proxy.go

package main

import (
	"net"
	"json"
	"http"
	"os"
	"io"
)

type Server map[string]string

func (s Server) ServeHTTP(out http.ResponseWriter, r *http.Request) {
	if addr, ok := s[r.Host]; ok {
		if c, e := net.Dial("tcp", "", addr); e == nil {
			if oc, _, e := out.Hijack(); e == nil {
				go func() {
					io.Copy(oc, c)
					oc.Close()
				}()
				go func() {
					r.Header["X-Forwarded-For"] = out.RemoteAddr()
					r.Write(c)
					io.Copy(c, oc)
					c.Close()
				}()
				return
			} else c.Close()
		} else os.Stderr.WriteString(os.Args[0] + ": " + e.String() + "\n")
	}
	out.WriteHeader(503)
	out.Write([]byte("Service Unavailable"))
}

func main() {
	var (
		f io.Reader
		e os.Error
	)
	c := new(struct {
		Host string
		Services Server
	})
	if f, e = os.Open("config.json", os.O_RDONLY, 0); e == nil {
		if e = json.NewDecoder(f).Decode(c); e == nil {
			var l net.Listener
			if l, e = net.Listen("tcp", c.Host); e == nil {
				if e = http.Serve(l, c.Services); e == nil {
					os.Exit(0)
				}
			}
		}
	}
	os.Stderr.WriteString(os.Args[0] + ": " + e.String() + "\n")
	os.Exit(1)
}