Basic holepunch working

network/network.go

@@ -0,0 +1,202 @@
+package network
+
+import (
+	"encoding/binary"
+	"encoding/json"
+	"fmt"
+	"log"
+	"net"
+	"time"
+
+	"github.com/google/gopacket"
+	"github.com/google/gopacket/layers"
+	"github.com/vishvananda/netlink"
+	"golang.org/x/net/bpf"
+	"golang.org/x/net/ipv4"
+)
+
+const (
+	udpProtocol = 17
+	// EmptyUDPSize is the size of an empty UDP packet
+	EmptyUDPSize = 28
+	timeout      = time.Second * 10
+)
+
+// Server stores data relating to the server
+type Server struct {
+	Hostname string
+	Addr     *net.IPAddr
+	Port     uint16
+}
+
+// PeerNet stores data about a peer's endpoint
+type PeerNet struct {
+	Resolved bool
+	IP       net.IP
+	Port     uint16
+	NewtID   string
+}
+
+// GetClientIP gets source ip address that will be used when sending data to dstIP
+func GetClientIP(dstIP net.IP) net.IP {
+	routes, err := netlink.RouteGet(dstIP)
+	if err != nil {
+		log.Fatalln("Error getting route:", err)
+	}
+	return routes[0].Src
+}
+
+// HostToAddr resolves a hostname, whether DNS or IP to a valid net.IPAddr
+func HostToAddr(hostStr string) *net.IPAddr {
+	remoteAddrs, err := net.LookupHost(hostStr)
+	if err != nil {
+		log.Fatalln("Error parsing remote address:", err)
+	}
+
+	for _, addrStr := range remoteAddrs {
+		if remoteAddr, err := net.ResolveIPAddr("ip4", addrStr); err == nil {
+			return remoteAddr
+		}
+	}
+	return nil
+}
+
+// SetupRawConn creates an ipv4 and udp only RawConn and applies packet filtering
+func SetupRawConn(server *Server, client *PeerNet) *ipv4.RawConn {
+	packetConn, err := net.ListenPacket("ip4:udp", client.IP.String())
+	if err != nil {
+		log.Fatalln("Error creating packetConn:", err)
+	}
+
+	rawConn, err := ipv4.NewRawConn(packetConn)
+	if err != nil {
+		log.Fatalln("Error creating rawConn:", err)
+	}
+
+	ApplyBPF(rawConn, server, client)
+
+	return rawConn
+}
+
+// ApplyBPF constructs a BPF program and applies it to the RawConn
+func ApplyBPF(rawConn *ipv4.RawConn, server *Server, client *PeerNet) {
+	const ipv4HeaderLen = 20
+	const srcIPOffset = 12
+	const srcPortOffset = ipv4HeaderLen + 0
+	const dstPortOffset = ipv4HeaderLen + 2
+
+	ipArr := []byte(server.Addr.IP.To4())
+	ipInt := uint32(ipArr[0])<<(3*8) + uint32(ipArr[1])<<(2*8) + uint32(ipArr[2])<<8 + uint32(ipArr[3])
+
+	bpfRaw, err := bpf.Assemble([]bpf.Instruction{
+		bpf.LoadAbsolute{Off: srcIPOffset, Size: 4},
+		bpf.JumpIf{Cond: bpf.JumpEqual, Val: ipInt, SkipFalse: 5, SkipTrue: 0},
+
+		bpf.LoadAbsolute{Off: srcPortOffset, Size: 2},
+		bpf.JumpIf{Cond: bpf.JumpEqual, Val: uint32(server.Port), SkipFalse: 3, SkipTrue: 0},
+
+		bpf.LoadAbsolute{Off: dstPortOffset, Size: 2},
+		bpf.JumpIf{Cond: bpf.JumpEqual, Val: uint32(client.Port), SkipFalse: 1, SkipTrue: 0},
+
+		bpf.RetConstant{Val: 1<<(8*4) - 1},
+		bpf.RetConstant{Val: 0},
+	})
+
+	if err != nil {
+		log.Fatalln("Error assembling BPF:", err)
+	}
+
+	err = rawConn.SetBPF(bpfRaw)
+	if err != nil {
+		log.Fatalln("Error setting BPF:", err)
+	}
+}
+
+// MakePacket constructs a request packet to send to the server
+func MakePacket(payload []byte, server *Server, client *PeerNet) []byte {
+	buf := gopacket.NewSerializeBuffer()
+
+	opts := gopacket.SerializeOptions{
+		FixLengths:       true,
+		ComputeChecksums: true,
+	}
+
+	ipHeader := layers.IPv4{
+		SrcIP:    client.IP,
+		DstIP:    server.Addr.IP,
+		Version:  4,
+		TTL:      64,
+		Protocol: layers.IPProtocolUDP,
+	}
+
+	udpHeader := layers.UDP{
+		SrcPort: layers.UDPPort(client.Port),
+		DstPort: layers.UDPPort(server.Port),
+	}
+
+	payloadLayer := gopacket.Payload(payload)
+
+	udpHeader.SetNetworkLayerForChecksum(&ipHeader)
+
+	gopacket.SerializeLayers(buf, opts, &ipHeader, &udpHeader, &payloadLayer)
+
+	return buf.Bytes()
+}
+
+// SendPacket sends packet to the Server
+func SendPacket(packet []byte, conn *ipv4.RawConn, server *Server, client *PeerNet) error {
+	fullPacket := MakePacket(packet, server, client)
+	_, err := conn.WriteToIP(fullPacket, server.Addr)
+	return err
+}
+
+// SendDataPacket sends a JSON payload to the Server
+func SendDataPacket(data interface{}, conn *ipv4.RawConn, server *Server, client *PeerNet) error {
+	jsonData, err := json.Marshal(data)
+	if err != nil {
+		return fmt.Errorf("failed to marshal payload: %v", err)
+	}
+
+	return SendPacket(jsonData, conn, server, client)
+}
+
+// RecvPacket receives a UDP packet from server
+func RecvPacket(conn *ipv4.RawConn, server *Server, client *PeerNet) ([]byte, int, error) {
+	err := conn.SetReadDeadline(time.Now().Add(timeout))
+	if err != nil {
+		return nil, 0, err
+	}
+
+	response := make([]byte, 4096)
+	n, err := conn.Read(response)
+	if err != nil {
+		return nil, n, err
+	}
+	return response, n, nil
+}
+
+// RecvDataPacket receives and unmarshals a JSON packet from server
+func RecvDataPacket(conn *ipv4.RawConn, server *Server, client *PeerNet) ([]byte, error) {
+	response, n, err := RecvPacket(conn, server, client)
+	if err != nil {
+		return nil, err
+	}
+
+	// Extract payload from UDP packet
+	payload := response[EmptyUDPSize:n]
+	return payload, nil
+}
+
+// ParseResponse takes a response packet and parses it into an IP and port
+func ParseResponse(response []byte) (net.IP, uint16) {
+	ip := net.IP(response[:4])
+	port := binary.BigEndian.Uint16(response[4:6])
+	return ip, port
+}
+
+func parseForBPF(response []byte) (srcIP net.IP, srcPort uint16, dstPort uint16) {
+	srcIP = net.IP(response[12:16])
+	srcPort = binary.BigEndian.Uint16(response[20:22])
+	dstPort = binary.BigEndian.Uint16(response[22:24])
+	return
+}