Ensure all app level unhandled exceptions are logged

Author: mathewc

src/WebJobs.Script.WebHost/Middleware/ExceptionMiddleware.cs

@@ -0,0 +1,49 @@
+// Copyright (c) .NET Foundation. All rights reserved.
+// Licensed under the MIT License. See License.txt in the project root for license information.
+
+using System;
+using System.Threading.Tasks;
+using Microsoft.AspNetCore.Http;
+using Microsoft.AspNetCore.Http.Features;
+using Microsoft.Azure.WebJobs.Host;
+using Microsoft.Extensions.Logging;
+
+namespace Microsoft.Azure.WebJobs.Script.WebHost.Middleware
+{
+    internal class ExceptionMiddleware
+    {
+        private readonly ILogger _logger;
+        private readonly RequestDelegate _next;
+
+        public ExceptionMiddleware(RequestDelegate next, ILogger<ExceptionMiddleware> logger)
+        {
+            _logger = logger;
+            _next = next;
+        }
+
+        public async Task Invoke(HttpContext context)
+        {
+            try
+            {
+                await _next.Invoke(context);
+            }
+            catch (Exception ex)
+            {
+                var responseFeature = context.Features.Get<IHttpResponseFeature>();
+                context.Response.StatusCode = StatusCodes.Status500InternalServerError;
+
+                if (ex is HttpException httpException)
+                {
+                    context.Response.StatusCode = httpException.StatusCode;
+                }
+
+                if (!(ex is FunctionInvocationException))
+                {
+                    // exceptions throw by function code are handled/logged elsewhere
+                    // our goal here is to log exceptions coming from our own runtime
+                    _logger.LogError(ex, "An unhandled host error has occurred.");
+                }
+            }
+        }
+    }
+}

src/WebJobs.Script.WebHost/Middleware/HttpExceptionMiddleware.cs

@@ -47,7 +47,7 @@ public static IApplicationBuilder UseWebJobsScriptHost(this IApplicationBuilder
                 builder.UseMiddleware<AppServiceHeaderFixupMiddleware>();
             }
 
-            builder.UseMiddleware<HttpExceptionMiddleware>();
+            builder.UseMiddleware<ExceptionMiddleware>();
             builder.UseMiddleware<ResponseBufferingMiddleware>();
             builder.UseMiddleware<HomepageMiddleware>();
             builder.UseWhen(context => !context.Request.IsAdminRequest(), config =>

src/WebJobs.Script.WebHost/WebJobsApplicationBuilderExtension.cs

@@ -0,0 +1,95 @@
+// Copyright (c) .NET Foundation. All rights reserved.
+// Licensed under the MIT License. See License.txt in the project root for license information.
+
+using System;
+using System.Linq;
+using System.Threading.Tasks;
+using Microsoft.AspNetCore.Http;
+using Microsoft.Azure.WebJobs.Host;
+using Microsoft.Azure.WebJobs.Script.WebHost;
+using Microsoft.Azure.WebJobs.Script.WebHost.Middleware;
+using Microsoft.Extensions.DependencyInjection;
+using Microsoft.Extensions.Hosting;
+using Microsoft.Extensions.Logging;
+using Microsoft.WebJobs.Script.Tests;
+using Xunit;
+
+namespace Microsoft.Azure.WebJobs.Script.Tests.Middleware
+{
+    public class ExceptionMiddlewareTests
+    {
+        private readonly ILogger<ExceptionMiddleware> _logger;
+        private readonly TestLoggerProvider _loggerProvider;
+
+        public ExceptionMiddlewareTests()
+        {
+            _loggerProvider = new TestLoggerProvider();
+            IHost host = new HostBuilder()
+                .ConfigureDefaultTestWebScriptHost()
+                .ConfigureLogging(l =>
+                {
+                    l.AddProvider(_loggerProvider);
+                })
+                .Build();
+
+            _logger = host.Services.GetService<ILogger<ExceptionMiddleware>>();
+        }
+
+        [Fact]
+        public async Task Invoke_HandlesHttpExceptions()
+        {
+            var ex = new HttpException(StatusCodes.Status502BadGateway);
+            RequestDelegate next = (ctxt) =>
+            {
+                throw ex;
+            };
+            var middleware = new ExceptionMiddleware(next, _logger);
+
+            var context = new DefaultHttpContext();
+            await middleware.Invoke(context);
+
+            Assert.Equal(ex.StatusCode, context.Response.StatusCode);
+
+            var log = _loggerProvider.GetAllLogMessages().Single();
+            Assert.Equal("An unhandled host error has occurred.", log.FormattedMessage);
+            Assert.Same(ex, log.Exception);
+        }
+
+        [Fact]
+        public async Task Invoke_HandlesNonHttpExceptions()
+        {
+            var ex = new Exception("Kaboom!");
+            RequestDelegate next = (ctxt) =>
+            {
+                throw ex;
+            };
+            var middleware = new ExceptionMiddleware(next, _logger);
+
+            var context = new DefaultHttpContext();
+            await middleware.Invoke(context);
+
+            Assert.Equal(StatusCodes.Status500InternalServerError, context.Response.StatusCode);
+
+            var log = _loggerProvider.GetAllLogMessages().Single();
+            Assert.Equal("An unhandled host error has occurred.", log.FormattedMessage);
+            Assert.Same(ex, log.Exception);
+        }
+
+        [Fact]
+        public async Task Invoke_HandlesFunctionInvocationExceptions()
+        {
+            var ex = new FunctionInvocationException("Kaboom!");
+            RequestDelegate next = (ctxt) =>
+            {
+                throw ex;
+            };
+            var middleware = new ExceptionMiddleware(next, _logger);
+
+            var context = new DefaultHttpContext();
+            await middleware.Invoke(context);
+
+            Assert.Equal(StatusCodes.Status500InternalServerError, context.Response.StatusCode);
+            Assert.Empty(_loggerProvider.GetAllLogMessages());
+        }
+    }
+}