From d63bf6fae303ec921335c363865e86c912286d6c Mon Sep 17 00:00:00 2001
From: Warren James <warren.james@mongodb.com>
Date: Thu, 12 Sep 2024 11:52:46 -0400
Subject: [PATCH] fix(NODE-6367): enable mixed use of iteration APIs (#4234)

---
 src/cursor/abstract_cursor.ts                 |   2 +-
 .../crud/find_cursor_methods.test.js          | 344 ++++++++++++++++++
 2 files changed, 345 insertions(+), 1 deletion(-)

diff --git a/src/cursor/abstract_cursor.ts b/src/cursor/abstract_cursor.ts
index 54447fe70e..eb2e6e7aeb 100644
--- a/src/cursor/abstract_cursor.ts
+++ b/src/cursor/abstract_cursor.ts
@@ -309,7 +309,7 @@ export abstract class AbstractCursor<
     return bufferedDocs;
   }
   async *[Symbol.asyncIterator](): AsyncGenerator<TSchema, void, void> {
-    if (this.isClosed) {
+    if (this.closed) {
       return;
     }
 
diff --git a/test/integration/crud/find_cursor_methods.test.js b/test/integration/crud/find_cursor_methods.test.js
index 6e7066d5fa..42eeda3e81 100644
--- a/test/integration/crud/find_cursor_methods.test.js
+++ b/test/integration/crud/find_cursor_methods.test.js
@@ -1,6 +1,7 @@
 'use strict';
 const { expect } = require('chai');
 const { filterForCommands } = require('../shared');
+const { promiseWithResolvers, MongoCursorExhaustedError } = require('../../mongodb');
 
