local-ip.sh/xip/xip.go

package xip

import (
	"fmt"
	"log"
	"net"
	"os"
	"regexp"
	"strings"
	"time"

	"github.com/miekg/dns"
)

type Xip struct {
	server      dns.Server
	nameServers []*dns.NS
}

type HardcodedRecord struct {
	A     []net.IP // => dns.A
	AAAA  []net.IP // => dns.AAAA
	TXT   []string // => dns.TXT
	MX    []*dns.MX
	CNAME []string // => dns.CNAME
	SRV   *dns.SRV
}

const (
	zone        = "local-ip.sh."
	nameservers = "ns1.local-ip.sh.,ns2.local-ip.sh."
)

var (
	flyRegion        = os.Getenv("FLY_REGION")
	dottedIpV4Regex  = regexp.MustCompile(`(?:^|(?:[\w\d])+\.)(((25[0-5]|(2[0-4]|1\d|[1-9]|)\d)\.?\b){4})($|[.-])`)
	dashedIpV4Regex  = regexp.MustCompile(`(?:^|(?:[\w\d])+\.)(((25[0-5]|(2[0-4]|1\d|[1-9]|)\d)\-?\b){4})($|[.-])`)
	hardcodedRecords = map[string]HardcodedRecord{
		"ns.local-ip.sh.": {
			// record holding ip addresses of ns1 and ns2
			A: []net.IP{
				net.IPv4(137, 66, 40, 11),
				net.IPv4(137, 66, 40, 12),
			},
		},
		"ns1.local-ip.sh.": {
			A: []net.IP{
				net.IPv4(137, 66, 40, 11), // fly.io edge-only ip address, see https://community.fly.io/t/custom-domains-certificate-is-stuck-on-awaiting-configuration/8329
			},
		},
		"ns2.local-ip.sh.": {
			A: []net.IP{
				net.IPv4(137, 66, 40, 12), // fly.io edge-only ip address #2
			},
		},
		"local-ip.sh.": {
			A: []net.IP{
				net.IPv4(137, 66, 40, 11), // fly.io edge-only ip address
			},
			TXT: []string{"v=spf1 include:capsulecorp.dev ~all"},
			MX: []*dns.MX{
				{Preference: 10, Mx: "email.capsulecorp.dev."},
			},
		},
		"autodiscover.local-ip.sh.": {
			CNAME: []string{
				"email.capsulecorp.dev.",
			},
		},
		"_autodiscover._tcp.local-ip.sh.": {
			SRV: &dns.SRV{
				Priority: 0,
				Weight:   0,
				Port:     443,
				Target:   "email.capsulecorp.dev.",
			},
		},
		"autoconfig.local-ip.sh.": {
			CNAME: []string{
				"email.capsulecorp.dev.",
			},
		},
		"_dmarc.local-ip.sh.": {
			TXT: []string{"v=DMARC1; p=none; rua=mailto:postmaster@local-ip.sh; ruf=mailto:admin@local-ip.sh"},
		},
		"dkim._domainkey.local-ip.sh.": {
			TXT: []string{
				"v=DKIM1;k=rsa;t=s;s=email;p=MIIBIjANBgkqhkiG9w0BAQEFAAOCAQ8AMIIBCgKCAQEAsMW6NFo34qzKRPbzK41GwbWncB8IDg1i2eA2VWznIVDmTzzsqILaBOGv2xokVpzZm0QRF9wSbeVUmvwEeQ7Z6wkfMjawenDEc3XxsNSvQUVBP6LU/xcm1zsR8wtD8r5J+Jm45pNFaateiM/kb/Eypp2ntdtd8CPsEgCEDpNb62LWdy0yzRdZ/M/fNn51UMN8hVFp4YfZngAt3bQwa6kPtgvTeqEbpNf5xanpDysNJt2S8zfqJMVGvnr8JaJiTv7ZlKMMp94aC5Ndcir1WbMyfmgSnGgemuCTVMWDGPJnXDi+8BQMH1b1hmTpWDiVdVlehyyWx5AfPrsWG9cEuDIfXwIDAQAB",
			},
		},
		"_acme-challenge.local-ip.sh.": {
			// will be filled in later when requesting the wildcard certificate
			TXT: []string{},
		},
	}
)

func (xip *Xip) SetTXTRecord(fqdn string, value string) {
	log.Printf("trying to set TXT record \"%s\" for fqdn \"%s\"", value, fqdn)
	if fqdn != "_acme-challenge.local-ip.sh." {
		log.Println("not allowed, abort")
		return
	}

	if records, ok := hardcodedRecords[fqdn]; ok {
		records.TXT = []string{value}
		hardcodedRecords["_acme-challenge.local-ip.sh."] = records
	}
}

func (xip *Xip) UnsetTXTRecord(fqdn string) {
	log.Printf("trying to unset TXT record for fqdn \"%s\"", fqdn)
	if fqdn != "_acme-challenge.local-ip.sh." {
		log.Println("not allowed, abort")
		return
	}

	if records, ok := hardcodedRecords[fqdn]; ok {
		records.TXT = []string{}
		hardcodedRecords["_acme-challenge.local-ip.sh."] = records
	}
}

