1 files changed, 65 insertions, 0 deletions
diff --git a/internal/server/handler.go b/internal/server/handler.go
new file mode 100644
index 0000000..2e2f08b
--- /dev/null
+++ b/internal/server/handler.go
@@ -0,0 +1,65 @@
+package server
+
+import (
+	"github.com/miekg/dns"
+	"log/slog"
+)
+
+func handleQuery(w dns.ResponseWriter, req *dns.Msg) {
+	if len(req.Question) == 0 {
+		m := new(dns.Msg)
+		m.SetRcode(req, dns.RcodeFormatError)
+		_ = w.WriteMsg(m)
+		return
+	}
+
+	resp := buildResponse(req)
+
+	if err := w.WriteMsg(resp); err != nil {
+		slog.Error("write response failed",
+			"err", err,
+			"qname", req.Question[0].Name,
+			"qtype", dns.TypeToString[req.Question[0].Qtype],
+		)
+		return
+	}
+	slog.Info("query served",
+		"qname", req.Question[0].Name,
+		"qtype", dns.TypeToString[req.Question[0].Qtype],
+		"rcode", dns.RcodeToString[resp.Rcode],
+		"client", w.RemoteAddr().String(),
+	)
+}
+
+func buildResponse(req *dns.Msg) *dns.Msg {
+	if len(req.Question) == 0 {
+		m := new(dns.Msg)
+		m.SetRcode(req, dns.RcodeFormatError)
+		return m
+	}
+	q := req.Question[0]
+	resp := new(dns.Msg)
+	resp.SetReply(req)
+	resp.Authoritative = false
+
+	if opt := req.IsEdns0(); opt != nil {
+		resp.SetEdns0(4096, false)
+	}
+
+	if q.Name == "example.com." && q.Qtype == dns.TypeA {
+		resp.Answer = []dns.RR{
+			&dns.A{
+				Hdr: dns.RR_Header{
+					Name:   q.Name,
+					Rrtype: dns.TypeA,
+					Class:  dns.ClassINET,
+					Ttl:    60,
+				},
+				A: []byte{127, 0, 0, 1},
+			},
+		}
+	} else {
+		resp.Rcode = dns.RcodeNameError
+	}
+	return resp
+}