go

package main

import (
    "log"
    "fmt"
    "github.com/valyala/fasthttp"
)

func main() {
    err := fasthttp.ListenAndServe("127.0.0.1:12345", handler); if err != nil {
        log.Fatalf("Error in ListenAndServe: %s", err)
    }
}

func handler(ctx *fasthttp.RequestCtx) {
    fmt.Fprintf(ctx, "HelloWorld")
}