fix(ChangeStream): handle null changes

NODE-2626

Author: emadum

src/change_stream.ts

@@ -348,8 +348,8 @@ class ChangeStreamCursor extends Cursor {
 
   _initializeCursor(callback: Function) {
     super._initializeCursor((err?: any, result?: any) => {
-      if (err) {
-        callback(err);
+      if (err || result == null) {
+        callback(err, result);
         return;
       }
 
@@ -504,6 +504,11 @@ function waitForTopologyConnected(topology: any, options: any, callback: Functio
 function processNewChange(changeStream: any, change: any, callback?: Function) {
   const cursor = changeStream.cursor;
 
+  // a null change means the cursor has been notified, implicitly closing the change stream
+  if (change == null) {
+    changeStream.closed = true;
+  }
+
   if (changeStream.closed) {
     if (callback) callback(new MongoError('ChangeStream is closed'));
     return;

src/cursor/core_cursor.ts

@@ -473,50 +473,41 @@ class CoreCursor extends Readable {
       }
 
       const result = r.message;
-      if (result.queryFailure) {
-        return done(new MongoError(result.documents[0]), null);
-      }
 
-      // Check if we have a command cursor
-      if (
-        Array.isArray(result.documents) &&
-        result.documents.length === 1 &&
-        (!cursor.cmd.find || (cursor.cmd.find && cursor.cmd.virtual === false)) &&
-        (typeof result.documents[0].cursor !== 'string' ||
-          result.documents[0]['$err'] ||
-          result.documents[0]['errmsg'] ||
-          Array.isArray(result.documents[0].result))
-      ) {
-        // We have an error document, return the error
-        if (result.documents[0]['$err'] || result.documents[0]['errmsg']) {
-          return done(new MongoError(result.documents[0]), null);
+      if (Array.isArray(result.documents) && result.documents.length === 1) {
+        const document = result.documents[0];
+
+        if (result.queryFailure) {
+          return done(new MongoError(document), null);
         }
 
-        // We have a cursor document
-        if (result.documents[0].cursor != null && typeof result.documents[0].cursor !== 'string') {
-          const id = result.documents[0].cursor.id;
-          // If we have a namespace change set the new namespace for getmores
-          if (result.documents[0].cursor.ns) {
-            cursor.ns = result.documents[0].cursor.ns;
+        // Check if we have a command cursor
+        if (!cursor.cmd.find || (cursor.cmd.find && cursor.cmd.virtual === false)) {
+          // We have an error document, return the error
+          if (document.$err || document.errmsg) {
+            return done(new MongoError(document), null);
           }
-          // Promote id to long if needed
-          cursor.cursorState.cursorId = typeof id === 'number' ? Long.fromNumber(id) : id;
-          cursor.cursorState.lastCursorId = cursor.cursorState.cursorId;
-          cursor.cursorState.operationTime = result.documents[0].operationTime;
-
-          // If we have a firstBatch set it
-          if (Array.isArray(result.documents[0].cursor.firstBatch)) {
-            cursor.cursorState.documents = result.documents[0].cursor.firstBatch; //.reverse();
-          }
-
-          // Return after processing command cursor
-          return done(null, result);
-        }
 
-        if (Array.isArray(result.documents[0].result)) {
-          cursor.cursorState.documents = result.documents[0].result;
-          cursor.cursorState.cursorId = Long.ZERO;
-          return done(null, result);
+          // We have a cursor document
+          if (document.cursor != null && typeof document.cursor !== 'string') {
+            const id = document.cursor.id;
+            // If we have a namespace change set the new namespace for getmores
+            if (document.cursor.ns) {
+              cursor.ns = document.cursor.ns;
+            }
+            // Promote id to long if needed
+            cursor.cursorState.cursorId = typeof id === 'number' ? Long.fromNumber(id) : id;
+            cursor.cursorState.lastCursorId = cursor.cursorState.cursorId;
+            cursor.cursorState.operationTime = document.operationTime;
+
+            // If we have a firstBatch set it
+            if (Array.isArray(document.cursor.firstBatch)) {
+              cursor.cursorState.documents = document.cursor.firstBatch;
+            }
+
+            // Return after processing command cursor
+            return done(null, result);
+          }
         }
       }
 

test/functional/change_stream.test.js

@@ -2799,3 +2799,49 @@ describe('Change Stream Resume Error Tests', function() {
     })
   });
 });
+context('NODE-2626 - handle null changes without error', function() {
+  let mockServer;
+  afterEach(() => mock.cleanup());
+  beforeEach(() => mock.createServer().then(server => (mockServer = server)));
+  it('changeStream should close if cursor id for initial aggregate is Long.ZERO', function(done) {
+    mockServer.setMessageHandler(req => {
+      const doc = req.document;
+      if (doc.ismaster) {
+        return req.reply(mock.DEFAULT_ISMASTER_36);
+      }
+      if (doc.aggregate) {
+        return req.reply({
+          ok: 1,
+          cursor: {
+            id: Long.ZERO,
+            firstBatch: []
+          }
+        });
+      }
+      if (doc.getMore) {
+        return req.reply({
+          ok: 1,
+          cursor: {
+            id: new Long(1407, 1407),
+            nextBatch: []
+          }
+        });
+      }
+      req.reply({ ok: 1 });
+    });
+    const client = this.configuration.newClient(`mongodb://${mockServer.uri()}/`, {
+      useUnifiedTopology: true
+    });
+    client.connect(err => {
+      expect(err).to.not.exist;
+      const collection = client.db('cs').collection('test');
+      const changeStream = collection.watch();
+      changeStream.next((err, doc) => {
+        expect(err).to.exist;
+        expect(doc).to.not.exist;
+        expect(err.message).to.equal('ChangeStream is closed');
+        changeStream.close(() => client.close(done));
+      });
+    });
+  });
+});