perf(spanner): optimize row creation by using a shared prototype for toJSON

handwritten/spanner/src/partial-result-stream.ts

@@ -121,6 +121,22 @@
   toJSON(options?: JSONOptions): Json;
 }
 
+/**
+ * Row implementation extending Array to provide a shared, non-enumerable
+ * toJSON method without per-row closures or Object.setPrototypeOf overhead.
+ */
+class RowImpl extends Array<Field> implements Row {
+  toJSON(options?: JSONOptions): Json {
+    return codec.convertFieldsToJson(this, options);
+  }
+}
+Object.defineProperty(RowImpl.prototype, 'constructor', {
+  value: Array,
+  writable: true,
+  configurable: true,
+  enumerable: false,
+});
+
 /**
  * @callback PartialResultStream~rowCallback
  * @param {Row|object} row The row data.
@@ -249,7 +265,7 @@
             this._options.columnsMetadata,
             name,
           )
             ? (this._options.columnsMetadata as any)[name]
             : undefined;
         if (codec.decode !== originalDecode) {
           return val =>
@@ -458,7 +474,7 @@
    */
   private _createRow(values: Value[]): Row {
     const len = values.length;
-    const fields = new Array(len);
+    const fields = new RowImpl(len);
     const decoders = this._decoders;
     const classFields = this._fields;
 
@@ -469,13 +485,7 @@
       };
     }
 
-    Object.defineProperty(fields, 'toJSON', {
-      value: (options?: JSONOptions): Json => {
-        return codec.convertFieldsToJson(fields, options);
-      },
-    });
-
-    return fields as Row;
+    return fields;
   }
   /**
    * Attempts to merge chunked values together.

handwritten/spanner/test/partial-result-stream.ts

@@ -30,7 +30,7 @@
 import {grpc} from 'google-gax';
 import {Row} from '../src/partial-result-stream';
 
 function toRawValue(value: any): any {
   if (value === null || value === undefined) {
     return null;
   }
@@ -44,7 +44,7 @@
     return value.toISOString();
   }
   if (value instanceof codec.Struct) {
     return Array.from(value).map((field: any) => toRawValue(field.value));
   }
   if (value instanceof codec.Int) {
     return value.value;
@@ -200,6 +200,45 @@
       stream.write(RESULT);
     });
 
+    it('should create rows with shared prototype and non-enumerable toJSON', done => {
+      const rows: prs.Row[] = [];
+      stream.on('error', done).on('data', row => {
+        rows.push(row);
+        if (rows.length === 2) {
+          try {
+            const [row1, row2] = rows;
+            assert.strictEqual(Array.isArray(row1), true);
+            assert.strictEqual(row1 instanceof Array, true);
+            assert.strictEqual(row1.constructor, Array);
+            assert.strictEqual(Array.isArray(row2), true);
+            assert.strictEqual(row2 instanceof Array, true);
+            assert.strictEqual(row2.constructor, Array);
+
+            // toJSON must be non-enumerable
+            assert.strictEqual(Object.keys(row1).includes('toJSON'), false);
+            assert.strictEqual(
+              Object.prototype.propertyIsEnumerable.call(row1, 'toJSON'),
+              false,
+            );
+
+            // toJSON must be shared on the prototype, not created as a per-row closure
+            assert.strictEqual(row1.toJSON, row2.toJSON);
+
+            // toJSON should correctly serialize the row
+            const json1 = row1.toJSON();
+            const expectedJson = codec.convertFieldsToJson(row1);
+            assert.deepStrictEqual(json1, expectedJson);
+            done();
+          } catch (error) {
+            done(error);
+          }
+        }
+      });
+
+      stream.write(RESULT);
+      stream.write({values: [convertToIValue(VALUE)]});
+    });
+
     it('should emit rows as JSON', done => {
       const jsonOptions = {};
       const stream = new PartialResultStream({json: true, jsonOptions});
@@ -411,8 +450,8 @@
           ],
         };
 
         const jsonRows: any[] = [];
         const standardRows: any[] = [];
 
         let jsonDone = false;
         let standardDone = false;
@@ -469,7 +508,7 @@
     describe('Multiple metadata chunks', () => {
       it('should respect the first metadata chunk and ignore subsequent ones', done => {
         const stream = new PartialResultStream({json: true});
         const rows: any[] = [];
 
         stream
           .on('error', done)
@@ -539,7 +578,7 @@
       // Pause the stream initially to force buffering
       stream.pause();
 
       const rows: any[] = [];
       stream.on('data', row => rows.push(row));
       stream.on('end', () => {
         try {
@@ -1024,7 +1063,7 @@
 
       const receivedRows: Row[] = [];
       partialResultStream(requestFnStub)
         .on('data', (row: any) => receivedRows.push(row))
         .on('error', done)
         .on('end', () => {
           try {