Hey everyone! :android-wave: So I've created a fairly simple network library using Ktor following th...

# ktor

[Richard Hajdu]

Hey everyone! 👋
So I've created a fairly simple network library using Ktor following the official guidelines, sharing common code in a multiplatform project.
I've configured the engines following the example in the official guidelines but I also wanted to follow the official guidelines for unit testing the Ktor clients but I struggle really hard with making this work and making both solutions work simultaneously.
Can someone help me either figuring out how to solve this issue or providing a solution right away, please?

[Aleksei Tirman [JB]]

What problems do you experience?

[Richard Hajdu]

Yeah, the problem... The testing guideline says that the engine should be a constructor parameter for the client in order to be exchangeable with a MockEngine in tests, but the example for configuring engines in multiplatform projects says that the engine should be defined only by the platform and not by the client implementation, but this way I cannot exchange the engine in tests.

[Richard Hajdu]

Basically the question is; How can I configure Ktor clients in multiplatform project with the ability to exchange the engine with MockEngine in tests?

[Aleksei Tirman [JB]]

I think you have to make the engine definable by the client implementation with a default engine defined by the platform.

[Richard Hajdu]

Hmm 🤔 So the clients may have the engine param in the constructor and that'd be a nullable type with a default value of null, so that the platform implementations can supply their respective engine in case the client didn't supply an other one (a MovkEngine) explicitly?

[Aleksei Tirman [JB]]

Yeah, that could be a solution.

[Richard Hajdu]

Yeah, that can work. Thanks for your help, I'll check this out! 👍🏻

[Richard Hajdu]

Now I can run the tests, but face another issue which I'm not even sure about what it is.

No transformation found: class io.ktor.utils.io.ByteBufferChannel (Kotlin reflection is not available) -> class dev.drathar.poktor.model.move.MoveTarget (Kotlin reflection is not available)

with response from http://localhost/api/v2/move-target/specific-move:

status: 200 OK

response headers:

Content-Type: application/json

I don't have the slightest clue on why the requests are targeting localhost.

The client configuration I'm using is

internal class DefaultApiClient(mockEngine: HttpClientEngine? = null) : ApiClient {
    override val httpClient = httpClient(mockEngine!!) {
        defaultRequest {
            url {
                protocol = URLProtocol.HTTPS
                host = "<http://pokeapi.co|pokeapi.co>"
                path("api/v2/")
            }
        }
        install(HttpCache)
        install(ContentNegotiation) {
            json(Json {
                prettyPrint = true
                isLenient = true
                ignoreUnknownKeys = true
            })
        }
    }
}

where the httpClient function is declared as

expect fun httpClient(mockEngine: HttpClientEngine? = null, config: HttpClientConfig<*>.() -> Unit = {}): HttpClient

and defined on JVM as

actual fun httpClient(mockEngine: HttpClientEngine?, config: HttpClientConfig<*>.() -> Unit) = mockEngine?.let(::HttpClient) ?: HttpClient(OkHttp) {
    config(this)

    engine {
        config {
            retryOnConnectionFailure(true)
            connectTimeout(0, TimeUnit.SECONDS)
        }
    }
}

All my tests are currently in the commonTest module.

Do you have any idea on what the problem might be @Aleksei Tirman [JB]?

[Aleksei Tirman [JB]]

What engine is used in tests? Can you share code for some test?

[Richard Hajdu]

An implementation of a client would look like this

internal class BerriesApiClient(mockEngine: HttpClientEngine? = null) : BerriesApi, ApiClient by DefaultApiClient(mockEngine) { ... }

and in a corresponding test I'd create the client as

private fun createClient(response: String): BerriesApiClient {
    val mockEngine = MockEngine {
        respond(
            content = response, headers = headersOf(HttpHeaders.ContentType, "application/json")
        )
    }

    return BerriesApiClient(mockEngine)
}

[Richard Hajdu]

Hey @Aleksei Tirman [JB]! 👋🏻
Any update on this? Any ideas regarding?

[Aleksei Tirman [JB]]

It's difficult to say something just by looking at the code above. The error tells that the expected type of a response or request body is MoveTarget but the body hasn't been transformed to that type (usually by the ContentNegotiation plugin).

[Richard Hajdu]

Yes, but it also tells that the response is from localhost, isn't that sus? I mean, if the MockEngine would be used it shouldn't be the case, right?

[Aleksei Tirman [JB]]

Most likely it would happen with the MockEngine because if you don't explicitly specify the host then the localhost is assumed.

[Richard Hajdu]

It's just interesting that if I don't configure platform-specific engines, but simply expect it as a parameter at runtime

internal class DefaultApiClient(engine: HttpClientEngine) : ApiClient {
    override val httpClient = HttpClient(engine) {
        defaultRequest {
            url {
                protocol = URLProtocol.HTTPS
                host = "<http://pokeapi.co|pokeapi.co>"
                path("api/v2/")
            }
        }
        install(HttpCache)
        install(ContentNegotiation) {
            json(Json {
                prettyPrint = true
                isLenient = true
                ignoreUnknownKeys = true
            })
        }
    }
}

and don't modify the unit tests, everything works fine, but as soon as I replace the HttpClient with the platform-specific one (which AFAIK inherits the ContentNegotiation plugin from the shared config defined above) it just falls apart.
I'll have time to dig deeper into this tomorrow, I'll try to identify the root cause.

[Richard Hajdu]

You were right, it was the absence of the ContentNegotiation plugin, because I didn't config the HttpClient properly with the optional MockEngine.
The code before

actual fun httpClient(mockEngine: HttpClientEngine?, config: HttpClientConfig<*>.() -> Unit) = mockEngine?.let(::HttpClient) ?: HttpClient(OkHttp) {
    config(this)
    ...
}

and after

actual fun httpClient(mockEngine: HttpClientEngine?, config: HttpClientConfig<*>.() -> Unit) = mockEngine?.let { HttpClient(it) { config(this) } } ?: HttpClient(OkHttp) {
    config(this)
    ...
}

See how I simply created the HttpClient using the default constructor without configuring the engine properly before.