Develop Reference

UseExceptionHandler won't catch tasks exceptions?

I've created a simple webapi .net core 3.1 app.
I want to catch all unhandled exceptions.So I put this code according to the docs :
app.UseExceptionHandler(c => c.Run(async context =>
{
var exception = context.Features
.Get<IExceptionHandlerPathFeature>()
.Error;
var response = new { error = exception.Message };
log.LogDebug(exception.Message);
}));
This is my action:
[HttpGet]
public IActionResult Get()
{
throw new Exception("this is a test");
}
When this code runs, I do see that UseExceptionHandler is working.
But when my code in the action is :
[HttpGet]
public IActionResult Get()
{
Task.Run(async () =>
{
await Task.Delay(4000);
throw new Exception("this is a test");
});
return Ok();
}
Then UseExceptionHandler is NOT working.
However - the following code does catch the task's exception :
AppDomain.CurrentDomain.FirstChanceException += (sender, eventArgs) =>
{
Debug.WriteLine(eventArgs.Exception.ToString());
};
Question:
Why does the task exception isn't recognized by UseExceptionHandler?
How can I catch ALL types of exceptions? Should I rely only on AppDomain.CurrentDomain.FirstChanceException?
nb , I did disabled app.UseDeveloperExceptionPage();

To answer your questions.
Why does the task exception isn't recognized by UseExceptionHandler?
As already suggested in the comments, you cannot use UseExceptionHandler to catch exceptions initiated inside non-awaited tasks. UseExceptionHandler wraps your request in ASP.NET Core middleware. Once the action returns OK to the client, the middleware is no longer able to catch any exceptions happening in tasks started from within the action.
How can I catch ALL types of exceptions? Should I rely only on AppDomain.CurrentDomain.FirstChanceException?
You can catch exceptions globally and log them this way if you'd like. But I wouldn't recommend you to do it this way. The only reason you need to implement this event, is that you are starting tasks/threads inside your web requests. You have no way of knowing if these tasks are kept running (application restart, recycle, etc.). If you are looking to launch background tasks with ASP.NET Core, you should use Worker Services which is the intended way of doing this:
.ConfigureServices((hostContext, services) =>
{
services.AddHostedService<MyWorker>();
});
public class MyWorker : BackgroundService
{
protected override async Task ExecuteAsync(CancellationToken stoppingToken)
{
while (!stoppingToken.IsCancellationRequested)
{
try
{
// Do work
}
catch (Exception e)
{
// Log it?
}
await Task.Delay(TimeSpan.FromMinutes(5), stoppingToken);
}
}
}

The cause of this particular symptom is that Get is starting a fire-and-forget task that the server knows nothing about. The request will complete before the task even has a chance to execute, so the UseExceptionHandler middleware will never see any exceptions. This is no longer a fire-and-forget task.
The real problem though, is executing a long running task in the background. The built-in way to do this is using a Background Service. The docs show how to create timed and queued background service, that act as job queues.
It's equally easy, if not easier, to publish messages with the desired data from, eg a controller to the background service using, eg Channels. No need to create our own queue, when the BCL already has an asynchronous one.
The service could look like this :
public class MyService: BackgroundService
{
private readonly ChannelReader<T> _reader;
public QueuedBspService(MessageQueue<T> queue)
{
_reader = queue.Reader;
}
protected internal async Task ExecuteAsync(CancellationToken stoppingToken)
{
try
{
await foreach (var msg in _reader.ReadAllAsync(stoppingToken))
{
try
{
//Process the message here
}
catch (Exception exc)
{
//Handle message-specific errors
}
}
}
catch (Exception exc)
{
//Handle cancellations and other critical errors
}
}
}
The MessageQueue<T> wraps the Channel, making it easier to inject it to both the BackgroundService and any publishers like eg, a Controller action:
public class MessageQueue<T>
{
private readonly Channel<T> _channel;
public ChannelReader<T> Reader => _channel;
public ChannelWriter<T> Writer => _channel;
public MessageChannel()
{
_channel = Channel.CreateBounded<T>(1);
}
}
I adjusted this code from a service that only allows a single operation at a time. That's a quick&dirty way of preventing controllers from making requests that can't be handled.
On the contolle side, this action will post a request to the queue if possible, and return a Busy response otherwise :
public class MyController
{
private readonly ChannelWriter<T> _writer;
public MyController(MessaggeQueue<T> queue)
{
_writer = queue.Writer;
}
[HttpPost]
[ProducesResponseType(StatusCodes.Status201Created)]
[ProducesResponseType(StatusCodes.Status503ServiceUnavailable)]
public async Task<ActionResult> Post(....)
{
var jobName="SomeJob";
var id=Guid.NewGuid();
var jobMsg=CreateMessage(id,...);
try
{
if (_writer.TryWrite(msg))
{
return CreatedAtAction("GetItem","Jobs",new {id});
}
else
{
return Problem(statusCode:(int) HttpStatusCode.ServiceUnavailable,detail:"Jobs in progress",title:"Busy");
}
}
catch (Exception exc)
{
_logger.LogError(exc,"Queueing {job} failed",jobName);
throw;
}
}
}
The Post action first checks if it can even post a job message. If it succeeds, it returns a 201 - Created response with a URL that could be checked eg to check the status of the jobs. return Created() could be used instead, but once you create a long running job, you also want to check its status.
If the channel is at capacity, the core returns 503 with an explanation

