// Test program to experiment the IETF draft draft-ietf-dnsop-rrserial (hereafter "the draft").
// Depends on godns <https://miek.nl/2014/august/16/go-dns-package/> <https://github.com/miekg/dns>.

// If you don't know Go:
//   go get github.com/miekg/dns
//   go build test-rrserial.go

package main

import (
	"encoding/binary"
	"fmt"
	"github.com/miekg/dns"
	"os"
	"strings"
)

const otype = 65024

func print_rrserial(msg *dns.Msg) {
	opt := msg.IsEdns0()
	for _, v := range opt.Option {
		switch v := v.(type) {
		case *dns.EDNS0_LOCAL:
			if v.Option() == otype {
				serial := binary.BigEndian.Uint32(v.Data)
				fmt.Printf("EDNS rrserial found, \"%d\"\n", serial)
			}
		default:
			continue
		}
	}
}

func main() {
	if len(os.Args) != 3 && len(os.Args) != 4 {
		fmt.Printf("%s SERVER QNAME [QTYPE]\n", os.Args[0])
		os.Exit(1)
	}
	ns := os.Args[1]
	qname := dns.Fqdn(os.Args[2])
	qtype := dns.TypeAAAA
	ok := true
	if len(os.Args) == 4 {
		if qtype, ok = dns.StringToType[strings.ToUpper(os.Args[3])]; ok {
			// Good value
		} else {
			fmt.Printf("%s is not a known record type\n", strings.ToUpper(os.Args[3]))
			os.Exit(1)
		}
	}
	m := new(dns.Msg)
	m.Question = make([]dns.Question, 1)
	c := new(dns.Client)
	o := new(dns.OPT)
	o.Hdr.Name = "."
	o.Hdr.Rrtype = dns.TypeOPT
	o.SetUDPSize(4096)
	e := new(dns.EDNS0_LOCAL)
	e.Code = otype
	e.Data = []byte{}
	o.Option = append(o.Option, e)
	m.Extra = append(m.Extra, o)
	m.Question[0] = dns.Question{qname, qtype, dns.ClassINET}
	in, _, err := c.Exchange(m, ns+":53")
	if err == nil && in != nil {
		if in.Rcode == dns.RcodeRefused {
			fmt.Printf("Query refused (may be %s is a resolver, we do not ask for recursion)\n", ns)
			os.Exit(1)
		} else if in.Rcode == dns.RcodeFormatError {
			fmt.Printf("%s claims our format is incorrect, it is wrong\n", ns)
			os.Exit(1)
		} else if in.Rcode == dns.RcodeNameError {
			fmt.Printf("%s not found\n", qname)
			gotSoa := false
			serial := uint32(0)
			for _, rsoa := range in.Ns {
				switch rsoa.(type) {
				case *dns.SOA:
					serial = rsoa.(*dns.SOA).Serial
					gotSoa = true
				default:
					continue
				}
			}
			if !gotSoa {
				fmt.Printf("No SOA in the answer :-(\n")
				os.Exit(1)
			} else {
				fmt.Printf("Serial number in SOA %d\n", serial)
			}
			os.Exit(0)
		} else if in.Rcode == dns.RcodeServerFailure {
			fmt.Printf("Server failure\n")
			print_rrserial(in)
			os.Exit(1)
		} else if in.Rcode != dns.RcodeSuccess {
			fmt.Printf("Wrong return code %d\n", in.Rcode)
			os.Exit(1)
		}
		if len(in.Answer) > 0 {
			for _, rec := range in.Answer {
				fmt.Printf("%s\n", rec)
			}
		} else if len(in.Answer) == 0 {
			fmt.Printf("Empty answer received\n")
		}
		print_rrserial(in)
	} else {
		if err != nil {
			fmt.Printf("Error in query: %s\n", err)
		} else if in == nil {
			fmt.Printf("No answer received\n")
		}
		os.Exit(1)
	}
}