APM: harden trace-agent against nil entries in malformed payloads

[ajgajg1134]

What does this PR do?

Follow-up to #53687. Prevents trace-agent crashes when a decoded trace payload contains nil pointers — nil spans, span links, span events, or nil span-event attribute values — which otherwise reach the processing pipeline and panic on a nil dereference.

Fixes span the full ingest → convert → process → serialize path:

• ConvertToIdx / traceChunksFromSpans: drop nil chunks, all-nil-span chunks, nil spans, nil links, nil events, and nil attribute values (via append) instead of leaving nil slots or dereferencing them.
• Converted-msgpack decoders (InternalTraceChunk/InternalSpan UnmarshalMsgConverted): drop nil span/link/event entries instead of storing them, keeping the wire buffer aligned.
• V0 Process pipeline: stripNilSpans compacts nil spans (and nil link/event entries) at one chokepoint before GetRoot; discardSpans guards nil.
• normalizeTraceChunkV1: compact nil spans in place (was skip-only) so GetRootV1/ReplaceV1/serialization never see a nil span.
• obfuscateSpanEvent / replaceAttributeAnyValue: guard nil attribute values.
• Receiver first-span lookup: both firstService closures now use the nil-safe getFirstSpan/getFirstSpanV1 helpers.

Motivation

While unlikely with well-behaved tracers, malformed msgpack/JSON payloads (e.g. a v0.4 JSON body like [[null]], or a nil msgpack array element) could crash the trace-agent. Some of these paths run in worker goroutines with no recover, so a single malformed payload could take down the whole agent.

Describe how you validated your changes

Added regression tests at the decoder, converter, HTTP endpoint, and Process/ProcessV1 levels — each panics without its corresponding fix. Full suites pass for pkg/trace/agent, pkg/trace/api, pkg/trace/filters, and pkg/proto/pbgo/trace/idx (984 tests, 5 skipped). The changes were reviewed across three independent adversarial review passes.

Additional Notes

Fix strategy is "drop nils at the earliest chokepoint" (decode/convert/normalize) so downstream consumers are safe by construction, rather than scattering per-site nil guards.

🤖 Generated with Claude Code

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[chatgpt-codex-connector]

Skip nil chunks before stripping spans

When convert-traces is disabled, a v0.7/msgpack TracerPayload can still contain a nil chunk: the generated decoder stores nil for nil chunks array elements (pkg/proto/pbgo/trace/tracer_payload_gen.go:469-475). The new nil-safe firstService path lets that payload leave the HTTP handler, but Process then dereferences the chunk here while trying to strip nil spans, so a malformed payload with a nil chunk can panic the worker goroutine instead of being dropped. Guard or remove nil chunks before touching chunk.Spans.

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[datadog-prod-us1-4]

🎯 Code Coverage (details)
• Patch Coverage: 84.87%
• Overall Coverage: 54.14% (+2.39%)

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🔗 Commit SHA: 65289cb | Docs | Datadog PR Page | Give us feedback!}

[dd-octo-sts]

Static quality checks

✅ Please find below the results from static quality gates
Comparison made with ancestor b94c61d
📊 Static Quality Gates Dashboard
🔗 SQG Job
SOME SIZE DELTAS ARE N/A (ANCESTOR METRICS NOT YET AVAILABLE). RETRY JOB

