Add custom dll resolver event

sources/Interop/Windows/Windows.cs

@@ -0,0 +1,67 @@
+// Copyright © Tanner Gooding and Contributors. Licensed under the MIT License (MIT). See License.md in the repository root for more information.
+
+// Ported from winrt/winstring.h in the Windows SDK for Windows 10.0.19041.0
+// Original source is Copyright © Microsoft. All rights reserved.
+
+using System;
+using System.Reflection;
+using System.Runtime.CompilerServices;
+using System.Runtime.InteropServices;
+
+namespace TerraFX.Interop
+{
+    public static unsafe partial class Windows
+    {
+        /// <summary>Raised whenever a native library is loaded by TerraFX.Interop.Windows. Handlers can be added to this event to customize how libraries are loaded, and they will be used first whenever a new native library is being resolved.</summary>
+        public static event DllImportResolver? ResolveLibrary;
+
+        /// <summary>Initializes the DLL resolver for the current assembly.</summary>
+        /// <returns>Just <see langword="null"/>, this method is only used to skip the static constructor and keep this type as <see langword="beforefieldinit"/>.</returns>
+        [ModuleInitializer]
+        internal static void SetDllImportResolver()
+        {
+            NativeLibrary.SetDllImportResolver(Assembly.GetExecutingAssembly(), OnDllImport);
+        }
+
+        /// <summary>The default <see cref="DllImportResolver"/> for TerraFX.Interop.Windows.</summary>
+        /// <inheritdoc cref="DllImportResolver"/>
+        private static IntPtr OnDllImport(string libraryName, Assembly assembly, DllImportSearchPath? searchPath)
+        {
+            if (TryResolveLibrary(libraryName, assembly, searchPath, out IntPtr nativeLibrary))
+            {
+                return nativeLibrary;
+            }
+
+            return NativeLibrary.Load(libraryName, assembly, searchPath);
+        }
+
+        /// <summary>Tries to resolve a native library using the handlers for the <see cref="ResolveLibrary"/> event.</summary>
+        /// <param name="libraryName">The native library to resolve.</param>
+        /// <param name="assembly">The assembly requesting the resolution.</param>
+        /// <param name="searchPath">The <see cref="DllImportSearchPath"/> value on the P/Invoke or assembly, or <see langword="null"/>.</param>
+        /// <param name="nativeLibrary">The loaded library, if one was resolved.</param>
+        /// <returns>Whether or not the requested library was successfully loaded.</returns>
+        private static bool TryResolveLibrary(string libraryName, Assembly assembly, DllImportSearchPath? searchPath, out IntPtr nativeLibrary)
+        {
+            var resolveLibrary = ResolveLibrary;
+
+            if (resolveLibrary != null)
+            {
+                var resolvers = resolveLibrary.GetInvocationList();
+
+                foreach (DllImportResolver resolver in resolvers)
+                {
+                    nativeLibrary = resolver(libraryName, assembly, searchPath);
+
+                    if (nativeLibrary != IntPtr.Zero)
+                    {
+                        return true;
+                    }
+                }
+            }
+
+            nativeLibrary = IntPtr.Zero;
+            return false;
+        }
+    }
+}