`arc.http` should allow mixing sync and async middleware

[alexbepple]

Is your feature request related to a problem? Please describe.

If my handler looks like the following, the arc.http and arc.http.async helpers in version 7.0.0 will complain with

TypeError: All arc.http middleware functions must be async

console logEvent = (event) => {
  console.log(event)
  return event
}

export const handler = arc.http(
  logEvent,

  async () => {
    // do async work
  },
)

However, it would be quite weird to have to turn the above logEvent into an async function.

Describe the solution you'd like
If you want to keep supporting the callback interface, I think it would be best to stick with the API of versions <7. Version 7.0.0 forces me to make functions async that are not async in nature.

Describe alternatives you've considered
An alternative could be to have arc.http be 'smart' the way it currently is in 7.0.0, but arc.http.async to behave the way it did <7.

[filmaj]

Currently (v8) arc.http does require all functions to be of the same type, either sync or async. It would be nice if this method was smart enough to inspect each middleware individually and execute appropriately. So, I'll accept this as a feature request.

However, it would be quite weird to have to turn the above logEvent into an async function.

Side note: I disagree, I don't think it's weird and works just fine 😄 I believe the only downside to having an async function with no await calls is that under the hood the function's return value is wrapped in a Promise. This may have a tiny performance impact - maybe? But how many middleware functions is one stringing together in an arc handler, really? Even if it was hundreds, I doubt that would register in benchmarks.

[alexbepple]

I agree that it works just fine. My – slight – gripe is that there is mismatch between language semantics & runtime behavior. If one forgets async, the error only shows at runtime, not while writing code. And later, when reading code, one might wonder why that function is async. One has to remember that it’s due to arc.http. It’s a small, but entirely unnecessary distraction.