lazy access body

Refs: nodejs/node#39520 (comment)

Author: ronag

src/node/response.js

@@ -33,7 +33,6 @@ function Response(req) {
   this.request = req;
   this.req = req.req;
   this.text = res.text;
-  this.body = res.body === undefined ? {} : res.body;
   this.files = res.files || {};
   this.buffered = req._resBuffered;
   this.headers = res.headers;
@@ -47,6 +46,21 @@ function Response(req) {
   res.on('error', this.emit.bind(this, 'error'));
 }
 
+// Lazy access res.body.
+// https://github.com/nodejs/node/pull/39520#issuecomment-889697136
+Object.defineProperty(Response.prototype, 'body', {
+  get () {
+    return this._body !== undefined
+      ? this._body
+      : this.res.body !== undefined
+        ? this.res.body
+        : {};
+  },
+  set (value) {
+    this._body = value;
+  }
+});
+
 /**
  * Inherit from `Stream`.
  */