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

[angel-ddog]

What does this PR do?

Fixes the MultiLineParser 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 ...TRUNCATED... markers, no IsTruncated flag, and no metric increment.

Now the MultiLineParser:

• Appends ...TRUNCATED... to content when the buffer exceeds lineLimit
• Prepends ...TRUNCATED... on the next continuation fragment
• Sets msg.ParsingExtra.IsTruncated = true on truncated messages
• Increments the LogsTruncated metric

Motivation

The MultiLineParser (which reassembles single log lines split across transport frames, ex. Docker 16KB chunks) was missing truncation enforcement.

Describe how you validated your changes

Unit testing. Updated the existing TestMultilineParserLimit test to assert truncation flags and IsTruncated state on oversized output, including continuation markers and state reset after the truncation sequence.

=== RUN   TestMultilineParser
--- PASS: TestMultilineParser (0.00s)
=== RUN   TestMultilineParserTimeout
--- PASS: TestMultilineParserTimeout (0.00s)
=== RUN   TestMultilineParserLimit
--- PASS: TestMultilineParserLimit (0.00s)
PASS

Manual QA

The MultiLineParser is only used by Docker file/stream parser, Kubernetes parser, encoded-text parser, and integrations parsers. These are sources that split a single logical line across multiple transport frames (like Docker's 16KB chunks). So I couldn't get the truncated:multi-line tag on the Datadog Log Explorer, but the Unit tests do confirm behavior.

Additional Notes

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Static quality checks

✅ Please find below the results from static quality gates
Comparison made with ancestor 1d257f5
📊 Static Quality Gates Dashboard
🔗 SQG Job

Successful checks

Info

	Quality gate	Change	Size (prev → curr → max)
✅	agent_deb_amd64_fips	+4.0 KiB (0.00% increase)	708.203 → 708.207 → 713.900
✅	agent_rpm_amd64_fips	+4.0 KiB (0.00% increase)	708.187 → 708.191 → 713.880
✅	agent_suse_amd64_fips	+4.0 KiB (0.00% increase)	708.187 → 708.191 → 713.880

27 successful checks with minimal change (< 2 KiB)

	Quality gate	Current Size
✅	agent_deb_amd64	751.311 MiB
✅	agent_heroku_amd64	311.713 MiB
✅	agent_rpm_amd64	751.294 MiB
✅	agent_rpm_arm64	729.690 MiB
✅	agent_rpm_arm64_fips	689.650 MiB
✅	agent_suse_amd64	751.294 MiB
✅	agent_suse_arm64	729.690 MiB
✅	agent_suse_arm64_fips	689.650 MiB
✅	docker_agent_amd64	811.581 MiB
✅	docker_agent_arm64	814.782 MiB
✅	docker_agent_jmx_amd64	1002.496 MiB
✅	docker_agent_jmx_arm64	994.476 MiB
✅	docker_cluster_agent_amd64	204.112 MiB
✅	docker_cluster_agent_arm64	218.547 MiB
✅	docker_cws_instrumentation_amd64	7.142 MiB
✅	docker_cws_instrumentation_arm64	6.689 MiB
✅	docker_dogstatsd_amd64	39.274 MiB
✅	docker_dogstatsd_arm64	37.508 MiB
✅	dogstatsd_deb_amd64	29.921 MiB
✅	dogstatsd_deb_arm64	28.070 MiB
✅	dogstatsd_rpm_amd64	29.921 MiB
✅	dogstatsd_suse_amd64	29.921 MiB
✅	iot_agent_deb_amd64	43.445 MiB
✅	iot_agent_deb_arm64	40.480 MiB
✅	iot_agent_deb_armhf	41.232 MiB
✅	iot_agent_rpm_amd64	43.446 MiB
✅	iot_agent_suse_amd64	43.446 MiB

On-wire sizes (compressed)

