Block an asynchronous call from a foreign API

Hello everyone!

I’m currently developing an HTTP server with Ktor backed by the BFT-SMaRt library.

The BFT-SMaRt library is a Byzantine Fault Tolerant State Machine Replication library, our usage is to replicate system operations across nodes.

This library has an async call invokeAsynchRequest, I need to call this method in a Ktor Route, however since it is asynchronous it gets called, goes on with it’s life and returns.
I want to somehow block the method.

The method receives a Listener that gets invoked whenever a reply to a request arrives, whenever we have enough we want the Ktor Route to return.

I have the following Listener:

class Listener(val proxy: AsynchServiceProxy, val handler: (List<TOMMessage>) -> Unit) : ReplyListener {
    val quorumSize = 4
    val replies = mutableListOf<TOMMessage>()

    override fun replyReceived(ctx: RequestContext, message: TOMMessage) {
        if (replies.size > quorumSize) {
            LOGGER.debug("handler size > quorum ${replies}")

    override fun reset() {
        LOGGER.debug("reset called")

It receives an handler: (List<TOMMessage>) -> Unit that gets called whenever I have sufficient messages, this handler should be the one signaling when the Route request is ready to return.

In the HTTP side I have this

    Listener(asyncServiceProxy) {

This however doesn’t work because call.respond needs to be called from a coroutine context.

I know the question might not be fully clear but any help would be appreciated and I’ll be glad to clarify any detail!
Thank you everyone in advance!