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我使用 OWIN 在控制台应用程序中自托管了一个小型 Web 应用程序。

在到达 ApiController 之前，注册了一个中间件：

public class HealthcheckMiddleware : OwinMiddleware
{
    private readonly string DeepHealthEndpointPath = "/monitoring/deep";
    private readonly string ShallowHealthEndpointPath = "/monitoring/shallow";

    public HealthcheckMiddleware(OwinMiddleware next)
        : base(next)
    {
    }

    public async override Task Invoke(IOwinContext context)
    {
        try
        {
            string requestPath = context.Request.Path.Value.TrimEnd('/');
            if (requestPath.Equals(ShallowHealthEndpointPath, StringComparison.InvariantCultureIgnoreCase)
                || requestPath.Equals(DeepHealthEndpointPath, StringComparison.InvariantCultureIgnoreCase))
            {
                context.Response.StatusCode = (int) HttpStatusCode.OK;
            }
            else
            {
                await Next.Invoke(context);
            }
        }
        catch (Exception ex)
        {
            // This try-catch block is inserted for debugging
        }
    }
}

这里 Next.Invoke 调用了控制器方法，它基本上将 http 请求异步转发到另一个 API，即感兴趣的主线是：

var response = await _httpClient.SendAsync(outgoingRequest);

但是，如果我尝试像这样向 API 提交 10 个 http 请求（不是故意等待它们，因为我想对 API 施加压力）

for (int i = 0; i < 10; i++)
{
    var httpRequestMessage = new HttpRequestMessage(HttpMethod.Post, "http://localhost:5558/forwarder");
    httpRequestMessage.Content = new StringContent(JsonConvert.SerializeObject(message), Encoding.UTF8, "application/json");
    httpClient.SendAsync(httpRequestMessage);
}

然后立即再提交 10 个，然后我在 HealthcheckMiddleware 的 catch 块中得到以下异常：

InvalidOperationException：提交响应后无法执行此操作。

堆栈跟踪：

at System.Net.HttpListenerResponse.set_ContentLength64(Int64 value)
at Microsoft.Owin.Host.HttpListener.RequestProcessing.ResponseHeadersDictionary.Set(String header, String value)
at Microsoft.Owin.Host.HttpListener.RequestProcessing.HeadersDictionaryBase.Set(String key, String[] value)
at Microsoft.Owin.Host.HttpListener.RequestProcessing.HeadersDictionaryBase.set_Item(String key, String[] value)
at Microsoft.Owin.HeaderDictionary.System.Collections.Generic.IDictionary<System.String,System.String[]>.set_Item(String key, String[] value)
at System.Web.Http.Owin.HttpMessageHandlerAdapter.SetHeadersForEmptyResponse(IDictionary`2 headers)
at System.Web.Http.Owin.HttpMessageHandlerAdapter.SendResponseMessageAsync(HttpRequestMessage request, HttpResponseMessage response, IOwinResponse owinResponse, CancellationToken cancellationToken)
at System.Web.Http.Owin.HttpMessageHandlerAdapter.<InvokeCore>d__0.MoveNext()
--- End of stack trace from previous location where exception was thrown ---
at System.Runtime.CompilerServices.TaskAwaiter.ThrowForNonSuccess(Task task)
at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task)
at System.Runtime.CompilerServices.TaskAwaiter.GetResult()
at DataRelay.NonGuaranteedDataForwarder.HealthcheckMiddleware.<Invoke>d__3.MoveNext() in C:\_code\DataRelay.NonGuaranteedDataForwarder\HealthcheckMiddleware.cs:line 30

我试过搜索 Stackoverflow 和 Google，但似乎找不到任何有价值的东西。例如，我找到了这个，但是这里开发人员在提交请求后阅读了请求，而我没有这样做。

以防万一，这里包含 ApiController 中的完整 POST 方法：

    public async Task<HttpResponseMessage> Post(HttpRequestMessage request)
    {
        try
        {
            MetricCollector.RecordIncomingRecommendation();
            using (MetricCollector.TimeForwardingOfRequest())
            {
                string requestContent = await request.Content.ReadAsStringAsync().ConfigureAwait(false);
                var data = JObject.Parse(requestContent);
                string payloadType = data.SelectToken("Headers.PayloadType").ToString();
                Log.Logger.Debug("Received message containing {PayloadType}", payloadType);

                var consumersForPayloadType = _consumers.Where(x => x.DataTypes.Contains(payloadType)).ToList();
                if (consumersForPayloadType.Any())
                {
                    Log.Logger.Debug("{NumberOfConsumers} interested in {PayloadType}",
                        consumersForPayloadType.Count,
                        payloadType);
                }
                else
                {
                    Log.Logger.Warning("No consumers are interested in {PayloadType}", payloadType);
                }

                foreach (var consumer in consumersForPayloadType)
                {
                    try
                    {
                        var outgoingRequest = new HttpRequestMessage(HttpMethod.Post, consumer.Endpoint);
                        outgoingRequest.Content = new StringContent(requestContent, Encoding.UTF8,
                            "application/json");

                        foreach (var header in request.Headers)
                        {
                            if (IsCustomHeader(header, _customHeaders))
                                outgoingRequest.Headers.Add(header.Key, header.Value);
                        }

                        if (!string.IsNullOrWhiteSpace(consumer.ApiKey))
                        {
                            request.Headers.Add("Authorization", "ApiKey " + consumer.ApiKey);
                        }

                        var response = await _httpClient.SendAsync(outgoingRequest);
                        if (!response.IsSuccessStatusCode)
                        {
                            Log.Logger.ForContext("HttpStatusCode", response.StatusCode.ToString())
                                .Error("Failed to forward message containing {PayloadType} to {ConsumerEndpoint}",
                                    payloadType, consumer.Endpoint);
                        }
                    }
                    catch (Exception ex)
                    {
                        MetricCollector.RecordException(ex);
                        Log.Logger.Error(ex,
                            "Failed to forward message containing {PayloadType} to {ConsumerEndpoint}", payloadType,
                            consumer.Endpoint);
                    }
                }

                return request.CreateResponse(HttpStatusCode.OK);
            }
        }
        catch (Exception ex)
        {
            return Request.CreateErrorResponse(HttpStatusCode.ServiceUnavailable, ex);
        }
    }
4

1 回答 1

0

尝试.ConfigureAwait(false)到处删除，看看是否有帮助。

例如这里：

string requestContent = await request.Content.ReadAsStringAsync().ConfigureAwait(false);

UPD1：好的。检查当你使用不同的客户端进行压力测试时，服务器是否会出现此异常。比如这个。你不等待的想法httpClient.SendAsync(...);很奇怪。

于 2017-09-09T12:39:27.497 回答