http_request.nim

var respChan: Channel[(string, string)]
var handlers: Table[string, proc (response: string)]

proc httpLoop() {.async.} =
  while true:
    let (received, resp) = respChan.tryRecv()
    if received:
      handlers[resp[0]](resp[1])
    await sleepAsync(1000)

proc doHttpRequest(url: string, handler: proc(response: string)) = # we can't modify the header of this proc
  echo "will do the request in background"
  handlers[url] = handler
  # dispatch some async stuff in the background, which will somehow call the `handler`



# After this line we can't modify the code
routes:
  get "/":
    echo "will do request"
    doHttpRequest("myurl", proc(r: string) = echo "got response")
    echo "response handled"
    resp Http200, "ok"

asyncCheck httpLoop
runForever()

# After the request to "/", we should see the following output
# will do request
# will do the request in background
# response handled
# ... some time passes
# got response