Capacitor P2P Counter Plugin

A Capacitor plugin that enables mesh network communication between multiple mobile devices using WebRTC with NFC handshake for initial device discovery. Supports real-time counter synchronization and duplicate entry detection across all connected devices.

Installation

npm install p2p-counter
npx cap sync

API

NFC Methods

• startNFCDiscovery(): Start NFC discovery mode
• stopNFCDiscovery(): Stop NFC discovery mode
• sendNFCMessage({ message: string }): Send NFC message for initial handshake

WebRTC Methods

• initializeWebRTC(): Initialize WebRTC connection
• createPeerConnection({ deviceId: string, isInitiator: boolean }): Create P2P connection with another device
• sendCounter({ code: string, isPresent: boolean }): Broadcast counter data and attendance status to all connected peers
• disconnectPeer({ deviceId: string }): Disconnect from a specific peer
• startKeepalive(): Start sending keepalive signals to maintain mesh stability
• stopKeepalive(): Stop sending keepalive signals

Events

• nfcDiscovered: Fired when NFC tag is discovered
• counterReceived: Fired when counter data is received from any peer
• peerConnected: Fired when peer connection is established
• peerDisconnected: Fired when peer connection is lost
• peerTimeout: Fired when a peer hasn't responded to keepalive signals
• duplicateDetected: Fired when a duplicate entry is detected

Network Health Monitoring

The plugin provides network health statistics through the getNetworkStats() method:

const stats = await P2PCounter.getNetworkStats();
console.log(stats.averageLatency);    // Average latency in ms
console.log(stats.packetLoss);        // Packet loss rate (0-1)
console.log(stats.keepaliveInterval); // Current keepalive interval in ms

Recommended thresholds:

• Good: < 500ms latency, < 5% packet loss
• Fair: < 1000ms latency, < 10% packet loss
• Poor: > 1000ms latency or > 10% packet loss

Connection Methods

The plugin supports multiple methods for establishing the initial WebRTC connection:

1. NFC Connection (Default)

// Start NFC discovery
await P2PCounter.startNFCDiscovery();

// Listen for NFC discovery
P2PCounter.addListener('nfcDiscovered', async (data) => {
  await P2PCounter.initializeWebRTC();
  await P2PCounter.createPeerConnection({
    deviceId: data.deviceId,
    isInitiator: true
  });
});

2. Share API Connection

// Share connection info using native share sheet
await P2PCounter.shareConnectionInfo();

// Receive shared connection info
P2PCounter.addListener('connectionReceived', async (data) => {
  await P2PCounter.receiveConnectionInfo({ sharedData: data.url });
});

3. QR Code Connection

// Generate QR code
const { qrData } = await P2PCounter.generateConnectionQR();
// Display qrData in your UI (base64 image)

// Scan QR code
await P2PCounter.scanConnectionQR();

Example Implementation

const initiateConnection = async () => {
  try {
    // Try Share API first on mobile
    if (platform === 'ios' || platform === 'android') {
      await P2PCounter.shareConnectionInfo();
    } else {
      // Fallback to QR code
      const { qrData } = await P2PCounter.generateConnectionQR();
      setQRCode(qrData); // Display in UI
    }
  } catch (err) {
    console.error('Connection initiation failed:', err);
  }
};

Each method will automatically establish the WebRTC connection once the initial handshake is complete.

Usage Example

import { P2PCounter } from 'capacitor-p2p-counter';

// Start NFC discovery
await P2PCounter.startNFCDiscovery();

// Listen for NFC discovery
P2PCounter.addListener('nfcDiscovered', async (data) => {
  // Initialize WebRTC when NFC is discovered
  await P2PCounter.initializeWebRTC();
  await P2PCounter.createPeerConnection({
    deviceId: data.deviceId,
    isInitiator: true
  });
});

// Listen for counter updates
P2PCounter.addListener('counterReceived', (data) => {
  console.log('Received code:', data.code, 'Present:', data.isPresent, 'at:', data.timestamp);
});

// Start keepalive system
await P2PCounter.startKeepalive();

// Listen for peer timeouts
P2PCounter.addListener('peerTimeout', (data) => {
  console.log('Peer timed out:', data.deviceId);
});
// Listen for duplicates
P2PCounter.addListener('duplicateDetected', (data) => {
  console.log('Duplicate code detected:', data.code);
});

// Monitor network health
setInterval(async () => {
  const stats = await P2PCounter.getNetworkStats();
  console.log('Network Health:', stats);
}, 5000);

// Send counter update
await P2PCounter.sendCounter({ code: 'QR123', isPresent: true });

// Update when attendee leaves
await P2PCounter.sendCounter({ code: 'QR123', isPresent: false });

// Disconnect from a peer
await P2PCounter.disconnectPeer({ deviceId: 'device123' });

Requirements

• iOS 13+
• Android API level 24+
• Capacitor 5+

Network Analysis and Scaling

Keepalive System Analysis

The plugin uses a 5-second ping/pong keepalive system. Here's the network traffic analysis:

1. Message Sizes:

   • Ping/Pong: ~65 bytes (including WebRTC overhead)
   • Counter Message: ~140 bytes

2. Traffic Per Device:

   Bandwidth per device = 52 × (n-1) bytes/second

   Where n is the number of connected devices

3. Practical Limits:

   • Optimal performance: 50-75 devices
   • Theoretical maximum: ~245 devices (using 10% of 1Mbps connection)

