从 JavaScript 访问 WCF WebService - 对预检请求的响应未通过访问控制检查

Question

我正在使用 WCF (.svc) WebService，它运行良好 - 我可以毫无问题地从 Postman、PHP 等调用它的方法。但是，当我尝试从 JavaScript/jQuery调用它时> 使用 AJAX，有一个明显的问题——我是从 WS 以外的其他域做的，所以它不会让我做。

这都是关于 POST 方法的。但是，即使我的页面首先发送一个 OPTIONS 方法，也会出现问题：

选项'WS ADDRESS' 405（不允许的方法）

XMLHttpRequest 无法加载 'WS ADDRESS' 对预检请求的响应没有 通过访问控制检查：没有“Access-Control-Allow-Origin”标头 出现在请求的资源上。因此，来源 'MY ADDRESS' 是不允许的 使用权。响应的 HTTP 状态代码为 405。

有详细回复：

好的，我阅读了有关跨域的信息，并且 WS 的 Web.config 包含所有必要的内容（？）

请让我知道我做错了什么，我无法从 JavaScript 访问我的 WS，即使在我看来它配置得很好。但是，它似乎没有发送这些特殊的标头作为响应......提前致谢。

Answer 1

XML HttpRequest 允许将数据从 Web 服务器传输到浏览器。然而，浏览器默认阻止CORS。 GET 请求不会更改服务器端的任何内容（没有创建/更新/删除任何内容） - 它只会返回一些数据。

但是，POST/PUT/DELETE 请求将处理请求并在服务器端更改某些内容并向浏览器发出响应。如果响应没有正确的Access-Control-Allow-Origin 标头，浏览器将阻止响应。但这并不重要，因为在发出响应时，服务器已经处理了请求并进行了更改，可能对数据库进行了更改。

为了防止服务器端处理POST/PUT/DELETE请求，浏览器会发送preflight request。

prefligth 请求是一个带有 OPTIONS 方法的 http 请求。因此，在发送 POST 请求之前，浏览器会发送一个 OPTIONS 请求，其中包含一个名为 Access-Control-Request-Method 的附加标头，其值为 POST。

405 (Method Not Allowed) 错误表示服务器未配置为接受 OPTIONS 请求。

您可以通过为您的网络调用方法使用通配符来解决此问题，类似于：

[OperationContract]
[WebInvoke(Method = "*", UriTemplate = "/Path", ResponseFormat = WebMessageFormat.Json)]

或者通过向您的[ServiceContract] 添加一个额外的[OperationContract] 来处理类似于这样的OPTIONS 请求：

 [OperationContract(Name = "OptionsMyFunction")]
 [WebInvoke(Method = "OPTIONS", UriTemplate = "/Path", ResponseFormat = WebMessageFormat.Json)]

Answer 2

您可以为此工作实现 .NET IDispatchMessageInspector。

• 创建一个实现IDispatchMessageInspector的类
• 创建一个实现Attribute,IEndpointBehavior,IOperationBehavior的类

只允许在你的类中实现IDispatchMessageInspector的OPTIONS

代码如下所示

using System;
using System.ServiceModel;
using System.ServiceModel.Channels;
using System.ServiceModel.Dispatcher;
using System.ServiceModel.Description;
using System.Collections.Generic;
using System.Net;

namespace WapstyPrintService
{
    public class MessageInspector : IDispatchMessageInspector
    {
        private ServiceEndpoint _serviceEndpoint;
        Dictionary<string, string> requiredHeaders;

        public MessageInspector(ServiceEndpoint serviceEndpoint)
        {
            _serviceEndpoint = serviceEndpoint;
            requiredHeaders = new Dictionary<string, string>();

            requiredHeaders.Add("Access-Control-Allow-Origin", "*");
            requiredHeaders.Add("Access-Control-Request-Method", "POST,GET,PUT,DELETE,OPTIONS");
            requiredHeaders.Add("Access-Control-Allow-Headers", "X-Requested-With,Content-Type");
        }

        /// <summary>
        /// Called when an inbound message been received
        /// </summary>
        /// <param name="request">The request message.</param>
        /// <param name="channel">The incoming channel.</param>
        /// <param name="instanceContext">The current service instance.</param>
        /// <returns>
        /// The object used to correlate stateMsg. 
        /// This object is passed back in the method.
        /// </returns>
        public object AfterReceiveRequest(ref Message request,
                                              IClientChannel channel,
                                              InstanceContext instanceContext)
        {
            var httpRequest = (HttpRequestMessageProperty)request
            .Properties[HttpRequestMessageProperty.Name];
            return new
            {
                origin = httpRequest.Headers["Origin"],
                handlePreflight = httpRequest.Method.Equals("OPTIONS",
                StringComparison.InvariantCultureIgnoreCase)
            };
        }

        /// <summary>
        /// Called after the operation has returned but before the reply message
        /// is sent.
        /// </summary>
        /// <param name="reply">The reply message. This value is null if the 
        /// operation is one way.</param>
        /// <param name="correlationState">The correlation object returned from
        ///  the method.</param>
        public void BeforeSendReply(ref Message reply, object correlationState)
        {
            var state = (dynamic)correlationState;
            if (state.handlePreflight)
            {
                reply = Message.CreateMessage(MessageVersion.None, "PreflightReturn");

                var httpResponse = new HttpResponseMessageProperty();
                reply.Properties.Add(HttpResponseMessageProperty.Name, httpResponse);

                httpResponse.SuppressEntityBody = true;
                httpResponse.StatusCode = HttpStatusCode.OK;
            }

            var httpHeader = reply.Properties["httpResponse"] as HttpResponseMessageProperty;
            foreach (var item in requiredHeaders)
            {
                httpHeader.Headers.Add(item.Key, item.Value);
            }
        }
    }
}

和

using System;
using System.ServiceModel.Channels;
using System.ServiceModel.Description;
using System.ServiceModel.Dispatcher;

namespace WapstyPrintService
{
    public class BehaviorAttribute : Attribute, IEndpointBehavior,
                                   IOperationBehavior
    {
        public void Validate(ServiceEndpoint endpoint) { }

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

        /// <summary>
        /// This service modify or extend the service across an endpoint.
        /// </summary>
        /// <param name="endpoint">The endpoint that exposes the contract.</param>
        /// <param name="endpointDispatcher">The endpoint dispatcher to be
        /// modified or extended.</param>
        public void ApplyDispatchBehavior(ServiceEndpoint endpoint,
                                          EndpointDispatcher endpointDispatcher)
        {
            // add inspector which detects cross origin requests
            endpointDispatcher.DispatchRuntime.MessageInspectors.Add(
                                                   new MessageInspector(endpoint));
        }

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

        public void Validate(OperationDescription operationDescription) { }

        public void ApplyDispatchBehavior(OperationDescription operationDescription,
                                          DispatchOperation dispatchOperation)
        { }

        public void ApplyClientBehavior(OperationDescription operationDescription,
                                        ClientOperation clientOperation)
        { }

        public void AddBindingParameters(OperationDescription operationDescription,
                                  BindingParameterCollection bindingParameters)
        { }

    }
}

然后将您的消息检查器添加到服务端点行为

ServiceHost host = new ServiceHost(typeof(myService), _baseAddress);
foreach (ServiceEndpoint EP in host.Description.Endpoints)
            EP.Behaviors.Add(new BehaviorAttribute());