Async Method Weaving: Parameters-Array value is not set when passing the array to OnEnter()

[Dhairya-Sangoi]

Hey,

It seems there is a bug in weaving async methods.

Attribute:

[InterceptorOptions(AlwaysCreateNewInstance = true)]
    public class TestingAnnotation : Attribute, IMethodInterceptor
    {
        public void OnEnter(Type declaringType, object instance, MethodBase methodbase, object[] values)
        {

        }

        public bool OnException(Exception e)
        {
            return true;
        }

        public void OnExit()
        {

        }
    }

Annotated class method:

class TestingClass
    {
        [TestingAnnotation]
        public async Task AsyncTestMethod(string inp1, int inp2)
        {
            await Task.Delay(1000);
        }

    }

Decompiled weaved code:

internal class TestingClass
  {
    [DebuggerStepThrough]
    [AsyncStateMachine(typeof (TestingClass.\u003CAsyncTestMethod\u003Ed__0))]
    public Task AsyncTestMethod(string inp1, int inp2)
    {
      IMethodInterceptor methodInterceptor = (IMethodInterceptor) new TestingAnnotation();
      TestingClass.\u003CAsyncTestMethod\u003Ed__0 stateMachine = new TestingClass.\u003CAsyncTestMethod\u003Ed__0();
      stateMachine.\u003C\u003E4__this = this;
      stateMachine.inp1 = inp1;
      stateMachine.inp2 = inp2;
      stateMachine.\u003C\u003Et__builder = AsyncTaskMethodBuilder.Create();
      stateMachine.\u003C\u003E1__state = -1;
      stateMachine.\u003CAsyncTestMethod\u003E_gtqmvl2i59zeb = methodInterceptor;
      stateMachine.\u003C\u003Et__builder.Start<TestingClass.\u003CAsyncTestMethod\u003Ed__0>(ref stateMachine);
      return stateMachine.\u003C\u003Et__builder.Task;
    }

    public TestingClass()
    {
      base.\u002Ector();
    }

    [CompilerGenerated]
    private sealed class \u003CAsyncTestMethod\u003Ed__0 : IAsyncStateMachine
    {
      public int \u003C\u003E1__state;
      public AsyncTaskMethodBuilder \u003C\u003Et__builder;
      public string inp1;
      public int inp2;
      public TestingClass \u003C\u003E4__this;
      private TaskAwaiter \u003C\u003Eu__1;
      public IMethodInterceptor \u003CAsyncTestMethod\u003E_gtqmvl2i59zeb;

      public \u003CAsyncTestMethod\u003Ed__0()
      {
        base.\u002Ector();
      }

      void IAsyncStateMachine.MoveNext()
      {
        int num1 = this.\u003C\u003E1__state;
        try
        {
          try
          {
            object[] values = new object[2];
            if (num1 != 0)
            {
              // ISSUE: method reference
              // ISSUE: type reference
              this.\u003CAsyncTestMethod\u003E_gtqmvl2i59zeb.OnEnter(typeof (TestingClass), (object) this.\u003C\u003E4__this, MethodBase.GetMethodFromHandle(__methodref (TestingClass.AsyncTestMethod), __typeref (TestingClass)), values);
            }
            TaskAwaiter awaiter;
            if (num1 != 0)
            {
              awaiter = Task.Delay(1000).GetAwaiter();
              if (!awaiter.IsCompleted)
              {
                int num2;
                this.\u003C\u003E1__state = num2 = 0;
                this.\u003C\u003Eu__1 = awaiter;
                TestingClass.\u003CAsyncTestMethod\u003Ed__0 stateMachine = this;
                this.\u003C\u003Et__builder.AwaitUnsafeOnCompleted<TaskAwaiter, TestingClass.\u003CAsyncTestMethod\u003Ed__0>(ref awaiter, ref stateMachine);
                return;
              }
            }
            else
            {
              awaiter = this.\u003C\u003Eu__1;
              this.\u003C\u003Eu__1 = new TaskAwaiter();
              this.\u003C\u003E1__state = num1 = -1;
            }
            awaiter.GetResult();
            if (num1 != 0)
              ;
          }
          finally
          {
            this.\u003CAsyncTestMethod\u003E_gtqmvl2i59zeb.OnExit();
          }
        }
        catch (Exception ex)
        {
          if (this.\u003CAsyncTestMethod\u003E_gtqmvl2i59zeb.OnException(ex))
          {
            this.\u003C\u003E1__state = -2;
            this.\u003C\u003Et__builder.SetException(ex);
            return;
          }
        }
        this.\u003C\u003E1__state = -2;
        this.\u003C\u003Et__builder.SetResult();
      }

      [DebuggerHidden]
      void IAsyncStateMachine.SetStateMachine(IAsyncStateMachine stateMachine)
      {
      }
    }
  }

As it can be seen, the object[] values in IAsyncStateMachine.MoveNext() is not getting initialized with the actual parameters that should be passed to the method.

This bug seems to be arising from Cauldron\Fody\Cauldron.Interception.Cecilator\Coders\Default\Coder.cs file.

I think this could fix the bug:

In GetParametersArray() method, changing:

foreach (var parameter in associatedMethod.methodReference.Parameters)
                    {
                        newBlock.Emit(OpCodes.Ldloc, variable.variable);
                        newBlock.Append(InstructionBlock.CreateCode(newBlock, null, counter++));
                        newBlock.Append(InstructionBlock.CreateCode(newBlock, BuilderTypes.Object, associatedMethod.AsyncMethodHelper.AsyncStateMachineType.GetField(parameter.Name)));
                        newBlock.Emit(OpCodes.Stelem_Ref);
                    }

to

foreach (var parameter in associatedMethod.AsyncMethodHelper.Method.methodReference.Parameters)
                    {
                        newBlock.Emit(OpCodes.Ldloc, variable.variable);
                        newBlock.Append(InstructionBlock.CreateCode(newBlock, null, counter++));
                        newBlock.Append(InstructionBlock.CreateCode(newBlock, BuilderTypes.Object, associatedMethod.AsyncMethodHelper.AsyncStateMachineType.GetField(parameter.Name)));
                        newBlock.Emit(OpCodes.Stelem_Ref);
                    }

This could be happening because, in case of async methods, the associatedMethod is an object of type AsyncStateMachineMoveNextMethod for which the associatedMethod.methodReference.Parameters.Count is 0.

[reflection-emit]

Hi I will look into this and fix this asap.

---

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[reflection-emit]

I uploaded a new package with the fix. Please confirm

[Dhairya-Sangoi]

Thanks for the quick fix. Will confirm and let you know.

[Dhairya-Sangoi]

Confirmed. Works as expected! Thanks for the quick fix :)