为 WCF REST 中的每个请求自动调用该方法

Question

我有一个 WCF Rest 服务，在调用服务方法时，我们需要验证作为每个请求消息的一部分的许可证密钥（请求和响应消息将是 JSON 格式）。要验证许可证密钥，我们需要为每个请求调用单独的方法，该方法将包含如下逻辑，如果输入请求包含无效的许可证密钥，那么我们需要在 JSON 中发送“无效的许可证密钥”之类的错误消息格式发给客户端。 为此，我们在 WCF Rest 中是否有任何方法可以自动为每个请求调用此方法，而不是为每个请求显式调用？

注意：-许可证密钥将在 Service Web.Config 文件中提供。

Answer 1

您可以使用消息检查器，该检查器会在每个到达服务的请求时调用。下面的代码显示了这种检查器的一种实现。

public class StackOverflow_25380450
{
    [ServiceContract]
    public class Service
    {
        [WebGet]
        public int Add(int x, int y)
        {
            return x + y;
        }
    }

    public class MyInspector : IDispatchMessageInspector, IEndpointBehavior
    {
        public const string LicenseHeaderName = "X-License";
        public const string ExpectedLicense = "abcdef";

        public object AfterReceiveRequest(ref Message request, IClientChannel channel, InstanceContext instanceContext)
        {
            HttpRequestMessageProperty reqProp = (HttpRequestMessageProperty)request.Properties[HttpRequestMessageProperty.Name];
            var license = reqProp.Headers[LicenseHeaderName];
            if (license != ExpectedLicense)
            {
                throw new WebFaultException<string>("License required", HttpStatusCode.Forbidden);
            }

            return null;
        }

        public void BeforeSendReply(ref Message reply, object correlationState)
        {
        }

        public void AddBindingParameters(ServiceEndpoint endpoint, BindingParameterCollection bindingParameters)
        {
        }

        public void ApplyClientBehavior(ServiceEndpoint endpoint, ClientRuntime clientRuntime)
        {
        }

        public void ApplyDispatchBehavior(ServiceEndpoint endpoint, EndpointDispatcher endpointDispatcher)
        {
            endpointDispatcher.DispatchRuntime.MessageInspectors.Add(this);
        }

        public void Validate(ServiceEndpoint endpoint)
        {
        }
    }

    public static string SendGet(string uri, Dictionary<string, string> headers)
    {
        string responseBody = null;

        HttpWebRequest req = (HttpWebRequest)HttpWebRequest.Create(uri);
        req.Method = "GET";
        if (headers != null)
        {
            foreach (string headerName in headers.Keys)
            {
                switch (headerName)
                {
                    case "Accept":
                        req.Accept = headers[headerName];
                        break;
                    default:
                        req.Headers[headerName] = headers[headerName];
                        break;
                }
            }
        }

        HttpWebResponse resp;
        try
        {
            resp = (HttpWebResponse)req.GetResponse();
        }
        catch (WebException e)
        {
            resp = (HttpWebResponse)e.Response;
        }

        if (resp == null)
        {
            responseBody = null;
            Console.WriteLine("Response is null");
        }
        else
        {
            Console.WriteLine("HTTP/{0} {1} {2}", resp.ProtocolVersion, (int)resp.StatusCode, resp.StatusDescription);
            foreach (string headerName in resp.Headers.AllKeys)
            {
                Console.WriteLine("{0}: {1}", headerName, resp.Headers[headerName]);
            }
            Console.WriteLine();
            Stream respStream = resp.GetResponseStream();
            if (respStream != null)
            {
                responseBody = new StreamReader(respStream).ReadToEnd();
                Console.WriteLine(responseBody);
            }
            else
            {
                Console.WriteLine("HttpWebResponse.GetResponseStream returned null");
            }
        }

        Console.WriteLine();
        Console.WriteLine("  *-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*  ");
        Console.WriteLine();

        return responseBody;
    }

    public static void Test()
    {
        string baseAddress = "http://" + Environment.MachineName + ":8000/Service";
        ServiceHost host = new ServiceHost(typeof(Service), new Uri(baseAddress));
        var endpoint = host.AddServiceEndpoint(typeof(Service), new WebHttpBinding(), "");
        endpoint.Behaviors.Add(new WebHttpBehavior { AutomaticFormatSelectionEnabled = true });
        endpoint.Behaviors.Add(new MyInspector());
        host.Open();
        Console.WriteLine("Host opened");

        Console.WriteLine("No license:");
        Dictionary<string, string> headers = new Dictionary<string, string>
        {
            { "Accept", "application/json" }
        };
        SendGet(baseAddress + "/Add?x=6&y=8", headers);

        Console.WriteLine("Incorrect license:");
        headers.Add(MyInspector.LicenseHeaderName, "incorrect");
        SendGet(baseAddress + "/Add?x=6&y=8", headers);

        headers[MyInspector.LicenseHeaderName] = MyInspector.ExpectedLicense;
        SendGet(baseAddress + "/Add?x=6&y=8", headers);

        Console.Write("Press ENTER to close the host");
        Console.ReadLine();
        host.Close();
    }
}

您可以在http://blogs.msdn.com/b/carlosfigueira/archive/2011/04/19/wcf-extensibility-message-inspectors.aspx 找到更多关于检查员的一般信息。