myfirstgo.go

package main

import (
  "fmt"
  "net/http"
)

const lenDownload = len("/dl/")

func downloadHandler(w http.ResponseWriter, r *http.Request) {
  http.ServeFile(w, r, "./files/" + r.URL.Path[lenDownload:])
}

func handler(w http.ResponseWriter, r *http.Request) {
  fmt.Fprintf(w, "Lemon")
}

func main() {
  http.HandleFunc("/", handler)
  http.HandleFunc("/dl/", downloadHandler)
  http.ListenAndServe(":8181", nil)
}