record_accessor raises ArgumentError instead of ConfigError for an array index that is not an integer

まず plugin_helper/record_accessor.rb、特に parse_dot_array_op と parse_bracket_notation を確認してください。ここで Integer(index_value) が報告されたエラーを発生させます。近くにある構文エラーの処理を読み、test/plugin_helper/test_record_accessor.rb を実行してください。整数でない配列インデックスが Fluent::ConfigError を発生させ、メッセージに無効なキーが含まれる状態を完了条件とします。

Describe the bug

A record_accessor key with an array index that is not an integer, such as $.a[x] or $['a'][x], makes Fluentd stop with ArgumentError instead of Fluent::ConfigError. Fluentd stops either way, but the error is not reported as a config error: on 1.20.1 it is logged as "unexpected error" without the file of the configuration, and on 1.16.11 Fluentd exits with a Ruby backtrace.

The cause is Integer(index_value) in plugin_helper/record_accessor.rb (line 143 in parse_dot_array_op and line 183 in parse_bracket_notation, on master af25743e1 and v1.20.1). The other syntax errors next to them, such as a missing ] or an empty [], raise Fluent::ConfigError, but the ArgumentError of Integer() is not converted.

This affects every plugin that uses record_accessor_create for a key from the configuration, for example filter_grep.

To Reproduce

With this configuration:

<source>
  @type sample
  tag t
</source>
<filter t>
  @type grep
  <regexp>
    key $.a[x]
    pattern /x/
  </regexp>
</filter>
<match t>
  @type stdout
</match>

run fluentd --dry-run -c fluent.conf.

The same happens without a configuration file:

require "fluent/version"
require "fluent/plugin_helper/record_accessor"

puts "Fluentd #{Fluent::VERSION}"
["$.a[x]", "$['a'][x]", "$.[bad"].each do |key|
  Fluent::PluginHelper::RecordAccessor::Accessor.new(key)
  puts "#{key}: no error"
rescue => e
  puts "#{key}: #{e.class}: #{e.message}"
end

On master (af25743e1) with Ruby 3.4.12, it prints:

Fluentd 1.20.1
$.a[x]: ArgumentError: invalid value for Integer(): "x"
$['a'][x]: ArgumentError: invalid value for Integer(): "x"
$.[bad: Fluent::ConfigError: '[' found but ']' not found. Invalid syntax: $.[bad

With fluentd --dry-run and the configuration above, with each key in <regexp>:

Expected behavior

Fluent::ConfigError, like the other syntax errors of a record_accessor key, so that Fluentd reports it as a config error with the file and the key, for example "array index must be an integer. Invalid syntax: $.a[x]".

Your Environment

• Fluentd version: master (af25743e1), 1.20.1 and 1.16.11
• Ruby version: 3.4.12 (master, 1.20.1), 3.2.11 (1.16.11)
• Operating system: Linux (Docker, ruby:3.4 and ruby:3.2)

Your Configuration

The configuration is in "To Reproduce" above.

Your Error Log

Fluentd 1.20.1 and master:

[info]: starting fluentd-1.20.1 as dry run mode ruby="3.4.12"
[error]: unexpected error error_class=ArgumentError error="invalid value for Integer(): \"x\""

Fluentd 1.16.11:

[info]: starting fluentd-1.16.11 as dry run mode ruby="3.2.11"
/usr/local/bundle/gems/fluentd-1.16.11/lib/fluent/plugin_helper/record_accessor.rb:143:in `Integer': invalid value for Integer(): "x" (ArgumentError)

For comparison, key $.[bad gives:

[error]: config error file="fluent.conf" error_class=Fluent::ConfigError error="'[' found but ']' not found. Invalid syntax: $.[bad"

Additional context

• I tried rescuing the ArgumentError of the two Integer(index_value) calls and raising Fluent::ConfigError on master. The keys above then raise Fluent::ConfigError, and test/plugin_helper/test_record_accessor.rb passes (63 tests). In parse_bracket_notation, the message should use orig_param, as the other errors there do, because param is only the rest of the key at that point.
• A related but different case: a key that ends with [ or . is accepted without an error, and the end is ignored. $.a[, $.a., $.a.. and $['a'][ all read the key "a", on master, 1.20.1 and 1.16.11. $.a[1 and $.[bad raise "'[' found but ']' not found". In parse_dot_array_op, the loop does not run when nothing follows [, and String#split('.') drops the empty strings at the end. These configurations start today, so making them an error could stop Fluentd after an update; a warning may fit better. I am not asking to change this here, but mention it, as it is next to the code above.
• This was found in fluent/fluent-plugin-rewrite-tag-filter, which reports the broken settings of its rules together at startup. To report this key with the others, it would have to rescue this ArgumentError by its message.