Add support for configuration (#19544)

* Add support for configuration

Fixes https://github.com/dotnet/aspnetcore/issues/18675

src/Components/Web.JS/src/Boot.WebAssembly.ts

@@ -4,10 +4,12 @@ import * as Environment from './Environment';
 import { monoPlatform } from './Platform/Mono/MonoPlatform';
 import { renderBatch } from './Rendering/Renderer';
 import { SharedMemoryRenderBatch } from './Rendering/RenderBatch/SharedMemoryRenderBatch';
-import { Pointer } from './Platform/Platform';
 import { shouldAutoStart } from './BootCommon';
 import { setEventDispatcher } from './Rendering/RendererEventDispatcher';
 import { WebAssemblyResourceLoader } from './Platform/WebAssemblyResourceLoader';
+import { WebAssemblyConfigLoader } from './Platform/WebAssemblyConfigLoader';
+import { BootConfigResult } from './Platform/BootConfig';
+import { Pointer } from './Platform/Platform';
 
 let started = false;
 
@@ -38,7 +40,12 @@ async function boot(options?: any): Promise<void> {
   });
 
   // Fetch the resources and prepare the Mono runtime
-  const resourceLoader = await WebAssemblyResourceLoader.initAsync();
+  const bootConfigResult = await BootConfigResult.initAsync();
+
+  const [resourceLoader] = await Promise.all([
+    WebAssemblyResourceLoader.initAsync(bootConfigResult.bootConfig),
+    WebAssemblyConfigLoader.initAsync(bootConfigResult)]);
+
   try {
     await platform.start(resourceLoader);
   } catch (ex) {

src/Components/Web.JS/src/Platform/BootConfig.ts

@@ -0,0 +1,38 @@
+export class BootConfigResult {
+  private constructor(public bootConfig: BootJsonData, public applicationEnvironment: string) {
+  }
+
+  static async initAsync(): Promise<BootConfigResult> {
+    const bootConfigResponse = await fetch('_framework/blazor.boot.json', {
+      method: 'GET',
+      credentials: 'include',
+      cache: 'no-cache'
+    });
+
+    // While we can expect an ASP.NET Core hosted application to include the environment, other
+    // hosts may not. Assume 'Production' in the absenc of any specified value.
+    const applicationEnvironment = bootConfigResponse.headers.get('Blazor-Environment') || 'Production';
+    const bootConfig: BootJsonData = await bootConfigResponse.json();
+
+    return new BootConfigResult(bootConfig, applicationEnvironment);
+  };
+}
+
+// Keep in sync with bootJsonData in Microsoft.AspNetCore.Components.WebAssembly.Build
+export interface BootJsonData {
+  readonly entryAssembly: string;
+  readonly resources: ResourceGroups;
+  readonly debugBuild: boolean;
+  readonly linkerEnabled: boolean;
+  readonly cacheBootResources: boolean;
+  readonly config: string[];
+}
+
+export interface ResourceGroups {
+  readonly assembly: ResourceList;
+  readonly pdb?: ResourceList;
+  readonly runtime: ResourceList;
+}
+
+export type ResourceList = { [name: string]: string };
+

src/Components/Web.JS/src/Platform/Mono/MonoPlatform.ts

@@ -1,9 +1,9 @@
-import { System_Object, System_String, System_Array, Pointer, Platform } from '../Platform';
 import { attachDebuggerHotkey, hasDebuggingEnabled } from './MonoDebugger';
 import { showErrorNotification } from '../../BootErrors';
 import { WebAssemblyResourceLoader, LoadingResource } from '../WebAssemblyResourceLoader';
+import { Platform, System_Array, Pointer, System_Object, System_String } from '../Platform';
 
-let mono_string_get_utf8: (managedString: System_String) => Mono.Utf8Ptr;
+let mono_string_get_utf8: (managedString: System_String) => Pointer;
 let mono_wasm_add_assembly: (name: string, heapAddress: number, length: number) => void;
 const appBinDirName = 'appBinDir';
 const uint64HighOrderShift = Math.pow(2, 32);
@@ -47,7 +47,7 @@ export const monoPlatform: Platform = {
     // FIXME this is unsafe, cuz raw objects could be GC'd.
 
     const utf8 = mono_string_get_utf8(managedString);
-    const res = Module.UTF8ToString(utf8);
+    const res = (<any>window['Module']).UTF8ToString(utf8);
     Module._free(utf8 as any);
     return res;
   },
@@ -168,7 +168,7 @@ function createEmscriptenModuleInstance(resourceLoader: WebAssemblyResourceLoade
   };
   module.preRun = [];
   module.postRun = [];
-  module.preloadPlugins = [];
+  (module as any).preloadPlugins = [];
 
   // Override the mechanism for fetching the main wasm file so we can connect it to our cache
   module.instantiateWasm = (imports, successCallback): WebAssembly.Exports => {
@@ -258,10 +258,10 @@ function getArrayDataPointer<T>(array: System_Array<T>): number {
   return <number><any>array + 12; // First byte from here is length, then following bytes are entries
 }
 
-function bindStaticMethod(assembly: string, typeName: string, method: string) : (...args: any[]) => any {
+function bindStaticMethod(assembly: string, typeName: string, method: string) {
   // Fully qualified name looks like this: "[debugger-test] Math:IntAdd"
   const fqn = `[${assembly}] ${typeName}:${method}`;
-  return Module.mono_bind_static_method(fqn);
+  return BINDING.bind_static_method(fqn);
 }
 
 function attachInteropInvoker(): void {

src/Components/Web.JS/src/Platform/Mono/MonoTypes.d.ts

@@ -1,31 +0,0 @@
-declare namespace Module {
-  function UTF8ToString(utf8: Mono.Utf8Ptr): string;
-  var preloadPlugins: any[];
-
-  function stackSave(): Mono.StackSaveHandle;
-  function stackAlloc(length: number): number;
-  function stackRestore(handle: Mono.StackSaveHandle): void;
-
-  // These should probably be in @types/emscripten
-  function FS_createPath(parent, path, canRead, canWrite);
-  function FS_createDataFile(parent, name, data, canRead, canWrite, canOwn);
-
-  function mono_bind_static_method(fqn: string): BoundStaticMethod;
-}
-
-declare namespace Mono {
-  interface Utf8Ptr { Utf8Ptr__DO_NOT_IMPLEMENT: any }
-  interface StackSaveHandle { StackSaveHandle__DO_NOT_IMPLEMENT: any }
-}
-
-// Mono uses this global to hang various debugging-related items on
-declare namespace MONO {
-  var loaded_files: string[];
-  var mono_wasm_runtime_is_ready: boolean;
-  function mono_wasm_runtime_ready (): void;
-  function mono_wasm_setenv (name: string, value: string): void;
-}
-
-// mono_bind_static_method allows arbitrary JS data types to be sent over the wire. However we are
-// artifically limiting it to a subset of types that we actually use.
-declare type BoundStaticMethod = (...args: (string | number | null)[]) => (string | number | null);

src/Components/Web.JS/src/Platform/Mono/MonoTypes.ts

@@ -0,0 +1,23 @@
+import { Pointer, System_String } from '../Platform';
+
+// Mono uses this global to hang various debugging-related items on
+
+declare interface MONO {
+  loaded_files: string[];
+  mono_wasm_runtime_ready (): void;
+  mono_wasm_setenv (name: string, value: string): void;
+}
+
+// Mono uses this global to hold low-level interop APIs
+declare interface BINDING {
+  js_string_to_mono_string(jsString: string): System_String;
+  js_typed_array_to_array(array: Uint8Array): Pointer;
+  js_typed_array_to_array<T>(array: Array<T>): Pointer;
+  conv_string(dotnetString: System_String | null): string | null;
+  bind_static_method(fqn: string, signature?: string): Function;
+}
+
+declare global {
+  var MONO: MONO;
+  var BINDING: BINDING;
+}

src/Components/Web.JS/src/Platform/Platform.ts

@@ -1,4 +1,4 @@
-import { WebAssemblyResourceLoader } from "./WebAssemblyResourceLoader";
+import { WebAssemblyResourceLoader } from './WebAssemblyResourceLoader';
 
 export interface Platform {
   start(resourceLoader: WebAssemblyResourceLoader): Promise<void>;

src/Components/Web.JS/src/Platform/WebAssemblyConfigLoader.ts

@@ -0,0 +1,28 @@
+import { BootConfigResult } from './BootConfig';
+import { System_String, Pointer } from './Platform';
+
+export class WebAssemblyConfigLoader {
+  static async initAsync(bootConfigResult: BootConfigResult): Promise<void> {
+    window['Blazor']._internal.getApplicationEnvironment = () => BINDING.js_string_to_mono_string(bootConfigResult.applicationEnvironment);
+
+    const configFiles = await Promise.all((bootConfigResult.bootConfig.config || [])
+      .filter(name => name === 'appsettings.json' || name === `appsettings.${bootConfigResult.applicationEnvironment}.json`)
+      .map(async name => ({ name, content: await getConfigBytes(name) })));
+
+    window['Blazor']._internal.getConfig = (dotNetFileName: System_String) : Pointer | undefined => {
+      const fileName = BINDING.conv_string(dotNetFileName);
+      const resolvedFile = configFiles.find(f => f.name === fileName);
+      return resolvedFile ? BINDING.js_typed_array_to_array(resolvedFile.content) : undefined;
+    };
+
+    async function getConfigBytes(file: string): Promise<Uint8Array> {
+      const response = await fetch(file, {
+        method: 'GET',
+        credentials: 'include',
+        cache: 'no-cache'
+      });
+
+      return new Uint8Array(await response.arrayBuffer());
+    }
+  }
+}

src/Components/Web.JS/src/Platform/WebAssemblyResourceLoader.ts

@@ -1,4 +1,5 @@
 import { toAbsoluteUri } from '../Services/NavigationManager';
+import { BootJsonData, ResourceList } from './BootConfig';
 const networkFetchCacheMode = 'no-cache';
 
 export class WebAssemblyResourceLoader {
@@ -6,20 +7,12 @@ export class WebAssemblyResourceLoader {
   private networkLoads: { [name: string]: LoadLogEntry } = {};
   private cacheLoads: { [name: string]: LoadLogEntry } = {};
 
-  static async initAsync(): Promise<WebAssemblyResourceLoader> {
-    const bootConfigResponse = await fetch('_framework/blazor.boot.json', {
-      method: 'GET',
-      credentials: 'include',
-      cache: networkFetchCacheMode
-    });
-    const bootConfig: BootJsonData = await bootConfigResponse.json();
+  static async initAsync(bootConfig: BootJsonData): Promise<WebAssemblyResourceLoader> {
     const cache = await getCacheToUseIfEnabled(bootConfig);
-
     return new WebAssemblyResourceLoader(bootConfig, cache);
   }
 
-  constructor (public readonly bootConfig: BootJsonData, private cacheIfUsed: Cache | null)
-  {
+  constructor(readonly bootConfig: BootJsonData, readonly cacheIfUsed: Cache | null) {
   }
 
   loadResources(resources: ResourceList, url: (name: string) => string): LoadingResource[] {
@@ -36,7 +29,7 @@ export class WebAssemblyResourceLoader {
       ? this.loadResourceWithCaching(this.cacheIfUsed, name, url, contentHash)
       : fetch(url, { cache: networkFetchCacheMode, integrity: this.bootConfig.cacheBootResources ? contentHash : undefined });
 
-      return { name, url, response };
+    return { name, url, response };
   }
 
   logToConsole() {
@@ -166,7 +159,7 @@ function countTotalBytes(loads: LoadLogEntry[]) {
 }
 
 function toDataSizeString(byteCount: number) {
-  return `${(byteCount / (1024*1024)).toFixed(2)} MB`;
+  return `${(byteCount / (1024 * 1024)).toFixed(2)} MB`;
 }
 
 function getPerformanceEntry(url: string): PerformanceResourceTiming | undefined {
@@ -175,21 +168,6 @@ function getPerformanceEntry(url: string): PerformanceResourceTiming | undefined
   }
 }
 
-// Keep in sync with bootJsonData in Microsoft.AspNetCore.Blazor.Build
-interface BootJsonData {
-  readonly entryAssembly: string;
-  readonly resources: ResourceGroups;
-  readonly debugBuild: boolean;
-  readonly linkerEnabled: boolean;
-  readonly cacheBootResources: boolean;
-}
-
-interface ResourceGroups {
-  readonly assembly: ResourceList;
-  readonly pdb?: ResourceList;
-  readonly runtime: ResourceList;
-}
-
 interface LoadLogEntry {
   responseBytes: number | undefined;
 }
@@ -199,5 +177,3 @@ export interface LoadingResource {
   url: string;
   response: Promise<Response>;
 }
-
-type ResourceList = { [name: string]: string };

src/Components/Web.JS/src/Rendering/RenderBatch/SharedMemoryRenderBatch.ts

@@ -1,5 +1,5 @@
 import { platform } from '../../Environment';
-import { RenderBatch, ArrayRange, ArrayRangeReader, ArrayBuilderSegment, RenderTreeDiff, RenderTreeEdit, RenderTreeFrame, ArrayValues, EditType, FrameType, RenderTreeFrameReader } from './RenderBatch';
+import { RenderBatch, ArrayRange, ArrayBuilderSegment, RenderTreeDiff, RenderTreeEdit, RenderTreeFrame, ArrayValues, EditType, FrameType, RenderTreeFrameReader } from './RenderBatch';
 import { Pointer, System_Array, System_Object } from '../../Platform/Platform';
 
