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Kaitai Struct

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Note: if you want to make changes to the project, do not fork this repository kaitai_struct. Instead, choose the component you want to modify in the file tree above and fork that individual component instead.

This is an umbrella repository, containing the components only as submodules to make it easier to check out the entire project. Unless you want to modify this README, it is not the repo where you can make edits.

What is Kaitai Struct?

Kaitai Struct is a declarative language used for describing various binary data structures laid out in files or in memory: i.e. binary file formats, network stream packet formats, etc.

The main idea is that a particular format is described in Kaitai Struct language only once and then can be compiled with a ksc into source files in one of the supported programming languages. These modules will include a generated code for a parser that can read described data structure from a file / stream and give access to it in a nice, easy-to-comprehend API.

What it's used for?

Have you ever found yourself writing repetitive, error-prone and hard-to-debug code that reads binary data structures from file / network stream and somehow represents them in memory for easier access?

Kaitai Struct tries to make this job easier — you only have to describe the binary format once and then everybody can use it from their programming languages — cross-language, cross-platform.

Kaitai Struct includes a growing collection of format descriptions, available in formats submodule repository.

Can you give me a quick example?

Sure. Consider this simple .ksy format description file that describes the header of a GIF file (a popular web image format):

meta:
  id: gif
  file-extension: gif
  endian: le
seq:
  - id: header
    type: header
  - id: logical_screen
    type: logical_screen
types:
  header:
    seq:
      - id: magic
        contents: 'GIF'
      - id: version
        size: 3
  logical_screen:
    seq:
      - id: image_width
        type: u2
      - id: image_height
        type: u2
      - id: flags
        type: u1
      - id: bg_color_index
        type: u1
      - id: pixel_aspect_ratio
        type: u1

It declares that GIF files usually have a .gif extension and use little-endian integer encoding. The file itself starts with two blocks: first comes header and then comes logical_screen:

This .ksy file can be compiled it into Gif.cs / Gif.java / Gif.js / Gif.php / gif.py / gif.rb and then instantly one can load .gif file and access, for example, it's width and height.

In C#

Gif g = Gif.FromFile("path/to/some.gif");
Console.WriteLine("width = " + g.LogicalScreen.ImageWidth);
Console.WriteLine("height = " + g.LogicalScreen.ImageHeight);

In Java

Gif g = Gif.fromFile("path/to/some.gif");
System.out.println("width = " + g.logicalScreen().imageWidth());
System.out.println("height = " + g.logicalScreen().imageHeight());

In JavaScript

See JavaScript notes in the documentation for a more complete quick start guide.

var g = new Gif(new KaitaiStream(someArrayBuffer));
console.log("width = " + g.logicalScreen.imageWidth);
console.log("height = " + g.logicalScreen.imageHeight);

In Lua

local g = Gif:from_file("path/to/some.gif")
print("width = " .. g.logical_screen.image_width)
print("height = " .. g.logical_screen.image_height)

In Nim

let g = Gif.fromFile("path/to/some.gif")
echo "width = " & $g.logicalScreen.imageWidth
echo "height = " & $g.logicalScreen.imageHeight

In PHP

$g = Gif::fromFile('path/to/some.gif');
printf("width = %d\n", $g->logicalScreen()->imageWidth());
printf("height = %d\n", $g->logicalScreen()->imageHeight());

In Python

g = Gif.from_file("path/to/some.gif")
print "width = %d" % (g.logical_screen.image_width)
print "height = %d" % (g.logical_screen.image_height)

In Ruby

g = Gif.from_file("path/to/some.gif")
puts "width = #{g.logical_screen.image_width}"
puts "height = #{g.logical_screen.image_height}"

Of course, this example shows only a very limited subset of what Kaitai Struct can do. Please refer to the tutorials and documentation for more insights.

Supported languages

Official Kaitai Struct compiler now supports compiling .ksy into source modules for the following languages:

Downloading and installing

The easiest way to check out the whole Kaitai Struct project is to download the main project repository that already imports all other parts as submodules. Use:

git clone --recursive https://github.com/kaitai-io/kaitai_struct.git

Note the --recursive option.

Alternatively, one can check out individual subprojects that consitute Kaitai Struct suite. They are:

Using KS in your project

Typically, using formats described in KS in your project, involves the following steps:

Check out the tutorial and documentation for more information.

Licensing