How to Write Parser Plugin
Fluentd supports pluggable and customizable formats for input plugins. The plugin filenames prefixed
parser_ are registered as Parser Plugins.Here is an example of a custom parser that parses the following newline-delimited log format:
<timestamp><SPACE>key1=value1<DELIMITER>key2=value2<DELIMITER>key3=value...
like this:
2014-04-01T00:00:00 name=jake age=100 action=debugging
While it is not hard to write a regular expression to match this format, it is tricky to extract and save key names.
Here is the code to parse this custom format (let's call it
time_key_value). It takes one optional parameter called delimiter, which is the delimiter for key/value pairs. It also takes time_format to parse the time string.require 'fluent/plugin/parser'
module Fluent::Plugin
class TimeKeyValueParser < Parser
# Register this parser as 'time_key_value'
Fluent::Plugin.register_parser('time_key_value', self)
# `delimiter` is configurable with ' ' as default
config_param :delimiter, :string, default: ' '
# `time_format` is configurable
config_param :time_format, :string, default: nil
def configure(conf)
super
if @delimiter.length != 1
raise ConfigError, "delimiter must be a single character. #{@delimiter} is not."
end
# `TimeParser` class is already available.
# It takes a single argument as the time format
# to parse the time string with.
@time_parser = Fluent::TimeParser.new(@time_format)
end
def parse(text)
time, key_values = text.split(' ', 2)
time = @time_parser.parse(time)
record = {}
key_values.split(@delimiter).each do |kv|
k, v = kv.split('=', 2)
record[k] = v
end
yield time, record
end
end
end
Save this code as
parser_time_key_value.rb in a loadable plugin path.With
in_tail configured as:# Other lines...
<source>
@type tail
path /path/to/input/file
<parse>
@type time_key_value
</parse>
</source>
this log line:
2014-01-01T00:00:00 k=v a=b
will be parsed as:
2014-01-01 00:00:00 +0000 test: {"k":"v","a":"b"}
Parser plugins are designed to be used with other plugins, like Input, Filter and Output. There is a Parser plugin helper solely for this purpose:
# in class definition
helpers :parser
# in #configure
@parser = parser_create(type: 'json')
# in input loop or #filter or ...
@parser.parse do |time, record|
# ...
end
Parser plugins have a method to parse input (text) data to a structured record (
Hash) with time.It gets input data as
text, and call &block to feed the results of the parser. The input text may contain two or more records so that means the parser plugin might call the &block two or more times for one argument.Parser plugins must implement this method.
Fluentd parser plugin has one or more points to be tested. Others (parsing configurations, controlling buffers, retries, flushes, etc.) are controlled by the Fluentd core.
Fluentd also provides the test driver for plugins. You can easily write tests for your own plugins:
# test/plugin/test_parser_your_own.rb
require 'test/unit'
require 'fluent/test/driver/parser'
# Your own plugin
require 'fluent/plugin/parser_your_own'
class ParserYourOwnTest < Test::Unit::TestCase
def setup
# Common setup
end
CONFIG = %[
pattern apache
]
def create_driver(conf = CONF)
Fluent::Test::Driver::Parser.new(Fluent::Plugin::YourOwnParser).configure(conf)
end
sub_test_case 'configured with invalid configurations' do
test 'empty' do
assert_raise(Fluent::ConfigError) do
create_driver('')
end
end
# ...
end
sub_test_case 'plugin will parse text' do
test 'record has a field' do
d = create_driver(CONFIG)
text = '192.168.0.1 - - [28/Feb/2013:12:00:00 +0900] "GET / HTTP/1.1" 200 777'
expected_time = event_time('28/Feb/2013:12:00:00 +0900', format: '%d/%b/%Y:%H:%M:%S %z')
expected_record = {
'method' => 'GET',
# ...
}
d.instance.parse(text) do |time, record|
assert_equal(expected_time, time)
assert_equal(expected_record, record)
end
end
end
end
Testing for parser plugins is mainly for:
- Validation of configuration (i.e.
#configure) - Validation of the parsed time and record
To make testing easy, the plugin test driver provides a logger and the functionality to override the system and parser configurations, etc.
The lifecycle of plugin and test driver is:
- 1.Instantiate plugin driver which then instantiates the plugin
- 2.Configure plugin
- 3.Run test code
- 4.Assert results of tests by data provided by the driver
For:
- configuration tests, repeat steps # 1-2
- full feature tests, repeat steps # 1-4
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.
Last modified 2yr ago