline: Document[], options?: AggregateOptions) {
     super(undefined, { ...options, dbName: ns.db });
 
-    this.options = options ?? {};
+    this.options = { ...options };
 
     // Covers when ns.collection is null, undefined or the empty string, use DB_AGGREGATE_COLLECTION
     this.target = ns.collection || DB_AGGREGATE_COLLECTION;
@@ -65,6 +65,8 @@ export class AggregateOperation<T = Document> extends CommandOperation<T> {
 
     if (this.hasWriteStage) {
       this.trySecondaryWrite = true;
+    } else {
+      delete this.options.writeConcern;
     }
 
     if (this.explain && this.writeConcern) {

src/operations/find.ts

@@ -77,7 +77,8 @@ export class FindOperation extends CommandOperation<Document> {
   ) {
     super(collection, options);
 
-    this.options = options;
+    this.options = { ...options };
+    delete this.options.writeConcern;
     this.ns = ns;
 
     if (typeof filter !== 'object' || Array.isArray(filter)) {

src/operations/indexes.ts

@@ -395,7 +395,8 @@ export class ListIndexesOperation extends CommandOperation<Document> {
   constructor(collection: Collection, options?: ListIndexesOptions) {
     super(collection, options);
 
-    this.options = options ?? {};
+    this.options = { ...options };
+    delete this.options.writeConcern;
     this.collectionNamespace = collection.s.namespace;
   }
 

src/operations/list_collections.ts

@@ -28,7 +28,8 @@ export class ListCollectionsOperation extends CommandOperation<string[]> {
   constructor(db: Db, filter: Document, options?: ListCollectionsOptions) {
     super(db, options);
 
-    this.options = options ?? {};
+    this.options = { ...options };
+    delete this.options.writeConcern;
     this.db = db;
     this.filter = filter;
     this.nameOnly = !!this.options.nameOnly;

