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Kaitai Struct: JavaScript notes

Quick start

Node.js

Create an empty directory and install the runtime from npm by running:

npm i kaitai-struct

Copy your compiled .ksy parser into this directory or download one parser from the format gallery (eg. Elf.js).

Create index.js with the following content:

const fs = require("fs");
const Elf = require("./Elf");
const KaitaiStream = require('kaitai-struct/KaitaiStream');

const fileContent = fs.readFileSync("/bin/ls");
const parsedElf = new Elf(new KaitaiStream(fileContent));
console.log(parsedElf);

Test the code by running node index.js.

Browser

Create an index.html with the following content:

<html>
<head>
    <script src="KaitaiStream.js"></script>
    <script src="Elf.js"></script>
</head>
<body>
    <pre id="dump">parsing in process...</pre>
    <script>
        var oReq = new XMLHttpRequest();
        oReq.open("GET", "sample.elf", true);
        oReq.responseType = "arraybuffer";

        oReq.onload = function (oEvent) {
            var arrayBuffer = oReq.response;
            var parsedElf = new Elf(new KaitaiStream(arrayBuffer));
            document.getElementById("dump").textContent =
                "machineType: " + Elf.Machine[parsedElf.header.machine] + "\n" +
                "program headers:\n" + parsedElf.header.sectionHeaders.map(x => " - " + x.name).join("\n");
        };

        oReq.send(null);
    </script>
</body>
</html>

Copy your compiled .ksy parser into this directory or download one parser from the format gallery (eg. Elf.js).

Also deploy the Kaitai Struct JavaScript Runtime (KaitaiStream.js) from Github or npm and a sample.elf file.

Publish the files on a webserver. Simplest method is running python -mSimpleHTTPServer and opening http://localhost:8000.

Approximate 64-bit integers

Current JavaScript specification lacks direct access to anything like int64 type. Instead, accessing long integers would automatically represent them internally as double-precision IEEE754 floats, potentially losing least significant bits. It should be ok for smaller integers (up to 53 significant bits), but note that JavaScript would use approximate values for everything beyond that.