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.gitignore vendored Normal file
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# build output

Dockerfile Normal file
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FROM golang:1.19-alpine AS build
COPY . .
RUN go mod download
RUN CGO_ENABLED=0 go build -o /app/local-ip
COPY --from=build /app/local-ip /
USER root
CMD ["/local-ip"]

LICENSE Normal file
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Apache License
Version 2.0, January 2004
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fly.toml Normal file
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app = "local-ip"
kill_signal = "SIGINT"
kill_timeout = 5
processes = []
PORT = "53"
allowed_public_ports = []
auto_rollback = true
internal_port = 53
protocol = "udp"
port = "53"

go.mod Normal file
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go 1.19
require ( v1.1.50 // indirect v0.4.2 // indirect v0.0.0-20210726213435-c6fcb2dbf985 // indirect v0.0.0-20210630005230-0f9fa26af87c // indirect v0.1.6-0.20210726203631-07bc1bf47fb2 // indirect v0.0.0-20200804184101-5ec99f83aff1 // indirect

go.sum Normal file
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@ -0,0 +1,34 @@ v1.1.50 h1:DQUfb9uc6smULcREF09Uc+/Gd46YWqJd5DbpPE9xkcA= v1.1.50/go.mod h1:e3IlAVfNqAllflbibAZEWOXOQ+Ynzk/dDozDxY7XnME= v1.3.5/go.mod h1:mwnBkeHKe2W/ZEtQ+71ViKU8L12m81fl3OWwC1Zlc8k= v0.0.0-20190308221718-c2843e01d9a2/go.mod h1:djNgcEr1/C05ACkg1iLfiJU5Ep61QUkGW8qpdssI0+w= v0.0.0-20191011191535-87dc89f01550/go.mod h1:yigFU9vqHzYiE8UmvKecakEJjdnWj3jj499lnFckfCI= v0.4.2 h1:Gz96sIWK3OalVv/I/qNygP42zyoKp3xptRVCWRFEBvo= v0.4.2/go.mod h1:s0Qsj1ACt9ePp/hMypM3fl4fZqREWJwdYDEqhRiZZUA= v0.0.0-20190404232315-eb5bcb51f2a3/go.mod h1:t9HGtf8HONx5eT2rtn7q6eTqICYqUVnKs3thJo3Qplg= v0.0.0-20190620200207-3b0461eec859/go.mod h1:z5CRVTTTmAJ677TzLLGU+0bjPO0LkuOLi4/5GtJWs/s= v0.0.0-20210405180319-a5a99cb37ef4/go.mod h1:p54w0d4576C0XHj96bSt6lcn1PtDYWL6XObtHCRCNQM= v0.0.0-20210726213435-c6fcb2dbf985 h1:4CSI6oo7cOjJKajidEljs9h+uP0rRZBPPPhcCbj5mw8= v0.0.0-20210726213435-c6fcb2dbf985/go.mod h1:9nx3DQGgdP8bBQD5qxJ1jj9UTztislL4KSBs9R2vV5Y= v0.0.0-20190423024810-112230192c58/go.mod h1:RxMgew5VJxzue5/jJTE5uejpjVlOe/izrB70Jof72aM= v0.0.0-20210220032951-036812b2e83c/go.mod h1:RxMgew5VJxzue5/jJTE5uejpjVlOe/izrB70Jof72aM= v0.0.0-20190215142949-d0b11bdaac8a/go.mod h1:STP8DvDyc/dI5b8T5hshtkjS+E42TnysNCUPdjciGhY= v0.0.0-20190412213103-97732733099d/go.mod h1:h1NjWce9XRLGQEsW7wpKNCjG9DtNlClVuFLEZdDNbEs= v0.0.0-20201119102817-f84b799fce68/go.mod h1:h1NjWce9XRLGQEsW7wpKNCjG9DtNlClVuFLEZdDNbEs= v0.0.0-20210330210617-4fbd30eecc44/go.mod h1:h1NjWce9XRLGQEsW7wpKNCjG9DtNlClVuFLEZdDNbEs= v0.0.0-20210423082822-04245dca01da/go.mod h1:h1NjWce9XRLGQEsW7wpKNCjG9DtNlClVuFLEZdDNbEs= v0.0.0-20210510120138-977fb7262007/go.mod h1:oPkhp1MJrh7nUepCBck5+mAzfO9JrbApNNgaTdGDITg= v0.0.0-20210630005230-0f9fa26af87c h1:F1jZWGFhYfh0Ci55sIpILtKKK8p3i2/krTr0H1rg74I= v0.0.0-20210630005230-0f9fa26af87c/go.mod h1:oPkhp1MJrh7nUepCBck5+mAzfO9JrbApNNgaTdGDITg= v0.0.0-20201126162022-7de9c90e9dd1/go.mod h1:bj7SfCRtBDWHUb9snDiAeCFNEtKQo2Wmx5Cou7ajbmo= v0.3.0/go.mod h1:NqM8EUOU14njkJ3fqMW+pc6Ldnwhi/IjpwHt7yyuwOQ= v0.3.3/go.mod h1:5Zoc/QRtKVWzQhOtBMvqHzDpF6irO9z98xDceosuGiQ= v0.3.6/go.mod h1:5Zoc/QRtKVWzQhOtBMvqHzDpF6irO9z98xDceosuGiQ= v0.0.0-20180917221912-90fa682c2a6e/go.mod h1:n7NCudcB/nEzxVGmLbDWY5pfWTLqBcC2KZ6jyYvM4mQ= v0.0.0-20191119224855-298f0cb1881e/go.mod h1:b+2E5dAYhXwXZwtnZ6UAqBI28+e2cm9otk0dWdXHAEo= v0.1.6-0.20210726203631-07bc1bf47fb2 h1:BonxutuHCTL0rBDnZlKjpGIQFTjyUVTexFOdWkB6Fg0= v0.1.6-0.20210726203631-07bc1bf47fb2/go.mod h1:o0xws9oXOQQZyjljx8fwUC0k7L1pTE6eaCbjGeHmOkk= v0.0.0-20190717185122-a985d3407aa7/go.mod h1:I/5z698sn9Ka8TeJc9MKroUUfqBBauWjQqLJ2OPfmY0= v0.0.0-20191011141410-1b5146add898/go.mod h1:I/5z698sn9Ka8TeJc9MKroUUfqBBauWjQqLJ2OPfmY0= v0.0.0-20200804184101-5ec99f83aff1 h1:go1bK/D/BFZV2I8cIQd1NKEZ+0owSTG1fDTci4IqFcE= v0.0.0-20200804184101-5ec99f83aff1/go.mod h1:I/5z698sn9Ka8TeJc9MKroUUfqBBauWjQqLJ2OPfmY0=