Successful checks

Info

	Quality gate	Change	Size (prev → curr → max)
✅	agent_deb_amd64	N/A	N/A → 749.826 → 758.200
✅	agent_deb_amd64_fips	N/A	N/A → 704.684 → 709.840
✅	agent_heroku_amd64	N/A	N/A → 307.701 → 315.230
✅	agent_rpm_amd64	N/A	N/A → 749.809 → 758.170
✅	agent_rpm_amd64_fips	N/A	N/A → 704.667 → 709.840
✅	agent_rpm_arm64	N/A	N/A → 726.443 → 729.660
✅	agent_rpm_arm64_fips	N/A	N/A → 684.994 → 688.860
✅	agent_suse_amd64	N/A	N/A → 749.809 → 758.170
✅	agent_suse_amd64_fips	N/A	N/A → 704.667 → 709.840
✅	agent_suse_arm64	N/A	N/A → 726.443 → 729.660
✅	agent_suse_arm64_fips	N/A	N/A → 684.994 → 688.860
✅	docker_agent_amd64	N/A	N/A → 808.532 → 813.790
✅	docker_agent_arm64	N/A	N/A → 810.171 → 815.030
✅	docker_agent_jmx_amd64	N/A	N/A → 999.430 → 1004.550
✅	docker_agent_jmx_arm64	N/A	N/A → 989.721 → 994.710
✅	docker_cluster_agent_amd64	N/A	N/A → 209.881 → 210.470
✅	docker_cluster_agent_arm64	N/A	N/A → 222.952 → 222.980
✅	docker_cws_instrumentation_amd64	N/A	N/A → 7.447 → 7.480
✅	docker_cws_instrumentation_arm64	N/A	N/A → 6.877 → 7.110
✅	docker_dogstatsd_amd64	N/A	N/A → 39.216 → 39.910
✅	docker_dogstatsd_arm64	N/A	N/A → 37.367 → 38.270
✅	docker_host_profiler_amd64	N/A	N/A → 303.107 → 317.640
✅	docker_host_profiler_arm64	N/A	N/A → 314.594 → 328.900
✅	dogstatsd_deb_amd64	N/A	N/A → 29.955 → 31.150
✅	dogstatsd_deb_arm64	N/A	N/A → 27.994 → 29.530
✅	dogstatsd_rpm_amd64	N/A	N/A → 29.955 → 31.150
✅	dogstatsd_suse_amd64	N/A	N/A → 29.955 → 31.150
✅	iot_agent_deb_amd64	N/A	N/A → 46.194 → 46.380
✅	iot_agent_deb_arm64	N/A	N/A → 42.882 → 43.720
✅	iot_agent_deb_armhf	N/A	N/A → 43.647 → 43.960
✅	iot_agent_rpm_amd64	N/A	N/A → 46.195 → 46.380
✅	iot_agent_suse_amd64	N/A	N/A → 46.194 → 46.380

[cit-pr-commenter-54b7da]

Regression Detector

Regression Detector Results

Metrics dashboard
Target profiles
Run ID: 4365ec4d-2120-42ed-b021-8e91fa3edb74

Baseline: d310d7d
Comparison: 65289cb
Diff

Optimization Goals: ✅ No significant changes detected

Fine details of change detection per experiment

perf	experiment	goal	Δ mean %	Δ mean % CI	trials	links
➖	quality_gate_logs	% cpu utilization	+1.42	[+0.45, +2.39]	1	Logs bounds checks dashboard
➖	quality_gate_idle	memory utilization	+0.55	[+0.50, +0.60]	1	Logs bounds checks dashboard
➖	quality_gate_metrics_logs	memory utilization	+0.20	[-0.05, +0.46]	1	Logs bounds checks dashboard
➖	quality_gate_security_no_fs_load	memory utilization	+0.05	[-0.05, +0.14]	1	Logs bounds checks dashboard
➖	quality_gate_idle_all_features	memory utilization	+0.04	[-0.02, +0.11]	1	Logs bounds checks dashboard
➖	quality_gate_security_mean_fs_load	memory utilization	+0.02	[-0.01, +0.06]	1	Logs bounds checks dashboard
➖	quality_gate_security_idle	memory utilization	-0.44	[-0.51, -0.37]	1	Logs bounds checks dashboard

