Remove System.Runtime.Loader dependency to enable net461 support. Use IApplicationLifetime instead of AssemblyLoadContext.Default.Unloading.

Author: SteveSandersonMS

src/Microsoft.AspNetCore.NodeServices.Sockets/SocketNodeInstance.cs

@@ -49,6 +49,7 @@ public SocketNodeInstance(NodeServicesOptions options, string socketAddress)
                 options.ProjectPath,
                 options.WatchFileExtensions,
                 MakeNewCommandLineOptions(socketAddress),
+                options.ApplicationStoppingToken,
                 options.NodeInstanceOutputLogger,
                 options.EnvironmentVariables,
                 options.InvocationTimeoutMilliseconds,

src/Microsoft.AspNetCore.NodeServices/Configuration/NodeServicesOptions.cs

@@ -1,5 +1,6 @@
 using System;
 using System.Collections.Generic;
+using System.Threading;
 using Microsoft.AspNetCore.NodeServices.HostingModels;
 using Microsoft.Extensions.Logging;
 using Microsoft.Extensions.DependencyInjection;
@@ -42,6 +43,12 @@ public NodeServicesOptions(IServiceProvider serviceProvider)
                 EnvironmentVariables["NODE_ENV"] = hostEnv.IsDevelopment() ? "development" : "production"; // De-facto standard values for Node
             }
 
+            var applicationLifetime = serviceProvider.GetService<IApplicationLifetime>();
+            if (applicationLifetime != null)
+            {
+                ApplicationStoppingToken = applicationLifetime.ApplicationStopping;
+            }
+
             // If the DI system gives us a logger, use it. Otherwise, set up a default one.
             var loggerFactory = serviceProvider.GetService<ILoggerFactory>();
             NodeInstanceOutputLogger = loggerFactory != null
@@ -93,5 +100,10 @@ public NodeServicesOptions(IServiceProvider serviceProvider)
         /// Specifies the maximum duration, in milliseconds, that your .NET code should wait for Node.js RPC calls to return.
         /// </summary>
         public int InvocationTimeoutMilliseconds { get; set; }
+
+        /// <summary>
+        /// A token that indicates when the host application is stopping.
+        /// </summary>
+        public CancellationToken ApplicationStoppingToken { get; set; }
     }
 }

src/Microsoft.AspNetCore.NodeServices/HostingModels/HttpNodeInstance.cs

@@ -42,6 +42,7 @@ public HttpNodeInstance(NodeServicesOptions options, int port = 0)
                 options.ProjectPath,
                 options.WatchFileExtensions,
                 MakeCommandLineOptions(port),
+                options.ApplicationStoppingToken,
                 options.NodeInstanceOutputLogger,
                 options.EnvironmentVariables,
                 options.InvocationTimeoutMilliseconds,

src/Microsoft.AspNetCore.NodeServices/HostingModels/OutOfProcessNodeInstance.cs

@@ -45,6 +45,7 @@ public abstract class OutOfProcessNodeInstance : INodeInstance
         /// <param name="projectPath">The root path of the current project. This is used when resolving Node.js module paths relative to the project root.</param>
         /// <param name="watchFileExtensions">The filename extensions that should be watched within the project root. The Node instance will automatically shut itself down if any matching file changes.</param>
         /// <param name="commandLineArguments">Additional command-line arguments to be passed to the Node.js instance.</param>
+        /// <param name="applicationStoppingToken">A token that indicates when the host application is stopping.</param>
         /// <param name="nodeOutputLogger">The <see cref="ILogger"/> to which the Node.js instance's stdout/stderr (and other log information) should be written.</param>
         /// <param name="environmentVars">Environment variables to be set on the Node.js process.</param>
         /// <param name="invocationTimeoutMilliseconds">The maximum duration, in milliseconds, to wait for RPC calls to complete.</param>
@@ -55,6 +56,7 @@ public OutOfProcessNodeInstance(
             string projectPath,
             string[] watchFileExtensions,
             string commandLineArguments,
+            CancellationToken applicationStoppingToken,
             ILogger nodeOutputLogger,
             IDictionary<string, string> environmentVars,
             int invocationTimeoutMilliseconds,
@@ -67,7 +69,7 @@ public OutOfProcessNodeInstance(
             }
 
