Guard TCP input debug logging with IsDebug() to halve per-event allocations

[Copilot]

Debugw in the TCP input hot path unconditionally constructs structured log args (including RemoteAddr.String()) for every received packet, even when debug is disabled. This adds ~500 allocations/op on the ingest path.

• Wrap the Debugw call with ctx.Logger.IsDebug(), consistent with the existing pattern used throughout the codebase (kafka client, autodiscover, CEL input, etc.)

if ctx.Logger.IsDebug() {
    ctx.Logger.Debugw(
        "Data received",
        "bytes", len(data),
        "remote_address", metadata.RemoteAddr.String(),
        "truncated", metadata.Truncated)
}

Benchmark results: 1014 → 518 allocs/op (−49%), no throughput regression.

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[mergify]

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[strawgate]

/ai are there other TCP benchmarks which show improvement with this change?

[coderabbitai]

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ℹ️ Recent review info

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📥 Commits

Reviewing files that changed from the base of the PR and between 61c2e9e and f677eb0.

📒 Files selected for processing (1)

• filebeat/input/net/tcp/input.go

🚧 Files skipped from review as they are similar to previous changes (1)

• filebeat/input/net/tcp/input.go

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📝 Walkthrough

Walkthrough

The TCP input Test method now creates the listener with net.ListenConfig{}.Listen(context.Background(), ...) instead of net.Listen(...), adding an explicit context. The "Data received" debug log is wrapped in if ctx.Logger.IsDebug() to avoid argument evaluation when debug logging is disabled. The TCP startup error message text was changed from "Failed to start TCP server: %w" to "failed to start TCP server: %w". Metrics recording, event timestamping, metadata handling, and event emission remain unchanged. No exported/public declarations were modified.

✨ Finishing Touches

📝 Generate docstrings

• Create stacked PR
• Commit on current branch

🧪 Generate unit tests (beta)

• Create PR with unit tests
• Commit unit tests in branch copilot/reduce-per-event-allocations

• 🛠️ Update Documentation: Commit on current branch
• 🛠️ Update Documentation: Create PR

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[elasticmachine]

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