Ktor Location API: mapping JSON to generic Map object - ktor

Question

When I use the regular routing API together with GSON, I can deserialize a JSON parameter to a Map<String, Any> with the following code snippet:
post("/books") {
val request = call.receive<Map<String, Any>>()
...
}
In my case request is an instance of com.google.gson.internal.LinkedTreeMap.
Is there a way to do the same using the Location API? It works fine when I define a data class with concrete members but I can't find a way to use a map. I'm trying it with a couple of things along those lines:
#Location ("/books")
<some magic class definition>
fun Application.bookModule() {
routing {
post<BookRequest> {
val request = call.receive<BookRequest>()
...
}
but I've not come up with anything that works. Help?

Answer 1

Locations represent path and query parameters of endpoints only, so there is no way to route depending on the request body. Properties of a location class should be mapped to path segments, e.g.
#Location ("/books/{title}/{author}") data class BookRequest(
val title: String,
val author: String,
)
To receive a request body and convert to it an object just use the ContentNegotiation plugin. Here is the example of a server that responds with 200 OK to the curl -v --header "Content-Type: application/json" --request POST --data '{"title":"Hitchhiker", "author":"DNA", "detail":{"foo": "bar"}}' http://localhost:8080/books request:
import io.ktor.application.*
import io.ktor.features.*
import io.ktor.gson.*
import io.ktor.http.*
import io.ktor.locations.*
import io.ktor.locations.post
import io.ktor.request.*
import io.ktor.response.*
import io.ktor.routing.routing
import io.ktor.server.engine.*
import io.ktor.server.netty.*
fun main(args: Array<String>) {
embeddedServer(Netty, port = 8080) {
install(ContentNegotiation) {
gson()
}
install(Locations)
bookModule()
}.start()
}
fun Application.bookModule() {
routing {
post<BookRequest> {
val request = call.receive<Map<String, Any>>()
println(request)
call.respond(HttpStatusCode.OK)
}
}
}
#Location ("/books") class BookRequest