             OutputLogger = nodeOutputLogger;
-            _entryPointScript = new StringAsTempFile(entryPointScript);
+            _entryPointScript = new StringAsTempFile(entryPointScript, applicationStoppingToken);
             _invocationTimeoutMilliseconds = invocationTimeoutMilliseconds;
             _launchWithDebugging = launchWithDebugging;
 

src/Microsoft.AspNetCore.NodeServices/Microsoft.AspNetCore.NodeServices.csproj

@@ -18,7 +18,6 @@
     <PackageReference Include="Microsoft.AspNetCore.Hosting.Abstractions" Version="$(AspNetCoreVersion)" />
     <PackageReference Include="Microsoft.Extensions.Logging.Console" Version="$(AspNetCoreVersion)" />
     <PackageReference Include="Newtonsoft.Json" Version="$(JsonNetVersion)" />
-    <PackageReference Include="System.Runtime.Loader" Version="$(CoreFxVersion)" />
   </ItemGroup>
 
   <Target Name="PrepublishScript" BeforeTargets="PrepareForPublish" Condition=" '$(IsCrossTargetingBuild)' != 'true' ">

src/Microsoft.AspNetCore.NodeServices/Util/StringAsTempFile.cs

@@ -1,5 +1,6 @@
 using System;
 using System.IO;
+using System.Threading;
 
 namespace Microsoft.AspNetCore.NodeServices
 {
@@ -11,22 +12,21 @@ public sealed class StringAsTempFile : IDisposable
         private bool _disposedValue;
         private bool _hasDeletedTempFile;
         private object _fileDeletionLock = new object();
+        private IDisposable _applicationLifetimeRegistration;
 
         /// <summary>
         /// Create a new instance of <see cref="StringAsTempFile"/>.
         /// </summary>
         /// <param name="content">The contents of the temporary file to be created.</param>
-        public StringAsTempFile(string content)
+        /// <param name="applicationStoppingToken">A token that indicates when the host application is stopping.</param>
+        public StringAsTempFile(string content, CancellationToken applicationStoppingToken)
         {
             FileName = Path.GetTempFileName();
             File.WriteAllText(FileName, content);
 
             // Because .NET finalizers don't reliably run when the process is terminating, also
             // add event handlers for other shutdown scenarios.
-            // Note that this still doesn't capture SIGKILL (at least on macOS) - there doesn't
-            // appear to be a way of doing that. So in that case, the temporary file will be
-            // left behind.
-            System.Runtime.Loader.AssemblyLoadContext.Default.Unloading += HandleAssemblyUnloading;
+            _applicationLifetimeRegistration = applicationStoppingToken.Register(EnsureTempFileDeleted);
         }
 
         /// <summary>
@@ -50,7 +50,7 @@ private void DisposeImpl(bool disposing)
                 if (disposing)
                 {
                     // Dispose managed state
-                    System.Runtime.Loader.AssemblyLoadContext.Default.Unloading -= HandleAssemblyUnloading;
+                    _applicationLifetimeRegistration.Dispose();
                 }
 
                 EnsureTempFileDeleted();
@@ -71,11 +71,6 @@ private void EnsureTempFileDeleted()
             }
         }
 
-        private void HandleAssemblyUnloading(System.Runtime.Loader.AssemblyLoadContext context)
-        {
-            EnsureTempFileDeleted();
-        }
-
         /// <summary>
         /// Implements the finalization part of the IDisposable pattern by calling Dispose(false).
         /// </summary>

src/Microsoft.AspNetCore.SpaServices/Prerendering/PrerenderTagHelper.cs

@@ -1,5 +1,6 @@
 using System;
 using System.Text;
+using System.Threading;
 using System.Threading.Tasks;
 using Microsoft.AspNetCore.Hosting;
 using Microsoft.AspNetCore.Http.Features;
@@ -24,6 +25,7 @@ public class PrerenderTagHelper : TagHelper
         private static INodeServices _fallbackNodeServices; // Used only if no INodeServices was registered with DI
 
         private readonly string _applicationBasePath;
+        private readonly CancellationToken _applicationStoppingToken;
         private readonly INodeServices _nodeServices;
 
         /// <summary>
@@ -35,6 +37,9 @@ public PrerenderTagHelper(IServiceProvider serviceProvider)
             var hostEnv = (IHostingEnvironment) serviceProvider.GetService(typeof(IHostingEnvironment));
             _nodeServices = (INodeServices) serviceProvider.GetService(typeof(INodeServices)) ?? _fallbackNodeServices;
             _applicationBasePath = hostEnv.ContentRootPath;
+            
+            var applicationLifetime = (IApplicationLifetime) serviceProvider.GetService(typeof(IApplicationLifetime));
+            _applicationStoppingToken = applicationLifetime.ApplicationStopping;
 
