simple subdomain based Proxy to a url

proxy.go

package main

import (
	"github.com/labstack/echo"
	"github.com/labstack/echo/middleware"
	"net/url"
	"strings"
)

var ServerPort = ":8000"

type (
	Balancer struct {
		M map[string]*middleware.ProxyTarget
		middleware.ProxyBalancer
	}
)

func NewBalancer(targets []*middleware.ProxyTarget) middleware.ProxyBalancer {
	b := Balancer{
		M: make(map[string]*middleware.ProxyTarget),
	}

	for i := range targets {
		key := strings.ToUpper(targets[i].Name)
		b.M[key] = targets[i]
	}

	return b
}

func (balancer Balancer) AddTarget(target *middleware.ProxyTarget) bool {
	return false
}

func (balancer Balancer) RemoveTarget(str string) bool { return false }

func (balancer Balancer) Next(ctx echo.Context) *middleware.ProxyTarget {
	host := ctx.Request().Host

	host = strings.ReplaceAll(host, ".localhost"+ServerPort, "")

	hostInfo := strings.Split(host, ".")

	if len(hostInfo) == 2 {
		key := strings.Split(host, ".")[1]
		key = strings.ToUpper(key)

		if val, ok := balancer.M[key]; ok {
			return val
		}
	}

	return balancer.M["S1"]
}

func main() {
	e := echo.New()
	e.Use(middleware.Recover())
	e.Use(middleware.Logger())

	s1, err := url.Parse("http://localhost:5000")
	if err != nil {
		e.Logger.Fatal(err)
	}

	s2, err := url.Parse("http://localhost:5001")
	if err != nil {
		e.Logger.Fatal(err)
	}

	targets := []*middleware.ProxyTarget{
		{
			Name: "S1",
			URL:  s1,
		},
		{
			Name: "S2",
			URL:  s2,
		},
	}
	e.Use(middleware.Proxy(NewBalancer(targets)))

	e.Logger.Fatal(e.Start(ServerPort))
}