1 files changed, 87 insertions, 0 deletions

diff --git a/src/WixToolset.Dnc.Host/BootstrapperApplicationFactory.cs b/src/WixToolset.Dnc.Host/BootstrapperApplicationFactory.cs
new file mode 100644
index 00000000..0c6ea367
--- /dev/null
+++ b/src/WixToolset.Dnc.Host/BootstrapperApplicationFactory.cs
@@ -0,0 +1,87 @@
+// Copyright (c) .NET Foundation and contributors. All rights reserved. Licensed under the Microsoft Reciprocal License. See LICENSE.TXT file in the project root for full license information.
+
+namespace WixToolset.Dnc.Host
+{
+    using System;
+    using System.Linq;
+    using System.Reflection;
+    using System.Runtime.InteropServices;
+
+    /// <summary>
+    /// Entry point for the .NET Core host to create and return the BA to the engine.
+    /// Reflection is used instead of referencing WixToolset.Mba.Core directly to avoid requiring it in the AssemblyLoadContext.
+    /// </summary>
+    public sealed class BootstrapperApplicationFactory : IBootstrapperApplicationFactory
+    {
+        private string baFactoryAssemblyName;
+        private string baFactoryAssemblyPath;
+
+        public BootstrapperApplicationFactory(string baFactoryAssemblyName, string baFactoryAssemblyPath)
+        {
+            this.baFactoryAssemblyName = baFactoryAssemblyName;
+            this.baFactoryAssemblyPath = baFactoryAssemblyPath;
+        }
+
+        /// <summary>
+        /// Loads the bootstrapper application assembly and calls its IBootstrapperApplicationFactory.Create method.
+        /// </summary>
+        /// <param name="pArgs">Pointer to BOOTSTRAPPER_CREATE_ARGS struct.</param>
+        /// <param name="pResults">Pointer to BOOTSTRAPPER_CREATE_RESULTS struct.</param>
+        /// <exception cref="MissingAttributeException">The bootstrapper application assembly
+        /// does not define the <see cref="BootstrapperApplicationFactoryAttribute"/>.</exception>
+        public void Create(IntPtr pArgs, IntPtr pResults)
+        {
+            // Load the BA's IBootstrapperApplicationFactory.
+            var baFactoryType = BootstrapperApplicationFactory.GetBAFactoryTypeFromAssembly(this.baFactoryAssemblyName, this.baFactoryAssemblyPath);
+            var baFactory = Activator.CreateInstance(baFactoryType);
+            if (null == baFactory)
+            {
+                throw new InvalidBootstrapperApplicationFactoryException();
+            }
+
+            var createMethod = baFactoryType.GetMethod(nameof(Create), new[] { typeof(IntPtr), typeof(IntPtr) });
+            if (null == createMethod)
+            {
+                throw new InvalidBootstrapperApplicationFactoryException();
+            }
+            createMethod.Invoke(baFactory, new object[] { pArgs, pResults });
+        }
+
+        /// <summary>
+        /// Locates the <see cref="BootstrapperApplicationFactoryAttribute"/> and returns the specified type.
+        /// </summary>
+        /// <param name="assemblyName">The assembly that defines the IBootstrapperApplicationFactory implementation.</param>
+        /// <returns>The bootstrapper application factory <see cref="Type"/>.</returns>
+        private static Type GetBAFactoryTypeFromAssembly(string assemblyName, string assemblyPath)
+        {
+            // The default ALC shouldn't need help loading the assembly, since the host should have provided the deps.json
+            // when starting the runtime. But it doesn't hurt so keep this in case an isolated ALC is ever needed.
+            var alc = new DnchostAssemblyLoadContext(assemblyPath, false);
+            var asm = alc.LoadFromAssemblyName(new AssemblyName(assemblyName));
+
+            var attr = asm.GetCustomAttributes()
+                          .Where(a => a.GetType().FullName == "WixToolset.Mba.Core.BootstrapperApplicationFactoryAttribute")
+                          .SingleOrDefault();
+
+            if (null == attr)
+            {
+                throw new MissingAttributeException();
+            }
+
+            var baFactoryTypeProperty = attr.GetType().GetProperty("BootstrapperApplicationFactoryType", typeof(Type));
+            if (baFactoryTypeProperty == null || baFactoryTypeProperty.GetMethod == null)
+            {
+                throw new MissingAttributeException();
+            }
+
+            var baFactoryType = (Type)baFactoryTypeProperty.GetMethod.Invoke(attr, null);
+            return baFactoryType;
+        }
+
+        // Entry point for the DNC host.
+        public static IBootstrapperApplicationFactory CreateBAFactory([MarshalAs(UnmanagedType.LPWStr)] string baFactoryAssemblyName, [MarshalAs(UnmanagedType.LPWStr)] string baFactoryAssemblyPath)
+        {
+            return new BootstrapperApplicationFactory(baFactoryAssemblyName, baFactoryAssemblyPath);
+        }
+    }
+}