Filter

Although Direktiv supports Knative Eventing which supports event filtering, Direktiv adds custom event filtering as well. Direktiv's event filters can be easlily configured and added as additional event route.

Javascript

Filters are based on Javascript and the filter has access to an event object which can be modified or the event can be dropped based on certain requirements. Direktiv provieds one additional function nslog which adds log entries to the namespace logs.

if (event["source"] == "mysource") {
  nslog("rename source")
  event["source"] = "newsource"
}

if (event["source"] == "hello") {
  nslog("drop me")
  return null
}

return event

The Javascript can return null which means the event will be dropped andn not handled by Direktiv or it returns the modified event object which goes into the system and will be handled by flows if there are any configured to handle it.

Add Filter

Assuming the above filter script is stored in filter.js it can be added to Direktiv with the following CLI command.

direktivctl events set-filter -n events -a http://myserver myfilter filter.js 

If the command was successful the filter is configured and ready to be used.

direktivctl events list-filters -n events -a http://myserver 
myfilter

To keep the event system performant each filter creates a event route where the rule will be applied. The API path for the filter is /api/namespaces/{namespace}/broadcast/{filtername}. The filter will be applied to every event hitting that API URL.

For the following event the source would be renamed.

{
    "specversion" : "1.0",
    "type" : "io.direktiv.myevent",
    "source" : "mysource",
    "subject" : "123"
}

This event would be dropped.

{
    "specversion" : "1.0",
    "type" : "io.direktiv.myevent",
    "source" : "hello",
    "subject" : "123"
}

A filter can be removed with the following command.

direktivctl events delete-filter -n events -a http://myserver myfilter