 // Used when running on Mono WebAssembly for shared-memory interop. The code here encapsulates

src/Components/WebAssembly/Build/src/Tasks/GenerateBlazorBootJson.cs

@@ -30,6 +30,8 @@ namespace Microsoft.AspNetCore.Components.WebAssembly.Build
         [Required]
         public bool CacheBootResources { get; set; }
 
+        public ITaskItem[] ConfigurationFiles { get; set; }
+
         [Required]
         public string OutputPath { get; set; }
 
@@ -59,7 +61,8 @@ namespace Microsoft.AspNetCore.Components.WebAssembly.Build
                 cacheBootResources = CacheBootResources,
                 debugBuild = DebugBuild,
                 linkerEnabled = LinkerEnabled,
-                resources = new Dictionary<ResourceType, ResourceHashesByNameDictionary>()
+                resources = new Dictionary<ResourceType, ResourceHashesByNameDictionary>(),
+                config = new List<string>(),
             };
 
             // Build a two-level dictionary of the form:
@@ -90,6 +93,14 @@ namespace Microsoft.AspNetCore.Components.WebAssembly.Build
                 }
             }
 
+            if (ConfigurationFiles != null)
+            {
+                foreach (var configFile in ConfigurationFiles)
+                {
+                    result.config.Add(Path.GetFileName(configFile.ItemSpec));
+                }
+            }
+
             var serializer = new DataContractJsonSerializer(typeof(BootJsonData), new DataContractJsonSerializerSettings
             {
                 UseSimpleDictionaryFormat = true
@@ -148,6 +159,11 @@ namespace Microsoft.AspNetCore.Components.WebAssembly.Build
             /// Gets a value that determines if the linker is enabled.
             /// </summary>
             public bool linkerEnabled { get; set; }
+
+            /// <summary>
+            /// Config files for the application
+            /// </summary>
+            public List<string> config { get; set; }
         }
 
         public enum ResourceType

src/Components/WebAssembly/Build/src/targets/Blazor.MonoRuntime.targets

@@ -40,6 +40,8 @@
         $(ComponentsWebAssemblyFrameworkPath)" />
 
       <_WebAssemblyBCLAssembly Include="%(_WebAssemblyBCLFolder.Identity)*.dll" />
+
+      <_BlazorConfigFile Include="wwwroot\appsettings*.json" />
     </ItemGroup>
 
     <!--
@@ -298,12 +300,43 @@
     </ItemGroup>
   </Target>
 
+  <Target Name="_GenerateBlazorBootJsonInputHash">
+    <ItemGroup>
+      <_BlazorBootJsonHashInput Include="@(IntermediateAssembly)" />
+      <_BlazorBootJsonHashInput Include="@(_BlazorOutputWithTargetPath)" />
+      <_BlazorBootJsonHashInput Include="@(_BlazorConfigFile)" />
+    </ItemGroup>
+
+    <Hash ItemsToHash="@(_BlazorBootJsonHashInput)">
+      <Output TaskParameter="HashResult" PropertyName="_BlazorBootJsonInputHash" />
+    </Hash>
+
+    <PropertyGroup>
+      <_BlazorBootJsonInputHashFile>$(_BlazorIntermediateOutputPath)boot.json.input</_BlazorBootJsonInputHashFile>
+    </PropertyGroup>
+
+    <WriteLinesToFile
+      Lines="$(_BlazorBootJsonInputHash)"
+      File="$(_BlazorBootJsonInputHashFile)"
+      Overwrite="True"
+      WriteOnlyWhenDifferent="True" />
+
+  </Target>
+
   <UsingTask TaskName="GenerateBlazorBootJson" AssemblyFile="$(_BlazorTasksPath)" />
 
   <Target
     Name="_GenerateBlazorBootJson"
-    Inputs="$(MSBuildAllProjects);@(_BlazorOutputWithTargetPath)"
+    DependsOnTargets="_GenerateBlazorBootJsonInputHash"
+    Inputs="$(MSBuildAllProjects);@(_BlazorOutputWithTargetPath);$(_BlazorBootJsonInputHashFile)"
     Outputs="$(_BlazorBootJsonIntermediateOutputPath)">
+
+    <PropertyGroup>
+      <_IsDebugBuild>false</_IsDebugBuild>
+      <_IsDebugBuild Condition="'$(Configuration)' == 'Debug'">true</_IsDebugBuild>
+      <BlazorCacheBootResources Condition="'$(BlazorCacheBootResources)' == ''">true</BlazorCacheBootResources>
+    </PropertyGroup>
+
     <ItemGroup>
       <_BlazorBootResource Include="@(_BlazorOutputWithTargetPath->HasMetadata('BootManifestResourceType'))" />
     </ItemGroup>
@@ -312,18 +345,14 @@
       <Output TaskParameter="Items" ItemName="_BlazorBootResourceWithHash" />
     </GetFileHash>
 
