Ktor - Keep POST alive until receiving websocket communication - multithreading

Question

I am building an API with Kotlin and Ktor that should be able to receive a normal POST request.
Upon receiving it, he should keep it alive and establish a series of asynchronous communications with other systems using websocket.
Only at the end of these communications and receiving certain information will it be able to respond to the POST request.
Needless to say, the request must be kept alive.
I'm not sure how to make this possible.
I have investigated using coroutines and threads but my inexperience prevents me from understanding what would be the best solution.

Answer 1

By default sequential code inside a coroutine is executed synchronously so you can just put your code for communication via Websockets inside a route's handler and in the end send a response. Here is an example:
import io.ktor.client.*
import io.ktor.client.engine.okhttp.*
import io.ktor.client.plugins.websocket.*
import io.ktor.client.plugins.websocket.WebSockets
import io.ktor.server.application.*
import io.ktor.server.engine.*
import io.ktor.server.netty.*
import io.ktor.server.response.*
import io.ktor.server.routing.*
import io.ktor.server.websocket.*
import io.ktor.websocket.*
fun main() {
val client = HttpClient(OkHttp) {
install(WebSockets)
}
embeddedServer(Netty, port = 12345) {
routing {
get("/") {
client.webSocket("ws://127.0.0.1:5050/ws") {
outgoing.send(Frame.Text("Hello"))
val frame = incoming.receive()
println((frame as Frame.Text).readText())
println("Websockets is done")
}
call.respondText { "Done" }
}
}
}.start(wait = false)
embeddedServer(Netty, port = 5050) {
install(io.ktor.server.websocket.WebSockets)
routing {
webSocket("/ws") {
outgoing.send(Frame.Text("Hello from server"))
}
}
}.start()
}