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.Net WebApi消息拦截器之MessageHandler的示例

2018年08月18日  | 移动技术网IT编程  | 我要评论

陈际瓦,巴巴万加,现在国家总理是谁

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:

  1. 读取或更改请求头 request headers
  2. 添加 response headers
  3. 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

  1. 处理请求信息
  2. 调用 base.sendasync 方法，吧请求发送给内部处理
  3. 内部处理完成之后，返回 response message(这个过程是异步的)
  4. 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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