BetterDesk/web-nodejs/services/wsRelay.js

/**
 * BetterDesk Console - WebSocket Relay Proxy
 * Bridges browser WebSocket connections to TCP connections for hbbs/hbbr
 * 
 * Provides two WebSocket endpoints:
 *   /ws/rendezvous - proxies to hbbs TCP (port 21116)
 *   /ws/relay      - proxies to hbbr TCP (port 21117)
 * 
 * IMPORTANT: hbbr treats loopback TCP connections as admin command interface
 * (relay_server.rs: `if !ws && ip.is_loopback()`). The relay proxy must
 * connect via a non-loopback IP so hbbr handles it as a relay request.
 */

const WebSocket = require('ws');
const net = require('net');
const os = require('os');
const config = require('../config/config');

// Maximum concurrent relay connections per IP
const MAX_CONNECTIONS_PER_IP = 5;
// Connection timeout (no data for 2 minutes = close)
const IDLE_TIMEOUT_MS = 120000;

// Track connections per IP
const connectionsPerIp = new Map();

/**
 * Check if a hostname resolves to a loopback address
 * @param {string} host
 * @returns {boolean}
 */
function isLoopbackHost(host) {
    if (!host) return false;
    const lower = host.toLowerCase();
    return lower === 'localhost' || lower === '127.0.0.1' || lower === '::1'
        || lower.startsWith('127.');
}

/**
 * Get first non-loopback IPv4 address of the machine.
 * Used to avoid hbbr's loopback command-mode check when proxying relay connections.
 * @returns {string|null}
 */
function getNonLoopbackIp() {
    const interfaces = os.networkInterfaces();
    for (const name of Object.keys(interfaces)) {
        for (const iface of interfaces[name]) {
            if (iface.family === 'IPv4' && !iface.internal) {
                return iface.address;
            }
        }
    }
    return null;
}

/**
 * Initialize WebSocket proxy servers and attach to HTTP server
 * @param {http.Server} server - The HTTP/HTTPS server instance
 */
function initWsProxy(server) {
    // Rendezvous proxy (hbbs)
    const rendezvousWss = new WebSocket.Server({ noServer: true });
    // Relay proxy (hbbr)
    const relayWss = new WebSocket.Server({ noServer: true });

    // Handle upgrade requests — verify session cookie before allowing WebSocket
    server.on('upgrade', (request, socket, head) => {
        const url = new URL(request.url, `http://${request.headers.host}`);
        const pathname = url.pathname;

        // Parse session cookie to verify authentication
        const cookies = {};
        const cookieHeader = request.headers.cookie || '';
        cookieHeader.split(';').forEach(c => {
            const [name, ...rest] = c.trim().split('=');
            if (name) cookies[name] = rest.join('=');
        });

        // Require valid session cookie for WebSocket connections
        if (!cookies['betterdesk.sid']) {
            console.warn(`WS proxy: Rejected upgrade to ${pathname} — no session cookie`);
            socket.write('HTTP/1.1 401 Unauthorized\r\n\r\n');
            socket.destroy();
            return;
        }

        if (pathname === '/ws/rendezvous') {
            rendezvousWss.handleUpgrade(request, socket, head, (ws) => {
                rendezvousWss.emit('connection', ws, request);
            });
        } else if (pathname === '/ws/relay') {
            relayWss.handleUpgrade(request, socket, head, (ws) => {
                relayWss.emit('connection', ws, request);
            });
        } else {
            socket.destroy();
        }
    });

    // Parse target host/port from config
    const hbbsHost = config.wsProxy?.hbbsHost || 'localhost';
    const hbbsPort = config.wsProxy?.hbbsPort || 21116;
    let hbbrHost = config.wsProxy?.hbbrHost || 'localhost';
    const hbbrPort = config.wsProxy?.hbbrPort || 21117;

