I hate kotlinx serialization errors so much they sometimes g

Question

I hate kotlinx serialization errors so much they sometimes give okay errors but other times it s ones that are so vague it makes it impossible to diagnose I cannot pinpoint the exact cause of the error in my application that has multiple layers for serialization is there anything I can try to at least narrow down the exact cause of an error

okarm · Answer

Can t expect to get help if you don t post the error

okarm · Answer

Be aware that sometimes `kotlinx serialization` errors will give you a completely different piece of the input than where the actual error occurred throwing you a red herring

okarm · Answer

If you get an error that points to an OBVIOUSLY correct input look at the adjacent space Especially with JSON arrays the error might have occurred at the beginning of the array while the library prints the tail as the incorrect input

zt · Answer

```io ktor serialization JsonConvertException Illegal input at io ktor serialization kotlinx KotlinxSerializationConverter deserialize KotlinxSerializationConverter kt 90 at io ktor serialization kotlinx KotlinxSerializationConverter$deserialize$1 invokeSuspend Unknown Source 15 at kotlin coroutines jvm internal BaseContinuationImpl resumeWith ContinuationImpl kt 33 at kotlinx coroutines DispatchedTask run DispatchedTask kt 106 at kotlinx coroutines internal LimitedDispatcher run LimitedDispatcher kt 42 at kotlinx coroutines scheduling TaskImpl run Tasks kt 95 at kotlinx coroutines scheduling CoroutineScheduler runSafely CoroutineScheduler kt 570 at kotlinx coroutines scheduling CoroutineScheduler$Worker executeTask CoroutineScheduler kt 750 at kotlinx coroutines scheduling CoroutineScheduler$Worker runWorker CoroutineScheduler kt 677 at kotlinx coroutines scheduling CoroutineScheduler$Worker run CoroutineScheduler kt 664 Caused by kotlinx serialization json internal JsonDecodingException Expected class kotlinx serialization json JsonArray Kotlin reflection is not available as the serialized body of kotlin collections ArrayList but had class kotlinx serialization json JsonObject Kotlin reflection is not available at kotlinx serialization json internal JsonExceptionsKt JsonDecodingException JsonExceptions kt 24 at kotlinx serialization json internal AbstractJsonTreeDecoder beginStructure TreeJsonDecoder kt 335 at kotlinx serialization internal AbstractCollectionSerializer merge CollectionSerializers kt 29 at kotlinx serialization internal AbstractCollectionSerializer deserialize CollectionSerializers kt 43 at kotlinx serialization json internal PolymorphicKt decodeSerializableValuePolymorphic Polymorphic kt 61 at kotlinx serialization json internal AbstractJsonTreeDecoder decodeSerializableValue TreeJsonDecoder kt 52 at kotlinx serialization internal TaggedDecoder decodeSerializableValue Tagged kt 207 at kotlinx serialization internal TaggedDecoder$decodeSerializableElement$1 invoke Tagged kt 280 at kotlinx serialization internal TaggedDecoder tagBlock Tagged kt 297 at kotlinx serialization internal TaggedDecoder decodeSerializableElement Tagged kt 280 at kotlinx serialization encoding CompositeDecoder$DefaultImpls decodeSerializableElement$default Decoding kt 533 at kotlinx serialization internal CollectionLikeSerializer readElement CollectionSerializers kt 80 at kotlinx serialization internal AbstractCollectionSerializer readElement$default CollectionSerializers kt 51 at kotlinx serialization internal AbstractCollectionSerializer merge CollectionSerializers kt 36 at kotlinx serialization internal AbstractCollectionSerializer deserialize CollectionSerializers kt 43 at kotlinx serialization json internal PolymorphicKt decodeSerializableValuePolymorphic Polymorphic kt 61 at kotlinx serialization json internal AbstractJsonTreeDecoder decodeSerializableValue TreeJsonDecoder kt 52 at kotlinx serialization internal TaggedDecoder decodeSerializableValue Tagged kt 207 at kotlinx serialization internal TaggedDecoder$decodeSerializableElement$1 invoke Tagged kt 280 at kotlinx serialization internal TaggedDecoder tagBlock Tagged kt 297 at kotlinx serialization internal TaggedDecoder decodeSerializableElement Tagged kt 280 at kotlinx serialization encoding CompositeDecoder$DefaultImpls decodeSerializableElement$default Decoding kt 533 at kotlinx serialization internal CollectionLikeSerializer readElement CollectionSerializers kt 80 at kotlinx serialization internal AbstractCollectionSerializer readElement$default CollectionSerializers kt 51 at kotlinx serialization internal AbstractCollectionSerializer merge CollectionSerializers kt 36 at kotlinx serialization internal AbstractCollectionSerializer deserialize CollectionSerializers kt 43 at kotlinx serialization json internal PolymorphicKt decodeSerializableValuePolymorphic Polymorphic kt 61 at kotlinx serialization json internal AbstractJsonTreeDecoder decodeSerializableValue TreeJsonDecoder kt 52 at kotlinx serialization json internal TreeJsonDecoderKt readJson TreeJsonDecoder kt 25 at kotlinx serialization json Json decodeFromJsonElement Json kt 127 at kotlinx serialization json JsonTransformingSerializer deserialize JsonTransformingSerializer kt 78 at kotlinx serialization json internal StreamingJsonDecoder decodeSerializableValue StreamingJsonDecoder kt 70 ``` + many more internal lines

Ben Woodworth · Answer

Was there more to the `Caused by` message It looks cut off in the middle of `reflection` I think the error comes from <https github com Kotlin kotlinx serialization blob f76d07314ead1db92f27c389494f537c12d3ea7b formats json commonMain src kotlinx serialization json internal TreeJsonEncoder kt L253 L256|here> and this full message seems like it would be useful I could see a JSON path being useful too but besides that the message has the JSON `value` it tried to parse and the `descriptor` it tried to parse it as and that seems pretty helpful Maybe intimidating though if you re new to the library

zt · Answer

Oh I didn t notice that I ve updated the stacktrace