Set Hot Reload controlling headers DOTNET-MODIFIABLE-ASSEMBLIES and ASPNETCORE-BROWSER-TOOLS regardless of the environment kind (#48953)

Author: tmat

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

@@ -9,7 +9,6 @@
 using Microsoft.AspNetCore.StaticFiles;
 using Microsoft.Extensions.DependencyInjection;
 using Microsoft.Extensions.FileProviders;
-using Microsoft.Extensions.Hosting;
 using Microsoft.Extensions.Primitives;
 using Microsoft.Net.Http.Headers;
 
@@ -20,6 +19,12 @@ namespace Microsoft.AspNetCore.Builder;
 /// </summary>
 public static class ComponentsWebAssemblyApplicationBuilderExtensions
 {
+    private static readonly string? s_dotnetModifiableAssemblies = GetNonEmptyEnvironmentVariableValue("DOTNET_MODIFIABLE_ASSEMBLIES");
+    private static readonly string? s_aspnetcoreBrowserTools = GetNonEmptyEnvironmentVariableValue("__ASPNETCORE_BROWSER_TOOLS");
+
+    private static string? GetNonEmptyEnvironmentVariableValue(string name)
+        => Environment.GetEnvironmentVariable(name) is { Length: >0 } value ? value : null;
+
     /// <summary>
     /// Configures the application to serve Blazor WebAssembly framework files from the path <paramref name="pathPrefix"/>. This path must correspond to a referenced Blazor WebAssembly application project.
     /// </summary>
@@ -42,23 +47,19 @@ public static IApplicationBuilder UseBlazorFrameworkFiles(this IApplicationBuild
             {
                 context.Response.Headers.Append("Blazor-Environment", webHostEnvironment.EnvironmentName);
 
-                if (webHostEnvironment.IsDevelopment())
+                // DOTNET_MODIFIABLE_ASSEMBLIES is used by the runtime to initialize hot-reload specific environment variables and is configured
+                // by the launching process (dotnet-watch / Visual Studio).
+                // Always add the header if the environment variable is set, regardless of the kind of environment.
+                if (s_dotnetModifiableAssemblies != null)
+                {
+                    context.Response.Headers.Append("DOTNET-MODIFIABLE-ASSEMBLIES", s_dotnetModifiableAssemblies);
+                }
+
+                // See https://github.com/dotnet/aspnetcore/issues/37357#issuecomment-941237000
+                // Translate the _ASPNETCORE_BROWSER_TOOLS environment configured by the browser tools agent in to a HTTP response header.
+                if (s_aspnetcoreBrowserTools != null)
                 {
-                    // DOTNET_MODIFIABLE_ASSEMBLIES is used by the runtime to initialize hot-reload specific environment variables and is configured
-                    // by the launching process (dotnet-watch / Visual Studio).
-                    // In Development, we'll transmit the environment variable to WebAssembly as a HTTP header. The bootstrapping code will read the header
-                    // and configure it as env variable for the wasm app.
-                    if (Environment.GetEnvironmentVariable("DOTNET_MODIFIABLE_ASSEMBLIES") is string dotnetModifiableAssemblies)
-                    {
-                        context.Response.Headers.Append("DOTNET-MODIFIABLE-ASSEMBLIES", dotnetModifiableAssemblies);
-                    }
-
-                    // See https://github.com/dotnet/aspnetcore/issues/37357#issuecomment-941237000
-                    // Translate the _ASPNETCORE_BROWSER_TOOLS environment configured by the browser tools agent in to a HTTP response header.
-                    if (Environment.GetEnvironmentVariable("__ASPNETCORE_BROWSER_TOOLS") is string blazorWasmHotReload)
-                    {
-                        context.Response.Headers.Append("ASPNETCORE-BROWSER-TOOLS", blazorWasmHotReload);
-                    }
+                    context.Response.Headers.Append("ASPNETCORE-BROWSER-TOOLS", s_aspnetcoreBrowserTools);
                 }
 
                 await next(context);