advanced-interception.md

Advanced interception

This approach of interception maximizes performance by precompiling the proxy object factory.

using Shouldly;
using Castle.DynamicProxy;
using System.Collections.Immutable;
using System.Linq.Expressions;
using System.Runtime.CompilerServices;
using Pure.DI;

// OnDependencyInjection = On
DI.Setup(nameof(Composition))
    .Bind().To<DataService>()
    .Bind().To<BusinessService>()
    .Root<IBusinessService>("BusinessService");

var log = new List<string>();
var composition = new Composition(log);
var businessService = composition.BusinessService;

// Use the services to verify interception.
businessService.Process();
businessService.DataService.Count();

log.ShouldBe(
    ImmutableArray.Create(
        "Process returns Processed",
        "get_DataService returns Castle.Proxies.IDataServiceProxy",
        "Count returns 55"));

public interface IDataService
{
    int Count();
}

class DataService : IDataService
{
    public int Count() => 55;
}

public interface IBusinessService
{
    IDataService DataService { get; }

    string Process();
}

class BusinessService(IDataService dataService) : IBusinessService
{
    public IDataService DataService { get; } = dataService;

    public string Process() => "Processed";
}

internal partial class Composition : IInterceptor
{
    private readonly List<string> _log = [];
    private static readonly IProxyBuilder ProxyBuilder = new DefaultProxyBuilder();
    private readonly IInterceptor[] _interceptors = [];

    public Composition(List<string> log)
    {
        _log = log;
        _interceptors = [this];
    }

    [MethodImpl(MethodImplOptions.AggressiveInlining)]
    private partial T OnDependencyInjection<T>(
        in T value,
        object? tag,
        Lifetime lifetime)
    {
        if (typeof(T).IsValueType)
        {
            return value;
        }

        return ProxyFactory<T>.GetFactory(ProxyBuilder)(
            value,
            _interceptors);
    }

    public void Intercept(IInvocation invocation)
    {
        invocation.Proceed();
        _log.Add($"{invocation.Method.Name} returns {invocation.ReturnValue}");
    }

    private static class ProxyFactory<T>
    {
        private static Func<T, IInterceptor[], T>? _factory;

        public static Func<T, IInterceptor[], T> GetFactory(IProxyBuilder proxyBuilder) =>
            _factory ?? CreateFactory(proxyBuilder);

        private static Func<T, IInterceptor[], T> CreateFactory(IProxyBuilder proxyBuilder)
        {
            // Compiles a delegate to create a proxy for the performance boost
            var proxyType = proxyBuilder.CreateInterfaceProxyTypeWithTargetInterface(
                typeof(T),
                Type.EmptyTypes,
                ProxyGenerationOptions.Default);
            var ctor = proxyType.GetConstructors()
                .Single(i => i.GetParameters().Length == 2);
            var instance = Expression.Parameter(typeof(T));
            var interceptors = Expression.Parameter(typeof(IInterceptor[]));
            var newProxyExpression = Expression.New(ctor, interceptors, instance);
            return _factory = Expression.Lambda<Func<T, IInterceptor[], T>>(
                    newProxyExpression,
                    instance,
                    interceptors)
                .Compile();
        }
    }
}

Running this code sample locally

• Make sure you have the .NET SDK 10.0 or later installed

dotnet --list-sdk

• Create a net10.0 (or later) console application

dotnet new console -n Sample

• Add references to the NuGet packages
  • Pure.DI
  • Shouldly
  • Castle.DynamicProxy

dotnet add package Pure.DI
dotnet add package Shouldly
dotnet add package Castle.DynamicProxy

• Copy the example code into the Program.cs file

You are ready to run the example 🚀

dotnet run

Note

Advanced interception provides high-performance proxy generation for scenarios where runtime interception overhead must be minimized.

The following partial class will be generated:

partial class Composition
{
  public IBusinessService BusinessService
  {
    [MethodImpl(MethodImplOptions.AggressiveInlining)]
    get
    {
      return OnDependencyInjection<IBusinessService>(new BusinessService(OnDependencyInjection<IDataService>(new DataService(), null, Lifetime.Transient)), null, Lifetime.Transient);
    }
  }


  private partial T OnDependencyInjection<T>(in T value, object? tag, Lifetime lifetime);
}

Class diagram:

---
 config:
  maxTextSize: 2147483647
  maxEdges: 2147483647
  class:
   hideEmptyMembersBox: true
---
classDiagram
	DataService --|> IDataService
	BusinessService --|> IBusinessService
	Composition ..> BusinessService : IBusinessService BusinessService
	BusinessService *--  DataService : IDataService
	namespace Pure.DI.UsageTests.Interception.AdvancedInterceptionScenario {
		class BusinessService {
				<<class>>
			+BusinessService(IDataService dataService)
		}
		class Composition {
		<<partial>>
		+IBusinessService BusinessService
		}
		class DataService {
				<<class>>
			+DataService()
		}
		class IBusinessService {
			<<interface>>
		}
		class IDataService {
			<<interface>>
		}
	}

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