Plugin Helper: Record Accessor

The record_accessor plugin helper provides unified access to the event record. It uses jsonpath like syntax for the target field. With this helper, you can easily access/delete a nested field in the plugin.

Here is an example:

require 'fluent/plugin/filter'

module Fluent::Plugin
  class ExampleFilter < Filter
    Fluent::Plugin.register_filter('example', self)

    # 1. Load record_accessor helper
    helpers :record_accessor

    def configure(conf)
      super

      # 2. Call `record_accessor_create` to create object
      @accessor = record_accessor_create('$.user.name')
    end

    # Omit `super`, `shutdown` and other plugin APIs

    def filter(tag, time, record)
      # 3. Call `call` method to get value
      value = @accessor.call(record) # With `$.user.name`, access to record["user"]["name"]
      # ...
    end
  end
end

Syntax

• dot notation: $. is the starting parameter. Chain fields with dots ..

For example:

$.event.level for record["event"]["level"]

$.key1[0].key2 for record["key1"][0]["key2"]

• bracket notation: $[ starting parameter. Chain fields with [].

Useful for special characters, ., whitespace, etc.

$['dot.key'][0]['space key'] for record["dot.key"][0]["space key"]

If you set non $. or $[ starting value, e.g. key log, it is the same as record["log"]. So, using record_accessor does not break the existing plugin behavior.

Methods

record_accessor_create(param)

This method returns the accessor object of the event record.

The param is a String.

See the "Syntax" section for more details.

record_accessor_create("log")
record_accessor_create("$.key1.key2")
record_accessor_create("$['key1'][0]['key2']")

After creating an object, call call/delete/set method with the record object.

accessor.call(record)       # get record field
accessor.delete(record)     # delete record field
accessor.set(record, value) # set new value to record field

NOTE: set method is supported since v1.10.3

Plugins using record_accessor

• filter_grep
• filter_parser
• filter_record_transformer

If this article is incorrect or outdated, or omits critical information, please let us know. Fluentd is an open-source project under Cloud Native Computing Foundation (CNCF). All components are available under the Apache 2 License.