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How ErikrafT Drop Works

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Connection Flow

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1. Initial Connection

1. WebSocket Connection: The client connects to the signaling server via WebSocket
2. Device Identification: A unique peer ID is generated and stored in sessionStorage
3. Network Detection: The server identifies the client’s IP address for local network grouping
4. WebRTC Capability Check: The browser’s WebRTC support is detected and reported

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2. Device Discovery

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Local Network Discovery

• Devices on the same IP address are automatically grouped together by the server
• The server maintains rooms based on IP addresses (_rooms[roomId])
• When a device connects, it receives a list of peers already in its IP-based room
• New connections trigger peer-joined events for existing devices

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Device Pairing

• Paired devices use encrypted 256-character room secrets stored in IndexedDB
• Room secrets are persisted across browser sessions using the PersistentStorage class
• The server matches devices with identical room secrets regardless of IP address
• Paired devices remain discoverable even when on different networks

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3. WebRTC Connection Process

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Signaling Phase

1. Offer Creation: The initiating peer creates a WebRTC offer using RTCPeerConnection.createOffer()
2. Signal Relay: The offer is sent through the WebSocket server to the target peer
3. Answer Creation: The receiving peer creates an answer using RTCPeerConnection.createAnswer()
4. ICE Exchange: Both peers exchange ICE candidates for network path discovery
5. Connection Establishment: WebRTC establishes a direct connection when possible

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DataChannel Setup

// From network.js lines 1126-1129
const channel = this._conn.createDataChannel('data-channel', {
    ordered: true,
    reliable: true
});

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File Transfer Process

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1. Transfer Request

1. File Metadata: The sender creates headers with file information (name, size, MIME type)
2. Transfer Request: A request message is sent to the recipient
3. User Confirmation: The recipient displays a transfer request dialog
4. Accept/Decline: The recipient responds with files-transfer-response

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2. File Chunking

// From network.js lines 1671-1672
this._chunkSize = 64000; // 64 KB chunks
this._maxPartitionSize = 1e6; // 1 MB partitions

• FileChunker Class: Breaks files into 64KB chunks
• Partition Management: Groups chunks into 1MB partitions for progress tracking
• Memory Management: Prevents browser memory overload with large files

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3. Data Transfer

1. Header Transmission: File metadata is sent first
2. Chunk Streaming: File chunks are sent sequentially via DataChannel
3. Progress Tracking: Both sender and receiver track transfer progress
4. Completion Notification: file-transfer-complete message confirms successful transfer

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Security Architecture

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WebRTC Encryption

• DTLS/SRTP: All WebRTC communications are encrypted by the browser
• Certificate Exchange: Peers exchange certificates during connection setup
• Perfect Forward Secrecy: Each session uses unique encryption keys

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Server Security

• No File Storage: The server never handles file content, only signaling
• Rate Limiting: Pairing attempts are limited to prevent abuse
• IP Validation: LAN-only mode restricts connections to local networks
• Hashed IDs: Peer IDs are salted and hashed for privacy

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Fallback Mechanisms

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WebSocket Fallback

1. Detection: The server detects WebRTC capability via webrtc_supported parameter
2. WSPeer Class: Creates WebSocket-based peer connections
3. Base64 Encoding: File chunks are encoded as base64 for WebSocket transmission
4. Server Relay: The WebSocket server relays all data between peers

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iOS Memory Management

// From network.js lines 819-822
if (window.iOS && request.totalSize >= 200*1024*1024) {
    // Request to send them in chunks of 200MB instead
    this.sendJSON({type: 'files-transfer-response', accepted: false, reason: 'ios-memory-limit'});
    return;
}

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Room Management

• IP Rooms: roomType: 'ip' - Devices on the same local network
• Secret Rooms: roomType: 'secret' - Paired devices using room secrets
• Public Rooms: roomType: 'public-id' - Temporary rooms with 5-character codes