Validator Support Mixin

This gem provides back-ports of new validators that have been added to Logstash core. By using this support adapter, plugin developers can use newly-introduced validators without constraining the versions of Logstash on which their plugin can run.

When a plugin using this adapter runs on a version of Logstash that does not provide the named validator, the back-ported validator provided by this adapter is used instead.


  1. Add this gem as a runtime dependency of your plugin. To avoid conflicts with other plugins, you should always use the pessimistic operator ~> to match the minimum 1.x that provides the back-ports you intend to use: do |s|
      # ...
      s.add_runtime_dependency 'logstash-mixin-validator_support', '~>1.0'
  2. In your plugin code, require this library and extend one or more of the provided validators into your plugin. For example, to use the :field_reference validator introduced in Logstash 7.11:

    require 'logstash/plugin_mixins/validator_support/field_reference_validation_adapter'
    class LogStash::Inputs::Foo < Logstash::Inputs::Base
      extend LogStash::PluginMixins::ValidatorSupport::FieldReferenceValidationAdapter
      # ...
  3. Use the validator as normal when defining config options; your plugin does not need to know whether the validator was provided by Logstash core or by this gem.

      config :target, :validate => :field_reference


This gem:

  • MUST remain API-stable at 1.x
  • MUST NOT introduce additional runtime dependencies

When developing back-ports, sometimes it may not be possible to provide a verbatim validation. In these cases, developers should err on the side of the back-port accepting input that the core implementation may consider invalid.

Each time a new validator is added, the runtime dependency of this library on Logstash core should be updated to require a minimium of the OLDEST supported release. This allows plugins using this adapter to supply patch-level fixes to any supported Logstash version without maintaining multiple branches.