pak file format read/write

pak.js

"use strict";

const fs = require('fs');

console.log(process.argv);


const version = 4;
const file = process.argv[2];
const data = fs.readFileSync(file);
const count = data.readUInt32LE(4);

let start = 9;
const resources = {};
const poses = {};
const positions = []
for (var i = 0; i < count + 1; i++) {
    const id = data.readUInt16LE(start);
    const pos = data.readUInt32LE(start + 2);
    start += 6;
    // console.log(id, pos);
    positions.push({id, pos});

}
for (var i = 0; i < count; i++) {
    const id = positions[i].id;
    const pos = positions[i].pos;
    const toPos = positions[i + 1].pos;
    resources[id] = data.slice(pos, toPos);
    poses[id] = {start: pos, end: toPos};

    const str = data.toString('utf8', pos, toPos)
    if (str.indexOf('WebInspector.Revealer.reveal=function(revealable,omitFocus)\n{') > -1) {
        replace(alert);
        console.log(id);
    }

    // console.log(id, Buffer.byteLength(resources[id]), toPos - pos);

    // console.assert(Buffer.byteLength(resources[id]) == toPos - pos, id);

}

Buffer.compare(data, gen(resources));
// gen({1: 'Yeah'});

// console.log(resources[21451].toString());

function gen(resources) {
    const keys = Object.keys(resources);
    // const len = keys.reduce((sum, id) => sum + poses[id].end - poses[id].start, (keys.length + 1) * 6 + 9);
    const len = keys.reduce((sum, id) => sum + Buffer.byteLength(resources[id], 'utf8'), (keys.length + 1) * 6 + 9);
    const buffer = new Buffer(len);
    buffer.writeUInt32LE(0); // version
    buffer.writeUInt32LE(4, keys.length); // count
    buffer.writeUInt8(8, 1); // encoding
    let pos = 9;
    let offset = pos + (keys.length + 1) * 6;
    for (var i = 0; i < keys.length; i++) {
        var id = keys[i];
        buffer.writeUInt16LE(id, pos);
        buffer.writeUInt32LE(offset, pos);
        buffer.fill(resources[id], offset);
        offset += Buffer.byteLength(resources[id]);
        pos += 6;
    }
    buffer.writeUInt16LE(0, pos);
    buffer.writeUInt32LE(buffer.length, pos + 2);
    return buffer;
}