module Docs::A_GETTING_STARTED::DSL_GUIDE

Overview

Declarative DSL & Scoped Pipelines

Crowbar provides an expressive block-based DSL to pinpoint specific regions of data, attach weighted mutators, and calculate post-transform checksums or lengths.

Executive Summary & Key Topics

Topic	Method / Anchor	Description
Scopes, Matchers, and Fixup Hooks	`.topic_01_scopes_and_fixups`	Scoping byte ranges, regex captures, and repairing headers with fixups.

Related Guides & Source References

src/crowbar/dsl/builder.cr
src/crowbar/selectors/base.cr

Defined in:

docs/a_getting_started/dsl_guide.cr

Class Method Summary

.topic_01_scopes_and_fixups : Nil
Scopes, Matchers, and Fixup Hooks: Scoping byte ranges, regex captures, and repairing headers with fixups.

Class Method Detail

def self.topic_01_scopes_and_fixups : Nil #

Scopes, Matchers, and Fixup Hooks: Scoping byte ranges, regex captures, and repairing headers with fixups.

Using Crowbar.define, you can isolate portions of an input payload:

Directive	Syntax	Description
`seed`	`seed 1234_u64`	Configures the deterministic PRNG
`pattern`	`pattern :burst`	Sets frequency (:once, :many, :burst)
`scope`	`scope :header, bytes: 0...16`	Constrains mutation to a byte range
`match`	`match /"([^"]+)"/, group: 1`	Targets regex match groups
`fixup`	`fixup do \	buf\	... end`	Post-mutation callback for checksums

Working Examples

fuzzer = Crowbar.define do
  seed 0x1337_u64
  pattern :many

  # Scope 1: Protect and mutate header
  scope :header, bytes: 0...16 do
    weight 0.2
    mutate :byte_flip, :byte_swap
  end

  # Scope 2: Mutate payload
  scope :payload, bytes: 16.. do
    weight 0.8
    mutate :boundary_number, :unicode
  end

  # Fixup: recalculate payload length
  fixup do |buffer|
    next if buffer.size < 16
    len = (buffer.size - 16).to_u32
    IO::ByteFormat::BigEndian.encode(len, buffer[0, 4])
  end
end

crowbar