Allow access (as strings) to the rdata of each RR

format.go

@@ -15,26 +15,39 @@
 //	%D	the TTL in seconds
 //	%Y	the type: MX, A, etc.
 //
-// The rdata of each RR differs, we allow each field to be printed as a string.
-//
-// Rdata: (TODO)
-//
-//	%0	the first rdata field
-//	%1	the second rdata field
-//	%2	the third rdata field
-//	..	...
-//	%9      the nineth rdata field
-//	%R	all rdata fields
-//
-// Non exsiting rdata fields will be printed as the empty string.
+// The rdata of each RR differs, we allow each field to be accessed as a string with
+// the Field function.
 //
 package dns
 
 import (
 	"fmt"
+	"reflect"
 	"strconv"
 )
 
+// Field returns the rdata field i as a string. Fields are indexed starting from 1.
+func Field(r RR, i int) string {
+	if i == 0 {
+		return ""
+	}
+	d := reflect.ValueOf(r).Elem().Field(i)
+	switch d.Kind() {
+	case reflect.String:
+		return d.String()
+	case reflect.Int, reflect.Int8, reflect.Int16, reflect.Int32, reflect.Int64:
+		return strconv.FormatInt(d.Int(), 10)
+	case reflect.Uint, reflect.Uint8, reflect.Uint16, reflect.Uint32, reflect.Uint64:
+		return strconv.FormatUint(d.Uint(), 10)
+	}
+	return ""
+}
+
+// NumField returns the number of rdata fields r has.
+func NumField(r RR) int {
+	return reflect.ValueOf(r).Elem().NumField() - 1 // Remove RR_Header
+}
+
 func format(r RR, f fmt.State, c rune) {
 	switch c {
 	case 'N':
@@ -47,7 +60,6 @@ func format(r RR, f fmt.State, c rune) {
 		f.Write([]byte(Type(r.Header().Rrtype).String()))
 	case 's':
 		f.Write([]byte(r.String()))
-
 	}
 }
 

parse_test.go

@@ -1341,22 +1341,31 @@ func TestNewRRSpecial(t *testing.T) {
 func TestPrintfVerbs(t *testing.T) {
 	x, _ := NewRR("www.miek.nl. IN A 127.0.0.1")
 	if fmt.Sprintf("%N", x) != "www.miek.nl." {
-		t.Errorf("%N does not return name")
+		t.Errorf("%%N does not return name")
 	}
 	if fmt.Sprintf("%C", x) != "IN" {
-		t.Errorf("%C does not return class")
+		t.Errorf("%%C does not return class")
 	}
 	if fmt.Sprintf("%D", x) != "3600" {
-		t.Errorf("%D does not return ttl")
+		t.Errorf("%%D does not return ttl")
 	}
 	if fmt.Sprintf("%Y", x) != "A" {
-		t.Errorf("%Y does not return type")
+		t.Errorf("%%Y does not return type")
 	}
 	if fmt.Sprintf("%Y %d", x, 5) != "A 5" {
-		t.Errorf("%N does not return name")
+		t.Errorf("%%N does not return name")
 	}
 	if fmt.Sprintf("%s", x) != "www.miek.nl.\t3600\tIN\tA\t127.0.0.1" {
-		t.Errorf("%s does return the correct string")
+		t.Errorf("%%s does return the correct string")
+	}
+}
+
+func TestPrintfVerbsRdata(t *testing.T) {
+	x, _ := NewRR("www.miek.nl. IN MX 20 mx.miek.nl.")
+	if Field(x, 1) != "20" {
+		t.Errorf("should be 20")
+	}
+	if Field(x, 2) != "mx.miek.nl." {
+		t.Errorf("should be mx.miek.nl.")
 	}
-	// TODO(miek): RDATA
 }