C#•2y ago

Uncaught exception

I have the following code as part of a class I'm building for impersonation. It works, but the UnauthorizedAccessException is being marked as unhandled. If I hit continue, it all works as expected. But why is it unhandled and how can I address that?

c#
try {
  WindowsIdentity.RunImpersonated(_safeAccessTokenHandle, () => {
    // This will throw if the impersonation fails
    //string impersonatedUser = WindowsIdentity.GetCurrent().Name;
    //Console.WriteLine("Impersonation successful, current user: " + impersonatedUser);

    try {
      string securePath = "";
      if (!Directory.Exists(securePath)) {
        throw new UnauthorizedAccessException($"Access to {securePath} was denied.");
      }
    } catch {
      throw;
    }
  });
} catch (Exception ex) {
  Console.WriteLine($"Impersonation validation failed: {ex.Message}");
  Dispose();
  // Re-throw to ensure the exception is handled by the caller
  throw;
}

c#
try {
  WindowsIdentity.RunImpersonated(_safeAccessTokenHandle, () => {
    // This will throw if the impersonation fails
    //string impersonatedUser = WindowsIdentity.GetCurrent().Name;
    //Console.WriteLine("Impersonation successful, current user: " + impersonatedUser);

    try {
      string securePath = "";
      if (!Directory.Exists(securePath)) {
        throw new UnauthorizedAccessException($"Access to {securePath} was denied.");
      }
    } catch {
      throw;
    }
  });
} catch (Exception ex) {
  Console.WriteLine($"Impersonation validation failed: {ex.Message}");
  Dispose();
  // Re-throw to ensure the exception is handled by the caller
  throw;
}

c#
try {
  WindowsIdentity.RunImpersonated(_safeAccessTokenHandle, () => {
    // This will throw if the impersonation fails
    //string impersonatedUser = WindowsIdentity.GetCurrent().Name;
    //Console.WriteLine("Impersonation successful, current user: " + impersonatedUser);

    try {
      string securePath = "";
      if (!Directory.Exists(securePath)) {
        throw new UnauthorizedAccessException($"Access to {securePath} was denied.");
      }
    } catch {
      throw;
    }
  });
} catch (Exception ex) {
  Console.WriteLine($"Impersonation validation failed: {ex.Message}");
  Dispose();
  // Re-throw to ensure the exception is handled by the caller
  throw;
}

c#
try {
  WindowsIdentity.RunImpersonated(_safeAccessTokenHandle, () => {
    // This will throw if the impersonation fails
    //string impersonatedUser = WindowsIdentity.GetCurrent().Name;
    //Console.WriteLine("Impersonation successful, current user: " + impersonatedUser);

    try {
      string securePath = "";
      if (!Directory.Exists(securePath)) {
        throw new UnauthorizedAccessException($"Access to {securePath} was denied.");
      }
    } catch {
      throw;
    }
  });
} catch (Exception ex) {
  Console.WriteLine($"Impersonation validation failed: {ex.Message}");
  Dispose();
  // Re-throw to ensure the exception is handled by the caller
  throw;
}

becquerel•6/26/24, 8:54 AM

you are re-throwing the exception in the final catch block

becquerel•6/26/24, 8:54 AM

is that what you mean by unhandled?

becquerel•6/26/24, 8:55 AM

incidentally, there is no point in a catch block that only contains a throw statement (your first one)

canton7•6/26/24, 9:31 AM

https://devblogs.microsoft.com/devops/understanding-exceptions-while-debugging-with-visual-studio/:

User-unhandled Exceptions: When a first chance exception is not caught (handled) in user code and is caught in “External Code” on the call stack, this is classified as a “user-unhandled” exception. This classification is only applicable when debugging Managed or JavaScript applications with Just My Codeenabled.

canton7•6/26/24, 9:31 AM

So WindowsIdentity.RunImpersonatedWindowsIdentity.RunImpersonated is catching the exception internally, then re-throwing it

Bbecquerel you are re-throwing the exception in the final catch block

canton7•6/26/24, 9:32 AM

VS will break (by default) when an exception is thrown, and is "user-unhandled".

engineertdogOP•6/26/24, 1:56 PM

I'm throwing the exception within the RunImpersonatedRunImpersonated function. Shouldn't the outer try/catch handle that? VS breaks on the throw new UnauthorizedAccessExceptionthrow new UnauthorizedAccessException line.

canton7•6/26/24, 2:23 PM

I tried to explain above

canton7•6/26/24, 2:24 PM

The body of RunImpersonated is something like (hugely simplified):

void RunImpersonated(,..., Action action)
{
    try
    {
        action();
    }
    catch
    {
        // ... 
        throw;
    }
}

void RunImpersonated(,..., Action action)
{
    try
    {
        action();
    }
    catch
    {
        // ... 
        throw;
    }
}

Because your exception is being caught by non-user code, it gets counted as user-unhandled. Yes I know you catch it later, but the first time it's thrown it's caught be non-user code

canton7•6/26/24, 2:24 PM

Because it's user-unhandled, VS breaks when it's thrown

engineertdogOP•6/26/24, 5:10 PM

Yeah, throwing any exception within action();action(); causes that issue. So as long as I don't throw it's fine

canton7•6/27/24, 7:25 AM

At the end of the day, when VS decides to break on an exception is just a best guess. You can untick the little box in the pop-up if it gets it wrong

Uncaught exception

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