determine-field-type.logstash-filter-ruby.rb

###############################################################################
# determine-field-type.logstash-filter-ruby.rb
# ---------------------------------
# A script for a Logstash Ruby Filter to determine a field's type
###############################################################################
#
# Copyright 2022 Ry Biesemeyer
#
# Permission is hereby granted, free of charge, to any person obtaining a copy
# of this software and associated documentation files (the "Software"), to deal
# in the Software without restriction, including without limitation the rights
# to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
# copies of the Software, and to permit persons to whom the Software is
# furnished to do so, subject to the following conditions:
#
# The above copyright notice and this permission notice shall be included in
# all copies or substantial portions of the Software.
#
# THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
# IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
# FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
# AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
# LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
# OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
# SOFTWARE.
def register(params)
  params = params.dup

  # source: the source field whose type needs to be determined
  @source = params.delete('source') or report_configuration_error("`source` is required!")

  # target: where to place the type of the field (defaults to a same-nested path in [@metadata][typeinfo])
  @target = params.delete('target') { "[@metadata][typeinfo][#{@source}]" }

  params.empty? || report_configuration_error("unknown script parameter(s): #{params.keys}.")
end

def report_configuration_error(message)
  raise LogStash::ConfigurationError, message
end

def filter(event)
  type = :unset unless event.include?(@source)
  type ||= case event.get(@source)
           when nil then :nil
           when String      then :string
           when true, false then :boolean
           when Numeric     then :number
           when Array       then :array
           when Hash        then :'key-value-map'
           else                  :unknown
           end
  event.set(@target, type.to_s)
rescue => e
  logger.error('failed to determine type', exception: e.message)
  event.tag('_type_determination_error')
ensure
  return [event]
end

###############################
# TESTING

common_test_event = {
  "int" => 1,
  "str" => "fubar",
  "empty_array" => [],
  "empty_hash" => {},
  "array" => [
    {"int" => 12},
    {"str" => "foobar"},
    {"empty_hash" => {}},
    {"empty_array" => []}
  ],
  "boolean-true" => true,
  "boolean-false" => false,
  "hash" => {
    "int" => 123,
    "str" => "FUBAR",
    "empty_hash" => {},
    "empty_array" => [],
    "non-empty_hash" => {
      "a" => "b",
      "nested" => {
        "another" => "level",
        "so" => "deep",
      },
      "empty_hash" => {},
    }
  }
}

shared_event_provider = Proc.new do
  in_event { ::Marshal.load(::Marshal.dump(common_test_event)) }
end

{
  'boolean-true' => 'boolean',
  'boolean-false' => 'boolean',
  'missing' => 'unset',
  'str' => 'string',
  'int' => 'number',
  'hash' => 'key-value-map',
  'array' => 'array',
  'empty_array' => 'array',
  '[hash][str]' => 'string',
  '[hash][int]' => 'number',
}.each do |field, expected_type|
  test "detect #{field} as #{expected_type}" do
    parameters { { 'source' => field } }
    instance_eval(&shared_event_provider)

    expect("detect field `#{field}` to have type `#{expected_type}`") do |events|
      event = events.first
      event.get("[@metadata][typeinfo][#{field}]") == expected_type
    end
  end
end