1 files changed, 84 insertions, 0 deletions
diff --git a/middleware/reflect/reflect.go b/middleware/reflect/reflect.go
new file mode 100644
index 000000000..6d5847b81
--- /dev/null
+++ b/middleware/reflect/reflect.go
@@ -0,0 +1,84 @@
+// Reflect provides middleware that reflects back some client properties.
+// This is the default middleware when Caddy is run without configuration.
+//
+// The left-most label must be `who`.
+// When queried for type A (resp. AAAA), it sends back the IPv4 (resp. v6) address.
+// In the additional section the port number and transport are shown.
+// Basic use pattern:
+//
+//	dig @localhost -p 1053 who.miek.nl A
+//
+//	;; ANSWER SECTION:
+//	who.miek.nl.		0	IN	A	127.0.0.1
+//
+//	;; ADDITIONAL SECTION:
+//	who.miek.nl.		0	IN	TXT	"Port: 56195 (udp)"
+package reflect
+
+import (
+	"errors"
+	"net"
+	"strings"
+
+	"github.com/miekg/coredns/middleware"
+	"github.com/miekg/dns"
+)
+
+type Reflect struct {
+	Next middleware.Handler
+}
+
+func (rl Reflect) ServeDNS(w dns.ResponseWriter, r *dns.Msg) (int, error) {
+	context := middleware.Context{Req: r, W: w}
+
+	class := r.Question[0].Qclass
+	qname := r.Question[0].Name
+	i, ok := dns.NextLabel(qname, 0)
+
+	if strings.ToLower(qname[:i]) != who || ok {
+		err := context.ErrorMessage(dns.RcodeFormatError)
+		w.WriteMsg(err)
+		return dns.RcodeFormatError, errors.New(dns.RcodeToString[dns.RcodeFormatError])
+	}
+
+	answer := new(dns.Msg)
+	answer.SetReply(r)
+	answer.Compress = true
+	answer.Authoritative = true
+
+	ip := context.IP()
+	proto := context.Proto()
+	port, _ := context.Port()
+	family := context.Family()
+	var rr dns.RR
+
+	switch family {
+	case 1:
+		rr = new(dns.A)
+		rr.(*dns.A).Hdr = dns.RR_Header{Name: qname, Rrtype: dns.TypeA, Class: class, Ttl: 0}
+		rr.(*dns.A).A = net.ParseIP(ip).To4()
+	case 2:
+		rr = new(dns.AAAA)
+		rr.(*dns.AAAA).Hdr = dns.RR_Header{Name: qname, Rrtype: dns.TypeAAAA, Class: class, Ttl: 0}
+		rr.(*dns.AAAA).AAAA = net.ParseIP(ip)
+	}
+
+	t := new(dns.TXT)
+	t.Hdr = dns.RR_Header{Name: qname, Rrtype: dns.TypeTXT, Class: class, Ttl: 0}
+	t.Txt = []string{"Port: " + port + " (" + proto + ")"}
+
+	switch context.Type() {
+	case "TXT":
+		answer.Answer = append(answer.Answer, t)
+		answer.Extra = append(answer.Extra, rr)
+	default:
+		fallthrough
+	case "AAAA", "A":
+		answer.Answer = append(answer.Answer, rr)
+		answer.Extra = append(answer.Extra, t)
+	}
+	w.WriteMsg(answer)
+	return 0, nil
+}
+
+const who = "who."