Functions in a remote interface are just regular functions in Kotlin that, when connected to a Web Frame, can be invoked from the web layer.

Functions can be declared any number of ways. The following examples are for a remote function that responds with the data that is sent to it from the web layer.

fun echo(call: Call) {
    call.respond(call.request.data)
}

class Echo {
    fun echo(call: Call) {
        call.respond(call.request.data)
    }
}

functions = mapOf(
    "echo" to { call ->
        call.respond(call.request.data)
    },
),

For the following example, we’ll be using a function declared like the following:

fun echo(call: Call) {
    call.respond(call.request.data)
}

Since functions have first-class support in Kotlin, we can pass them as references to the Web Frame configuration.

val configuration = WebFrame.Configuration(
    baseUrl: ...
    functions = mapOf(
        "echo" to ::echo,
    ),
    observables = emptyMap(),
)

typealias RemoteFunction = (Call) -> Unit

An instance of the Call class represents a single invocation of a remote function.

The Request instance associated with this call.

Complete the call by responding with empty data.

Complete the call by responding with a UTF-8 encoded string.

Complete the call by responding with arbitrary data.

Data must be JSON content on Android. One delightful way of creating arbitrary JSON content is by using the buildJsonObject helper from the KotlinX Serialization library:

call.respond(buildJsonObject {
    put("width", 100)
    put("height", 100)
})

Complete the call by responding with a serializable object.

The easiest way to make a class serializable is by annotating it with @Serializable from the KotlinX Serialization library:

import kotlinx.serialization.*
import kotlinx.serialization.json.*

@Serializable
data class SizeResponse(val width: Double, val height: Double)

Then, objects can be passed to .respond() directly:

call.respond(SizeResponse(100, 100))

Complete the call (marking it as failed) by responding with an error message and code.

This will cause the web client to throw a ClientError exception.

Contains the request data from the web layer and helpers to extract it.

The raw data from the web layer.

The data decoded as a UTF-8 string.

The data converted to a serializable object.

Annotate classes with @Serializable:

@Serializable
data class SizeRequest(
    val name: String
)

Then, pass the type as a generic parameter to .json():

val sizeRequest = call.request.json<SizeRequest>()
val shapeName = sizeRequest.name