Is the encoding parameter being used as the Documentation states ?

[gadiego92]

Describe the bug

The Official Documentation states regarding the encoding for the tail plugin:

encoding, from_encoding

type	default	version
string	nil (string encoding is ASCII-8BIT)	0.14.0

Specifies the encoding of reading lines.

By default, in_tail emits string value as ASCII-8BIT encoding.

These options change it:

• If encoding is specified, in_tail changes string to encoding.

  This uses Ruby's String#force_encoding.

• If encoding and from_encoding both are specified, in_tail tries to

  encode string from from_encoding to encoding. This uses Ruby's

  String#encode.

source: tail#encoding-from_encoding

I have been checking Fluentd source code and:

1. Regarding the first bullet.
   I think encoding parameter is not being used as it states in the Documentation.
   I cannot find the function String#force_encoding using the encoding parameter.
   On the other side I have found the String#force_encoding function with the from_encoding parameter in few places.
   I think line 992 might be wrong:
   https://github.com/fluent/fluentd/blob/74db9477f445ef83384eca6da8d6c2049945d8cd/lib/fluent/plugin/in_tail.rb#L992
   If the Documentation is not wrong the function String#force_encoding should use the encoding value not the from_encoding value.

2. Regarding the second bullet.
   It states the String#encode function is used when from _encoding parameter is set but it seems String#encode is used by default is you set encoding parameter to something different than ASCII-8BIT because from_encoding is set by default to ASCII-8BIT. For example, String#encode is used if you set encoding parameter to UTF-8 but according to the Documentation String#force_encoding should be used when you set the encoding parameter and not String#encode.

To Reproduce

Just start a Fluentd container with GROK plugin.

Then run the command:

td-agent --config /home/td-agent/fluentd.conf

Expected behavior

2023-11-23 15:58:46.005162458 +0100 encoding: {"message":"Zürich","timestamp":"2023-11-22 18:18:09.823+0100"}
2023-11-23 15:58:46.005176717 +0100 encoding: {"message":"Geneva","timestamp":"2023-11-22 18:18:09.823+0100"}

Your Environment

- Fluentd version: 1.11.2
- TD Agent version: 1.11.2
- Operating system: Alma Linux 9
- Kernel version: Linux 5.14.0-284.30.1.el9_2.x86_64 x86_64

Your Configuration

# /home/td-agent/patterns.conf

CUSTOM_LOG_WORKS %{TIMESTAMP_ISO8601:timestamp} %{GREEDYDATA:message}
# HTTPDATE has ä character
# Source: https://github.com/fluent/fluent-plugin-grok-parser/blob/903dfe222984b90c4e1c1151530038d1f242157d/patterns/legacy/grok-patterns#L51
CUSTOM_LOG_FAILS %{HTTPDATE:timestamp} %{NUMBER:response}

# /tmp/encoding-test.log

2023-11-22 18:18:09.823+0100 Testing Zürich
2023-11-22 18:18:09.823+0100 Testing Geneva

# /home/td-agent/fluentd.conf
<source>

  @type tail

  path /tmp/encoding-test.log
  read_from_head true
  encoding UTF-8
  tag encoding

  <parse>

    @type grok

    grok_failure_key grokfailure
    custom_pattern_path /home/td-agent/patterns.conf

