// A RFC 868 (Time protocol) client

package main

import (
	"fmt"
	"flag"
	"time"
	"net"
	"os"
	"encoding/binary"
)

func main() {
	var (
		port     = "37"
		thetime  int64
		response = make([]byte, 4)
	)
	if flag.NArg() != 1 {
		fmt.Printf("Usage: time-rfc-868 host\n")
		os.Exit(1)
	}
	host := flag.Arg(0)
	remote := host + ":" + port
	con, error := net.Dial("tcp4", "", remote)
	if error != nil {
		fmt.Printf("Cannot connect to %s: %s\n", host, error)
		os.Exit(1)
	}
	defer con.Close()
	in, error := con.Read(response)
	if error != nil || in != 4 {
		fmt.Printf("Error reading data: %s, in: %d\n", error, in)
		os.Exit(2)
	}
	// RFC 868 sets the epoch in 1900 but Go's libraries use 1970
	theoffsettime, error := time.Parse(time.RFC3339, "1900-01-01T00:00:00Z")
	theoffsetseconds := theoffsettime.Seconds()
	thetime = int64(binary.BigEndian.Uint32(response))
	theparsedtime := time.SecondsToUTC(thetime + theoffsetseconds)
	fmt.Printf("Time at %s is %d (which is %s)\n",
		remote, thetime, theparsedtime)
}