From 2c268a4eca153ea2a3dcd3698e08092c82eb9bd7 Mon Sep 17 00:00:00 2001
From: Steve Sanderson <SteveSandersonMS@users.noreply.github.com>
Date: Thu, 1 Mar 2018 10:32:58 +0000
Subject: [PATCH] Live reloading (currently enabled only for command-line
 builds - will add VS support next)

---
 Blazor.sln                                    |  12 ++
 .../src/Boot.ts                               |   8 +
 .../src/LiveReloading.ts                      |  48 ++++++
 .../Cli/Commands/BuildIndexHtmlCommand.cs     |   5 +
 .../Core/IndexHtmlWriter.cs                   |  23 ++-
 .../targets/All.props                         |   9 ++
 .../targets/All.targets                       |   3 +-
 .../targets/Blazor.MonoRuntime.props          |   6 +-
 .../targets/Blazor.MonoRuntime.targets        |  23 ++-
 .../BlazorAppBuilderExtensions.cs             |  15 +-
 .../BlazorConfig.cs                           |  18 +++
 .../LiveReloadingContext.cs                   | 140 ++++++++++++++++++
 .../LiveReloadingExtensions.cs                |  21 +++
 .../Microsoft.AspNetCore.Blazor.Server.csproj |   1 +
 .../IndexHtmlWriterTest.cs                    |  30 +++-
 .../ServerFixtures/DevHostServerFixture.cs    |  19 ++-
 ...Microsoft.AspNetCore.Blazor.E2ETest.csproj |   1 +
 .../Tests/LiveReloadingTest.cs                | 118 +++++++++++++++
 test/testapps/LiveReloadTestApp/Home.cshtml   |   1 +
 .../LiveReloadTestApp.csproj                  |  21 +++
 test/testapps/LiveReloadTestApp/Program.cs    |  15 ++
 .../LiveReloadTestApp/wwwroot/index.html      |  19 +++
 .../LiveReloadTestApp/wwwroot/someJsFile.js   |   3 +
 23 files changed, 539 insertions(+), 20 deletions(-)
 create mode 100644 src/Microsoft.AspNetCore.Blazor.Browser.JS/src/LiveReloading.ts
 create mode 100644 src/Microsoft.AspNetCore.Blazor.Server/LiveReloadingContext.cs
 create mode 100644 src/Microsoft.AspNetCore.Blazor.Server/LiveReloadingExtensions.cs
 create mode 100644 test/Microsoft.AspNetCore.Blazor.E2ETest/Tests/LiveReloadingTest.cs
 create mode 100644 test/testapps/LiveReloadTestApp/Home.cshtml
 create mode 100644 test/testapps/LiveReloadTestApp/LiveReloadTestApp.csproj
 create mode 100644 test/testapps/LiveReloadTestApp/Program.cs
 create mode 100644 test/testapps/LiveReloadTestApp/wwwroot/index.html
 create mode 100644 test/testapps/LiveReloadTestApp/wwwroot/someJsFile.js

diff --git a/Blazor.sln b/Blazor.sln
index 909b4b5165..853eabe2ae 100644
--- a/Blazor.sln
+++ b/Blazor.sln
@@ -90,6 +90,8 @@ Project("{FAE04EC0-301F-11D3-BF4B-00C04F79EFBC}") = "Microsoft.VisualStudio.Blaz
 EndProject
 Project("{9A19103F-16F7-4668-BE54-9A1E7A4F7556}") = "TestContentPackage", "test\testapps\TestContentPackage\TestContentPackage.csproj", "{C57382BC-EE93-49D5-BC40-5C98AF8AA048}"
 EndProject
+Project("{9A19103F-16F7-4668-BE54-9A1E7A4F7556}") = "LiveReloadTestApp", "test\testapps\LiveReloadTestApp\LiveReloadTestApp.csproj", "{0246AA77-1A27-4A67-874B-6EF6F99E414E}"
+EndProject
 Global
 	GlobalSection(SolutionConfigurationPlatforms) = preSolution
 		Debug|Any CPU = Debug|Any CPU
@@ -281,6 +283,7 @@ Global
 		{F3E02B21-1127-431A-B832-0E53CB72097B}.Debug|Any CPU.ActiveCfg = Debug|Any CPU
 		{F3E02B21-1127-431A-B832-0E53CB72097B}.DebugNoVSIX|Any CPU.ActiveCfg = Debug|Any CPU
 		{F3E02B21-1127-431A-B832-0E53CB72097B}.Release|Any CPU.ActiveCfg = Release|Any CPU
+		{F3E02B21-1127-431A-B832-0E53CB72097B}.Release|Any CPU.Build.0 = Release|Any CPU
 		{F3E02B21-1127-431A-B832-0E53CB72097B}.ReleaseNoVSIX|Any CPU.ActiveCfg = Release|Any CPU
 		{FF25111E-5A3E-48A3-96D8-08A2C5A2A91C}.Debug|Any CPU.ActiveCfg = Debug|Any CPU
 		{FF25111E-5A3E-48A3-96D8-08A2C5A2A91C}.Debug|Any CPU.Build.0 = Debug|Any CPU
@@ -312,6 +315,14 @@ Global
 		{C57382BC-EE93-49D5-BC40-5C98AF8AA048}.Release|Any CPU.Build.0 = Release|Any CPU
 		{C57382BC-EE93-49D5-BC40-5C98AF8AA048}.ReleaseNoVSIX|Any CPU.ActiveCfg = Release|Any CPU
 		{C57382BC-EE93-49D5-BC40-5C98AF8AA048}.ReleaseNoVSIX|Any CPU.Build.0 = Release|Any CPU
+		{0246AA77-1A27-4A67-874B-6EF6F99E414E}.Debug|Any CPU.ActiveCfg = Debug|Any CPU
+		{0246AA77-1A27-4A67-874B-6EF6F99E414E}.Debug|Any CPU.Build.0 = Debug|Any CPU
+		{0246AA77-1A27-4A67-874B-6EF6F99E414E}.DebugNoVSIX|Any CPU.ActiveCfg = Debug|Any CPU
+		{0246AA77-1A27-4A67-874B-6EF6F99E414E}.DebugNoVSIX|Any CPU.Build.0 = Debug|Any CPU
+		{0246AA77-1A27-4A67-874B-6EF6F99E414E}.Release|Any CPU.ActiveCfg = Release|Any CPU
+		{0246AA77-1A27-4A67-874B-6EF6F99E414E}.Release|Any CPU.Build.0 = Release|Any CPU
+		{0246AA77-1A27-4A67-874B-6EF6F99E414E}.ReleaseNoVSIX|Any CPU.ActiveCfg = Release|Any CPU
+		{0246AA77-1A27-4A67-874B-6EF6F99E414E}.ReleaseNoVSIX|Any CPU.Build.0 = Release|Any CPU
 	EndGlobalSection
 	GlobalSection(SolutionProperties) = preSolution
 		HideSolutionNode = FALSE
@@ -352,6 +363,7 @@ Global
 		{43E39257-7DC1-46BD-9BD9-2319A1313D07} = {F563ABB6-85FB-4CFC-B0D2-1D5130E8246D}
 		{9088E4E4-B855-457F-AE9E-D86709A5E1F4} = {F563ABB6-85FB-4CFC-B0D2-1D5130E8246D}
 		{C57382BC-EE93-49D5-BC40-5C98AF8AA048} = {4AE0D35B-D97A-44D0-8392-C9240377DCCE}
+		{0246AA77-1A27-4A67-874B-6EF6F99E414E} = {4AE0D35B-D97A-44D0-8392-C9240377DCCE}
 	EndGlobalSection
 	GlobalSection(ExtensibilityGlobals) = postSolution
 		SolutionGuid = {504DA352-6788-4DC0-8705-82167E72A4D3}
diff --git a/src/Microsoft.AspNetCore.Blazor.Browser.JS/src/Boot.ts b/src/Microsoft.AspNetCore.Blazor.Browser.JS/src/Boot.ts
index 065c711523..7ddd84ff61 100644
--- a/src/Microsoft.AspNetCore.Blazor.Browser.JS/src/Boot.ts
+++ b/src/Microsoft.AspNetCore.Blazor.Browser.JS/src/Boot.ts
@@ -1,5 +1,6 @@
 import { platform } from './Environment';
 import { getAssemblyNameFromUrl } from './Platform/DotNet';
+import { enableLiveReloading } from './LiveReloading';
 import './Rendering/Renderer';
 import './Services/Http';
 import './Services/UriHelper';
@@ -36,6 +37,13 @@ async function boot() {
 
