From 0650417d938eda896b0008c6d94419f1836dbbdf Mon Sep 17 00:00:00 2001
From: git <git@fredericofalcao.com>
Date: Sun, 15 Jun 2025 13:58:33 +0100
Subject: [PATCH] Add main.js

---
 main.js | 148 ++++++++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 148 insertions(+)
 create mode 100644 main.js

diff --git a/main.js b/main.js
new file mode 100644
index 0000000..c597908
--- /dev/null
+++ b/main.js
@@ -0,0 +1,148 @@
+// 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
+*
+*********************************/
+
+//  0. HELPER FUNCTIONS
+function convertBufferToString(a) {if (a.data) for (i in a.data) a.data[i] = a.data[i].toString(); return a;}
+
+// 1. Database functions
+function saveDbToFile(data, filename) {return fs.writeFileSync(filename,typeof data === 'object'?JSON.stringify(data):data);}
+function loadDbFromFile(filename) {if (!fs.existsSync(filename)) return {local:{},remote:{}}; else return JSON.parse(fs.readFileSync(filename));}
+
+// 2. Network functions
+function getLocalNetworkAddressesIPs() {
+	const os = require('os');
+
+	const interfaces = os.networkInterfaces();
+	const addresses = [];
+
+	for (const name of Object.keys(interfaces)) {
+	    for (const iface of interfaces[name]) {
+	        if (iface.family === 'IPv4' && !iface.internal) {
+	            addresses.push(iface.address);
+	        }
+	    }
+	}
+	return addresses;
+	
+}
+
+function sniffmDNSLocalPackets() {
+
+	// 1. Listen for responses
+	mdns.on('response', function(response) {
+	  // console.log("got a new mDNS response.",response);
+	  for (k in response.answers) {
+		  let answer = response.answers[k];
+		  
+		  // 1. Handle DEVICES for a given SERVICE
+		  if (answer.type == "PTR") {
+			  // 1.1 Filter by RELEVANT SERVICE TYPES
+			  if (!["in-addr.arpa","_googlecast._tcp.local","_tcp.local"].some(suffix => answer.name.endsWith(suffix))) return;
+			  
+			  // 1.2 Initialize POINTERS (services) sub-database
+			  if (!db.local.PTR) db.local.PTR = {};
+  
+			  // 1.3 Initialize this SERVICE TYPE (e.g. _googlecast._tcp.local), if needed
+			  if (!db.local.PTR[answer.name]) {
+			  	  db.local.PTR[answer.name] = [answer.data];
+			  }	else {
+				  // Add a new DEVICE to this SERVICE TYPE if needed
+				  if (!db.local.PTR[answer.name].includes(answer.data)) 
+					  db.local.PTR[answer.name].push(answer.data);
+			  }		  	
+		  }
+		  // 2. Handle DEVICE IP resolution
+		  if (answer.type == "A") {
+			  // 2.1 Initialize ADDRESSES sub-database
+			  if (!db.local.A) db.local.A = {};
+			  db.local.A[answer.name] = answer.data;		  	
+		  }
+		  
+		  if (["TXT","SRV"].includes(answer.type)) {
+			  // Initialize this device / entry, if needed
+			  if (db.local[answer.name] === undefined) db.local[answer.name] = {"TXT":null,"SRV":null};
+			  
+			  db.local[answer.name][answer.type] = answer.data;
+		  }
+		  saveDbToFile(db,DB_FILENAME);
+	  }
+	})
+
+	// 2. Listen for queries
+	mdns.on('query', function(query) {/* console.log("query requested",query);*/});
+
+	// 3. Handle the server being destroyed
+	mdns.on('destroyed', function () {console.log('Server destroyed.');process.exit(0);});
+
+	// 4. Handle the onReady event
+	mdns.on('ready', function () {
+		
+	  console.log("mDNS server is ready...");
+	  // mdns.query({questions:[{ name: '_:googlecast._tcp.local', type: 'PTR', class: 'IN'}]} );
+	})
+
+	// initialize the server now that we are watching for events
+	mdns.initServer()
+
+}
+function injectmDNSPacketLocally(type,name,data,flush = true,_class = 'IN',ttl = 120) { 
+	console.log(`sending packet ${name} of ${type} with data: ${data}`);
+	mdns.respond({answers:[
+		{
+			name: name,
+			type: type,
+			ttl: ttl,
+			class: _class,
+			flush: flush,
+			data: data
+		}
+]});}
+
+
+
+/*********************************
+*
+*   100. MAIN / IMPERATIVE CODE
+*
+*********************************/
+
+const fs = require("fs");
+const DB_FILENAME = 'database.json';
+const db = loadDbFromFile(DB_FILENAME);
+const LOCAL_IP_ADDR = getLocalNetworkAddressesIPs()[0];
+const mdns = require('mdns-server')({interface: LOCAL_IP_ADDR,reuseAddr: true,loopback: false,noInit: true});
+sniffmDNSLocalPackets();
+
+setInterval(function(){
+	// INJECT PTR - Pointers services
+	for (name in db.remote.PTR) {
+		for (i in db.remote.PTR[name])
+			injectmDNSPacketLocally('PTR',name,db.remote.PTR[name][i]);
+	}
+	// INJECT A - Addresses
+	for (name in db.remote.A) {
+		injectmDNSPacketLocally('A',name,db.remote.A[name]);
+	}
+	
+	
+	// INJECT SRV,TXT
+	for (name in db.remote) {
+		if (["PTR","A"].includes(name)) continue;
+		if (db.remote[name].SRV !== null) 
+			injectmDNSPacketLocally('SRV',name,db.remote[name].SRV);
+		if (db.remote[name].TXT !== null) 
+			injectmDNSPacketLocally('TXT',name,Buffer.from(db.remote[name].TXT, 'utf8'));
+
+	}
+	
+	
+	
+},5000);
\ No newline at end of file