How do you implement a custom DNS server in Node.js?

Question

Accepted Answer

**Custom DNS server** — resolve domain names with custom logic.

```javascript
const dgram = require("dgram");
const dns = require("dns");

const server = dgram.createSocket("udp4");

const records = {
    "example.com": "192.168.1.1",
    "api.example.com": "192.168.1.2",
};

server.on("message", (msg, rinfo) => {
    const request = parseDNSRequest(msg);
    const domain = request.questions[0].name;
    const ip = records[domain] || "127.0.0.1";

const response = buildDNSResponse(request, ip);
    server.send(response, rinfo.port, rinfo.address);
});

server.bind(53, () => {
    console.log("DNS server listening on port 53");
});

function parseDNSRequest(buffer) {
    return {
        id: buffer.readUInt16BE(0),
        questions: [{ name: "example.com", type: 1 }],
    };
}

function buildDNSResponse(request, ip) {
    const response = Buffer.alloc(128);
    response.writeUInt16BE(request.id, 0);
    response.writeUInt16BE(0x8180, 2); // flags
    response.writeUInt16BE(1, 4); // questions
    response.writeUInt16BE(1, 6); // answers
    // ... write answer record
    return response;
}
```

Node.js: How do you implement a custom DNS server in Node.js?