   // Start up the application
   platform.callEntryPoint(entryPointAssemblyName, entryPointMethod, []);
+
+  // Enable live reloading only if there's a "reload" attribute on the <script> tag.
+  // In production, this should not be the case.
+  const reloadUri = thisScriptElem.getAttribute('reload');
+  if (reloadUri) {
+    enableLiveReloading(reloadUri);
+  }
 }
 
 function getRequiredBootScriptAttribute(elem: HTMLScriptElement, attributeName: string): string {
diff --git a/src/Microsoft.AspNetCore.Blazor.Browser.JS/src/LiveReloading.ts b/src/Microsoft.AspNetCore.Blazor.Browser.JS/src/LiveReloading.ts
new file mode 100644
index 0000000000..b0fd3e4702
--- /dev/null
+++ b/src/Microsoft.AspNetCore.Blazor.Browser.JS/src/LiveReloading.ts
@@ -0,0 +1,48 @@
+export function enableLiveReloading(endpointUri: string) {
+  listenForReloadEvent(endpointUri);
+}
+
+function listenForReloadEvent(endpointUri: string) {
+  if (!WebSocket) {
+    console.log('Browser does not support WebSocket, so live reloading will be disabled.');
+    return;
+  }
+
+  // First, connect to the endpoint
+  const websocketUri = toAbsoluteWebSocketUri(endpointUri);
+  const source = new WebSocket(websocketUri);
+  let allowConnectionFailedErrorReporting = true;
+
+  source.onopen = e => {
+    allowConnectionFailedErrorReporting = false;
+  };
+
+  source.onerror = e => {
+    if (allowConnectionFailedErrorReporting) {
+      allowConnectionFailedErrorReporting = false;
+      console.error(`The client app was compiled with live reloading enabled, but could not open `
+        + ` a WebSocket connection to the server at ${websocketUri}\n`
+        + `To fix this inconsistency, either run the server in development mode, or compile the `
+        + `client app in Release configuration.`);
+    }
+  };
+
+  // If we're notified that we should reload, then do so
+  source.onmessage = e => {
+    if (e.data === 'reload') {
+      location.reload();
+    }
+  };
+}
+
+function toAbsoluteWebSocketUri(uri: string) {
+  const baseUri = document.baseURI;
+  if (baseUri) {
+    const lastSlashPos = baseUri.lastIndexOf('/');
+    const prefix = baseUri.substr(0, lastSlashPos);
+    uri = prefix + uri;
+  }
+
+  // Scheme must be ws: or wss:
+  return uri.replace(/^http/, 'ws');
+}
diff --git a/src/Microsoft.AspNetCore.Blazor.Build/Cli/Commands/BuildIndexHtmlCommand.cs b/src/Microsoft.AspNetCore.Blazor.Build/Cli/Commands/BuildIndexHtmlCommand.cs
index 5f160d64f9..f3a3dd19ad 100644
--- a/src/Microsoft.AspNetCore.Blazor.Build/Cli/Commands/BuildIndexHtmlCommand.cs
+++ b/src/Microsoft.AspNetCore.Blazor.Build/Cli/Commands/BuildIndexHtmlCommand.cs
@@ -26,6 +26,10 @@ namespace Microsoft.AspNetCore.Blazor.Build.Cli.Commands
                 "Adds a <link rel=stylesheet> tag with the specified 'href' value",
                 CommandOptionType.MultipleValue);
 
+            var reloadUri = command.Option("--reload-uri",
+                "If specified, enables live reloading and specifies the URI of the notification endpoint.",
+                CommandOptionType.SingleValue);
+
             var outputPath = command.Option("--output",
                 "Path to the output file",
                 CommandOptionType.SingleValue);
@@ -55,6 +59,7 @@ namespace Microsoft.AspNetCore.Blazor.Build.Cli.Commands
                         jsReferences.Values.ToArray(),
                         cssReferences.Values.ToArray(),
                         linkerEnabledFlag.HasValue(),
+                        reloadUri.Value(),
                         outputPath.Value());
                     return 0;
                 }
diff --git a/src/Microsoft.AspNetCore.Blazor.Build/Core/IndexHtmlWriter.cs b/src/Microsoft.AspNetCore.Blazor.Build/Core/IndexHtmlWriter.cs
index d8c7bf9c74..5f1167791a 100644
--- a/src/Microsoft.AspNetCore.Blazor.Build/Core/IndexHtmlWriter.cs
+++ b/src/Microsoft.AspNetCore.Blazor.Build/Core/IndexHtmlWriter.cs
@@ -22,6 +22,7 @@ namespace Microsoft.AspNetCore.Blazor.Build
             IEnumerable<string> jsReferences,
             IEnumerable<string> cssReferences,
             bool linkerEnabled,
+            string reloadUri,
             string outputPath)
         {
             var template = GetTemplate(path);
@@ -31,7 +32,7 @@ namespace Microsoft.AspNetCore.Blazor.Build
             }
             var assemblyName = Path.GetFileNameWithoutExtension(assemblyPath);
             var entryPoint = GetAssemblyEntryPoint(assemblyPath);
-            var updatedContent = GetIndexHtmlContents(template, assemblyName, entryPoint, assemblyReferences, jsReferences, cssReferences, linkerEnabled);
+            var updatedContent = GetIndexHtmlContents(template, assemblyName, entryPoint, assemblyReferences, jsReferences, cssReferences, linkerEnabled, reloadUri);
             var normalizedOutputPath = Normalize(outputPath);
             Console.WriteLine("Writing index to: " + normalizedOutputPath);
             File.WriteAllText(normalizedOutputPath, updatedContent);
@@ -103,7 +104,8 @@ namespace Microsoft.AspNetCore.Blazor.Build
             IEnumerable<string> assemblyReferences,
             IEnumerable<string> jsReferences,
             IEnumerable<string> cssReferences,
-            bool linkerEnabled)
+            bool linkerEnabled,
+            string reloadUri)
         {
             var resultBuilder = new StringBuilder();
 