-    <PropertyGroup>
-      <_IsDebugBuild>false</_IsDebugBuild>
-      <_IsDebugBuild Condition="'$(Configuration)' == 'Debug'">true</_IsDebugBuild>
-      <BlazorCacheBootResources Condition="'$(BlazorCacheBootResources)' == ''">true</BlazorCacheBootResources>
-    </PropertyGroup>
     <GenerateBlazorBootJson
       AssemblyPath="@(IntermediateAssembly)"
       Resources="@(_BlazorBootResourceWithHash)"
       DebugBuild="$(_IsDebugBuild)"
       LinkerEnabled="$(BlazorWebAssemblyEnableLinking)"
       CacheBootResources="$(BlazorCacheBootResources)"
-      OutputPath="$(_BlazorBootJsonIntermediateOutputPath)" />
+      OutputPath="$(_BlazorBootJsonIntermediateOutputPath)"
+      ConfigurationFiles="@(_BlazorConfigFile)" />
 
     <ItemGroup>
       <_BlazorOutputWithTargetPath Include="$(_BlazorBootJsonIntermediateOutputPath)" TargetOutputPath="$(_BaseBlazorRuntimeOutputPath)$(_BlazorBootJsonName)" />

src/Components/WebAssembly/Build/test/RuntimeDependenciesResolverTest.cs

@@ -51,8 +51,13 @@ namespace Microsoft.AspNetCore.Components.WebAssembly.Build
                 "Microsoft.Bcl.AsyncInterfaces.dll",
                 "Microsoft.Extensions.Configuration.Abstractions.dll",
                 "Microsoft.Extensions.Configuration.dll",
+                "Microsoft.Extensions.Configuration.FileExtensions.dll",
+                "Microsoft.Extensions.Configuration.Json.dll",
                 "Microsoft.Extensions.DependencyInjection.Abstractions.dll",
                 "Microsoft.Extensions.DependencyInjection.dll",
+                "Microsoft.Extensions.FileProviders.Abstractions.dll",
+                "Microsoft.Extensions.FileProviders.Physical.dll",
+                "Microsoft.Extensions.FileSystemGlobbing.dll",
                 "Microsoft.Extensions.Logging.Abstractions.dll",
                 "Microsoft.Extensions.Primitives.dll",
                 "Microsoft.JSInterop.dll",

src/Components/WebAssembly/DevServer/src/Server/Program.cs

@@ -7,7 +7,6 @@ using System.Linq;
 using Microsoft.AspNetCore.Hosting;
 using Microsoft.Extensions.Configuration;
 using Microsoft.Extensions.Hosting;
-using Microsoft.Extensions.Logging;
 
 namespace Microsoft.AspNetCore.Components.WebAssembly.DevServer.Server
 {
@@ -33,6 +32,7 @@ namespace Microsoft.AspNetCore.Components.WebAssembly.DevServer.Server
 
                     var inMemoryConfiguration = new Dictionary<string, string>
                     {
+                        [WebHostDefaults.EnvironmentKey] = "Development",
                         ["Logging:LogLevel:Microsoft"] = "Warning",
                         ["Logging:LogLevel:Microsoft.Hosting.Lifetime"] = "Information",
                         [WebHostDefaults.StaticWebAssetsKey] = name,

src/Components/WebAssembly/Server/src/ComponentsWebAssemblyApplicationBuilderExtensions.cs

@@ -51,10 +51,12 @@ namespace Microsoft.AspNetCore.Builder
             !rest.StartsWithSegments("/_framework/blazor.server.js"),
             subBuilder =>
             {
-                subBuilder.Use(async (ctx, next) =>
+                subBuilder.Use(async (context, next) =>
                 {
+                    context.Response.Headers.Append("Blazor-Environment", webHostEnvironment.EnvironmentName);
+
                     // This will invoke the static files middleware plugged-in below.
-                    NegotiateEncoding(ctx, webHostEnvironment);
+                    NegotiateEncoding(context, webHostEnvironment);
                     await next();
                 });
 

src/Components/WebAssembly/WebAssembly.Authentication/test/WebAssemblyAuthenticationServiceCollectionExtensionsTests.cs

@@ -2,8 +2,6 @@
 // Licensed under the Apache License, Version 2.0. See License.txt in the project root for license information.
 
