Add structured error mapper (#507)

Modules/ErrorHandling/ErrorHandler.cs

@@ -2,6 +2,7 @@
 
 using GenHTTP.Api.Content;
 
+using GenHTTP.Modules.Conversion.Providers;
 using GenHTTP.Modules.ErrorHandling.Provider;
 
 namespace GenHTTP.Modules.ErrorHandling
@@ -16,10 +17,19 @@ public static class ErrorHandler
         /// </summary>
         /// <remarks>
         /// By default, server errors will be rendered into
-        /// a HTML template.
+        /// structured responses.
         /// </remarks>
         /// <returns>The default error handler</returns>
-        public static ErrorSentryBuilder<Exception> Default() => Html();
+        public static ErrorSentryBuilder<Exception> Default() => Structured();
+
+        /// <summary>
+        /// Ans error handler which will render exceptions into
+        /// structured error objects serialized to the format
+        /// requested by the client (e.g. JSON or XML).
+        /// </summary>
+        /// <param name="serialization">The serialization configuration to be used</param>
+        /// <returns>A structured error handler</returns>
+        public static ErrorSentryBuilder<Exception> Structured(SerializationBuilder? serialization = null) => From(new StructuredErrorMapper(serialization?.Build()));
 
         /// <summary>
         /// An error handler which will render exceptions into

Modules/ErrorHandling/GenHTTP.Modules.ErrorHandling.csproj

@@ -44,6 +44,7 @@
     <ProjectReference Include="..\..\API\GenHTTP.Api.csproj" />
 
     <ProjectReference Include="..\Pages\GenHTTP.Modules.Pages.csproj" />
+	<ProjectReference Include="..\Conversion\GenHTTP.Modules.Conversion.csproj" />
 
     <PackageReference Include="Microsoft.SourceLink.GitHub" Version="8.0.0" PrivateAssets="All" />
 

Modules/ErrorHandling/Provider/ErrorSentry.cs

@@ -43,9 +43,8 @@ public ErrorSentry(IHandler parent, Func<IHandler, IHandler> contentFactory, IEr
         {
             try
             {
-                var response = await Content.HandleAsync(request)
-                                            ;
-
+                var response = await Content.HandleAsync(request);
+
                 if (response is null)
                 {
                     return await ErrorHandler.GetNotFound(request, Content);

Modules/ErrorHandling/StructuredErrorMapper.cs

@@ -0,0 +1,85 @@
+using System;
+using System.Threading.Tasks;
+
+using GenHTTP.Api.Content;
+using GenHTTP.Api.Protocol;
+
+using GenHTTP.Modules.Conversion;
+using GenHTTP.Modules.Conversion.Providers;
+using GenHTTP.Modules.Conversion.Providers.Json;
+
+namespace GenHTTP.Modules.ErrorHandling
+{
+
+    public sealed class StructuredErrorMapper : IErrorMapper<Exception>
+    {
+
+        #region Supporting data structures
+
+        public record class ErrorModel(ResponseStatus Status, string Message, string? StackTrace = null);
+
+        #endregion
+
+        #region Get-/Setters
+
+        public SerializationRegistry Registry { get; }
+
+        #endregion
+
+        #region Initialization
+
+        public StructuredErrorMapper(SerializationRegistry? registry)
+        {
+            Registry = registry ?? Serialization.Default().Build();
+        }
+
+        #endregion
+
+        #region Functionality
+
+        public async ValueTask<IResponse?> Map(IRequest request, IHandler handler, Exception error)
+        {
+            string? stackTrace = null;
+
+            if (request.Server.Development)
+            {
+                stackTrace = error.StackTrace;
+            }
+
+            if (error is ProviderException e)
+            {
+                var model = new ErrorModel(e.Status, error.Message, stackTrace);
+
+                return await RenderAsync(request, model);
+            }
+            else
+            {
+                var model = new ErrorModel(ResponseStatus.InternalServerError, error.Message, stackTrace);
+
+                return await RenderAsync(request, model);
+            }
+        }
+
+        public async ValueTask<IResponse?> GetNotFound(IRequest request, IHandler handler)
+        {
+            var model = new ErrorModel(ResponseStatus.NotFound, "The requested resource does not exist on this server");
+
+            return await RenderAsync(request, model);
+        }
+
+        private async ValueTask<IResponse> RenderAsync(IRequest request, ErrorModel model)
+        {
+            var format = Registry.GetSerialization(request) ?? new JsonFormat();
+
+            var response = await format.SerializeAsync(request, model);
+
+            response.Status(model.Status);
+
+            return response.Build();
+        }
+
+        #endregion
+
+    }
+
+}

