How do we configure serialization now with Ktor 2.0 on an Android client? This example for previous...

# android

[Nathan Kleinschmidt]

How do we configure serialization now with Ktor 2.0 on an Android client? This example for previous versions is deprecated and no longer works:

client = HttpClient(Android) {
    install(JsonFeature) {
      serializer = KotlinxSerializer()
    }
}

The migration guide says to use the content negotiation plugin, but there are no examples of how to do this on Android that I can see.

[Dominaezzz]

install(ContentNegotiation) { json() }

[Amit]

https://ktor.io/docs/serialization-client.html. this link has more detailed info, but you will need to follow format by @Dominaezzz.

[Nathan Kleinschmidt]

Thanks, I see it now. I was also missing the dependency of implementation("io.ktor:ktor-client-content-negotiation:$ktor_version")

[Nathan Kleinschmidt]

I have serialization configured and there are no errors at build time, but when I run the app I get this error: java.lang.IllegalStateException: No request transformation found:

thrown by this function:

val response = client
  .post(HttpRoutes.LOGIN) {
    contentType(ContentType.Application.Json)
    setBody(loginRequest) // <- this line fails
  }

where client : HttpClient and loginRequest is

@Serializable
data class LoginRequest(
  val email : String,
  val password : String
)

Am I not serializing the request correctly?
Apparently not - the setBody call needs to instead be:

setBody(Json.encodeToString(LoginRequest.serializer(), loginRequest))

[Nathan Kleinschmidt]

So finally I would like to parse the response from the above POST request, using the .body() method:

val userData : UserData = client
  .post(HttpRoutes.LOGIN) {
    contentType(ContentType.Application.Json)
    setBody(Json.encodeToString(LoginRequest.serializer(), loginRequest))
  }
  .body<UserData>()

This fails with the error:
io.ktor.client.call.NoTransformationFoundException: No transformation found: class io.ktor.utils.io.ByteBufferChannel -> class UserData
Why is it ByteBufferChannel and not a Json or text?

[Dominaezzz]

Can I see the configuration?

[Nathan Kleinschmidt]

fun create() : AuthService {
  return AuthServiceImpl(
    client = HttpClient(Android) {
      install(ContentNegotiation) {
        json()
      }
    }
  )
}

[Nathan Kleinschmidt]

I’m thinking it may be an issue with my Ktor server. The Content-Type header is indeed text/plain; charset=UTF-8 where I would have expected application/json. My server is running Ktor 2.0, and the response is sent using

call.respond(result.statusCode, ResponseSerializer.encodeToString(result))

The docs say that content-type gets set automatically by serialization. Is it possible to set this manually or override the default?

[Nathan Kleinschmidt]

The solution is apparently to cast the output from .body() explicitly, instead of just passing a type argument as the docs suggest.

This works:

val userData = Json.decodeFromString(
  client
    .post(HttpRoutes.LOGIN) {
      contentType(ContentType.Application.Json)
      setBody(Json.encodeToString(LoginRequest.serializer(), loginRequest))
    }
    .body()
) as UserData

This does not work:

val userData : UserData = client
  .post(HttpRoutes.LOGIN) {
    contentType(ContentType.Application.Json)
    setBody(Json.encodeToString(LoginRequest.serializer(), loginRequest))
  }
  .body<UserData>()

I’m not really sure what the difference is, but body() is not able to either parse or cast the Json string from the response.

[caique]

hey, did you fix that?

[Nero Nguyễn]

beware of syntax
correct is
install(ContentNegotiation) {
json(Json {
prettyPrint = true
isLenient = true
})
}

not
install(ContentNegotiation) {
Json {
prettyPrint = true
isLenient = true
}
}