 using System;
-using System.Collections.Generic;
-using System.Net;
 using Microsoft.AspNetCore.Components.WebAssembly.Hosting;
 using Microsoft.Extensions.DependencyInjection;
 using Microsoft.Extensions.DependencyInjection.Extensions;

src/Components/WebAssembly/WebAssembly/src/Hosting/IWebAssemblyHostEnvironment.cs

@@ -0,0 +1,17 @@
+// 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.
+
+namespace Microsoft.AspNetCore.Components.WebAssembly.Hosting
+{
+    /// <summary>
+    /// Provides information about the hosting environment an application is running in.
+    /// </summary>
+    public interface IWebAssemblyHostEnvironment
+    {
+        /// <summary>
+        /// Gets the name of the environment. This is configured to use the environment of the application hosting the Blazor WebAssembly application.
+        /// Configured to "Production" when not specified by the host.
+        /// </summary>
+        string Environment { get; }
+    }
+}

src/Components/WebAssembly/WebAssembly/src/Hosting/WebAssemblyHostBuilder.cs

@@ -3,10 +3,13 @@
 
 using System;
 using System.Collections.Generic;
+using System.IO;
 using System.Linq;
+using System.Runtime.InteropServices;
 using Microsoft.AspNetCore.Components.Routing;
 using Microsoft.AspNetCore.Components.WebAssembly.Services;
 using Microsoft.Extensions.Configuration;
+using Microsoft.Extensions.Configuration.Json;
 using Microsoft.Extensions.DependencyInjection;
 using Microsoft.Extensions.DependencyInjection.Extensions;
 using Microsoft.Extensions.Logging;
@@ -59,6 +62,41 @@ namespace Microsoft.AspNetCore.Components.WebAssembly.Hosting
             {
                 return Services.BuildServiceProvider();
             };
+
+            InitializeEnvironment();
+        }
+
+        private void InitializeEnvironment()
+        {
+            if (!RuntimeInformation.IsOSPlatform(OSPlatform.Create("WEBASSEMBLY")))
+            {
+                // The remainder of this method relies on the ability to make .NET WebAssembly-specific JSInterop calls.
+                // Note that this short-circuit exists as a way for unit tests running in .NET Core without JSInterop to run.
+                return;
+            }
+
+            var applicationEnvironment = DefaultWebAssemblyJSRuntime.Instance.InvokeUnmarshalled<string>("Blazor._internal.getApplicationEnvironment");
+            Services.AddSingleton<IWebAssemblyHostEnvironment>(new WebAssemblyHostEnvironment(applicationEnvironment));
+
+            var configFiles = new[]
+            {
+                "appsettings.json",
+                $"appsettings.{applicationEnvironment}.json"
+            };
+
+            foreach (var configFile in configFiles)
+            {
+                var appSettingsJson = DefaultWebAssemblyJSRuntime.Instance.InvokeUnmarshalled<string, byte[]>(
+                    "Blazor._internal.getConfig",
+                    configFile);
+
+                if (appSettingsJson != null)
+                {
+                    // Perf: Using this over AddJsonStream. This allows the linker to trim out the "File"-specific APIs and assemblies
+                    // for Configuration, of where there are several.
+                    Configuration.Add<JsonStreamConfigurationSource>(s => s.Stream = new MemoryStream(appSettingsJson));
+                }
+            }
         }
 
         /// <summary>
@@ -130,7 +168,7 @@ namespace Microsoft.AspNetCore.Components.WebAssembly.Hosting
             return new WebAssemblyHost(services, scope, configuration, RootComponents.ToArray());
         }
 
-        private void InitializeDefaultServices()
+        internal void InitializeDefaultServices()
         {
             Services.AddSingleton<IJSRuntime>(DefaultWebAssemblyJSRuntime.Instance);
             Services.AddSingleton<NavigationManager>(WebAssemblyNavigationManager.Instance);

src/Components/WebAssembly/WebAssembly/src/Hosting/WebAssemblyHostEnvironment.cs

@@ -0,0 +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.
+
+namespace Microsoft.AspNetCore.Components.WebAssembly.Hosting
+{
+    internal sealed class WebAssemblyHostEnvironment : IWebAssemblyHostEnvironment
+    {
+        public WebAssemblyHostEnvironment(string environment) => Environment = environment;
+
+        public string Environment { get; }
+    }
+}

src/Components/WebAssembly/WebAssembly/src/Microsoft.AspNetCore.Components.WebAssembly.csproj

