[AGNTLOG-574] Multiline Parser Now Marks Truncation and Enforces 900KB Cap

[angel-ddog]

What does this PR do?

Fixes the MultiLineParser (pkg/logs/internal/decoder/line_parser.go) to properly mark truncation when reassembled log lines exceed the 900KB size cap. Previously, when the buffer hit the limit, sendLine() would flush content with no IsTruncated flag, so downstream handlers had no way to know the log was truncated.

Now the MultiLineParser sets IsTruncated = true on the message when the buffer exceeds lineLimit, and preserves any upstream IsTruncated already set by the framer. SingleLineHandler handles the ...TRUNCATED... byte markers and metric increment downstream — this avoids double-tagging and double-counting.

Motivation

The MultiLineParser (which reassembles single log lines split across transport frames, e.g. Docker 16KB chunks) was missing truncation signaling that MultiLineHandler already had. Affected sources: Docker file/stream, Kubernetes, encoded-text, and integrations parsers.

Describe how you validated your changes

• Updated TestMultilineParserLimit to assert IsTruncated on oversized chunks and verify state resets cleanly
• Verified TestDecoderWithDockerJSONPartialLineDetectionOnlyMarksOversizedLogicalLineTruncated passes (end-to-end Docker JSON partial line truncation)
• Manual QA with local agent build using max_message_size_bytes: 100 and tag_truncated_logs: true

Additional Notes

Design choice: MultiLineParser only sets the boolean flag — no ...TRUNCATED... byte markers or LogsTruncated metric increment. This prevents double-tagging since SingleLineHandler already appends/prepends markers and increments the metric when it sees IsTruncated = true.

[chatgpt-codex-connector]

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[chatgpt-codex-connector]

Avoid flagging exact-limit complete lines as truncated

This new >= check marks the aggregate as truncated even when it only reaches lineLimit. If a parser emits a complete line (IsPartial == false) whose content is exactly at the configured cap, sendLine() now sets IsTruncated=true, so downstream handlers add ...TRUNCATED... and can treat the next line as a continuation. Exact-boundary lines should remain untruncated; truncation should be set only when content exceeds the cap (or when an upstream frame already marked truncation).

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[dd-octo-sts]

Files inventory check summary

File checks results against ancestor 56151085:

Results for datadog-agent_7.80.0~devel.git.61.dbb8d89.pipeline.108615299-1_amd64.deb:

No change detected

[cit-pr-commenter-54b7da]

Regression Detector

Regression Detector Results

Metrics dashboard
Target profiles
Run ID: d9b5d97b-348d-46e3-9c1e-744a776e2735

Baseline: ef638b5
Comparison: 6cd55da
Diff

Optimization Goals: ✅ No significant changes detected

Experiments ignored for regressions

Regressions in experiments with settings containing erratic: true are ignored.

perf	experiment	goal	Δ mean %	Δ mean % CI	trials	links
➖	docker_containers_cpu	% cpu utilization	+1.57	[-1.45, +4.59]	1	Logs

Fine details of change detection per experiment

perf	experiment	goal	Δ mean %	Δ mean % CI	trials	links
➖	quality_gate_logs	% cpu utilization	+2.57	[+0.90, +4.25]	1	Logs bounds checks dashboard
➖	docker_containers_cpu	% cpu utilization	+1.57	[-1.45, +4.59]	1	Logs
➖	quality_gate_metrics_logs	memory utilization	+1.07	[+0.84, +1.31]	1	Logs bounds checks dashboard
➖	quality_gate_idle_all_features	memory utilization	+0.52	[+0.49, +0.55]	1	Logs bounds checks dashboard
➖	docker_containers_memory	memory utilization	+0.49	[+0.41, +0.57]	1	Logs
➖	otlp_ingest_metrics	memory utilization	+0.25	[+0.09, +0.40]	1	Logs
➖	otlp_ingest_logs	memory utilization	+0.23	[+0.12, +0.33]	1	Logs
➖	ddot_metrics	memory utilization	+0.22	[+0.05, +0.40]	1	Logs
➖	file_to_blackhole_100ms_latency	egress throughput	+0.04	[-0.08, +0.16]	1	Logs
➖	file_tree	memory utilization	+0.03	[-0.03, +0.09]	1	Logs
➖	file_to_blackhole_1000ms_latency	egress throughput	+0.02	[-0.41, +0.45]	1	Logs
➖	ddot_metrics_sum_cumulativetodelta_exporter	memory utilization	+0.02	[-0.20, +0.24]	1	Logs
➖	file_to_blackhole_0ms_latency	egress throughput	+0.01	[-0.52, +0.53]	1	Logs
➖	tcp_dd_logs_filter_exclude	ingress throughput	+0.00	[-0.10, +0.10]	1	Logs
➖	uds_dogstatsd_to_api_v3	ingress throughput	+0.00	[-0.20, +0.20]	1	Logs
➖	uds_dogstatsd_20mb_12k_contexts_20_senders	memory utilization	-0.00	[-0.07, +0.06]	1	Logs
➖	uds_dogstatsd_to_api	ingress throughput	-0.01	[-0.21, +0.20]	1	Logs
➖	file_to_blackhole_500ms_latency	egress throughput	-0.03	[-0.44, +0.37]	1	Logs
➖	ddot_metrics_sum_delta	memory utilization	-0.20	[-0.38, -0.03]	1	Logs
➖	quality_gate_idle	memory utilization	-0.36	[-0.42, -0.31]	1	Logs bounds checks dashboard
➖	ddot_logs	memory utilization	-0.38	[-0.44, -0.33]	1	Logs
➖	ddot_metrics_sum_cumulative	memory utilization	-0.68	[-0.83, -0.53]	1	Logs
➖	tcp_syslog_to_blackhole	ingress throughput	-0.91	[-1.09, -0.73]	1	Logs

