Add msgpack-jackson3 module for Jackson 3.x support

[komamitsu]

Summary

• Adds a new msgpack-jackson3 submodule (jackson-dataformat-msgpack3) that ports the existing Jackson 2.x integration to Jackson 3.x (tools.jackson namespace)
• Requires Java 17+ and Jackson 3.1.2; the module is excluded from the build on older JDKs so existing Java 8 users are unaffected
• Includes JMH benchmarks (src/jmh/java) runnable via ./sbt "msgpack-jackson3/jmh:run"

Key differences from msgpack-jackson

• Package namespace: com.fasterxml.jackson → tools.jackson
• TokenStreamLocation replaces JsonLocation; byte offset passed as columnNr (truncates for inputs > 2 GB)
• SimpleStreamWriteContext used for write-context tracking; _verifyValueWrite / writeName checks aligned with CBORGenerator pattern
• MessagePackFactory.snapshot() now delegates to copy() and rebuild() is implemented via MessagePackFactoryBuilder
• MessagePackSerializedString: all append*, put*, write* methods fully implemented
• MessagePackGenerator.close() correctly sets isClosed() via super.close(); _releaseBuffers() releases the cached OutputStream reference
• MessagePackParser: byte-array sources always reset the unpacker on reuse; ThreadLocal cleared on close to prevent memory leaks
• MessagePackFactory._createParser(byte[], int, int): uses ArrayBufferInput(data, offset, len) directly — no unnecessary copy
• ByteBuffer serialization: uses bb.arrayOffset() + bb.position() for array-backed buffers; bb.duplicate().get(data) for direct buffers to avoid advancing the caller's position
• MessagePackFactoryBuilder: extTypeCustomDesers deep-copied via copy constructor so rebuilt factories have independent state
• JavaInfo / char-array optimization removed — always false on Java 17+ since String.value is byte[]
• OSGi importPackage excludes android.os and sun.* matching msgpack-core

Test plan

• ./sbt "msgpack-jackson3/test" — 95 tests pass
• ./sbt "msgpack-jackson3/jmh:compile" — JMH benchmarks compile cleanly
• Existing msgpack-core and msgpack-jackson tests unaffected

[komamitsu]

/gemini review

[Copilot]

Pull request overview

Adds a new Jackson 3.x integration module (msgpack-jackson3 / jackson-dataformat-msgpack3) targeting Java 17+, alongside build/CI updates to keep existing Java 8+ users unaffected.

Changes:

• Introduces msgpack-jackson3 implementation of MessagePack TokenStreamFactory, parser, generator, and mapper using the tools.jackson.* APIs.
• Adds a Jackson 3.x test suite and JMH benchmarks for read/write performance comparisons.
• Updates SBT build/CI to conditionally include/test the new module only on Java 17+ and adds the SBT JMH plugin.

Reviewed changes

Copilot reviewed 37 out of 38 changed files in this pull request and generated no comments.

