6. abp中的攔截器

abp攔截器基本定義

攔截器介面定義：

public interface IAbpInterceptor
{
    void Intercept(IAbpMethodInvocation invocation);

    Task InterceptAsync(IAbpMethodInvocation invocation);
}

預設抽象類定義：

public abstract class AbpInterceptor : IAbpInterceptor
{
    public abstract void Intercept(IAbpMethodInvocation invocation);

    public virtual Task InterceptAsync(IAbpMethodInvocation invocation)
    {
        Intercept(invocation);
        return Task.CompletedTask;
    }
}

abp的攔截器實現是基於Autofac.Extras.DynamicProxy，這個包依賴兩個組件：Autofac、Castle.Core(實質上是調用內部組件DynamicProxy實現動態代理)。關於此組件的資料參考

.NET 通過 Autofac 和 DynamicProxy 實現AOP

Type Interceptors

Abp攔截器的設計軌跡

此類的作用就是將aspnetcore預設的DI服務容器(ServiceCollection)替換為Autofac。

public static IServiceProvider BuildServiceProviderFromFactory<TContainerBuilder>([NotNull] this IServiceCollection services, Action<TContainerBuilder> builderAction = null)
{
    Check.NotNull(services, nameof(services));

    var serviceProviderFactory = services.GetSingletonInstanceOrNull<IServiceProviderFactory<TContainerBuilder>>();
    if (serviceProviderFactory == null)
    {
        throw new AbpException($"Could not find {typeof(IServiceProviderFactory<TContainerBuilder>).FullName} in {services}.");
    }

    var builder = serviceProviderFactory.CreateBuilder(services);
    builderAction?.Invoke(builder);
    return serviceProviderFactory.CreateServiceProvider(builder);
}

CreateBuilder函數源碼：

/// <summary>
/// Creates a container builder from an <see cref="T:Microsoft.Extensions.DependencyInjection.IServiceCollection" />.
/// </summary>
/// <param name="services">The collection of services</param>
/// <returns>A container builder that can be used to create an <see cref="T:System.IServiceProvider" />.</returns>
public ContainerBuilder CreateBuilder(IServiceCollection services)
{
    _services = services;
    
    _builder.Populate(services);
    
    return _builder;
}

Populate函數源碼：

public static void Populate(
        this ContainerBuilder builder,
        IServiceCollection services)
{
    builder.RegisterType<AutofacServiceProvider>().As<IServiceProvider>();
    builder.RegisterType<AutofacServiceScopeFactory>().As<IServiceScopeFactory>();

    Register(builder, services);
}

Register函數：

/// 註冊攔截器
private static void Register(
        ContainerBuilder builder,
        IServiceCollection services)
{
    var moduleContainer = services.GetSingletonInstance<IModuleContainer>();
    var registrationActionList = services.GetRegistrationActionList();

    // 遍歷DI服務容器中的服務
    foreach (var service in services)
    {
        if (service.ImplementationType != null)
        {
            // 判斷服務是否是泛型
            var serviceTypeInfo = service.ServiceType.GetTypeInfo();
            if (serviceTypeInfo.IsGenericTypeDefinition)
            {
                builder
                    .RegisterGeneric(service.ImplementationType)
                    .As(service.ServiceType)
                    .ConfigureLifecycle(service.Lifetime)
                    .ConfigureAbpConventions(moduleContainer, registrationActionList);
            }
            else
            {
                builder
                    .RegisterType(service.ImplementationType)
                    .As(service.ServiceType)
                    .ConfigureLifecycle(service.Lifetime)
                    .ConfigureAbpConventions(moduleContainer, registrationActionList);
            }
        }
        // 其餘實現
        ......
    }
}

ConfigureAbpConventions函數源碼：

public static IRegistrationBuilder<TLimit, TActivatorData, TRegistrationStyle> ConfigureAbpConventions<TLimit, TActivatorData, TRegistrationStyle>(
    this IRegistrationBuilder<TLimit, TActivatorData, TRegistrationStyle> registrationBuilder, 
    IModuleContainer moduleContainer, 
    ServiceRegistrationActionList registrationActionList)
where TActivatorData : ReflectionActivatorData
{
    // 其餘實現
    .....
    
    // 這裡就是調用OnRegistred函數裡面的Action委托
    registrationBuilder = registrationBuilder.InvokeRegistrationActions(registrationActionList, serviceType, implementationType);

    return registrationBuilder;
}

InvokeRegistrationActions函數源碼：

private static IRegistrationBuilder<TLimit, TActivatorData, TRegistrationStyle> InvokeRegistrationActions<TLimit, TActivatorData, TRegistrationStyle>(this IRegistrationBuilder<TLimit, TActivatorData, TRegistrationStyle> registrationBuilder, ServiceRegistrationActionList registrationActionList, Type serviceType, Type implementationType) 
    where TActivatorData : ReflectionActivatorData
{
    var serviceRegistredArgs = new OnServiceRegistredContext(serviceType, implementationType);

    foreach (var registrationAction in registrationActionList)
    {
        // 調用OnRegistred函數裡面的Action委托，註入攔截器
        registrationAction.Invoke(serviceRegistredArgs);
    }

