Initial commit: Go DNS microservice boilerplate

2026-02-27 01:40:12 +00:00 · 2026-02-24 13:44:34 -05:00
commit 247f81d616
13 changed files with 451 additions and 0 deletions
--- a/internal/dns/resolver.go
+++ b/internal/dns/resolver.go
@@ -0,0 +1,112 @@
+package dns
+
+import (
+	"fmt"
+	"strings"
+	"time"
+
+	mdns "github.com/miekg/dns"
+)
+
+var defaultTypes = []string{"A", "AAAA", "MX", "TXT", "NS", "CNAME", "SOA", "CAA", "SRV"}
+
+const defaultResolver = "8.8.8.8:53"
+
+var typeMap = map[string]uint16{
+	"A":     mdns.TypeA,
+	"AAAA":  mdns.TypeAAAA,
+	"MX":    mdns.TypeMX,
+	"TXT":   mdns.TypeTXT,
+	"NS":    mdns.TypeNS,
+	"CNAME": mdns.TypeCNAME,
+	"SOA":   mdns.TypeSOA,
+	"CAA":   mdns.TypeCAA,
+	"SRV":   mdns.TypeSRV,
+}
+
+func Lookup(req LookupRequest) (*LookupResponse, error) {
+	domain := req.Domain
+	if !strings.HasSuffix(domain, ".") {
+		domain += "."
+	}
+
+	types := req.Types
+	if len(types) == 0 {
+		types = defaultTypes
+	}
+
+	start := time.Now()
+	records := make(map[string][]Record)
+	hasDNSSEC := false
+
+	c := new(mdns.Client)
+	c.Net = "udp"
+
+	for _, t := range types {
+		qtype, ok := typeMap[strings.ToUpper(t)]
+		if !ok {
+			continue
+		}
+
+		m := new(mdns.Msg)
+		m.SetQuestion(domain, qtype)
+		m.SetEdns0(4096, true)
+
+		r, _, err := c.Exchange(m, defaultResolver)
+		if err != nil {
+			continue
+		}
+
+		if r.AuthenticatedData {
+			hasDNSSEC = true
+		}
+
+		recs := parseRecords(r.Answer, strings.ToUpper(t))
+		if len(recs) > 0 {
+			records[strings.ToUpper(t)] = recs
+		}
+	}
+
+	return &LookupResponse{
+		Domain:      req.Domain,
+		Records:     records,
+		Resolver:    "8.8.8.8",
+		QueryTimeMs: time.Since(start).Milliseconds(),
+		DNSSEC:      hasDNSSEC,
+		Timestamp:   time.Now().UTC(),
+	}, nil
+}
+
+func parseRecords(answers []mdns.RR, qtype string) []Record {
+	var records []Record
+	for _, ans := range answers {
+		rec := Record{TTL: ans.Header().Ttl}
+		switch rr := ans.(type) {
+		case *mdns.A:
+			rec.Value = rr.A.String()
+		case *mdns.AAAA:
+			rec.Value = rr.AAAA.String()
+		case *mdns.MX:
+			rec.Value = strings.TrimSuffix(rr.Mx, ".")
+			rec.Priority = rr.Preference
+		case *mdns.TXT:
+			rec.Value = strings.Join(rr.Txt, " ")
+		case *mdns.NS:
+			rec.Value = strings.TrimSuffix(rr.Ns, ".")
+		case *mdns.CNAME:
+			rec.Value = strings.TrimSuffix(rr.Target, ".")
+		case *mdns.SOA:
+			rec.Value = fmt.Sprintf("%s %s %d %d %d %d %d",
+				rr.Ns, rr.Mbox, rr.Serial, rr.Refresh, rr.Retry, rr.Expire, rr.Minttl)
+		case *mdns.CAA:
+			rec.Value = fmt.Sprintf("%d %s \"%s\"", rr.Flag, rr.Tag, rr.Value)
+		case *mdns.SRV:
+			rec.Value = fmt.Sprintf("%d %d %d %s", rr.Priority, rr.Weight, rr.Port, strings.TrimSuffix(rr.Target, "."))
+			rec.Priority = rr.Priority
+		default:
+			continue
+		}
+		records = append(records, rec)
+	}
+	return records
+}