@bun-win32/comdlg32

Zero-dependency, zero-overhead Win32 Comdlg32 bindings for Bun on Windows.

Overview

@bun-win32/comdlg32 exposes the comdlg32.dll exports using Bun's FFI. It provides a single class, Comdlg32, which lazily binds native symbols on first use. You can optionally preload a subset or all symbols up-front via Preload().

The bindings are strongly typed for a smooth DX in TypeScript.

Features

• Bun-first ergonomics on Windows 10/11.
• Direct FFI to comdlg32.dll (native Open/Save file dialogs, Color picker, Font picker, Print dialog, Page Setup, Find/Replace, and last-error reporting).
• In-source docs in structs/Comdlg32.ts with links to Microsoft Docs.
• Lazy binding on first call; optional eager preload (Comdlg32.Preload()).
• No wrapper overhead; calls map 1:1 to native APIs.
• Strongly-typed Win32 aliases (see types/Comdlg32.ts).

Requirements

• Bun runtime
• Windows 10 or later

Installation

bun add @bun-win32/comdlg32

Quick Start

import Comdlg32, { OpenFileNameFlag } from '@bun-win32/comdlg32';

// Build an OPENFILENAMEW struct (152 bytes on x64) for GetOpenFileNameW
const OPENFILENAMEW_SIZE = 152;
const ofn = Buffer.alloc(OPENFILENAMEW_SIZE);
const view = new DataView(ofn.buffer);

// Filter: pipe-separated label/pattern pairs, NUL-terminated, double-NUL at end
const filter = Buffer.from('All Files (*.*)\0*.*\0\0', 'utf16le');

// Output buffer for the chosen path (260 wide chars)
const fileBuf = Buffer.alloc(260 * 2);

view.setUint32(0x00, OPENFILENAMEW_SIZE, true);            // lStructSize
view.setBigUint64(0x18, BigInt(filter.ptr!), true);        // lpstrFilter
view.setBigUint64(0x30, BigInt(fileBuf.ptr!), true);       // lpstrFile
view.setUint32(0x38, 260, true);                           // nMaxFile
view.setUint32(0x60, OpenFileNameFlag.OFN_EXPLORER | OpenFileNameFlag.OFN_FILEMUSTEXIST, true);

if (Comdlg32.GetOpenFileNameW(ofn.ptr!)) {
  const path = fileBuf.toString('utf16le').replace(/\0.*$/, '');
  console.log('Selected:', path);
} else {
  console.log('Cancelled. Error code:', Comdlg32.CommDlgExtendedError());
}

[!NOTE] AI agents: see AI.md for the package binding contract and source-navigation guidance. It explains how to use the package without scanning the entire implementation.

Examples

Run the included examples:

bun run example:palette-painter        # Interactive color picker — build a palette of colors
bun run example:file-dialog-diagnostic # Open file dialog with full OPENFILENAMEW field dump

Notes

• Either rely on lazy binding or call Comdlg32.Preload().
• All A/W pairs are bound; prefer the W (Unicode) variants for modern code.
• The common dialog APIs are interactive — they display modal windows. Use CommDlgExtendedError() to inspect failure codes after a FALSE/0 return.
• Windows only. Bun runtime required.
• SAL types & naming: nullability is in the type — Optional<T> (formally optional, SAL _*opt_) and Nullable<T> (plain [in]/[out] the docs say can be NULL), the null sentinel derived from T (null for pointers LP*/P*, 0n for handles/by-value addresses); direction is in the parameter name — _out (_Out_), _in_out (_Inout_), _In_ bare. See AI.md and the repo AGENTS.md.