Allow for escaping of dots in domainnames

msg.go

@@ -147,6 +147,7 @@ func packDomainName(s string, msg []byte, off int) (off1 int, ok bool) {
 
 	// Each dot ends a segment of the name.
 	// We trade each dot byte for a length byte.
+	// Except for escaped dots (\.), which are normal dots.
 	// There is also a trailing zero.
 	// Check that we have all the space we need.
 	tot := len(s) + 1
@@ -156,22 +157,32 @@ func packDomainName(s string, msg []byte, off int) (off1 int, ok bool) {
 
 	// Emit sequence of counted strings, chopping at dots.
 	begin := 0
-	for i := 0; i < len(s); i++ {
-		if s[i] == '.' {
+        bs := []byte(s)
+        ls := len(bs)
+	for i := 0; i < ls; i++ {
+		if bs[i] == '\\' {
+                        for j := i; j < len(s)-1; j++ {
+                                bs[j] = bs[j+1]
+                        }
+                        ls--
+                        continue
+		}
+
+		if bs[i] == '.' {
                         if i-begin >= 1<<6 { // top two bits of length must be clear
                                 return len(msg), false
                         }
                         msg[off] = byte(i - begin)
                         off++
                         for j := begin; j < i; j++ {
-				msg[off] = s[j]
+                                msg[off] = bs[j]
                                 off++
                         }
                         begin = i + 1
 		}
 	}
 	// Root label is special
-	if s == "." {
+	if string(bs) == "." {
 		return off, true
 	}
 	msg[off] = 0
@@ -399,7 +410,7 @@ func packStructValue(val *reflect.StructValue, msg []byte, off int) (off1 int, o
 					return len(msg), false
 				}
 			case "size-hex":
-                                fallthrough;
+				fallthrough
 			case "hex":
 				// There is no length encoded here
 				h, e := hex.DecodeString(s)
@@ -605,7 +616,7 @@ func unpackStructValue(val *reflect.StructValue, msg []byte, off int) (off1 int,
 				case "RR_NSEC3PARAM":
 					consumed = 5 // Hash(1) + Flags(1) + Iterations(2) + SaltLength(1)
 				case "RR_RFC3597":
-                                        fallthrough; // Rest is the unknown data
+					fallthrough // Rest is the unknown data
 				default:
 					consumed = 0 // return len(msg), false?
 				}

parse_test.go

@@ -134,5 +134,24 @@ func TestQuadA(t *testing.T) {
 		t.Log(str)
 		t.Fail()
 	}
-
+}
+
+func TestDotInName(t *testing.T) {
+	buf := make([]byte, 20)
+	packDomainName("aa\\.bb.nl", buf, 0)
+        // index 3 must be a real dot
+        if buf[3] != '.' {
+                t.Log("Dot should be a real dot")
+                t.Fail()
+        }
+
+        if buf[6] != 2 {
+                t.Log("This must have the value 2")
+                t.Fail()
+        }
+
+        dom, _, ok := unpackDomainName(buf, 0)
+        // printing it should yield the backspace again
+        println(dom)
+        println(ok)
 }