	Quality gate	Change	Size (prev → curr → max)
✅	agent_deb_amd64	+22.45 KiB (0.01% increase)	174.602 → 174.624 → 178.360
✅	agent_deb_amd64_fips	-17.51 KiB (0.01% reduction)	165.206 → 165.189 → 172.790
✅	agent_heroku_amd64	-4.48 KiB (0.01% reduction)	74.837 → 74.833 → 79.970
✅	agent_rpm_amd64	neutral	177.442 MiB → 181.830
✅	agent_rpm_amd64_fips	+25.7 KiB (0.02% increase)	167.282 → 167.307 → 173.370
✅	agent_rpm_arm64	+17.57 KiB (0.01% increase)	159.383 → 159.400 → 163.060
✅	agent_rpm_arm64_fips	-33.4 KiB (0.02% reduction)	151.232 → 151.199 → 156.170
✅	agent_suse_amd64	neutral	177.442 MiB → 181.830
✅	agent_suse_amd64_fips	+25.7 KiB (0.02% increase)	167.282 → 167.307 → 173.370
✅	agent_suse_arm64	+17.57 KiB (0.01% increase)	159.383 → 159.400 → 163.060
✅	agent_suse_arm64_fips	-33.4 KiB (0.02% reduction)	151.232 → 151.199 → 156.170
✅	docker_agent_amd64	neutral	267.974 MiB → 272.480
✅	docker_agent_arm64	neutral	255.133 MiB → 261.060
✅	docker_agent_jmx_amd64	neutral	336.620 MiB → 341.100
✅	docker_agent_jmx_arm64	+6.13 KiB (0.00% increase)	319.777 → 319.783 → 325.620
✅	docker_cluster_agent_amd64	neutral	71.430 MiB → 72.920
✅	docker_cluster_agent_arm64	neutral	67.052 MiB → 68.220
✅	docker_cws_instrumentation_amd64	neutral	2.999 MiB → 3.330
✅	docker_cws_instrumentation_arm64	neutral	2.729 MiB → 3.090
✅	docker_dogstatsd_amd64	neutral	15.181 MiB → 15.820
✅	docker_dogstatsd_arm64	neutral	14.498 MiB → 14.830
✅	dogstatsd_deb_amd64	+2.91 KiB (0.04% increase)	7.901 → 7.904 → 8.790
✅	dogstatsd_deb_arm64	neutral	6.786 MiB → 7.710
✅	dogstatsd_rpm_amd64	neutral	7.912 MiB → 8.800
✅	dogstatsd_suse_amd64	neutral	7.912 MiB → 8.800
✅	iot_agent_deb_amd64	neutral	11.443 MiB → 13.040
✅	iot_agent_deb_arm64	-2.67 KiB (0.03% reduction)	9.761 → 9.758 → 11.450
✅	iot_agent_deb_armhf	neutral	9.976 MiB → 11.620
✅	iot_agent_rpm_amd64	neutral	11.460 MiB → 13.060
✅	iot_agent_suse_amd64	neutral	11.460 MiB → 13.060

[cit-pr-commenter-54b7da]

Regression Detector

Regression Detector Results

Metrics dashboard
Target profiles
Run ID: f84a4b9b-4b11-4fbf-9355-35876f035cc3

Baseline: 1d257f5
Comparison: e57957f
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	-2.08	[-5.02, +0.86]	1	Logs

