WCF 整合 Enterprise Library Policy Injection 實戰

背景：為何需要 Policy Injection？

Enterprise Library Policy Injection Application Block (PIAB) 透過方法攔截 實現 AOP，將快取、授權、交易、稽核、例外處理等橫切關注點封裝為 CallHandler，再以 Attribute 或設定檔套用至目標方法。核心在於必須透過 PolicyInjector.Wrap 建立或包裝物件，攔截器才會生效。因此 WCF 整合 PIAB 的關鍵在於：自訂 InstanceProvider，在建立 Service Instance 時經由 PolicyInjector 包裝。

PolicyInjectionInstanceProvider 實作

namespace Artech.WCFExtensions
{
    public class PolicyInjectionInstanceProvider : IInstanceProvider
    {
        private readonly Type _serviceContractType;
        private readonly string _policyInjectorName;

        public PolicyInjectionInstanceProvider(Type serviceContractType, string policyInjectorName)
        {
            _serviceContractType = serviceContractType;
            _policyInjectorName = policyInjectorName;
        }

        public object GetInstance(InstanceContext instanceContext, Message message)
        {
            PolicyInjector policyInjector = string.IsNullOrEmpty(_policyInjectorName)
                ? new PolicyInjectorFactory().Create()
                : new PolicyInjectorFactory().Create(_policyInjectorName);

            Type serviceType = instanceContext.Host.Description.ServiceType;
            object serviceInstance = Activator.CreateInstance(serviceType);

            // RemotingPolicyInjector 需要目標型別實作介面或繼承 MarshalByRefObject
            if (!_serviceContractType.IsInterface && !serviceType.IsMarshalByRef && policyInjector is RemotingPolicyInjector)
                return serviceInstance;

            return policyInjector.Wrap(serviceInstance, _serviceContractType);
        }

        public object GetInstance(InstanceContext instanceContext) => GetInstance(instanceContext, null);

        public void ReleaseInstance(InstanceContext instanceContext, object instance)
        {
            (instance as IDisposable)?.Dispose();
        }
    }
}

兩種 Behavior 套用方式

1. Contract Behavior (Attribute 方式)

[AttributeUsage(AttributeTargets.Interface)]
public class PolicyInjectionBehaviorAttribute : Attribute, IContractBehavior
{
    public string PolicyInjectorName { get; set; }

    public void ApplyDispatchBehavior(ContractDescription contractDescription,
        ServiceEndpoint endpoint, DispatchRuntime dispatchRuntime)
    {
        dispatchRuntime.InstanceProvider = new PolicyInjectionInstanceProvider(
            contractDescription.ContractType, PolicyInjectorName);
    }
    // 其他介面成員略...
}

套用：[PolicyInjectionBehavior] 標註於 Service Contract 介面。

2. Endpoint Behavior (設定檔方式)

public class PolicyInjectionBehavior : IEndpointBehavior
{
    private readonly string _policyInjectorName;
    public PolicyInjectionBehavior(string policyInjectorName) => _policyInjectorName = policyInjectorName;

    public void ApplyDispatchBehavior(ServiceEndpoint endpoint, EndpointDispatcher endpointDispatcher)
    {
        endpointDispatcher.DispatchRuntime.InstanceProvider = new PolicyInjectionInstanceProvider(
            endpoint.Contract.ContractType, _policyInjectorName);
    }
    // 其他介面成員略...
}

public class PolicyInjectionBehaviorElement : BehaviorExtensionElement
{
    [ConfigurationProperty("policyInjectorName", DefaultValue = "")]
    public string PolicyInjectorName { get => (string)this["policyInjectorName"]; set => this["policyInjectorName"] = value; }
    public override Type BehaviorType => typeof(PolicyInjectionBehavior);
    protected override object CreateBehavior() => new PolicyInjectionBehavior(PolicyInjectorName);
}

設定檔註冊 behaviorExtensions，於 endpointBehaviors 參考。

實戰驗證：TimeService + CachingCallHandler

• Contract：ITime 含 GetCurrentTime()，標註 [PolicyInjectionBehavior]。
• Service：TimeService 實作 GetCurrentTime 掛上 [CachingCallHandler]，回傳 DateTime.Now。
• Client：迴圈呼叫 10 次，間隔 1 秒。