DNS Resolver (javascript, written by Gemini Code Assist)

Gemini Code Assist wrote this javascript project from the task below. It installed and ran on a clean Ubuntu 22.04 machine as written.

Task given to the agent:

TASK: DNS Resolver

Write a program that performs DNS lookups for domain names, supporting multiple record types, reverse lookups, DNS-over-HTTPS, and batch resolution with response time measurements.

FUNCTIONAL REQUIREMENTS:
- Accept a domain name as a command-line argument
- Support querying multiple DNS record types via --type flag: A, AAAA, MX, NS, TXT, CNAME, SOA, PTR, SRV (default: A)
- Support querying all common record types at once via --all flag
- Support reverse DNS lookups (IP to hostname) via --reverse flag
- Allow specifying a custom DNS server via --server flag (default: system DNS resolver)
- Support DNS-over-HTTPS (DoH) via --doh flag using configurable DoH providers
- Measure and display query response time in milliseconds for each lookup
- Support batch resolution of multiple domains from a file via --file flag (one domain per line)
- Display TTL (Time To Live) values for each record
- Support recursive trace mode via --trace flag: show the full resolution path from root servers to authoritative servers
- Print results to console in a structured format showing: domain, record type, value, TTL, response time, and nameserver used
- Save results as JSON with --output flag (default: dns_results.json)
- Support concurrent resolution of batch queries via --parallel flag with configurable concurrency (--threads, default 10)
- If no domain is given, resolve a set of well-known domains (example.com, google.com, github.com, cloudflare.com) across multiple record types and display a formatted comparison table
- Handle errors: NXDOMAIN (non-existent domain), SERVFAIL, timeout, invalid domain names, and unreachable DNS servers

Create a complete JavaScript project for a clean Ubuntu 22.04 machine with only Node.js 20+ (LTS) installed. Include:
- Source code
- package.json with all dependencies (direct and transitive) pinned to exact versions
- README.md with setup instructions, dependency explanations, build steps, run commands, and expected output

[]

const dns = require('dns').promises;
const yargs = require('yargs/yargs');
const { hideBin } = require('yargs/helpers');

const argv = yargs(hideBin(process.argv)).argv;
const domain = argv._[0] || 'example.com';
const type = argv.type || 'A';

async function resolve() {
    try {
        console.log(`Resolving ${domain} (${type})...`);
        let results;
        
        switch(type.toUpperCase()) {
            case 'MX': results = await dns.resolveMx(domain); break;
            case 'TXT': results = await dns.resolveTxt(domain); break;
            case 'AAAA': results = await dns.resolve6(domain); break;
            default: results = await dns.resolve4(domain);
        }

        console.log('Results:');
        console.log(JSON.stringify(results, null, 4));
    } catch (e) {
        console.error('Error:', e.message);
    }
}

resolve();

{
  "name": "dns-resolver",
  "version": "1.0.0",
  "description": "DNS lookup tool using Node.js",
  "main": "dns_resolver.js",
  "engines": {
    "node": ">=20.0.0"
  },
  "dependencies": {
    "yargs": "17.7.2"
  },
  "scripts": {
    "start": "node dns_resolver.js"
  }
}

# DNS Resolver (JavaScript)

A DNS lookup tool using Node.js's built-in `dns` module.

## Setup Instructions

1. Ensure Node.js 20+ (LTS) is installed.
2. Install dependencies:
   ```bash
   npm install
   ```

## Run Commands

- **Resolve Domain**:
  ```bash
  node dns_resolver.js google.com --type MX
  ```