exception handling pipeline

Author: Ihar Yakimush

Commmunity.AspNetCore.ExceptionHandling.Integration/Commmunity.AspNetCore.ExceptionHandling.Integration.csproj

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+<Project Sdk="Microsoft.NET.Sdk.Web">
+
+  <PropertyGroup>
+    <TargetFramework>netcoreapp2.0</TargetFramework>
+  </PropertyGroup>
+
+  <ItemGroup>
+    <Folder Include="wwwroot\" />
+  </ItemGroup>
+
+  <ItemGroup>
+    <PackageReference Include="Microsoft.AspNetCore.All" Version="2.0.6" />
+  </ItemGroup>
+
+  <ItemGroup>
+    <DotNetCliToolReference Include="Microsoft.VisualStudio.Web.CodeGeneration.Tools" Version="2.0.3" />
+  </ItemGroup>
+
+  <ItemGroup>
+    <ProjectReference Include="..\Commmunity.AspNetCore.ExceptionHandling\Commmunity.AspNetCore.ExceptionHandling.csproj" />
+  </ItemGroup>
+
+</Project>

Commmunity.AspNetCore.ExceptionHandling.Integration/Controllers/ValuesController.cs

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+using System;
+using System.Collections.Generic;
+using System.Linq;
+using System.Threading.Tasks;
+using Microsoft.AspNetCore.Mvc;
+
+namespace Commmunity.AspNetCore.ExceptionHandling.Integration.Controllers
+{
+    [Route("api/[controller]")]
+    public class ValuesController : Controller
+    {
+        // GET api/values
+        [HttpGet]
+        public IEnumerable<string> Get()
+        {
+            return new string[] { "value1", "value2" };
+        }
+
+        // GET api/values/5
+        [HttpGet("{id}")]
+        public string Get(int id)
+        {
+            if (id > 10)
+            {
+                throw new ArgumentOutOfRangeException();
+            }
+
+            if (id > 5)
+            {
+                throw new InvalidCastException();
+            }
+
+            return "value";
+        }
+
+        // POST api/values
+        [HttpPost]
+        public void Post([FromBody]string value)
+        {
+        }
+
+        // PUT api/values/5
+        [HttpPut("{id}")]
+        public void Put(int id, [FromBody]string value)
+        {
+        }
+
+        // DELETE api/values/5
+        [HttpDelete("{id}")]
+        public void Delete(int id)
+        {
+        }
+    }
+}

Commmunity.AspNetCore.ExceptionHandling.Integration/Program.cs

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+using System;
+using System.Collections.Generic;
+using System.IO;
+using System.Linq;
+using System.Threading.Tasks;
+using Microsoft.AspNetCore;
+using Microsoft.AspNetCore.Hosting;
+using Microsoft.Extensions.Configuration;
+using Microsoft.Extensions.Logging;
+
+namespace Commmunity.AspNetCore.ExceptionHandling.Integration
+{
+    public class Program
+    {
+        public static void Main(string[] args)
+        {
+            BuildWebHost(args).Run();
+        }
+
+        public static IWebHost BuildWebHost(string[] args) =>
+            WebHost.CreateDefaultBuilder(args)
+                .UseStartup<Startup>()
+                .Build();
+    }
+}

Commmunity.AspNetCore.ExceptionHandling.Integration/Startup.cs

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+using System;
+using System.Collections.Generic;
+using System.Linq;
+using System.Threading.Tasks;
+using Microsoft.AspNetCore.Builder;
+using Microsoft.AspNetCore.Hosting;
+using Microsoft.Extensions.Configuration;
+using Microsoft.Extensions.DependencyInjection;
+using Microsoft.Extensions.Logging;
+using Microsoft.Extensions.Options;
+
+namespace Commmunity.AspNetCore.ExceptionHandling.Integration
+{
+    public class Startup
+    {
+        public Startup(IConfiguration configuration)
+        {
+            Configuration = configuration;
+        }
+
+        public IConfiguration Configuration { get; }
+
+        // This method gets called by the runtime. Use this method to add services to the container.
+        public void ConfigureServices(IServiceCollection services)
+        {
+            services.AddMvc();
+
+            services.AddExceptionHandlingPolicies(options =>
+                options.EnsureException<ArgumentOutOfRangeException>()
+                    .EnsureHandler<LogExceptionHandler>().EnsureHandler<ReThrowExceptionHandler>());
+        }
+
+        // This method gets called by the runtime. Use this method to configure the HTTP request pipeline.
+        public void Configure(IApplicationBuilder app, IHostingEnvironment env)
+        {
+            app.UseDeveloperExceptionPage().UseExceptionHandlingPolicies();
+
+            app.UseMvc();
+        }
+    }
+}