Show a summary per file

File	Description
project/plugins.sbt	Adds sbt-jmh plugin required for the new module’s JMH benchmarks.
plans/preexisting-issues.md	Documents preexisting issues found during the port and their fix status.
build.sbt	Adds msgpack-jackson3 subproject with Java 17 toolchain settings and conditional aggregation.
.github/workflows/CI.yml	Ensures CI includes msgpack-jackson3 changes and skips its tests on JDK < 17.
msgpack-jackson3/src/main/java/org/msgpack/jackson/dataformat/Tuple.java	Adds tuple helper used for parser resource reuse.
msgpack-jackson3/src/main/java/org/msgpack/jackson/dataformat/TimestampExtensionModule.java	Ports timestamp extension module to Jackson 3.x APIs.
msgpack-jackson3/src/main/java/org/msgpack/jackson/dataformat/PackageVersion.java	Defines module version metadata for Jackson Versioned.
msgpack-jackson3/src/main/java/org/msgpack/jackson/dataformat/MessagePackSerializerFactory.java	Jackson 3 serializer factory override for map key serialization.
msgpack-jackson3/src/main/java/org/msgpack/jackson/dataformat/MessagePackSerializedString.java	Implements SerializableString utilities used for efficient key handling.
msgpack-jackson3/src/main/java/org/msgpack/jackson/dataformat/MessagePackReadContext.java	Implements read-context tracking compatible with Jackson 3 token/location APIs.
msgpack-jackson3/src/main/java/org/msgpack/jackson/dataformat/MessagePackParser.java	Implements MessagePack-to-Jackson token parsing, including reuse/memory-leak fixes.
msgpack-jackson3/src/main/java/org/msgpack/jackson/dataformat/MessagePackMapper.java	Adds ObjectMapper wrapper/builder for MessagePack with Jackson 3.x.
msgpack-jackson3/src/main/java/org/msgpack/jackson/dataformat/MessagePackKeySerializer.java	Serializes map keys through MessagePackSerializedString.
msgpack-jackson3/src/main/java/org/msgpack/jackson/dataformat/MessagePackGenerator.java	Implements Jackson 3 generator behavior with node buffering and updated write-context rules.
msgpack-jackson3/src/main/java/org/msgpack/jackson/dataformat/MessagePackFactoryBuilder.java	Implements builder-based factory rebuild support for Jackson 3.x.
msgpack-jackson3/src/main/java/org/msgpack/jackson/dataformat/MessagePackFactory.java	Ports factory to Jackson 3 BinaryTSFactory and updates parser creation paths.
msgpack-jackson3/src/main/java/org/msgpack/jackson/dataformat/MessagePackExtensionType.java	Defines extension type wrapper and serializer integration.
msgpack-jackson3/src/main/java/org/msgpack/jackson/dataformat/JsonArrayFormat.java	Adds array-shape introspector used for schema-less/0.6-style serialization.
msgpack-jackson3/src/main/java/org/msgpack/jackson/dataformat/ExtensionTypeCustomDeserializers.java	Provides extension-type deserializer registry with copy-constructor support.
msgpack-jackson3/src/test/java/org/msgpack/jackson/dataformat/TimestampExtensionModuleTest.java	Tests timestamp extension serialization/deserialization and format sizes.
msgpack-jackson3/src/test/java/org/msgpack/jackson/dataformat/MessagePackParserTest.java	Comprehensive parser compatibility and regression tests (incl. byte[] reuse behavior).
msgpack-jackson3/src/test/java/org/msgpack/jackson/dataformat/MessagePackMapperTest.java	Tests BigInteger/BigDecimal “as string” configuration behavior.
msgpack-jackson3/src/test/java/org/msgpack/jackson/dataformat/MessagePackGeneratorTest.java	Comprehensive generator tests + multiple regressions (close/state, offsets, contexts).
msgpack-jackson3/src/test/java/org/msgpack/jackson/dataformat/MessagePackFactoryTest.java	Tests copy(), snapshot(), rebuild() behavior and config copying semantics.
msgpack-jackson3/src/test/java/org/msgpack/jackson/dataformat/MessagePackDataformatTestBase.java	Shared test fixtures for mapper/parser/generator tests.
msgpack-jackson3/src/test/java/org/msgpack/jackson/dataformat/MessagePackDataformatForPojoTest.java	POJO round-trip tests and JsonArrayFormat schema-less behavior.
msgpack-jackson3/src/test/java/org/msgpack/jackson/dataformat/MessagePackDataformatForFieldIdTest.java	Tests mixed integer/string map keys with supportIntegerKeys.
msgpack-jackson3/src/test/java/org/msgpack/jackson/dataformat/ExampleOfTypeInformationSerDe.java	Demonstrates type metadata serde example under Jackson 3.x.
msgpack-jackson3/src/jmh/java/org/msgpack/jackson/dataformat/benchmark/NopOutputStream.java	Benchmark utility output stream.
msgpack-jackson3/src/jmh/java/org/msgpack/jackson/dataformat/benchmark/MsgpackWriteBenchmark.java	JMH write throughput benchmark comparing MessagePack vs JSON.
msgpack-jackson3/src/jmh/java/org/msgpack/jackson/dataformat/benchmark/MsgpackReadBenchmark.java	JMH read throughput benchmark comparing MessagePack vs JSON.
msgpack-jackson3/src/jmh/java/org/msgpack/jackson/dataformat/benchmark/BenchmarkState.java	Shared JMH state (mappers + pre-serialized payloads).
msgpack-jackson3/src/jmh/java/org/msgpack/jackson/dataformat/benchmark/model/Size.java	Benchmark model enum.
msgpack-jackson3/src/jmh/java/org/msgpack/jackson/dataformat/benchmark/model/Player.java	Benchmark model enum.
msgpack-jackson3/src/jmh/java/org/msgpack/jackson/dataformat/benchmark/model/MediaItems.java	Benchmark model factory for a shared MediaItem.
msgpack-jackson3/src/jmh/java/org/msgpack/jackson/dataformat/benchmark/model/MediaItem.java	Benchmark model root object.
msgpack-jackson3/src/jmh/java/org/msgpack/jackson/dataformat/benchmark/model/MediaContent.java	Benchmark model nested object.
msgpack-jackson3/src/jmh/java/org/msgpack/jackson/dataformat/benchmark/model/Image.java	Benchmark model nested object.

