EVM won't wait for 'step' event handler to finish before continuing execution

[thevaizman]

Hey, was trying to bump our version of ethereumjs in our evm.codes project.

I am using the latest (6.0.0) @ethereumjs/vm and the latest (1.0.0) @ethereumjs/evm packages.
When my handler to the step event is called with a function as the 2nd arg, the EVM won't wait until the function is called and will just keep executing till the end.

My event handler declaration:

    const contFunc = () => {};

    vm.evm.events!.on('step', (e: InterpreterStep) => {
      _stepInto(e, contFunc)
    })

My handler function:

  const _stepInto = (
    { depth, pc, gasLeft, opcode, stack, memory }: InterpreterStep,
    continueFunc: () => void,
  ) => {

    // skip internal calls
    if (depth !== 0) {
      continueFunc()
      return
    }
  }

From the docs, I understand that EVM execution should wait until I call continueFunc() in my handler, but this is not the case. The execution just continues. I do know for sure that my _stepInto() handler is called as I can see console.logs from there.

I know that the event emitting properties of EVM/VM changed in the last few versions, could it be a bug? Or am I doing something wrong?

Would appreciate your help, as you were always extremely helpful for us! :) @jochem-brouwer @holgerd77

[jochem-brouwer]

You need to add a second argument to the event listener.

vm.events.on('step', async (e: InterpreterStep, contFun: Function) => {await someFun(); contFun()})

[thevaizman]

Thanks a lot for the quick answer @jochem-brouwer! For future reference of people who may be getting into the same problem and bump into this ticket, when using Function, it ended up asking me for a different type for the 2nd argument of the event handler, but it's now working after I used:

    vm.evm.events!.on('step', (e: InterpreterStep, contFunc: ((result?: any) => void) | undefined) => {
      _stepInto(e, contFunc)
    })

[holgerd77]

Is this sufficiently described in the code docs? Otherwise it would be good to add.

Will add as an eventual TODO to #2105