Logstash 5.0 :Ruby exception occurred

The filter works fine with logstash 2.X, when it upgrade to 5.0
Ruby exception occurred: undefined method `[]'

ruby {
init =>"@kname =['time_local','jsoncontent']"
code =>"event.append(Hash[@kname.zip(event['message'].split(' INFO '))])"

input: 2016-10-20 11:04:25,197 INFO {json}

Logstash 5 has a new event API. event no longer has the API of a hash; it uses get and set methods, so event["message"] needs to be event.get("message"). I'm not sure what event.append should be replaced with.

Thanks magnus
Is there any reference guide for ruby-plugin API ?
or how to split the message field into 2 new fields with other filter