DataView doesn't work with Buffer from pool

[skomski]

I wanted to simplify the various .read{Type} or .write{Type} by using a DataView implementation and
found out that is not possible to use the Buffer's ArrayBuffer if the buffer was sliced from the pool.

const assert = require('assert');
const SlowBuffer = require('buffer').SlowBuffer;

const buffer = new Buffer(4).fill(0);
new DataView(buffer.buffer).setFloat32(0, 1, true);
console.log(buffer.buffer.byteLength);
console.log(buffer);

const slowBuffer = new SlowBuffer(4).fill(0);
new DataView(slowBuffer.buffer).setFloat32(0, 1, true);
console.log(slowBuffer.buffer.byteLength);
console.log(slowBuffer);

assert.deepEqual(buffer, slowBuffer);

results into

8192
<Buffer 00 00 00 00>
4
<Buffer 00 00 80 3f>

AssertionError: <Buffer 00 00 00 00> deepEqual <Buffer 00 00 80 3f>

The problem is the underlying ArrayBuffer for the new sliced TypedArray does not change.

[targos]

The ArrayBuffer changes, but not at the right index. If you want your DataView to start at the same offset as the Buffer object, you need to instantiate it with the byteOffset option:
new DataView(buffer.buffer, buffer.byteOffset)

[skomski]

Thanks. This behaviour is a bit counter-intuitive since I would suspect the underlying ArrayBuffer in .buffer is not the pool ArrayBuffer but a sliced version of it where byteOffset would be 0.

Correct usage:

const buffer = new Buffer(4).fill(0);
const dataView = new DataView(buffer.buffer, buffer.byteOffset, buffer.byteLength);
dataView.setFloat32(0, 1, true)

[targos]

I guess that if it was a slice, there would be no point in having a pool in the first place.
btw you can achieve the same without constructing a DataView with buffer.writeFloatLE(1, 0)

[skomski]

With slice I mean subarray because slice and subarray are the same thing for a Buffer.
From a design standpoint it would be better if the pool would be not visible in the returned Buffer and the underlying ArrayBuffer would be a view to the pool ArrayBuffer.

I want to simplify write{Type} or read{Type} by using DataView ;)

[trevnorris]

Remember that Buffer is now just a Uint8Array with an assigned __proto__. All that is due to current specification. :-)