AppException

Sealed exception hierarchy providing typed error handling across all layers of the application.

Module: :core

Definition

sealed class AppException(message: String?) : Exception(message) {
    class NetworkException(message: String?) : AppException(message)
    class TimeoutException(message: String?) : AppException(message)
    class UnauthorizedException(message: String?) : AppException(message)
    class ForbiddenException(message: String?) : AppException(message)
    class NotFoundException(message: String?) : AppException(message)
    class ServerException(val code: Int, message: String?) : AppException(message)
    class UnknownException(cause: Throwable?) : AppException(cause?.message)
}

Exception Types

Type	HTTP Status	When
NetworkException	—	No internet / connection refused
TimeoutException	—	Request timed out
UnauthorizedException	401	Invalid or expired token
ForbiddenException	403	Insufficient permissions
NotFoundException	404	Resource not found
ServerException	5xx	Server error (code is preserved)
UnknownException	—	Catch-all for unexpected errors

Pattern Matching

when (exception) {
    is AppException.UnauthorizedException -> {
        // Token expired — navigate to login
        navigateToLogin()
    }
    is AppException.NetworkException -> {
        // No connectivity
        showOfflineMessage()
    }
    is AppException.ServerException -> {
        // Server error with status code
        showServerError("Server error: ${exception.code}")
    }
    is AppException.TimeoutException -> {
        showRetryDialog()
    }
    is AppException.NotFoundException -> {
        showNotFound()
    }
    is AppException.ForbiddenException -> {
        showPermissionDenied()
    }
    is AppException.UnknownException -> {
        showGenericError(exception.message)
    }
}

Usage with BaseViewModel

In execute() and collect(), the onError reducer receives AppException:

fun loadProducts() = execute(
    call = { getProductsUseCase() },
    onSuccess = { copy(products = it) },
    onError = { exception ->
        when (exception) {
            is AppException.UnauthorizedException -> copy(needsLogin = true)
            else -> copy(error = exception.message)
        }
    },
    errorEvent = { exception ->
        ProductEvent.ShowError(exception.message ?: "Something went wrong")
    }
)

Automatic Mapping

The :network module's safeApiCall automatically maps HTTP responses and Ktor exceptions to AppException. You never need to create these exceptions manually when using ApiService.