Retrying HttpClient Unsuccessful Requests

Retrying HttpClient Unsuccessful Requests

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?

Answer by Vitalii Vasylenko for Retrying HttpClient Unsuccessful Requests

i have almost the same issue. HttpWebRequest queueing library, which guarantees request delivery I just updated (see EDIT3) my approach to avoid crashes, but i still need general mechanism to guarantee message delivery (or re-delivery in case message was not delivered).

Answer by VladL for Retrying HttpClient Unsuccessful Requests

Duplicating the StringContent isn't probably the best idea. But simple modification could fix the problem. Just modify the function and create the StringContent object inside of the loop, something like:

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

and then call it

ExecuteWithRetry("http://www.requestb.in/xfxcva" /*valid url*/, "Hello World");  

Answer by Dan Bjorge for Retrying HttpClient Unsuccessful Requests

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 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;          }            // ...      }  }  

Answer by Ohad Schneider for Retrying HttpClient Unsuccessful Requests

The current answers won't work as expected in all cases, specifically in the very common case of request timeout (see my comments there).

In addition, they implement a very naive retry strategy - many times you'd want something a bit more sophosticated, such as exponential backoff (which is the default in the Azure Storage Client API).

I stumbled upon TOPAZ while reading a related blog post (also offering the misguided internal retry approach). Here's what I came up with:

// sample usage: var response = await RequestAsync(() => httpClient.GetAsync(url));  Task RequestAsync(Func> requester)  {      var retryPolicy = new RetryPolicy(transientErrorDetectionStrategy, retryStrategy);      //you can subscribe to the RetryPolicy.Retrying event here to be notified       //of retry attempts (e.g. for logging purposes)      return retryPolicy.ExecuteAsync(async () =>      {          HttpResponseMessage response;          try          {              response = await requester().ConfigureAwait(false);          }          catch (TaskCanceledException e) //HttpClient throws this on timeout          {              //we need to convert it to a different exception              //otherwise ExecuteAsync will think we requested cancellation              throw new HttpRequestException("Request timed out", e);          }          //assuming you treat an unsuccessful status code as an error          //otherwise just return the respone here          return response.EnsureSuccessStatusCode();       });  }  

Note the requester delegate parameter. It should not be an HttpRequestMessage since you can't send the same request multiple times. As for the strategies, that depends on your use case. For example, a transient error detection strategy could be as simple as:

private sealed class TransientErrorCatchAllStrategy : ITransientErrorDetectionStrategy  {      public bool IsTransient(Exception ex)      {          return true;      }  }  

As for the retry strategy, TOPAZ offers three options:

1. FixedInterval
2. Incremental
3. ExponentialBackoff

For example, here's the TOPAZ equivalent of what the Azure Client Storage Library uses for default:

int retries = 3;  var minBackoff = TimeSpan.FromSeconds(3.0);  var maxBackoff = TimeSpan.FromSeconds(120.0);  var deltaBackoff= TimeSpan.FromSeconds(4.0);  var strategy = new ExponentialBackoff(retries, minBackoff, maxBackoff, deltaBackoff);  

For more information see http://msdn.microsoft.com/en-us/library/hh680901(v=pandp.50).aspx

Answer by Colin Chen for Retrying HttpClient Unsuccessful Requests

you also refer to Building a Transient Retry Handler for the .NET HttpClient visit http://blog.devscrum.net/index.php/2014/05/11/building-a-transient-retry-handler-for-the-net-httpclient/#comment-28

Fatal error: Call to a member function getElementsByTagName() on a non-object in D:\XAMPP INSTALLASTION\xampp\htdocs\endunpratama9i\www-stackoverflow-info-proses.php on line 71