This code show a complex stuff done in few lines and 60ms max out of which 20ms come from the origin having hard time serving an HTML file...

KTGW_VTX.kt

import io.netty.buffer.ByteBufInputStream
import io.vertx.core.Vertx
import io.vertx.ext.web.client.WebClient
import org.jsoup.Jsoup
import org.jsoup.nodes.Element

fun main(args: Array<String>) {
    val vertx = Vertx.vertx()
    val server = vertx.createHttpServer()
    val client = WebClient.create(vertx)
    server.requestHandler { req ->
        client.get(80,"www.programaths.be",req.uri()).send{ get ->
            if(get.succeeded()){
                with(req.response()){
                    putHeader("content-type",get.result().getHeader("content-type"))
                    try {
                        if(get.result().getHeader("content-type")=="text/html") {
                            val parsed = Jsoup.parse(ByteBufInputStream(get.result().body().byteBuf), "utf8", "/")
                            parsed.getElementsByTag("div").append("ho ho ho")
                            parsed.getElementsByTag("img").forEach(::adjustSrc)
                            parsed.getElementsByTag("img").forEach(::adjustSrc)
                            end(parsed.toString())
                        }else{
                            end(get.result().body())
                        }
                    }catch(e:Exception) {
                        end("processing error")
                    }
                }
            }else{
                with(req.response()){
                    putHeader("content-type","text/plain")
                    end("sorry")
                }
            }
        }
    }
    server.listen(8080)
}

fun adjustSrc(el:Element){
    if (!el.attr("src").startsWith("http")) {
        el.attr("src", "http://www.programaths.be/" + el.attr("src"))
    }
}

It take an HTML document, locate each "div" and append the text "ho ho ho".
It also look at attributes of "script" and "img" tags to prefix them with "http://www.programaths.be/" if they do not start with "http".

So, that's quite heavy processing here, done in 40ms !