util: prevent leaking inspect internals

doc/api/util.md

@@ -388,6 +388,10 @@ stream.write('With ES6');
 <!-- YAML
 added: v0.3.0
 changes:
+  - version: REPLACEME
+    pr-url: https://github.com/nodejs/node/pull/24971
+    description: Internal properties no longer appear in the context argument
+                 of a custom inspection function.
   - version: v11.7.0
     pr-url: https://github.com/nodejs/node/pull/25006
     description: ArrayBuffers now also show their binary contents.

lib/internal/encoding.js

@@ -320,7 +320,7 @@ class TextEncoder {
   [inspect](depth, opts) {
     validateEncoder(this);
     if (typeof depth === 'number' && depth < 0)
-      return opts.stylize('[Object]', 'special');
+      return this;
     var ctor = getConstructorOf(this);
     var obj = Object.create({
       constructor: ctor === null ? TextEncoder : ctor
@@ -517,7 +517,7 @@ function makeTextDecoderJS() {
       [inspect](depth, opts) {
         validateDecoder(this);
         if (typeof depth === 'number' && depth < 0)
-          return opts.stylize('[Object]', 'special');
+          return this;
         var ctor = getConstructorOf(this);
         var obj = Object.create({
           constructor: ctor === null ? TextDecoder : ctor

lib/internal/url.js

@@ -343,7 +343,7 @@ class URL {
     }
 
     if (typeof depth === 'number' && depth < 0)
-      return opts.stylize('[Object]', 'special');
+      return this;
 
     var ctor = getConstructorOf(this);
 

lib/internal/util/inspect.js

@@ -516,18 +516,22 @@ function formatValue(ctx, value, recurseTimes, typedArray) {
         maybeCustom !== inspect &&
         // Also filter out any prototype objects using the circular check.
         !(value.constructor && value.constructor.prototype === value)) {
+      // Remove some internal properties from the options before passing it
+      // through to the user function. This also prevents option manipulation.
+      // eslint-disable-next-line no-unused-vars
+      const { budget, seen, indentationLvl, ...plainCtx } = ctx;
       // This makes sure the recurseTimes are reported as before while using
       // a counter internally.
       const depth = ctx.depth === null ? null : ctx.depth - recurseTimes;
-      const ret = maybeCustom.call(value, depth, ctx);
+      const ret = maybeCustom.call(value, depth, plainCtx);
 
       // If the custom inspection method returned `this`, don't go into
       // infinite recursion.
       if (ret !== value) {
         if (typeof ret !== 'string') {
           return formatValue(ctx, ret, recurseTimes);
         }
-        return ret;
+        return ret.replace(/\n/g, `\n${' '.repeat(ctx.indentationLvl)}`);
       }
     }
   }

test/parallel/test-util-inspect.js

@@ -775,9 +775,21 @@ util.inspect({ hasOwnProperty: null });
 
   assert.strictEqual(util.inspect(subject), "{ foo: 'bar' }");
 
-  subject[util.inspect.custom] = (depth, opts) => {
-    assert.strictEqual(opts.customInspectOptions, true);
-  };
+  subject[util.inspect.custom] = common.mustCall((depth, opts) => {
+    const clone = { ...opts };
+    // This might change at some point but for now we keep the stylize function.
+    // The function should either be documented or an alternative should be
+    // implemented.
+    assert.strictEqual(typeof opts.stylize, 'function');
+    assert.strictEqual(opts.seen, undefined);
+    assert.strictEqual(opts.budget, undefined);
+    assert.strictEqual(opts.indentationLvl, undefined);
+    assert.strictEqual(opts.showHidden, false);
+    opts.showHidden = true;
+    return { [util.inspect.custom]: common.mustCall((depth, opts2) => {
+      assert.deepStrictEqual(clone, opts2);
+    }) };
+  });
 
   util.inspect(subject, { customInspectOptions: true });
 
@@ -1584,7 +1596,7 @@ util.inspect(process);
   );
   const longList = util.inspect(list, { depth: Infinity });
   const match = longList.match(/next/g);
-  assert(match.length > 1000 && match.length < 10000);
+  assert(match.length > 500 && match.length < 10000);
   assert(longList.includes('[Object: Inspection interrupted ' +
     'prematurely. Maximum call stack size exceeded.]'));
 }

test/parallel/test-whatwg-encoding-custom-textdecoder.js

@@ -134,7 +134,7 @@ if (common.hasIntl) {
 // Test TextDecoder inspect with negative depth
 {
   const dec = new TextDecoder();
-  assert.strictEqual(util.inspect(dec, { depth: -1 }), '[Object]');
+  assert.strictEqual(util.inspect(dec, { depth: -1 }), '[TextDecoder]');
 }
 
 {

test/parallel/test-whatwg-url-custom-inspect.js

@@ -63,7 +63,7 @@ assert.strictEqual(
 
 assert.strictEqual(
   util.inspect({ a: url }, { depth: 0 }),
-  '{ a: [Object] }');
+  '{ a: [URL] }');
 
 class MyURL extends URL {}
 assert(util.inspect(new MyURL(url.href)).startsWith('MyURL {'));