dns/prime.go

package main

import (
	"fmt"
	"math/big"
	"regexp"
	"strings"

	"github.com/miekg/dns"
)

var numberRegex = regexp.MustCompile(`^[0-9]+$`)

var maximumPrimeNumber, _ = new(big.Int).SetString("0xFFFF_FFFF_FFFF_FFFF", 0)

func IsNumber(stringToCheck string) bool {
	return numberRegex.MatchString(stringToCheck)
}

func HandlePrimeNumberChecker(question dns.Question) dns.RR {
	mainDomainPartindex := strings.LastIndex(question.Name, "prime.cringe-studios.com")
	if mainDomainPartindex == 0 || mainDomainPartindex == 1 {
		// TODO handle ns page part.. maybe send back a CNAME for a page to enter the number

		return nil
	}

	isQuestionPartIndex := strings.LastIndex(question.Name, "is.prime.cringe-studios.com")
	if isQuestionPartIndex == 0 || isQuestionPartIndex == 1 {
		// TODO handle resource found
		return nil
	}

	isnotQuestionPartIndex := strings.LastIndex(question.Name, "isnot.prime.cringe-studios.com")
	if isnotQuestionPartIndex == 0 || isnotQuestionPartIndex == 1 {
		// TODO handle resource found
		return nil
	}

	maybeQuestionPartIndex := strings.LastIndex(question.Name, "maybe.prime.cringe-studios.com")
	if maybeQuestionPartIndex == 0 || maybeQuestionPartIndex == 1 {
		// TODO handle resource found
		return nil
	}

	mainDomainPart := question.Name[0 : mainDomainPartindex-1] // subtract 1 for the p in prime

	if !strings.HasSuffix(mainDomainPart, ".") {
		// unknown subdomain like 123prime.cringe-studios.com
		return nil
	}

	mainDomainPart = mainDomainPart[0 : len(mainDomainPart)-2] // subtract 1 to accomodate for the length being one bigger then the last index, and subtract another one for the dot at the end

	if len(mainDomainPart) == 0 {
		// .prime.cringe-studios.com
		return nil
	}

	firstIsIndex := strings.Index(mainDomainPart, "is.")

	if firstIsIndex == 0 || firstIsIndex == 1 {
		// word "is." found at the beginning of the question.. trim
		mainDomainPart = mainDomainPart[len("is.") : len(mainDomainPart)-1]
	}

	if len(mainDomainPart) == 0 {
		// requested domain was is.prime.cringe-studios.com or something like that...
		// TODO
		return nil
	}

	if !IsNumber(mainDomainPart) {
		// TODO return cname to isnot.prime.cringe-studios.com
		return nil
	}

	bigNumber := new(big.Int)
	fmt.Sscan(mainDomainPart, bigNumber)

	if bigNumber.Cmp(maximumPrimeNumber) == 1 {
		// number is bigger than the maximum limit for the propablyprime function
		// TODO return CNAME for maybe.prime.cringe-studios.com

		return nil
	}

	if bigNumber.ProbablyPrime(20) {
		// is prime, because the cases bigger than 2^64-1 have been catched above
		return &dns.CNAME{
			Hdr: dns.RR_Header{
				Name:   question.Name,
				Rrtype: dns.TypeCNAME,
				Class:  dns.ClassINET,
				Ttl:    30,
			},
			Target: "is.prime.cringe-studios.com.",
		}
	} else {
		// is not prime
		return &dns.CNAME{
			Hdr: dns.RR_Header{
				Name:   question.Name,
				Rrtype: dns.TypeCNAME,
				Class:  dns.ClassINET,
				Ttl:    30,
			},
			Target: "isnot.prime.cringe-studios.com.",
		}
	}
}