Exception Handling

When the backend code throws an unhandled exception, it will be logged on the server side and then propagated by KVision to the frontend side. There are of course many different classes of exceptions on the JVM and it's not possible to transform those types directly to the JS side. So only the exception message is propagated and the generic Exception object is created on the frontend side.

There is a special io.kvision.remote.ServiceException class defined in common KVision code. Unlike all other exception classes this one will be propagated directly from ServiceException to ServiceException and will not be logged on the backend side. It should be used as typical business error indication.

Backend.kt

@Suppress("ACTUAL_WITHOUT_EXPECT")
actual class PasswordService : IPasswordService {
    override suspend fun changePassword(oldPassword: String, newPassword: String) {
        if (oldPassword == newPassword) {
            throw ServiceException("You should really change your password")
        }
        // ...
    }
}

Frontend.kt

val passwordService = PasswordService()
try {
    passwordService.changePassword(oldPassword, newPassword)
} catch (e: ServiceException) {
    Alert.show("Error", e.message)
}

User-defined exceptions

Since KVision 5.8.2 it is possible to define custom exception types in the common module, that will be propagated from the backend to the fronted side. Such exceptions need to inherit from AbstractServiceException and need to be annotated with @KVServiceException annotation.

@KVServiceException
class MyFirstException(override val message: String) : AbstractServiceException()

@KVServiceException
class MySecondException(override val message: String) : AbstractServiceException()

Such exceptions are automatically registered by the framework and you should be able to throw custom exceptions on the backend side and catch them on the frontend side.

Returning Result<T>

When returning Result<T> from the remote methods, the exceptions wrapped in the Result class are serialized and deserialized the same way as when being thrown. So you can safely use ServiceException and other user-defined exceptions when working with Result<T> on both the frontend and the backend side of your application.