4. Limiting Factors:

   • Network latency
   • Message processing overhead
   • Connection management
   • Counter messages priority

5. Adaptive Keepalive System: The plugin implements an intelligent keepalive system that automatically adjusts based on network conditions:

   • Base interval: 5 seconds
   • Dynamic range: 5-30 seconds
   • Adjustment factors:
     • Network latency
     • Packet loss rate
     • Number of connected peers

   The system:

   • Monitors RTT (Round Trip Time) for each peer
   • Tracks packet loss patterns
   • Adjusts intervals per-peer when needed
   • Prevents cascade failures

6. Scaling Recommendations:

   • Increase keepalive interval to 10-15 seconds for larger networks
   • Implement hierarchical mesh with subnet coordinators
   • Use binary protocol instead of JSON for better efficiency

Notes

• NFC capabilities must be enabled in your app's capabilities (iOS) and manifest (Android)
• WebRTC connections require proper STUN/TURN server configuration for NAT traversal

Advanced Features Documentation

Mesh Network Management

MeshDiscoveryManager

Handles peer discovery and network topology management:

• startDiscovery(): Initiates peer discovery process
• stopDiscovery(): Stops peer discovery
• handleAnnouncement(deviceId: string, data: JSONObject): Processes peer announcements
• getDiscoverySnapshot(): Returns current network topology state
• cleanupStaleEntries(): Removes inactive peers

Configuration:

const discoveryConfig = {
announcementInterval: 10000, // 10 seconds
peerTimeout: 30000, // 30 seconds
maxPeers: 10 // Maximum direct connections
}

MeshTopologyManager

Manages mesh network topology and message routing:

• addPeer(deviceId: string, connectedPeers: string[]): Adds new peer to mesh
• removePeer(deviceId: string): Removes peer from mesh
• shouldRelayMessage(sourceId: string, targetId: string): Determines if local node should relay message
• getOptimalRoute(targetId: string): Calculates optimal message path
• reorganizeMesh(): Optimizes mesh connections

Configuration:

const topologyConfig = {
maxHops: 5, // Maximum message relay hops
minPeersPerNode: 2, // Minimum direct connections
maxPeersPerNode: 5, // Maximum direct connections
reorganizationCooldown: 10000 // 10 seconds between reorganizations
}

Message Management

MessagePriorityManager

Handles message prioritization and delivery guarantees:

• Priority Levels:
  • CRITICAL: Immediate delivery, max retries
  • HIGH: Prioritized delivery, multiple retries
  • MEDIUM: Standard delivery, limited retries
  • LOW: Best-effort delivery, no retries

await P2PCounter.sendCounter({
code: 'QR123',
isPresent: true,
priority: 'HIGH'
});

MessageProcessor

Handles message fragmentation and reassembly:

• Automatic message chunking (16KB chunks)
• Compression for messages > 1KB
• Guaranteed order delivery
• Message assembly and validation

MessageDeduplicator

Prevents duplicate message processing:

• Message fingerprinting
• Time-based deduplication window
• Cross-device synchronization

Network Analysis Tools

Enhanced statistics available through getNetworkStats():

interface DetailedNetworkStats {
averageLatency: number; // ms
packetLoss: number; // 0-1
keepaliveInterval: number; // ms
messageCount: number; // Total messages processed
networkStrength: number; // 0-1
peerStats: {
deviceId: string;
latency: number;
packetLoss: number;
connectionQuality: number;
}[];
topologyHealth: {
redundancy: number; // Network path redundancy
avgHopCount: number; // Average hops between nodes
fragmentationRisk: number; // Risk of network splitting
};
}

Message Flow Visualization

The plugin provides a visualization system for debugging and monitoring:

P2PCounter.addListener('messageStatus', (event: MessageStatusEvent) => {
console.log('Message:', event.messageId);
console.log('Status:', event.status);
console.log('Path:', event.path);
console.log('Attempts:', event.attempts);
console.log('Latency:', event.latency);
});

Advanced Usage Examples

Implementing Custom Message Priority

// Configure message priority
const message = {
type: 'counter',
code: 'QR123',
priority: 'HIGH',
retryPolicy: {
maxAttempts: 3,
backoffMs: 1000,
timeout: 5000
}
};
// Send with priority
await P2PCounter.sendPrioritizedMessage(message);

Mesh Network Optimization

// Configure mesh optimization
await P2PCounter.configureMesh({
optimizationInterval: 30000, // 30 seconds
targetRedundancy: 2, // Minimum path redundancy
loadBalancing: true, // Enable load balancing
adaptiveRouting: true // Enable adaptive routing
});
// Monitor mesh health
P2PCounter.addListener('meshHealth', (stats) => {
console.log('Redundancy:', stats.redundancy);
console.log('Average Hop Count:', stats.avgHopCount);
console.log('Network Stability:', stats.stability);
});

Performance Considerations

1. Message Priority System:

   • Critical messages: < 100ms delivery target
   • High priority: < 500ms delivery target
   • Standard messages: < 2000ms delivery target

2. Resource Usage:

   • Memory: ~50MB per 100 connected peers
   • CPU: 2-5% average utilization
   • Battery: ~2% per hour with 10 peers

3. Scaling Characteristics:

   • Linear bandwidth growth per peer
   • Quadratic message processing overhead
   • Optimized for 50-75 device mesh networks