Signaling Server Architecture

The ErikrafT Drop signaling server facilitates peer discovery and WebRTC connection establishment through WebSocket communication. Built with Node.js and the ws library, it manages room-based peer grouping and message routing.

Server Overview

Main Server Entry Point

The server is initialized in server.js:

// From server.js lines 33-39
new ErikrafTdropWsServer(server, {
    rtcConfig,
    wsFallback: false,
    debugMode: process.env.DEBUG_MODE === "true",
    rateLimit: false,
    allowLocalOnly: true
});

Configuration Endpoints

The server provides configuration via HTTP endpoints:

// From server.js lines 14-21
if (req.url === "/config") {
    res.writeHead(200, { "Content-Type": "application/json" });
    res.end(JSON.stringify({
        lanOnly: true,
        rtcConfig
    }));
    return;
}

WebSocket Server Implementation

ErikrafTdropWsServer Class

The core WebSocket server is implemented in server/ws-server.js:

export default class ErikrafTdropWsServer {
    constructor(server, conf) {
        this._conf = conf;
        this._rooms = {}; // { roomId: peers[] }
        this._roomSecrets = {}; // { pairKey: roomSecret }
        this._keepAliveTimers = {};

        this._wss = new WebSocketServer({ server });
        this._wss.on('connection', (socket, request) => this._onConnection(new Peer(socket, request, conf)));
    }
}

Connection Management

Peer Connection Process

1. Connection Validation

// From ws-server.js lines 46-54
_onConnection(peer) {
    if (this._conf.allowLocalOnly && !isLocalIp(peer.ip)) {
        try {
            peer.socket.close(1008, 'LAN only');
        } catch (e) {
            peer.socket.terminate();
        }
        return;
    }

    peer.socket.on('message', message => this._onMessage(peer, message));
    peer.socket.onerror = e => console.error(e);
    this._keepAlive(peer);
}

2. IP Validation

The server validates local IP addresses for LAN-only mode:

// From ws-server.js lines 7-30
function isLocalIp(ip) {
    if (!ip) return false;
    if (ip === '127.0.0.1' || ip === '::1') return true;
    if (!ip.includes(":")) {
        return LOCAL_IPV4_PATTERNS.some(pattern => pattern.test(ip));
    }

    // IPv6 local address validation
    const firstWord = ip.split(":").find(el => !!el);
    if (/^fe[c-f][0-9a-f]$/.test(firstWord)) return true;
    if (/^fc[0-9a-f]{2}$/.test(firstWord)) return true;
    if (/^fd[0-9a-f]{2}$/.test(firstWord)) return true;
    if (firstWord === "fe80") return true;
    if (firstWord === "100") return true;

    return false;
}

3. Initial Configuration

// From ws-server.js lines 61-77
this._send(peer, {
    type: 'ws-config',
    wsConfig: {
        rtcConfig: this._conf.rtcConfig,
        wsFallback: this._conf.wsFallback
    }
});

// send displayName
this._send(peer, {
    type: 'display-name',
    displayName: peer.name.displayName,
    deviceName: peer.name.deviceName,
    clientType: peer.name.clientType,
    peerId: peer.id,
    peerIdHash: hasher.hashCodeSalted(peer.id)
});

Room Management

Room Types

The server manages three types of rooms:

1. IP-Based Rooms (Local Network)

// From ws-server.js lines 349-351
_joinIpRoom(peer) {
    this._joinRoom(peer, 'ip', peer.ip);
}

2. Secret Rooms (Paired Devices)

// From ws-server.js lines 353-358
_joinSecretRoom(peer, roomSecret) {
    this._joinRoom(peer, 'secret', roomSecret);
    peer.addRoomSecret(roomSecret);
}

3. Public Rooms (Temporary Rooms)

// From ws-server.js lines 360-367
_joinPublicRoom(peer, publicRoomId) {
    this._leavePublicRoom(peer); // prevent joining multiple public rooms
    this._joinRoom(peer, 'public-id', publicRoomId);
    peer.publicRoomId = publicRoomId;
}

