TUN-6666: Define packet package

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

packet/packet.go

@@ -0,0 +1,115 @@
+package packet
+
+import (
+	"fmt"
+	"net/netip"
+
+	"github.com/google/gopacket"
+	"github.com/google/gopacket/layers"
+	"golang.org/x/net/icmp"
+)
+
+const (
+	defaultTTL    uint8 = 64
+	ipv4HeaderLen       = 20
+	ipv6HeaderLen       = 40
+)
+
+// Packet represents an IP packet or a packet that is encapsulated by IP
+type Packet interface {
+	// IPLayer returns the IP of the packet
+	IPLayer() *IP
+	// EncodeLayers returns the layers that make up this packet. They can be passed to an Encoder to serialize into RawPacket
+	EncodeLayers() ([]gopacket.SerializableLayer, error)
+}
+
+// IP represents a generic IP packet. It can be embedded in more specific IP protocols
+type IP struct {
+	Src      netip.Addr
+	Dst      netip.Addr
+	Protocol layers.IPProtocol
+}
+
+func newIPv4(ipLayer *layers.IPv4) (*IP, error) {
+	src, ok := netip.AddrFromSlice(ipLayer.SrcIP)
+	if !ok {
+		return nil, fmt.Errorf("cannot convert source IP %s to netip.Addr", ipLayer.SrcIP)
+	}
+	dst, ok := netip.AddrFromSlice(ipLayer.DstIP)
+	if !ok {
+		return nil, fmt.Errorf("cannot convert source IP %s to netip.Addr", ipLayer.DstIP)
+	}
+	return &IP{
+		Src:      src,
+		Dst:      dst,
+		Protocol: ipLayer.Protocol,
+	}, nil
+}
+
+func newIPv6(ipLayer *layers.IPv6) (*IP, error) {
+	src, ok := netip.AddrFromSlice(ipLayer.SrcIP)
+	if !ok {
+		return nil, fmt.Errorf("cannot convert source IP %s to netip.Addr", ipLayer.SrcIP)
+	}
+	dst, ok := netip.AddrFromSlice(ipLayer.DstIP)
+	if !ok {
+		return nil, fmt.Errorf("cannot convert source IP %s to netip.Addr", ipLayer.DstIP)
+	}
+	return &IP{
+		Src:      src,
+		Dst:      dst,
+		Protocol: ipLayer.NextHeader,
+	}, nil
+}
+
+func (ip *IP) IPLayer() *IP {
+	return ip
+}
+
+func (ip *IP) isIPv4() bool {
+	return ip.Src.Is4()
+}
+
+func (ip *IP) EncodeLayers() ([]gopacket.SerializableLayer, error) {
+	if ip.isIPv4() {
+		return []gopacket.SerializableLayer{
+			&layers.IPv4{
+				Version:  4,
+				SrcIP:    ip.Src.AsSlice(),
+				DstIP:    ip.Dst.AsSlice(),
+				Protocol: layers.IPProtocol(ip.Protocol),
+				TTL:      defaultTTL,
+			},
+		}, nil
+	} else {
+		return []gopacket.SerializableLayer{
+			&layers.IPv6{
+				Version:    6,
+				SrcIP:      ip.Src.AsSlice(),
+				DstIP:      ip.Dst.AsSlice(),
+				NextHeader: layers.IPProtocol(ip.Protocol),
+				HopLimit:   defaultTTL,
+			},
+		}, nil
+	}
+}
+
+// ICMP represents is an IP packet + ICMP message
+type ICMP struct {
+	*IP
+	*icmp.Message
+}
+
+func (i *ICMP) EncodeLayers() ([]gopacket.SerializableLayer, error) {
+	ipLayers, err := i.IP.EncodeLayers()
+	if err != nil {
+		return nil, err
+	}
+
+	msg, err := i.Marshal(nil)
+	if err != nil {
+		return nil, err
+	}
+	icmpLayer := gopacket.Payload(msg)
+	return append(ipLayers, icmpLayer), nil
+}