Hoist UTF-8 selection and specialize Timestamp/Duration typed accessors; add regression test and perf baseline

[Fyzu]

Motivation

• Reduce per-field dispatch and avoid repeated JSONWriter.isUTF8() checks by hoisting the UTF-8 selection once per message and enable faster typed runtime encoding.
• Improve runtime-typed encoding for well-known Timestamp and Duration fields by using direct seconds/nanos formatting matching generated encoders and avoid descriptor-based generic WKT dispatch in hot paths.
• Add a regression to ensure repeated Timestamp/Duration arrays serialize identically across all encoder paths and record a Java 25 runtime encode/decode baseline to guide further runtime specialization.

Description

• Hoist UTF-8 selection into TypedMessageSchema.writeFields and change FieldName.writeTo to accept an isUtf8 boolean so callers pass the chosen form once per message.
• Add a boolean utf8 parameter to TypedFieldAccessor.write and update all accessor implementations to use name.writeTo(jw, utf8).
• Introduce typed handling for Timestamp/Duration values and collections by adding writeTimestampValue, writeDurationValue, PresenceTimestampAccessor, PresenceDurationAccessor, RepeatedTimestampAccessor, and RepeatedDurationAccessor, and wire them through TypedFieldAccessorFactory via createPresenceMessageAccessor and createRepeatedMessageAccessor.
• Ensure safe fallback to generic WellKnownTypes.write for non-standard Message implementations and update a few javadocs/comments related to typed accessors and well-known types.
• Add a unit regression repeatedTimestampAndDurationMatchAcrossAllPaths in BuffJsonEncodingRegressionTest and include Java 25 runtime encode/decode baseline artifacts: a measurement report (.md) and CSV results.

Testing

• Ran the project unit test suite (mvn test) and the tests completed successfully, including the new repeatedTimestampAndDurationMatchAcrossAllPaths regression.
• No new benchmark jobs were executed in CI; the PR includes measured JMH baseline artifacts (docs/performance-results/* and docs/java25-runtime-encode-performance.md) for reference.
• Existing automated tests covering protobuf JSON encoding were preserved and passed after the changes.

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Codex Task

[github-actions]

Performance comparison

Workflow and raw JMH artifacts
Commit: e80f7bb

Java 21 performance

Base: ad10fe5 → candidate: e80f7bb
Shared benchmark source: ddb898473de6f0f66081d1bdef7adf18cd447119

Throughput alerts are advisory. Existing allocation budgets are enforced separately.
A timing signal needs at least 10% change and separated JMH 99.9% intervals; otherwise it is inconclusive.
Allocation alerts need both >5% and >16 B/op growth (or >16 B/op from zero).

