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Custom middleware-like Chain Of Responsibility implementation
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| namespace Interceptors; | |
| public class FirstInterceptor : IInterceptor | |
| { | |
| public async Task InvokeAsync(PipelineStep next, EventContext ctx) | |
| { | |
| Console.WriteLine($"Hello from interceptor {nameof(FirstInterceptor)}"); | |
| await next.Invoke(ctx); | |
| } | |
| } | |
| public class SecondInterceptor : IInterceptor | |
| { | |
| public async Task InvokeAsync(PipelineStep next, EventContext ctx) | |
| { | |
| await next.Invoke(ctx); | |
| Console.WriteLine($"Hello from interceptor {nameof(SecondInterceptor)}"); | |
| } | |
| } | |
| public class ThirdInterceptor : IInterceptor | |
| { | |
| public async Task InvokeAsync(PipelineStep next, EventContext ctx) | |
| { | |
| Console.WriteLine($"Data: {string.Join(", ", ctx.SomeContextData)}"); | |
| await next.Invoke(ctx); | |
| } | |
| } |
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| using Microsoft.Extensions.DependencyInjection; | |
| namespace Interceptors; | |
| // Func<EventContext, Task> | |
| public delegate Task PipelineStep(EventContext ctx); | |
| public interface IInterceptor | |
| { | |
| Task InvokeAsync(PipelineStep next, EventContext ctx); | |
| } | |
| public class EventContext | |
| { | |
| public IEnumerable<string> SomeContextData { get; set; } | |
| } | |
| // Null-object pattern | |
| public class DeadEndInterceptor : IInterceptor | |
| { | |
| public Task InvokeAsync(PipelineStep next, EventContext _) => Task.CompletedTask; | |
| } | |
| /// <summary> | |
| /// Instance-based interceptor pipeline. | |
| /// </summary> | |
| public class InterceptorPipelineBuilder | |
| { | |
| private readonly LinkedList<IInterceptor> _interceptorsList; | |
| public InterceptorPipelineBuilder() | |
| { | |
| _interceptorsList = new LinkedList<IInterceptor>(); | |
| } | |
| public InterceptorPipelineBuilder AddInterceptor(IInterceptor interceptor) | |
| { | |
| _interceptorsList.AddFirst(interceptor); | |
| return this; | |
| } | |
| public PipelineStep Build() | |
| { | |
| var currentStep = CreateStep(new DeadEndInterceptor(), _ => Task.CompletedTask); | |
| foreach (var interceptor in _interceptorsList) | |
| { | |
| var nextStep = currentStep; | |
| currentStep = CreateStep(interceptor, nextStep); | |
| } | |
| return currentStep; | |
| } | |
| private PipelineStep CreateStep(IInterceptor interceptor, PipelineStep next) => | |
| async ctx => | |
| { | |
| await interceptor.InvokeAsync(next, ctx); | |
| }; | |
| } | |
| /// <summary> | |
| /// Dependency injection container based interceptor pipeline. | |
| /// </summary> | |
| public class InterceptorTypePipelineBuilder | |
| { | |
| private readonly IServiceProvider _serviceProvider; | |
| private readonly LinkedList<Type> _interceptorsList; | |
| public InterceptorTypePipelineBuilder(IServiceProvider serviceProvider) | |
| { | |
| _serviceProvider = serviceProvider; | |
| _interceptorsList = new LinkedList<Type>(); | |
| } | |
| public InterceptorTypePipelineBuilder AddInterceptor<TInterceptor>() | |
| where TInterceptor : IInterceptor | |
| { | |
| _interceptorsList.AddFirst(typeof(TInterceptor)); | |
| return this; | |
| } | |
| public PipelineStep Build() | |
| { | |
| var currentStep = CreateStep(typeof(DeadEndInterceptor), _ => Task.CompletedTask); | |
| foreach (var interceptorType in _interceptorsList) | |
| { | |
| var nextStep = currentStep; | |
| currentStep = CreateStep(interceptorType, nextStep); | |
| } | |
| return currentStep; | |
| } | |
| private PipelineStep CreateStep(Type interceptorType, PipelineStep next) => | |
| async ctx => | |
| { | |
| var interceptorInstance = (IInterceptor)_serviceProvider.GetRequiredService(interceptorType); | |
| await interceptorInstance.InvokeAsync(next, ctx); | |
| }; | |
| } |
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| using Interceptors; | |
| using Microsoft.Extensions.DependencyInjection; | |
| async Task WithoutDependencyInjection(EventContext context) | |
| { | |
| var pipeline = new InterceptorPipelineBuilder() | |
| .AddInterceptor(new FirstInterceptor()) | |
| .AddInterceptor(new SecondInterceptor()) | |
| .AddInterceptor(new ThirdInterceptor()) | |
| .Build(); | |
| await pipeline.Invoke(context); | |
| } | |
| async Task WithDependencyInjection(EventContext context) | |
| { | |
| var serviceProvider = new ServiceCollection() | |
| .AddSingleton(sp => new InterceptorTypePipelineBuilder(sp) | |
| .AddInterceptor<FirstInterceptor>() | |
| .AddInterceptor<SecondInterceptor>() | |
| .AddInterceptor<ThirdInterceptor>()) | |
| .AddTransient<DeadEndInterceptor>() | |
| .AddTransient<FirstInterceptor>() | |
| .AddTransient<SecondInterceptor>() | |
| .AddTransient<ThirdInterceptor>() | |
| .BuildServiceProvider(); | |
| var pipeline = serviceProvider.GetRequiredService<InterceptorTypePipelineBuilder>().Build(); | |
| await pipeline.Invoke(context); | |
| } | |
| var context = new EventContext | |
| { | |
| SomeContextData = new[] | |
| { | |
| "Hello", "World" | |
| } | |
| }; | |
| await WithoutDependencyInjection(context); | |
| await WithDependencyInjection(context); |
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