Backport PR #16313 to 8.14: Json normalization performance

[github-actions]

Backport PR #16313 to 8.14 branch, original message:

---

Release notes

• Restores performance of JSON-encoding operation by deferring an encoding operation and reducing unnecessary memory copying

What does this PR do?

• Eliminates wasteful computation when encoding JSON

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

The safety added by 8.14.1's unicode normalization came at the cost of requiring all deeply-nested strings to be encoded to utf-8 prior to being passed to jrjackson, but separate upstream fixes in jrjackson eliminated this need for most cases.

This PR restores some of the lost performance while keeping identical behaviour. We can chase down the remaining performance gap (which may require a behavior change) in a separate effort.

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

How to test this PR locally

1. export an environment variable containing deeply-nested JSON structure

   export MESSAGE='{"one":{"two":{"three":{"four":{"five":{"six":{"seven":{"eight":{"nine":{"ten":{"eleven":{"twelve":{"thirteen":{"fourteen":{"fifteen":{}}}}}}}}}}}}}}}}'
   

2. use that environment variable as input to a simple logstash pipeline with generator and json codec that invokes LogStash::Json.dump:

   bin/logstash -e 'input { generator { threads => 4 message => "${MESSAGE}" codec => json } } filter { ruby { code => "::LogStash::Json.dump(event.to_hash)" } } output { sink { } }'
   

3. observe throughput:

   watch --color '(curl --silent -XGET http://localhost:9600/_node/stats | jq --color-output "pick(.process, .flow)")'
   

   On my M3 laptop, this translated to:

   scenario	valid utf-8	preserved utf-8	throughput	cpu
   no normalization (8.13.x)	⚠️	✅	440k eps	48%
   pre-normalization (8.14.2)	✅	✅	270k eps	62%
   jackson normalization (8.14.2)	✅	⚠️	440k eps	49%
   filtered pre-normalization (POC)	✅	✅	320k eps	57%
   reduced copy pre-normalization (this PR)	✅	✅	360k eps	55%

   • valid utf-8:
     • ✅ : output is always valid UTF-8, a pre-requisite for being valid JSON
     • ⚠️ : when inputs are non-UTF-8 or invalid-UTF-8, output can be corrupt
   • preserved utf-8:
     • ✅ : valid UTF-8 sequences in binary-flagged strings are preserved
     • ⚠️ : each byte in a valid multibyte UTF-8 sequences in binary-flagged strings is replaced with the unicode replacement character (lossy)

[yaauie]

I've converted this 8.14 backport to a draft so that we can be intentional about merging it.

• If a BC2 for 8.14.3 is planned: then this should be merged and DRA staging should be kicked off to include it
• Else if 8.14.4 is planned: then this PR should be merged after 8.14.3 is tagged
• Else this PR should be closed unmerged.

[elastic-sonarqube]

Quality Gate passed

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[elasticmachine]

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