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kaitaigo

kaitaigo is a compiler and runtime to create Go parsers from Kaitai Struct files.

Installation

go get dfir.software/kaitaigo

Usage

First we need a .ksy file. We take this simple example, but there are many more.

# my_format.ksy
meta:
  id: my_format
seq:
  - id: data_size
    type: u1
  - id: data
    size: data_size

To create the Go code we use the kaitaigo command: kaitaigo my_format.ksy. This creates the ready to use my_format.ksy.go.

The parser can be used in other scripts like the following. Change package in my_format.ksy.go to main. Afterward you can run the script and use our new parser with go run main.go my_format.ksy.go.

// main.go
package main

import (
	"bytes"
	"log"
)

func main() {
	f := bytes.NewReader([]byte("\x05Hello world!"))
	var r MyFormat
	err := r.Decode(f) // Decode takes any io.ReadSeeker
	if err != nil {
		log.Fatal(err)
	}
	log.Print(string(r.Data())) // Prints "Hello"
}

kaitaigo features

This is not the official kaitai compiler. The official kaitai compiler contains go support as well. More information in the issue for Go language support.

Supported kaitai features:

• Type specification
  • meta
    • endianess*
  • doc
  • seq
  • instances
  • enums
• Attribute specification
  • id
  • doc
  • contents
  • repeat, repeat-expr, repeat-until
  • if
  • size, size-eos
  • process
  • terminator
  • consume
  • include
  • pad
  • eos-error
• Primitive data types
• Processing specification
  • xor
  • rol
  • ror
  • zlib
• Instance specification
  • pos
  • value

*partially

Additional features:

whence

Can be used togher with pos the define the reference point of the position. Valid values are seek_set, seek_end and seek_cur (default).

Limitations

• No _io (Most uses can be replaced with whence)
• Accessing nested types with :: is not allowed
• No fancy enums
• No nested endianess
• No encoding
• No comparison of string, []byte or custom types
• No min or max functions
• fix type inference
• -2 % 8 = -2
• xor, ror, rol and zlib only work on bytes
• float + int fails

Licenses

The kaitaigo compiler is licensed as GPLv3. The runtime (/runtime) is licensed under MIT license. Everything else is licensed as GPLv3.