    <grok>
       pattern %{CUSTOM_LOG_FAILS:message}
    </grok>

    <grok>
       pattern %{CUSTOM_LOG_WORKS:message}
    </grok>

  </parse>

</source>

<match encoding>

    @type stdout

</match>

Your Error Log

[td-agent@dc60c1c5967e ~]$ /opt/td-agent/bin/fluentd --config /home/td-agent/fluentd.conf
2023-11-23 15:58:45 +0100 [info]: parsing config file is succeeded path="/home/td-agent/fluentd.conf"
2023-11-23 15:58:45 +0100 [info]: gem 'fluent-plugin-elasticsearch' version '4.2.2'
2023-11-23 15:58:45 +0100 [info]: gem 'fluent-plugin-elasticsearch' version '4.1.1'
2023-11-23 15:58:45 +0100 [info]: gem 'fluent-plugin-grok-parser' version '2.6.2'
2023-11-23 15:58:45 +0100 [info]: gem 'fluent-plugin-kafka' version '0.14.1'
2023-11-23 15:58:45 +0100 [info]: gem 'fluent-plugin-prometheus' version '1.8.2'
2023-11-23 15:58:45 +0100 [info]: gem 'fluent-plugin-prometheus_pushgateway' version '0.0.2'
2023-11-23 15:58:45 +0100 [info]: gem 'fluent-plugin-record-modifier' version '2.1.0'
2023-11-23 15:58:45 +0100 [info]: gem 'fluent-plugin-rewrite-tag-filter' version '2.3.0'
2023-11-23 15:58:45 +0100 [info]: gem 'fluent-plugin-s3' version '1.4.0'
2023-11-23 15:58:45 +0100 [info]: gem 'fluent-plugin-systemd' version '1.0.2'
2023-11-23 15:58:45 +0100 [info]: gem 'fluent-plugin-td' version '1.1.0'
2023-11-23 15:58:45 +0100 [info]: gem 'fluent-plugin-webhdfs' version '1.2.5'
2023-11-23 15:58:45 +0100 [info]: gem 'fluentd' version '1.11.2'
2023-11-23 15:58:45 +0100 [info]: Expanded the pattern %{CUSTOM_LOG_FAILS:message} into (?<message>(?<timestamp>(?:(?:(?:0[1-9])|(?:[12][0-9])|(?:3[01])|[1-9]))/(?:\b(?:[Jj]an(?:uary|uar)?|[Ff]eb(?:ruary|ruar)?|[Mm](?:a|ä)?r(?:ch|z)?|[Aa]pr(?:il)?|[Mm]a(?:y|i)?|[Jj]un(?:e|i)?|[Jj]ul(?:y|i)?|[Aa]ug(?:ust)?|[Ss]ep(?:tember)?|[Oo](?:c|k)?t(?:ober)?|[Nn]ov(?:ember)?|[Dd]e(?:c|z)(?:ember)?)\b)/(?:(?>\d\d){1,2}):(?:(?!<[0-9])(?:(?:2[0123]|[01]?[0-9])):(?:(?:[0-5][0-9]))(?::(?:(?:(?:[0-5]?[0-9]|60)(?:[:.,][0-9]+)?)))(?![0-9])) (?:(?:[+-]?(?:[0-9]+)))) (?<response>(?:(?:(?<![0-9.+-])(?>[+-]?(?:(?:[0-9]+(?:\.[0-9]+)?)|(?:\.[0-9]+)))))))
2023-11-23 15:58:45 +0100 [info]: Expanded the pattern %{CUSTOM_LOG_WORKS:message} into (?<message>(?<timestamp>(?:(?>\d\d){1,2})-(?:(?:0?[1-9]|1[0-2]))-(?:(?:(?:0[1-9])|(?:[12][0-9])|(?:3[01])|[1-9]))[T ](?:(?:2[0123]|[01]?[0-9])):?(?:(?:[0-5][0-9]))(?::?(?:(?:(?:[0-5]?[0-9]|60)(?:[:.,][0-9]+)?)))?(?:(?:Z|[+-](?:(?:2[0123]|[01]?[0-9]))(?::?(?:(?:[0-5][0-9])))))?) (?<message>.*))
2023-11-23 15:58:45 +0100 [warn]: 'pos_file PATH' parameter is not set to a 'tail' source.
2023-11-23 15:58:45 +0100 [warn]: this parameter is highly recommended to save the position to resume tailing.
2023-11-23 15:58:45 +0100 [info]: using configuration file: <ROOT>
  <source>
    @type tail
    path "/tmp/encoding-test.log"
    tag "encoding"
    read_from_head true
    encoding "UTF-8"
    <parse>
      @type "grok"
      grok_failure_key "grokfailure"
      custom_pattern_path "/home/td-agent/patterns.conf"
      unmatched_lines
      <grok>
        pattern "%{CUSTOM_LOG_FAILS:message}"
      </grok>
      <grok>
        pattern "%{CUSTOM_LOG_WORKS:message}"
      </grok>
    </parse>
  </source>
  <match encoding>
    @type stdout
  </match>
</ROOT>
2023-11-23 15:58:45 +0100 [info]: starting fluentd-1.11.2 pid=715 ruby="2.7.1"
2023-11-23 15:58:45 +0100 [info]: spawn command to main:  cmdline=["/opt/td-agent/bin/ruby", "-Eascii-8bit:ascii-8bit", "/opt/td-agent/bin/fluentd", "--config", "/home/td-agent/fluentd.conf", "--under-supervisor"]
2023-11-23 15:58:45 +0100 [info]: adding match pattern="encoding" type="stdout"
2023-11-23 15:58:45 +0100 [info]: adding source type="tail"
2023-11-23 15:58:46 +0100 [info]: #0 Expanded the pattern %{CUSTOM_LOG_FAILS:message} into (?<message>(?<timestamp>(?:(?:(?:0[1-9])|(?:[12][0-9])|(?:3[01])|[1-9]))/(?:\b(?:[Jj]an(?:uary|uar)?|[Ff]eb(?:ruary|ruar)?|[Mm](?:a|ä)?r(?:ch|z)?|[Aa]pr(?:il)?|[Mm]a(?:y|i)?|[Jj]un(?:e|i)?|[Jj]ul(?:y|i)?|[Aa]ug(?:ust)?|[Ss]ep(?:tember)?|[Oo](?:c|k)?t(?:ober)?|[Nn]ov(?:ember)?|[Dd]e(?:c|z)(?:ember)?)\b)/(?:(?>\d\d){1,2}):(?:(?!<[0-9])(?:(?:2[0123]|[01]?[0-9])):(?:(?:[0-5][0-9]))(?::(?:(?:(?:[0-5]?[0-9]|60)(?:[:.,][0-9]+)?)))(?![0-9])) (?:(?:[+-]?(?:[0-9]+)))) (?<response>(?:(?:(?<![0-9.+-])(?>[+-]?(?:(?:[0-9]+(?:\.[0-9]+)?)|(?:\.[0-9]+)))))))
2023-11-23 15:58:46 +0100 [info]: #0 Expanded the pattern %{CUSTOM_LOG_WORKS:message} into (?<message>(?<timestamp>(?:(?>\d\d){1,2})-(?:(?:0?[1-9]|1[0-2]))-(?:(?:(?:0[1-9])|(?:[12][0-9])|(?:3[01])|[1-9]))[T ](?:(?:2[0123]|[01]?[0-9])):?(?:(?:[0-5][0-9]))(?::?(?:(?:(?:[0-5]?[0-9]|60)(?:[:.,][0-9]+)?)))?(?:(?:Z|[+-](?:(?:2[0123]|[01]?[0-9]))(?::?(?:(?:[0-5][0-9])))))?) (?<message>.*))
2023-11-23 15:58:46 +0100 [warn]: #0 'pos_file PATH' parameter is not set to a 'tail' source.
2023-11-23 15:58:46 +0100 [warn]: #0 this parameter is highly recommended to save the position to resume tailing.
2023-11-23 15:58:46 +0100 [info]: #0 starting fluentd worker pid=720 ppid=715 worker=0
2023-11-23 15:58:46 +0100 [info]: #0 following tail of /tmp/encoding-test.log
2023-11-23 15:58:46.005131856 +0100 encoding: {"message":"Z��rich","timestamp":"2023-11-22 18:18:09.823+0100"}
2023-11-23 15:58:46.005146527 +0100 encoding: {"message":"Z��rich","timestamp":"2023-11-22 18:18:09.823+0100"}
2023-11-23 15:58:46.005152826 +0100 encoding: {"message":"Z��rich","timestamp":"2023-11-22 18:18:09.823+0100"}
2023-11-23 15:58:46.005157747 +0100 encoding: {"message":"Z��rich","timestamp":"2023-11-22 18:18:09.823+0100"}
2023-11-23 15:58:46.005162458 +0100 encoding: {"message":"Z��rich","timestamp":"2023-11-22 18:18:09.823+0100"}
2023-11-23 15:58:46.005176717 +0100 encoding: {"message":"Geneva","timestamp":"2023-11-22 18:18:09.823+0100"}
2023-11-23 15:58:46 +0100 [info]: #0 fluentd worker is now running worker=0

