Davi NFC Agent

A lightweight NFC card reader agent with WebSocket broadcasting capabilities. Reads and writes NDEF formatted data from NFC tags and broadcasts to connected clients in real-time. This is for use for the NFC-related functionality integrated into the Davi platform.

Features

• Multiple Device Support: Hardware NFC readers and remote devices simultaneously
• Remote NFC Devices: Smartphones, browsers with WebNFC, or any device that can connect to the API
• Rich NDEF Read/Write: Text, URI, smart poster, vCard, MIME, geo, tel/sms/mailto, Android Application Records, and fully custom raw records
• Reliable Writes: Read-after-write verification, automatic retry on transient failures, and pre-flight capacity checks
• Tag Locking & Erase: Make tags read-only or wipe them back to an empty NDEF message
• Tag Capabilities: Memory size, usable capacity, and write/lock/password support reported with every scan
• Real-time WebSocket: Instant tag data broadcasting
• Secure by Default: Automatic TLS (WSS) with a CA bootstrap server, plus optional API-secret authentication
• Auto-discovery: mDNS/Bonjour advertising for zero-config device setup
• Cross-platform: Linux, macOS, Windows
• System Tray UI: Device management and status

Supported Devices

Hardware Readers: ACR122U, ACR1252U, and other PC/SC-compatible readers

Remote Devices: Any NFC-capable device that connects via the Device API, including:

• Smartphones (iPhone 7+/iOS 13+, Android 4.4+)
• Browsers with WebNFC (Chrome on Android)
• Custom hardware or IoT devices

Card Types: MIFARE Classic (incl. NDEF formatting and custom keys), DESFire, Ultralight, NTAG21x, ISO14443-4 Type 4A (experimental)

Quick Start

Download pre-built binaries from releases, or build from source:

git clone https://github.com/dotside-studios/davi-nfc-agent.git
cd davi-nfc-agent
go build .
./davi-nfc-agent

See the Installation Guide for platform-specific setup and troubleshooting.

Command-line Options

./davi-nfc-agent                       # System tray mode (default)
./davi-nfc-agent -version              # Print version information and exit
./davi-nfc-agent -device "ACS ACR122U" # Use a specific PC/SC reader by name
./davi-nfc-agent -device-port 9480     # Custom agent server port (default 9470, serves both devices and clients)
./davi-nfc-agent -api-secret mysecret  # Set the API authentication secret
./davi-nfc-agent -auto-tls=false       # Disable automatic TLS certificate management
./davi-nfc-agent -cert cert.pem -key key.pem  # Use your own TLS certificate
./davi-nfc-agent -config-dir ./config  # Override the config directory

By default the agent generates and persists a TLS certificate and an API secret under a platform-specific config directory, so paired devices keep working across restarts. Run ./davi-nfc-agent -help for the full list of flags.

Usage Examples

The agent runs a single server on one port that fills both roles, plus a bootstrap helper:

• Agent Server (port 9470): Serves both NFC devices (readers and smartphones, via /ws?mode=device) and client applications (via /ws) on the same port. The port is configurable via -device-port.
• CA Bootstrap Server (port 9472): Serves the TLS root certificate for device setup (auto-TLS only)

JavaScript / TypeScript

Use the included client library for browser or Node.js applications.

const client = new NFCClient('http://localhost:9470');

client.on('tagData', (data) => {
  console.log('Card:', data.uid, data.text);
});

await client.connect();

// Write to a card
await client.write({
  records: [{ type: 'text', content: 'Hello, NFC!' }]
});

Android (Kotlin)

Connect to the agent's client endpoint via WebSocket using OkHttp or similar.

val client = OkHttpClient()
val request = Request.Builder()
    .url("ws://192.168.1.100:9470/ws")
    .build()

val listener = object : WebSocketListener() {
    override fun onMessage(webSocket: WebSocket, text: String) {
        val msg = JSONObject(text)
        if (msg.getString("type") == "tagData") {
            val payload = msg.getJSONObject("payload")
            Log.d("NFC", "Card UID: ${payload.getString("uid")}")
        }
    }
}

client.newWebSocket(request, listener)

See API Reference for the full WebSocket protocol.

Use Your Phone as an NFC Reader

Connect your smartphone to the agent using the NFCDeviceClient.

const device = new NFCDeviceClient('ws://192.168.1.100:9470');

device.on('registered', ({ deviceID }) => {
  console.log('Registered as:', deviceID);
});

await device.connect();

// Start scanning with WebNFC (Chrome on Android)
if (NFCDeviceClient.isWebNFCSupported()) {
  await device.startNFCScanning();
}

Raw WebSocket

Connect directly without a client library. See API Reference for all message types.

const ws = new WebSocket('ws://localhost:9470/ws');

ws.onmessage = (event) => {
  const msg = JSON.parse(event.data);
  if (msg.type === 'tagData') {
    console.log('Card UID:', msg.payload.uid);
  }
};

// Write request
ws.send(JSON.stringify({
  type: 'writeRequest',
  payload: {
    records: [{ type: 'text', content: 'Hello!' }]
  }
}));

Extending

The agent's modular NFC layer supports adding custom readers and tag types beyond the built-in PC/SC and smartphone support. See Extending NFC Support to integrate your own hardware or protocols.

Contributing

See CONTRIBUTING.md for development setup, cross-compilation, and guidelines.

License

MIT License

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Copyright © 2025-2026 Ned Palacios and Dotside Studios. All rights reserved.