Start making standalone hosting work again by automatically locating the client app assembly

samples/HostedInAspNet.Server/Startup.cs

@@ -25,7 +25,7 @@ namespace HostedInAspNet.Server
                 app.UseBlazorDevelopmentServer("../HostedInAspNet.Client");
             }
 
-            app.UseBlazor<Client.Program>();
+            app.UseBlazor(clientAssembly: typeof(Client.Program).Assembly);
         }
     }
 }

samples/MonoSanity/Startup.cs

@@ -15,7 +15,7 @@ namespace MonoSanity
         {
             app.UseDeveloperExceptionPage();
             app.UseFileServer();
-            app.UseBlazor<MonoSanityClient.Examples>();         
+            app.UseBlazor(clientAssembly: typeof(MonoSanityClient.Examples).Assembly);
         }
     }
 }

samples/MonoSanityClient/Examples.cs

@@ -6,7 +6,7 @@ using System.Text;
 
 namespace MonoSanityClient
 {
-    public class Examples
+    public static class Examples
     {
         public static string AddNumbers(int a, int b)
             => (a + b).ToString();

src/Microsoft.Blazor.DevHost/Server/Startup.cs

@@ -1,8 +1,12 @@
 // Copyright (c) .NET Foundation. All rights reserved.
 // Licensed under the Apache License, Version 2.0. See License.txt in the project root for license information.
 
+using System;
+using System.Reflection;
 using Microsoft.AspNetCore.Builder;
+using Microsoft.AspNetCore.Hosting;
 using Microsoft.Extensions.DependencyInjection;
+using System.IO;
 
 namespace Microsoft.Blazor.DevHost.Server
 {
@@ -17,7 +21,35 @@ namespace Microsoft.Blazor.DevHost.Server
         {
             app.UseDeveloperExceptionPage();
             app.UseBlazorDevelopmentServer(".");
-            app.UseBlazor<object>(); // TODO
+            app.UseBlazor(clientAssembly: FindClientAssembly(app));
+        }
+
+        private static Assembly FindClientAssembly(IApplicationBuilder app)
+        {
+            var env = app.ApplicationServices.GetRequiredService<IHostingEnvironment>();
+            var contentRoot = env.ContentRootPath;
+            var binDir = FindClientBinDir(contentRoot);
+            var appName = Path.GetFileName(contentRoot); // TODO: Allow for the possibility that the assembly name has been overridden
+            var assemblyPath = Path.Combine(binDir, $"{appName}.dll");
+            if (!File.Exists(assemblyPath))
+            {
+                throw new FileNotFoundException($"Could not locate application assembly at expected location {assemblyPath}");
+            }
+
+            return Assembly.LoadFile(assemblyPath);
+        }
+
+        private static string FindClientBinDir(string clientAppSourceRoot)
+        {
+            var binDebugDir = Path.Combine(clientAppSourceRoot, "bin", "Debug");
+            var subdirectories = Directory.GetDirectories(binDebugDir);
+            if (subdirectories.Length != 1)
+            {
+                throw new InvalidOperationException($"Could not locate bin directory for Blazor app. " +
+                    $"Expected to find exactly 1 subdirectory in '{binDebugDir}', but found {subdirectories.Length}.");
+            }
+
+            return Path.Combine(binDebugDir, subdirectories[0]);
         }
     }
 }

src/Microsoft.Blazor.Server/BlazorAppBuilderExtensions.cs

@@ -5,19 +5,20 @@ using Microsoft.AspNetCore.StaticFiles;
 using Microsoft.Blazor.Server.ClientFilesystem;
 using System.Collections.Generic;
 using System.Net.Mime;
+using System.Reflection;
 
 namespace Microsoft.AspNetCore.Builder
 {
     public static class BlazorAppBuilderExtensions
     {
-        public static void UseBlazor<TProgram>(this IApplicationBuilder applicationBuilder)
+        public static void UseBlazor(
+            this IApplicationBuilder applicationBuilder,
+            Assembly clientAssembly)
         {
-            var clientAppAssembly = typeof(TProgram).Assembly;
-
             applicationBuilder.UseStaticFiles(new StaticFileOptions
             {
                 RequestPath = "/_framework",
-                FileProvider = ClientFileProvider.Instantiate(clientAppAssembly),
+                FileProvider = ClientFileProvider.Instantiate(clientAssembly),
                 ContentTypeProvider = CreateContentTypeProvider(),
             });
         }