    // CRITICAL: hbbr treats loopback TCP connections as admin command interface
    // and will NOT process relay requests from 127.0.0.0/8.
    // If hbbrHost is loopback, replace with the machine's non-loopback IP.
    if (isLoopbackHost(hbbrHost)) {
        const nonLoopback = getNonLoopbackIp();
        if (nonLoopback) {
            console.log(`  WebSocket proxy: hbbr host changed from '${hbbrHost}' to '${nonLoopback}' (avoiding loopback command mode)`);
            hbbrHost = nonLoopback;
        } else {
            console.warn('  WebSocket proxy: WARNING - could not find non-loopback IP for hbbr, relay connections may fail!');
        }
    }

    // Rendezvous connections
    rendezvousWss.on('connection', (ws, req) => {
        handleProxyConnection(ws, req, hbbsHost, hbbsPort, 'rendezvous');
    });

    // Relay connections
    relayWss.on('connection', (ws, req) => {
        handleProxyConnection(ws, req, hbbrHost, hbbrPort, 'relay');
    });

    console.log(`  WebSocket proxy: /ws/rendezvous -> ${hbbsHost}:${hbbsPort}`);
    console.log(`  WebSocket proxy: /ws/relay -> ${hbbrHost}:${hbbrPort}`);

    return { rendezvousWss, relayWss };
}

/**
 * Handle a single proxied WebSocket connection
 */
function handleProxyConnection(ws, req, targetHost, targetPort, label) {
    const clientIp = req.headers['x-forwarded-for']?.split(',')[0]?.trim()
        || req.socket.remoteAddress
        || 'unknown';

    // Rate limit connections per IP
    const currentCount = connectionsPerIp.get(clientIp) || 0;
    if (currentCount >= MAX_CONNECTIONS_PER_IP) {
        console.warn(`WS proxy [${label}]: Connection limit reached for ${clientIp}`);
        ws.close(1008, 'Too many connections');
        return;
    }
    connectionsPerIp.set(clientIp, currentCount + 1);

    // Idle timeout
    let idleTimer = null;
    const resetIdleTimer = () => {
        if (idleTimer) clearTimeout(idleTimer);
        idleTimer = setTimeout(() => {
            console.log(`WS proxy [${label}]: Idle timeout for ${clientIp}`);
            cleanup();
        }, IDLE_TIMEOUT_MS);
    };

    // Connect to target TCP server
    const tcp = net.createConnection({ host: targetHost, port: targetPort }, () => {
        resetIdleTimer();
    });

    tcp.on('error', (err) => {
        console.error(`WS proxy [${label}]: TCP error (${targetHost}:${targetPort}):`, err.message);
        cleanup();
    });

    tcp.on('close', () => {
        cleanup();
    });

    // TCP -> WebSocket
    tcp.on('data', (data) => {
        resetIdleTimer();
        if (ws.readyState === WebSocket.OPEN) {
            ws.send(data);
        }
    });

    // WebSocket -> TCP
    ws.on('message', (data) => {
        resetIdleTimer();
        if (!tcp.destroyed) {
            // Ensure we send Buffer, not string
            const buf = Buffer.isBuffer(data) ? data : Buffer.from(data);
            tcp.write(buf);
        }
    });

    ws.on('close', () => {
        cleanup();
    });

    ws.on('error', (err) => {
        console.error(`WS proxy [${label}]: WebSocket error:`, err.message);
        cleanup();
    });

    let cleaned = false;
    function cleanup() {
        if (cleaned) return;
        cleaned = true;

        if (idleTimer) clearTimeout(idleTimer);

        if (!tcp.destroyed) {
            tcp.destroy();
        }
        if (ws.readyState === WebSocket.OPEN || ws.readyState === WebSocket.CONNECTING) {
            ws.close();
        }

        // Decrement connection counter
        const count = connectionsPerIp.get(clientIp) || 1;
        if (count <= 1) {
            connectionsPerIp.delete(clientIp);
        } else {
            connectionsPerIp.set(clientIp, count - 1);
        }
    }
}

module.exports = { initWsProxy };