split-traffic.go

package main

import (
	"fmt"
	"io"
	"math/rand"
	"net"
	"net/http"
)

func sortVariation() string {
	variations := []string{"A", "B", "C", "D", "E", "F", "G", "H", "I", "J"}
	n := rand.Int() % len(variations)
	return variations[n]
}

func userVariation(w http.ResponseWriter, r *http.Request) string {
	var variation string

	cookie, _ := r.Cookie("variation")
	if cookie != nil {
		variation = fmt.Sprintf("%s", cookie.Value)
	} else {
		cleanHost, _, _ := net.SplitHostPort(r.Host)
		path := r.URL.Path
		variation = sortVariation()

		cookie := http.Cookie{Name: "variation", Value: variation, Domain: cleanHost, Path: path}
		http.SetCookie(w, &cookie)
	}

	return variation
}

func renderView(w http.ResponseWriter, r *http.Request) {
	variation := userVariation(w, r)
	io.WriteString(w, fmt.Sprintf("Hello world %s!", variation))
}

func main() {
	http.HandleFunc("/", renderView)
	http.ListenAndServe(":8000", nil)
}