Backport PR #16968 to 8.17: Fix BufferedTokenizer to properly resume after a buffer full condition respecting the encoding of the input string

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Backport PR #16968 to 8.17 branch, original message:

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Release notes

[rn:skip]

What does this PR do?

This is a second take to fix the processing of tokens from the tokenizer after a buffer full error. The first try #16482 was rollbacked to the encoding error #16694.
The first try failed on returning the tokens in the same encoding of the input.
This PR does a couple of things:

• accumulates the tokens, so that after a full condition can resume with the next tokens after the offending one.
• respect the encoding of the input string. Use concat method instead of addAll, which avoid to convert RubyString to String and back to RubyString. When return the head StringBuilder it enforce the encoding with the input charset.

Why is it important/What is the impact to the user?

Permit to use effectively the tokenizer also in context where a line is bigger than a limit.

Checklist

• My code follows the style guidelines of this project
• I have commented my code, particularly in hard-to-understand areas
• [ ] I have made corresponding changes to the documentation
• [ ] I have made corresponding change to the default configuration files (and/or docker env variables)
• I have added tests that prove my fix is effective or that my feature works

Author's Checklist

• [ ]

How to test this PR locally

The test plan has two sides:

• one to check that the behaviour of size limiting acts as expected. In such case follow the instructions in BufferedTokenizer doesn't dice correctly the payload when restart processing after buffer full error #16483.
• the other to verify the encoding is respected.

How to test the encoding is respected

Startup a REPL with Logstash and exercise the tokenizer:

$> bin/logstash -i irb
> buftok = FileWatch::BufferedTokenizer.new
> buftok.extract("\xA3".force_encoding("ISO8859-1")); buftok.flush.bytes

or use the following script

require 'socket'

hostname = 'localhost'
port = 1234

socket = TCPSocket.open(hostname, port)

text = "\xA3" # the £ symbol in ISO-8859-1 aka Latin-1
text.force_encoding("ISO-8859-1")
socket.puts(text)

socket.close

with the Logstash run as

bin/logstash -e "input { tcp { port => 1234 codec => line { charset => 'ISO8859-1' } } } output { stdout { codec => rubydebug } }"

In the output the £ as to be present and not £

Related issues

• Closes Character encoding issues with refactored BufferedTokenizerExt #16694
• Relates Bugfix for BufferedTokenizer to completely consume lines in case of lines bigger then sizeLimit #16482
• Relates BufferedTokenizer doesn't dice correctly the payload when restart processing after buffer full error #16483

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Quality Gate passed

Issues
0 New issues
0 Fixed issues
0 Accepted issues

Measures
0 Security Hotspots
No data about Coverage
0.0% Duplication on New Code

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