anvilToNbt.js

var anvilToNbt = {};
global.anvilToNbt = anvilToNbt

var SECTOR = 4096;

anvilToNbt.getNbts = function (mcaRaw) {
    var mca = new Uint8Array(mcaRaw);
    var nbts = [];

    var offsets = [];
    for (let i = 0; i < SECTOR; i+=4) {
        var slice = new Uint8Array([0, ...mca.slice(i, i + 3)]);
        var offset = new DataView(slice.buffer).getUint32() * SECTOR;
        var chunkSize = new DataView(mca.buffer).getUint8(i + 3) * SECTOR;
        offsets.push(offset);
        if (offset === 0 && chunkSize === 0) continue;

        var nbt = anvilToNbt._getNbt(mca, offset);
        nbts.push(nbt);
    }

    return nbts;
};

anvilToNbt._getNbt = function (mca, offset) {
    var length = new DataView(new Uint8Array(mca.slice(offset, offset + 4)).buffer).getUint32();
    var compression = mca[offset + 4];
    if (compression !== 2) throw new Error('Invalid compression type');
    var dataOffset = offset + 5;
    var rem = length % SECTOR;
    var padding = (rem) ? SECTOR - (rem) : 0;
    var compressedData = new Uint8Array(mca.slice(dataOffset, dataOffset + length + padding));
    return compressedData;
};