util: increase function length when using callbackify()

The returned function from `util.callbackify()` should increase the
`length` property by one due to the added callback.

PR-URL: #26893
Fixes: #26890
Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Jeremiah Senkpiel <fishrock123@rocketmail.com>
Reviewed-By: Michaël Zasso <targos@protonmail.com>

lib/util.js

@@ -195,8 +195,13 @@ function callbackify(original) {
   }
 
   Object.setPrototypeOf(callbackified, Object.getPrototypeOf(original));
-  Object.defineProperties(callbackified,
-                          Object.getOwnPropertyDescriptors(original));
+  const descriptors = Object.getOwnPropertyDescriptors(original);
+  // It is possible to manipulate a functions `length` property. This guards
+  // against the manipulation.
+  if (typeof descriptors.length.value === 'number') {
+    descriptors.length.value++;
+  }
+  Object.defineProperties(callbackified, descriptors);
   return callbackified;
 }
 

test/parallel/test-util-callbackify.js

@@ -74,6 +74,7 @@ const values = [
     }
 
     const cbAsyncFn = callbackify(asyncFn);
+    assert.strictEqual(cbAsyncFn.length, 1);
     cbAsyncFn(common.mustCall((err, ret) => {
       assert.strictEqual(ret, undefined);
       if (err instanceof Error) {
@@ -146,6 +147,7 @@ const values = [
     }
 
     const cbAsyncFn = callbackify(asyncFn);
+    assert.strictEqual(cbAsyncFn.length, 2);
     cbAsyncFn(value, common.mustCall((err, ret) => {
       assert.ifError(err);
       assert.strictEqual(ret, value);
@@ -155,8 +157,16 @@ const values = [
       assert.strictEqual(arg, value);
       return Promise.resolve(arg);
     }
+    const obj = {};
+    Object.defineProperty(promiseFn, 'length', {
+      value: obj,
+      writable: false,
+      enumerable: false,
+      configurable: true
+    });
 
     const cbPromiseFn = callbackify(promiseFn);
+    assert.strictEqual(promiseFn.length, obj);
     cbPromiseFn(value, common.mustCall((err, ret) => {
       assert.ifError(err);
       assert.strictEqual(ret, value);