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[v10.x backport] util: handle null prototype on inspect #23655

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[v10.x backport] util: handle null prototype on inspect #23655

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87 changes: 64 additions & 23 deletions lib/internal/util/inspect.js
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Original file line number Diff line number Diff line change
Expand Up @@ -286,6 +286,7 @@ function getEmptyFormatArray() {
}

function getConstructorName(obj) {
let firstProto;
while (obj) {
const descriptor = Object.getOwnPropertyDescriptor(obj, 'constructor');
if (descriptor !== undefined &&
Expand All @@ -295,25 +296,35 @@ function getConstructorName(obj) {
}

obj = Object.getPrototypeOf(obj);
if (firstProto === undefined) {
firstProto = obj;
}
}

if (firstProto === null) {
return null;
}
// TODO(BridgeAR): Improve prototype inspection.
// We could use inspect on the prototype itself to improve the output.

return '';
}

function getPrefix(constructor, tag, fallback) {
if (constructor === null) {
if (tag !== '') {
return `[${fallback}: null prototype] [${tag}] `;
}
return `[${fallback}: null prototype] `;
}

if (constructor !== '') {
if (tag !== '' && constructor !== tag) {
return `${constructor} [${tag}] `;
}
return `${constructor} `;
}

if (tag !== '')
return `[${tag}] `;

if (fallback !== undefined)
return `${fallback} `;

return '';
}

Expand Down Expand Up @@ -387,21 +398,49 @@ function findTypedConstructor(value) {
}
}

let lazyNullPrototypeCache;
// Creates a subclass and name
// the constructor as `${clazz} : null prototype`
function clazzWithNullPrototype(clazz, name) {
if (lazyNullPrototypeCache === undefined) {
lazyNullPrototypeCache = new Map();
} else {
const cachedClass = lazyNullPrototypeCache.get(clazz);
if (cachedClass !== undefined) {
return cachedClass;
}
}
class NullPrototype extends clazz {
get [Symbol.toStringTag]() {
return '';
}
}
Object.defineProperty(NullPrototype.prototype.constructor, 'name',
{ value: `[${name}: null prototype]` });
lazyNullPrototypeCache.set(clazz, NullPrototype);
return NullPrototype;
}

