DotNet WebApi消息拦截器之MessageHandler

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

image

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

Task 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 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;
    }
}

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...
    }
}

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 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();
      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
The resource can be found at {0}.", 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;
  }
}

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 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);
        }
    }
}

作者：CoderMiner
链接：https://www.jianshu.com/p/a38487f9b692