Filtering on nested json fields of varying length

[cyoez]

Hello everyone,
First of all, I am new to Logstash, so I would not be surprised if what I am asking is not within the scope of what Logstash can do.
So, I am working on a project where I need to do multiple GeoIP lookups on a nested json string. Here is what the input string would look like, beautified:

{
  "testid": "abdc",
  "ipversion": "v4",
  "flow": [
    {
      "destination_port": 33434,
      "dub": [
        {
          "index": 1,
          "ip": "192.168.1.254"
        },
        {
          "index": 2,
          "ip": "82.255.159.254"
        },
        {
          "index": 3,
          "ip": "82.255.210.12"
        }
      ]
    },
    {
      "destination_port": 33438,
      "dub": [
        {
          "index": 1,
          "ip": "172.2.12.12"
        },
        {
          "index": 2,
          "ip": "84.8.15.123"
        }
      ]
    }
  ]
}

What I want is to add a GeoIP lookup result field under each "ip" field. I tried to brute-force it by applying filters to every field of the array (even non-existent ones), which worked but was very ugly. I am wondering if there exists a cleaner way to do it by using the Split filter or some other trick I am not yet aware of.

Many thanks in advance,

[Badger]

@cyoez

I am wondering if there exists a cleaner way to do it by using the Split filter or some other trick I am not yet aware of.

You could add an id field to the event, split each of the arrays, and then aggregate based on the id field, but I am not sure that counts as "cleaner".

[cyoez]

Thank you for the suggestion, I have been tinkering with a Ruby filter in the meantime, I will go back to your solution if mine is failing. Thank you for your time anyway!

[cyoez]

Nevermind, I managed to solve my problem with a Ruby filter. I'm leaving my solution here in case it helps someone:

input {
  file { 
    path => "/path/to/file/file.json"
    codec => "json"
    start_position => "beginning"
  }
}
filter {
   ruby {
      init => "
         require 'logstash/filters/geoip'
      "
      code => "
         nflow = event.get('flow_number') - 1
         for idflow in 0..nflow do
             nhops = event.get(%([flow][#{idflow}])+'[hops_count]') - 1
             for idhop in 0..nhops do
                @geoip = LogStash::Filters::GeoIP.new({'source' => %([flow][#{idflow}][dub][#{idhop}][ip]),
                                       'target' => %([flow][#{idflow}][dub][#{idhop}][geoip])
                                       })

                @geoip.register

                @geoip.filter(event)

             end
         end
      "
   }
}

Not the cleanest, but the code is short and completes in a reasonable time.

I'll mark this post as a solution so the topic can be closed.