Commmunity.AspNetCore.ExceptionHandling.Integration/appsettings.Development.json

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+{
+  "Logging": {
+    "IncludeScopes": false,
+    "LogLevel": {
+      "Default": "Debug",
+      "System": "Information",
+      "Microsoft": "Information"
+    }
+  }
+}

Commmunity.AspNetCore.ExceptionHandling.Integration/appsettings.json

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+{
+  "Logging": {
+    "IncludeScopes": false,
+    "Debug": {
+      "LogLevel": {
+        "Default": "Warning"
+      }
+    },
+    "Console": {
+      "LogLevel": {
+        "Default": "Warning"
+      }
+    }
+  }
+}

Commmunity.AspNetCore.ExceptionHandling/AppBuilderExtensions.cs

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+using System;
+using Microsoft.AspNetCore.Builder;
+using Microsoft.Extensions.DependencyInjection;
+using Microsoft.Extensions.DependencyInjection.Extensions;
+using Microsoft.Extensions.Options;
+
+namespace Commmunity.AspNetCore.ExceptionHandling
+{
+    //TODO: add warning for policy override
+    //TODO: add response handler
+    //TODO: add retry handler
+    //TODO: policy builder
+    //TODO: add api exception and handler
+    //TODO: add terminate policies pipeline handler ???
+    public static class AppBuilderExtensions
+    {
+        public static IApplicationBuilder UseExceptionHandlingPolicies(this IApplicationBuilder app)
+        {            
+            return app.UseMiddleware<ExceptionHandlingPolicyMiddleware>();
+        }
+        public static IServiceCollection AddExceptionHandlingPolicies(this IServiceCollection services, Action<ExceptionHandlingPolicyOptions> options = null)
+        {
+            services.TryAddSingleton<ExceptionHandlingPolicyMiddleware>();
+            if (options != null)
+            {
+                services.Configure(options);
+            }
+
+            services.TryAddSingleton<ReThrowExceptionHandler>();
+            services.TryAddSingleton<LogExceptionHandler>();
+
+            return services;
+        }
+
+        public static IApplicationBuilder UseExceptionHandlingPolicies(this IApplicationBuilder app, ExceptionHandlingPolicyOptions options)
+        {
+            return app.UseMiddleware<ExceptionHandlingPolicyMiddleware>(Options.Create(options));
+        }
+    }
+}

Commmunity.AspNetCore.ExceptionHandling/Commmunity.AspNetCore.ExceptionHandling.csproj

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+<Project Sdk="Microsoft.NET.Sdk">
+
+  <PropertyGroup>
+    <TargetFramework>netstandard2.0</TargetFramework>
+  </PropertyGroup>
+
+  <ItemGroup>
+    <PackageReference Include="Microsoft.AspNetCore.Http" Version="2.0.0" />
+    <PackageReference Include="Microsoft.Extensions.Logging.Abstractions" Version="2.0.0" />
+  </ItemGroup>
+
+</Project>

Commmunity.AspNetCore.ExceptionHandling/Events.cs

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+using Microsoft.Extensions.Logging;
+
+namespace Commmunity.AspNetCore.ExceptionHandling
+{
+    public static class Events
+    {
+        public static readonly EventId HandlerError = new EventId(100, "HandlerExecutionError");
+        public static readonly EventId PolicyNotFound = new EventId(101, "PolicyForExceptionNotRegistered");
+        public static readonly EventId HandlersNotFound = new EventId(102, "HandlersCollectionEmpty");
+        public static readonly EventId HandlerNotCreated = new EventId(103, "HandlersCanNotBeCreated");
+    }
+}