Assert Method not reached in Try-Catch statement

I am trying to unit test my code to see if I try to view an account's details without a sessionKey, it will throw an exception. The unit test will go and execute the statement in the try-catch and despite knowing an exception will occur, it lists the test as successful even though Assert should be false. Assert is reached in similar functions, but not always. What would be the cause of the problem?
Original Function
/// <summary>
/// Displays the account details to the user
/// </summary>
/// <returns>HttpResponseMessage deserialized into AccountResponses object</returns>
public async Task<AccountResponse> Details()
{
HttpClient client = new HttpClient();
client.DefaultRequestHeaders.Add("X-Session-Key", sessionKey);
try
{
HttpResponseMessage response = await client.GetAsync(_baseUrl + "/Account/Details");
response.EnsureSuccessStatusCode();
string details = await response.Content.ReadAsStringAsync();
AccountResponse temp = JsonConvert.DeserializeObject<AccountResponse>(details);
return temp
}
catch (HttpRequestException ex)
{
throw ex;
}
}
Working Live Unit Test Function
[TestCategory("Account/Logon")]
[TestMethod]
public void LogOnNegativeBadPasswordTest()
{
try
{
string sessionKey = dmWeb.Account.LogOn(new DMWeb_REST.AccountLogOn { Password = "test#pasasdfasfsword" }).GetAwaiter().GetResult().ToString();
}
catch (HttpRequestException ex)
{
Assert.IsTrue(ex.Message.Contains("400"));
}
}
Not Working Live Unit Test Function
[TestCategory("Account/Details")]
[TestMethod]
public void DisplayDetailsNegativeNoSessionKeyTest()
{
try
{
string details = dmWeb.Account.Details().GetAwaiter().GetResult().ToString();
}
catch (HttpRequestException ex)
{
Assert.IsTrue(ex.Message.Contains("401"));
}
}

The test will be treated as successful as long as no errors are thrown. If no error is being caught in the catch block, this almost definitely means that no error was thrown by the code you're testing.
So place an Assert.Fail() after the statement that's supposed to throw an error:
public void TestMethod()
{
try
{
string details = ThingIAmTesting();
// shouldn't get here
Assert.Fail();
}
catch (Exception ex)
{
Assert.IsTrue(ex.Message.Contains("401");
}
}

