Relay `process_id` on side-effects performed after ProcessConclusionEvent

[renatomassaro]

FileDownload[Failed], FileUpload[Failed], ServerPasswordAcquired, Bruteforce[Failed]

This is quite common so check if it's possible to make it abstract/generic somehow.

[renatomassaro]

The "abstract" implementation is quite cool:

• Generate a "process_hash" from the *ProcessedEvent.
• Send this hash to the client via ProcessCompletedEvent
• Relay this hash on events that are emitted as a result from the first *ProcessedEvent
• Now, every event that was a result of the process completion will have the hash. The client knows all events related to the process.

Here's the "as-transparent-as-it-can-be" interface:

event = generate_process_hash(event)  # On TOP completion

process_completed_event = ProcessCompletedEvent.new(...., event)  # Includes the has on ProcessCompletedEvent

### On the handler ###

def handle(event) do
  if sucess do
    Event.emit(my_successful_event, from: event)
  else
    Event.emit(my_bad_bad_event, from: event)
  end
end

### On Helix.Event.emit/2 ###

def emit(event, from: prev_event) do
  get_hash(prev_event) |> put_hash(event) |> emit()
end

There's another benefit to this: since the Event emission API is generic (it's not specific to process hash), we may extend this behavior later on, like generating a linked graph from all events being emitted, or pass on an request/event identifier, etc.

[renatomassaro]

@kress95 how would that work out for you?

• You get the process hash on the ProcessCompletedEvent
• Store it on the client, similar to how event_id is handled
• Later on, you'll get a e..g FileDownloadedEvent, or FileDownloadFailedEvent with the process hash on a meta field, like event.__meta__.process_hash
• With that information, you can correlate any event with the process that caused its creation

Possible gotcha: There may have some events containing the process_hash that you, as a client, is not interested at all. I guess you would simply have to ignore this, so not a problem.

[renatomassaro]

And I just realized the process_hash can be the process_id itself :joy: