How to implement ndjson Response converter

[ag2s20150909]

When using retrofit it can do something like this

class NdJsonResponseBodyConverter<T>(
    private val loader: DeserializationStrategy<T>,
    private val format: StringFormat
) : Converter<ResponseBody, Flow<T>> {
    override fun convert(value: ResponseBody): Flow<T> = callbackFlow {
        value.charStream().forEachLine { line->
            if(line.isNotEmpty()){

                val obj=if (line.startsWith("data:")){
                    //
                    format.decodeFromString(loader,line.substringAfter("data:"))
                }else{
                    format.decodeFromString(loader,line)
                }

                trySendBlocking(obj)
            }

        }
        awaitClose {
            value.close()
        }
    }
}

class NdJsonConverterFactory(private val format:StringFormat): Converter.Factory() {

    override fun responseBodyConverter(
        type: Type,
        annotations: Array<out Annotation>,
        retrofit: Retrofit
    ): Converter<ResponseBody, *>? {

        if (getRawType(type) != Flow::class.java) {
            return null
        }
        check(type is ParameterizedType) { "Flow return type must be parameterized as Flow<Foo> or Flow<out Foo>" }
        val responseType = getParameterUpperBound(0, type)

        val loader =format.serializersModule.serializer(responseType)

        return NdJsonResponseBodyConverter(loader,format)
    }
}

fun StringFormat.newNdJsonFactory()=NdJsonConverterFactory(this)



@Serializable
data class FooResponse(
    @SerialName("aa")
    val aa: String,
    @SerialName("bb")
    val bb: String
)


interface TestService{
    
    
    @GET("/api/test")
    suspend fun test(): Flow<FooResponse>
}


val ktjson=  Json {
            isLenient = true
            ignoreUnknownKeys = true
            coerceInputValues = true
            encodeDefaults = false
            allowStructuredMapKeys = true

        }

 val retrofit= Retrofit.Builder()
      ....
     .addConverterFactory(ktjson.newNdJsonFactory())
      .addConverterFactory(ktjson.asConverterFactory("application/json; charset=UTF8".toMediaType()))

[ag2s20150909]

The current solution is to write it manually, it would be nice to generate it automatically.

interface TestService{

    @Streaming
    @GET("/api/test")
    suspend fun _test() : HttpStatement
}

fun TestService.testFlow():Flow<FooResponse> = callbackFlow {
    val channel: ByteReadChannel=_test().body()
    while (!channel.isClosedForRead) {
        val line = channel.readUTF8Line()

        if (!line.isNullOrBlank()) {
            try {
                val obj=if (line.startsWith("data:")){
                    //for SSE text/event-stream
                    ktjson.decodeFromString(FooResponse.serializer(),line.substringAfter("data:"))
                }else{
                    //for NdJson application/x-ndjson
                    ktjson.decodeFromString(FooResponse.serializer(),line)
                }
                trySendBlocking(obj)
            }catch (e:Exception){
                throw e
            }
           
        }
    }
    awaitClose {

    }
}

or

inline fun  <reified T> HttpStatement.asFlow(format: StringFormat=ktjson):Flow<T> = callbackFlow {
    val content:ByteReadChannel=this@asFlow.body()

    while (!content.isClosedForRead) {
        val line = content.readUTF8Line()
        try {
            if (!line.isNullOrEmpty()) {
                val obj=if (line.startsWith("data:")){
                    //for SSE text/event-stream
                    format.decodeFromString<T>(line.substringAfter("data:"))
                }else{
                    //for NdJson application/x-ndjson
                   format.decodeFromString<T>(line)
                }
                trySendBlocking(obj)
            }

        }catch (e:Exception){
            throw e
        }
    }
    awaitClose {

    }

}

[ag2s20150909]

Another attempt. It works, but it's not streaming.

.......
        install(ContentNegotiation){
                json(ktjson)
                register(NDJson, NdjsonContentConverter(ktjson))
                register(SSE, NdjsonContentConverter(ktjson))
            }

.....



 private val NDJson =  ContentType("application","x-ndjson")
 private val SSE =ContentType("text","event-stream")
 class NdjsonContentConverter(private val format: StringFormat): ContentConverter{
        override suspend fun deserialize(
            charset: Charset,
            typeInfo: TypeInfo,
            content: ByteReadChannel
        ): Any? {


            check(typeInfo.type==Flow::class){"For NdjsonContentConverter the return type must be kotlinx.coroutines.flow.Flow ,like  Flow<Foo> or Flow<out Foo>"}
            val responseType = typeInfo.upperBoundType(0)!!.type.javaObjectType
            val loader =format.serializersModule.serializer(responseType)
            return callbackFlow {
                while (!content.isClosedForRead) {
                    val line = content.readUTF8Line()
                    try {
                        if (!line.isNullOrEmpty()) {
                            val obj=if (line.startsWith("data:")){
                                //for SSE text/event-stream
                                ktjson.decodeFromString(loader,line.substringAfter("data:"))
                            }else{
                                //for NdJson application/x-ndjson
                                ktjson.decodeFromString(loader,line)
                            }
                            trySendBlocking(obj)
                        }

                    }catch (e:Exception){
                        throw e
                    }

                }
                awaitClose {  }

            }

        }