How to log the "path taken" by the code and its exceptions

I have a requirement of compose the log message through the path taken by a code in a user click. Let me give an example:
Imagine the classical example: A user clicks in a button in a View, that calls code from the Business Layer that call code from Data Access Layer, that returns data to the Business, that return to a View.
I want to compose my log message through these layers. The caller method (in a View) that started the whole process will receive the full message. Here are some code sample just to help me explain what i am trying to achieve.
public void ViewMethod()
{
try
{
BussinessMethod();
}
catch (Exception ex)
{
Logger.Enqueue("exception occured");
Logger.Print();
}
}
public void BussinessMethod()
{
try
{
DataAcessMethod();
}
catch (Exception ex)
{
Logger.Enqueue("exception occured in the bussiness method")
}
}
public void DataAcessMethod()
{
try
{
// some code that executes an SQL command
// Log the SQL Command 1
// Log the SQL Command 2 and do on...
}
catch (Exception ex)
{
Logger.Enqueue("Error occurred, sqls executed are ...", sqlExecuted);
}
}
EDIT: The reason i am needing it is that i need to log all the SQL's executed in the whole process. If an error occurs in any point of the whole process, the user cant be warned, i need to store as much as possible information becouse the support technician will need it later.
My question is if there is any design pattern to develop it or passing a Logger reference across the "layers" are acceptable?

I would do something like this
public class Context
{
[ThreadStatic]
private static LogStore _store;
public static Log(....)
{
.....
}
}
public void ViewMethod()
{
var response = BussinessMethod();
if (response.Status = ResponseStatus.Success)
// do something with response.Data
else
// show message?
}
public BusinessMethodResponse BussinessMethod()
{
var response = new BusinessMethodResponse() {Status = ResponseStatus.Failure};
SomeData data;
try
{
data = DataAcessMethod();
}
catch (Exception ex)
{
Context.Log(....);
response.Message = "Data retrieval failed";
return response;
}
try
{
// massage the data here
response.Status = ResponseStatus.Success;
response.Data = myMassagedData;
}
catch (Exception ex)
{
Context.Log(....);
response.Message = "Something failed";
}
return response;
}
public void DataAcessMethod()
{
// some code that executes an SQL command
}
What this do? Now you can call your business objects from MVC, WPF, WinForms, Web Forms, etc...

ASP.NET MVC 4.5 WebSocket server loses connection after a few messages have been transferred

I've just started to play around with WebSockets and ASP.NET and have run into a weird issue. I'm building a very primitive ASP.NET 4.5 WebAPI application that is supposed to function as an echo-server like so:
using Microsoft.Web.WebSockets;
// ...
namespace MyControllers
{
internal class EchoHandler : WebSocketHandler
{
public override void OnClose()
{
System.Diagnostics.Debug.Write("Close");
}
public override void OnError()
{
System.Diagnostics.Debug.Write("Error: " + this.Error.ToString());
}
public override void OnOpen()
{
System.Diagnostics.Debug.Write("Open");
}
public override void OnMessage(string message)
{
System.Diagnostics.Debug.Write("Message: " + message);
this.Send("Echo: " + message);
}
}
public class EchoController : ApiController
{
public HttpResponseMessage Get()
{
if (HttpContext.Current.IsWebSocketRequest)
{
HttpContext.Current.AcceptWebSocketRequest(new EchoHandler());
return Request.CreateResponse(HttpStatusCode.SwitchingProtocols);
}
else
{
return Request.CreateResponse(HttpStatusCode.BadRequest);
}
}
}
}
I'm connecting to this service using a Windows Store Application written in C#. The relevant code looks like this:
class WebsocketTest
{
private MessageWebSocket webSocket;
private DataWriter messageWriter;
private async Task Connect()
{
var server = new Uri("ws://127.0.0.1:81/");
webSocket = new MessageWebSocket();
webSocket.Control.MessageType = SocketMessageType.Utf8;
webSocket.MessageReceived += messageWebSocket_MessageReceived;
webSocket.Closed += messageWebSocket_Closed;
await webSocket.ConnectAsync(server);
messageWebSocket = webSocket;
messageWriter = new DataWriter(webSocket.OutputStream);
}
private async Task Send(string message)
{
try
{
messageWriter.WriteString(message);
await messageWriter.StoreAsync();
}
catch (Exception ex)
{
var error = WebSocketError.GetStatus(ex.GetBaseException().HResult);
}
}
}
This works well for a while, but after an arbitrary number of messages have been sent back and forth, OnError() is invoked on the server and I get the following exception: "The I/O operation has been aborted because of either a thread exit or an application request" (It's the "this.Send(...)" that seems to be causing it). If I keep sending stuff on the client, I get a "ConnectionAborted" error when calling "dataWriter.StoreAsync()".
The error occurs every time, but it takes a varying number of messages before it does. Using longer messages seems to speed up the process.
For testing, I also tried using plain AspNetWebSockets instead of a WebSocketHandler but with the same outcome.
Any ideas?
Thanks a ton in advance,
Kai