    //如果有攔截器
    if (serviceRegistredArgs.Interceptors.Any())
    {
        // 在某個服務類型(ServiceType)類上註冊攔截器
        registrationBuilder = registrationBuilder.AddInterceptors(
            serviceType,
            serviceRegistredArgs.Interceptors
        );
    }

    return registrationBuilder;
}

AddInterceptors函數源碼：

private static IRegistrationBuilder<TLimit, TActivatorData, TRegistrationStyle> AddInterceptors<TLimit, TActivatorData, TRegistrationStyle>(
    this IRegistrationBuilder<TLimit, TActivatorData, TRegistrationStyle> registrationBuilder, 
    Type serviceType,
    IEnumerable<Type> interceptors)
    where TActivatorData : ReflectionActivatorData
    {
        // 啟用攔截器
        // 如果是介面類型，那麼動態創建一個介面代理
        // 否則 創建一個目標類的子類代理類，這裡需要註意的是只會攔截虛方法，重寫方法
        if (serviceType.IsInterface)
        {
            registrationBuilder = registrationBuilder.EnableInterfaceInterceptors();
        }
        else
        {
            (registrationBuilder as IRegistrationBuilder<TLimit, ConcreteReflectionActivatorData, TRegistrationStyle>)?.EnableClassInterceptors();
        }
    
        foreach (var interceptor in interceptors)
        {
            // 動態註入攔截器，指定攔截器類型為傳入的攔截器
            registrationBuilder.InterceptedBy(
               typeof(CastleAbpInterceptorAdapter<>).MakeGenericType(interceptor)
            );
        }
    
        return registrationBuilder;
    }

CastleAbpInterceptorAdapter是Castle.Core庫通過適配器來定義了一個標準、針對IAbpInterceptor的實現。源碼：

// 泛型攔截器為 基於AbpIterceptor的攔截器類型
public class CastleAbpInterceptorAdapter<TInterceptor> : IInterceptor
    where TInterceptor : IAbpInterceptor
{
    private static readonly MethodInfo MethodExecuteWithoutReturnValueAsync =
        typeof(CastleAbpInterceptorAdapter<TInterceptor>)
            .GetMethod(
                nameof(ExecuteWithoutReturnValueAsync),
                BindingFlags.NonPublic | BindingFlags.Instance
            );

    private static readonly MethodInfo MethodExecuteWithReturnValueAsync =
        typeof(CastleAbpInterceptorAdapter<TInterceptor>)
            .GetMethod(
                nameof(ExecuteWithReturnValueAsync),
                BindingFlags.NonPublic | BindingFlags.Instance
            );

    // 這裡的TInterceptor就是在InterceptedBy方法那裡傳入的攔截器類型
    // 也就是我們基於AbpInterceptor抽象類創建的攔截器
    private readonly TInterceptor _abpInterceptor;

    public CastleAbpInterceptorAdapter(TInterceptor abpInterceptor)
    {
        _abpInterceptor = abpInterceptor;
    }
    
    // 其餘代碼
}

IAbpMethodInvocation介面封裝了被攔截方法調用時的各種參數，例如，被攔截方法在調用時所傳遞的參數，返回值類型，方法定義等。Castle.Core庫通過適配器來定義了一個標準、針對IAbpMethodInvocation的實現。源碼：

public class CastleAbpMethodInvocationAdapter : IAbpMethodInvocation
{
    public object[] Arguments => Invocation.Arguments;

    public IReadOnlyDictionary<string, object> ArgumentsDictionary => _lazyArgumentsDictionary.Value;
    private readonly Lazy<IReadOnlyDictionary<string, object>> _lazyArgumentsDictionary;

    public Type[] GenericArguments => Invocation.GenericArguments;

    public object TargetObject => Invocation.InvocationTarget ?? Invocation.MethodInvocationTarget;

    public MethodInfo Method => Invocation.MethodInvocationTarget ?? Invocation.Method;

    public object ReturnValue
    {
        get => _actualReturnValue ?? Invocation.ReturnValue;
        set => Invocation.ReturnValue = value;
    }

    private object _actualReturnValue;

    protected IInvocation Invocation { get; }
    protected IInvocationProceedInfo ProceedInfo { get; }

    public CastleAbpMethodInvocationAdapter(IInvocation invocation, IInvocationProceedInfo proceedInfo)
    {
        Invocation = invocation;
        ProceedInfo = proceedInfo;

        _lazyArgumentsDictionary = new Lazy<IReadOnlyDictionary<string, object>>(GetArgumentsDictionary);
    }

    // 內部調用 Castle.DynamicProxy
    public void Proceed()
    {
        // 省略實現
    }

    public Task ProceedAsync()
    {
        // 省略實現
    }

    private IReadOnlyDictionary<string, object> GetArgumentsDictionary()
    {
        // 省略實現
    }
}

CastleAbpMethodInvocationAdapter適配器的調用處在CastleAbpInterceptorAdapter適配器類的Intercept函數：

// 調用自定義、基於AbpInterceptor的攔截器
private void InterceptSyncMethod(IInvocation invocation, IInvocationProceedInfo proceedInfo)
{
    _abpInterceptor.Intercept(new CastleAbpMethodInvocationAdapter(invocation, proceedInfo));
}

參考：[Abp vNext 源碼分析] - 3. 依賴註入與攔截器