Sample for REST API using Location and JSON - ktor

Question

The title already says what I'm trying to do in a nutshell: implement a simple REST API that uses ktor's Location feature and accepts requests with JSON as payload.
Let's say that I want to have a resource "books" that is available under the URI /books. A get request should return a list of available books, a post request with data for a new book should create a new book and return a redirect to the newly created book. My implementation looks like this:
#Location ("/books") data class BookRequest(val title: String = "" )
fun Application.bookModule() {
routing {
get<BookRequest> {
val books = bookHandler.listBooks()
//generate HTML from books and respond
}
post<BookRequest> {
val request = call.receive<BookRequest>()
//create a new book resource from the data in request
//and respond with redirect to new book
}
}
The get request works as intended but when I try to POST a new book using curl like this
curl --header "Content-Type: application/json" \
--request POST \
--data '{"title":"Hitchhiker"}' \
http://localhost:8080/books
the content of the title attribute of the request is empty.
Does anyone have a pointer to a working example using Locations with POST and JSON?

Answer 1

You need to install ContentNegotiation plugin for deserializing JSON data to a BookRequest object and if you use kotlinx.serialization then mark the BookRequest class with Serializable annotation. Here is the full example:
import io.ktor.application.*
import io.ktor.features.*
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.serialization.*
import io.ktor.server.engine.*
import io.ktor.server.netty.*
import kotlinx.serialization.Serializable
fun main(args: Array<String>) {
embeddedServer(Netty, port = 8080) {
install(ContentNegotiation) {
json()
}
install(Locations)
routing {
post<BookRequest> {
val r = call.receive<BookRequest>()
call.respondText { r.title }
}
}
}.start()
}
#Location("/books")
#Serializable
data class BookRequest(val title: String = "")