.Net WebApi消息拦截器之MessageHandler的示例

2020-01-17 22:10:34

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消息拦截器是一个类，接收 HTTP request并返回 HTTP response,Message handler 继承自抽象类 HttpMessageHandler
可以自定义 MessageHandler,消息拦截器的作用如:

读取或更改请求头 request headers
添加 response headers
在到达 controller 之前，进行参数验证

自定义 Message Handlers

自定义 MessageHandler 需要继承 System.Net.Http.DelegatingHander 并且重载SendAsync方法

Task<HttpResponseMessage> SendAsync(  HttpRequestMessage request, CancellationToken cancellationToken);

这个方法的一般的处理流程是

处理请求信息
调用 base.SendAsync 方法，吧请求发送给内部处理
内部处理完成之后，返回 response message(这个过程是异步的)
处理 response 之后，返回给调用者

public class MessageHandler1 : DelegatingHandler{  protected async override Task<HttpResponseMessage> SendAsync(    HttpRequestMessage request, CancellationToken cancellationToken)  {    Debug.WriteLine("Process request");    // Call the inner handler.    var response = await base.SendAsync(request, cancellationToken);    Debug.WriteLine("Process response");    return response;  }}

消息拦截器生效

在 WebApiConfig中注册相关

public static class WebApiConfig{  public static void Register(HttpConfiguration config)  {    config.MessageHandlers.Add(new MessageHandler1());    config.MessageHandlers.Add(new MessageHandler2());    // Other code not shown...  }}

https 请求拦截器

要求所有的请求都必须是https的请求，可以自定义一个https的拦截器，如果是https请求，就继续处理，否则就返回相关的提示信息

public class RequireHttpsHandler : DelegatingHandler{ public RequireHttpsHandler(int httpsPort) {   _httpsPort = httpsPort; } public RequireHttpsHandler()   : this(443) { } protected override Task<HttpResponseMessage> SendAsync(HttpRequestMessage request, CancellationToken cancellationToken) {   //判断是否是 https 请求   if (request.RequestUri.Scheme == Uri.UriSchemeHttps)     return base.SendAsync(request, cancellationToken);   var response = CreateResponse(request);   var tcs = new TaskCompletionSource<HttpResponseMessage>();   tcs.SetResult(response);   return tcs.Task; } private HttpResponseMessage CreateResponse(HttpRequestMessage request) {   HttpResponseMessage response;   var uri = new UriBuilder(request.RequestUri);   uri.Scheme = Uri.UriSchemeHttps;   uri.Port = _httpsPort;   var body = string.Format("HTTPS is required<br/>The resource can be found at <a href=/"{0}/">{0}</a>.", uri.Uri.AbsoluteUri);   if (request.Method.Equals(HttpMethod.Get) || request.Method.Equals(HttpMethod.Head))   {     response = request.CreateResponse(HttpStatusCode.Found);     response.Headers.Location = uri.Uri;     if (request.Method.Equals(HttpMethod.Get))       response.Content = new StringContent(body, Encoding.UTF8, "text/html");   }   else   {     response = request.CreateResponse(HttpStatusCode.NotFound);     response.Content = new StringContent(body, Encoding.UTF8, "text/html");   }   return response; }}

Enable CORS 拦截器

public class SimpleCorsHandler : DelegatingHandler{  private const string origin = "Origin";  private const string accessControlRequestMethod = "Access-Control-Request-Method";  private const string accessControlRequestHeaders = "Access-Control-Request-Headers";  private const string accessControlAllowOrigin = "Access-Control-Allow-Origin";  private const string accessControlAllowMethods = "Access-Control-Allow-Methods";  private const string accessControlAllowHeaders = "Access-Control-Allow-Headers";  protected override Task<HttpResponseMessage> SendAsync(HttpRequestMessage request,                              CancellationToken cancellationToken)  {    var isCorsRequest = request.Headers.Contains(origin);    var isPreflightRequest = request.Method == HttpMethod.Options;    if (isCorsRequest)    {      if (isPreflightRequest)      {        return Task.Factory.StartNew(() =>            {              var response = new HttpResponseMessage(HttpStatusCode.OK);              response.Headers.Add(accessControlAllowOrigin,                        request.Headers.GetValues(origin).First());              var currentAccessControlRequestMethod =                request.Headers.GetValues(accessControlRequestMethod).                  FirstOrDefault();              if (currentAccessControlRequestMethod != null)              {                response.Headers.Add(accessControlAllowMethods,                          currentAccessControlRequestMethod);              }              var requestedHeaders = string.Join(", ", request.Headers.GetValues(accessControlRequestHeaders));              if (!string.IsNullOrEmpty(requestedHeaders))              {                response.Headers.Add(accessControlAllowHeaders,                          requestedHeaders);              }              return response;            }, cancellationToken);      }      else      {        return base.SendAsync(request, cancellationToken).ContinueWith(t =>            {              var resp = t.Result;              resp.Headers.Add(                accessControlAllowOrigin,                request.Headers.GetValues(origin).First());              return resp;            });      }    }    else    {      return base.SendAsync(request, cancellationToken);    }  }}

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