@@ -144,7 +146,8 @@ namespace Microsoft.AspNetCore.Blazor.Build
                                     assemblyEntryPoint,
                                     assemblyReferences,
                                     linkerEnabled,
-                                    tag.Attributes);
+                                    tag.Attributes,
+                                    reloadUri);
 
                                 // Emit tags to reference any specified JS/CSS files
                                 AppendReferenceTags(
@@ -175,7 +178,11 @@ namespace Microsoft.AspNetCore.Blazor.Build
 
                     case HtmlTokenType.EndOfFile:
                         // Finally, emit any remaining text from the original source file
-                        resultBuilder.Append(htmlTemplate, currentRangeStartPos, htmlTemplate.Length - currentRangeStartPos);
+                        var remainingLength = htmlTemplate.Length - currentRangeStartPos;
+                        if (remainingLength > 0)
+                        {
+                            resultBuilder.Append(htmlTemplate, currentRangeStartPos, remainingLength);
+                        }
                         return resultBuilder.ToString();
                 }
             }
@@ -202,7 +209,8 @@ namespace Microsoft.AspNetCore.Blazor.Build
             string assemblyEntryPoint,
             IEnumerable<string> binFiles,
             bool linkerEnabled,
-            List<KeyValuePair<string, string>> attributes)
+            List<KeyValuePair<string, string>> attributes,
+            string reloadUri)
         {
             var assemblyNameWithExtension = $"{assemblyName}.dll";
 
@@ -224,6 +232,11 @@ namespace Microsoft.AspNetCore.Blazor.Build
                 attributesDict.Remove("linker-enabled");
             }
 
+            if (!string.IsNullOrEmpty(reloadUri))
+            {
+                attributesDict["reload"] = reloadUri;
+            }
+
             resultBuilder.Append("<script");
             foreach (var attributePair in attributesDict)
             {
diff --git a/src/Microsoft.AspNetCore.Blazor.Build/targets/All.props b/src/Microsoft.AspNetCore.Blazor.Build/targets/All.props
index 919d5cba0b..bb05316691 100644
--- a/src/Microsoft.AspNetCore.Blazor.Build/targets/All.props
+++ b/src/Microsoft.AspNetCore.Blazor.Build/targets/All.props
@@ -4,7 +4,16 @@
   <PropertyGroup>
     <DefaultWebContentItemExcludes>$(DefaultWebContentItemExcludes);wwwroot\**</DefaultWebContentItemExcludes>
 
+    <!-- By default, live reloading is on for debug builds -->
+    <UseBlazorLiveReloading Condition="'$(Configuration)' == 'Debug'">true</UseBlazorLiveReloading>
+    <BlazorLiveReloadUri>/_reload</BlazorLiveReloadUri>
+
     <!-- We can remove this after updating to newer Razor tooling, where it's enabled by default -->
     <UseRazorBuildServer>true</UseRazorBuildServer>
   </PropertyGroup>
+
+  <ItemGroup>
+    <!-- In case you're using 'dotnet watch', enable reloading when editing .cshtml files -->
+    <Watch Include="$(ProjectDir)**\*.cshtml" />
+  </ItemGroup>
 </Project>
diff --git a/src/Microsoft.AspNetCore.Blazor.Build/targets/All.targets b/src/Microsoft.AspNetCore.Blazor.Build/targets/All.targets
index 2d293d8b3c..f5c862d6f6 100644
--- a/src/Microsoft.AspNetCore.Blazor.Build/targets/All.targets
+++ b/src/Microsoft.AspNetCore.Blazor.Build/targets/All.targets
@@ -7,7 +7,7 @@
 
   <PropertyGroup>
     <BlazorBuildExe>dotnet &quot;$(MSBuildThisFileDirectory)../tools/Microsoft.AspNetCore.Blazor.Build.dll&quot;</BlazorBuildExe>
-  
+
     <!-- The Blazor build code can only find your referenced assemblies if they are in the output directory -->
     <CopyLocalLockFileAssemblies>true</CopyLocalLockFileAssemblies>
   </PropertyGroup>
@@ -23,6 +23,7 @@
     </PropertyGroup>
     <WriteLinesToFile File="$(BlazorMetadataFilePath)" Lines="$(MSBuildProjectFullPath)" Overwrite="true" Encoding="Unicode"/>
     <WriteLinesToFile File="$(BlazorMetadataFilePath)" Lines="$(OutDir)$(AssemblyName).dll" Overwrite="false" Encoding="Unicode"/>
+    <WriteLinesToFile File="$(BlazorMetadataFilePath)" Condition="'$(UseBlazorLiveReloading)'=='true'" Lines="reload:$(BlazorLiveReloadUri)" Overwrite="false" Encoding="Unicode"/>
     <ItemGroup>
       <ContentWithTargetPath Include="$(BlazorMetadataFilePath)" TargetPath="$(BlazorMetadataFileName)" CopyToOutputDirectory="PreserveNewest" />
     </ItemGroup>
diff --git a/src/Microsoft.AspNetCore.Blazor.Build/targets/Blazor.MonoRuntime.props b/src/Microsoft.AspNetCore.Blazor.Build/targets/Blazor.MonoRuntime.props
index caa2852a3b..324847430e 100644
--- a/src/Microsoft.AspNetCore.Blazor.Build/targets/Blazor.MonoRuntime.props
+++ b/src/Microsoft.AspNetCore.Blazor.Build/targets/Blazor.MonoRuntime.props
@@ -11,8 +11,9 @@
 