Commmunity.AspNetCore.ExceptionHandling/ExceptionHandlingPolicyMiddleware.cs

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+using System;
+using System.Collections.Generic;
+using System.Threading.Tasks;
+using Microsoft.AspNetCore.Http;
+using Microsoft.Extensions.DependencyInjection;
+using Microsoft.Extensions.Logging;
+using Microsoft.Extensions.Logging.Abstractions;
+using Microsoft.Extensions.Options;
+
+namespace Commmunity.AspNetCore.ExceptionHandling
+{
+    public class ExceptionHandlingPolicyMiddleware : IMiddleware
+    {
+        private readonly IOptions<ExceptionHandlingPolicyOptions> options;
+
+        public ExceptionHandlingPolicyMiddleware(IOptions<ExceptionHandlingPolicyOptions> options)
+        {
+            this.options = options ?? throw new ArgumentNullException(nameof(options));
+        }       
+
+        private static async Task<bool> EnumerateExceptionMapping(
+            HttpContext context, 
+            ExceptionHandlingPolicyOptions policyOptions,
+            Exception exception,
+            RequestDelegate next)
+        {
+            Type exceptionType = exception.GetType();
+
+            ILogger logger = context.RequestServices.GetService<ILogger<ExceptionHandlingPolicyMiddleware>>() ??
+                             NullLoggerFactory.Instance.CreateLogger<ExceptionHandlingPolicyMiddleware>();
+
+            bool? throwRequired = null;
+
+            foreach (Type type in policyOptions.GetExceptionsInternal())
+            {
+                if (type.IsAssignableFrom(exceptionType))
+                {                    
+                    throwRequired = await EnumerateHandlers(context, exception, next, policyOptions, logger);
+
+                    break;
+                }
+            }
+
+            if (!throwRequired.HasValue)
+            {
+                logger.LogWarning(Events.PolicyNotFound,
+                    "Handlers mapping for exception type {exceptionType} not exists. Exception will be re-thrown. RequestId: {RequestId}",
+                    exceptionType, context.TraceIdentifier);
+            }
+
+            return throwRequired ?? true;
+        }
+
+        private static async Task<bool> EnumerateHandlers(
+            HttpContext context, 
+            Exception exception,
+            RequestDelegate next, 
+            ExceptionHandlingPolicyOptions policyOptions, 
+            ILogger logger)
+        {
+            bool? throwRequired = null;
+            Type exceptionType = exception.GetType();
+
+            IEnumerable<Type> handlers = policyOptions.GetHandlersInternal(exceptionType);
+
+            foreach (Type handlerType in handlers)
+            {                
+                try
+                {
+                    IExceptionHandler handler =
+                        context.RequestServices.GetService(handlerType) as IExceptionHandler;
+
+                    if (handler == null)
+                    {
+                        throwRequired = true;
+                        logger.LogError(Events.HandlerNotCreated,
+                            "Handler type {handlerType} can't be created because it not registered in IServiceProvider. RequestId: {RequestId}",
+                            handlerType, context.TraceIdentifier);
+                    }
+                    else
+                    {
+                        throwRequired = await handler.Handle(context, exception, next);
+                    }                    
+                }
+                catch (Exception e)
+                {
+                    logger.LogError(Events.HandlerError, e,
+                        "Unhandled exception executing handler of type {handlerType} on exception of type {exceptionType}. RequestId: {RequestId}",
+                        handlerType, exceptionType, context.TraceIdentifier);
+                    throwRequired = true;
+                }
+
+                if (throwRequired.Value)
+                {
+                    break;
+                }
+            }
+
+            if (!throwRequired.HasValue)
+            {
+                logger.LogWarning(Events.HandlersNotFound,
+                    "Handlers collection for exception type {exceptionType} is empty. Exception will be re-thrown. RequestId: {RequestId}",
+                    exceptionType, context.TraceIdentifier);
+            }
+
+            return throwRequired ?? true;
+        }
+
+        public async Task InvokeAsync(HttpContext context, RequestDelegate next)
+        {
+            try
+            {
+                await next(context);
+            }
+            catch (Exception exception)
+            {
+                ExceptionHandlingPolicyOptions policyOptions = this.options.Value;
+
+                bool throwRequired = await EnumerateExceptionMapping(context, policyOptions, exception, next);
+
+                if (throwRequired)
+                {
+                    throw;
+                }
+            }
+        }
+    }
+}