For HMR, proxy all requests including /__webpack_hmr. Fixes #271.

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

@@ -30,6 +30,7 @@ namespace Microsoft.AspNetCore.SpaServices.Webpack
             _pathPrefix = pathPrefix;
             _options = options;
             _httpClient = new HttpClient(new HttpClientHandler());
+            _httpClient.Timeout = _options.RequestTimeout;
         }
 
         public async Task Invoke(HttpContext context)

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

@@ -1,16 +1,20 @@
+using System;
+
 namespace Microsoft.AspNetCore.SpaServices.Webpack
 {
     internal class ConditionalProxyMiddlewareOptions
     {
-        public ConditionalProxyMiddlewareOptions(string scheme, string host, string port)
+        public ConditionalProxyMiddlewareOptions(string scheme, string host, string port, TimeSpan requestTimeout)
         {
             Scheme = scheme;
             Host = host;
             Port = port;
+            RequestTimeout = requestTimeout;
         }
 
         public string Scheme { get; }
         public string Host { get; }
         public string Port { get; }
+        public TimeSpan RequestTimeout { get; }
     }
 }

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

@@ -1,5 +1,6 @@
 using System;
 using System.IO;
+using System.Threading;
 using System.Threading.Tasks;
 using Microsoft.AspNetCore.NodeServices;
 using Microsoft.AspNetCore.SpaServices.Webpack;
@@ -7,6 +8,7 @@ using Microsoft.AspNetCore.Builder;
 using Microsoft.AspNetCore.Hosting;
 using Microsoft.Extensions.PlatformAbstractions;
 using Newtonsoft.Json;
+using Microsoft.AspNetCore.Http;
 
 namespace Microsoft.AspNetCore.Builder
 {
@@ -15,8 +17,6 @@ namespace Microsoft.AspNetCore.Builder
     /// </summary>
     public static class WebpackDevMiddleware
     {
-        private const string WebpackDevMiddlewareScheme = "http";
-        private const string WebpackHotMiddlewareEndpoint = "/__webpack_hmr";
         private const string DefaultConfigFile = "webpack.config.js";
 
         /// <summary>
@@ -75,12 +75,18 @@ namespace Microsoft.AspNetCore.Builder
                 "/Content/Node/webpack-dev-middleware.js");
             var nodeScript = new StringAsTempFile(script); // 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
+            // of a request.
+            var hmrEndpoint = "/__webpack_hmr";
+
             // Tell Node to start the server hosting webpack-dev-middleware
             var devServerOptions = new
             {
                 webpackConfigPath = Path.Combine(nodeServicesOptions.ProjectPath, options.ConfigFile ?? DefaultConfigFile),
                 suppliedOptions = options,
-                understandsMultiplePublicPaths = true
+                understandsMultiplePublicPaths = true,
+                hotModuleReplacementEndpointUrl = hmrEndpoint
             };
             var devServerInfo =
                 nodeServices.InvokeExportAsync<WebpackDevServerInfo>(nodeScript.FileName, "createWebpackDevServer",
@@ -94,33 +100,30 @@ namespace Microsoft.AspNetCore.Builder
             }
 
             // Proxy the corresponding requests through ASP.NET and into the Node listener
+            // Anything under /<publicpath> (e.g., /dist) is proxied as a normal HTTP request with a typical timeout (100s is the default from HttpClient),
+            // plus /__webpack_hmr is proxied with infinite timeout, because it's an EventSource (long-lived request).
+            foreach (var publicPath in devServerInfo.PublicPaths)
+            {
+                appBuilder.UseProxyToLocalWebpackDevMiddleware(publicPath, devServerInfo.Port, TimeSpan.FromSeconds(100));
+            }
+            appBuilder.UseProxyToLocalWebpackDevMiddleware(hmrEndpoint, devServerInfo.Port, Timeout.InfiniteTimeSpan);
+        }
+
+        private static void UseProxyToLocalWebpackDevMiddleware(this IApplicationBuilder appBuilder, string publicPath, int proxyToPort, TimeSpan requestTimeout)
+        {
             // Note that this is hardcoded to make requests to "localhost" regardless of the hostname of the
             // server as far as the client is concerned. This is because ConditionalProxyMiddlewareOptions is
             // the one making the internal HTTP requests, and it's going to be to some port on this machine
             // because aspnet-webpack hosts the dev server there. We can't use the hostname that the client
             // sees, because that could be anything (e.g., some upstream load balancer) and we might not be
             // able to make outbound requests to it from here.
-            var proxyOptions = new ConditionalProxyMiddlewareOptions(WebpackDevMiddlewareScheme,
+            // Also note that the webpack HMR service always uses HTTP, even if your app server uses HTTPS,
-                "localhost", devServerInfo.Port.ToString());
+            // because the HMR service has no need for HTTPS (the client doesn't see it directly - all traffic
-            foreach (var publicPath in devServerInfo.PublicPaths)
+            // to it is proxied), and the HMR service couldn't use HTTPS anyway (in general it wouldn't have
-            {
+            // the necessary certificate).
-                appBuilder.UseMiddleware<ConditionalProxyMiddleware>(publicPath, proxyOptions);
+            var proxyOptions = new ConditionalProxyMiddlewareOptions(
-            }
+                "http", "localhost", proxyToPort.ToString(), requestTimeout);
-
+            appBuilder.UseMiddleware<ConditionalProxyMiddleware>(publicPath, proxyOptions);
-            // While it would be nice to proxy the /__webpack_hmr requests too, these return an EventStream,
-            // and the Microsoft.AspNetCore.Proxy code doesn't handle that entirely - it throws an exception after
-            // a while. So, just serve a 302 for those. But note that we must use the hostname that the client
-            // sees, not "localhost", so that it works even when you're not running on localhost (e.g., Docker).
-            appBuilder.Map(WebpackHotMiddlewareEndpoint, builder =>
-            {
-                builder.Use(next => ctx =>
-                {
-                    var hostname = ctx.Request.Host.Host;
-                    ctx.Response.Redirect(
-                        $"{WebpackDevMiddlewareScheme}://{hostname}:{devServerInfo.Port.ToString()}{WebpackHotMiddlewareEndpoint}");
-                    return Task.FromResult(0);
-                });
-            });
         }
 
