From d21f6112891c3b29fd5c5d5cb95690212695eed2 Mon Sep 17 00:00:00 2001
From: TheArrayser <thearrayser@cringe-studios.com>
Date: Sun, 12 Jan 2025 13:35:02 +0100
Subject: [PATCH] added basic prime number checker

---
 main.go  |  12 +++++-
 prime.go | 111 +++++++++++++++++++++++++++++++++++++++++++++++++++++++
 2 files changed, 122 insertions(+), 1 deletion(-)
 create mode 100644 prime.go

diff --git a/main.go b/main.go
index 358ef46..a01b705 100644
--- a/main.go
+++ b/main.go
@@ -22,6 +22,16 @@ func (h *dnsHandler) ServeDNS(w dns.ResponseWriter, r *dns.Msg) {
 		fmt.Printf("Received query: %s (%d)\n", question.Name, question.Qtype)
 
 		if question.Qtype == dns.TypeCNAME || question.Qtype == dns.TypeA || question.Qtype == dns.TypeAAAA {
+			if strings.HasSuffix(question.Name, "prime.cringe-studios.com") || strings.HasSuffix(question.Name, "prime.cringe-studios.com.") {
+				primeAnswer := HandlePrimeNumberChecker(question)
+
+				if primeAnswer != nil {
+					msg.Answer = append(msg.Answer, primeAnswer)
+				}
+
+				continue
+			}
+
 			if question.Name == "google.com." {
 				msg.Answer = append(msg.Answer, &dns.CNAME{
 					Hdr: dns.RR_Header{
@@ -109,7 +119,7 @@ func getPage(w http.ResponseWriter, r *http.Request) {
 }
 
 func main() {
-	log.Println("Starting Server!");
+	log.Println("Starting Server!")
 
 	handler := new(dnsHandler)
 
diff --git a/prime.go b/prime.go
new file mode 100644
index 0000000..0cab9f6
--- /dev/null
+++ b/prime.go
@@ -0,0 +1,111 @@
+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.",
+		}
+	}
+}