From bbf39bcfecd3eda49ae2993937ddbc0b73416b72 Mon Sep 17 00:00:00 2001
From: Ruben Bridgewater <ruben@bridgewater.de>
Date: Sun, 1 Dec 2019 01:08:37 +0100
Subject: [PATCH] util: never trigger any proxy traps using `format()`

Backport-PR-URL: https://github.com/nodejs/node/pull/31431
PR-URL: https://github.com/nodejs/node/pull/30767
Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Denys Otrishko <shishugi@gmail.com>
Reviewed-By: Rich Trott <rtrott@gmail.com>
---
 lib/internal/util/inspect.js             | 7 +++++++
 test/parallel/test-util-inspect-proxy.js | 3 +++
 2 files changed, 10 insertions(+)

diff --git a/lib/internal/util/inspect.js b/lib/internal/util/inspect.js
index 09f755ac00649f..38665d1bc2a515 100644
--- a/lib/internal/util/inspect.js
+++ b/lib/internal/util/inspect.js
@@ -1646,6 +1646,13 @@ function format(...args) {
 }
 
 function hasBuiltInToString(value) {
+  // Prevent triggering proxy traps.
+  const getFullProxy = false;
+  const proxyTarget = getProxyDetails(value, getFullProxy);
+  if (proxyTarget !== undefined) {
+    value = proxyTarget;
+  }
+
   // Count objects that have no `toString` function as built-in.
   if (typeof value.toString !== 'function') {
     return true;
diff --git a/test/parallel/test-util-inspect-proxy.js b/test/parallel/test-util-inspect-proxy.js
index 5e85b92f713175..5789a6ffbcf6c5 100644
--- a/test/parallel/test-util-inspect-proxy.js
+++ b/test/parallel/test-util-inspect-proxy.js
@@ -41,6 +41,9 @@ proxyObj = new Proxy(target, handler);
 // Inspecting the proxy should not actually walk it's properties
 util.inspect(proxyObj, opts);
 
+// Make sure inspecting object does not trigger any proxy traps.
+util.format('%s', proxyObj);
+
 // getProxyDetails is an internal method, not intended for public use.
 // This is here to test that the internals are working correctly.
 let details = processUtil.getProxyDetails(proxyObj, true);