Webpack HMR EventSource requests are now proxied (rather than redirected) to the local HMR server. 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

@@ -7,6 +7,7 @@ using Microsoft.AspNetCore.Builder;
 using Microsoft.AspNetCore.Hosting;
 using Microsoft.Extensions.PlatformAbstractions;
 using Newtonsoft.Json;
+using System.Threading;
 
 // Putting in this namespace so it's always available whenever MapRoute is
 
@@ -14,8 +15,6 @@ namespace Microsoft.AspNetCore.Builder
 {
     public static class WebpackDevMiddleware
     {
-        private const string WebpackDevMiddlewareScheme = "http";
-        private const string WebpackHotMiddlewareEndpoint = "/__webpack_hmr";
         private const string DefaultConfigFile = "webpack.config.js";
 
         public static void UseWebpackDevMiddleware(
@@ -62,30 +61,27 @@ namespace Microsoft.AspNetCore.Builder
                     JsonConvert.SerializeObject(devServerOptions)).Result;
 
             // 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).
+            appBuilder.UseProxyToLocalWebpackDevMiddleware(devServerInfo.PublicPath, devServerInfo.Port, TimeSpan.FromSeconds(100));
+            appBuilder.UseProxyToLocalWebpackDevMiddleware("/__webpack_hmr", 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,
-                "localhost", devServerInfo.Port.ToString());
-            appBuilder.UseMiddleware<ConditionalProxyMiddleware>(devServerInfo.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);
-                });
-            });
+            // Also note that the webpack HMR service always uses HTTP, even if your app server uses HTTPS,
+            // because the HMR service has no need for HTTPS (the client doesn't see it directly - all traffic
+            // to it is proxied), and the HMR service couldn't use HTTPS anyway (in general it wouldn't have
+            // the necessary certificate).
+            var proxyOptions = new ConditionalProxyMiddlewareOptions(
+                "http", "localhost", proxyToPort.ToString(), requestTimeout);
+            appBuilder.UseMiddleware<ConditionalProxyMiddleware>(publicPath, proxyOptions);
         }
 
 #pragma warning disable CS0649