fix(NODE-2035): Exceptions thrown from awaited cursor forEach do not propagate (#2852)

Author: W-A-James

lib/cursor.js

@@ -742,7 +742,12 @@ class Cursor extends CoreCursor {
           return false;
         }
         if (doc != null) {
-          iterator(doc);
+          try {
+            iterator(doc);
+          } catch (error) {
+            callback(error);
+            return false;
+          }
           return true;
         }
         if (doc == null && callback) {
@@ -762,7 +767,12 @@ class Cursor extends CoreCursor {
             fulfill(null);
             return false;
           } else {
-            iterator(doc);
+            try {
+              iterator(doc);
+            } catch (error) {
+              reject(error);
+              return false;
+            }
             return true;
           }
         });

test/functional/cursor.test.js

@@ -4372,6 +4372,70 @@ describe('Cursor', function() {
     }
   );
 
+  describe('Cursor forEach Error propagation', function() {
+    let configuration;
+    let client;
+    let cursor;
+    let collection;
+
+    beforeEach(function(done) {
+      configuration = this.configuration;
+      client = configuration.newClient({ w: 1 }, { maxPoolSize: 1 });
+      client
+        .connect()
+        .then(() => {
+          collection = client.db(configuration.db).collection('cursor_session_tests2');
+          done();
+        })
+        .catch(error => {
+          done(error);
+        });
+    });
+
+    afterEach(function(done) {
+      if (cursor) {
+        cursor
+          .close()
+          .then(() => client.close())
+          .then(() => done());
+      } else {
+        client.close().then(() => done());
+      }
+    });
+
+    // NODE-2035
+    it('should propagate error when exceptions are thrown from an awaited forEach call', function(done) {
+      const docs = [{ unique_key_2035: 1 }, { unique_key_2035: 2 }, { unique_key_2035: 3 }];
+      collection
+        .insertMany(docs)
+        .then(() => {
+          cursor = collection.find({
+            unique_key_2035: {
+              $exists: true
+            }
+          });
+          cursor
+            .forEach(() => {
+              throw new Error('FAILURE IN FOREACH CALL');
+            })
+            .then(
+              () => {
+                done(new Error('Error in forEach call not caught'));
+              },
+              err => {
+                try {
+                  expect(err.message).to.deep.equal('FAILURE IN FOREACH CALL');
+                  done();
+                } catch (error) {
+                  done(error);
+                }
+              }
+            );
+        })
+        .catch(error => done(error));
+    });
+  });
+
   it('should return a promise when no callback supplied to forEach method', function(done) {
     const configuration = this.configuration;
     const client = configuration.newClient({ w: 1 }, { poolSize: 1, auto_reconnect: false });