Fine details of change detection per experiment

perf	experiment	goal	Δ mean %	Δ mean % CI	trials	links
➖	quality_gate_logs	% cpu utilization	+2.07	[+0.48, +3.65]	1	Logs bounds checks dashboard
➖	otlp_ingest_metrics	memory utilization	+1.02	[+0.86, +1.18]	1	Logs
➖	quality_gate_idle	memory utilization	+0.20	[+0.15, +0.25]	1	Logs bounds checks dashboard
➖	otlp_ingest_logs	memory utilization	+0.05	[-0.04, +0.14]	1	Logs
➖	uds_dogstatsd_20mb_12k_contexts_20_senders	memory utilization	+0.04	[-0.03, +0.11]	1	Logs
➖	file_to_blackhole_0ms_latency	egress throughput	+0.03	[-0.51, +0.56]	1	Logs
➖	file_to_blackhole_100ms_latency	egress throughput	+0.02	[-0.10, +0.15]	1	Logs
➖	uds_dogstatsd_to_api	ingress throughput	+0.01	[-0.19, +0.21]	1	Logs
➖	uds_dogstatsd_to_api_v3	ingress throughput	+0.00	[-0.20, +0.20]	1	Logs
➖	tcp_dd_logs_filter_exclude	ingress throughput	-0.00	[-0.10, +0.10]	1	Logs
➖	file_to_blackhole_1000ms_latency	egress throughput	-0.03	[-0.47, +0.41]	1	Logs
➖	ddot_logs	memory utilization	-0.03	[-0.09, +0.03]	1	Logs
➖	file_to_blackhole_500ms_latency	egress throughput	-0.06	[-0.46, +0.34]	1	Logs
➖	ddot_metrics_sum_cumulativetodelta_exporter	memory utilization	-0.07	[-0.29, +0.16]	1	Logs
➖	ddot_metrics_sum_delta	memory utilization	-0.07	[-0.25, +0.10]	1	Logs
➖	ddot_metrics	memory utilization	-0.10	[-0.29, +0.09]	1	Logs
➖	ddot_metrics_sum_cumulative	memory utilization	-0.16	[-0.30, -0.02]	1	Logs
➖	quality_gate_idle_all_features	memory utilization	-0.19	[-0.23, -0.15]	1	Logs bounds checks dashboard
➖	file_tree	memory utilization	-0.27	[-0.33, -0.22]	1	Logs
➖	docker_containers_memory	memory utilization	-0.42	[-0.50, -0.34]	1	Logs
➖	tcp_syslog_to_blackhole	ingress throughput	-0.98	[-1.18, -0.79]	1	Logs
➖	quality_gate_metrics_logs	memory utilization	-1.31	[-1.54, -1.08]	1	Logs bounds checks dashboard
➖	docker_containers_cpu	% cpu utilization	-2.08	[-5.02, +0.86]	1	Logs

Bounds Checks: ✅ Passed

perf	experiment	bounds_check_name	replicates_passed	observed_value	links
✅	docker_containers_cpu	simple_check_run	10/10	695 ≥ 26
✅	docker_containers_memory	memory_usage	10/10	273.61MiB ≤ 370MiB
✅	docker_containers_memory	simple_check_run	10/10	710 ≥ 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	0.23GiB ≤ 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	0.21GiB ≤ 1.20GiB
✅	file_to_blackhole_500ms_latency	missed_bytes	10/10	0B = 0B
✅	quality_gate_idle	intake_connections	10/10	3 = 3	bounds checks dashboard
✅	quality_gate_idle	memory_usage	10/10	174.80MiB ≤ 181MiB	bounds checks dashboard
✅	quality_gate_idle_all_features	intake_connections	10/10	3 = 3	bounds checks dashboard
✅	quality_gate_idle_all_features	memory_usage	10/10	490.89MiB ≤ 550MiB	bounds checks dashboard
✅	quality_gate_logs	intake_connections	10/10	3 ≤ 6	bounds checks dashboard
✅	quality_gate_logs	memory_usage	10/10	202.11MiB ≤ 220MiB	bounds checks dashboard
✅	quality_gate_logs	missed_bytes	10/10	0B = 0B	bounds checks dashboard
✅	quality_gate_metrics_logs	cpu_usage	10/10	365.54 ≤ 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	395.37MiB ≤ 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_metrics_logs, bounds check missed_bytes: 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 memory_usage: 10/10 replicas passed. Gate passed.
• quality_gate_metrics_logs, 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_idle, 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_idle_all_features, bounds check intake_connections: 10/10 replicas passed. Gate passed.
• quality_gate_idle_all_features, bounds check memory_usage: 10/10 replicas passed. Gate passed.

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Files inventory check summary

File checks results against ancestor 1d257f5d:

Results for datadog-agent_7.79.0~devel.git.570.e57957f.pipeline.106907144-1_amd64.deb:

No change detected