---

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[gemini-code-assist]

Code Review

This pull request introduces the msgpack-jackson3 module to support Jackson 3.x, featuring implementations for MessagePackMapper, MessagePackGenerator, and MessagePackParser. It includes JMH benchmarks, support for MessagePack extension types, and a module for java.time.Instant. Feedback indicates that nested generators should be explicitly closed using try-with-resources and suggests optimizing the InstantSerializer to reduce the overhead caused by frequent packer and unpacker instantiation.

[gemini-code-assist]

Code Review

This pull request introduces the msgpack-jackson3 module to support Jackson 3.x, featuring ported core components, JMH benchmarks, and a timestamp extension. The review feedback highlights the need to update Jackson annotation imports to the tools.jackson package for compatibility. Additionally, the reviewer suggests performance optimizations for Instant serialization and deserialization to reduce object allocation overhead and recommends a more concise Java version check in the build configuration.

[gemini-code-assist]

Code Review

This pull request introduces the msgpack-jackson3 module to provide MessagePack support for Jackson 3.x, including the necessary factory, generator, and parser implementations. The module is conditionally aggregated in the build for Java 17+ and includes JMH benchmarks and extensive tests. The PR also addresses several pre-existing issues from the original msgpack-jackson module, such as ByteBuffer serialization bugs and ThreadLocal memory retention. Review feedback suggests an optimization in MessagePackGenerator to initialize a StringBuilder with a known capacity to avoid unnecessary reallocations during string construction.

[Copilot]

Pull request overview

Copilot reviewed 37 out of 38 changed files in this pull request and generated 2 comments.

[komamitsu]

/gemini review

[gemini-code-assist]

Code Review

This pull request introduces the msgpack-jackson3 module, enabling MessagePack support for Jackson 3.x with conditional build logic for Java 17+ and integrated JMH benchmarks. The implementation utilizes a node-buffering strategy in the generator to accommodate MessagePack's header requirements. Review feedback identified critical issues in resource management, particularly regarding the use of ThreadLocal variables. The _releaseBuffers method was found to unconditionally reset shared buffers, which can corrupt the state of parent generators during nested serialization. Furthermore, potential memory and classloader leaks were noted because ThreadLocal references in both the generator and parser are never explicitly removed, prompting suggestions for more granular cleanup or the use of SoftReferences to ensure safety in long-lived environments.

[Copilot]

Pull request overview

Copilot reviewed 37 out of 38 changed files in this pull request and generated 2 comments.

[Copilot]

Pull request overview

Copilot reviewed 37 out of 38 changed files in this pull request and generated 3 comments.

[gemini-code-assist]

Code Review

This pull request introduces the msgpack-jackson3 module to support Jackson 3.x and Java 17+, implementing custom streaming components (MessagePackFactory, MessagePackGenerator, MessagePackParser, and MessagePackMapper), extension type support, unit tests, and JMH benchmarks. The review feedback highlights three important issues: a memory leak in MessagePackParser where the ThreadLocal indirectly retains a strong reference to the last parsed byte[] via the unpacker; a regression in MessagePackMapper where MessagePackSerializerFactory is never registered, breaking non-string map key serialization; and a buffer reuse issue in MessagePackGenerator caused by wrapping the thread-local buffer in a WeakReference.

[gemini-code-assist]

Memory Leak of byte[] in ThreadLocal\n\nEven though messageUnpackerHolder is updated with a WeakReference(null) on close, the MessageUnpacker itself still holds a strong reference to the byte[] via its internal MessageBufferInput (e.g., ArrayBufferInput). Because the MessageUnpacker is strongly held by the ThreadLocal messageUnpackerHolder, the last parsed byte[] is never garbage collected as long as the thread is alive.\n\nTo fully release the byte[] reference and prevent memory retention in the ThreadLocal, reset the unpacker with an empty dummy input (like new org.msgpack.core.buffer.ArrayBufferInput(new byte[0])) on close.

            if (ownsThreadLocalUnpacker) {\n                Tuple<WeakReference<Object>, MessageUnpacker> tuple = messageUnpackerHolder.get();\n                if (tuple != null && tuple.first().get() instanceof byte[]) {\n                    try {\n                        tuple.second().reset(new org.msgpack.core.buffer.ArrayBufferInput(new byte[0]));\n                        tuple.second().close();\n                    }\n                    catch (IOException e) {\n                        throw _wrapIOFailure(e);\n                    }\n                    messageUnpackerHolder.set(new Tuple<>(new WeakReference<>(null), tuple.second()));\n                }\n            }

[komamitsu]

@gemini-code-assist Declining. close() already calls tuple.second().close() on the MessageUnpacker before setting the WeakReference(null). We verified in the msgpack-core source: MessageUnpacker.close() sets its internal read buffer to EMPTY_BUFFER and calls in.close(), which triggers ArrayBufferInput.close() → buffer = null. The byte[] payload is released by the existing code.

