This release provides several new features, including a major Cbor configuration rework. It uses Kotlin 2.0.20 by default.

Cbor feature set for COSE compliance

This change brings a lot of features to the CBOR format, namely:

• Serial Labels — see @CborLabel annotation and preferCborLabelsOverNames flag.
• Tagging of keys and values — see encode*Tags and verify*Tags set of flags
• Definite length encoding — see useDefiniteLengthEncoding. This flag affects object encoding, since decoding of arrays with definite lenghts is automatically supported.
• Option to globally prefer major type 2 for byte array encoding — see alwaysUseByteString flag.

Since there are quite a lot of flags now, they were restructured to a separate CborConfiguration class, similarly to JsonConfiguration. It is possible to retrieve this configuration from CborEncoder/CborDecoder interfaces in your custom serializers (see their documentation for details).

All of these features make it possible to serialize and parse COSE-compliant CBOR, for example, ISO/IEC 18013-5:2021-compliant mobile driving license data. In case you want to make use of them, there is a predefined Cbor.CoseCompliant instance. However, some canonicalization steps (such as sorting keys) still need to be performed manually.

This functionality was contributed to us by Bernd Prünster and Christian.

Keeping generated serializers

One of the most requested features for serialization plugin was to continue to generate a serializer even if a custom one is specified for the class. It allows using a plugin-generated serializer in a fallback or delegate strategy, accessing type structure via descriptor, using default serialization behavior in inheritors that do not use custom serializers.

Starting with this release, you can specify the @KeepGeneratedSerializer annotation on the class declaration to instruct the plugin to continue generating the serializer. In this case, the serializer will be accessible using the .generatedSerializer() function on the class's companion object.

This annotation is currently experimental. Kotlin 2.0.20 or higher is required for this feature to work.

You can check out the examples in the documentation and in the PRs: #2758, #2669.

Serializer for kotlin.uuid.Uuid

Kotlin 2.0.20 added a common class to represent UUIDs in a multiplatform code. kotlinx.serialization 1.7.2 provides a corresponding Uuid.serializer() for it, making it possible to use it in @Serializable classes.

Note that for now, serializer should be provided manually with @Contextual annotation. Plugin will be able to automatically insert Uuid serializer in Kotlin 2.1.0.

See more details in the corresponding PR.

Other bugfixes and improvements

• Prohibited using of zero and negative field numbers in ProtoNumber (#2766)
• Improve readability of protobuf decoding exception messages (#2768) (thanks to xiaozhikang0916)
• docs(serializers): Fix grammatical errors (#2779) (thanks to jamhour1g)
• Fixed VerifyError after ProGuard optimization (#2728)
• Add wasm-wasi target to Okio integration (#2727)