             // Consider removing the following. Having it means you can get away with not putting app.AddNodeServices()
             // in your startup file, but then again it might be confusing that you don't need to.
@@ -101,6 +106,7 @@ public override async Task ProcessAsync(TagHelperContext context, TagHelperOutpu
             var result = await Prerenderer.RenderToString(
                 _applicationBasePath,
                 _nodeServices,
+                _applicationStoppingToken,
                 new JavaScriptModuleExport(ModuleName)
                 {
                     ExportName = ExportName

src/Microsoft.AspNetCore.SpaServices/Prerendering/Prerenderer.cs

@@ -1,4 +1,5 @@
 using System;
+using System.Threading;
 using System.Threading.Tasks;
 using Microsoft.AspNetCore.NodeServices;
 
@@ -9,22 +10,16 @@ namespace Microsoft.AspNetCore.SpaServices.Prerendering
     /// </summary>
     public static class Prerenderer
     {
-        private static readonly Lazy<StringAsTempFile> NodeScript;
+        private static readonly object CreateNodeScriptLock = new object();
 
-        static Prerenderer()
-        {
-            NodeScript = new Lazy<StringAsTempFile>(() =>
-            {
-                var script = EmbeddedResourceReader.Read(typeof(Prerenderer), "/Content/Node/prerenderer.js");
-                return new StringAsTempFile(script); // Will be cleaned up on process exit
-            });
-        }
+        private static StringAsTempFile NodeScript;
 
         /// <summary>
         /// Performs server-side prerendering by invoking code in Node.js.
         /// </summary>
         /// <param name="applicationBasePath">The root path to your application. This is used when resolving project-relative paths.</param>
         /// <param name="nodeServices">The instance of <see cref="INodeServices"/> that will be used to invoke JavaScript code.</param>
+        /// <param name="applicationStoppingToken">A token that indicates when the host application is stopping.</param>
         /// <param name="bootModule">The path to the JavaScript file containing the prerendering logic.</param>
         /// <param name="requestAbsoluteUrl">The URL of the currently-executing HTTP request. This is supplied to the prerendering code.</param>
         /// <param name="requestPathAndQuery">The path and query part of the URL of the currently-executing HTTP request. This is supplied to the prerendering code.</param>
@@ -35,6 +30,7 @@ static Prerenderer()
         public static Task<RenderToStringResult> RenderToString(
             string applicationBasePath,
             INodeServices nodeServices,
+            CancellationToken applicationStoppingToken,
             JavaScriptModuleExport bootModule,
             string requestAbsoluteUrl,
             string requestPathAndQuery,
@@ -43,7 +39,7 @@ public static Task<RenderToStringResult> RenderToString(
             string requestPathBase)
         {
             return nodeServices.InvokeExportAsync<RenderToStringResult>(
-                NodeScript.Value.FileName,
+                GetNodeScriptFilename(applicationStoppingToken),
                 "renderToString",
                 applicationBasePath,
                 bootModule,
@@ -53,5 +49,19 @@ public static Task<RenderToStringResult> RenderToString(
                 timeoutMilliseconds,
                 requestPathBase);
         }
+
+        private static string GetNodeScriptFilename(CancellationToken applicationStoppingToken)
+        {
+            lock(CreateNodeScriptLock)
+            {
+                if (NodeScript == null)
+                {
+                    var script = EmbeddedResourceReader.Read(typeof(Prerenderer), "/Content/Node/prerenderer.js");
+                    NodeScript = new StringAsTempFile(script, applicationStoppingToken); // Will be cleaned up on process exit
+                }
+            }
+
+            return NodeScript.FileName;
+        }
     }
 }

src/Microsoft.AspNetCore.SpaServices/Webpack/WebpackDevMiddleware.cs

@@ -68,7 +68,7 @@ public static void UseWebpackDevMiddleware(
             // Get a filename matching the middleware Node script
             var script = EmbeddedResourceReader.Read(typeof(WebpackDevMiddleware),
                 "/Content/Node/webpack-dev-middleware.js");
-            var nodeScript = new StringAsTempFile(script); // Will be cleaned up on process exit
+            var nodeScript = new StringAsTempFile(script, nodeServicesOptions.ApplicationStoppingToken); // Will be cleaned up on process exit
 
             // Ideally, this would be relative to the application's PathBase (so it could work in virtual directories)
             // but it's not clear that such information exists during application startup, as opposed to within the context