Exception/error reporting

[cdupont]

Hello, if the function called via RPC throws an exception, what will happen? In general, how do you advice to report errors in simpleRPC?

[jfjlaros]

Currently there is no exception handling at all. So for now I would suggest to handle any exceptions in the called function itself, by lack of a better solution.

What kind of behaviour would you like to see?

[cdupont]

There are various solutions for error handling... Some functions uses the return value for error codes and uses an argument reference to pass the result. Some others return NULL or -1 for errors. Both solutions are ugly in my opinion :)

[cdupont]

So, at the moment I don't see any necessary modification...

[jfjlaros]

I was actually thinking about setting an error bit on the response and depending on this bit, either the result or an error string follows.

This will require a change in the RPC protocol, as well as in the client implementation. There are a couple of other things I want to change in the protocol, so perhaps this could be added to the list.

[cdupont]

It would be nice to return a sort of sum type: Error | Result Is it possible right now? Maybe with Object? I didn't quite much understood how to use the Object type.

[jfjlaros]

Maybe something like this? I can't test it myself at the moment.

Object<uint8_t, int> fWithException(int a, int b) {
  Object<uint8_t, int> r = {0, 0};  // Error code, return value.

  try {
    get<1>(r) = a / b;
  }
  catch (...) {
    get<0>(r) = 1;
  }
  return r;
}

[cdupont]

Thanks a lot, it works.

[jfjlaros]

Perhaps this is the way to go then.

I noticed that an extra compiler option is required to enable exception handling (-fexceptions), so adding exception handling in the library itself will make it less user friendly.

It is a nice use case to describe in the documentation though.

[cdupont]

Yes I'm now using Object<uint8_t, char *> as a result structure. The first element holds an error code (0 = success) and the second element is my returned value. I read it in python like that:

(r, val) = interface.foo(arg)
match r:
        case 0:
            print(val)
        case 1:
            print("Error: XXX")
        case 2: ...