Room Operations

Generic Room Join

// From ws-server.js lines 369-385
_joinRoom(peer, roomType, roomId) {
    if (this._rooms[roomId] && this._rooms[roomId][peer.id]) {
        this._leaveRoom(peer, roomType, roomId);
    }

    if (!this._rooms[roomId]) {
        this._rooms[roomId] = {};
    }

    this._notifyPeers(peer, roomType, roomId);
    this._rooms[roomId][peer.id] = peer;
}

Peer Notification

// From ws-server.js lines 435-468
_notifyPeers(peer, roomType, roomId) {
    if (!this._rooms[roomId]) return;

    // notify all other peers that peer joined
    for (const otherPeerId in this._rooms[roomId]) {
        if (otherPeerId === peer.id) continue;
        const otherPeer = this._rooms[roomId][otherPeerId];

        let msg = {
            type: 'peer-joined',
            peer: peer.getInfo(),
            roomType: roomType,
            roomId: roomId
        };

        this._send(otherPeer, msg);
    }

    // notify peer about peers already in the room
    const otherPeers = [];
    for (const otherPeerId in this._rooms[roomId]) {
        if (otherPeerId === peer.id) continue;
        otherPeers.push(this._rooms[roomId][otherPeerId].getInfo());
    }

    let msg = {
        type: 'peers',
        peers: otherPeers,
        roomType: roomType,
        roomId: roomId
    };

    this._send(peer, msg);
}

Device Pairing System

Pairing Initiation

// From ws-server.js lines 222-237
_onPairDeviceInitiate(sender) {
    let roomSecret = randomizer.getRandomString(256);
    let pairKey = this._createPairKey(sender, roomSecret);

    if (sender.pairKey) {
        this._removePairKey(sender.pairKey);
    }
    sender.pairKey = pairKey;

    this._send(sender, {
        type: 'pair-device-initiated',
        roomSecret: roomSecret,
        pairKey: pairKey
    });
    this._joinSecretRoom(sender, roomSecret);
}

Pair Key Generation

// From ws-server.js lines 327-340
_createPairKey(creator, roomSecret) {
    let pairKey;
    do {
        pairKey = crypto.randomInt(1000000, 1999999).toString().substring(1);
    } while (pairKey in this._roomSecrets)

    this._roomSecrets[pairKey] = {
        roomSecret: roomSecret,
        creator: creator
    }

    return pairKey;
}

Pairing Join Process

// From ws-server.js lines 239-265
_onPairDeviceJoin(sender, message) {
    if (sender.rateLimitReached()) {
        this._send(sender, { type: 'join-key-rate-limit' });
        return;
    }

    if (!this._roomSecrets[message.pairKey] || sender.id === this._roomSecrets[message.pairKey].creator.id) {
        this._send(sender, { type: 'pair-device-join-key-invalid' });
        return;
    }

    const roomSecret = this._roomSecrets[message.pairKey].roomSecret;
    const creator = this._roomSecrets[message.pairKey].creator;
    this._removePairKey(message.pairKey);

    this._send(sender, {
        type: 'pair-device-joined',
        roomSecret: roomSecret,
        peerId: creator.id
    });
    this._send(creator, {
        type: 'pair-device-joined',
        roomSecret: roomSecret,
        peerId: sender.id
    });
    this._joinSecretRoom(sender, roomSecret);
    this._removePairKey(sender.pairKey);
}

Message Handling

Message Router

// From ws-server.js lines 80-150
_onMessage(sender, message) {
    try {
        message = JSON.parse(message);
    } catch (e) {
        console.warn("WS: Received JSON is malformed");
        return;
    }

    switch (message.type) {
        case 'disconnect':
            this._onDisconnect(sender);
            break;
        case 'pong':
            this._setKeepAliveTimerToNow(sender);
            break;
        case 'join-ip-room':
            this._joinIpRoom(sender);
            break;
        case 'room-secrets':
            this._onRoomSecrets(sender, message);
            break;
        case 'pair-device-initiate':
            this._onPairDeviceInitiate(sender);
            break;
        case 'signal':
            this._signalAndRelay(sender, message);
            break;
        // ... other message types
    }
}