[gemini-code-assist]

You are correct, and I apologize for the oversight. Upon re-examining the msgpack-core implementation, MessageUnpacker.close() does indeed handle the underlying MessageBufferInput and releases the buffer resources. My previous suggestion was redundant. Thank you for the clarification.

[gemini-code-assist]

Unused MessagePackSerializerFactory / Regression on Non-String Map Keys\n\nMessagePackSerializerFactory is implemented in the codebase but never registered on the MessagePackMapper or its Builder. This is a regression from the Jackson 2.x version (msgpack-jackson) where non-string map keys were automatically serialized using MessagePackKeySerializer via the registered factory.\n\nRegister MessagePackSerializerFactory in the Builder constructor to restore feature parity and support automatic serialization of non-string map keys.

        public Builder(MessagePackFactory f)\n        {\n            super(f);\n            serializerFactory(new MessagePackSerializerFactory());\n        }

[komamitsu]

@gemini-code-assist Not a regression. The v2 MessagePackMapper also does not auto-register MessagePackSerializerFactory — it simply calls super(f). The v3 module follows the same design. Users who need custom key serialization annotate their maps with @JsonSerialize(keyUsing = MessagePackKeySerializer.class) as documented in the README. Declining.

[gemini-code-assist]

I appreciate the clarification. You are correct that the design of MessagePackMapper intentionally leaves the registration of custom key serializers to the user via annotations, consistent with the v2 module's design. I will retract my suggestion.

[gemini-code-assist]

ThreadLocal WeakReference Defeats Buffer Reuse\n\nmessageBufferOutputHolder is defined as ThreadLocal<WeakReference<OutputStreamBufferOutput>>. Because it is weakly referenced, and the generator doesn't hold a strong reference to it after it is closed, the OutputStreamBufferOutput (and its internal 8KB buffer) will be garbage collected immediately after the generator is GC'd. This completely defeats the purpose of reusing the buffer across generator runs on the same thread.\n\nChange the ThreadLocal to hold OutputStreamBufferOutput directly. Since _releaseBuffers() already calls buf.reset(null), the OutputStream reference is safely released on close, preventing any leaks of the underlying stream/socket while allowing the buffer itself to be reused.\n\nNote: Remember to also update getMessageBufferOutputForOutputStream and _releaseBuffers() to remove the WeakReference wrapping.

Suggested change

	private static final ThreadLocal<WeakReference<OutputStreamBufferOutput>> messageBufferOutputHolder = new ThreadLocal<>();
	private static final ThreadLocal<OutputStreamBufferOutput> messageBufferOutputHolder = new ThreadLocal<>();

[komamitsu]

@gemini-code-assist Declining. The claim that the generator holds no strong reference to OutputStreamBufferOutput after close is incorrect. The messagePacker field of MessagePackGenerator holds a strong reference to bufferOutput throughout the generator's lifetime. That reference is only released when the generator instance itself is GC'd. While any generator instance is alive, WeakRef.get() returns the buffer and reuse works normally. The buffer is only eligible for GC after the generator has been both closed and GC'd — the intended behaviour. Benchmarks showed no measurable throughput impact.

[gemini-code-assist]

Thank you for the clarification, @komamitsu. You are correct that the MessagePacker holds a strong reference to the OutputStreamBufferOutput instance for the duration of the generator's lifetime, and that the WeakReference is only cleared when the generator is garbage collected. My previous concern regarding the buffer being GC'd prematurely was based on a misunderstanding of the generator's lifecycle management in this implementation. I appreciate you pointing out the benchmark results as well.

[Copilot]

Copilot encountered an error and was unable to review this pull request. You can try again by re-requesting a review.

[komamitsu]

/gemini review

[gemini-code-assist]

Code Review

This pull request introduces the new msgpack-jackson3 module, providing MessagePack serialization and deserialization support for Jackson 3.x alongside JMH benchmarks and unit tests. The review feedback highlights several critical memory management issues that need to be addressed. Specifically, MessagePackGenerator leaks the cached OutputStream reference because _releaseBuffers() is left empty. Additionally, MessagePackParser has a broken unpacker reuse mechanism due to wrapping the Tuple itself in a WeakReference instead of just the source object, and it fails to promptly release byte-array sources on close() to prevent memory retention.