Bounds Checks: ✅ Passed

perf	experiment	bounds_check_name	replicates_passed	observed_value	links
✅	quality_gate_idle	intake_connections	10/10	3 ≤ 4	bounds checks dashboard
✅	quality_gate_idle	memory_usage	10/10	146.23MiB ≤ 154MiB	bounds checks dashboard
✅	quality_gate_idle	total_bytes_received	10/10	730.46KiB ≤ 819.20KiB	bounds checks dashboard
✅	quality_gate_idle_all_features	intake_connections	10/10	3 ≤ 4	bounds checks dashboard
✅	quality_gate_idle_all_features	memory_usage	10/10	490.59MiB ≤ 495MiB	bounds checks dashboard
✅	quality_gate_idle_all_features	total_bytes_received	10/10	1.12MiB ≤ 1.25MiB	bounds checks dashboard
✅	quality_gate_logs	intake_connections	10/10	4 ≤ 6	bounds checks dashboard
✅	quality_gate_logs	memory_usage	10/10	181.04MiB ≤ 195MiB	bounds checks dashboard
✅	quality_gate_logs	missed_bytes	10/10	0B = 0B	bounds checks dashboard
✅	quality_gate_logs	total_bytes_received	10/10	264.16MiB ≤ 292MiB	bounds checks dashboard
✅	quality_gate_metrics_logs	cpu_usage	10/10	366.81 ≤ 2000	bounds checks dashboard
✅	quality_gate_metrics_logs	intake_connections	10/10	3 ≤ 6	bounds checks dashboard
✅	quality_gate_metrics_logs	memory_usage	10/10	410.91MiB ≤ 430MiB	bounds checks dashboard
✅	quality_gate_metrics_logs	missed_bytes	10/10	0B = 0B	bounds checks dashboard
✅	quality_gate_metrics_logs	total_bytes_received	10/10	0.94GiB ≤ 1.04GiB	bounds checks dashboard
✅	quality_gate_security_idle	cpu_usage	10/10	32.69 ≤ 100	bounds checks dashboard
✅	quality_gate_security_idle	memory_usage	10/10	300.01MiB ≤ 330MiB	bounds checks dashboard
✅	quality_gate_security_mean_fs_load	cpu_usage	10/10	63.36 ≤ 200	bounds checks dashboard
✅	quality_gate_security_mean_fs_load	memory_usage	10/10	276.06MiB ≤ 310MiB	bounds checks dashboard
✅	quality_gate_security_no_fs_load	cpu_usage	10/10	23.69 ≤ 100	bounds checks dashboard
✅	quality_gate_security_no_fs_load	memory_usage	10/10	278.86MiB ≤ 320MiB	bounds checks dashboard

Explanation

Confidence level: 90.00%
Effect size tolerance: |Δ mean %| ≥ 5.00%

Performance changes are noted in the perf column of each table:

• ✅ = significantly better comparison variant performance
• ❌ = significantly worse comparison variant performance
• ➖ = no significant change in performance

A regression test is an A/B test of target performance in a repeatable rig, where "performance" is measured as "comparison variant minus baseline variant" for an optimization goal (e.g., ingress throughput). Due to intrinsic variability in measuring that goal, we can only estimate its mean value for each experiment; we report uncertainty in that value as a 90.00% confidence interval denoted "Δ mean % CI".

For each experiment, we decide whether a change in performance is a "regression" -- a change worth investigating further -- if all of the following criteria are true:

1. Its estimated |Δ mean %| ≥ 5.00%, indicating the change is big enough to merit a closer look.

2. Its 90.00% confidence interval "Δ mean % CI" does not contain zero, indicating that if our statistical model is accurate, there is at least a 90.00% chance there is a difference in performance between baseline and comparison variants.

3. Its configuration does not mark it "erratic".

Replicate Execution Details

We run multiple replicates for each experiment/variant. However, we allow replicates to be automatically retried if there are any failures, up to 8 times, at which point the replicate is marked dead and we are unable to run analysis for the entire experiment. We call each of these attempts at running replicates a replicate execution. This section lists all replicate executions that failed due to the target crashing or being oom killed.

Note: In the below tables we bucket failures by experiment, variant, and failure type. For each of these buckets we list out the replicate indexes that failed with an annotation signifying how many times said replicate failed with the given failure mode. In the below example the baseline variant of the experiment named experiment_with_failures had two replicates that failed by oom kills. Replicate 0, which failed 8 executions, and replicate 1 which failed 6 executions, all with the same failure mode.

