text/plain; charset=utf-8 and pr feedback

Author: halter73

src/Middleware/Diagnostics/src/DeveloperExceptionPage/DeveloperExceptionPageMiddleware.cs

@@ -145,7 +145,7 @@ private Task DisplayException(ErrorContext errorContext)
             // If the client does not ask for HTML just format the exception as plain text
             if (acceptHeader == null || !acceptHeader.Any(h => h.IsSubsetOf(_textHtmlMediaType)))
             {
-                httpContext.Response.ContentType = "text/plain";
+                httpContext.Response.ContentType = "text/plain; charset=utf-8";
 
                 var sb = new StringBuilder();
                 sb.AppendLine(errorContext.Exception.ToString());

src/Middleware/Diagnostics/test/UnitTests/DeveloperExceptionPageMiddlewareTest.cs

@@ -119,13 +119,16 @@ public async Task ErrorPageWithoutAcceptHeaderForHtmlReturnsPlainText()
 
             var responseText = await response.Content.ReadAsStringAsync();
             Assert.Equal("text/plain", response.Content.Headers.ContentType.MediaType);
+            Assert.Equal("utf-8", response.Content.Headers.ContentType.CharSet);
             Assert.Contains("Test exception", responseText);
             Assert.DoesNotContain("<html", responseText);
         }
 
         [Fact]
         public async Task StatusCodeFromBadHttpRequestExceptionIsPreserved()
         {
+            const int statusCode = 418;
+
             // Arrange
             using var host = new HostBuilder()
                 .ConfigureWebHost(webHostBuilder =>
@@ -137,7 +140,7 @@ public async Task StatusCodeFromBadHttpRequestExceptionIsPreserved()
                         app.UseDeveloperExceptionPage();
                         app.Run(context =>
                         {
-                            throw new BadHttpRequestException("Not found!", 404);
+                            throw new BadHttpRequestException("Not found!", statusCode);
                         });
                     });
                 }).Build();
@@ -150,7 +153,7 @@ public async Task StatusCodeFromBadHttpRequestExceptionIsPreserved()
             var response = await server.CreateClient().GetAsync("/path");
 
             // Assert
-            Assert.Equal(StatusCodes.Status404NotFound, (int)response.StatusCode);
+            Assert.Equal(statusCode, (int)response.StatusCode);
 
             var responseText = await response.Content.ReadAsStringAsync();
             Assert.Contains("Not found!", responseText);