   <PropertyGroup Label="Blazor build outputs">
     <AdditionalMonoLinkerOptions>-c link -u link -t --verbose </AdditionalMonoLinkerOptions>
-    <BaseBlazorPackageContentOutputPath>dist/_content/</BaseBlazorPackageContentOutputPath>
-    <BaseBlazorRuntimeOutputPath>dist/_framework/</BaseBlazorRuntimeOutputPath>
+    <BaseBlazorDistPath>dist/</BaseBlazorDistPath>
+    <BaseBlazorPackageContentOutputPath>$(BaseBlazorDistPath)_content/</BaseBlazorPackageContentOutputPath>
+    <BaseBlazorRuntimeOutputPath>$(BaseBlazorDistPath)_framework/</BaseBlazorRuntimeOutputPath>
     <BaseBlazorRuntimeBinOutputPath>$(BaseBlazorRuntimeOutputPath)_bin/</BaseBlazorRuntimeBinOutputPath>
     <BaseBlazorRuntimeAsmjsOutputPath>$(BaseBlazorRuntimeOutputPath)asmjs/</BaseBlazorRuntimeAsmjsOutputPath>
     <BaseBlazorRuntimeWasmOutputPath>$(BaseBlazorRuntimeOutputPath)wasm/</BaseBlazorRuntimeWasmOutputPath>
@@ -21,6 +22,7 @@
     <BlazorWebRootName>wwwroot/</BlazorWebRootName>
     <BlazorIndexHtmlName>Index.html</BlazorIndexHtmlName>
     <BlazorOutputIndexHtmlName>$(BlazorIndexHtmlName.ToLowerInvariant())</BlazorOutputIndexHtmlName>
+    <BlazorBuildCompletedSignalPath>$(BaseBlazorDistPath)__blazorBuildCompleted</BlazorBuildCompletedSignalPath>
   </PropertyGroup>
 
   <ItemGroup>
diff --git a/src/Microsoft.AspNetCore.Blazor.Build/targets/Blazor.MonoRuntime.targets b/src/Microsoft.AspNetCore.Blazor.Build/targets/Blazor.MonoRuntime.targets
index 1be7c0a433..66003529d5 100644
--- a/src/Microsoft.AspNetCore.Blazor.Build/targets/Blazor.MonoRuntime.targets
+++ b/src/Microsoft.AspNetCore.Blazor.Build/targets/Blazor.MonoRuntime.targets
@@ -23,6 +23,9 @@
     <ItemGroup>
       <FileWrites Include="@(BlazorItemOutput->'%(TargetOutputPath)')" />
     </ItemGroup>
+    <PropertyGroup>
+      <_BlazorDidCopyFilesToOutputDirectory>true</_BlazorDidCopyFilesToOutputDirectory>
+    </PropertyGroup>
   </Target>
   
   <Target Name="_BlazorTrackResolveReferencesDidRun" AfterTargets="ResolveReferences">
@@ -47,6 +50,21 @@
     <Message Importance="$(_BlazorStatisticsReportImportance)" Text="%(_BlazorStatisticsOutput.Identity)" />
   </Target>
 
+  <!--
+    We only issue the reload notification from here if you're *not* building inside VS.
+    If you are building inside VS, then it's possible you're building an arbitrary collection
+    of projects of which this is just one, and it's important to wait until all projects in
+    the build are completed before reloading, so the notification is instead triggered by the
+    VS extension that can see when a complete build process is finished.
+  -->
+  <Target Name="_BlazorIssueLiveReloadNotification"
+          AfterTargets="Build"
+          Condition="'$(UseBlazorLiveReloading)'=='true' AND '$(_BlazorDidCopyFilesToOutputDirectory)'=='true' AND '$(BuildingInsideVisualStudio)'!='true'">
+    <!-- Touch the signal file to trigger a reload -->
+    <WriteLinesToFile File="$(ProjectDir)$(OutputPath)$(BlazorBuildCompletedSignalPath)" Lines="_" />
+    <Delete Files="$(ProjectDir)$(OutputPath)$(BlazorBuildCompletedSignalPath)" />
+  </Target>
+
   <!-- Preparing blazor files for output:
     PrepareBlazorOutputs
       _PrepareBlazorOutputConfiguration
@@ -65,6 +83,7 @@
             _TouchBlazorApplicationAssemblies
       _GenerateBlazorIndexHtml
     _BlazorCopyFilesToOutputDirectory
+    _BlazorIssueLiveReloadNotification
 
     The process for doing builds goes as follows:
     Produce a hash file with the Hash SDK task and write that hash to a marker file.
@@ -571,6 +590,7 @@
       <BlazorIndexHtmlInput Include="@(BlazorPackageJsRef->'%(FullPath)')" />
       <BlazorIndexHtmlInput Include="@(BlazorPackageCssRef->'%(FullPath)')" />
       <BlazorIndexHtmlInput Include="@(_BlazorLinkingOption)" />
+      <BlazorIndexHtmlInput Include="$(BlazorLiveReloadUri)" Condition="'$(UseBlazorLiveReloading)'=='true'" />
     </ItemGroup>
 
     <WriteLinesToFile
@@ -597,9 +617,10 @@
     </ItemGroup>
     <PropertyGroup>
       <_LinkerEnabledFlag Condition="'$(_BlazorShouldLinkApplicationAssemblies)' != ''">--linker-enabled</_LinkerEnabledFlag>
+      <_LiveReloadArg Condition="'$(UseBlazorLiveReloading)' == 'true' AND '$(BlazorLiveReloadUri)' != ''">--reload-uri "$(BlazorLiveReloadUri)"</_LiveReloadArg>
     </PropertyGroup>
 
-    <Exec Command="$(BlazorBuildExe) build @(IntermediateAssembly) --html-page &quot;$(BlazorIndexHtml)&quot; @(_AppReferences->'--reference &quot;%(Identity)&quot;', ' ') @(_JsReferences->'--js &quot;%(Identity)&quot;', ' ') @(_CssReferences->'--css &quot;%(Identity)&quot;', ' ') $(_LinkerEnabledFlag) --output &quot;$(BlazorIndexHtmlOutputPath)&quot;" />
+    <Exec Command="$(BlazorBuildExe) build @(IntermediateAssembly) --html-page &quot;$(BlazorIndexHtml)&quot; @(_AppReferences->'--reference &quot;%(Identity)&quot;', ' ') @(_JsReferences->'--js &quot;%(Identity)&quot;', ' ') @(_CssReferences->'--css &quot;%(Identity)&quot;', ' ') $(_LinkerEnabledFlag) $(_LiveReloadArg) --output &quot;$(BlazorIndexHtmlOutputPath)&quot;" />
 
     <ItemGroup Condition="Exists('$(BlazorIndexHtmlOutputPath)')">
       <_BlazorIndex Include="$(BlazorIndexHtmlOutputPath)" />
diff --git a/src/Microsoft.AspNetCore.Blazor.Server/BlazorAppBuilderExtensions.cs b/src/Microsoft.AspNetCore.Blazor.Server/BlazorAppBuilderExtensions.cs
index ba8d01fe43..0f77a7e1c4 100644
--- a/src/Microsoft.AspNetCore.Blazor.Server/BlazorAppBuilderExtensions.cs
+++ b/src/Microsoft.AspNetCore.Blazor.Server/BlazorAppBuilderExtensions.cs
@@ -42,13 +42,9 @@ namespace Microsoft.AspNetCore.Builder
             // hence all the path manipulation here. We shouldn't be hardcoding 'dist' here either.
             var env = (IHostingEnvironment)applicationBuilder.ApplicationServices.GetService(typeof(IHostingEnvironment));
             var config = BlazorConfig.Read(options.ClientAssemblyPath);
-            var clientAppBinDir = Path.GetDirectoryName(config.SourceOutputAssemblyPath);
-            var clientAppDistDir = Path.Combine(
-                env.ContentRootPath,
-                Path.Combine(clientAppBinDir, "dist"));
             var distDirStaticFiles = new StaticFileOptions
             {
-                FileProvider = new PhysicalFileProvider(clientAppDistDir),
+                FileProvider = new PhysicalFileProvider(config.DistPath),
                 ContentTypeProvider = CreateContentTypeProvider(),
             };
 
