ONEPROOF.LinkHid 0.0.9

ONEPROOF.LinkHid

Pure .NET library for communicating with the ONEPROOF LINK over USB HID. Zero native dependencies.

Features

• Barcode scanning - QR codes and PDF417 barcodes via HID events
• Device commands - Device ID, reboot, NFC status, peripheral reset, and more
• PC/SC reader listing - Enumerate smart card readers
• Zero native DLLs - Uses raw Windows HID API via P/Invoke. No external dependencies.

Requirements

• .NET 9 (Windows)
• ONEPROOF LINK

Installation

dotnet add package ONEPROOF.LinkHid

Quick Start

using LinkHid;
using LinkHid.Models;

using var device = new LinkDevice();

device.BarcodeScanned += (sender, e) =>
{
    Console.WriteLine($"{e.Type}: {e.Data}");
};

device.Connect();

string id = device.Settings!.GetDeviceId();  // "ONEPROOF:LINK"
string[] readers = LinkDevice.ListReaders();

WPF Usage

Events fire on a background thread. Marshal to the UI thread:

device.BarcodeScanned += (s, e) =>
{
    Dispatcher.Invoke(() => BarcodeText.Text = e.Data);
};

API Reference

LinkDevice

LinkDeviceSettings (via device.Settings)

IMPORTANT: ResetPeripherals()

What it does

ResetPeripherals() resets the NFC reader and barcode scanner on the LINK back to their idle/discovery state without disconnecting USB. Think of it as "clear the board and start fresh."

Why it exists

The LINK has multiple peripherals (NFC reader, barcode scanner) that maintain internal state during a transaction:

• The NFC reader enters passthrough mode when a phone taps for mDL verification. After BLE takes over, it stays in passthrough mode and won't detect new cards until reset.
• The barcode scanner can get stuck in a partial-read state after errors or timeouts.
• After BLE verification completes, the phone may still be physically on the reader. Without resetting, the LINK will re-detect the phone and fire a stale notification, causing errors.

Without calling ResetPeripherals(), the LINK will stop responding to new scans or NFC taps after the first transaction.

When to call it

1. After BLE verification completes (REQUIRED)

After your app finishes a BLE mDL verification flow, the NFC reader is still in passthrough mode. You must reset before the LINK can accept new input.

device.BarcodeScanned += async (s, e) =>
{
    // QR code scanned, start BLE verification
    var result = await RunBleVerification(e.Data);
    
    // BLE verification done, MUST reset peripherals.
    // NFC reader is still in passthrough mode from the handover.
    // Without this, the LINK won't detect new cards or barcodes.
    device.Settings!.ResetPeripherals();
    
    UpdateUI("Ready for next verification");
};

2. After any error or timeout during a transaction (REQUIRED)

If something goes wrong mid-transaction, the LINK may be stuck in a partial state. Reset clears it.

device.BarcodeScanned += async (s, e) =>
{
    try
    {
        var result = await RunBleVerification(e.Data);
        DisplayResult(result);
    }
    catch (Exception ex)
    {
        LogError(ex);
    }
    finally
    {
        // ALWAYS reset after a transaction, success or failure.
        device.Settings!.ResetPeripherals();
    }
};

3. Before each new verification cycle in a continuous loop (RECOMMENDED)

If your app runs in kiosk/loop mode, call reset at the top of each cycle to guarantee a clean state.

while (running)
{
    // Reset to clean state before waiting for input
    device.Settings!.ResetPeripherals();
    
    await WaitForNextVerification();
}

When you do NOT need to call it

Summary

Connect() > Scan barcode > BLE verification > ResetPeripherals() > Ready for next
                                  |
                                  |-- Success > ResetPeripherals()
                                  |-- Error   > ResetPeripherals()

Rule of thumb: if you did anything with BLE or NFC, call ResetPeripherals() before accepting new input.

License

Proprietary. Copyright (c) 2026 ONEPROOF Inc. All rights reserved.