func (xip *Xip) fqdnToA(fqdn string) []*dns.A {
	normalizedFqdn := strings.ToLower(fqdn)
	if hardcodedRecords[normalizedFqdn].A != nil {
		var records []*dns.A

		for _, record := range hardcodedRecords[normalizedFqdn].A {
			records = append(records, &dns.A{
				Hdr: dns.RR_Header{
					Ttl:    uint32((time.Minute * 5).Seconds()),
					Name:   fqdn,
					Rrtype: dns.TypeA,
					Class:  dns.ClassINET,
				},
				A: record,
			})
		}

		return records
	}

	for _, ipV4RE := range []*regexp.Regexp{dashedIpV4Regex, dottedIpV4Regex} {
		if ipV4RE.MatchString(fqdn) {
			match := ipV4RE.FindStringSubmatch(fqdn)[1]
			match = strings.ReplaceAll(match, "-", ".")
			ipV4Address := net.ParseIP(match).To4()
			if ipV4Address == nil {
				return nil
			}

			return []*dns.A{{
				Hdr: dns.RR_Header{
					Ttl:    uint32((time.Minute * 5).Seconds()),
					Name:   fqdn,
					Rrtype: dns.TypeA,
					Class:  dns.ClassINET,
				},
				A: ipV4Address,
			}}
		}
	}

	return nil
}

func (xip *Xip) answerWithAuthority(question dns.Question, message *dns.Msg) {
	message.Ns = append(message.Ns, xip.soaRecord(question))
}

func (xip *Xip) handleA(question dns.Question, message *dns.Msg) {
	fqdn := question.Name
	records := xip.fqdnToA(fqdn)

	if len(records) == 0 {
		message.Rcode = dns.RcodeNameError
		xip.answerWithAuthority(question, message)
		return
	}

	for _, record := range records {
		log.Printf("(%s) %s => %s\n", flyRegion, fqdn, record.A)
		message.Answer = append(message.Answer, record)
	}
}

func (xip *Xip) handleAAAA(question dns.Question, message *dns.Msg) {
	fqdn := question.Name
	normalizedFqdn := strings.ToLower(fqdn)
	if hardcodedRecords[normalizedFqdn].AAAA == nil {
		xip.answerWithAuthority(question, message)
		return
	}

	for _, record := range hardcodedRecords[normalizedFqdn].AAAA {
		message.Answer = append(message.Answer, &dns.AAAA{
			Hdr: dns.RR_Header{
				Ttl:    uint32((time.Minute * 5).Seconds()),
				Name:   fqdn,
				Rrtype: dns.TypeAAAA,
				Class:  dns.ClassINET,
			},
			AAAA: record,
		})
	}
}

func (xip *Xip) handleNS(question dns.Question, message *dns.Msg) {
	fqdn := question.Name
	nameServers := []*dns.NS{}
	additionals := []*dns.A{}
	for _, ns := range xip.nameServers {
		nameServers = append(nameServers, &dns.NS{
			Hdr: dns.RR_Header{
				Ttl:    uint32((time.Minute * 5).Seconds()),
				Name:   fqdn,
				Rrtype: dns.TypeNS,
				Class:  dns.ClassINET,
			},
			Ns: ns.Ns,
		})

		additionals = append(additionals, xip.fqdnToA(ns.Ns)...)
	}

	for _, record := range nameServers {
		message.Answer = append(message.Answer, record)
	}

	for _, record := range additionals {
		message.Extra = append(message.Extra, record)
	}
}

func chunkBy(str string, chunkSize int) (chunks []string) {
	for chunkSize < len(str) {
		str, chunks = str[chunkSize:], append(chunks, str[0:chunkSize])
	}
	return append(chunks, str)
}

func (xip *Xip) handleTXT(question dns.Question, message *dns.Msg) {
	fqdn := question.Name
	normalizedFqdn := strings.ToLower(fqdn)
	if hardcodedRecords[normalizedFqdn].TXT == nil {
		xip.answerWithAuthority(question, message)
		return
	}

	for _, record := range hardcodedRecords[normalizedFqdn].TXT {
		message.Answer = append(message.Answer, &dns.TXT{
			Hdr: dns.RR_Header{
				Ttl:    uint32((time.Minute * 5).Seconds()),
				Name:   fqdn,
				Rrtype: dns.TypeTXT,
				Class:  dns.ClassINET,
			},
			Txt: chunkBy(record, 255),
		})
	}
}

func (xip *Xip) handleMX(question dns.Question, message *dns.Msg) {
	fqdn := question.Name
	normalizedFqdn := strings.ToLower(fqdn)
	if hardcodedRecords[normalizedFqdn].MX == nil {
		xip.answerWithAuthority(question, message)
		return
	}

	for _, record := range hardcodedRecords[normalizedFqdn].MX {
		message.Answer = append(message.Answer, &dns.MX{
			Hdr: dns.RR_Header{
				Ttl:    uint32((time.Minute * 5).Seconds()),
				Name:   fqdn,
				Rrtype: dns.TypeMX,
				Class:  dns.ClassINET,
			},
			Mx:         record.Mx,
			Preference: record.Preference,
		})
	}
}