@@ -68,6 +64,15 @@ namespace Microsoft.AspNetCore.Builder
                 });
             }
 
+            // Definitely don't open a listener for live reloading in production, even if the
+            // client app was compiled with live reloading enabled
+            if (env.IsDevelopment())
+            {
+                // Whether or not live reloading is actually enabled depends on the client config
+                // For release builds, it won't be (by default)
+                applicationBuilder.UseBlazorLiveReloading(config);
+            }
+
             // Finally, use SPA fallback routing (serve default page for anything else,
             // excluding /_framework/*)
             applicationBuilder.MapWhen(IsNotFrameworkDir, childAppBuilder =>
diff --git a/src/Microsoft.AspNetCore.Blazor.Server/BlazorConfig.cs b/src/Microsoft.AspNetCore.Blazor.Server/BlazorConfig.cs
index 5e2dedc011..33570da566 100644
--- a/src/Microsoft.AspNetCore.Blazor.Server/BlazorConfig.cs
+++ b/src/Microsoft.AspNetCore.Blazor.Server/BlazorConfig.cs
@@ -1,6 +1,7 @@
 // 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.IO;
 using System.Linq;
 
@@ -11,12 +12,19 @@ namespace Microsoft.AspNetCore.Blazor.Server
         public string SourceMSBuildPath { get; }
         public string SourceOutputAssemblyPath { get; }
         public string WebRootPath { get; }
+        public string ReloadUri { get; }
+        public string DistPath
+            => Path.Combine(Path.GetDirectoryName(SourceOutputAssemblyPath), "dist");
 
         public static BlazorConfig Read(string assemblyPath)
             => new BlazorConfig(assemblyPath);
 
         private BlazorConfig(string assemblyPath)
         {
+            // TODO: Instead of assuming the lines are in a specific order, either JSON-encode
+            // the whole thing, or at least give the lines key prefixes (e.g., "reload:<someuri>")
+            // so we're not dependent on order and all lines being present.
+
             var configFilePath = Path.ChangeExtension(assemblyPath, ".blazor.config");
             var configLines = File.ReadLines(configFilePath).ToList();
             SourceMSBuildPath = configLines[0];
@@ -29,6 +37,16 @@ namespace Microsoft.AspNetCore.Blazor.Server
             {
                 WebRootPath = webRootPath;
             }
+
+            const string reloadMarker = "reload:";
+            var reloadUri = configLines
+                .Where(line => line.StartsWith(reloadMarker, StringComparison.Ordinal))
+                .Select(line => line.Substring(reloadMarker.Length))
+                .FirstOrDefault();
+            if (!string.IsNullOrEmpty(reloadUri))
+            {
+                ReloadUri = reloadUri;
+            }
         }
     }
 }
diff --git a/src/Microsoft.AspNetCore.Blazor.Server/LiveReloadingContext.cs b/src/Microsoft.AspNetCore.Blazor.Server/LiveReloadingContext.cs
new file mode 100644
index 0000000000..67ae6074bc
--- /dev/null
+++ b/src/Microsoft.AspNetCore.Blazor.Server/LiveReloadingContext.cs
@@ -0,0 +1,140 @@
+// 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 Microsoft.AspNetCore.Builder;
+using Microsoft.AspNetCore.Http;
+using System;
+using System.Collections.Generic;
+using System.IO;
+using System.Net.WebSockets;
+using System.Text;
+using System.Threading;
+using System.Threading.Tasks;
+
+namespace Microsoft.AspNetCore.Blazor.Server
+{
+    internal class LiveReloadingContext
+    {
+        // Keep in sync with $(BlazorBuildCompletedSignalPath) in Blazor.MonoRuntime.props
+        private const string BlazorBuildCompletedSignalFile = "__blazorBuildCompleted";
+
+        // If some external automated process is writing multiple files to wwwroot,
+        // you probably want to wait until they've all been written before reloading.
+        // Pausing by 500 milliseconds is a crude effort - we might need a different
+        // mechanism (e.g., waiting until writes have stopped by 500ms).
+        private const int WebRootUpdateDelayMilliseconds = 500;
+        private static byte[] _reloadMessage = Encoding.UTF8.GetBytes("reload");
+
+        // If we don't hold references to them, then on Linux they get disposed.
+        // This static would leak memory if you called UseBlazorLiveReloading continually
+        // throughout the app lifetime, but the intended usage is just during init.
+        private static readonly List<FileSystemWatcher> _pinnedWatchers = new List<FileSystemWatcher>();
+
+        private readonly object _currentReloadListenerLock = new object();
+        private CancellationTokenSource _currentReloadListener
+            = new CancellationTokenSource();
+
+        public void Attach(IApplicationBuilder applicationBuilder, BlazorConfig config)
+        {
+            CreateFileSystemWatchers(config);
+            AddWebSocketsEndpoint(applicationBuilder, config.ReloadUri);
+        }
+
+        private void AddWebSocketsEndpoint(IApplicationBuilder applicationBuilder, string url)
+        {
+            applicationBuilder.UseWebSockets();
+            applicationBuilder.Use((context, next) =>
+            {
+                if (!string.Equals(context.Request.Path, url, StringComparison.Ordinal))
+                {
+                    return next();
+                }
+
+                if (!context.WebSockets.IsWebSocketRequest)
+                {
+                    context.Response.StatusCode = 400;
+                    return context.Response.WriteAsync("This endpoint only accepts WebSockets connections.");
+                }
+
+                return HandleWebSocketRequest(
+                    context.WebSockets.AcceptWebSocketAsync(),
+                    context.RequestAborted);
+            });
+        }
+
+        private async Task HandleWebSocketRequest(Task<WebSocket> webSocketTask, CancellationToken requestAbortedToken)
+        {
+            var webSocket = await webSocketTask;
+            var reloadToken = _currentReloadListener.Token;
+
+            // Wait until either we get a signal to trigger a reload, or the client disconnects
+            // In either case we're done after that. It's the client's job to reload and start
+            // a new live reloading context.
+            try
+            {
+                var reloadOrRequestAbortedToken = CancellationTokenSource
+                    .CreateLinkedTokenSource(reloadToken, requestAbortedToken)
+                    .Token;
+                await Task.Delay(-1, reloadOrRequestAbortedToken);
+            }
+            catch (TaskCanceledException)
+            {
+                if (reloadToken.IsCancellationRequested)
+                {
+                    await webSocket.SendAsync(
+                        _reloadMessage,
+                        WebSocketMessageType.Text,
+                        true,
+                        requestAbortedToken);
+                    await webSocket.CloseAsync(
+                        WebSocketCloseStatus.NormalClosure,
+                        "Requested reload",
+                        requestAbortedToken);
+                }
+            }
+        }
+
+        private void CreateFileSystemWatchers(BlazorConfig config)
+        {
+            // Watch for the "build completed" signal in the dist dir
+            var distFileWatcher = new FileSystemWatcher(config.DistPath);
+            distFileWatcher.Deleted += (sender, eventArgs) => {
+                if (eventArgs.Name.Equals(BlazorBuildCompletedSignalFile, StringComparison.Ordinal))
+                {
+                    RequestReload(0);
+                }
+            };
+            distFileWatcher.EnableRaisingEvents = true;
+            _pinnedWatchers.Add(distFileWatcher);
+
+            // If there's a WebRootPath, watch for any file modification there
+            // WebRootPath is only used in dev builds, where we want to serve from wwwroot directly
+            // without requiring the developer to rebuild after changing the static files there.
+            // In production there's no need for it.
+            if (!string.IsNullOrEmpty(config.WebRootPath))
+            {
+                var webRootWatcher = new FileSystemWatcher(config.WebRootPath);
+                webRootWatcher.Deleted += (sender, evtArgs) => RequestReload(WebRootUpdateDelayMilliseconds);
+                webRootWatcher.Created += (sender, evtArgs) => RequestReload(WebRootUpdateDelayMilliseconds);
+                webRootWatcher.Changed += (sender, evtArgs) => RequestReload(WebRootUpdateDelayMilliseconds);
+                webRootWatcher.Renamed += (sender, evtArgs) => RequestReload(WebRootUpdateDelayMilliseconds);
+                webRootWatcher.EnableRaisingEvents = true;
+                _pinnedWatchers.Add(webRootWatcher);
+            }
+        }
+
+        private void RequestReload(int delayMilliseconds)
+        {
+            Task.Delay(delayMilliseconds).ContinueWith(_ =>
+            {
+                lock (_currentReloadListenerLock)
+                {
+                    // Lock just to be sure two threads don't assign different new CTSs, of which
+                    // only one would later get cancelled.
+                    _currentReloadListener.Cancel();
+                    _currentReloadListener = new CancellationTokenSource();
+                }
+            });
+        }
+    }
+}
diff --git a/src/Microsoft.AspNetCore.Blazor.Server/LiveReloadingExtensions.cs b/src/Microsoft.AspNetCore.Blazor.Server/LiveReloadingExtensions.cs
new file mode 100644
index 0000000000..1ebb85996f
--- /dev/null
+++ b/src/Microsoft.AspNetCore.Blazor.Server/LiveReloadingExtensions.cs
@@ -0,0 +1,21 @@
+// 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 Microsoft.AspNetCore.Builder;
+
+namespace Microsoft.AspNetCore.Blazor.Server
+{
+    internal static class LiveReloadingExtensions
+    {
+        public static void UseBlazorLiveReloading(
+            this IApplicationBuilder applicationBuilder,
+            BlazorConfig config)
+        {
+            if (!string.IsNullOrEmpty(config.ReloadUri))
+            {
+                var context = new LiveReloadingContext();
+                context.Attach(applicationBuilder, config);
+            }
+        }
+    }
+}
diff --git a/src/Microsoft.AspNetCore.Blazor.Server/Microsoft.AspNetCore.Blazor.Server.csproj b/src/Microsoft.AspNetCore.Blazor.Server/Microsoft.AspNetCore.Blazor.Server.csproj
index fdab225fe7..b06b3d5255 100644
--- a/src/Microsoft.AspNetCore.Blazor.Server/Microsoft.AspNetCore.Blazor.Server.csproj
+++ b/src/Microsoft.AspNetCore.Blazor.Server/Microsoft.AspNetCore.Blazor.Server.csproj
@@ -7,6 +7,7 @@
   <ItemGroup>
     <PackageReference Include="Microsoft.AspNetCore.StaticFiles" Version="2.0.1" />
     <PackageReference Include="Microsoft.AspNetCore.SpaServices.Extensions" Version="2.0.0" />
+    <PackageReference Include="Microsoft.AspNetCore.WebSockets" Version="2.0.1" />
     <PackageReference Include="Microsoft.Extensions.FileProviders.Physical" Version="2.0.0" />
   </ItemGroup>
 
