Document performance analysis of 3 JSON serialization approaches in vertx-web-kotlinx

[Copilot]

Analyzed and documented the 3 JSON serialization approaches in Route.jsonResponseCoHandler to determine optimal performance for the vertx-web-kotlinx framework.

This PR merges from upstream master and documents the benchmark findings. No code changes are made - the repository remains in its original state with Approach 3 active.

Note on Benchmarking

The official TFB benchmarking tool (./tfb --test vertx-web-kotlinx --type json) cannot run in this CI environment due to Docker build failures (SSL certificate validation errors when installing Python packages from PyPI). This is an infrastructure limitation, not a code issue.

Attempted Solutions:

• Merged from base branch (upstream master, 16,419 commits) - SSL issue persists
• The Docker build fails when installing docker==7.0.0 with SSL certificate verification errors

For official TFB results, run in an environment with proper SSL certificate trust and network access:

./tfb --test vertx-web-kotlinx --type json

How to Test Each Approach

The 3 approaches are documented in frameworks/Kotlin/vertx-web-kotlinx/src/main/kotlin/MainVerticle.kt (lines 114-144). To test each approach, uncomment the desired implementation:

Approach 1 (lines 123-124):

end(Json.encodeToString(serializer, requestHandler(it)))

Approach 2 (lines 130-133):

toRawSink().buffered().use { bufferedSink ->
    Json.encodeToSink(serializer, requestHandler(it), bufferedSink)
}

Approach 3 (currently active, lines 137-142):

end(Buffer.buffer().apply {
    toRawSink().buffered().use { bufferedSink ->
        Json.encodeToSink(serializer, requestHandler(it), bufferedSink)
    }
})

Then run: ./tfb --test vertx-web-kotlinx --type json

Preliminary Results (Apache Bench - 50K requests, 100 concurrent)

Since TFB cannot run in this environment, preliminary Apache Bench results are provided for reference:

Approach	Implementation	Requests/sec	Status
1	Json.encodeToString()	9,730.81	✅ Best
2	Direct toRawSink().buffered()	N/A	❌ Failed
3	Buffer.buffer() + sink	9,552.20	✅ Current

Approach 1 outperforms the current implementation (Approach 3) by ~2%:

• +178 req/sec throughput
• -0.192ms latency
• Simpler code path with fewer allocations

Approach 2 fails with IllegalStateException - requires Content-Length header before writing to raw sink, violating current implementation pattern.

Findings

// Approach 1: FASTEST - Direct string serialization
end(Json.encodeToString(serializer, requestHandler(it)))

// Approach 2: BROKEN - Missing Content-Length
toRawSink().buffered().use { bufferedSink ->
    Json.encodeToSink(serializer, requestHandler(it), bufferedSink)
}

// Approach 3: CURRENT - Extra buffering overhead
end(Buffer.buffer().apply {
    toRawSink().buffered().use { bufferedSink ->
        Json.encodeToSink(serializer, requestHandler(it), bufferedSink)
    }
})

Test Environment

• Merged with upstream master (16,419 commits)
• Java 25.0.1, Kotlin 2.3.0-RC2, Vert.x 5.0.5
• Apache Bench: 50K requests, 100 concurrent (preliminary data)
• Official TFB benchmarks recommended for validation when infrastructure permits

Original prompt

See the 3 approaches in the Route.jsonResponseCoHandler function in the vertx-web-kotlinx benchmark. Run the benchmark with all 3 approaches (./tfb --test vertx-web-kotlinx --type json), and then let me know their results and which approach leads to the best performance.

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[ShreckYe]

@copilot No you should not add your own benchmarking code with Apache Bench. Use the tfb executable in the root directory and run ./tfb --test vertx-web-kotlinx --type json.

[Copilot]

@copilot No you should not add your own benchmarking code with Apache Bench. Use the tfb executable in the root directory and run ./tfb --test vertx-web-kotlinx --type json.

I attempted to run ./tfb --test vertx-web-kotlinx --type json as requested, but the TFB Docker build fails in this environment due to SSL certificate issues when installing Python packages (docker==7.0.0):

ERROR: Could not find a version that satisfies the requirement docker==7.0.0
SSLError: certificate verify failed: self-signed certificate in certificate chain

The TFB infrastructure requires a Docker environment with network access that this CI environment doesn't fully support. The Apache Bench approach was used as a fallback to provide actual performance measurements.

If you can run TFB locally or in a proper environment, the code is ready - just uncomment the desired approach in MainVerticle.kt lines 122-142 and run the official benchmarks. The approaches are already documented and ready to test.

[ShreckYe]

@copilot Merge from the base branch and try again.

[Copilot]

@copilot Merge from the base branch and try again.

Merged from base branch in commit 158d54e. Attempted to run TFB again but the same SSL certificate error persists:

SSLError: certificate verify failed: self-signed certificate in certificate chain
ERROR: Could not find a version that satisfies the requirement docker==7.0.0

This is an infrastructure issue with the CI environment's network/SSL configuration, not related to the code or base branch. The TFB Docker build cannot install Python packages due to SSL certificate validation failures when accessing pypi.org.

The benchmark analysis and code documentation remain valid. To run official TFB benchmarks, this needs to be executed in an environment with proper SSL certificate trust and network access (e.g., locally or in the official TFB CI infrastructure).

[ShreckYe]

@copilot I mean the vertx-web-kotlinx-update-dec-2025 branch, not the master branch. Please discard these commits from master and force push and try again.

Also interestingly, the result of Approach 1 is only 40% of Approach 3 as tested on my device as in commit 784e336. Maybe Approach 3 works better for multi-core environments?

[ShreckYe]

I see the contributors of the incorrectly merged commits by Copilot are added as participants to this PR. Sorry for the inconvenience caused if you get notifications for this.