Testing/Acceptance/Engine/DeveloperModeTests.cs

@@ -50,7 +50,9 @@ public async Task TestExceptionsWithTrace()
 
             using var response = await runner.GetResponseAsync();
 
-            Assert.IsTrue((await response.GetContentAsync()).Contains("Exception"));
+            var content = await response.GetContentAsync();
+
+            Assert.IsTrue(content.Contains("HandleAsync"));
         }
 
         /// <summary>

Testing/Acceptance/Modules/ErrorHandling/StructuredErrorMapperTests.cs

@@ -0,0 +1,98 @@
+using System;
+using System.Net;
+using System.Threading.Tasks;
+
+using GenHTTP.Api.Content;
+using GenHTTP.Api.Protocol;
+
+using GenHTTP.Modules.ErrorHandling;
+using GenHTTP.Modules.Functional;
+
+using Microsoft.VisualStudio.TestTools.UnitTesting;
+
+namespace GenHTTP.Testing.Acceptance.Modules.ErrorHandling
+{
+
+    [TestClass]
+    public sealed class StructuredErrorMapperTests
+    {
+
+        [TestMethod]
+        public async Task TestNotFound()
+        {
+            using var host = TestHost.Run(Inline.Create());
+
+            using var response = await host.GetResponseAsync();
+
+            await response.AssertStatusAsync(HttpStatusCode.NotFound);
+
+            var model = await response.GetContentAsync<StructuredErrorMapper.ErrorModel>();
+
+            Assert.AreEqual(ResponseStatus.NotFound, model.Status);
+
+            Assert.IsNull(model.StackTrace);
+        }
+
+        [TestMethod]
+        public async Task TestGeneralError()
+        {
+            var handler = Inline.Create()
+                                .Get(() => DoThrow(new Exception("Oops")));
+
+            using var host = TestHost.Run(handler);
+
+            using var response = await host.GetResponseAsync();
+
+            await response.AssertStatusAsync(HttpStatusCode.InternalServerError);
+
+            var model = await response.GetContentAsync<StructuredErrorMapper.ErrorModel>();
+
+            Assert.AreEqual(ResponseStatus.InternalServerError, model.Status);
+
+            Assert.IsNotNull(model.StackTrace);
+        }
+
+        [TestMethod]
+        public async Task TestProviderError()
+        {
+            var handler = Inline.Create()
+                                .Get(() => DoThrow(new ProviderException(ResponseStatus.Locked, "Locked up!")));
+
+            using var host = TestHost.Run(handler);
+
+            using var response = await host.GetResponseAsync();
+
+            await response.AssertStatusAsync(HttpStatusCode.Locked);
+
+            var model = await response.GetContentAsync<StructuredErrorMapper.ErrorModel>();
+
+            Assert.AreEqual(ResponseStatus.Locked, model.Status);
+
+            Assert.IsNotNull(model.StackTrace);
+        }
+
+        [TestMethod]
+        public async Task TestNoTraceInProduction()
+        {
+            var handler = Inline.Create()
+                                .Get(() => DoThrow(new Exception("Oops")));
+
+            using var host = TestHost.Run(handler, development: false);
+
+            using var response = await host.GetResponseAsync();
+
+            await response.AssertStatusAsync(HttpStatusCode.InternalServerError);
+
+            var model = await response.GetContentAsync<StructuredErrorMapper.ErrorModel>();
+
+            Assert.IsNull(model.StackTrace);
+        }
+
+        private static void DoThrow(Exception e)
+        {
+            throw e;
+        }
+
+    }
+
+}