spun

Composable binary layouts, inspection, and schemes.

What is it?

spun is a retained binary layout engine. Instead of writing bytes immediately, you build an in-memory graph of typed nodes — then resolve, inspect, edit, and emit whenever you're ready.

import { layout, section, tag, u16, u32, reserve, emit } from "@gottheflag/spun";

const fileSize = reserve.u32();

const file = layout(
  section("header",
    tag("EXE"),
    fileSize,
    u16(1),
  ),
);

fileSize.set(emit(file).byteLength);
const buf = emit(file);

Features

• Retained graph — construct now, emit later.
• Schemes — parse any binary file into a named, inspectable layout.
• Symbolic refs — ref(node) resolves to byte offsets automatically.
• Deferred values — reserve.u32() for checksums, sizes, and patches.
• Inspection — inspect() returns a full JSON-serializable tree.
• Extensible — subclass LayoutNode to create custom node types.
• Zero dependencies — no runtime deps, works everywhere.

Install

npm install @gottheflag/spun

Documentation

Full API reference and guides at docs/index.html.

License

Apache 2.0