From 747e70ca0032d0aad95302dbda47bf778a95333e Mon Sep 17 00:00:00 2001
From: Damian Edwards <damian@damianedwards.com>
Date: Tue, 17 Dec 2024 10:39:48 -0800
Subject: [PATCH] Make developer exception page work during dev in the sample

---
 samples/RazorSlices.Samples.WebApp/Program.cs | 10 ++++
 .../Properties/launchSettings.json            |  6 ++-
 .../ResponseBufferingMiddleware.cs            | 52 +++++++++++++++++++
 3 files changed, 66 insertions(+), 2 deletions(-)
 create mode 100644 samples/RazorSlices.Samples.WebApp/ResponseBufferingMiddleware.cs

diff --git a/samples/RazorSlices.Samples.WebApp/Program.cs b/samples/RazorSlices.Samples.WebApp/Program.cs
index ad1c9bd..5ab302c 100644
--- a/samples/RazorSlices.Samples.WebApp/Program.cs
+++ b/samples/RazorSlices.Samples.WebApp/Program.cs
@@ -22,6 +22,16 @@
 app.UseStatusCodePages();
 app.UseStaticFiles();
 
+if (app.Environment.IsDevelopment())
+{
+    app.UseDeveloperExceptionPage();
+    if (Environment.GetEnvironmentVariable("ENABLE_RESPONSE_BUFFERING") == "true")
+    {
+        // Enable response buffering middleware to allow for response interception during local development
+        app.UseResponseBuffering();
+    }
+}
+
 app.MapGet("/lorem", () => Results.Redirect("/lorem-static"));
 app.MapGet("/lorem-static", () => Results.Extensions.RazorSlice<Slices.Lorem.LoremStatic>());
 app.MapGet("/lorem-dynamic", (int? paraCount, int? paraLength) =>
diff --git a/samples/RazorSlices.Samples.WebApp/Properties/launchSettings.json b/samples/RazorSlices.Samples.WebApp/Properties/launchSettings.json
index a436f57..4d606c3 100644
--- a/samples/RazorSlices.Samples.WebApp/Properties/launchSettings.json
+++ b/samples/RazorSlices.Samples.WebApp/Properties/launchSettings.json
@@ -6,7 +6,8 @@
       "launchBrowser": true,
       "applicationUrl": "http://localhost:5270",
       "environmentVariables": {
-        "ASPNETCORE_ENVIRONMENT": "Development"
+        "ASPNETCORE_ENVIRONMENT": "Development",
+        "ENABLE_RESPONSE_BUFFERING": "true"
       }
     },
     "https": {
@@ -15,7 +16,8 @@
       "launchBrowser": true,
       "applicationUrl": "https://localhost:7194;http://localhost:5270",
       "environmentVariables": {
-        "ASPNETCORE_ENVIRONMENT": "Development"
+        "ASPNETCORE_ENVIRONMENT": "Development",
+        "ENABLE_RESPONSE_BUFFERING": "true"
       }
     }
   }
diff --git a/samples/RazorSlices.Samples.WebApp/ResponseBufferingMiddleware.cs b/samples/RazorSlices.Samples.WebApp/ResponseBufferingMiddleware.cs
new file mode 100644
index 0000000..322a447
--- /dev/null
+++ b/samples/RazorSlices.Samples.WebApp/ResponseBufferingMiddleware.cs
@@ -0,0 +1,52 @@
+namespace RazorSlices.Samples.WebApp;
+
+using System.IO;
+using System.Threading.Tasks;
+using Microsoft.AspNetCore.Builder;
+using Microsoft.AspNetCore.Http;
+
+internal sealed class ResponseBufferingMiddleware(RequestDelegate next)
+{
+    public async Task InvokeAsync(HttpContext context)
+    {
+        // Save the original response body stream
+        var originalBodyStream = context.Response.Body;
+
+        try
+        {
+            // Create a memory stream to buffer the response
+            using var memoryStream = new MemoryStream();
+            context.Response.Body = memoryStream;
+
+            // Call the next middleware
+            await next(context);
+
+            // If no exception occurs, write the buffered response to the original body
+            memoryStream.Seek(0, SeekOrigin.Begin);
+            await memoryStream.CopyToAsync(originalBodyStream);
+        }
+        catch
+        {
+            // Clear the existing response
+            context.Response.Clear();
+            context.Response.StatusCode = StatusCodes.Status500InternalServerError;
+
+            // Rethrow to let the Developer Exception Page middleware handle it
+            throw;
+        }
+        finally
+        {
+            // Restore the original body stream
+            context.Response.Body = originalBodyStream;
+        }
+    }
+}
+
+internal static class ResponseBufferingMiddlewareExtensions
+{
+    public static IApplicationBuilder UseResponseBuffering(this IApplicationBuilder app)
+    {
+        return app.UseMiddleware<ResponseBufferingMiddleware>();
+    }
+}
+