How to use Buffer.from to create Buffer view

Question

I want to create view of part of a buffer, after checking in node.js documentation I found that method Buffer.from(arrayBuffer[, byteOffset[, length]]) should do exactly what I wanted. I started with the simple case but it already produces unexpected results so I'm definitely doing something wrong

var firstBuffer = Buffer.from('hello world');
var secondBuffer = Buffer.from(firstBuffer.buffer, 0, firstBuffer.length);

assert (firstBuffer.0 == secondBuffer.0) // fails

console.log (firstBuffer) // <Buffer 68 65 6c 6c 6f 20 77 6f 72 6c 64>
console.log (secondBuffer) // <Buffer da 07 00 00 da 07 00 00 db 07 00>

How to create buffer view?

To add more context, you should also specify the type of string to be ascii in your case var firstBuffer = Buffer.from('hello world','ascii'); — Malice
– Malice, Commented Mar 12, 2018 at 14:39

Bartosz Matuszewski · Accepted Answer · 2018-03-12 16:38:13Z

0

It turns out that result of Buffer.from(string) can have offset property different than 0

Knowing that modified code works:

var firstBuffer = Buffer.from('hello world');
var secondBuffer = Buffer.from(firstBuffer.buffer, firstBuffer.offset, firstBuffer.length);


console.log (firstBuffer)  // <Buffer 68 65 6c 6c 6f 20 77 6f 72 6c 64>
console.log (secondBuffer) // <Buffer 68 65 6c 6c 6f 20 77 6f 72 6c 64>

assert (firstBuffer[0] == secondBuffer[0]) // pass

But it a shame that in official documentation there was no info about this "feature"

answered Mar 12, 2018 at 16:38

Bartosz Matuszewski

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2 Comments

Han Over a year ago

This is not a view. This is a copy. I guess it suits your need but it is not the answer for people looking for buffer view creation.

Wilderness Ranger Mar 14 at 0:58

The property name is byteOffset. And it is documented (now), though at a trivial place...

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