test/integration/read-write-concern/write_concern.test.ts

@@ -0,0 +1,174 @@
+import { expect } from 'chai';
+import { on, once } from 'events';
+
+import { Collection, Db, LEGACY_HELLO_COMMAND, MongoClient } from '../../mongodb';
+import * as mock from '../../tools/mongodb-mock/index';
+
+describe('Write Concern', function () {
+  it('should respect writeConcern from uri', function (done) {
+    const client = this.configuration.newClient(
+      `${this.configuration.url()}&w=0&monitorCommands=true`
+    );
+    const events: any[] = [];
+    client.on('commandStarted', event => {
+      if (event.commandName === 'insert') {
+        events.push(event);
+      }
+    });
+
+    expect(client.writeConcern).to.eql({ w: 0 });
+    client
+      .db('test')
+      .collection('test')
+      .insertOne({ a: 1 }, (err, result) => {
+        expect(err).to.not.exist;
+        expect(result).to.exist;
+        expect(events).to.be.an('array').with.lengthOf(1);
+        expect(events[0]).to.containSubset({
+          commandName: 'insert',
+          command: {
+            writeConcern: { w: 0 }
+          }
+        });
+        client.close(done);
+      });
+  });
+
+  describe('mock server write concern test', () => {
+    let server;
+    before(() => {
+      return mock.createServer().then(s => {
+        server = s;
+      });
+    });
+
+    after(() => mock.cleanup());
+
+    // TODO(NODE-3816): the mock server response is looking for writeConcern on all messages, but endSessions doesn't have it
+    it.skip('should pipe writeConcern from client down to API call', function () {
+      server.setMessageHandler(request => {
+        if (request.document && request.document[LEGACY_HELLO_COMMAND]) {
+          return request.reply(mock.HELLO);
+        }
+        expect(request.document.writeConcern).to.exist;
+        expect(request.document.writeConcern.w).to.equal('majority');
+        return request.reply({ ok: 1 });
+      });
+
+      const uri = `mongodb://${server.uri()}`;
+      const client = new MongoClient(uri, { writeConcern: { w: 'majority' } });
+      return client
+        .connect()
+        .then(() => {
+          const db = client.db('wc_test');
+          const collection = db.collection('wc');
+
+          return collection.insertMany([{ a: 2 }]);
+        })
+        .then(() => {
+          return client.close();
+        });
+    });
+  });
+
+  context('when performing read operations', function () {
+    context('when writeConcern = 0', function () {
+      describe('cursor creating operations with a getMore', function () {
+        let client: MongoClient;
+        let db: Db;
+        let col: Collection;
+
+        beforeEach(async function () {
+          client = this.configuration.newClient({ writeConcern: { w: 0 } });
+          await client.connect();
+          db = client.db('writeConcernTest');
+          col = db.collection('writeConcernTest');
+
+          const docs: any[] = [];
+          for (let i = 0; i < 100; i++) {
+            docs.push({ a: i, b: i + 1 });
+          }
+
+          await col.insertMany(docs);
+        });
+
+        afterEach(async function () {
+          await db.dropDatabase();
+          await client.close();
+        });
+
+        it('succeeds on find', async function () {
+          const findResult = col.find({}, { batchSize: 2 });
+          const err = await findResult.toArray().catch(e => e);
+
+          expect(err).to.not.be.instanceOf(Error);
+        });
+
+        it('succeeds on listCollections', async function () {
+          const collections: any[] = [];
+          for (let i = 0; i < 10; i++) {
+            collections.push(`writeConcernTestCol${i + 1}`);
+          }
+
+          for (const colName of collections) {
+            await db.createCollection(colName).catch(() => null);
+          }
+
+          const cols = db.listCollections({}, { batchSize: 2 });
+
+          const err = await cols.toArray().catch(e => e);
+
+          expect(err).to.not.be.instanceOf(Error);
+        });
+
+        it('succeeds on aggregate', async function () {
+          const aggResult = col.aggregate([{ $match: { a: { $gte: 0 } } }], { batchSize: 2 });
+          const err = await aggResult.toArray().catch(e => e);
+
+          expect(err).to.not.be.instanceOf(Error);
+        });
+
+        it('succeeds on listIndexes', async function () {
+          await col.createIndex({ a: 1 });
+          await col.createIndex({ b: -1 });
+          await col.createIndex({ a: 1, b: -1 });
+
+          const listIndexesResult = col.listIndexes({ batchSize: 2 });
+          const err = await listIndexesResult.toArray().catch(e => e);
+
+          expect(err).to.not.be.instanceOf(Error);
+        });
+
+        it('succeeds on changeStream', {
+          metadata: { requires: { topology: 'replicaset' } },
+          async test() {
+            const changeStream = col.watch(undefined, { batchSize: 2 });
+            const changes = on(changeStream, 'change');
+            await once(changeStream.cursor, 'init');
+
+            await col.insertMany(
+              [
+                { a: 10 },
+                { a: 10 },
+                { a: 10 },
+                { a: 10 },
+                { a: 10 },
+                { a: 10 },
+                { a: 10 },
+                { a: 10 },
+                { a: 10 },
+                { a: 10 },
+                { a: 10 },
+                { a: 10 }
+              ],
+              { writeConcern: { w: 'majority' } }
+            );
+
+            const err = await changes.next().catch(e => e);
+            expect(err).to.not.be.instanceOf(Error);
+          }
+        });
+      });
+    });
+  });
+});

test/unit/operations/find.test.ts

@@ -21,15 +21,15 @@ describe('FindOperation', function () {
     const operation = new FindOperation(undefined, namespace, filter, options);
 
     it('sets the namespace', function () {
-      expect(operation.ns).to.equal(namespace);
+      expect(operation.ns).to.deep.equal(namespace);
     });
 
     it('sets options', function () {
-      expect(operation.options).to.equal(options);
+      expect(operation.options).to.deep.equal(options);
     });
 
     it('sets filter', function () {
-      expect(operation.filter).to.equal(filter);
+      expect(operation.filter).to.deep.equal(filter);
     });
   });