Its a bug (reported by me):
https://connect.microsoft.com/VisualStudio/feedbackdetail/view/976851/server-websocket-closed-abruptly-the-i-o-operation-has-been-aborted-because-of-either-a-thread-exit-or-an-application-request
I have been trying to find a workaround for quite some time without being successful. I'm using the HttpListener but the symptom is the same. Now I have changed implementation to a third party library and the problem seems to have been resolved.

COMException on Main Thread of WPF application

WPF, Excel AddIn, C#,
I have multiple asychronous calls to get data from web service on main thread, then in call back,
I will plot the data in Excel. I tracked call back and they run on main thread, too.
but I still get COMException 0x800AC472, googled and it seems this is a multi-thread issue.
but I am confused why this happened.
I think there is only one main thread and since all callback are run on main thread and there is no reason to have the exception?
Edit:
On main UI thread, ribbon/button is clicked, it will call web service BuildMetaData,
once it is returned back, in its callback MetaDataCompleteCallback, another web service call is sent
Once it is returned back, in its callback DataRequestJobFinished, it will call plot to plot data on Excel. see below
On Main UI class:
Btn_Click()
{
...
_reportObjs[index].GenerateReport();
}
on Class to GenerateReport
public void GenerateReport()
{
Request.ParseFunction();
Request.MetacompleteCallBack = MetaDataCompleteCallback;
Request.BuildMetaData();
}
public void MetaDataCompleteCallback(int id)
{
try
{
if (Request.IsRequestCancelled)
{
Request.FormulaCell.Dispose();
return;
}
ErrorMessage = Request.ErrorMessage;
if (string.IsNullOrEmpty(Request.ErrorMessage))
{
_queryJob = new DataQueryJob(UnityContainer, Request.BuildQueryString(), DataRequestJobFinished, Request);
}
else
{
ModifyCommentOnFormulaCellPublishRefreshEvent();
}
}
catch (Exception ex)
{
ErrorMessage = ex.Message;
ModifyCommentOnFormulaCellPublishRefreshEvent();
}
finally
{
Request.MetacompleteCallBack = null;
}
}
public void DataRequestJobFinished(DataRequestResponse response)
{
Dispatcher.Invoke(new Action<DataRequestResponse>(DataRequestJobFinishedUI), response);
}
public void DataRequestJobFinished(DataRequestResponse response)
{
try
{
if (Request.IsRequestCancelled)
{
return;
}
if (response.status != Status.COMPLETE)
{
ErrorMessage = ManipulateStatusMsg(response);
}
else // COMPLETE
{
// TODO: Convert this into factory pattern
var tmpReq = Request as DataRequest;
if (tmpReq == null) return;
new VerticalTemplate(tmpReq, response, IsOffice2003).Plot();
}
}
catch (Exception e)
{
ErrorMessage = e.Message;
MIMICShared.Helper.LogError(e);
}
finally
{
//if (token != null)
// this.UnityContainer.Resolve<IEventAggregator>().GetEvent<DataQueryJobComplete>().Unsubscribe(token);
ModifyCommentOnFormulaCellPublishRefreshEvent();
Request.FormulaCell.Dispose();
}
}
on plot class
public void Plot()
{
...
attributeRange.Value2 = headerArray;
DataRange.Value2 = ....
DataRange.NumberFormat = ...
}

I saw this stackoverflow.com/questions/5246288/errormessage-in-excel, social.msdn.microsoft.com/forums/en-US/vsto/thread/… It seems there is no solution to the issue except wait/retry.
THis post talks about how to check if Excel is in edit. http://www.add-in-express.com/creating-addins-blog/2011/03/23/excel-check-user-edit-cell/