From ca5c3d9413b483f2b4dd42ef1ffd6131da25e8dd Mon Sep 17 00:00:00 2001
From: Muhammad Rehan Saeed <rehansaeed@gmail.com>
Date: Wed, 24 Aug 2022 10:34:07 +0100
Subject: [PATCH] Add request cancelled middleware

---
 .../ApplicationBuilderExtensions.cs           | 29 +++++++++++
 Source/Boxed.AspNetCore/LoggerExtensions.cs   |  6 +++
 .../Middleware/HttpExceptionMiddleware.cs     |  9 +---
 .../Middleware/RequestCanceledMiddleware.cs   | 48 +++++++++++++++++++
 .../RequestCanceledMiddlewareOptions.cs       | 19 ++++++++
 5 files changed, 104 insertions(+), 7 deletions(-)
 create mode 100644 Source/Boxed.AspNetCore/Middleware/RequestCanceledMiddleware.cs
 create mode 100644 Source/Boxed.AspNetCore/Middleware/RequestCanceledMiddlewareOptions.cs

diff --git a/Source/Boxed.AspNetCore/ApplicationBuilderExtensions.cs b/Source/Boxed.AspNetCore/ApplicationBuilderExtensions.cs
index b3106c32..3cfa6017 100644
--- a/Source/Boxed.AspNetCore/ApplicationBuilderExtensions.cs
+++ b/Source/Boxed.AspNetCore/ApplicationBuilderExtensions.cs
@@ -34,6 +34,35 @@ public static IApplicationBuilder UseHttpException(
         return application.UseMiddleware<HttpExceptionMiddleware>(options);
     }
 
+    /// <summary>
+    /// Handles <see cref="OperationCanceledException"/> caused by the HTTP request being aborted, then shortcuts and
+    /// returns an error status code.
+    /// See https://andrewlock.net/using-cancellationtokens-in-asp-net-core-minimal-apis/.
+    /// </summary>
+    /// <param name="application">The application builder.</param>
+    /// <returns>The same application builder.</returns>
+    public static IApplicationBuilder UseRequestCancelled(this IApplicationBuilder application) =>
+        UseRequestCancelled(application, null);
+
+    /// <summary>
+    /// Handles <see cref="OperationCanceledException"/> caused by the HTTP request being aborted, then shortcuts and
+    /// returns an error status code.
+    /// See https://andrewlock.net/using-cancellationtokens-in-asp-net-core-minimal-apis/.
+    /// </summary>
+    /// <param name="application">The application builder.</param>
+    /// <param name="configureOptions">The middleware options.</param>
+    /// <returns>The same application builder.</returns>
+    public static IApplicationBuilder UseRequestCancelled(
+        this IApplicationBuilder application,
+        Action<RequestCanceledMiddlewareOptions>? configureOptions)
+    {
+        ArgumentNullException.ThrowIfNull(application);
+
+        var options = new RequestCanceledMiddlewareOptions();
+        configureOptions?.Invoke(options);
+        return application.UseMiddleware<RequestCanceledMiddleware>(options);
+    }
+
     /// <summary>
     /// Measures the time the request takes to process and returns this in a Server-Timing trailing HTTP header.
     /// It is used to surface any back-end server timing metrics (e.g. database read/write, CPU time, file system
diff --git a/Source/Boxed.AspNetCore/LoggerExtensions.cs b/Source/Boxed.AspNetCore/LoggerExtensions.cs
index b3a0d494..cf5ac6ed 100644
--- a/Source/Boxed.AspNetCore/LoggerExtensions.cs
+++ b/Source/Boxed.AspNetCore/LoggerExtensions.cs
@@ -13,4 +13,10 @@ internal static partial class LoggerExtensions
         Level = LogLevel.Information,
         Message = "Executing HttpExceptionMiddleware, setting HTTP status code {StatusCode}.")]
     public static partial void SettingHttpStatusCode(this ILogger logger, Exception exception, int statusCode);
+
+    [LoggerMessage(
+        EventId = 4001,
+        Level = LogLevel.Information,
+        Message = "Request was cancelled.")]
+    public static partial void RequestCancelled(this ILogger logger);
 }
diff --git a/Source/Boxed.AspNetCore/Middleware/HttpExceptionMiddleware.cs b/Source/Boxed.AspNetCore/Middleware/HttpExceptionMiddleware.cs
index a01927cb..a0befbf3 100644
--- a/Source/Boxed.AspNetCore/Middleware/HttpExceptionMiddleware.cs
+++ b/Source/Boxed.AspNetCore/Middleware/HttpExceptionMiddleware.cs
@@ -13,19 +13,14 @@ namespace Boxed.AspNetCore.Middleware;
 /// <seealso cref="IMiddleware" />
 public class HttpExceptionMiddleware : IMiddleware
 {
-    private readonly RequestDelegate next;
     private readonly HttpExceptionMiddlewareOptions options;
 
