ActionController::Parameters -> permit_recursive_params

permit_recursive_params.out

{"tree"=>
  {"name"=>"Australia",
   "value"=>39904,
   "id"=>6,
   "description"=>"",
   "string_array"=>["one", "two"],
   "array_with_hashes"=>[{"a"=>"1"}, {"a"=>"2"}],
   "type"=>{"name"=>"Other", "icon"=>"<i class=\"fa fa-pagelines\"></i>"},
   "children"=>
    [{"name"=>"Boxes",
      "value"=>451609,
      "id"=>7,
      "description"=>"Used to store things.",
      "type"=>{"name"=>"Storage", "icon"=>"<i class=\"fa fa-archive\"></i>"},
      "children"=>
       [{"name"=>"Boxes",
         "value"=>451609,
         "id"=>7,
         "description"=>"Used to store things.",
         "type"=>
          {"name"=>"Storage", "icon"=>"<i class=\"fa fa-archive\"></i>"},
         "children"=>
          [{"name"=>"Boxes",
            "value"=>451609,
            "id"=>7,
            "description"=>"Used to store things.",
            "type"=>
             {"name"=>"Storage",
              "icon"=>"<i class=\"fa fa-archive\"></i>"}}]}]},
     {"name"=>"Boxes",
      "value"=>451609,
      "id"=>7,
      "description"=>"Used to store things.",
      "type"=>{"name"=>"Storage", "icon"=>"<i class=\"fa fa-archive\"></i>"}},
     {"name"=>"Boxes",
      "value"=>451609,
      "id"=>7,
      "description"=>"Used to store things.",
      "type"=>
       {"name"=>"Storage", "icon"=>"<i class=\"fa fa-archive\"></i>"}}]}}

permit_recursive_params.rb

require 'pp'
require 'active_support/core_ext/object/try'
require 'action_controller'

def permit_recursive_params(params)
  (params.try(:to_unsafe_h) || params).map do |key, value|
    if value.is_a?(Array)
      if value.first.respond_to?(:map)
        { key => [ permit_recursive_params(value.first) ] }
      else
        { key => [] }
      end
    elsif value.is_a?(Hash)
      { key => permit_recursive_params(value) }
    else
      key
    end
  end
end

params = ActionController::Parameters.new(
  budget: {
    tree: {
      name: "Australia",
      value: 39904,
      id: 6,
      description: "",
      string_array: ["one", "two"],
      array_with_hashes: [{
        a: "1"
      }, {
        a: "2"
      }],
      type: {
        name: "Other",
        icon: "<i class=\"fa fa-pagelines\"></i>"
      },
      children: [
        {
          name: "Boxes",
          value: 451609,
          id: 7,
          description: "Used to store things.",
          type: {
            name: "Storage",
            icon: "<i class=\"fa fa-archive\"></i>"
          },
          children: [
            {
              name: "Boxes",
              value: 451609,
              id: 7,
              description: "Used to store things.",
              type: {
                name: "Storage",
                icon: "<i class=\"fa fa-archive\"></i>"
              },
              children: [
                {
                  name: "Boxes",
                  value: 451609,
                  id: 7,
                  description: "Used to store things.",
                  type: {
                    name: "Storage",
                    icon: "<i class=\"fa fa-archive\"></i>"
                  }
                }
              ]
            }
          ]
        },
        {
          name: "Boxes",
          value: 451609,
          id: 7,
          description: "Used to store things.",
          type: {
            name: "Storage",
            icon: "<i class=\"fa fa-archive\"></i>"
          }
        },
        {
          name: "Boxes",
          value: 451609,
          id: 7,
          description: "Used to store things.",
          type: {
            name: "Storage",
            icon: "<i class=\"fa fa-archive\"></i>"
          }
        }
      ]
    }
  }
)


pp params.require(:budget).permit(tree: permit_recursive_params(params[:budget][:tree])).to_h

What do you think about adding rescue in method to handle nil values correctly.
https://gist.github.com/koenpunt/ac279e05cfeb0954ca763344fc0240b4#file-permit_recursive_params-rb-L18

def permit_recursive_params(params)
   # ...
rescue StandardError => e
  Rails.logger.warn e
  nil
end

@serg-kovalev - I went with a guard clause at the beginning instead - return if params.nil?. it's a bit safer than swallowing standarderror

I don't think this solution is working on every scenario:

require 'pp'
require 'active_support/core_ext/object/try'
require 'action_controller'

def permit_recursive_params(params)
  (params.try(:to_unsafe_h) || params).map do |key, value|
    if value.is_a?(Array)
      if value.first.respond_to?(:map)
        { key => [ permit_recursive_params(value.first) ] }
      else
        { key => [] }
      end
    elsif value.is_a?(Hash)
      { key => permit_recursive_params(value) }
    else
      key
    end
  end
end

params = ActionController::Parameters.new(
document: { id: 1212, token_map: {"1": [{"page": 1, "type": "signature", "coords": {"x": 75, "y": 285}, "fontSize": 16}, {"page": 1, "type": "text", "field": "fullname", "coords": {"x": 335, "y": 316}, "fontSize": 16}, {"page": 1, "type": "text", "field": "date", "coords": {"x": 75, "y": 380}, "fontSize": 16}]} }
)


pp params.require(:document).permit(token_map: permit_recursive_params(params[:document][:token_map])).to_h

For some reason, it does not whitelist the field node. I believe it's because you are whitelisting only the first node. In any case, I'm trying to fix it and I'll post it here when/if I finish it.