Using DataView with nodejs Buffer

Question

I'm trying to read/write some binary data using the DataView object. It seems to work correctly when the buffer is initialized from a UInt8Array, however it if pass it a nodejs Buffer object the results seem to be off. Am I using the API incorrectly?


    import { expect } from 'chai';

    describe('read binary data', () => {

      it('test buffer', () => {
        let arr = Buffer.from([0x55,0xaa,0x55,0xaa,0x60,0x00,0x00,0x00,0xd4,0x03,0x00,0x00,0x1c,0xd0,0xbb,0xd3,0x00,0x00,0x00,0x00])
        let read = new DataView(arr.buffer).getUint32(0, false);
        expect(read).to.eq(0x55aa55aa);
      })

      it('test uint8array', () => {
        let arr = new Uint8Array([0x55,0xaa,0x55,0xaa,0x60,0x00,0x00,0x00,0xd4,0x03,0x00,0x00,0x1c,0xd0,0xbb,0xd3,0x00,0x00,0x00,0x00])
        let read = new DataView(arr.buffer).getUint32(0, false);
        expect(read).to.eq(0x55aa55aa);
      })

    })

The one with the buffer fails with

AssertionError: expected 1768779887 to equal 1437226410
      + expected - actual

      -1768779887
      +1437226410

Riad Baghbanli · Accepted Answer · 2022-02-21 19:12:53Z

3

Nodejs Buffer is just a view over underlying allocated buffer that can be a lot larger. This is how to get ArrayBuffer out of Buffer:

function getArrayBufferFromBuffer( buffer ) {
  return buffer.buffer.slice( buffer.byteOffset, buffer.byteOffset + buffer.byteLength ) );
}

answered Feb 21, 2022 at 19:12

Riad Baghbanli

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Comments

Parag Thakur · Accepted Answer · 2019-10-21 08:42:43Z

0

This helped (not sure if this is the most elegant):

const buff = Buffer.from(msgBody, 'base64');
let uint8Array = new Uint8Array(buff.length);
for(let counter=0;counter<buff.length;counter++) {
    uint8Array[counter] = buff[counter];
    //console.debug(`uint8Array[${counter}]=${uint8Array[counter]}`);
}
let dataview = new DataView(uint8Array.buffer, 0, uint8Array.length);

answered Oct 21, 2019 at 8:42

Parag Thakur

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1 Comment

Jorge Fuentes González Feb 13 at 16:10

DataView should not only point to the length of the uint8array, but also the start offset of the underlying ArrayBuffer. This code may lead to bugs in production.

januw a · Accepted Answer · 2021-07-08 01:06:29Z

0

try use this buf.copy

const buf = fs.readFileSync(`...`);
const uint8arr = new Uint8Array(buf.byteLength);

buf.copy(uint8arr, 0, 0, buf.byteLength);
const v = new DataView(uint8arr.buffer);

edited Jul 8, 2021 at 1:06

answered Jul 6, 2021 at 13:56

januw a

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1 Comment

Sven Eberth Over a year ago

While this code may answer the question, providing additional context regarding how and/or why it solves the problem would improve the answer's long-term value.

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