Expose error name for MessageBus.invoke() errors

[elyscape]

♻️ Current situation

MessageBus.invoke() takes a callback, the first argument of which is the error encountered, if any, and the remaining arguments are the return arguments of the D-Bus method call. Per the D-Bus spec, messages of type ERROR are described as follows:

Error reply. If the first argument exists and is a string, it is an error message.

Additionally, these messages must have an ERROR_NAME header field, which is a string that indicates the type of error they represent.

Currently, if an error occurs, MessageBus.invoke() passes the return arguments, and not the error name, to the callback. The upshot of this is that the callback receives only the user-friendly explanation of what went wrong, not the machine-usable error type.

💡 Proposed solution

This changes the behavior of MessageBus.invoke() to, when an error occurs, invoke the callback passing as the first argument an object that looks like this:

{
  name: "ERROR_NAME",
  message: "what used to be passed in as the first argument"
}

⚙️ Release Notes

• Breaking change: When an error occurs in MessageBus.invoke() or MessageBus.invokeDbus(), the first argument passed to the callback (err) is now an object containing two keys: name is the D-Bus error name, and message is what previously was passed in as this argument.

➕ Additional Information

See homebridge/HAP-NodeJS#980 (comment)

[elyscape]

cc: @Supereg

[Supereg]

Update: actually, I had a better idea for this. Don't merge it yet, please.

I had this in my E-Mail. Does this still apply?

[elyscape]

Nope, I changed my mind.

[elyscape]

That is to say, this is good to go whenever.