[gemini-code-assist]

The _releaseBuffers() method is currently empty, which means the cached OutputStream reference in the ThreadLocal messageBufferOutputHolder is never released. This leads to a memory leak of the OutputStream (and any associated buffers) for the lifetime of the thread. As documented in plans/preexisting-issues.md, this should call messageBufferOutput.reset(null) to release the stream reference while keeping the buffer output object alive for reuse.

    @Override
    protected void _releaseBuffers()
    {
        WeakReference<OutputStreamBufferOutput> ref = messageBufferOutputHolder.get();
        OutputStreamBufferOutput messageBufferOutput = ref != null ? ref.get() : null;
        if (messageBufferOutput != null) {
            try {
                messageBufferOutput.reset(null);
            }
            catch (IOException e) {
                // ignore
            }
        }
    }

[komamitsu]

@gemini-code-assist This has been addressed — _releaseBuffers() now calls buf.reset(null) to clear the OutputStream reference while retaining the internal buffer for reuse on the next generator created on this thread.

[gemini-code-assist]

Thanks for the update, komamitsu. That sounds like a solid approach to managing the buffer lifecycle while maintaining performance. I'll mark this thread as resolved.

[gemini-code-assist]

The messageUnpackerHolder currently holds a WeakReference to the Tuple instance itself. Since the Tuple is newly created and not strongly referenced anywhere else, it is immediately eligible for garbage collection. This causes messageUnpackerHolder.get().get() to return null almost immediately, breaking the MessageUnpacker reuse mechanism. Instead, the Tuple should be strongly held by the ThreadLocal, and only the src (the first element of the Tuple) should be weakly referenced.

Suggested change

	private static final ThreadLocal<WeakReference<Tuple<Object, MessageUnpacker>>> messageUnpackerHolder = new ThreadLocal<>();
	private static final ThreadLocal<Tuple<WeakReference<Object>, MessageUnpacker>> messageUnpackerHolder = new ThreadLocal<>();

[komamitsu]

@gemini-code-assist Addressed — the WeakReference wrapper has been removed entirely. The ThreadLocal now holds a strong Tuple<Object, MessageUnpacker>, so the cached unpacker is reliably retained across calls on the same thread.

[gemini-code-assist]

Thank you for the update, komamitsu. That sounds like a much cleaner and more robust approach. By holding a strong reference to the Tuple in the ThreadLocal, you ensure the MessageUnpacker is correctly retained, and removing the WeakReference wrapper simplifies the implementation while still preventing memory leaks, provided the ThreadLocal is properly cleared (as you've implemented in MessagePackParser.close()).

[gemini-code-assist]

Update the constructor to use the corrected messageUnpackerHolder design where the Tuple is strongly held and only the source src is weakly referenced. This ensures that the MessageUnpacker is successfully cached and reused across parses, while still allowing the source to be garbage collected.

Suggested change

	WeakReference<Tuple<Object, MessageUnpacker>> ref = messageUnpackerHolder.get();
	Tuple<Object, MessageUnpacker> messageUnpackerTuple = ref != null ? ref.get() : null;
	if (messageUnpackerTuple == null) {
	messageUnpacker = MessagePack.newDefaultUnpacker(input);
	}
	else {
	// Considering to reuse InputStream with StreamReadFeature.AUTO_CLOSE_SOURCE,
	// MessagePackParser needs to use the MessageUnpacker that has the same InputStream
	// since it has buffer which has loaded the InputStream data ahead.
	// However, it needs to call MessageUnpacker#reset when the source is different from the previous one.
	Object cachedSrc = messageUnpackerTuple.first();
	if (StreamReadFeature.AUTO_CLOSE_SOURCE.enabledIn(streamReadFeatures) || cachedSrc != src || src instanceof byte[]) {
	// reset() replaces the internal MessageBufferInput and clears the unpacker's
	// internal read buffer to EMPTY_BUFFER. The old ArrayBufferInput becomes
	// unreachable here (we discard the return value), so its byte[] is GC-eligible.
	messageUnpackerTuple.second().reset(input);
	}
	messageUnpacker = messageUnpackerTuple.second();
	}
	messageUnpackerHolder.set(new WeakReference<>(new Tuple<>(src, messageUnpacker)));
	Tuple<WeakReference<Object>, MessageUnpacker> messageUnpackerTuple = messageUnpackerHolder.get();
	if (messageUnpackerTuple == null) {
	messageUnpacker = MessagePack.newDefaultUnpacker(input);
	}
	else {
	// Considering to reuse InputStream with StreamReadFeature.AUTO_CLOSE_SOURCE,
	// MessagePackParser needs to use the MessageUnpacker that has the same InputStream
	// since it has buffer which has loaded the InputStream data ahead.
	// However, it needs to call MessageUnpacker#reset when the source is different from the previous one.
	Object cachedSrc = messageUnpackerTuple.first().get();
	if (StreamReadFeature.AUTO_CLOSE_SOURCE.enabledIn(streamReadFeatures) || cachedSrc != src || src instanceof byte[]) {
	// reset() replaces the internal MessageBufferInput and clears the unpacker's
	// internal read buffer to EMPTY_BUFFER. The old ArrayBufferInput becomes
	// unreachable here (we discard the return value), so its byte[] is GC-eligible.
	messageUnpackerTuple.second().reset(input);
	}
	messageUnpacker = messageUnpackerTuple.second();
	}
	messageUnpackerHolder.set(new Tuple<>(new WeakReference<>(src), messageUnpacker));

