ico-extract

Extract icons (.ico) from Windows PE files (.dll / .exe).

A small, dependency-free Rust PE parser that reads the RT_GROUP_ICON / RT_ICON resources of a Windows executable and reassembles a standard .ico file. It does not call any OS API — it just parses the file format — so it runs on any platform and compiles to WebAssembly for use from Node.js.

Typical use: pull the native folder icon out of imageres.dll / shell32.dll, no Windows tooling (Resource Hacker, PowerShell) required.

Windows 10/11 note: stock icons are no longer stored in the .dll itself but in a matching .mun file under C:\Windows\SystemResources\ (e.g. imageres.dll.mun). A .mun is a regular PE, so point the extractor at it. For example, the generic folder icon is resource id 4 in imageres.dll.mun.

Why

Windows embeds its stock icons inside DLLs as PE resources. Reading them is pure byte parsing of a documented format (PE → .rsrc directory tree → icon groups), not an OS feature — so it can be done portably and shipped as a single .wasm artifact on npm.

Install

npm i ico-extract

Usage (Node.js)

import { extractIcon, listIconGroups } from 'ico-extract';
import fs from 'fs';

const pe = fs.readFileSync('C:\\Windows\\System32\\imageres.dll');

// List the resource ids of every icon group in the file.
const groups = listIconGroups(pe);

// Extract the first icon group as a multi-size .ico.
const ico = extractIcon(pe, 0);
fs.writeFileSync('folder.ico', ico);

Node reads the file and passes the bytes; the WASM module never touches the disk. This works even when the .dll comes from another machine.

API

| Function | Signature | Returns | | -------- | --------- | ------- | | listIconGroups(peBytes) | (Uint8Array) => Uint32Array | resource ids of each RT_GROUP_ICON (tree order) | | extractIcon(peBytes, groupIndex) | (Uint8Array, number) => Uint8Array | .ico bytes for the group at groupIndex (0-based) | | extractIconById(peBytes, id) | (Uint8Array, number) => Uint8Array | .ico bytes for the group whose Windows resource id is id |

Build from source

Requires the Rust toolchain and wasm-pack.

# native tests (no wasm needed)
cargo test

# build the npm/WASM package into pkg/
rustup target add wasm32-unknown-unknown
cargo install wasm-pack
npm run build        # -> pkg/  (publish that directory)

The native library has zero dependencies; wasm-bindgen is pulled in only for the optional wasm feature used by wasm-pack.

Scope

• ✅ Read / extract icon groups from PE files.
• ❌ Writing or replacing resources (a full Resource-Hacker clone) is out of scope.

License

MIT