How do I handle Request Body Error in Ktor - postman

Question

I am new to Ktor and I have a route with a request body which i am parsing with Kotlin Serialization.
I know that the request body is expected to conform to the request body data class but then, I tested by passing the wrong field in my test payload and it crashed the app.
I want to be able to handle such scenarios and respond to the client that such a field is not allowed. How do i go about that.
This is my sample data class:
#kotlinx.serialization.Serializable
data class UserLoginDetails(
var email: String = "",
var password: String = ""
)
This is the route:
post("/user/login") {
val userInfo = call.receive<UserLoginDetails>()
//my code here
}
The payload below works
{
"email": "test#email.com",
"password": "password"
}
But if use an alternative payload for instance:
{
"phone": "test#email.com",
"password": "password"
}
The app crashes with the crash message:
kotlinx.serialization.json.internal.JsonDecodingException: Unexpected
JSON token at offset 7: Encountered an unknown key 'emai'. Use
'ignoreUnknownKeys = true' in 'Json {}' builder to ignore unknown
keys.

Answer 1

You have two options in Ktor:
call.receive is the function which can throw an exception in this case, you can simply catch it:
try {
val userInfo = call.receive<UserLoginDetails>()
} catch (t: Throwable) {
// handle error
}
Catching exceptions globally using Status Pages:
install(StatusPages) {
exception<SerializationException> { cause ->
call.respond(/* */)
}
}

Answer 2

The error message says you can setup your Json with the config ignoreUnknownKeys = true where you are creating the Json object. Here's the doc link.
a tip: You might also want to check other configuration options so you can avoid setting empty string as default values.