being able to do something like this would be more elegant once we have more messages, but not sure if flow+JS supports it

if I remember correctly I received comments in the past that we should try to avoid switch/case in JS and stick to if/else and early exit, but I don't recall the reason behind this 😅

This line is problematic for me because we are not sure yet, that type of message is TBMessage, it wasn't validated yet.

I think first we need to call a validator for the entire TBMessage (see my comment in tunnelbroker-messages.js), and then call handleTBMessage (it expects TBMessage so it should be already validated).

Then in handleTBMessage you can run some action based only on type field of message, without additional validation,

maybe refreshKeysValidatorTBMessage? the point is to try to avoid starting const name with a capital letter to avoid confusion.

When you have (not yet, but in the future it will be) a union of types you can do the same with validators.

something like:

export const messageFromTBValidator: TUnion<TBMessage> =
  t.union([
    TBRefreshKeysValidator,
  ]);

and then only once call messageFromTBValidator.is(message).

we should call this on union of validators to reflect the flow type, but we can not create tcomb's union with only one element: tcomb: expected an array of at least 2 types

https://phab.comm.dev/D8752#inline-58071

Would it be valuable to have a generic type like: TBRequest which would contain type field being an union of fixed strings and deviceId field? Correct me if I am wrong but I think we discussed such possibility and agreed it would be most beneficial for good typing there.

Current types are based on client <-> keyserver types. Not sure how the types you suggested should work