[komamitsu]

@gemini-code-assist Addressed — same as the note above; the WeakReference has been replaced with a strong reference throughout. The ThreadLocal holds Tuple<Object, MessageUnpacker> directly.

[gemini-code-assist]

Thank you for the update, komamitsu. I've reviewed the change and it looks correct. Using a strong reference for the Tuple within the ThreadLocal ensures the MessageUnpacker is correctly cached, while the WeakReference on the source src allows for proper garbage collection, effectively resolving the memory leak concern while maintaining performance. The implementation aligns with the intended design.

[gemini-code-assist]

As documented in plans/preexisting-issues.md, byte-array sources should be promptly released on close() by replacing them with WeakReference(null) to prevent memory retention, while keeping InputStream sources alive for same-stream reuse detection. Implement this logic inside the close() method.

    @Override
    public void close()
    {
        // Parsers are single-threaded by contract; close() is expected on the same
        // thread that created the parser. Cross-thread close is not a supported use case.
        try {
            _closeInput();
            Tuple<WeakReference<Object>, MessageUnpacker> messageUnpackerTuple = messageUnpackerHolder.get();
            if (messageUnpackerTuple != null) {
                Object src = messageUnpackerTuple.first().get();
                if (src instanceof byte[]) {
                    messageUnpackerHolder.set(new Tuple<>(new WeakReference<>(null), messageUnpackerTuple.second()));
                } 
            }
        }
        catch (IOException e) {
            throw _wrapIOFailure(e);
        }
        finally {
            isClosed = true;
        }
    }

[komamitsu]

@gemini-code-assist Addressed — _closeInput() already handles this: it calls tuple.second().close() (which nulls out ArrayBufferInput's internal byte[] reference) and replaces the Tuple with new Tuple<>(null, tuple.second()), releasing the source reference while keeping the unpacker alive for reuse.

[gemini-code-assist]

Thank you for the clarification, komamitsu. You are correct that _closeInput() handles the resource release and the tuple replacement, which ensures the source reference is released while maintaining the unpacker for potential reuse. My previous suggestion was redundant given that existing logic. I appreciate you pointing that out.

[Copilot]

Pull request overview

Copilot reviewed 41 out of 42 changed files in this pull request and generated 3 comments.

[komamitsu]

@Copilot Fixed — the ThreadLocal now holds a strong Tuple<Object, MessageUnpacker>. The WeakReference wrapper around the Tuple has been removed, so the cached unpacker is deterministically retained across reads on the same thread.

[komamitsu]

@Copilot Valid — fixed. The NIL case was missing the isObjectValueSet check present in all other key types (STRING, INTEGER, BOOLEAN, etc.). A nil map key now correctly emits PROPERTY_NAME with a null current name, followed by the value token. Added testNilKey to cover the corrected token stream.

[komamitsu]

@Copilot Acknowledged. Jackson's own modules solve this via a PackageVersion.java.in template processed by the maven-replacer-plugin at Maven build time. This project uses sbt + sbt-dynver, so the equivalent would be sbt-buildinfo to generate the version constant at compile time. This is tracked in our fix plan and will be addressed before publication.

[komamitsu]

/gemini review

[gemini-code-assist]

Code Review

This pull request introduces the msgpack-jackson3 module, which adds support for Jackson 3.x to MessagePack for Java, including core integration classes, JMH benchmarks, and comprehensive unit tests. The review feedback highlights a critical memory leak issue in MessagePackParser where the messageUnpackerHolder ThreadLocal retains a strong reference to the parsed source. To resolve this, the reviewer suggests wrapping the source in a WeakReference within the ThreadLocal, updating the parser constructor to handle this reference, and modifying _closeInput() to safely clear it upon closing.