function noPrototypeIterator(ctx, value, recurseTimes) {
let newVal;
// TODO: Create a Subclass in case there's no prototype and show
// `null-prototype`.
if (isSet(value)) {
const clazz = Object.getPrototypeOf(value) || Set;
const clazz = Object.getPrototypeOf(value) ||
clazzWithNullPrototype(Set, 'Set');
newVal = new clazz(setValues(value));
} else if (isMap(value)) {
const clazz = Object.getPrototypeOf(value) || Map;
const clazz = Object.getPrototypeOf(value) ||
clazzWithNullPrototype(Map, 'Map');
newVal = new clazz(mapEntries(value));
} else if (Array.isArray(value)) {
const clazz = Object.getPrototypeOf(value) || Array;
const clazz = Object.getPrototypeOf(value) ||
clazzWithNullPrototype(Array, 'Array');
newVal = new clazz(value.length || 0);
} else if (isTypedArray(value)) {
const clazz = findTypedConstructor(value) || Uint8Array;
let clazz = Object.getPrototypeOf(value);
if (!clazz) {
const constructor = findTypedConstructor(value);
clazz = clazzWithNullPrototype(constructor, constructor.name);
}
newVal = new clazz(value);
}
if (newVal) {
Expand Down Expand Up @@ -492,29 +531,32 @@ function formatRaw(ctx, value, recurseTimes) {
if (Array.isArray(value)) {
keys = getOwnNonIndexProperties(value, filter);
// Only set the constructor for non ordinary ("Array [...]") arrays.
const prefix = getPrefix(constructor, tag);
const prefix = getPrefix(constructor, tag, 'Array');
braces = [`${prefix === 'Array ' ? '' : prefix}[`, ']'];
if (value.length === 0 && keys.length === 0)
return `${braces[0]}]`;
extrasType = kArrayExtrasType;
formatter = formatArray;
} else if (isSet(value)) {
keys = getKeys(value, ctx.showHidden);
const prefix = getPrefix(constructor, tag);
const prefix = getPrefix(constructor, tag, 'Set');
if (value.size === 0 && keys.length === 0)
return `${prefix}{}`;
braces = [`${prefix}{`, '}'];
formatter = formatSet;
} else if (isMap(value)) {
keys = getKeys(value, ctx.showHidden);
const prefix = getPrefix(constructor, tag);
const prefix = getPrefix(constructor, tag, 'Map');
if (value.size === 0 && keys.length === 0)
return `${prefix}{}`;
braces = [`${prefix}{`, '}'];
formatter = formatMap;
} else if (isTypedArray(value)) {
keys = getOwnNonIndexProperties(value, filter);
braces = [`${getPrefix(constructor, tag)}[`, ']'];
const prefix = constructor !== null ?
getPrefix(constructor, tag) :
getPrefix(constructor, tag, findTypedConstructor(value).name);
braces = [`${prefix}[`, ']'];
if (value.length === 0 && keys.length === 0 && !ctx.showHidden)
return `${braces[0]}]`;
formatter = formatTypedArray;
Expand All @@ -540,7 +582,7 @@ function formatRaw(ctx, value, recurseTimes) {
return '[Arguments] {}';
braces[0] = '[Arguments] {';
} else if (tag !== '') {
braces[0] = `${getPrefix(constructor, tag)}{`;
braces[0] = `${getPrefix(constructor, tag, 'Object')}{`;
if (keys.length === 0) {
return `${braces[0]}}`;
}
Expand Down Expand Up @@ -587,13 +629,12 @@ function formatRaw(ctx, value, recurseTimes) {
base = `[${base.slice(0, stackStart)}]`;
}
} else if (isAnyArrayBuffer(value)) {
let prefix = getPrefix(constructor, tag);
if (prefix === '') {
prefix = isArrayBuffer(value) ? 'ArrayBuffer ' : 'SharedArrayBuffer ';
}
// Fast path for ArrayBuffer and SharedArrayBuffer.
// Can't do the same for DataView because it has a non-primitive
// .buffer property that we need to recurse for.
const arrayType = isArrayBuffer(value) ? 'ArrayBuffer' :
'SharedArrayBuffer';
const prefix = getPrefix(constructor, tag, arrayType);
if (keys.length === 0)
return prefix +
`{ byteLength: ${formatNumber(ctx.stylize, value.byteLength)} }`;
Expand Down Expand Up @@ -658,9 +699,9 @@ function formatRaw(ctx, value, recurseTimes) {
} else if (keys.length === 0) {
if (isExternal(value))
return ctx.stylize('[External]', 'special');
return `${getPrefix(constructor, tag)}{}`;
return `${getPrefix(constructor, tag, 'Object')}{}`;
} else {
braces[0] = `${getPrefix(constructor, tag)}{`;
braces[0] = `${getPrefix(constructor, tag, 'Object')}{`;
}
}
}
Expand Down
96 changes: 77 additions & 19 deletions test/parallel/test-util-inspect.js
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Original file line number Diff line number Diff line change
Expand Up @@ -258,15 +258,15 @@ assert.strictEqual(
name: { value: 'Tim', enumerable: true },
hidden: { value: 'secret' }
}), { showHidden: true }),
"{ name: 'Tim', [hidden]: 'secret' }"
"[Object: null prototype] { name: 'Tim', [hidden]: 'secret' }"
);

assert.strictEqual(
util.inspect(Object.create(null, {
name: { value: 'Tim', enumerable: true },
hidden: { value: 'secret' }
})),
"{ name: 'Tim' }"
"[Object: null prototype] { name: 'Tim' }"
);

// Dynamic properties.
Expand Down Expand Up @@ -502,11 +502,17 @@ assert.strictEqual(util.inspect(-5e-324), '-5e-324');
set: function() {}
}
});
assert.strictEqual(util.inspect(getter, true), '{ [a]: [Getter] }');
assert.strictEqual(util.inspect(setter, true), '{ [b]: [Setter] }');
assert.strictEqual(
util.inspect(getter, true),
'[Object: null prototype] { [a]: [Getter] }'
);
assert.strictEqual(
util.inspect(setter, true),
'[Object: null prototype] { [b]: [Setter] }'
);
assert.strictEqual(
util.inspect(getterAndSetter, true),
'{ [c]: [Getter/Setter] }'
'[Object: null prototype] { [c]: [Getter/Setter] }'
);
}

Expand Down Expand Up @@ -1134,7 +1140,7 @@ if (typeof Symbol !== 'undefined') {

{
const x = Object.create(null);
assert.strictEqual(util.inspect(x), '{}');
assert.strictEqual(util.inspect(x), '[Object: null prototype] {}');
}

{
Expand Down Expand Up @@ -1274,7 +1280,7 @@ util.inspect(process);

assert.strictEqual(util.inspect(
Object.create(null, { [Symbol.toStringTag]: { value: 'foo' } })),
'[foo] {}');
'[Object: null prototype] [foo] {}');

assert.strictEqual(util.inspect(new Foo()), "Foo [bar] { foo: 'bar' }");