@@ -9,7 +9,7 @@
 
   <ItemGroup>
     <Reference Include="Microsoft.AspNetCore.Components.Web" />
-    <Reference Include="Microsoft.Extensions.Configuration" />
+    <Reference Include="Microsoft.Extensions.Configuration.Json" />
     <Reference Include="Microsoft.JSInterop.WebAssembly" />
   </ItemGroup>
 

src/Components/test/E2ETest/Tests/WebAssemblyConfigurationHostedTest.cs

@@ -0,0 +1,55 @@
+// 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 BasicTestApp;
+using Microsoft.AspNetCore.Components.E2ETest;
+using Microsoft.AspNetCore.Components.E2ETest.Infrastructure;
+using Microsoft.AspNetCore.Components.E2ETest.Infrastructure.ServerFixtures;
+using Microsoft.AspNetCore.E2ETesting;
+using OpenQA.Selenium;
+using Xunit;
+using Xunit.Abstractions;
+
+namespace Microsoft.AspNetCore.Components.E2ETest.Tests
+{
+    public class WebAssemblyConfigurationHostedTest : ServerTestBase<BasicTestAppServerSiteFixture<TestServer.ClientStartup>>
+    {
+        private IWebElement _appElement;
+
+        public WebAssemblyConfigurationHostedTest(
+             BrowserFixture browserFixture,
+             BasicTestAppServerSiteFixture<TestServer.ClientStartup> serverFixture,
+             ITestOutputHelper output) :
+             base(browserFixture, serverFixture, output)
+        {
+        }
+
+        protected override void InitializeAsyncCore()
+        {
+            base.InitializeAsyncCore();
+
+            Navigate(ServerPathBase, noReload: false);
+            _appElement = Browser.MountTestComponent<ConfigurationComponent>();
+        }
+
+        [Fact]
+        public void WebAssemblyConfiguration_Works()
+        {
+            // Verify values from the default 'appsettings.json' are read.
+            Browser.Equal("Default key1-value", () => _appElement.FindElement(By.Id("key1")).Text);
+
+            // Verify values overriden by an environment specific 'appsettings.$(Environment).json are read
+            Assert.Equal("Prod key2-value", _appElement.FindElement(By.Id("key2")).Text);
+
+            // Lastly for sanity, make sure values specified in an environment specific 'appsettings.$(Environment).json are read
+            Assert.Equal("Prod key3-value", _appElement.FindElement(By.Id("key3")).Text);
+        }
+
+        [Fact]
+        public void WebAssemblyHostingEnvironment_Works()
+        {
+            // Verify values from the default 'appsettings.json' are read.
+            Browser.Equal("Production", () => _appElement.FindElement(By.Id("environment")).Text);
+        }
+    }
+}

src/Components/test/E2ETest/Tests/WebAssemblyConfigurationTest.cs

@@ -0,0 +1,57 @@
+// 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 BasicTestApp;
+using Microsoft.AspNetCore.Components.E2ETest;
+using Microsoft.AspNetCore.Components.E2ETest.Infrastructure;
+using Microsoft.AspNetCore.Components.E2ETest.Infrastructure.ServerFixtures;
+using Microsoft.AspNetCore.E2ETesting;
+using OpenQA.Selenium;
+using TestServer;
+using Xunit;
+using Xunit.Abstractions;
+
+namespace Microsoft.AspNetCore.Components.E2ETest.Tests
+{
+    public class WebAssemblyConfigurationTest : ServerTestBase<DevHostServerFixture<BasicTestApp.Program>>
+    {
+        private IWebElement _appElement;
+
+        public WebAssemblyConfigurationTest(
+             BrowserFixture browserFixture,
+             DevHostServerFixture<BasicTestApp.Program> serverFixture,
+             ITestOutputHelper output) :
+             base(browserFixture, serverFixture, output)
+        {
+            _serverFixture.PathBase = "/subdir";
+        }
+
+        protected override void InitializeAsyncCore()
+        {
+            base.InitializeAsyncCore();
+
+            Navigate(ServerPathBase, noReload: false);
+            _appElement = Browser.MountTestComponent<ConfigurationComponent>();
+        }
+
+        [Fact]
+        public void WebAssemblyConfiguration_Works()
+        {
+            // Verify values from the default 'appsettings.json' are read.
+            Browser.Equal("Default key1-value", () => _appElement.FindElement(By.Id("key1")).Text);
+
+            // Verify values overriden by an environment specific 'appsettings.$(Environment).json are read
+            Assert.Equal("Development key2-value", _appElement.FindElement(By.Id("key2")).Text);
+
+            // Lastly for sanity, make sure values specified in an environment specific 'appsettings.$(Environment).json are read
+            Assert.Equal("Development key3-value", _appElement.FindElement(By.Id("key3")).Text);
+        }
+
+        [Fact]
+        public void WebAssemblyHostingEnvironment_Works()
+        {
+            // Dev-Server defaults to Development. It's in the name!
+            Browser.Equal("Development", () => _appElement.FindElement(By.Id("environment")).Text);
+        }
+    }
+}