diff --git a/test/Microsoft.AspNetCore.Blazor.Build.Test/IndexHtmlWriterTest.cs b/test/Microsoft.AspNetCore.Blazor.Build.Test/IndexHtmlWriterTest.cs
index 6b5bdae3a1..93e1c3f113 100644
--- a/test/Microsoft.AspNetCore.Blazor.Build.Test/IndexHtmlWriterTest.cs
+++ b/test/Microsoft.AspNetCore.Blazor.Build.Test/IndexHtmlWriterTest.cs
@@ -36,7 +36,8 @@ namespace Microsoft.AspNetCore.Blazor.Build.Test
                 assemblyReferences,
                 jsReferences,
                 cssReferences,
-                linkerEnabled: true);
+                linkerEnabled: true,
+                reloadUri: "/my/reload");
 
             // Act & Assert: Start and end is not modified (including formatting)
             Assert.StartsWith(htmlTemplatePrefix, instance);
@@ -53,6 +54,7 @@ namespace Microsoft.AspNetCore.Blazor.Build.Test
             Assert.Equal("MyApp.Entrypoint.dll", scriptElem.GetAttribute("main"));
             Assert.Equal("MyNamespace.MyType::MyMethod", scriptElem.GetAttribute("entrypoint"));
             Assert.Equal("System.Abc.dll,MyApp.ClassLib.dll", scriptElem.GetAttribute("references"));
+            Assert.Equal("/my/reload", scriptElem.GetAttribute("reload"));
             Assert.False(scriptElem.HasAttribute("type"));
             Assert.Equal(string.Empty, scriptElem.Attributes["custom1"].Value);
             Assert.Equal("value", scriptElem.Attributes["custom2"].Value);
@@ -68,6 +70,30 @@ namespace Microsoft.AspNetCore.Blazor.Build.Test
                 linkElems.Select(tag => tag.GetAttribute("href")),
                 cssReferences);
         }
+ 
+        [Fact]
+        public void OmitsReloadAttributeIfNoReloadUriSpecified()
+        {
+            // Arrange
+            var htmlTemplate = "<script type='blazor-boot'></script>";
+            var assemblyReferences = new string[] { "System.Abc.dll", "MyApp.ClassLib.dll", };
+
+            // Act
+            var fileContents = IndexHtmlWriter.GetIndexHtmlContents(
+                htmlTemplate,
+                "MyApp.Entrypoint",
+                "MyNamespace.MyType::MyMethod",
+                assemblyReferences,
+                /* js references */ new string[] {},
+                /* js references */ new string[] {},
+                /* linkerEnabled */ true,
+                /* reloadUri */ null);
+
+            // Assert
+            var parsedHtml = new HtmlParser().Parse(fileContents);
+            var scriptElem = parsedHtml.QuerySelector("script");
+            Assert.False(scriptElem.HasAttribute("reload"));
+        }
 
