feature: support initializing Buffer from an ArrayBuffer

[feross]

I propose we make the Buffer constructor also accept ArrayBuffer.

Currently this is what happens:

var u = new Uint8Array([1, 2, 3, 4]);
var ab = u.buffer;
var b = new Buffer(ab);
console.log(b); // <Buffer >

This is what should happen:

console.log(b); // <Buffer 01 02 03 04>

When writing isomorphic code (i.e. code that runs on the server and in the browser), it's often the case that you'll get an ArrayBuffer from a DOM API (xhr, websockets, webrtc, etc.) and need to convert it to a Buffer to work with modules in the npm ecosystem. Users often expect that new Buffer(arraybuffer) will work and they open issues when it doesn't.

We have the buffer npm module which gives us the same Buffer API in the browser (and is used by browserify), however it tracks the node.js/io.js buffer exactly, so we can't add support for new Buffer(arraybuffer) unless core does too.

I know the Buffer constructor already takes a million different argument types, so it couldn't hurt to add one more, right? Curious to see what the community thinks about this. If there's interest, I can send a PR.

[chrisdickinson]

Curious: would this copy the memory represented by the ArrayBuffer, or act as a view onto it?

[vkurchatkin]

@chrisdickinson It should behave the same way as new Buffer(buffer) i.e. copy, but the latter is impossible anyway