Omni Ktor is an Omni-MVI core's feature which allows developers execute code and communicate its result back to Ktor. It follows the same principle of intents execution via containers, just like Omni-MVI
In order to include omni-ktor, add the following dependencies to your project build.gradle file:
dependencies {
implementation("org.jetbrains.kotlinx:kotlinx-coroutines-core:1.6.4")
implementation("net.asere.omni.mvi:core:$version")
implementation("net.asere.omni.mvi:result:$version")
implementation("net.asere.omni.mvi:ktor:$version")
}Communication with Ktor framework when using Omni-Ktor occurs via the ResponseContainerHost interface and its intents API. You can turn any class into a host by implementing ResponseContainerHost interface. To define a Ktor container host follow the syntax below:
class ExampleController : ResponseContainerHost<Any, Any> {
override val container = responseContainer(
exceptionMapper = ExampleErrorMapper(),
)
...
}Interfaces Return generic parameter is the type of data your host returns, the one to be delivered to the user, for example, what mappers return. Input generic parameter is the one your intents return. In many cases you would want this to be <Any, Any to allow you return any kind of type of data. For that you can use AnyResponseContainerHost which a type alias for ResponseContainerHost<Any, Any>
The responseContainer() builder function requires you to pass 4 arguments, 3 of them optionals:
coroutineScope: Coroutine scope of intents execution. Defaulted to empty context coroutine scopecoroutineExceptionHandler: The exception handler used to capture exception on intents execution, defaulted to anEmptyCoroutineExceptionHandler.exceptionMapper: Is going to be triggered every time an exception occurs. Captured exceptions are mapped and returned to Ktor framework as call answers. It's defaulted to null.responseMapper: Transforms intents returned values into responses.
As mentioned before, ExceptionMapper will translate any thrown error to a valid response. This will apply to any intent executed in the host. To define a custom exception mapper you just have to implement the ExceptionMapper interface:
class ExampleErrorMapper : ExceptionMapper<Any> {
override fun valueOf(input: Throwable): Response<Any> {
return when (input) {
is UserNotFoundError -> Response(code = 404, body = ApiError("user_not_found"))
else -> Response(code = 500, body = ApiError("internal_server_error"))
}
}
}ResponseMapper will do the same as ExceptionMapper but for any returned value from intents. Define a custom response mapper by implementing the ResponseMapper interface:
class ExampleResponseMapper : ResponseMapper<Any, Any> {
override fun valueOf(input: Any): Response<Any> {
if (input is List<*> && input.isEmpty())
return Response(code = 204, input)
return Response(code = 200, input)
}
}Intents are suspending jobs running under a specific and controlled scope which grants access to possible thrown errors. Returned data at responseIntent will then be mapped using the ResponseMapper. To define a responseIntent you just have to follow the syntax bellow:
fun message() = responseIntent {
Message("This a 'happy path' response message provided by Omni-Ktor")
}In case you prefer to override error mapper for a specific intent you can call onError top level extension and either provide an inline lambda declaration:
fun overriddenError() = responseIntent {
onError {
when (it) {
is IllegalStateException -> Response(code = 400, ApiError("bad_request"))
else -> Response(code = 500, body = ApiError("internal_server_error"))
}
}
throw IllegalStateException()
}You can also provide an ExceptionResponseMapper instance by calling its extension property lambda:
private val localMapper = ExceptionResponseMapper<Any> { input ->
when (input) {
is IllegalStateException -> Response(code = 400, ApiError("bad_request"))
else -> Response(code = 500, body = ApiError("internal_server_error"))
}
}
fun overriddenError() = responseIntent {
onError(localMapper.lambda)
throw IllegalStateException()
}To call intents you just have to use the top level extension function respond of Ktor's ApplicationCall:
fun start() = runBlocking {
embeddedServer(Netty, port = 3000) {
install(ContentNegotiation) {
json()
}
routing {
get("example/message") {
call.respond(controller::message)
}
get("example/error/internal") {
call.respond(controller::error500)
}
get("example/error/user") {
call.respond(controller::errorUserNotFound)
}
get("example/error/overridden") {
call.respond(controller::overriddenError)
}
get("example/no-content") {
call.respond(controller::noContent)
}
}
}.start(wait = true)
}Omni Result is an Omni-MVI core's feature which allows the suspend execution of an intent to obtain its result.
In order to include omni-result, add the following dependencies to your project build.gradle file:
dependencies {
implementation("org.jetbrains.kotlinx:kotlinx-coroutines-core:1.6.4")
implementation("net.asere.omni.mvi:core:$version")
implementation("net.asere.omni.mvi:result:$version")
}Omni-Result allows to define standalone result containers. Standalone result containers let you execute result intents, these sort of intents handle their own result type. Every intent declared under a ResultContainerHost have their own result type. You can declare a ResultContainerHost using the following code:
class ExampleController(
private val operationUseCase: OperationUseCase,
) : ResultContainerHost {
override val container: ResultContainer = resultContainer()
...
}Use resultIntent top level extension to declare a result intent:
class ExampleController(
private val operationUseCase: OperationUseCase,
) : ResultContainerHost {
override val container = resultContainer()
fun performOperation() = resultIntent {
onError {
OperationResult.Failed
}
operationUseCase()
OperationResult.Success
}
}resultIntent execution returns a ResultIntent object. Use awaitResult() top level extension suspend function to await and retrieve the returning value. You can access the running job from the return intent.
val controller = ExampleController()
val operationIntent = controller.performOperation()
val result = operationIntent.awaitResult()Just like ResultContainerHost, ConstrainedResultContainerHost allows you to execute resultIntent and constrainedIntent. Similar to resultIntent, constraintIntent returns a suspended result, but this one is bound to the container's result type. Use ConstrainedResultContainerHost when you need all intents in that host returns a common type. To declare a constrained host follow the code below:
class ExampleController(
private val operationUseCase: OperationUseCase,
) : ConstrainedResultContainerHost<OperationReslt> {
override val container = constrainedResultContainer()
fun performOperation() = constrainedIntent {
onError {
OperationResult.Failed
}
operationUseCase()
OperationResult.Success
}
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