repl completion for large buffers fails to display named properties

[killagu]

• Version: v10.5.0
• Platform: macOS
• Subsystem:REPL

When alloc a large buffer, and input a. then press tab. It's a warning.

> a = Buffer.alloc(1024*1024)
<Buffer 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ... >
> a.
(node:7432) REPLWarning: The current array, Buffer or TypedArray has too many entries. Certain properties may be missing from completion output.

But it works well, when alloc a small buffer.

> a = Buffer.alloc(1024)
<Buffer 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ... >
> a.
a.__defineGetter__      a.__defineSetter__      a.__lookupGetter__      a.__lookupSetter__      a.__proto__             a.constructor           a.hasOwnProperty        a.isPrototypeOf         a.propertyIsEnumerable
a.toLocaleString        a.toString              a.valueOf               

a.buffer                a.byteLength            a.byteOffset            a.copyWithin            a.entries               a.every                 a.fill                  a.filter                a.find
a.findIndex             a.forEach               a.includes              a.indexOf               a.join                  a.keys                  a.lastIndexOf           a.length                a.map
a.reduce                a.reduceRight           a.reverse               a.set                   a.slice                 a.some                  a.sort                  a.subarray              a.values

a.BYTES_PER_ELEMENT     

a.asciiSlice            a.asciiWrite            a.base64Slice           a.base64Write           a.compare               a.copy                  a.equals                a.hexSlice              a.hexWrite
a.inspect               a.latin1Slice           a.latin1Write           a.offset                a.parent                a.readDoubleBE          a.readDoubleLE          a.readFloatBE           a.readFloatLE
a.readInt16BE           a.readInt16LE           a.readInt32BE           a.readInt32LE           a.readInt8              a.readIntBE             a.readIntLE             a.readUInt16BE          a.readUInt16LE
a.readUInt32BE          a.readUInt32LE          a.readUInt8             a.readUIntBE            a.readUIntLE            a.swap16                a.swap32                a.swap64                a.toJSON
a.ucs2Slice             a.ucs2Write             a.utf8Slice             a.utf8Write             a.write                 a.writeDoubleBE         a.writeDoubleLE         a.writeFloatBE          a.writeFloatLE
a.writeInt16BE          a.writeInt16LE          a.writeInt32BE          a.writeInt32LE          a.writeInt8             a.writeIntBE            a.writeIntLE            a.writeUInt16BE         a.writeUInt16LE
a.writeUInt32BE         a.writeUInt32LE         a.writeUInt8            a.writeUIntBE           a.writeUIntLE           

[ghost]

The relevant part is

node/lib/repl.js

Lines 910 to 918 in 4dbfb09

	function mayBeLargeObject(obj) {
	if (Array.isArray(obj)) {
	return obj.length > ARRAY_LENGTH_THRESHOLD ? ['length'] : null;
	} else if (isTypedArray(obj)) {
	return obj.length > ARRAY_LENGTH_THRESHOLD ? [] : null;
	}
	return null;
	}

In order to list accessible properties, the REPL script has to obtain all properties of the given object. Without the above check, Node.js may crash due to out of memory error.

I don't think this is fixable.

[Fishrock123]

I think it might be fixable. We should lookup named properties first, which should be possible.

[thatshailesh]

Interesred in picking this up.. need some guidance

[ghost]

Re: @͏Fishrock123

I would be very happy to see how it can be fixed. In order to obtain named properties of an object, the repl script should call Object.getOwnPropertyNames on the given object. However, consider this example:

> var a = Buffer.alloc(2 ** 30)
undefined
> a.someProperty = 'someValue'
'someValue'
> a.
(node:1932) REPLWarning: The current array, Buffer or TypedArray has too many entries. Certain properties may be missing from completion output.

In order to enumerate someProperty as a property of the object a, either Object.getOwnPropertyNames or Object.keys should be called. But, both of them result in out of memory error:

> Object.keys(a)
RangeError: Invalid array length
    at Function.keys (<anonymous>)
> Object.getOwnPropertyNames(a)
FATAL ERROR: invalid table size Allocation failed - JavaScript heap out of memory

[bnoordhuis]

We should lookup named properties first, which should be possible.

Not without changes to V8 first. There is currently no way to retrieve a bounded number of own properties.

We might be able to make do with a for/in loop and check each key with Object#hasOwnProperty().