HidClient

Common library class to receive updates from a USB HID and reconnect automatically when disconnected

1. Introduction
2. Prerequisites
3. Installation
4. Usage
5. Testing

Introduction

This library provides AbstractHidClient, a class that layers on top of HidSharp and provides the following useful abstractions.

• Automatically connect to a device with the given Vendor ID and Product ID
• If the device is not physically connected yet, wait for it to be available and use it automatically as soon as it's ready
• If the device disconnects, wait for it and automatically reconnect when it's available again
• Properties and events that let you observe the connection state
• Automatically run a message pump thread to receive data from the device

This common logic was extracted from Aldaviva/PowerMate so it could be reused in Aldaviva/WebScale.Net. It is intended to help developers write device-specific HID libraries without duplicating boilerplate connection management code in each project.

Prerequisites

• Any .NET runtime that supports .NET Standard 2.0 or later:
  • .NET 5.0 or later
  • .NET Core 2.0 or later
  • .NET Framework 4.6.1 or later
• Operating systems:
  • Windows
  • MacOS
  • Linux (although HidSharp seems to be unable to detect most devices on Linux)

Installation

dotnet add package HidClient

Usage

1. Create a subclass of AbstractHidClient and stub out the mandatory overrides.

   public class WebScale: AbstractHidClient {
   
       public WebScale() { }
       public WebScale(DeviceList deviceList): base(deviceList) { }
   
       protected override int VendorId { get; }
       protected override int ProductId { get; }
   
       protected override void OnHidRead(byte[] readBuffer) { }
   
   }

2. Override the VendorId and ProductId properties to return the VID and PID of your device.
   • In Windows, these can be found in Device Manager as the hexadecimal VID and PID values under Hardware Ids.
   • In Linux, these can be found in the output of lsusb as the hexadecimal ID colon-delimited value.

   protected override int VendorId { get; } = 0x2474;
   protected override int ProductId { get; } = 0x0550;

3. If you need to run initialization logic each time the device connects, for example resetting LED brightness that the device doesn't persist on its own, you may optionally override the OnConnect() method.

   protected override void OnConnect() {
       DeviceStream?.SetFeature(new byte[]{ 0x00, 0x41, 0x01, 0x01, 0x00, 0x50, 0x00, 0x00, 0x00 });
   }

4. Override the OnHidRead(byte[]) method to handle the bytes read from the device.

   protected override void OnHidRead(byte[] readBuffer) {
       double ounces = BitConverter.ToInt16(readBuffer, 4) / 10.0;
       Weight = Force.FromOunceForce(ounces);
   }

5. To send commands to the device, call DeviceStream.Write(byte[]) or DeviceStream.WriteAsync(byte[], int, int).

   public void Tare() {
       DeviceStream?.Write(new byte[]{ 0x04, 0x01 });
   }

Testing

See Aldaviva/PowerMate and Aldaviva/WebScale.Net for examples of unit testing HidClient. These test suites mock HidSharp using FakeItEasy so they don't need real devices connected to the build machines.