Plugin Helper: Record Accessor

record_accessor helper provides the unified access for event record. record_accessor uses jsonpath like syntax for target field. With this helper, you can easy to access nested field in the plugin.

Here is the code example with record_accessor helper:

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('$.user.name')
end
# omit super, shutdown and other plugin API
def filter(tag, time, record)
# 3. call `call` method to get value
value = @accessor.call(record) # With `$.user.name`, access to record["user"]["name"]
# ...
end
end
end

Syntax

  • dot notation: $. started parameter. Chain fields by .

This is simple syntax. For example, $.event.level for record["event"]["level"], $.key1[0].key2 for record["key1"][0]["key2"]

  • bracket notation: $[ started parameter. Chain fields by []

Useful for special characters, ., ` and etc:$['dot.key'][0]['space key']forrecord["dot.key"][0]["space key"]`

If you set non $. or $[ started value, e.g. key log, it is same as record["log"]. So using record_accessor doesn't break existing plugin behaviour.

Methods

record_accessor_create(param)

This method returns accessor object for event record. param is a string and see "Syntax" section for supported syntax.

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

After create object, call #call method with record object.

accessor.call(record) # access record field.

record_accessor used plugins

If this article is incorrect or outdated, or omits critical information, please let us know.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