C#•2w 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;
}

6 Replies

Becquerel•2w ago

you are re-throwing the exception in the final catch block is that what you mean by unhandled? incidentally, there is no point in a catch block that only contains a throw statement (your first one)

canton7•2w ago

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.

So WindowsIdentity.RunImpersonated is catching the exception internally, then re-throwing it VS will break (by default) when an exception is thrown, and is "user-unhandled".

engineertdog•2w ago

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

canton7•2w ago

I tried to explain above 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 Because it's user-unhandled, VS breaks when it's thrown

engineertdog•2w ago

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

canton7•2w ago

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

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Uncaught exception