How to rethrow InnerException without losing stack trace in C#?

Rooby_Noob_3205 0
Viewed 95595

I am calling, through reflection, a method which may cause an exception. How can I pass the exception to my caller without the wrapper reflection puts around it?
I am rethrowing the InnerException, but this destroys the stack trace.
Example code:

public void test1()
{
    // Throw an exception for testing purposes
    throw new ArgumentException("test1");
}

void test2()
{
    try
    {
        MethodInfo mi = typeof(Program).GetMethod("test1");
        mi.Invoke(this, null);
    }
    catch (TargetInvocationException tiex)
    {
        // Throw the new exception
        throw tiex.InnerException;
    }
}
exception .net c#
11 Answers

It is possible to preserve the stack trace before rethrowing without reflection:

static void PreserveStackTrace (Exception e)
{
    var ctx = new StreamingContext  (StreamingContextStates.CrossAppDomain) ;
    var mgr = new ObjectManager     (null, ctx) ;
    var si  = new SerializationInfo (e.GetType (), new FormatterConverter ()) ;

    e.GetObjectData    (si, ctx)  ;
    mgr.RegisterObject (e, 1, si) ; // prepare for SetObjectData
    mgr.DoFixups       ()         ; // ObjectManager calls SetObjectData

    // voila, e is unmodified save for _remoteStackTraceString
}

This wastes a lot of cycles compared to calling InternalPreserveStackTrace via cached delegate, but has the advantage of relying only on public functionality. Here are a couple of common usage patterns for stack-trace preserving functions:

// usage (A): cross-thread invoke, messaging, custom task schedulers etc.
catch (Exception e)
{
    PreserveStackTrace (e) ;

    // store exception to be re-thrown later,
    // possibly in a different thread
    operationResult.Exception = e ;
}

// usage (B): after calling MethodInfo.Invoke() and the like
catch (TargetInvocationException tiex)
{
    PreserveStackTrace (tiex.InnerException) ;

    // unwrap TargetInvocationException, so that typed catch clauses 
    // in library/3rd-party code can work correctly;
    // new stack trace is appended to existing one
    throw tiex.InnerException ;
}
Anton_Tykhyy_777240

I think your best bet would be to just put this in your catch block:

throw;

And then extract the innerexception later.

Rich_B_56400

Based on Paul Turners answer I made an extension method

    public static Exception Capture(this Exception ex)
    {
        ExceptionDispatchInfo.Capture(ex).Throw();
        return ex;
    }

the return ex ist never reached but the advantage is that I can use throw ex.Capture() as a one liner so the compiler won't raise an not all code paths return a value error.

    public static object InvokeEx(this MethodInfo method, object obj, object[] parameters)
    {
        {
            return method.Invoke(obj, parameters);
        }
        catch (TargetInvocationException ex) when (ex.InnerException != null)
        {
            throw ex.InnerException.Capture();
        }
    }
user_984910

Even more reflection...

catch (TargetInvocationException tiex)
{
    // Get the _remoteStackTraceString of the Exception class
    FieldInfo remoteStackTraceString = typeof(Exception)
        .GetField("_remoteStackTraceString",
            BindingFlags.Instance | BindingFlags.NonPublic); // MS.Net

    if (remoteStackTraceString == null)
        remoteStackTraceString = typeof(Exception)
        .GetField("remote_stack_trace",
            BindingFlags.Instance | BindingFlags.NonPublic); // Mono

    // Set the InnerException._remoteStackTraceString
    // to the current InnerException.StackTrace
    remoteStackTraceString.SetValue(tiex.InnerException,
        tiex.InnerException.StackTrace + Environment.NewLine);

    // Throw the new exception
    throw tiex.InnerException;
}

Keep in mind that this may break at any time, as private fields are not part of API. See further discussion on Mono bugzilla.

Rooby_Noob_32050

First: don't lose the TargetInvocationException - it's valuable information when you will want to debug things.
Second: Wrap the TIE as InnerException in your own exception type and put an OriginalException property that links to what you need (and keep the entire callstack intact).
Third: Let the TIE bubble out of your method.

kokos_10650

Guys, you are cool.. I'm gonna be a necromancer soon.

    public void test1()
    {
        // Throw an exception for testing purposes
        throw new ArgumentException("test1");
    }

    void test2()
    {
            MethodInfo mi = typeof(Program).GetMethod("test1");
            ((Action)Delegate.CreateDelegate(typeof(Action), mi))();

    }
user_2419860

Anpother sample code which uses exception serialization/deserialization. It does not require the actual exception type to be serializable. Also it uses only public/protected methods.

    static void PreserveStackTrace(Exception e)
    {
        var ctx = new StreamingContext(StreamingContextStates.CrossAppDomain);
        var si = new SerializationInfo(typeof(Exception), new FormatterConverter());
        var ctor = typeof(Exception).GetConstructor(BindingFlags.NonPublic | BindingFlags.Instance, null, new Type[] { typeof(SerializationInfo), typeof(StreamingContext) }, null);

        e.GetObjectData(si, ctx);
        ctor.Invoke(e, new object[] { si, ctx });
    }
user_13098890

This is just a nice clean, modern implementation of some of the other ideas here, tested in .NET 6:

public static class ExceptionExtensions
{
    [DoesNotReturn]
    public static void Rethrow(this Exception ex) 
        => ExceptionDispatchInfo.Capture(ex).Throw();
}

I wanted the value of the PropertyName property on myObject but this will work just as well when using reflection to call methods (as per OP's problem) or anything else that results in you wanting to re-throw an inner exception.

try
{
    object? value = myObject.GetType().GetProperty("PropertyName")?.GetValue(myObject);
}
catch (TargetInvocationException ex)
{
    (ex.InnerException ?? ex).Rethrow();
}
user_7236450
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