TUN-6666: Define packet package

This package defines IP and ICMP packet, decoders, encoder and flow

packet/encoder.go

@@ -0,0 +1,39 @@
+package packet
+
+import "github.com/google/gopacket"
+
+var (
+	serializeOpts = gopacket.SerializeOptions{
+		FixLengths:       true,
+		ComputeChecksums: true,
+	}
+)
+
+// RawPacket represents a raw packet or one encoded by Encoder
+type RawPacket struct {
+	Data []byte
+}
+
+type Encoder struct {
+	// buf is reusable because SerializeLayers calls the Clear method before each encoding
+	buf gopacket.SerializeBuffer
+}
+
+func NewEncoder() *Encoder {
+	return &Encoder{
+		buf: gopacket.NewSerializeBuffer(),
+	}
+}
+
+func (e Encoder) Encode(packet Packet) (RawPacket, error) {
+	encodedLayers, err := packet.EncodeLayers()
+	if err != nil {
+		return RawPacket{}, err
+	}
+	if err := gopacket.SerializeLayers(e.buf, serializeOpts, encodedLayers...); err != nil {
+		return RawPacket{}, err
+	}
+	return RawPacket{
+		Data: e.buf.Bytes(),
+	}, nil
+}