Serve 'Blazor-Environment' header

Author: MackinnonBuck

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

@@ -2,6 +2,7 @@
 // The .NET Foundation licenses this file to you under the MIT license.
 
 using Microsoft.AspNetCore.Builder;
+using Microsoft.AspNetCore.Hosting;
 using Microsoft.AspNetCore.Http;
 using Microsoft.Extensions.Configuration;
 using Microsoft.Extensions.DependencyInjection;
@@ -29,27 +30,29 @@ public static void Configure(IApplicationBuilder app, IConfiguration configurati
 
         app.UseWebAssemblyDebugging();
 
-        bool applyCopHeaders = configuration.GetValue<bool>("ApplyCopHeaders");
+        var webHostEnvironment = app.ApplicationServices.GetRequiredService<IWebHostEnvironment>();
+        var applyCopHeaders = configuration.GetValue<bool>("ApplyCopHeaders");
 
-        if (applyCopHeaders)
+        app.Use(async (ctx, next) =>
         {
-            app.Use(async (ctx, next) =>
+            if (ctx.Request.Path.StartsWithSegments("/_framework") && !ctx.Request.Path.StartsWithSegments("/_framework/blazor.server.js") && !ctx.Request.Path.StartsWithSegments("/_framework/blazor.web.js"))
             {
-                if (ctx.Request.Path.StartsWithSegments("/_framework") && !ctx.Request.Path.StartsWithSegments("/_framework/blazor.server.js") && !ctx.Request.Path.StartsWithSegments("/_framework/blazor.web.js"))
+                ctx.Response.Headers.Append("Blazor-Environment", webHostEnvironment.EnvironmentName);
+
+                if (applyCopHeaders)
                 {
-                    string fileExtension = Path.GetExtension(ctx.Request.Path);
-                    if (string.Equals(fileExtension, ".js"))
+                    var fileExtension = Path.GetExtension(ctx.Request.Path);
+                    if (string.Equals(fileExtension, ".js", StringComparison.Ordinal))
                     {
                         // Browser multi-threaded runtime requires cross-origin policy headers to enable SharedArrayBuffer.
                         ApplyCrossOriginPolicyHeaders(ctx);
                     }
                 }
+            }
 
-                await next(ctx);
-            });
-        }
+            await next(ctx);
+        });
 
-        //app.UseBlazorFrameworkFiles();
         app.UseRouting();
 
         app.UseStaticFiles(new StaticFileOptions

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

@@ -37,6 +37,9 @@ 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 that the dev server always correctly serves the 'Blazor-Environment: Development' header.
+        Browser.Equal("Development", () => _appElement.FindElement(By.Id("environment")).Text);
+
         if (_serverFixture.TestTrimmedOrMultithreadingApps)
         {
             // Verify values overriden by an environment specific 'appsettings.$(Environment).json are read