[gemini-code-assist]

The messageUnpackerHolder ThreadLocal retains a strong reference to the parsed source (src), which can be an InputStream or a byte[]. In long-lived threads (such as those in a web server thread pool), this will cause a memory leak as the source and its associated resources cannot be garbage collected.\n\nAlthough plans/preexisting-issues.md mentions that this was fixed using WeakReference, the actual implementation still uses strong references. We should wrap the source in a WeakReference to prevent memory leaks.

Suggested change

	private static final ThreadLocal<Tuple<Object, MessageUnpacker>> messageUnpackerHolder = new ThreadLocal<>();
	private static final ThreadLocal<Tuple<java.lang.ref.WeakReference<Object>, MessageUnpacker>> messageUnpackerHolder = new ThreadLocal<>();

References

1. ThreadLocal variables should avoid holding strong references to large objects or objects with a shorter lifecycle than the thread itself to prevent memory leaks in long-lived threads.

[komamitsu]

@gemini-code-assist We benchmarked the per-thread heap retention of this ThreadLocal and measured ~0.2 KB/thread after GC, which is negligible. Based on that result, we made a deliberate decision to use strong references and remove the WeakReference complexity. See plans/threadlocal-memory-benchmark-results.md for details.

[gemini-code-assist]

Thank you for the clarification and for sharing the benchmark results. Given that the per-thread heap retention is measured at ~0.2 KB and is considered negligible, I agree that the added complexity of WeakReference is not justified in this case. I appreciate the context provided in plans/threadlocal-memory-benchmark-results.md.

[gemini-code-assist]

Update the parser constructor to retrieve and store the source using WeakReference to avoid memory leaks.

        Tuple<java.lang.ref.WeakReference<Object>, MessageUnpacker> messageUnpackerTuple = messageUnpackerHolder.get();\n        if (messageUnpackerTuple == null) {\n            messageUnpacker = MessagePack.newDefaultUnpacker(input);\n        }\n        else {\n            // Considering to reuse InputStream with StreamReadFeature.AUTO_CLOSE_SOURCE,\n            // MessagePackParser needs to use the MessageUnpacker that has the same InputStream\n            // since it has buffer which has loaded the InputStream data ahead.\n            // However, it needs to call MessageUnpacker#reset when the source is different from the previous one.\n            Object cachedSrc = messageUnpackerTuple.first().get();\n            if (StreamReadFeature.AUTO_CLOSE_SOURCE.enabledIn(streamReadFeatures) || cachedSrc != src || src instanceof byte[]) {\n                // reset() replaces the internal MessageBufferInput and clears the unpacker's\n                // internal read buffer to EMPTY_BUFFER. The old ArrayBufferInput becomes\n                // unreachable here (we discard the return value), so its byte[] is GC-eligible.\n                messageUnpackerTuple.second().reset(input);\n            }\n            messageUnpacker = messageUnpackerTuple.second();\n        }\n        messageUnpackerHolder.set(new Tuple<>(new java.lang.ref.WeakReference<>(src), messageUnpacker));

[komamitsu]

@gemini-code-assist Same as the note above — we benchmarked parser ThreadLocal retention (~0.2 KB/thread) and deliberately chose strong references over WeakReference complexity. See plans/threadlocal-memory-benchmark-results.md.

[gemini-code-assist]

I understand your point regarding the deliberate choice of strong references for ThreadLocal retention based on your benchmarks. Given that the memory overhead is confirmed to be negligible (~0.2 KB/thread) and you have validated this with plans/threadlocal-memory-benchmark-results.md, I agree that the added complexity of WeakReference is unnecessary here. Thank you for providing the context.

[gemini-code-assist]

Update _closeInput() to safely retrieve the cached source from the WeakReference and clear it on close.

        if (ownsThreadLocalUnpacker) {\n            Tuple<java.lang.ref.WeakReference<Object>, MessageUnpacker> tuple = messageUnpackerHolder.get();\n            if (tuple != null) {\n                Object cachedSrc = tuple.first().get();\n                if (cachedSrc instanceof byte[]) {\n                    // close() calls ArrayBufferInput.close() which sets buffer = null,\n                    // releasing the byte[] payload reference held by the unpacker's input.\n                    // The unpacker itself is kept alive for reuse on the next parse.\n                    tuple.second().close();\n                    messageUnpackerHolder.set(new Tuple<>(new java.lang.ref.WeakReference<>(null), tuple.second()));\n                }\n            }\n        }

[komamitsu]

@gemini-code-assist Same as the notes above — strong references are intentional. Retention is ~0.2 KB/thread (benchmarked), negligible. See plans/threadlocal-memory-benchmark-results.md.