Expand Down Expand Up @@ -1618,20 +1624,12 @@ util.inspect(process);
'prematurely. Maximum call stack size exceeded.]'));
}

// Verify the output in case the value has no prototype.
// Sadly, these cases can not be fully inspected :(
[
[/a/, '/undefined/undefined'],
[new DataView(new ArrayBuffer(2)),
'DataView {\n byteLength: undefined,\n byteOffset: undefined,\n ' +
'buffer: undefined }'],
[new SharedArrayBuffer(2), 'SharedArrayBuffer { byteLength: undefined }']
].forEach(([value, expected]) => {
{
assert.strictEqual(
util.inspect(Object.setPrototypeOf(value, null)),
expected
util.inspect(Object.setPrototypeOf(/a/, null)),
'/undefined/undefined'
);
});
}

// Verify that throwing in valueOf and having no prototype still produces nice
// results.
Expand Down Expand Up @@ -1667,6 +1665,39 @@ util.inspect(process);
}
});
assert.strictEqual(util.inspect(value), expected);
value.foo = 'bar';
assert.notStrictEqual(util.inspect(value), expected);
delete value.foo;
value[Symbol('foo')] = 'yeah';
assert.notStrictEqual(util.inspect(value), expected);
});

[
[[1, 3, 4], '[Array: null prototype] [ 1, 3, 4 ]'],
[new Set([1, 2]), '[Set: null prototype] { 1, 2 }'],
[new Map([[1, 2]]), '[Map: null prototype] { 1 => 2 }'],
[new Promise((resolve) => setTimeout(resolve, 10)),
'[Promise: null prototype] { <pending> }'],
[new WeakSet(), '[WeakSet: null prototype] { [items unknown] }'],
[new WeakMap(), '[WeakMap: null prototype] { [items unknown] }'],
[new Uint8Array(2), '[Uint8Array: null prototype] [ 0, 0 ]'],
[new Uint16Array(2), '[Uint16Array: null prototype] [ 0, 0 ]'],
[new Uint32Array(2), '[Uint32Array: null prototype] [ 0, 0 ]'],
[new Int8Array(2), '[Int8Array: null prototype] [ 0, 0 ]'],
[new Int16Array(2), '[Int16Array: null prototype] [ 0, 0 ]'],
[new Int32Array(2), '[Int32Array: null prototype] [ 0, 0 ]'],
[new Float32Array(2), '[Float32Array: null prototype] [ 0, 0 ]'],
[new Float64Array(2), '[Float64Array: null prototype] [ 0, 0 ]'],
[new BigInt64Array(2), '[BigInt64Array: null prototype] [ 0, 0 ]'],
[new BigUint64Array(2), '[BigUint64Array: null prototype] [ 0, 0 ]'],
[new ArrayBuffer(16), '[ArrayBuffer: null prototype] ' +
'{ byteLength: undefined }'],
[new DataView(new ArrayBuffer(16)),
'[DataView: null prototype] {\n byteLength: undefined,\n ' +
'byteOffset: undefined,\n buffer: undefined }'],
[new SharedArrayBuffer(2), '[SharedArrayBuffer: null prototype] ' +
'{ byteLength: undefined }']
].forEach(([value, expected]) => {
assert.strictEqual(
util.inspect(Object.setPrototypeOf(value, null)),
expected
Expand Down Expand Up @@ -1748,3 +1779,30 @@ assert.strictEqual(
'[ 3, 2, 1, [Symbol(a)]: false, [Symbol(b)]: true, a: 1, b: 2, c: 3 ]'
);
}

// Manipulate the prototype to one that we can not handle.
{
let obj = { a: true };
let value = (function() { return function() {}; })();
Object.setPrototypeOf(value, null);
Object.setPrototypeOf(obj, value);
assert.strictEqual(util.inspect(obj), '{ a: true }');

obj = { a: true };
value = [];
Object.setPrototypeOf(value, null);
Object.setPrototypeOf(obj, value);
assert.strictEqual(util.inspect(obj), '{ a: true }');
}

// Check that the fallback always works.
{
const obj = new Set([1, 2]);
const iterator = obj[Symbol.iterator];
Object.setPrototypeOf(obj, null);
Object.defineProperty(obj, Symbol.iterator, {
value: iterator,
configurable: true
});
assert.strictEqual(util.inspect(obj), '[Set: null prototype] { 1, 2 }');
}