[client] Add reverse dns zone (#3217)

client/internal/dns.go

@@ -0,0 +1,111 @@
+package internal
+
+import (
+	"fmt"
+	"net"
+	"slices"
+	"strings"
+
+	"github.com/miekg/dns"
+	log "github.com/sirupsen/logrus"
+
+	nbdns "github.com/netbirdio/netbird/dns"
+)
+
+func createPTRRecord(aRecord nbdns.SimpleRecord, ipNet *net.IPNet) (nbdns.SimpleRecord, bool) {
+	ip := net.ParseIP(aRecord.RData)
+	if ip == nil || ip.To4() == nil {
+		return nbdns.SimpleRecord{}, false
+	}
+
+	if !ipNet.Contains(ip) {
+		return nbdns.SimpleRecord{}, false
+	}
+
+	ipOctets := strings.Split(ip.String(), ".")
+	slices.Reverse(ipOctets)
+	rdnsName := dns.Fqdn(strings.Join(ipOctets, ".") + ".in-addr.arpa")
+
+	return nbdns.SimpleRecord{
+		Name:  rdnsName,
+		Type:  int(dns.TypePTR),
+		Class: aRecord.Class,
+		TTL:   aRecord.TTL,
+		RData: dns.Fqdn(aRecord.Name),
+	}, true
+}
+
+// generateReverseZoneName creates the reverse DNS zone name for a given network
+func generateReverseZoneName(ipNet *net.IPNet) (string, error) {
+	networkIP := ipNet.IP.Mask(ipNet.Mask)
+	maskOnes, _ := ipNet.Mask.Size()
+
+	// round up to nearest byte
+	octetsToUse := (maskOnes + 7) / 8
+
+	octets := strings.Split(networkIP.String(), ".")
+	if octetsToUse > len(octets) {
+		return "", fmt.Errorf("invalid network mask size for reverse DNS: %d", maskOnes)
+	}
+
+	reverseOctets := make([]string, octetsToUse)
+	for i := 0; i < octetsToUse; i++ {
+		reverseOctets[octetsToUse-1-i] = octets[i]
+	}
+
+	return dns.Fqdn(strings.Join(reverseOctets, ".") + ".in-addr.arpa"), nil
+}
+
+// zoneExists checks if a zone with the given name already exists in the configuration
+func zoneExists(config *nbdns.Config, zoneName string) bool {
+	for _, zone := range config.CustomZones {
+		if zone.Domain == zoneName {
+			log.Debugf("reverse DNS zone %s already exists", zoneName)
+			return true
+		}
+	}
+	return false
+}
+
+// collectPTRRecords gathers all PTR records for the given network from A records
+func collectPTRRecords(config *nbdns.Config, ipNet *net.IPNet) []nbdns.SimpleRecord {
+	var records []nbdns.SimpleRecord
+
+	for _, zone := range config.CustomZones {
+		for _, record := range zone.Records {
+			if record.Type != int(dns.TypeA) {
+				continue
+			}
+
+			if ptrRecord, ok := createPTRRecord(record, ipNet); ok {
+				records = append(records, ptrRecord)
+			}
+		}
+	}
+
+	return records
+}
+
+// addReverseZone adds a reverse DNS zone to the configuration for the given network
+func addReverseZone(config *nbdns.Config, ipNet *net.IPNet) {
+	zoneName, err := generateReverseZoneName(ipNet)
+	if err != nil {
+		log.Warn(err)
+		return
+	}
+
+	if zoneExists(config, zoneName) {
+		log.Debugf("reverse DNS zone %s already exists", zoneName)
+		return
+	}
+
+	records := collectPTRRecords(config, ipNet)
+
+	reverseZone := nbdns.CustomZone{
+		Domain:  zoneName,
+		Records: records,
+	}
+
+	config.CustomZones = append(config.CustomZones, reverseZone)
+	log.Debugf("added reverse DNS zone: %s with %d records", zoneName, len(records))
+}