From 61d1334e5bc422f72ddc7eb5ad259d7b38f3bcdf Mon Sep 17 00:00:00 2001
From: Ruben Bridgewater <ruben@bridgewater.de>
Date: Sun, 24 Mar 2019 21:59:20 +0100
Subject: [PATCH] util: increase function length when using `callbackify()`
MIME-Version: 1.0
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: 8bit

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

PR-URL: https://github.com/nodejs/node/pull/26893
Fixes: https://github.com/nodejs/node/issues/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                            |  9 +++++++--
 test/parallel/test-util-callbackify.js | 10 ++++++++++
 2 files changed, 17 insertions(+), 2 deletions(-)

diff --git a/lib/util.js b/lib/util.js
index f6f99f82b45..1935955ad28 100644
--- a/lib/util.js
+++ b/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;
 }
 
diff --git a/test/parallel/test-util-callbackify.js b/test/parallel/test-util-callbackify.js
index c381924e1b5..4d7d46658a8 100644
--- a/test/parallel/test-util-callbackify.js
+++ b/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);