func (xip *Xip) handleCNAME(question dns.Question, message *dns.Msg) {
	fqdn := question.Name
	normalizedFqdn := strings.ToLower(fqdn)
	if hardcodedRecords[normalizedFqdn].CNAME == nil {
		xip.answerWithAuthority(question, message)
		return
	}

	for _, record := range hardcodedRecords[normalizedFqdn].CNAME {
		message.Answer = append(message.Answer, &dns.CNAME{
			Hdr: dns.RR_Header{
				Ttl:    uint32((time.Minute * 5).Seconds()),
				Name:   fqdn,
				Rrtype: dns.TypeCNAME,
				Class:  dns.ClassINET,
			},
			Target: record,
		})
	}
}

func (xip *Xip) handleSRV(question dns.Question, message *dns.Msg) {
	fqdn := question.Name
	normalizedFqdn := strings.ToLower(fqdn)
	if hardcodedRecords[normalizedFqdn].SRV == nil {
		xip.answerWithAuthority(question, message)
		return
	}

	message.Answer = append(message.Answer, &dns.SRV{
		Hdr: dns.RR_Header{
			Ttl:    uint32((time.Minute * 5).Seconds()),
			Name:   fqdn,
			Rrtype: dns.TypeSRV,
			Class:  dns.ClassINET,
		},
		Priority: hardcodedRecords[normalizedFqdn].SRV.Priority,
		Weight:   hardcodedRecords[normalizedFqdn].SRV.Weight,
		Port:     hardcodedRecords[normalizedFqdn].SRV.Port,
		Target:   hardcodedRecords[normalizedFqdn].SRV.Target,
	})
}

func (xip *Xip) handleSOA(question dns.Question, message *dns.Msg) {
	message.Answer = append(message.Answer, xip.soaRecord(question))
}

func (xip *Xip) soaRecord(question dns.Question) *dns.SOA {
	soa := new(dns.SOA)
	soa.Hdr = dns.RR_Header{
		Name:     question.Name,
		Rrtype:   dns.TypeSOA,
		Class:    dns.ClassINET,
		Ttl:      uint32((time.Minute * 5).Seconds()),
		Rdlength: 0,
	}
	soa.Ns = "ns1.local-ip.sh."
	soa.Mbox = "admin.local-ip.sh."
	soa.Serial = 2022102800
	soa.Refresh = uint32((time.Minute * 15).Seconds())
	soa.Retry = uint32((time.Minute * 15).Seconds())
	soa.Expire = uint32((time.Minute * 30).Seconds())
	soa.Minttl = uint32((time.Minute * 5).Seconds())

	return soa
}

func (xip *Xip) handleQuery(message *dns.Msg) {
	for _, question := range message.Question {
		switch question.Qtype {
		case dns.TypeA:
			xip.handleA(question, message)
		case dns.TypeAAAA:
			xip.handleAAAA(question, message)
		case dns.TypeNS:
			xip.handleNS(question, message)
		case dns.TypeTXT:
			xip.handleTXT(question, message)
		case dns.TypeMX:
			xip.handleMX(question, message)
		case dns.TypeCNAME:
			xip.handleCNAME(question, message)
		case dns.TypeSRV:
			xip.handleSRV(question, message)
		case dns.TypeSOA:
			xip.handleSOA(question, message)
		default:
			xip.handleSOA(question, message)
		}
	}
}

func (xip *Xip) handleDnsRequest(response dns.ResponseWriter, request *dns.Msg) {
	go func() {
		message := new(dns.Msg)
		message.SetReply(request)
		message.Compress = true
		message.Authoritative = true
		message.RecursionAvailable = false

		switch request.Opcode {
		case dns.OpcodeQuery:
			xip.handleQuery(message)
		default:
			message.MsgHdr.Rcode = dns.RcodeRefused
		}

		error := response.WriteMsg(message)
		if error != nil {
			log.Printf("Error writing answer \"%s\": %s\n", message.String(), error.Error())
		}
	}()
}

func (xip *Xip) StartServer() {
	err := xip.server.ListenAndServe()
	defer xip.server.Shutdown()
	if err != nil {
		if strings.Contains(err.Error(), "fly-global-services: no such host") {
			// we're not running on fly, bind to 0.0.0.0 instead
			port := strings.Split(xip.server.Addr, ":")[1]
			xip.server = dns.Server{
				Addr: fmt.Sprintf(":%s", port),
				Net:  "udp",
			}

			xip.StartServer()
			return
		}

		log.Fatalf("Failed to start server: %s\n ", err.Error())
	}
	log.Printf("Listening on %s\n", xip.server.Addr)
}

func NewXip(port int) (xip *Xip) {
	xip = &Xip{}

	for _, ns := range strings.Split(nameservers, ",") {
		xip.nameServers = append(xip.nameServers, &dns.NS{Ns: ns})
	}

	xip.server = dns.Server{
		Addr: fmt.Sprintf("fly-global-services:%d", port),
		Net:  "udp",
	}

	dns.HandleFunc(zone, xip.handleDnsRequest)

	return xip
}