Support connection via serial number

src/HidApi.Net.Tests/StringTests.cs

@@ -53,4 +53,17 @@ public void TestUtf32()
             }
         }
     }
+
+
+    [TestMethod]
+    public unsafe void CanCreateNullTerminatedString()
+    {
+        var result = "MyString";
+        var nullTerminatedString = WCharT.CreateNullTerminatedString(result);
+        fixed (byte* ptr = nullTerminatedString)
+        {
+            var r = WCharT.GetString(ptr);
+            r.Should().Be(result);   
+        }
+    }
 }

src/HidApi.Net/Device.cs

@@ -15,7 +15,21 @@ public class Device : IDisposable
     /// <param name="productId">product id of target device</param>
     public Device(ushort vendorId, ushort productId)
     {
-        handle = NativeMethods.Open(vendorId, productId, string.Empty);
+        handle = NativeMethods.Open(vendorId, productId, NullTerminatedString.Empty);
+
+        if (handle.IsInvalid)
+            HidException.Throw(handle);
+    }
+
+    /// <summary>
+    /// Connects to a given device.
+    /// </summary>
+    /// <param name="vendorId">Vendor id of target device</param>
+    /// <param name="productId">Product id of target device</param>
+    /// <param name="serialNumber">Serial number of target device</param>
+    public Device(ushort vendorId, ushort productId, string serialNumber)
+    {
+        handle = NativeMethods.Open(vendorId, productId, WCharT.CreateNullTerminatedString(serialNumber));
 
         if (handle.IsInvalid)
             HidException.Throw(handle);

src/HidApi.Net/HidApi.Net.csproj

@@ -26,7 +26,7 @@
   </PropertyGroup>
 
   <ItemGroup>
-    <PackageReference Include="Microsoft.SourceLink.GitHub" Version="1.1.1" PrivateAssets="All"/>
+    <PackageReference Include="Microsoft.SourceLink.GitHub" Version="1.1.1" PrivateAssets="All" />
     <InternalsVisibleTo Include="$(AssemblyName).Tester" />
     <InternalsVisibleTo Include="$(AssemblyName).Tests" />
     <None Include="../../readme.md" Pack="true" PackagePath="/" />

src/HidApi.Net/Internal/NativeMethods.cs

@@ -36,6 +36,17 @@ private static IntPtr Resolve(string libraryName, Assembly assembly, DllImportSe
         throw new Exception($"Could not find hidapi library tried: {string.Join(", ", libraries)}");
     }
 
+    public static DeviceSafeHandle Open(ushort vendorId, ushort productId, NullTerminatedString serialNumber)
+    {
+        unsafe
+        {
+            fixed(byte* ptr = serialNumber)
+            {
+                return Open(vendorId, productId, ptr);
+            }   
+        }
+    }
+
     public static int Write(DeviceSafeHandle device, ReadOnlySpan<byte> data)
     {
         return Write(device, ref MemoryMarshal.GetReference(data), (nuint) data.Length);
@@ -99,7 +110,7 @@ public static int GetInputReport(DeviceSafeHandle device, ReadOnlySpan<byte> dat
     public static extern unsafe void FreeEnumeration(NativeDeviceInfo* devices);
 
     [DllImport(Library, EntryPoint = "hid_open")]
-    public static extern DeviceSafeHandle Open(ushort vendorId, ushort productId, [MarshalAs(UnmanagedType.LPWStr)] string serialNumber);
+    private static extern unsafe DeviceSafeHandle Open(ushort vendorId, ushort productId, byte* serialNumber);
 
     [DllImport(Library, EntryPoint = "hid_open_path")]
     public static extern DeviceSafeHandle OpenPath([MarshalAs(UnmanagedType.LPStr)] string path);

src/HidApi.Net/Internal/NullTerminatedString.cs

@@ -0,0 +1,20 @@
+namespace HidApi;
+
+internal readonly ref struct NullTerminatedString
+{
+    public static NullTerminatedString Empty => new ();
+
+    private readonly ReadOnlySpan<byte> data;
+
+    public NullTerminatedString()
+    {
+        data = ReadOnlySpan<byte>.Empty;
+    }
+
+    internal NullTerminatedString(ref byte[] str)
+    {
+        data = str;
+    }
+
+    public ref readonly byte GetPinnableReference() => ref data.GetPinnableReference();
+}

src/HidApi.Net/Internal/Unicode.cs

@@ -4,6 +4,15 @@ namespace HidApi;
 
 internal static class Unicode
 {
+    public static NullTerminatedString CreateNullTerminatedString(string str)
+    {
+        var src = Encoding.Unicode.GetBytes(str);
+        var dest = new byte[src.Length + sizeof(ushort)];
+        Array.Copy(src, dest, src.Length);
+
+        return new NullTerminatedString(ref dest);
+    }
+
     public static ReadOnlySpan<byte> CreateBuffer(int size)
     {
         return new byte[size * sizeof(ushort)];

src/HidApi.Net/Internal/Utf32.cs

@@ -4,6 +4,15 @@ namespace HidApi;
 
 internal static class Utf32
 {
+    public static NullTerminatedString CreateNullTerminatedString(string str)
+    {
+        var src = Encoding.UTF32.GetBytes(str);
+        var dest = new byte[src.Length + sizeof(uint)];
+        Array.Copy(src, dest, src.Length);
+
+        return new NullTerminatedString(ref dest);
+    }
+
     public static ReadOnlySpan<byte> CreateBuffer(int size)
     {
         return new byte[size * sizeof(uint)];

src/HidApi.Net/Internal/WCharT.cs

@@ -46,4 +46,18 @@ public static ReadOnlySpan<byte> CreateBuffer(int size)
 
         throw new Exception("Unsupported platform to create a buffer");
     }
+
+    public static NullTerminatedString CreateNullTerminatedString(string str)
+    {
+        if (RuntimeInformation.IsOSPlatform(OSPlatform.Linux))
+            return Utf32.CreateNullTerminatedString(str);
+
+        if (RuntimeInformation.IsOSPlatform(OSPlatform.Windows))
+            return Unicode.CreateNullTerminatedString(str);
+
+        if (RuntimeInformation.IsOSPlatform(OSPlatform.OSX))
+            return Utf32.CreateNullTerminatedString(str);
+
+        throw new Exception("Unsupported platform to create a null terminated string");
+    }
 }