 describe('Find Cursor', function () {
   let client;
@@ -361,4 +362,347 @@ describe('Find Cursor', function () {
       }
     });
   });
+
+  describe('mixing iteration APIs', function () {
+    let client;
+    let collection;
+    let cursor;
+
+    beforeEach(async function () {
+      client = this.configuration.newClient();
+      await client.connect();
+      collection = client.db('next-symbolasynciterator').collection('bar');
+      await collection.deleteMany({}, { writeConcern: { w: 'majority' } });
+      await collection.insertMany([{ a: 1 }, { a: 2 }], { writeConcern: { w: 'majority' } });
+    });
+
+    afterEach(async function () {
+      await cursor.close();
+      await client.close();
+    });
+
+    context('when all documents are retrieved in the first batch', function () {
+      it('allows combining iteration modes', async function () {
+        let count = 0;
+        cursor = collection.find().map(doc => {
+          count++;
+          return doc;
+        });
+
+        await cursor.next();
+        // eslint-disable-next-line no-unused-vars
+        for await (const _ of cursor) {
+          /* empty */
+        }
+
+        expect(count).to.equal(2);
+      });
+
+      it('works with next + next() loop', async function () {
+        let count = 0;
+        cursor = collection.find().map(doc => {
+          count++;
+          return doc;
+        });
+
+        await cursor.next();
+
+        let doc;
+        while ((doc = (await cursor.next()) && doc != null)) {
+          /** empty */
+        }
+
+        expect(count).to.equal(2);
+      });
+
+      context('when next() is called in a loop after a single invocation', function () {
+        it('iterates over all documents', async function () {
+          let count = 0;
+          cursor = collection.find({}).map(doc => {
+            count++;
+            return doc;
+          });
+
+          await cursor.next();
+
+          let doc;
+          while ((doc = (await cursor.next()) && doc != null)) {
+            /** empty */
+          }
+
+          expect(count).to.equal(2);
+        });
+      });
+
+      context(
+        'when cursor.next() is called after cursor.stream() is partially iterated',
+        function () {
+          it('returns null', async function () {
+            cursor = collection.find({});
+
+            const stream = cursor.stream();
+            const { promise, resolve, reject } = promiseWithResolvers();
+
+            stream.once('data', v => {
+              resolve(v);
+            });
+
+            stream.once('error', v => {
+              reject(v);
+            });
+            await promise;
+
+            expect(await cursor.next()).to.be.null;
+          });
+        }
+      );
+
+      context('when cursor.tryNext() is called after cursor.stream()', function () {
+        it('returns null', async function () {
+          cursor = collection.find({});
+
+          const stream = cursor.stream();
+          const { promise, resolve, reject } = promiseWithResolvers();
+
+          stream.once('data', v => {
+            resolve(v);
+          });
+
+          stream.once('error', v => {
+            reject(v);
+          });
+          await promise;
+
+          expect(await cursor.tryNext()).to.be.null;
+        });
+      });
+
+      context(
+        'when cursor.[Symbol.asyncIterator] is called after cursor.stream() is partly iterated',
+        function () {
+          it('returns an empty iterator', async function () {
+            cursor = collection.find({});
+
+            const stream = cursor.stream();
+            const { promise, resolve, reject } = promiseWithResolvers();
+
+            stream.once('data', v => {
+              resolve(v);
+            });
+
+            stream.once('error', v => {
+              reject(v);
+            });
+            await promise;
+
+            let count = 0;
+            // eslint-disable-next-line no-unused-vars
+            for await (const _ of cursor) {
+              count++;
+            }
+
+            expect(count).to.equal(0);
+          });
+        }
+      );
+
+      context('when cursor.readBufferedDocuments() is called after cursor.next()', function () {
+        it('returns an array with remaining buffered documents', async function () {
+          cursor = collection.find({});
+
+          await cursor.next();
+          const docs = cursor.readBufferedDocuments();
+
+          expect(docs).to.have.lengthOf(1);
+        });
+      });
+
+      context('when cursor.next() is called after cursor.toArray()', function () {
+        it('returns null', async function () {
+          cursor = collection.find({});
+
+          await cursor.toArray();
+          expect(await cursor.next()).to.be.null;
+        });
+      });
+
+      context('when cursor.tryNext is called after cursor.toArray()', function () {
+        it('returns null', async function () {
+          cursor = collection.find({});
+
+          await cursor.toArray();
+          expect(await cursor.tryNext()).to.be.null;
+        });
+      });
+
+      context('when cursor.[Symbol.asyncIterator] is called after cursor.toArray()', function () {
+        it('should not iterate', async function () {
+          cursor = collection.find({});
+
+          await cursor.toArray();
+          // eslint-disable-next-line no-unused-vars
+          for await (const _ of cursor) {
+            expect.fail('should not iterate');
+          }
+        });
+      });
+
+      context('when cursor.readBufferedDocuments() is called after cursor.toArray()', function () {
+        it('return and empty array', async function () {
+          cursor = collection.find({});
+
+          await cursor.toArray();
+          expect(cursor.readBufferedDocuments()).to.have.lengthOf(0);
+        });
+      });
+
+      context('when cursor.stream() is called after cursor.toArray()', function () {
+        it('returns an empty stream', async function () {
+          cursor = collection.find({});
+          await cursor.toArray();
+
+          const s = cursor.stream();
+          const { promise, resolve, reject } = promiseWithResolvers();
+
+          s.once('data', d => {
+            reject(d);
+          });
+
+          s.once('end', d => {
+            resolve(d);
+          });
+
+          expect(await promise).to.be.undefined;
+        });
+      });
+    });
+
+    context('when there are documents that are not retrieved in the first batch', function () {
+      it('allows combining next() and for await syntax', async function () {
+        let count = 0;
+        cursor = collection.find({}, { batchSize: 1 }).map(doc => {
+          count++;
+          return doc;
+        });
+
+        await cursor.next();
+        // eslint-disable-next-line no-unused-vars
+        for await (const _ of cursor) {
+          /* empty */
+        }
+
+        expect(count).to.equal(2);
+      });
+
+      context(
+        'when a cursor is partially iterated with for await and then .next() is called',
+        function () {
+          it('throws a MongoCursorExhaustedError', async function () {
+            cursor = collection.find({}, { batchSize: 1 });
+
+            // eslint-disable-next-line no-unused-vars
+            for await (const _ of cursor) {
+              /* empty */
+              break;
+            }
+
+            const maybeError = await cursor.next().then(
+              () => null,
+              e => e
+            );
+            expect(maybeError).to.be.instanceof(MongoCursorExhaustedError);
+          });
+        }
+      );
+
+      context('when next() is called in a loop after a single invocation', function () {
+        it('iterates over all documents', async function () {
+          let count = 0;
+          cursor = collection.find({}, { batchSize: 1 }).map(doc => {
+            count++;
+            return doc;
+          });
+
+          await cursor.next();
+
+          let doc;
+          while ((doc = (await cursor.next()) && doc != null)) {
+            /** empty */
+          }
+
+          expect(count).to.equal(2);
+        });
+      });
+
+      context('when cursor.readBufferedDocuments() is called after cursor.next()', function () {
+        it('returns an empty array', async function () {
+          cursor = collection.find({}, { batchSize: 1 });
+
+          await cursor.next();
+          const docs = cursor.readBufferedDocuments();
+
+          expect(docs).to.have.lengthOf(0);
+        });
+      });
+
+      context('when cursor.next() is called after cursor.toArray()', function () {
+        it('returns null', async function () {
+          cursor = collection.find({}, { batchSize: 1 });
+
+          await cursor.toArray();
+          expect(await cursor.next()).to.be.null;
+        });
+      });
+
+      context('when cursor.tryNext is called after cursor.toArray()', function () {
+        it('returns null', async function () {
+          cursor = collection.find({}, { batchSize: 1 });
+
+          await cursor.toArray();
+          expect(await cursor.tryNext()).to.be.null;
+        });
+      });
+
+      context('when cursor.[Symbol.asyncIterator] is called after cursor.toArray()', function () {
+        it('should not iterate', async function () {
+          cursor = collection.find({}, { batchSize: 1 });
+
+          await cursor.toArray();
+          // eslint-disable-next-line no-unused-vars
+          for await (const _ of cursor) {
+            expect.fail('should not iterate');
+          }
+        });
+      });
+
+      context('when cursor.readBufferedDocuments() is called after cursor.toArray()', function () {
+        it('return and empty array', async function () {
+          cursor = collection.find({}, { batchSize: 1 });
+
+          await cursor.toArray();
+          expect(cursor.readBufferedDocuments()).to.have.lengthOf(0);
+        });
+      });
+
+      context('when cursor.stream() is called after cursor.toArray()', function () {
+        it('returns an empty stream', async function () {
+          cursor = collection.find({}, { batchSize: 1 });
+          await cursor.toArray();
+
+          const s = cursor.stream();
+          const { promise, resolve, reject } = promiseWithResolvers();
+
+          s.once('data', d => {
+            reject(d);
+          });
+
+          s.once('end', d => {
+            resolve(d);
+          });
+
+          expect(await promise).to.be.undefined;
+        });
+      });
+    });
+  });
 });