Benchmark	Base ops/s	Candidate ops/s	Change	Timing	B/op base → candidate	Allocation
simpleCodegenUtf16	10,524,751 ±258,149	10,621,331 ±149,459	+0.9%	inconclusive	295.5 → 295.5	within alert threshold
simpleCodegenUtf8	10,923,849 ±88,253	11,076,167 ±294,085	+1.4%	inconclusive	271.5 → 271.5	within alert threshold
simpleTypedUtf16	6,450,336 ±1,250,305	7,133,990 ±90,270	+10.6%	inconclusive	295.5 → 295.5	within alert threshold
simpleTypedUtf8	7,483,660 ±214,447	7,457,128 ±215,664	-0.4%	inconclusive	271.5 → 271.5	within alert threshold
simpleReflectionUtf16	3,544,336 ±340,150	3,653,461 ±317,299	+3.1%	inconclusive	340.0 → 340.0	within alert threshold
simpleReflectionUtf8	3,880,537 ±32,086	3,700,673 ±326,704	-4.6%	inconclusive	316.0 → 316.0	within alert threshold
complexCodegenUtf16	698,155 ±12,150	698,716 ±7,847	+0.1%	inconclusive	1481.9 → 1481.9	within alert threshold
complexCodegenUtf8	730,587 ±48,018	716,738 ±4,796	-1.9%	inconclusive	1433.9 → 1457.9	within alert threshold
complexTypedUtf16	658,380 ±23,456	647,915 ±12,597	-1.6%	inconclusive	1289.9 → 1289.9	within alert threshold
complexTypedUtf8	673,596 ±4,501	698,535 ±4,167	+3.7%	inconclusive	1265.9 → 1265.9	within alert threshold
complexReflectionUtf16	371,311 ±8,936	377,562 ±2,628	+1.7%	inconclusive	1353.9 → 1353.9	within alert threshold
complexReflectionUtf8	397,916 ±2,319	394,998 ±11,964	-0.7%	inconclusive	1329.9 → 1329.9	within alert threshold
mapCodegenUtf16	101,645 ±3,962	104,495 ±3,174	+2.8%	inconclusive	5025.2 → 5025.3	within alert threshold
mapCodegenUtf8	103,839 ±9,318	101,559 ±4,477	-2.2%	inconclusive	5001.3 → 5001.3	within alert threshold
mapTypedUtf16	75,397 ±6,172	73,923 ±4,418	-2.0%	inconclusive	4805.5 → 4805.6	within alert threshold
mapTypedUtf8	76,050 ±4,781	76,764 ±4,162	+0.9%	inconclusive	4781.6 → 4781.6	within alert threshold
mapReflectionUtf16	48,565 ±1,676	49,431 ±2,801	+1.8%	inconclusive	7634.1 → 7634.0	within alert threshold
mapReflectionUtf8	51,398 ±3,398	50,001 ±848	-2.7%	inconclusive	7610.1 → 7610.1	within alert threshold
structCodegenUtf16	732,411 ±4,441	753,058 ±15,089	+2.8%	inconclusive	735.7 → 735.7	within alert threshold
structCodegenUtf8	710,290 ±13,610	703,799 ±3,314	-0.9%	inconclusive	711.7 → 711.7	within alert threshold
structTypedUtf16	740,686 ±44,751	739,977 ±6,656	-0.1%	inconclusive	735.7 → 735.7	within alert threshold
structTypedUtf8	709,858 ±18,798	692,814 ±18,926	-2.4%	inconclusive	711.7 → 711.7	within alert threshold
structReflectionUtf16	706,195 ±5,312	716,799 ±5,201	+1.5%	inconclusive	735.7 → 735.7	within alert threshold
structReflectionUtf8	670,283 ±6,391	675,229 ±23,056	+0.7%	inconclusive	711.7 → 711.7	within alert threshold
timestampCodegenUtf16	4,192,168 ±125,961	4,273,229 ±18,862	+1.9%	inconclusive	464.0 → 464.0	within alert threshold
timestampCodegenUtf8	4,555,874 ±35,002	4,551,910 ±19,672	-0.1%	inconclusive	440.0 → 440.0	within alert threshold
timestampTypedUtf16	3,471,225 ±81,448	3,769,463 ±43,491	+8.6%	inconclusive	464.0 → 464.0	within alert threshold
timestampTypedUtf8	3,696,916 ±66,703	4,005,862 ±33,470	+8.4%	inconclusive	440.0 → 440.0	within alert threshold
timestampReflectionUtf16	2,617,309 ±26,866	2,604,524 ±6,940	-0.5%	inconclusive	464.0 → 464.0	within alert threshold
timestampReflectionUtf8	2,720,237 ±118,686	2,785,666 ±29,537	+2.4%	inconclusive	440.0 → 440.0	within alert threshold

Java 25 performance

Base: ad10fe5 → candidate: e80f7bb
Shared benchmark source: ddb898473de6f0f66081d1bdef7adf18cd447119

Throughput alerts are advisory. Existing allocation budgets are enforced separately.
A timing signal needs at least 10% change and separated JMH 99.9% intervals; otherwise it is inconclusive.
Allocation alerts need both >5% and >16 B/op growth (or >16 B/op from zero).

