NODEJS-668: Handle empty pages in async pagination

lib/types/result-set.js

@@ -233,7 +233,7 @@ ResultSet.prototype[asyncIteratorSymbol] = function getAsyncGenerator() {
   let pageState = this.rawPageState;
   let rows = this.rows;
 
-  if (!rows || rows.length === 0) {
+  if (!pageState && (!rows || rows.length === 0)) {
     return { next: () => Promise.resolve({ done: true }) };
   }
 
@@ -257,7 +257,13 @@ ResultSet.prototype[asyncIteratorSymbol] = function getAsyncGenerator() {
         return { done: false, value: rows[index++] };
       }
 
-      return { done: true };
+      if (!pageState) {
+        return { done: true };
+      }
+
+      // We could reach this point if an empty page is returned.
+      // An empty page doesn't necessarily mean the end of the results.
+      return this.next();
     }
   };
 };

test/unit/result-set-tests.js

@@ -135,6 +135,26 @@ describe('ResultSet', function () {
         assert.ok(rs.nextPageAsync.firstCall.calledWithExactly(pageState));
       });
 
+      it('should continue past empty pages', async () => {
+        const pageState = utils.allocBuffer(1);
+        const rs = new ResultSet( { rows: [ 100, 101, 102 ], meta: { pageState } });
+        const pages = [
+          [],
+          [],
+          [],
+          [ 103, 104, 105 ],
+        ];
+        rs.nextPageAsync = sinon.spy(function () {
+          const rows = pages.shift();
+          return Promise.resolve({ rows: rows, rawPageState: pages.length > 0 ? pageState : undefined });
+        });
+
+        const result = await helper.asyncIteratorToArray(rs);
+        assert.deepEqual(result, [ 100, 101, 102, 103, 104, 105 ]);
+        assert.strictEqual(rs.nextPageAsync.callCount, 4);
+        assert.ok(rs.nextPageAsync.firstCall.calledWithExactly(pageState));
+      });
+
       it('should reject when nextPageAsync rejects', async () => {
         const rs = new ResultSet( { rows: [ 100 ], meta: { pageState: utils.allocBuffer(1)} });
         const error = new Error('Test dummy error');