/* Tries several IP addresses to connect (IPv4 and IPv6) but with a short timeout, to keep the eyeballs happy. Author unknown. Retrieved from http://www.pastie.org/1528545 */

package main

import (
	"net"
	"time"
	"flag"
	"fmt"
	"strconv"
)


func multiHomeConnect(host string, port int, nsTimeout int64) net.Conn {
	r := make(chan net.Conn, 1)   // non-blocking chan
	timeout := make(chan bool, 1) // idem

	var fd net.Conn
	listAddr, err := net.LookupHost(host)
	if err != nil {
		return nil
	}

	connect := func(host, port string) {
		c, err := net.Dial("tcp", host+":"+port)
		if err != nil {
			return
		}
		r <- c
	}

	launchTimeout := func(ns int64) {
		time.Sleep(ns)
		timeout <- true
	}

	fmt.Println("Connecting to ", host)
done:
	for _, h := range listAddr {
		fmt.Println("try to connect to ", h)
		go connect(host, strconv.Itoa(port))
		go launchTimeout(nsTimeout)
		select {
		case fd = <-r:
			break done
		case <-timeout:
			nsTimeout >>= 1
		}
	}

	return fd
}


func main() {
	host := flag.String("host", "www.bortzmeyer.org", "host")
	port := flag.Int("port", 80, "port")
	timeout := flag.Int64("timeout", 100, "timeout in ms")
	flag.Parse()

	start := time.Nanoseconds()
	ok := multiHomeConnect(*host, *port, *timeout*1e6)
	stop := time.Nanoseconds()

	if ok != nil {
		fmt.Println("Connected to ", *host, " in ", (stop-start)/1e6, "ms")
		return
	}
	fmt.Println("*** Timeout ***")
}