Signal Relay

// From ws-server.js lines 152-168
_signalAndRelay(sender, message) {
    const room = message.roomType === 'ip'
        ? sender.ip
        : message.roomId;

    // relay message to recipient
    if (message.to && Peer.isValidUuid(message.to) && this._rooms[room]) {
        const recipient = this._rooms[room][message.to];
        delete message.to;
        // add sender
        message.sender = {
            id: sender.id,
            rtcSupported: sender.rtcSupported
        };
        this._send(recipient, message);
    }
}

Connection Monitoring

Keep-Alive System

// From ws-server.js lines 489-509
_keepAlive(peer) {
    this._cancelKeepAlive(peer);
    let timeout = 1000;

    if (!this._keepAliveTimers[peer.id]) {
        this._keepAliveTimers[peer.id] = {
            timer: 0,
            lastBeat: Date.now()
        };
    }

    if (Date.now() - this._keepAliveTimers[peer.id].lastBeat > 5 * timeout) {
        this._disconnect(peer);
        return;
    }

    this._send(peer, { type: 'ping' });
    this._keepAliveTimers[peer.id].timer = setTimeout(() => this._keepAlive(peer), timeout);
}

Rate Limiting

// From peer.js lines 34-42
rateLimitReached() {
    if (this.requestRate >= 10) {
        return true;
    }
    this.requestRate += 1;
    setTimeout(() => this.requestRate -= 1, 10000);
    return false;
}

Security Features

IP Filtering

LAN-Only Mode: Restricts connections to local IP addresses
IP Validation: Comprehensive IPv4 and IPv6 local address detection
Connection Rejection: Automatic termination of non-local connections

Input Validation

JSON Parsing: Safe parsing with error handling
UUID Validation: Strict peer ID format validation
Room Secret Validation: Length and character validation

Rate Limiting

Request Throttling: 10 requests per 10 seconds per peer
Pairing Limits: Prevents brute force pairing attempts
Connection Limits: Configurable maximum connections

Performance Optimization

Memory Management

Room Cleanup: Automatic removal of empty rooms
Timer Management: Proper cleanup of keep-alive timers
Connection Cleanup: Graceful connection termination

Message Efficiency

Binary Support: WebSocket binary frame support for file transfers
Message Batching: Efficient message routing within rooms
Compression: Optional message compression for large payloads

This signaling server provides a robust foundation for peer discovery and WebRTC connection establishment while maintaining security and performance.

Documentation Index

​Signaling Server Architecture

​Server Overview

​Main Server Entry Point

​Configuration Endpoints

​WebSocket Server Implementation

​ErikrafTdropWsServer Class

​Connection Management

​Peer Connection Process

​1. Connection Validation

​2. IP Validation

​3. Initial Configuration

​Room Management

​Room Types

​1. IP-Based Rooms (Local Network)

​2. Secret Rooms (Paired Devices)

​3. Public Rooms (Temporary Rooms)

​Room Operations

​Generic Room Join

​Peer Notification

​Device Pairing System

​Pairing Initiation

​Pair Key Generation

​Pairing Join Process

​Message Handling

​Message Router

​Signal Relay

​Connection Monitoring

​Keep-Alive System

​Rate Limiting

​Security Features

​IP Filtering

​Input Validation

​Rate Limiting

​Performance Optimization

​Memory Management

​Message Efficiency

Signaling Server Architecture

Server Overview

Main Server Entry Point

Configuration Endpoints

WebSocket Server Implementation

ErikrafTdropWsServer Class

Connection Management

Peer Connection Process

1. Connection Validation

2. IP Validation

3. Initial Configuration

Room Management

Room Types

1. IP-Based Rooms (Local Network)

2. Secret Rooms (Paired Devices)

3. Public Rooms (Temporary Rooms)

Room Operations

Generic Room Join

Peer Notification

Device Pairing System

Pairing Initiation

Pair Key Generation

Pairing Join Process

Message Handling

Message Router

Signal Relay

Connection Monitoring

Keep-Alive System

Rate Limiting

Security Features

IP Filtering

Input Validation

Rate Limiting

Performance Optimization

Memory Management

Message Efficiency