rename dnscompress to rfc1035label

2 files changed, 126 insertions, 0 deletions

diff --git a/rfc1035label/label.go b/rfc1035label/label.go
new file mode 100644
index 0000000..c63b4af
--- /dev/null
+++ b/rfc1035label/label.go
@@ -0,0 +1,60 @@
+package rfc1035label
+
+import (
+	"fmt"
+	"strings"
+)
+
+// This implements the compression from RFC 1035, section 4.1.4
+// https://tools.ietf.org/html/rfc1035
+
+// LabelsFromBytes decodes a serialized stream and returns a list of labels
+func LabelsFromBytes(buf []byte) ([]string, error) {
+	var (
+		pos     = 0
+		domains = make([]string, 0)
+		label   = ""
+	)
+	for {
+		if pos >= len(buf) {
+			return domains, nil
+		}
+		length := int(buf[pos])
+		pos++
+		if length == 0 {
+			domains = append(domains, label)
+			label = ""
+		}
+		if len(buf)-pos < length {
+			return nil, fmt.Errorf("DomainNamesFromBytes: invalid short label length")
+		}
+		if label != "" {
+			label += "."
+		}
+		label += string(buf[pos : pos+length])
+		pos += length
+	}
+}
+
+// LabelToBytes encodes a label and returns a serialized stream of bytes
+func LabelToBytes(label string) []byte {
+	var encodedLabel []byte
+	if len(label) == 0 {
+		return []byte{0}
+	}
+	for _, part := range strings.Split(label, ".") {
+		encodedLabel = append(encodedLabel, byte(len(part)))
+		encodedLabel = append(encodedLabel, []byte(part)...)
+	}
+	return append(encodedLabel, 0)
+}
+
+// LabelsToBytes encodes a list of labels and returns a serialized stream of
+// bytes
+func LabelsToBytes(labels []string) []byte {
+	var encodedLabels []byte
+	for _, label := range labels {
+		encodedLabels = append(encodedLabels, LabelToBytes(label)...)
+	}
+	return encodedLabels
+}
diff --git a/rfc1035label/label_test.go b/rfc1035label/label_test.go
new file mode 100644
index 0000000..f91110b
--- /dev/null
+++ b/rfc1035label/label_test.go
@@ -0,0 +1,66 @@
+package rfc1035label
+
+import (
+	"bytes"
+	"testing"
+)
+
+func TestLabelsFromBytes(t *testing.T) {
+	labels, err := LabelsFromBytes([]byte{
+		0x9, 's', 'l', 'a', 'c', 'k', 'w', 'a', 'r', 'e',
+		0x2, 'i', 't',
+		0x0,
+	})
+	if err != nil {
+		t.Fatal(err)
+	}
+	if len(labels) != 1 {
+		t.Fatalf("Invalid labels length. Expected: 1, got: %v", len(labels))
+	}
+	if labels[0] != "slackware.it" {
+		t.Fatalf("Invalid label. Expected: %v, got: %v'", "slackware.it", labels[0])
+	}
+}
+
+func TestLabelsFromBytesZeroLength(t *testing.T) {
+	labels, err := LabelsFromBytes([]byte{})
+	if err != nil {
+		t.Fatal(err)
+	}
+	if len(labels) != 0 {
+		t.Fatalf("Invalid labels length. Expected: 0, got: %v", len(labels))
+	}
+}
+
+func TestLabelsFromBytesInvalidLength(t *testing.T) {
+	labels, err := LabelsFromBytes([]byte{0x3, 0xaa, 0xbb}) // short length
+	if err == nil {
+		t.Fatal("Expected error, got nil")
+	}
+	if len(labels) != 0 {
+		t.Fatalf("Invalid labels length. Expected: 0, got: %v", len(labels))
+	}
+	if labels != nil {
+		t.Fatalf("Invalid label. Expected nil, got %v", labels)
+	}
+}
+
+func TestLabelToBytes(t *testing.T) {
+	encodedLabel := LabelToBytes("slackware.it")
+	expected := []byte{
+		0x9, 's', 'l', 'a', 'c', 'k', 'w', 'a', 'r', 'e',
+		0x2, 'i', 't',
+		0x0,
+	}
+	if !bytes.Equal(encodedLabel, expected) {
+		t.Fatalf("Invalid label. Expected: %v, got: %v", expected, encodedLabel)
+	}
+}
+
+func TestLabelToBytesZeroLength(t *testing.T) {
+	encodedLabel := LabelToBytes("")
+	expected := []byte{0}
+	if !bytes.Equal(encodedLabel, expected) {
+		t.Fatalf("Invalid label. Expected: %v, got: %v", expected, encodedLabel)
+	}
+}