I'm trying to call PostAsync method using System.Net.Http.HttpClient from the Web API. I get the following error:
System.AggregateException "A task was canceled."
Task:
Id = 1, Status = System.Threading.Tasks.TaskStatus.Canceled, Method = "{null}", Result = "{Not yet computed}"
Code:
using (HttpClientHandler handler = new HttpClientHandler())
{
handler.Credentials = new NetworkCredential("MyUsername", "p@ssw0rd");
using (HttpClient client = new HttpClient(handler))
{
var postData = new List<KeyValuePair<string, string>>();
postData.Add(new KeyValuePair<string, string>("status", "Hello world"));
HttpContent content = new FormUrlEncodedContent(postData);
var responseTask = client.PostAsync(url, content).ContinueWith(
(postTask) =>
{
postTask.Result.EnsureSuccessStatusCode();
});
}
I assume the responseTask will force the method to run synchronously?
It's a WPF application, not ASP.NET.
PostAsync(String, HttpContent) Send a POST request to the specified Uri as an asynchronous operation. PostAsync(Uri, HttpContent) Send a POST request to the specified Uri as an asynchronous operation.
AggregateException is used to consolidate multiple failures into a single, throwable exception object. It is used extensively in the Task Parallel Library (TPL) and Parallel LINQ (PLINQ). For more information, see Exception Handling and How to: Handle Exceptions in a PLINQ Query.
I was getting this same error and tracked it down to my HttpClient was timing out. The default timeout is 100 seconds. I added the following to the create of the HttpClient.
HttpClient httpClient = new HttpClient();
httpClient.Timeout = TimeSpan.FromMinutes(10);
In terms of debugging you could try writing an extension method to get the exception:
public static HttpResponseMessage PostAsyncSafe(this HttpClient client, string requestUri, string content)
{
var requestContent = new StringContent(content, Encoding.UTF8, "application/x-www-form-urlencoded");
return PerformActionSafe(() => (client.PostAsync(requestUri, requestContent)).Result);
}
public static HttpResponseMessage PerformActionSafe(Func<HttpResponseMessage> action)
{
try
{
return action();
}
catch (AggregateException aex)
{
Exception firstException = null;
if (aex.InnerExceptions != null && aex.InnerExceptions.Any())
{
firstException = aex.InnerExceptions.First();
if (firstException.InnerException != null)
firstException = firstException.InnerException;
}
var response = new HttpResponseMessage(HttpStatusCode.InternalServerError)
{
Content =
new StringContent(firstException != null
? firstException.ToString()
: "Encountered an AggreggateException without any inner exceptions")
};
return response;
}
}
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