C# Web API中的SendAsync返回null

当用户的授权令牌过期或令牌无效时，如果用户试图调用服务，我将尝试返回相应的错误消息

我遇到的问题是，第一次调用它时，消息被正确发送，但在第一次调用SendAsync方法4次之后，消息数据返回null

我不明白为什么它会循环4次，我试着单步通过它，但我无法进一步了解代码

代码如下：

protected override Task<HttpResponseMessage> SendAsync(HttpRequestMessage request,
                                                           CancellationToken cancellationToken)
    {
        if (request.Headers != null)
        {

             // ....

             if (request.Headers.GetValues(CustomTokenHeader).FirstOrDefault() == null)
             {
                  //unauthorized response(401)
                  return FromResult(_unauthorizedResponse);
             }
             var authHeader = request.Headers.GetValues(CustomTokenHeader).FirstOrDefault();
             if (String.IsNullOrWhiteSpace(authHeader))
             {
                 //unauthorized response(401)
                 return FromResult(_unauthorizedResponse);
             }

             //authenticate token
             return HandleTokenAuthentication(request, cancellationToken, authHeader);
        }
    }

    static Task<T> FromResult<T>(T t)
    {
        var tcs = new TaskCompletionSource<T>();
        tcs.SetResult(t);
        return tcs.Task;
    }


    private Task<HttpResponseMessage> HandleTokenAuthentication(HttpRequestMessage request, CancellationToken cancellationToken, string authHeader)
    {
        //parse token
        var token = ParseToken(authHeader);
        if (String.IsNullOrWhiteSpace(token))
        {
            //unauthorized response(401)
            return FromResult(_unauthorizedResponse);
        }

        //decrypt token
        var tokenInfo = DecryptToken(token);
        if (tokenInfo == null)
        {
            //unauthorized response(401)
            return FromResult(_unauthorizedResponse);
        }

        //validate token
        var claims = ValidateToken(tokenInfo, token);
        if (claims == null)
        {
            //unauthorized response(401)
            return FromResult(_unauthorizedTokenExpired);
        }
        var principal = CheckCustomAuthorization(claims);
         if (principal == null)
        {
            //unauthorized response(401)
            return FromResult(_unauthorizedResponse);
        }
        if (!principal.Identity.IsAuthenticated)
        {

            var loginFailureMessage = new HttpResponseMessage(HttpStatusCode.Unauthorized)
            {
                Content = new StringContent(((AgencyClaims)principal.Identity).LoginFailureReason)
            };

            return FromResult(loginFailureMessage);
        }
        //assign principal
        Thread.CurrentPrincipal = principal;

        return base.SendAsync(request, cancellationToken)
                               .ContinueWith(task => AuthorizedResponse(request, task.Result));
    }

    static HttpResponseMessage AuthorizedResponse(HttpRequestMessage request, HttpResponseMessage response)
    {
        if ((request.Method == HttpMethod.Get && response.StatusCode == HttpStatusCode.OK
            && !response.Headers.Contains(CustomTokenHeader))
            || (request.Method == HttpMethod.Post && response.StatusCode == HttpStatusCode.Created
            && !response.Headers.Contains(CustomTokenHeader)))
        {
            var token = ((AgencyClaims) Thread.CurrentPrincipal.Identity).Token;
            response.Headers.Add(CustomTokenHeader, Convert.ToBase64String(Encoding.ASCII.GetBytes(token)));
        }
        return response;
    }

readonly HttpResponseMessage _unauthorizedResponse =
        new HttpResponseMessage(HttpStatusCode.Unauthorized) { Content = new StringContent("PROPER ERROR MESSAGE")};

---

好的，我能够解决这个问题。

\u unauthorizedResponse

类变量以某种方式允许代码成功运行一次，但不是第二次。这个问题与readonly修饰符无关，因为没有它它仍然无法工作。我不确定这是如何工作的（也许这里有人可以解释），但是通过将它们移动到方法中的本地范围，每次都可以正确运行

向我们显示

HandleTokenAuthentication

Sure的代码。刚刚更新了代码。我还添加了

AuthorizedResponse

方法。但我不确定这是否是问题所在，因为消息是在调用

HandleTokenAuthentication

方法之前返回的。

 <data contentType="text/plain; charset=utf-8" contentLength="21"><![CDATA[Authentication failed]]></data>

<data contentType="null" contentLength="0"><![CDATA[]]></data>

GET http://localhost:20559/api/Service?Name=Jack HTTP/1.1