How to dynamically move nested key value to root level

[arefeh]

This is my logstash config file:

input {
   http {
    id => bulkHttpInput
    port => 8088
    additional_codecs => {"application/json" => "es_bulk"}
    codec => es_bulk
  }
}
filter {
  mutate {
    remove_field => [ "headers"] 
  }
}
output {
  elasticsearch {
   id => elasticOutputOfHttp
   index => "%{[@metadata][_index]}"
   document_type => "%{[@metadata][_type]}"
   document_id => "%{[doc][docID]}"
   doc_as_upsert => "true"
  }
}

and the output is like :
{
"host" => "127.0.0.1",
"@timestamp" => 2019-05-07T14:22:58.364Z,
"@version" => "1",
"doc" => {
"field1" => "my_field1",
"field2" => "my_field2",
"field3" => "my_field3"
}
}

I wanna move all fields within doc to root level. This is possible by defining add_field and move all nesteds fields from doc but field names are dynamic for-example "field4" may be added and some other fields may be removed . How to do it dynamically?

[Badger]

    ruby {
        code => '
            event.get("doc").each { |k, v|
                event.set(k,v)
            }
            event.remove("doc")
        '
    }

[arefeh]

It works,
Thank you