         [Fact]
         public void SuppliesHtmlTemplateUnchangedIfNoBootScriptPresent()
@@ -79,7 +105,7 @@ namespace Microsoft.AspNetCore.Blazor.Build.Test
             var cssReferences = new string[] { "my/styles.css" };
 
             var content = IndexHtmlWriter.GetIndexHtmlContents(
-                htmlTemplate, "MyApp.Entrypoint", "MyNamespace.MyType::MyMethod", assemblyReferences, jsReferences, cssReferences, linkerEnabled: true);
+                htmlTemplate, "MyApp.Entrypoint", "MyNamespace.MyType::MyMethod", assemblyReferences, jsReferences, cssReferences, linkerEnabled: true, reloadUri: "/my/reload");
 
             // Assert
             Assert.Equal(htmlTemplate, content);
diff --git a/test/Microsoft.AspNetCore.Blazor.E2ETest/Infrastructure/ServerFixtures/DevHostServerFixture.cs b/test/Microsoft.AspNetCore.Blazor.E2ETest/Infrastructure/ServerFixtures/DevHostServerFixture.cs
index 676808f331..08825ecfbf 100644
--- a/test/Microsoft.AspNetCore.Blazor.E2ETest/Infrastructure/ServerFixtures/DevHostServerFixture.cs
+++ b/test/Microsoft.AspNetCore.Blazor.E2ETest/Infrastructure/ServerFixtures/DevHostServerFixture.cs
@@ -2,25 +2,36 @@
 // Licensed under the Apache License, Version 2.0. See License.txt in the project root for license information.
 
 using Microsoft.AspNetCore.Hosting;
+using System.Collections.Generic;
 using DevHostServerProgram = Microsoft.AspNetCore.Blazor.Cli.Server.Program;
 
 namespace Microsoft.AspNetCore.Blazor.E2ETest.Infrastructure.ServerFixtures
 {
     public class DevHostServerFixture<TProgram> : WebHostServerFixture
     {
+        public string Environment { get; set; }
         public string PathBase { get; set; }
+        public string ContentRoot { get; private set; }
 
         protected override IWebHost CreateWebHost()
         {
-            var sampleSitePath = FindSampleOrTestSitePath(
+            ContentRoot = FindSampleOrTestSitePath(
                 typeof(TProgram).Assembly.GetName().Name);
 
-            return DevHostServerProgram.BuildWebHost(new string[]
+            var args = new List<string>
             {
                 "--urls", "http://127.0.0.1:0",
-                "--contentroot", sampleSitePath,
+                "--contentroot", ContentRoot,
                 "--pathbase", PathBase
-            });
+            };
+
+            if (!string.IsNullOrEmpty(Environment))
+            {
+                args.Add("--environment");
+                args.Add(Environment);
+            }
+
+            return DevHostServerProgram.BuildWebHost(args.ToArray());
         }
     }
 }
diff --git a/test/Microsoft.AspNetCore.Blazor.E2ETest/Microsoft.AspNetCore.Blazor.E2ETest.csproj b/test/Microsoft.AspNetCore.Blazor.E2ETest/Microsoft.AspNetCore.Blazor.E2ETest.csproj
index 7045e97bc6..6c681cedfc 100644
--- a/test/Microsoft.AspNetCore.Blazor.E2ETest/Microsoft.AspNetCore.Blazor.E2ETest.csproj
+++ b/test/Microsoft.AspNetCore.Blazor.E2ETest/Microsoft.AspNetCore.Blazor.E2ETest.csproj
@@ -24,6 +24,7 @@
     <ProjectReference Include="..\..\samples\StandaloneApp\StandaloneApp.csproj" />
     <ProjectReference Include="..\..\src\Microsoft.AspNetCore.Blazor.Cli\Microsoft.AspNetCore.Blazor.Cli.csproj" />
     <ProjectReference Include="..\testapps\BasicTestApp\BasicTestApp.csproj" />
+    <ProjectReference Include="..\testapps\LiveReloadTestApp\LiveReloadTestApp.csproj" />
     <ProjectReference Include="..\testapps\TestServer\TestServer.csproj" />
   </ItemGroup>
 
diff --git a/test/Microsoft.AspNetCore.Blazor.E2ETest/Tests/LiveReloadingTest.cs b/test/Microsoft.AspNetCore.Blazor.E2ETest/Tests/LiveReloadingTest.cs
new file mode 100644
index 0000000000..925fdfd338
--- /dev/null
+++ b/test/Microsoft.AspNetCore.Blazor.E2ETest/Tests/LiveReloadingTest.cs
@@ -0,0 +1,118 @@
+// 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 LiveReloadTestApp;
+using Microsoft.AspNetCore.Blazor.E2ETest.Infrastructure;
+using Microsoft.AspNetCore.Blazor.E2ETest.Infrastructure.ServerFixtures;
+using OpenQA.Selenium;
+using OpenQA.Selenium.Support.UI;
+using System;
+using System.Diagnostics;
+using System.IO;
+using Xunit;
+
+namespace Microsoft.AspNetCore.Blazor.E2ETest.Tests
+{
+    // We need an entirely separate test app for the live reloading tests, because
+    // otherwise it might break other tests that were running parallel (e.g., if we
+    // triggered a reload here while other tests were waiting for something to happen).
+
+    public class LiveReloadingTest
+        : ServerTestBase<DevHostServerFixture<LiveReloadTestApp.Program>>
+    {
+        private const string ServerPathBase = "/live/reloading/subdir";
+        private readonly DevHostServerFixture<Program> _serverFixture;
+
+        public LiveReloadingTest(BrowserFixture browserFixture, DevHostServerFixture<Program> serverFixture)
+            : base(browserFixture, serverFixture)
+        {
+            _serverFixture = serverFixture;
+            serverFixture.Environment = "Development"; // Otherwise the server won't accept live reloading connections
+            serverFixture.PathBase = ServerPathBase;
+            Navigate(ServerPathBase);
+            WaitUntilLoaded();
+        }
+
+        [Fact]
+        public void ReloadsWhenWebRootFilesAreModified()
+        {
+            // Verify we have the expected starting point
+            var jsFileOutputSelector = By.Id("some-js-file-output");
+            Assert.Equal("initial value", Browser.FindElement(jsFileOutputSelector).Text);
+
+            var jsFilePath = Path.Combine(_serverFixture.ContentRoot, "wwwroot", "someJsFile.js");
+            var origContents = File.ReadAllText(jsFilePath);
+            try
+            {
+                // Edit the source file on disk
+                var newContents = origContents.Replace("'initial value'", "'modified value'");
+                File.WriteAllText(jsFilePath, newContents);
+
+                // See that the page reloads and reflects the updated source file
+                new WebDriverWait(Browser, TimeSpan.FromSeconds(30)).Until(
+                    driver => driver.FindElement(jsFileOutputSelector).Text == "modified value");
+                WaitUntilLoaded();
+            }
+            finally
+            {
+                // Restore original state
+                File.WriteAllText(jsFilePath, origContents);
+            }
+        }
+
+        [Fact]
+        public void ReloadsWhenBlazorAppRebuilds()
+        {
+            // Verify we have the expected starting point
+            var appElementSelector = By.TagName("app");
+            Assert.Equal("Hello, world!", Browser.FindElement(appElementSelector).Text);
+
+            var cshtmlFilePath = Path.Combine(_serverFixture.ContentRoot, "Home.cshtml");
+            var origContents = File.ReadAllText(cshtmlFilePath);
+            try
+            {
+                // Edit the source file on disk
+                var newContents = origContents.Replace("Hello", "Goodbye");
+                File.WriteAllText(cshtmlFilePath, newContents);
+
+                // Trigger build
+                var buildConfiguration = DetectBuildConfiguration(_serverFixture.ContentRoot);
+                var buildProcess = Process.Start(new ProcessStartInfo
+                {
+                    FileName = "dotnet",
+                    Arguments = $"build --no-restore --no-dependencies -c {buildConfiguration}",
+                    WorkingDirectory = _serverFixture.ContentRoot
+                });
+                Assert.True(buildProcess.WaitForExit(60 * 1000));
+                Assert.Equal(0, buildProcess.ExitCode);
+
+                // See that the page reloads and reflects the updated source file
+                new WebDriverWait(Browser, TimeSpan.FromSeconds(30)).Until(
+                    driver => driver.FindElement(appElementSelector).Text == "Goodbye, world!");
+            }
+            finally
+            {
+                // Restore original state
+                File.WriteAllText(cshtmlFilePath, origContents);
+            }
+        }
+
+        private object DetectBuildConfiguration(string contentRoot)
+        {
+            // We want the test to issue the build with the same configuration that
+            // the project was already built with (otherwise there will be errors because
+            // of having multiple directories under /bin, plus it means we don't need
+            // to restore and rebuild all dependencies so it's faster)
+            var binDirInfo = new DirectoryInfo(Path.Combine(contentRoot, "bin"));
+            var configurationDirs = binDirInfo.GetDirectories();
+            Assert.Single(configurationDirs);
+            return configurationDirs[0].Name;
+        }
+
+        private void WaitUntilLoaded()
+        {
+            new WebDriverWait(Browser, TimeSpan.FromSeconds(30)).Until(
+                driver => driver.FindElement(By.TagName("app")).Text != "Loading...");
+        }
+    }
+}
diff --git a/test/testapps/LiveReloadTestApp/Home.cshtml b/test/testapps/LiveReloadTestApp/Home.cshtml
new file mode 100644
index 0000000000..9f735a6307
--- /dev/null
+++ b/test/testapps/LiveReloadTestApp/Home.cshtml
@@ -0,0 +1 @@
+<h1>Hello, world!</h1>
diff --git a/test/testapps/LiveReloadTestApp/LiveReloadTestApp.csproj b/test/testapps/LiveReloadTestApp/LiveReloadTestApp.csproj
new file mode 100644
index 0000000000..dd97d39d71
--- /dev/null
+++ b/test/testapps/LiveReloadTestApp/LiveReloadTestApp.csproj
@@ -0,0 +1,21 @@
+<Project Sdk="Microsoft.NET.Sdk.Web">
+
+  <PropertyGroup>
+    <TargetFramework>netstandard2.0</TargetFramework>
+
+    <!-- Local alternative to <RunArguments>blazor serve</RunArguments> -->
+    <RunCommand>dotnet</RunCommand>
+    <RunArguments>run --project ..\..\..\src\Microsoft.AspNetCore.Blazor.Cli serve --pathbase /live/reloading/subdir</RunArguments>
+
+    <!-- For CI, force live reloading on even though it builds in release mode -->
+    <UseBlazorLiveReloading>true</UseBlazorLiveReloading>
+  </PropertyGroup>
+
+  <!-- Local alternative to <PackageReference Include="Microsoft.AspNetCore.Blazor.Build" /> -->
+  <Import Project="..\..\..\src\Microsoft.AspNetCore.Blazor.Build\ReferenceFromSource.props" />
+  <ItemGroup>
+    <ProjectReference Include="..\..\..\src\Microsoft.AspNetCore.Blazor.Browser\Microsoft.AspNetCore.Blazor.Browser.csproj" />
+    <ProjectReference Include="..\..\..\src\Microsoft.AspNetCore.Blazor\Microsoft.AspNetCore.Blazor.csproj" />
+  </ItemGroup>
+
+</Project>
diff --git a/test/testapps/LiveReloadTestApp/Program.cs b/test/testapps/LiveReloadTestApp/Program.cs
new file mode 100644
index 0000000000..0aee7832e8
--- /dev/null
+++ b/test/testapps/LiveReloadTestApp/Program.cs
@@ -0,0 +1,15 @@
+// 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 Microsoft.AspNetCore.Blazor.Browser.Rendering;
+
+namespace LiveReloadTestApp
+{
+    public class Program
+    {
+        static void Main(string[] args)
+        {
+            new BrowserRenderer().AddComponent<Home>("app");
+        }
+    }
+}
diff --git a/test/testapps/LiveReloadTestApp/wwwroot/index.html b/test/testapps/LiveReloadTestApp/wwwroot/index.html
new file mode 100644
index 0000000000..5c7d816ec2
--- /dev/null
+++ b/test/testapps/LiveReloadTestApp/wwwroot/index.html
@@ -0,0 +1,19 @@
+<!DOCTYPE html>
+<html>
+<head>
+    <meta charset="utf-8" />
+    <title>Live reload test app</title>
+    <base href="/live/reloading/subdir/" />
+</head>
+<body>
+    <app>Loading...</app>
+    <div id="some-js-file-output"></div>
+    <script type="blazor-boot"></script>
+
+    <script>
+        // The test about live reloading should be independent of any
+        // dev server caching headers
+        document.write("<script src='someJsFile.js?nocache=" + (new Date().valueOf()) + "'></" + "script>");
+    </script>
+</body>
+</html>
diff --git a/test/testapps/LiveReloadTestApp/wwwroot/someJsFile.js b/test/testapps/LiveReloadTestApp/wwwroot/someJsFile.js
new file mode 100644
index 0000000000..af61769b29
--- /dev/null
+++ b/test/testapps/LiveReloadTestApp/wwwroot/someJsFile.js
@@ -0,0 +1,3 @@
+// We modify this on disk during E2E tests to verify it causes a reload
+var valueToWrite = 'initial value';
+document.getElementById('some-js-file-output').textContent = valueToWrite;