src/Components/test/testassets/BasicTestApp/ConfigurationComponent.razor

@@ -0,0 +1,10 @@
+@inject Microsoft.Extensions.Configuration.IConfiguration Config
+@inject Microsoft.AspNetCore.Components.WebAssembly.Hosting.IWebAssemblyHostEnvironment HostEnvironment
+
+<ul>
+    <li id="key1">@Config["key1"]</li>
+    <li id="key2">@Config["key2"]</li>
+    <li id="key3">@Config["key3"]</li>
+</ul>
+
+<div id="environment">@HostEnvironment.Environment</div>

src/Components/test/testassets/BasicTestApp/Index.razor

@@ -12,6 +12,7 @@
         <option value="BasicTestApp.CascadingValueTest.CascadingValueSupplier">Cascading values</option>
         <option value="BasicTestApp.ComponentRefComponent">Component ref component</option>
         <option value="BasicTestApp.ConcurrentRenderParent">Concurrent rendering</option>
+        <option value="BasicTestApp.ConfigurationComponent">Configuration</option>
         <option value="BasicTestApp.CounterComponent">Counter</option>
         <option value="BasicTestApp.CounterComponentUsingChild">Counter using child component</option>
         <option value="BasicTestApp.CounterComponentWrapper">Counter wrapped in parent</option>
@@ -28,12 +29,12 @@
         <option value="BasicTestApp.EventPreventDefaultComponent">Event preventDefault</option>
         <option value="BasicTestApp.ExternalContentPackage">External content package</option>
         <option value="BasicTestApp.FocusEventComponent">Focus events</option>
+        <option value="BasicTestApp.FormsTest.ExperimentalValidationComponent">Experimental validation</option>
         <option value="BasicTestApp.FormsTest.NotifyPropertyChangedValidationComponent">INotifyPropertyChanged validation</option>
         <option value="BasicTestApp.FormsTest.SimpleValidationComponent">Simple validation</option>
         <option value="BasicTestApp.FormsTest.SimpleValidationComponentUsingExperimentalValidator">Simple validation using experimental validator</option>
         <option value="BasicTestApp.FormsTest.TypicalValidationComponent">Typical validation</option>
         <option value="BasicTestApp.FormsTest.TypicalValidationComponentUsingExperimentalValidator">Typical validation using experimental validator</option>
-        <option value="BasicTestApp.FormsTest.ExperimentalValidationComponent">Experimental validation</option>
         <option value="BasicTestApp.GlobalizationBindCases">Globalization Bind Cases</option>
         <option value="BasicTestApp.HierarchicalImportsTest.Subdir.ComponentUsingImports">Imports statement</option>
         <option value="BasicTestApp.HtmlBlockChildContent">ChildContent HTML Block</option>
@@ -60,10 +61,10 @@
         <option value="BasicTestApp.ParentChildComponent">Parent component with child</option>
         <option value="BasicTestApp.PropertiesChangedHandlerParent">Parent component that changes parameters on child</option>
         <option value="BasicTestApp.RazorTemplates">Razor Templates</option>
+        <option value="BasicTestApp.Reconnection.ReconnectionComponent">Reconnection server-side blazor</option>
         <option value="BasicTestApp.RedTextComponent">Red text</option>
         <option value="BasicTestApp.ReliabilityComponent">Server reliability component</option>
         <option value="BasicTestApp.RenderFragmentToggler">Render fragment renderer</option>
-        <option value="BasicTestApp.Reconnection.ReconnectionComponent">Reconnection server-side blazor</option>
         <option value="BasicTestApp.ReorderingFocusComponent">Reordering focus retention</option>
         <option value="BasicTestApp.RouterTest.NavigationManagerComponent">NavigationManager Test</option>
         <option value="BasicTestApp.RouterTest.TestRouter">Router</option>

src/Components/test/testassets/BasicTestApp/wwwroot/appsettings.Development.json

@@ -0,0 +1,4 @@
+{
+  "key2": "Development key2-value",
+  "key3": "Development key3-value"
+}

src/Components/test/testassets/BasicTestApp/wwwroot/appsettings.Production.json

@@ -0,0 +1,4 @@
+{
+  "key2": "Prod key2-value",
+  "key3": "Prod key3-value"
+}

src/Components/test/testassets/BasicTestApp/wwwroot/appsettings.json

@@ -0,0 +1,4 @@
+{
+  "key1": "Default key1-value",
+  "key2": "Default key2-value"
+}