     /// <summary>
     /// Initializes a new instance of the <see cref="HttpExceptionMiddleware"/> class.
     /// </summary>
-    /// <param name="next">The next.</param>
     /// <param name="options">The options.</param>
-    public HttpExceptionMiddleware(RequestDelegate next, HttpExceptionMiddlewareOptions options)
-    {
-        this.next = next;
+    public HttpExceptionMiddleware(HttpExceptionMiddlewareOptions options) =>
         this.options = options;
-    }
 
     /// <inheritdoc/>
     public async Task InvokeAsync(HttpContext context, RequestDelegate next)
@@ -35,7 +30,7 @@ public async Task InvokeAsync(HttpContext context, RequestDelegate next)
 
         try
         {
-            await this.next.Invoke(context).ConfigureAwait(false);
+            await next.Invoke(context).ConfigureAwait(false);
         }
         catch (HttpException httpException)
         {
diff --git a/Source/Boxed.AspNetCore/Middleware/RequestCanceledMiddleware.cs b/Source/Boxed.AspNetCore/Middleware/RequestCanceledMiddleware.cs
new file mode 100644
index 00000000..e0e16c71
--- /dev/null
+++ b/Source/Boxed.AspNetCore/Middleware/RequestCanceledMiddleware.cs
@@ -0,0 +1,48 @@
+namespace Boxed.AspNetCore.Middleware;
+
+using System;
+using System.Threading.Tasks;
+using Microsoft.AspNetCore.Http;
+using Microsoft.Extensions.Logging;
+
+/// <summary>
+/// A middleware which handles <see cref="OperationCanceledException"/> caused by the HTTP request being aborted, then
+/// shortcuts and returns an error status code.
+/// </summary>
+/// <seealso cref="IMiddleware" />
+public class RequestCanceledMiddleware : IMiddleware
+{
+    private readonly ILogger<RequestCanceledMiddleware> logger;
+    private readonly RequestCanceledMiddlewareOptions options;
+
+    /// <summary>
+    /// Initializes a new instance of the <see cref="RequestCanceledMiddleware"/> class.
+    /// </summary>
+    /// <param name="options">The middleware options.</param>
+    /// <param name="logger">A logger.</param>
+    public RequestCanceledMiddleware(
+        RequestCanceledMiddlewareOptions options,
+        ILogger<RequestCanceledMiddleware> logger)
+    {
+        this.options = options;
+        this.logger = logger;
+    }
+
+    /// <inheritdoc/>
+    public async Task InvokeAsync(HttpContext context, RequestDelegate next)
+    {
+        ArgumentNullException.ThrowIfNull(context);
+        ArgumentNullException.ThrowIfNull(next);
+
+        try
+        {
+            await next(context).ConfigureAwait(false);
+        }
+        catch (OperationCanceledException operationCanceledException)
+        when (operationCanceledException.CancellationToken == context.RequestAborted)
+        {
+            this.logger.RequestCancelled();
+            context.Response.StatusCode = this.options.StatusCode;
+        }
+    }
+}
diff --git a/Source/Boxed.AspNetCore/Middleware/RequestCanceledMiddlewareOptions.cs b/Source/Boxed.AspNetCore/Middleware/RequestCanceledMiddlewareOptions.cs
new file mode 100644
index 00000000..97e30774
--- /dev/null
+++ b/Source/Boxed.AspNetCore/Middleware/RequestCanceledMiddlewareOptions.cs
@@ -0,0 +1,19 @@
+namespace Boxed.AspNetCore.Middleware;
+
+/// <summary>
+/// Options controlling <see cref="RequestCanceledMiddleware"/>.
+/// </summary>
+public class RequestCanceledMiddlewareOptions
+{
+    /// <summary>
+    /// The non-standard 499 status code 'Client Closed Request' used by NGINX to signify an aborted/cancelled request.
+    /// </summary>
+    public const int ClientClosedRequest = 499;
+
+    /// <summary>
+    /// Gets or sets the status code to return for a cancelled request. The default is the non-standard 499
+    /// 'Client Closed Request' used by NGINX.
+    /// See https://stackoverflow.com/questions/46234679/what-is-the-correct-http-status-code-for-a-cancelled-request.
+    /// </summary>
+    public int StatusCode { get; set; } = ClientClosedRequest;
+}