@bun-win32/dnsapi

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

Overview

@bun-win32/dnsapi exposes the dnsapi.dll exports using Bun's FFI. It provides a single class, Dnsapi, 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 dnsapi.dll (DNS queries for every record type, name validation, server discovery, DNS-SD service browsing, mDNS, and async resolution).
• In-source docs in structs/Dnsapi.ts with links to Microsoft Docs.
• Lazy binding on first call; optional eager preload (Dnsapi.Preload()).
• No wrapper overhead; calls map 1:1 to native APIs.
• Strongly-typed Win32 aliases (see types/Dnsapi.ts).

Requirements

• Bun runtime
• Windows 10 or later

Installation

bun add @bun-win32/dnsapi

Quick Start

import { read, toArrayBuffer, type Pointer } from 'bun:ffi';

import Dnsapi, { DnsFreeType, DnsQueryOption, DnsType } from '@bun-win32/dnsapi';

// Query A records for example.com
const name = Buffer.from('example.com\0', 'utf16le');
const out = Buffer.alloc(8);

const status = Dnsapi.DnsQuery_W(name.ptr, DnsType.DNS_TYPE_A, DnsQueryOption.DNS_QUERY_STANDARD, null, out.ptr, null);

if (status !== 0) {
  throw new Error(`DnsQuery_W failed with status ${status}`);
}

const head = read.ptr(out.ptr) as Pointer | null;
let cur: Pointer | null = head;

while (cur) {
  // DNS_RECORD header is 32 bytes; DNS_A_DATA places the IPv4 octets at offset 32
  const buf = Buffer.from(toArrayBuffer(cur, 0, 40));
  const pNext = Number(buf.readBigUInt64LE(0));
  const wType = buf.readUInt16LE(16);

  if (wType === DnsType.DNS_TYPE_A) {
    console.log(`${buf[32]}.${buf[33]}.${buf[34]}.${buf[35]}`);
  }

  cur = pNext !== 0 ? (pNext as Pointer) : null;
}

if (head) Dnsapi.DnsRecordListFree(head, DnsFreeType.DnsFreeRecordList);

[!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:dns-tree
bun run example:dns-forensics
bun run example:dns-forensics microsoft.com github.com   # custom targets

Notes

• Either rely on lazy binding or call Dnsapi.Preload().
• DNS records returned by DnsQuery_W/DnsQuery_A/DnsQuery_UTF8 are a linked list rooted at the pointer written into the ppQueryResults out-buffer; release the whole list with DnsRecordListFree(head, DnsFreeType.DnsFreeRecordList).
• 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.