Bounds Checks: ✅ Passed

perf	experiment	bounds_check_name	replicates_passed	observed_value	links
✅	docker_containers_cpu	simple_check_run	10/10	539 ≥ 26
✅	docker_containers_memory	memory_usage	10/10	275.37MiB ≤ 370MiB
✅	docker_containers_memory	simple_check_run	10/10	692 ≥ 26
✅	file_to_blackhole_0ms_latency	memory_usage	10/10	0.19GiB ≤ 1.20GiB
✅	file_to_blackhole_0ms_latency	missed_bytes	10/10	0B = 0B
✅	file_to_blackhole_1000ms_latency	memory_usage	10/10	0.24GiB ≤ 1.20GiB
✅	file_to_blackhole_1000ms_latency	missed_bytes	10/10	0B = 0B
✅	file_to_blackhole_100ms_latency	memory_usage	10/10	0.20GiB ≤ 1.20GiB
✅	file_to_blackhole_100ms_latency	missed_bytes	10/10	0B = 0B
✅	file_to_blackhole_500ms_latency	memory_usage	10/10	0.22GiB ≤ 1.20GiB
✅	file_to_blackhole_500ms_latency	missed_bytes	10/10	0B = 0B
✅	quality_gate_idle	intake_connections	10/10	4 = 4	bounds checks dashboard
✅	quality_gate_idle	memory_usage	10/10	175.45MiB ≤ 181MiB	bounds checks dashboard
✅	quality_gate_idle_all_features	intake_connections	10/10	4 = 4	bounds checks dashboard
✅	quality_gate_idle_all_features	memory_usage	10/10	498.19MiB ≤ 550MiB	bounds checks dashboard
✅	quality_gate_logs	intake_connections	10/10	4 ≤ 6	bounds checks dashboard
✅	quality_gate_logs	memory_usage	10/10	214.97MiB ≤ 220MiB	bounds checks dashboard
✅	quality_gate_logs	missed_bytes	10/10	0B = 0B	bounds checks dashboard
✅	quality_gate_metrics_logs	cpu_usage	10/10	349.22 ≤ 2000	bounds checks dashboard
✅	quality_gate_metrics_logs	intake_connections	10/10	4 ≤ 6	bounds checks dashboard
✅	quality_gate_metrics_logs	memory_usage	10/10	409.05MiB ≤ 475MiB	bounds checks dashboard
✅	quality_gate_metrics_logs	missed_bytes	10/10	0B = 0B	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".

CI Pass/Fail Decision

✅ Passed. All Quality Gates passed.

• quality_gate_logs, bounds check missed_bytes: 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_idle, bounds check intake_connections: 10/10 replicas passed. Gate passed.
• quality_gate_idle, bounds check memory_usage: 10/10 replicas passed. Gate passed.
• quality_gate_metrics_logs, bounds check memory_usage: 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 intake_connections: 10/10 replicas passed. Gate passed.
• quality_gate_metrics_logs, bounds check cpu_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 intake_connections: 10/10 replicas passed. Gate passed.

[angel-ddog]

/merge

[gh-worker-devflow-routing-ef8351]

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2026-04-20 18:34:28 UTC ℹ️ Start processing command /merge

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2026-04-20 18:34:33 UTC ℹ️ MergeQueue: pull request added to the queue

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2026-04-20 19:12:11 UTC ℹ️ MergeQueue: This merge request was merged