Additional details

If I set both encoding parameters to UTF-8 I get a warning on the Fluentd logs but the special characters are represented.
I don't know if this is the proper way to represent the special characters since I get a warning. Shouldn't this warning be change to info ?

Configuration

    @type tail
    path "/tmp/encoding-test.log"
    tag "encoding"
    read_from_head true
    from_encoding "UTF-8"
    encoding "UTF-8"

Warning

2023-11-23 14:44:12 +0100 [warn]: #0 fluent/log.rb:348:warn: 'encoding' and 'from_encoding' are same encoding. No effect

Output

2023-11-23 14:44:12.044957269 +0100 encoding: {"message":"Zürich","timestamp":"2023-11-22 18:18:09.823+0100"}
2023-11-23 14:44:12.044962081 +0100 encoding: {"message":"Geneva","timestamp":"2023-11-22 18:18:09.823+0100"}

Documentation not clear or wrong

Another option could be that Fluentd works as expected but the Documentation is not clear enough or it's wrong.

[ashie]

Thanks for your report!
Obviously the documentation is wrong.

• The first bullet is incorrect: When only encoding parameter is set, in_tail tries to convert input string from ASCII-8BIT to encoding
  • Ruby tries to convert the original string from ASCII-8BIT to UTF-8 before converting it to encoding.
• The second bullet is correct.

[gadiego92]

What do you mean when you say the following ?

• Ruby tries to convert the original string from ASCII-8BIT to UTF-8 before converting it to encoding.

Do you mean there are two encoding process ?
If I'm not wrong by default both from_encoding and encoding value is ASCII-8BIT. So by default the encode function is not called.