重试HttpClient的请求不成功 [英] Retrying HttpClient Unsuccessful Requests

问题描述

我构建给予HttpContent对象的函数，将问题要求，然后重试失败。不过，我得到异常说HttpContent对象发出请求后处理。反正是有复制或复制HttpContent对象，这样我可以发出多个请求。

 公共HttpResponseMessage ExecuteWithRetry（字符串URL，HttpContent内容）
 {
 HttpResponseMessage结果= NULL; 
 BOOL成功= FALSE; 
用做
 {
（VAR的客户=新的HttpClient（））
 {
结果= client.PostAsync（URL，内容）。结果; 
成功= result.IsSuccessStatusCode; 
} 
} 
，而（成功！）; 
 
返回结果; 
} 
 
 //也不例外工作，如果第一个请求是成功的
 ExecuteWithRetry（http://www.requestb.in/xfxcva/ *有效的URL * /新的StringContent（的Hello World））; 
 //抛出，如果请求被重试... 
 ExecuteWithRetry（http://www.requestb.in/badurl/ *无效的URL * /，新的StringContent（Hello World的） ）; 
  

（很显然，我不下去尝试，但上面的代码基本上是我想要什么）。

它会产生此异常

  System.AggregateException：出现一个或多个错误。 ---> System.ObjectDisposedException：无法访问已释放的对象。 
对象名称：'System.Net.Http.StringContent。在System.Net.Http.HttpContent.CheckDisposed 
（）
在System.Net.Http.HttpContent.CopyToAsync（流流，TransportContext上下文）
在System.Net.Http.HttpClientHandler。 GetRequestStreamCallback（IAsyncResult的AR）
 ---内部异常堆栈跟踪--- 
在System.Threading.Tasks.Task.ThrowIfExceptional（布尔includeTaskCanceledExceptions）
在System.Threading.Tasks结束。 Task`1.GetResultCore（布尔waitCompletionNotification）
在System.Threading.Tasks.Task`1.get_Result（）
在提交＃8.ExecuteWithRetry（字符串URL，HttpContent内容）
  

反正是有重复的HttpContent对象或重用呢？

解决方案

无需实现重试包装了的HttpClient ，可考虑构建功能的的HttpClient 以 HttpMessageHandler 在内部进行了重试逻辑。例如：

<预类=郎-CS prettyprint-覆盖> 公共类RetryHandler：DelegatingHandler
{
//强烈考虑限制重试次数 - 重试永远是
//可能不是最用户友好的方式，你可以回应的
//网线得到了拔出。
私人const int的MaxRetries = 3;

公共RetryHandler（HttpMessageHandler innerHandler）
：基地（innerHandler）
{}

保护覆盖异步任务< HttpResponseMessage> SendAsync（
HttpRequestMessage要求，
的CancellationToken的CancellationToken）
{
HttpResponseMessage响应;
的for（int i = 0; I< MaxRetries;我++）
{
响应=等待base.SendAsync（请求的CancellationToken）;
如果（response.IsSuccessStatusCode）{
返回响应;
}
}

返回响应;
}
}

公共类BusinessLogic
{
公共无效FetchSomeThingsSynchronously（）
{
// ...

//考虑使用（VAR的客户=新的HttpClient（新RetryHandler（新HttpClientHandler（））））这个抽象建造工厂或IoC容器

{
myResult = client.PostAsync（yourUri，yourHttpContent）。结果;
}

// ...
}
}


I am building a function that given an HttpContent Object, will issues request and retry on failure. However I get exceptions saying that HttpContent Object is disposed after issuing the request. Is there anyway to copy or duplicate the HttpContent Object so that I can issue multiple requests.

 public HttpResponseMessage ExecuteWithRetry(string url, HttpContent content)
 {
  HttpResponseMessage result = null;
  bool success = false;
  do
  {
      using (var client = new HttpClient())
      {
          result = client.PostAsync(url, content).Result;
          success = result.IsSuccessStatusCode;
      }
  }
  while (!success);

 return result;
} 

// Works with no exception if first request is successful
ExecuteWithRetry("http://www.requestb.in/xfxcva" /*valid url*/, new StringContent("Hello World"));
// Throws if request has to be retried ...
ExecuteWithRetry("http://www.requestb.in/badurl" /*invalid url*/, new StringContent("Hello World"));

(Obviously I don't try indefinitely but the code above is essentially what i want).

It yields this exception

System.AggregateException: One or more errors occurred. ---> System.ObjectDisposedException: Cannot access a disposed object.
Object name: 'System.Net.Http.StringContent'.
   at System.Net.Http.HttpContent.CheckDisposed()
   at System.Net.Http.HttpContent.CopyToAsync(Stream stream, TransportContext context)
   at System.Net.Http.HttpClientHandler.GetRequestStreamCallback(IAsyncResult ar)
   --- End of inner exception stack trace ---
   at System.Threading.Tasks.Task.ThrowIfExceptional(Boolean includeTaskCanceledExceptions)
   at System.Threading.Tasks.Task`1.GetResultCore(Boolean waitCompletionNotification)
   at System.Threading.Tasks.Task`1.get_Result()
   at Submission#8.ExecuteWithRetry(String url, HttpContent content)

Is there anyway to duplicate an HttpContent Object or reuse it?

解决方案

Instead of implementing retry functionality that wraps the HttpClient, consider constructing the HttpClient with a HttpMessageHandler that performs the retry logic internally. For example:

public class RetryHandler : DelegatingHandler
{
    // Strongly consider limiting the number of retries - "retry forever" is
    // probably not the most user friendly way you could respond to "the
    // network cable got pulled out."
    private const int MaxRetries = 3;

    public RetryHandler(HttpMessageHandler innerHandler)
        : base(innerHandler)
    { }

    protected override async Task<HttpResponseMessage> SendAsync(
        HttpRequestMessage request,
        CancellationToken cancellationToken)
    {
        HttpResponseMessage response;
        for (int i = 0; i < MaxRetries; i++)
        {
            response = await base.SendAsync(request, cancellationToken);
            if (response.IsSuccessStatusCode) {
                return response;
            }
        }

        return response;
    }
}

public class BusinessLogic
{
    public void FetchSomeThingsSynchronously()
    {
        // ...

        // Consider abstracting this construction to a factory or IoC container
        using (var client = new HttpClient(new RetryHandler(new HttpClientHandler())))
        {
            myResult = client.PostAsync(yourUri, yourHttpContent).Result;
        }

        // ...
    }
}

这篇关于重试HttpClient的请求不成功的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！