android - How to get body from a server response with code 400 in Kotlin with coroutine and retrofit?

Question

I have a xampp server connected to my android app. When I perform an api call, it would return either a response code 200 or a response code 400. If the response code is 200, I'm able to get the body of the response.

Here is the response body:

{"message": "User was created."}

However, I'm unable to get the response body when the code is 400.

It is null.

This is my interface:

@POST("api/user/createUser.php")
suspend fun register(@Body details : JsonObject) : Response<JsonElement>

This is how I call it:

val service = Server.ApiClient.createService(ServerInterface::class.java)
        
        CoroutineScope(Dispatchers.IO).launch {

            try {
                val response = service.register(details)
                Log.wtf("Message",response.body().toString())
            }
            catch (e : Exception){
                Log.wtf("Error",e.message)
            }
        }

Here is the log :

Response code 200:

E/Message: {"message":"User was created."}

Response code 400:

E/Message: null

Does anybody know how to solve this ?

Answer 1

If I remember correctly, retrofit handles response codes outside 200-399 range as errors, so the message should be available using response.errorBody() instead of response.body().