import asynchttpserver, asyncdispatch, os, osproc

proc openProc() {.async.} =
  let process = startProcess("youtube-dl.exe", "", @[r"https://www.youtube.com/watch?t=4&v=BaW_jenozKc"])
  let processwait =  waitForExit(process)
  close(process)

var server = newAsyncHttpServer()
proc cb(req: Request) {.async.} =
  await req.respond(Http200, "test")
  if req.reqMethod == HttpMethod.HttpPost:
    var x = openProc() #this blocks new requests

waitFor server.serve(Port(8080), cb)