kotlinx.serialization: Strict JSON encountered unknown key

I tried some basic tests and I came across an unexpected scenario

This scenario works perfectly:

@Serializable
data class SimpleApiResponse (val id: String, val label: String)

{
    "id": "123456789,
    "label": "abc"
}

But when added another key into the json above, like this:

{
    "id": "123456789,
    "label": "abc",
    "anotherKey": "def"
}

I got this error

kotlinx.serialization.SerializationException: Strict JSON encountered unknown key: anotherKey
                      at kotlinx.serialization.json.JSON$JsonInput.readElement(JSON.kt:294)
                      at co.stone.kyc.datasource.webservice.PendingQuestionsResponse$$serializer.load(Unknown Source:18)
                      at co.stone.kyc.datasource.webservice.PendingQuestionsResponse$$serializer.load(payload.kt:13)
                      at kotlinx.serialization.KInput.read(Serialization.kt:209)
                      at kotlinx.serialization.json.JSON.parse(JSON.kt:43)
                      at kotlinx.serialization.json.JSON$Companion.parse(JSON.kt:53)
                      at co.stone.kyc.datasource.KYCDefaultDataSource$loadData$1.onResponse(KYCDefaultDataSource.kt:132)
                      at okhttp3.RealCall$AsyncCall.execute(RealCall.java:153)
                      at okhttp3.internal.NamedRunnable.run(NamedRunnable.java:32)
                      at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1162)
                      at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:636)
                      at java.lang.Thread.run(Thread.java:764)

Is there any way to escape unmapped keys? Any annotation?

About this issue

Original URL
State: closed
Created 6 years ago
Reactions: 7
Comments: 18 (7 by maintainers)

Most upvoted comments

Latest versions of both Kotlin Serialization and JakeWharton’s Converter should do:

Json {
    ignoreUnknownKeys = true
}.asConverterFactory(contentType)

+19

joaquini on Jan 30, 2021

Because you easily noticed the problem that it was stricter than desired but the opposite you would most likely not have noticed.

+13

pdvrieze on Jul 10, 2018

In other words, I should use Json.nonstrict.parse() instead of Json.parse(). Found it. Thanks.

+10

raydenvoldeskine on Apr 4, 2019

JSON.nonstrict

JakeWharton on Jul 9, 2018

Any reason for nonstrict not be used as default

Yes, by default, we opt-in for maximal safety, including type checks and runtime checks. If frontend sends to backend slightly malformed JSON, it’s better to know about it in advance, not when your system failed because field name has a typo and some value was ignored. In most cases, such check prevents errors on integration testing stage.

Though sometimes, you have to ignore missing fields, then you can use nonstrict mode

How to use this for retrofit? Does this only apply for custom / manual JSON serialization?

@qwwdfsad @sandwwraith

EDITED For those doesn’t using custom Json de/serialization, use JsonConfiguration(strictMode = false) on retrofit converter factory

E.g:

// your retrofit builder
.addConverterFactory(
    Json(
        JsonConfiguration(strictMode = false)
    ).asConverterFactory(MediaType.get("application/json"))
)

mochadwi on Sep 9, 2019

val json = Json { ignoreUnknownKeys = true isLenient = true }

val strategies = ExchangeStrategies
    .builder()
    .codecs { clientDefaultCodecsConfigurer ->
        run {
            clientDefaultCodecsConfigurer.defaultCodecs()
                .kotlinSerializationJsonDecoder(KotlinSerializationJsonDecoder(json))
            clientDefaultCodecsConfigurer.defaultCodecs()
                .kotlinSerializationJsonEncoder(KotlinSerializationJsonEncoder(json))

        }
    }.build()

return WebClient
    .builder()
    .exchangeStrategies(strategies)
    .baseUrl(baseUrl!!)
    .build()

FerhatBahceci on Mar 22, 2021

Tks! Any reason for nonstrict not be used as default?

rodrigohsb on Jul 9, 2018

Using the Spring Webclient awaitBody() will trigger Kotlin serialization for the respective @Serializable receiver response class.

Unknown keys exception is thrown on the receiver side since some of the fields are missing.

Is it possible to set ignoreUnknownKeys = true somehow for these receiver classes other than implementing custom serializers?

SenderA(id,name,age) --> GET awaitBody<(id,name)>() throws unknown keys.

FerhatBahceci on Mar 16, 2021

Is it possible to save all encountered unknown keys to some Map<String, JsonObj> value? e.g.

data class MyData(val x: Int, val unknown: Map<String,JsonObj>)

ngortheone on Sep 21, 2019

@mochadwi I think your question is more related to the repository of retrofit converter (https://github.com/JakeWharton/retrofit2-kotlinx-serialization-converter). But yes, I think your solution is correct

sandwwraith on Sep 13, 2019