 #pragma warning disable CS0649

src/Microsoft.AspNetCore.SpaServices/npm/aspnet-webpack/src/WebpackDevMiddleware.ts

@@ -19,6 +19,7 @@ export interface CreateDevServerCallback {
 interface CreateDevServerOptions {
     webpackConfigPath: string;
     suppliedOptions: DevServerOptions;
+    hotModuleReplacementEndpointUrl: string;
 }
 
 // These are the options configured in C# and then JSON-serialized, hence the C#-style naming
@@ -28,7 +29,7 @@ interface DevServerOptions {
     ReactHotModuleReplacement: boolean;
 }
 
-function attachWebpackDevMiddleware(app: any, webpackConfig: webpack.Configuration, enableHotModuleReplacement: boolean, enableReactHotModuleReplacement: boolean, hmrEndpoint: string) {
+function attachWebpackDevMiddleware(app: any, webpackConfig: webpack.Configuration, enableHotModuleReplacement: boolean, enableReactHotModuleReplacement: boolean, hmrClientEndpoint: string, hmrServerEndpoint: string) {
     // Build the final Webpack config based on supplied options
     if (enableHotModuleReplacement) {
         // For this, we only support the key/value config format, not string or string[], since
@@ -44,7 +45,7 @@ function attachWebpackDevMiddleware(app: any, webpackConfig: webpack.Configurati
         // Augment all entry points so they support HMR (unless they already do)
         Object.getOwnPropertyNames(entryPoints).forEach(entryPointName => {
             const webpackHotMiddlewareEntryPoint = 'webpack-hot-middleware/client';
-            const webpackHotMiddlewareOptions = `?path=` + encodeURIComponent(hmrEndpoint);
+            const webpackHotMiddlewareOptions = `?path=` + encodeURIComponent(hmrClientEndpoint);
             if (typeof entryPoints[entryPointName] === 'string') {
                 entryPoints[entryPointName] = [webpackHotMiddlewareEntryPoint + webpackHotMiddlewareOptions, entryPoints[entryPointName]];
             } else if (firstIndexOfStringStartingWith(entryPoints[entryPointName], webpackHotMiddlewareEntryPoint) < 0) {
@@ -117,7 +118,9 @@ function attachWebpackDevMiddleware(app: any, webpackConfig: webpack.Configurati
         } catch (ex) {
             throw new Error('HotModuleReplacement failed because of an error while loading \'webpack-hot-middleware\'. Error was: ' + ex.stack);
         }
-        app.use(webpackHotMiddlewareModule(compiler));
+        app.use(webpackHotMiddlewareModule(compiler, {
+            path: hmrServerEndpoint
+        }));
     }
 }
 
@@ -198,8 +201,16 @@ export function createWebpackDevServer(callback: CreateDevServerCallback, option
                     }
                     normalizedPublicPaths.push(removeTrailingSlash(publicPath));
 
-                    const hmrEndpoint = `http://localhost:${listener.address().port}/__webpack_hmr`;
+                    // Newer versions of Microsoft.AspNetCore.SpaServices will explicitly pass an HMR endpoint URL
-                    attachWebpackDevMiddleware(app, webpackConfig, enableHotModuleReplacement, enableReactHotModuleReplacement, hmrEndpoint);
+                    // (because it's relative to the app's URL space root, which the client doesn't otherwise know).
+                    // For back-compatibility, fall back on connecting directly to the underlying HMR server (though
+                    // that won't work if the app is hosted on HTTPS because of the mixed-content rule, and we can't
+                    // run the HMR server itself on HTTPS because in general it has no valid cert).
+                    const hmrClientEndpoint = options.hotModuleReplacementEndpointUrl   // The URL that we'll proxy (e.g., /__asp_webpack_hmr)
+                        || `http://localhost:${listener.address().port}/__webpack_hmr`; // Fall back on absolute URL to bypass proxying
+                    const hmrServerEndpoint = options.hotModuleReplacementEndpointUrl
+                        || '/__webpack_hmr';                                            // URL is relative to webpack dev server root
+                    attachWebpackDevMiddleware(app, webpackConfig, enableHotModuleReplacement, enableReactHotModuleReplacement, hmrClientEndpoint, hmrServerEndpoint);
                 }
             });