One or more errors occurred: PostAsJsonAsync

Question

This is the error I get:

One or more errors occurred.
   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 myProject.mymethod(Int32[] myIds) in path\MyClass.cs:line 758

And here's that method:

private void mymethod(int[] myIds)
{
    var uri = new Uri(string.Format(UriPath, string.Format(MyPath)));
    var client = GetHttpClient(uri);

    var postModel = new PostModel
    {
        Ids = myIds,
        LastUpdate = NewItem ? null : _lastUpdated
    };

    if (client != null)
    {
        var response = client.PostAsJsonAsync(uri, postModel).Result;//this line crashes

        if (response.IsSuccessStatusCode)
        {
            //doSomething
        }
    }
}

I call a lot of methods like this and all of them work except this one. When it's hit, it takes a lot of time and then this exception is throws. With all of the other methods the error doesn't happen.

This is the inner exception:

Inner.System.Threading.Tasks.TaskCanceledException: A task was canceled.

Here's my GetCLient() method:

private HttpClient GetHttpClient(Uri uri)
{
    var handler = new HttpClientHandler
    {
        CookieContainer = CoockieContainer
    };

    return new HttpClient(handler)
    {
        BaseAddress = uri
    };
}

Here's the API method:

[HttpPost]
    public IList<MyModel> MyAPIMethod(PostModel model)
    {
        List<MyModel> myTranslations;
        using (var db = new myEntities(GetDbConnStrByUser(new GetCookies().GetUserName())))
        {
            myTranslations = db.tblTranslations.Where(it => model.Ids.Contains(it.id)
                                    && (!model.Update.HasValue || it.update > model.LastUpdate.Value))
                                    .Select(it => new MyModel
                                    {
                                        Id = it.id,
                                        Name = it.name,
                                        Description = it.desc,
                                        LanguageId = it.language_id                                            
                                    }).ToList();
        }

        return myTranslations.GroupBy(x => new { x.Id, x.LanguageId }).Select(x => x.First()).ToList();
    }

Maybe a timeout occurs.

Fiddler returns this error: The wait operation timed out.

Don't use blocking statements, go with async instead. Look at the inner exception. — Jeroen Vannevel, Oct 13 '14 at 15:51
The call to `.Result` is a synchronous statement; you're never using the asynchronicity that you could have. More here on proper async-await usage: http://msdn.microsoft.com/en-us/library/hh191443.aspx — Jeroen Vannevel, Oct 13 '14 at 15:55
Post the entire exception. The problem is you only show the "outer" exception so we can't see what happened. Look at the InnerException property on the exception to see what really went wrong. — Moby Disk, Oct 13 '14 at 16:01
@MobyDisk This is the inner exception: Inner.System.Threading.Tasks.TaskCanceledException: A task was canceled. — petko_stankoski, Oct 13 '14 at 18:55
@JeroenVannevel This is the inner exception: Inner.System.Threading.Tasks.TaskCanceledException: A task was canceled. — petko_stankoski, Oct 13 '14 at 18:55
I suspect this is not a problem with the code you posted. Is there a timeout or something? Maybe look at the server side. — Moby Disk, Oct 13 '14 at 19:11
@MobyDisk I posted the code from the API too. Maybe there is a timeout. How to fix it? — petko_stankoski, Oct 14 '14 at 06:15
@MobyDisk Fiddler returns this error: The wait operation timed out. — petko_stankoski, Oct 14 '14 at 09:15
@JeroenVannevel Fiddler returns this error: The wait operation timed out. — petko_stankoski, Oct 14 '14 at 09:15

score 14 · Answer 1 · edited May 23 '17 at 12:30

.Result tries to turn Task into T. It synchronously blocks waiting for the task to complete and will only return T if no exceptions occur. The two types of exceptions you should anticipate are OperationCanceledExceptions/TaskCanceledExceptions (when the HTTP request times out or a CancellationToken was used and the token was cancelled--I don't think the latter is applicable here) and general/HTTP-related exceptions.

You're probably running into the HTTP timeout scenario. Is it taking a long time for the exception to get thrown? If not, what does your GetHttpClient method look like? Is it explicitly setting timeouts or cancellation tokens?

If you want to stick with the synchronous approach and not returns Tasks, you should do something like this instead:

try
{    
    var response = client.PostAsJsonAsync(uri, postModel).Result;//this line crashes
} 
catch (OperationCanceledException oce) 
{
    // Tell the user that the request timed our or you cancelled a CancellationToken
}
catch (Exception exc) 
{
    // Look at the HttpClient docs and try to catch something more specific.  You don't want
    // to swallow StackOverflowExceptions or OutOfMemoryExceptions.
}

If you're willing to take the async plunge, this is more what you're looking for:

private async Task mymethodAsync(int[] myIds)
{
    var uri = new Uri(string.Format(UriPath, string.Format(MyPath)));
    var client = GetHttpClient(uri);

    var postModel = new PostModel { ... };

    if (client != null)
    {
        try 
        {
            var response = await client.PostAsJsonAsync(uri, postModel);

            if (response.IsSuccessStatusCode)
            {
                //doSomething
            }
        }
        catch (OperationCanceledException oce) 
        {
            // because timeouts are still possible
        }
        catch (Exception exc) {
            // Because other things can still go wrong too (HTTP 500, parsing errors)
        }
    }
}

See here for more info on how .Result call works w/HttpClient: What happens while waiting on a Task's Result?

The inner exception is TaskCanceledExceptions. Your first solution doesn't actually solveanything, it just adds try-catch blocks. — petko_stankoski, Oct 14 '14 at 06:05
The Result operation is waiting for the Task to complete. The HttpClient has a default timeout of (I think) 30 seconds. Therefore, .Result waits up to 30 seconds for one of these 3 things: the result, a timeout, or an exception. You are only anticipating the result, but you are running into the timeout scenario. Assuming your request is valid, your core issue is likely on the remote server end (taking > 30 seconds to generate a response) or network related. Read the link at the end of my post for more details. — scottt732, Oct 14 '14 at 21:43

One or more errors occurred: PostAsJsonAsync

1 Answers1