230 lines
7.0 KiB
Go
230 lines
7.0 KiB
Go
package edns
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import (
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"crypto/rand"
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"encoding/base64"
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"encoding/binary"
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"fmt"
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"net"
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"strings"
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"golang.org/x/net/dns/dnsmessage"
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"golang.org/x/net/idna"
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)
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var recordTypes = map[string]dnsmessage.Type{
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"A": dnsmessage.TypeA,
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"AAAA": dnsmessage.TypeAAAA,
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"CNAME": dnsmessage.TypeCNAME,
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"MX": dnsmessage.TypeMX,
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"TXT": dnsmessage.TypeTXT,
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"NS": dnsmessage.TypeNS,
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"SOA": dnsmessage.TypeSOA,
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"CAA": dnsmessage.Type(257),
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"SRV": dnsmessage.TypeSRV,
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"SVCB": dnsmessage.TypeSVCB,
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"HTTPS": dnsmessage.TypeHTTPS,
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}
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func BuildQuery(name, recordType string) ([]byte, QueryInfo, uint16, error) {
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canonical, err := canonicalName(name)
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if err != nil {
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return nil, QueryInfo{}, 0, err
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}
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typeName := strings.ToUpper(recordType)
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qtype, ok := recordTypes[typeName]
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if !ok {
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return nil, QueryInfo{}, 0, fmt.Errorf("unsupported record type %q", recordType)
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}
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dnsName, err := dnsmessage.NewName(canonical + ".")
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if err != nil {
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return nil, QueryInfo{}, 0, fmt.Errorf("encode domain name: %w", err)
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}
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var randomID [2]byte
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if _, err := rand.Read(randomID[:]); err != nil {
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return nil, QueryInfo{}, 0, fmt.Errorf("generate DNS transaction ID: %w", err)
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}
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id := binary.BigEndian.Uint16(randomID[:])
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message := dnsmessage.Message{
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Header: dnsmessage.Header{ID: id, RecursionDesired: true},
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Questions: []dnsmessage.Question{{
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Name: dnsName,
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Type: qtype,
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Class: dnsmessage.ClassINET,
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}},
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}
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wire, err := message.Pack()
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if err != nil {
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return nil, QueryInfo{}, 0, fmt.Errorf("pack DNS query: %w", err)
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}
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return wire, QueryInfo{Name: canonical, Type: typeName}, id, nil
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}
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func ParseResponse(wire []byte, expectedID uint16, query QueryInfo) (DNSInfo, error) {
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var message dnsmessage.Message
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if err := message.Unpack(wire); err != nil {
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return DNSInfo{}, fmt.Errorf("unpack DNS response: %w", err)
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}
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if !message.Header.Response {
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return DNSInfo{}, fmt.Errorf("received a DNS query instead of a response")
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}
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if message.Header.ID != expectedID {
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return DNSInfo{}, fmt.Errorf("DNS transaction ID mismatch")
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}
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if len(message.Questions) != 1 {
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return DNSInfo{}, fmt.Errorf("DNS response contains %d questions, want 1", len(message.Questions))
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}
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wantType := recordTypes[query.Type]
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question := message.Questions[0]
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if trimRoot(question.Name.String()) != query.Name || question.Type != wantType {
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return DNSInfo{}, fmt.Errorf("DNS response question does not match request")
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}
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answers := make([]AnswerRecord, 0, len(message.Answers))
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for _, resource := range message.Answers {
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answers = append(answers, normalizeAnswer(resource))
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}
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return DNSInfo{
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RCode: rcodeName(message.Header.RCode),
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RCodeValue: int(message.Header.RCode),
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ResolverReportsDNSSECAuthenticated: message.Header.AuthenticData,
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ClientValidatedDNSSEC: false,
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Answers: answers,
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}, nil
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}
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func canonicalName(input string) (string, error) {
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name := strings.TrimSuffix(strings.TrimSpace(input), ".")
