mdns-sync/main.js

// mdns-sync.js
// A single-file mDNS sync tool acting as client or server
// Uses mdns-server for mDNS and Express for HTTP

/*********************************
*
*   1. LIBRARY FUNCTIONS
*
*********************************/

const os    = require('os');
const mysql = require('mysql2/promise');
const mdns  = require('mdns-server'); // we'll initialize below

// 0. HELPER FUNCTIONS
// Extract password from ~/.ssh/id_rsa.pub (last 6 characters of base64)
function getDbPassword() {
  const pubKeyContent = require('fs').readFileSync(
    `${os.homedir()}/.ssh/id_rsa.pub`,
    'utf8'
  );
  const base64Part = pubKeyContent.split(' ')[1];
  return base64Part.slice(-7, -1);
}

// Insert/update data into MariaDB
async function updateMariaDB(record) {
  const { Type, Name } = record;
  if (!['A','PTR','SRV','TXT'].includes(Type)) return;

  const host    = DB_USER;
  const dataStr = typeof record.Data === 'object'
    ? JSON.stringify(record.Data)
    : record.Data;

  try {
    const sql = `
      INSERT INTO ${DB_TABLE} (Host, Type, Name, Data)
      VALUES (?, ?, ?, ?)
      ON DUPLICATE KEY UPDATE Data = VALUES(Data)
    `;
    await dbPool.execute(sql, [host, Type, Name, dataStr]);
  } catch (err) {
    console.error('DB Upsert Error:', err);
  }
}

// 1. Network functions

function getLocalNetworkAddressesIPs() {
  const interfaces = os.networkInterfaces();
  return Object.values(interfaces)
    .flat()
    .filter(iface => iface.family === 'IPv4' && !iface.internal)
    .map(iface => iface.address);
}

function sniffmDNSLocalPackets() {
  mdns.on('response', async response => {
    const answers = response.answers.concat(response.additionals);

    for (const ans of answers) {
      // only care about standard types
      if (!['A','PTR','SRV','TXT'].includes(ans.type)) continue;

      // For each answer, immediately upsert to MariaDB
      await updateMariaDB({
        Type: ans.type,
        Name: ans.name,
        Data: ans.data
      });
    }
  });

  mdns.on('destroyed', () => {
    console.log('Server destroyed.'); process.exit(0);
  });

  mdns.on('ready', () => {
    console.log('mDNS server is ready...');
  });
}

function replyLocallyWithRemoteDevicesData(name, type) {
  const answers = [];
  if (type === 'PTR' && db.remote.PTR[name]) {
    db.remote.PTR[name].forEach(ptrData =>
      answers.push({ name, type:'PTR', class:'IN', ttl:120, data: ptrData })
    );
  }
  if (type === 'A' && db.remote.A[name]) {
    answers.push({ name, type:'A', class:'IN', ttl:120, data: db.remote.A[name] });
  }
  if (type === 'SRV' && db.remote.services[name]?.SRV) {
    answers.push({ name, type:'SRV', class:'IN', ttl:120, data: db.remote.services[name].SRV });
  }
  if (type === 'TXT' && db.remote.services[name]?.TXT) {
    answers.push({
      name, type:'TXT', class:'IN', ttl:120,
      data: db.remote.services[name].TXT.map(e => Buffer.from(e.data, 'utf8'))
    });
  }
  if (type === 'ANY') {
    // same as above but for ANY
    ['PTR','A','SRV','TXT'].forEach(t => 
      replyLocallyWithRemoteDevicesData(name, t)
    );
  }

  if (answers.length) {
    console.log(`Responding with ${answers.length} answer(s) for ${name}`);
    mdns.respond({ answers });
  }
}

async function fetchRemoteDevicesData() {
  try {
    const [rows] = await dbPool.execute(
      `SELECT Type, Name, Data 
         FROM ${DB_TABLE} 
        WHERE Host <> ? 
          AND MakeAvailableEverywhere = 1`,
      [DB_USER]
    );

    // reinitialize remote cache
    db.remote = { A: {}, PTR: {}, services: {} };
    for (const { Type, Name, Data } of rows) {
      const parsed = ['[','{'].includes(Data[0]) ? JSON.parse(Data) : Data;
      if (Type === 'A') {
        db.remote.A[Name] = parsed;
      } else if (Type === 'PTR') {
        db.remote.PTR[Name] = parsed;
      } else { // SRV or TXT
        db.remote.services[Name] ||= { TXT:null, SRV:null };
        db.remote.services[Name][Type] = parsed;
      }
    }
    console.log(
      `Remote DB updated. A: ${Object.keys(db.remote.A).length}, PTR: ${Object.keys(db.remote.PTR).length}`
    );
  } catch (err) {
    console.error('Error fetching remote DB:', err);
  }
}

/*********************************
*
*   100. MAIN / IMPERATIVE CODE
*
*********************************/

// MariaDB Configuration
const DB_HOST  = '10.10.8.1';
const DB_NAME  = 'NETWORK';
const DB_TABLE = 'mDNS';
const DB_USER  = os.hostname();

// Initialize in-memory cache
const db = { remote: { A: {}, PTR: {}, services: {} } };

// Pick first non-internal v4 address
const LOCAL_IP_ADDR = getLocalNetworkAddressesIPs()[0];

const mdnsServer = mdns({
  interface: LOCAL_IP_ADDR,
  reuseAddr: true,
  loopback: false,
  noInit: true
});

// Init MariaDB connection pool
const dbPool = mysql.createPool({
  host: DB_HOST,
  user: DB_USER,
  password: getDbPassword(),
  database: DB_NAME,
  connectionLimit: 5
});

console.log(
  `Connecting to SQL ${DB_HOST} as ${DB_USER}, DB=${DB_NAME}`
);

sniffmDNSLocalPackets();

mdnsServer.on('query', ({ questions }) => {
  for (const { name, type } of questions) {
    console.log(`Query for ${name} (${type})`);
    replyLocallyWithRemoteDevicesData(name, type);
  }
});

// fetch remote every 15s
setInterval(fetchRemoteDevicesData, 15_000);
fetchRemoteDevicesData();

// now start the server
mdnsServer.initServer();