Changing dotted json field names to valid json form for Logstash

[Sanghyeon_Park]

Hello!
I'm new to Logstash, and I'm trying filtering and mutating input logs from Filebeat.

First of all, I have read this article, and I know that I cannot use dot separated field names.
Field name cannot contain dots

My question is that how can I change json fields automatically from an input json log?

The example input is the NFCT json file this ulogd stack
stack=ct1:NFCT,ip2bin1:IP2BIN,jsonnfwct:JSON

and this is what made from

{
"timestamp": "2019-03-06T05:21:51",
"dvc": "devicename",
"orig.ip.protocol": 17,
"orig.l4.sport": 60770,
"orig.l4.dport": 1900,
"orig.raw.pktlen": 0,
"orig.raw.pktcount": 0,
"reply.ip.protocol": 17,
"reply.l4.sport": 1900,
"reply.l4.dport": 60770,
"reply.raw.pktlen": 0,
"reply.raw.pktcount": 0,
"ct.mark": 0,
"ct.id": 3190284752,
"ct.event": 1,
"flow.start.sec": 1551849711,
"flow.start.usec": 151034,
"oob.family": 2,
"oob.protocol": 0
}

As you see, It emits dotted field name that is json form.
And to recognize by Kibana, It has to be changed to another word.

Here is what I want

{
    "timestamp": "2019-03-06T05:21:51",
    "dvc": "devicename", 
    "orig": { 
        "ip": { 
            "protocol": "17"
        },
        "l4": {
            "sport": "60770",
            "dport": "1900"
        },
        "raw": {
            "pktlen": "0",
            "pktcount": "0"
        }
    },
    "reply": {
        "ip": {
            "protocol": "17"
        },
        "l4": {
            "sport": "1900",
            "dport": "60770"
        },
        "raw": {
            "pktlen": "0",
            "pktcount": "0"
        }
    },
    "ct": {
        "mark": "0",
        "id": "3190284752",
        "event": "1"
    },
    "flow": {
        "start": {
            "sec": "1551849711",
            "usec": "151034"
        }
    },
    "oob": {
        "family": "2",
        "protocol": "0"
    }
}

Actually, before I ask this, I was trying to use the gsub module to replace '.' to '_'
The configuration pipeline was this

filter {
    mutate {                           
        gsub => [ "message", "\.+", "_" ]
    }
}

But it changed every '.' to '_', now those are just single values without the relationship.
Can I make it?

Thanks in advance.

[Badger]

A dedot filter with the nested option enabled would do what you want.

[Sanghyeon_Park]

Yay! That is what i want!
Thanks for your great help!!