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if name == "" {
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return "", fmt.Errorf("domain name is empty")
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}
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if net.ParseIP(name) != nil {
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return "", fmt.Errorf("IP literals are not accepted as domain names")
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}
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ascii, err := idna.Lookup.ToASCII(name)
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if err != nil {
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return "", fmt.Errorf("convert domain name to IDNA ASCII: %w", err)
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}
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ascii = strings.ToLower(ascii)
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if len(ascii) > 253 {
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return "", fmt.Errorf("domain name exceeds 253 bytes")
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}
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for _, label := range strings.Split(ascii, ".") {
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if label == "" || len(label) > 63 {
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return "", fmt.Errorf("domain name contains an invalid label")
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}
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}
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blocked := []string{"localhost", ".local", ".internal", ".lan", ".arpa"}
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for _, suffix := range blocked {
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if ascii == strings.TrimPrefix(suffix, ".") || strings.HasSuffix(ascii, suffix) {
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return "", fmt.Errorf("domain name is blocked by the local-name policy")
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}
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}
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return ascii, nil
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}
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func normalizeAnswer(resource dnsmessage.Resource) AnswerRecord {
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record := AnswerRecord{
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"name": trimRoot(resource.Header.Name.String()),
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"type": typeName(resource.Header.Type),
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"ttl": resource.Header.TTL,
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}
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switch body := resource.Body.(type) {
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case *dnsmessage.AResource:
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record["address"] = net.IP(body.A[:]).String()
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case *dnsmessage.AAAAResource:
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record["address"] = net.IP(body.AAAA[:]).String()
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case *dnsmessage.CNAMEResource:
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record["target"] = trimRoot(body.CNAME.String())
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case *dnsmessage.MXResource:
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record["priority"] = body.Pref
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record["exchange"] = trimRoot(body.MX.String())
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case *dnsmessage.TXTResource:
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record["strings"] = body.TXT
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case *dnsmessage.NSResource:
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record["host"] = trimRoot(body.NS.String())
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case *dnsmessage.PTRResource:
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record["target"] = trimRoot(body.PTR.String())
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case *dnsmessage.SOAResource:
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record["primary_ns"] = trimRoot(body.NS.String())
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record["responsible_mailbox"] = trimRoot(body.MBox.String())
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record["serial"] = body.Serial
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record["refresh"] = body.Refresh
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record["retry"] = body.Retry
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record["expire"] = body.Expire
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record["minimum_ttl"] = body.MinTTL
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case *dnsmessage.SRVResource:
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record["priority"] = body.Priority
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record["weight"] = body.Weight
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record["port"] = body.Port
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record["target"] = trimRoot(body.Target.String())
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case *dnsmessage.SVCBResource:
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addSVCBFields(record, body.Priority, body.Target, body.Params)
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case *dnsmessage.HTTPSResource:
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addSVCBFields(record, body.Priority, body.Target, body.Params)
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case *dnsmessage.UnknownResource:
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if resource.Header.Type == dnsmessage.Type(257) && len(body.Data) >= 2 {
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record["flags"] = body.Data[0]
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tagLength := int(body.Data[1])
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if 2+tagLength <= len(body.Data) {
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record["tag"] = string(body.Data[2 : 2+tagLength])
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record["value"] = string(body.Data[2+tagLength:])
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} else {
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record["rdata_base64"] = base64.StdEncoding.EncodeToString(body.Data)
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}
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} else {
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record["rdata_base64"] = base64.StdEncoding.EncodeToString(body.Data)
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}
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}
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return record
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}
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func addSVCBFields(record AnswerRecord, priority uint16, target dnsmessage.Name, params []dnsmessage.SVCParam) {
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record["priority"] = priority
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record["target"] = trimRoot(target.String())
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values := make([]map[string]any, 0, len(params))
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for _, param := range params {
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values = append(values, map[string]any{
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"key": param.Key.String(),
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"key_value": uint16(param.Key),
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"value_base64": base64.StdEncoding.EncodeToString(param.Value),
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})
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}
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record["params"] = values
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}
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func trimRoot(name string) string {
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return strings.TrimSuffix(strings.ToLower(name), ".")
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}
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func typeName(recordType dnsmessage.Type) string {
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for name, value := range recordTypes {
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if value == recordType {
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return name
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}
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}
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return fmt.Sprintf("TYPE%d", recordType)
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}
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func rcodeName(rcode dnsmessage.RCode) string {
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names := map[dnsmessage.RCode]string{
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dnsmessage.RCodeSuccess: "NOERROR",
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dnsmessage.RCodeFormatError: "FORMERR",
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dnsmessage.RCodeServerFailure: "SERVFAIL",
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dnsmessage.RCodeNameError: "NXDOMAIN",
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dnsmessage.RCodeNotImplemented: "NOTIMP",
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dnsmessage.RCodeRefused: "REFUSED",
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}
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if name, ok := names[rcode]; ok {
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return name
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}
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return fmt.Sprintf("RCODE%d", rcode)
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}
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