Benchmark	Base ops/s	Candidate ops/s	Change	Timing	B/op base → candidate	Allocation
simpleCodegenUtf16	13,118,749 ±1,586,071	12,557,705 ±588,887	-4.3%	inconclusive	295.5 → 295.5	within alert threshold
simpleCodegenUtf8	16,177,686 ±1,660,980	16,749,920 ±89,915	+3.5%	inconclusive	271.5 → 271.5	within alert threshold
simpleTypedUtf16	10,786,153 ±1,043,315	10,309,971 ±1,136,207	-4.4%	inconclusive	295.5 → 295.5	within alert threshold
simpleTypedUtf8	10,571,036 ±1,377,098	12,122,861 ±442,342	+14.7%	inconclusive	271.5 → 271.5	within alert threshold
simpleReflectionUtf16	5,276,987 ±309,030	5,803,090 ±267,011	+10.0%	inconclusive	340.0 → 340.0	within alert threshold
simpleReflectionUtf8	5,992,004 ±342,975	6,157,083 ±347,784	+2.8%	inconclusive	316.0 → 316.0	within alert threshold
complexCodegenUtf16	1,063,763 ±105,648	1,083,825 ±18,229	+1.9%	inconclusive	1481.9 → 1481.9	within alert threshold
complexCodegenUtf8	1,207,612 ±8,568	1,196,020 ±92,869	-1.0%	inconclusive	1457.9 → 1457.9	within alert threshold
complexTypedUtf16	1,054,163 ±65,797	1,105,327 ±27,044	+4.9%	inconclusive	1289.9 → 1289.9	within alert threshold
complexTypedUtf8	1,157,791 ±11,565	1,156,285 ±67,695	-0.1%	inconclusive	1265.9 → 1265.9	within alert threshold
complexReflectionUtf16	669,442 ±57,182	698,211 ±6,561	+4.3%	inconclusive	1353.9 → 1353.9	within alert threshold
complexReflectionUtf8	715,658 ±37,198	701,358 ±48,673	-2.0%	inconclusive	1329.9 → 1329.9	within alert threshold
mapCodegenUtf16	167,580 ±1,159	167,006 ±2,158	-0.3%	inconclusive	4589.5 → 4589.5	within alert threshold
mapCodegenUtf8	160,430 ±11,155	170,239 ±4,259	+6.1%	inconclusive	4565.5 → 4565.5	within alert threshold
mapTypedUtf16	129,449 ±8,420	134,331 ±2,195	+3.8%	inconclusive	4805.5 → 4805.5	within alert threshold
mapTypedUtf8	143,170 ±3,369	142,421 ±7,042	-0.5%	inconclusive	4781.5 → 4781.5	within alert threshold
mapReflectionUtf16	87,772 ±4,045	83,325 ±9,189	-5.1%	inconclusive	7634.1 → 7634.1	within alert threshold
mapReflectionUtf8	88,346 ±1,971	85,708 ±7,451	-3.0%	inconclusive	7610.1 → 7610.1	within alert threshold
structCodegenUtf16	750,893 ±23,094	748,362 ±34,444	-0.3%	inconclusive	735.7 → 735.7	within alert threshold
structCodegenUtf8	762,038 ±7,642	756,872 ±3,464	-0.7%	inconclusive	711.7 → 711.7	within alert threshold
structTypedUtf16	743,061 ±54,784	748,861 ±58,241	+0.8%	inconclusive	735.7 → 735.7	within alert threshold
structTypedUtf8	752,760 ±33,540	757,077 ±12,555	+0.6%	inconclusive	711.7 → 711.7	within alert threshold
structReflectionUtf16	743,233 ±20,202	715,432 ±56,228	-3.7%	inconclusive	735.7 → 735.7	within alert threshold
structReflectionUtf8	746,101 ±12,439	717,819 ±66,698	-3.8%	inconclusive	711.7 → 711.7	within alert threshold
timestampCodegenUtf16	5,898,912 ±512,835	5,877,493 ±416,266	-0.4%	inconclusive	464.0 → 464.0	within alert threshold
timestampCodegenUtf8	6,171,915 ±287,104	6,120,851 ±170,957	-0.8%	inconclusive	440.0 → 440.0	within alert threshold
timestampTypedUtf16	5,405,782 ±485,355	5,844,804 ±99,141	+8.1%	inconclusive	464.0 → 464.0	within alert threshold
timestampTypedUtf8	6,535,873 ±259,808	5,916,549 ±402,825	-9.5%	inconclusive	440.0 → 440.0	within alert threshold
timestampReflectionUtf16	4,292,367 ±35,377	4,153,841 ±413,081	-3.2%	inconclusive	464.0 → 464.0	within alert threshold
timestampReflectionUtf8	4,829,771 ±89,879	4,740,780 ±355,300	-1.8%	inconclusive	440.0 → 440.0	within alert threshold