Provide an easy way to create an HttpService from a Kotlin coroutine

[Dogacel]

Similar to

• Add CoroutineServerInterceptor #4669
• Support kotlin coroutine decorators #4725

We should have HttpService based on coroutines. Currently, only way to implement a suspend http service is using AnnotatedService. In some scenarios, users might want to use the HttpService or AbstractHttpService, which in my opinion has more granularly defined signatures which seem less like magic.

Sample proposed implementation 1 (inheritance)

abstract class CoroutineHttpService : HttpService {
    final override fun serve(ctx: ServiceRequestContext, req: HttpRequest): HttpResponse {
        val future = CoroutineScope(ctx.asCoroutineContext()).future {
            serveAsync(ctx, req)
        }

        return HttpResponse.of(future)
    }

    abstract suspend fun serveAsync(ctx: ServiceRequestContext, req: HttpRequest): HttpResponse
}

Sample proposed implementation 2 (composition)

interface CoroutineHttpService {
    fun serve(ctx: ServiceRequestContext, req: HttpRequest): HttpResponse
}

fun CoroutineHttpService.asHttpService(): HttpService {
    return HttpService { ctx, req ->
        HttpResponse.of(CoroutineScope(ctx.asCoroutineContext()).future {
            serve(ctx, req)
        })
    }
}

Ditto for AbstractHttpService.

Inheritance

Pros:

• Drop-in replacement to HttpService because it inherits.

Cons:

• Function name needs to be different such as serveAsync or coServe.
• Needs to be an abstract class to prevent overriding serve.

Composition

Pros:

• Method signatures are the same
• Interface, similar to HttpService.

Cons:

• Need to use .asHttpService() method to convert to an HttpService

Also need to check if we lose any valuable method if we don't inherit HttpService.

[minwoox]

Thanks, @Dogacel for the design. 👍

Needs to be an abstract class to prevent overriding serve.

I believe that we don't have to make it an abstract class as we do for CoroutineServerInterceptor:

armeria/grpc-kotlin/src/main/kotlin/com/linecorp/armeria/server/grpc/kotlin/CoroutineServerInterceptor.kt

Line 59 in df826c0

override fun <I : Any, O : Any> asyncInterceptCall(

Because users don't have to call .asHttpService() when using it, I prefer the first option.
Here is the interface version.
I also rename the method to suspendedServe. 😉

interface CoroutineHttpService : HttpService {

    override fun serve(ctx: ServiceRequestContext, req: HttpRequest): HttpResponse {
        return HttpResponse.of(CoroutineScope(ctx.asCoroutineContext()).future { // Do we also need to add user context?
            suspendedServe(ctx, req)
        })
    }

    suspend fun suspendedServe(ctx: ServiceRequestContext, req: HttpRequest): HttpResponse
}

[Dogacel]

Thanks, @Dogacel for the design. 👍

Needs to be an abstract class to prevent overriding serve.

I believe that we don't have to make it an abstract class as we do for CoroutineServerInterceptor:

If this risk is something accepted down the line, I'm fine with it 😄.

armeria/grpc-kotlin/src/main/kotlin/com/linecorp/armeria/server/grpc/kotlin/CoroutineServerInterceptor.kt

Line 59 in df826c0

override fun <I : Any, O : Any> asyncInterceptCall(

Because users don't have to call .asHttpService() when using it, I prefer the first option. Here is the interface version. I also rename the method to suspendedServe. 😉

interface CoroutineHttpService : HttpService {

    override fun serve(ctx: ServiceRequestContext, req: HttpRequest): HttpResponse {
        return HttpResponse.of(CoroutineScope(ctx.asCoroutineContext()).future { // Do we also need to add user context?
            suspendedServe(ctx, req)
        })
    }

    suspend fun suspendedServe(ctx: ServiceRequestContext, req: HttpRequest): HttpResponse
}

LGTM 👍 Consistency is desired.

[minwoox]

Thanks! By the way, this issue has been assigned to a participant for our internal sprint. 😉