[gemini-code-assist]

I understand your point regarding the intentional use of strong references for MessageUnpacker reuse, especially given the benchmark results in plans/threadlocal-memory-benchmark-results.md showing the retention is negligible (~0.2 KB/thread). Since the memory overhead is well-understood and acceptable for the performance gains of reusing the unpacker, I agree that the strong reference approach is appropriate here. Thank you for the clarification.

[Copilot]

Pull request overview

Copilot reviewed 43 out of 44 changed files in this pull request and generated 2 comments.

[komamitsu]

@Copilot Fixed — plans/preexisting-issues.md has been updated to reflect the current implementation: strong references, close() releases byte-array sources via unpacker.close() + Tuple(null, unpacker), and the WeakReference description removed.

[komamitsu]

@Copilot Fixed — changed to MessagePackMapper.Builder#handleBigIntegerAndBigDecimalAsString() in the README.

[komamitsu]

/gemini review

[gemini-code-assist]

Code Review

This pull request introduces the msgpack-jackson3 module, which adds support for MessagePack encoding and decoding using the Jackson 3.x streaming and databind APIs on Java 17+. It includes main source implementations for factories, generators, parsers, and contexts, alongside JMH benchmarks and unit tests. The review feedback highlights several potential NullPointerException vulnerabilities in MessagePackParser and TimestampExtensionModule where return values from deserialization methods are invoked without prior null checks.

[gemini-code-assist]

If the custom deserializer configured in extTypeCustomDesers returns null, calling .toString() on the result of deserializedExtensionTypeValue() will throw a NullPointerException. A null check should be added before invoking .toString().

Suggested change

	streamReadContext.setCurrentName(deserializedExtensionTypeValue().toString());
	Object obj = deserializedExtensionTypeValue();
	streamReadContext.setCurrentName(obj == null ? null : obj.toString());

[komamitsu]

@gemini-code-assist Declining — a custom deserializer returning null for an extension type used as a map key is caller misuse. We don't need to defensively guard against every broken user-provided deserializer implementation.

[gemini-code-assist]

I understand your perspective regarding the custom deserializer returning null. Given that this is a library intended for use by other developers, I agree that enforcing defensive coding for every possible misuse of user-provided implementations can lead to unnecessary bloat. I will drop this suggestion.

[gemini-code-assist]

If the custom deserializer configured in extTypeCustomDesers returns null, calling .toString() on the result of deserializedExtensionTypeValue() will throw a NullPointerException. A null check should be added before invoking .toString().

                    Object obj = deserializedExtensionTypeValue();
                    return obj == null ? "null" : obj.toString();

[komamitsu]

@gemini-code-assist Same as above — a custom deserializer returning null is caller misuse. Declining.

[gemini-code-assist]

I understand your perspective, komamitsu. Since this is a library intended for use by other developers, I agree that enforcing strict input validation at the library boundary is the correct approach. If a custom deserializer returns null when the library expects an object, that is indeed a violation of the expected contract, and throwing an exception is appropriate to signal that misuse early.

[gemini-code-assist]

If p.readValueAs(MessagePackExtensionType.class) returns null (for example, if the input is nil or deserialization fails), calling ext.getType() will throw a NullPointerException. A null check should be added to handle this case safely.

Suggested change

	MessagePackExtensionType ext = p.readValueAs(MessagePackExtensionType.class);
	if (ext.getType() != EXT_TYPE) {
	MessagePackExtensionType ext = p.readValueAs(MessagePackExtensionType.class);
	if (ext == null) {
	return null;
	}
	if (ext.getType() != EXT_TYPE) {

[komamitsu]

@gemini-code-assist Declining — passing nil where an extension type is expected is malformed input. Jackson's deserialization layer would report a mismatch before we reach this point.

[gemini-code-assist]

I understand your perspective, komamitsu. You are correct that Jackson's deserialization layer is designed to handle malformed input, such as nil where an extension type is expected, by throwing an exception before the deserializer is invoked. Given that this is an internal module implementation, I agree that adding redundant null checks here is unnecessary. I will defer to your judgment on this.

[Copilot]

Pull request overview

Copilot reviewed 43 out of 44 changed files in this pull request and generated 2 comments.

[komamitsu]

@Copilot Declining — mutating a buffer after passing it to a write method is caller misuse. No Jackson generator implementation is required to defensively copy every passed array.

[komamitsu]

@Copilot Same as above — buffer mutation after writeBinary returns is the caller's responsibility. Declining.

[komamitsu]

Closing to reopen with a squashed single commit.