Experiment	Variant	Replicates	Failure	Logs	Debug Dashboard
experiment_with_failures	baseline	0 (x8) 1 (x6)	Oom killed		Debug Dashboard

The debug dashboard links will take you to a debugging dashboard specifically designed to investigate replicate execution failures.

❌ Retried Profiling Replicate Execution Failures (ddprof)

Note: Profiling replicas may still be executing. See the debug dashboard for up to date status.

Experiment	Variant	Replicates	Failure	Debug Dashboard
quality_gate_idle	baseline	10	Oom killed	Debug Dashboard
quality_gate_idle	comparison	10	Oom killed	Debug Dashboard
quality_gate_idle_all_features	baseline	10	Oom killed	Debug Dashboard
quality_gate_idle_all_features	comparison	10	Oom killed	Debug Dashboard
quality_gate_logs	baseline	10	Oom killed	Debug Dashboard
quality_gate_logs	comparison	10	Oom killed	Debug Dashboard
quality_gate_metrics_logs	baseline	10	Oom killed	Debug Dashboard
quality_gate_metrics_logs	comparison	10	Oom killed	Debug Dashboard
quality_gate_security_idle	comparison	10	Crashed (exit code: 134)	Debug Dashboard
quality_gate_security_mean_fs_load	comparison	10	Crashed (exit code: 134)	Debug Dashboard
quality_gate_security_no_fs_load	baseline	10	Crashed (exit code: 134)	Debug Dashboard
quality_gate_security_no_fs_load	comparison	10	Oom killed	Debug Dashboard

CI Pass/Fail Decision

✅ Passed. All Quality Gates passed.

• quality_gate_security_no_fs_load, bounds check memory_usage: 10/10 replicas passed. Gate passed.
• quality_gate_security_no_fs_load, bounds check cpu_usage: 10/10 replicas passed. Gate passed.
• quality_gate_idle, bounds check memory_usage: 10/10 replicas passed. Gate passed.
• quality_gate_idle, bounds check intake_connections: 10/10 replicas passed. Gate passed.
• quality_gate_idle, bounds check total_bytes_received: 10/10 replicas passed. Gate passed.
• quality_gate_metrics_logs, bounds check cpu_usage: 10/10 replicas passed. Gate passed.
• quality_gate_metrics_logs, bounds check intake_connections: 10/10 replicas passed. Gate passed.
• quality_gate_metrics_logs, bounds check missed_bytes: 10/10 replicas passed. Gate passed.
• quality_gate_metrics_logs, bounds check total_bytes_received: 10/10 replicas passed. Gate passed.
• quality_gate_metrics_logs, bounds check memory_usage: 10/10 replicas passed. Gate passed.
• quality_gate_idle_all_features, bounds check memory_usage: 10/10 replicas passed. Gate passed.
• quality_gate_idle_all_features, bounds check total_bytes_received: 10/10 replicas passed. Gate passed.
• quality_gate_idle_all_features, bounds check intake_connections: 10/10 replicas passed. Gate passed.
• quality_gate_logs, bounds check memory_usage: 10/10 replicas passed. Gate passed.
• quality_gate_logs, bounds check intake_connections: 10/10 replicas passed. Gate passed.
• quality_gate_logs, bounds check missed_bytes: 10/10 replicas passed. Gate passed.
• quality_gate_logs, bounds check total_bytes_received: 10/10 replicas passed. Gate passed.
• quality_gate_security_mean_fs_load, bounds check memory_usage: 10/10 replicas passed. Gate passed.
• quality_gate_security_mean_fs_load, bounds check cpu_usage: 10/10 replicas passed. Gate passed.
• quality_gate_security_idle, bounds check cpu_usage: 10/10 replicas passed. Gate passed.
• quality_gate_security_idle, bounds check memory_usage: 10/10 replicas passed. Gate passed.