main.go Normal file
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package main
import (
const zone = ""
func main() {
dns.HandleFunc(zone, handleDnsRequest)
port, err := strconv.Atoi(os.Getenv("PORT"))
if err != nil {
port = 9053
server := &dns.Server{
Addr: ":" + strconv.Itoa(port),
Net: "udp",
log.Printf("Starting at %d\n", port)
err = server.ListenAndServe()
defer server.Shutdown()
if err != nil {
log.Fatalf("Failed to start server: %s\n ", err.Error())
func handleDnsRequest(response dns.ResponseWriter, request *dns.Msg) {
go func() {
message := new(dns.Msg)
message.Compress = true
switch request.Opcode {
case dns.OpcodeQuery:
func handleQuery(message *dns.Msg) {
for _, question := range message.Question {
switch question.Qtype {
case dns.TypeA:
ip := extractIp(question.Name)
log.Printf("%s => %s\n", question.Name, ip)
if ip == nil {
resource := new(dns.A)
resource.Hdr = dns.RR_Header{Ttl: 10, Name: question.Name, Rrtype: dns.TypeA, Class: dns.ClassINET}
resource.A = ip
message.Answer = append(message.Answer, resource)
func extractIp(fqdn string) net.IP {
var ip string
dashedIpRegex := regexp.MustCompile(fmt.Sprintf(`^(((25[0-5]|(2[0-4]|1\d|[1-9]|)\d)\-?\b){4}).%s$`, zone))
matches := dashedIpRegex.FindStringSubmatch(fqdn)
if len(matches) < 2 {
return nil
ip = strings.ReplaceAll(matches[1], "-", ".")
return net.ParseIP(ip)
func refuseMessage(message *dns.Msg) {
message.MsgHdr.Rcode = dns.RcodeRefused
soa := new(dns.SOA)
soa.Hdr = dns.RR_Header{
Name: "",
Rrtype: dns.TypeSOA,
Class: dns.ClassINET,
Ttl: 10,
Rdlength: 0,
soa.Ns = ""
soa.Mbox = ""
soa.Serial = 2022102400
soa.Refresh = 10
soa.Retry = 10
soa.Expire = 10
soa.Minttl = 10
message.Ns = append(message.Ns, soa)