Test receiving multicast packets over UDP

PiperOrigin-RevId: 304098611

4 files changed, 361 insertions, 56 deletions

diff --git a/test/packetimpact/testbench/BUILD b/test/packetimpact/testbench/BUILD
index a34c81fcc..4a9d8efa6 100644
--- a/test/packetimpact/testbench/BUILD
+++ b/test/packetimpact/testbench/BUILD
@@ -16,6 +16,7 @@ go_library(
     ],
     deps = [
         "//pkg/tcpip",
+        "//pkg/tcpip/buffer",
         "//pkg/tcpip/header",
         "//pkg/tcpip/seqnum",
         "//pkg/usermem",
diff --git a/test/packetimpact/testbench/connections.go b/test/packetimpact/testbench/connections.go
index b7aa63934..8d1f562ee 100644
--- a/test/packetimpact/testbench/connections.go
+++ b/test/packetimpact/testbench/connections.go
@@ -36,19 +36,6 @@ var remoteIPv4 = flag.String("remote_ipv4", "", "remote IPv4 address for test pa
 var localMAC = flag.String("local_mac", "", "local mac address for test packets")
 var remoteMAC = flag.String("remote_mac", "", "remote mac address for test packets")
 
-// TCPIPv4 maintains state about a TCP/IPv4 connection.
-type TCPIPv4 struct {
-	outgoing     Layers
-	incoming     Layers
-	LocalSeqNum  seqnum.Value
-	RemoteSeqNum seqnum.Value
-	SynAck       *TCP
-	sniffer      Sniffer
-	injector     Injector
-	portPickerFD int
-	t            *testing.T
-}
-
 // pickPort makes a new socket and returns the socket FD and port. The caller
 // must close the FD when done with the port if there is no error.
 func pickPort() (int, uint16, error) {
@@ -75,12 +62,25 @@ func pickPort() (int, uint16, error) {
 	return fd, uint16(newSockAddrInet4.Port), nil
 }
 
+// TCPIPv4 maintains state about a TCP/IPv4 connection.
+type TCPIPv4 struct {
+	outgoing     Layers
+	incoming     Layers
+	LocalSeqNum  seqnum.Value
+	RemoteSeqNum seqnum.Value
+	SynAck       *TCP
+	sniffer      Sniffer
+	injector     Injector
+	portPickerFD int
+	t            *testing.T
+}
+
 // tcpLayerIndex is the position of the TCP layer in the TCPIPv4 connection. It
 // is the third, after Ethernet and IPv4.
 const tcpLayerIndex int = 2
 
 // NewTCPIPv4 creates a new TCPIPv4 connection with reasonable defaults.
-func NewTCPIPv4(t *testing.T, dut DUT, outgoingTCP, incomingTCP TCP) TCPIPv4 {
+func NewTCPIPv4(t *testing.T, outgoingTCP, incomingTCP TCP) TCPIPv4 {
 	lMAC, err := tcpip.ParseMACAddress(*localMAC)
 	if err != nil {
 		t.Fatalf("can't parse localMAC %q: %s", *localMAC, err)
@@ -109,18 +109,16 @@ func NewTCPIPv4(t *testing.T, dut DUT, outgoingTCP, incomingTCP TCP) TCPIPv4 {
 	}
 
 	newOutgoingTCP := &TCP{
-		DataOffset: Uint8(header.TCPMinimumSize),
-		WindowSize: Uint16(32768),
-		SrcPort:    &localPort,
+		SrcPort: &localPort,
 	}
 	if err := newOutgoingTCP.merge(outgoingTCP); err != nil {
-		t.Fatalf("can't merge %v into %v: %s", outgoingTCP, newOutgoingTCP, err)
+		t.Fatalf("can't merge %+v into %+v: %s", outgoingTCP, newOutgoingTCP, err)
 	}
 	newIncomingTCP := &TCP{
 		DstPort: &localPort,
 	}
 	if err := newIncomingTCP.merge(incomingTCP); err != nil {
-		t.Fatalf("can't merge %v into %v: %s", incomingTCP, newIncomingTCP, err)
+		t.Fatalf("can't merge %+v into %+v: %s", incomingTCP, newIncomingTCP, err)
 	}
 	return TCPIPv4{
 		outgoing: Layers{
@@ -149,8 +147,9 @@ func (conn *TCPIPv4) Close() {
 	conn.portPickerFD = -1
 }
 
-// Send a packet with reasonable defaults and override some fields by tcp.
-func (conn *TCPIPv4) Send(tcp TCP, additionalLayers ...Layer) {
+// CreateFrame builds a frame for the connection with tcp overriding defaults
+// and additionalLayers added after the TCP header.
+func (conn *TCPIPv4) CreateFrame(tcp TCP, additionalLayers ...Layer) Layers {
 	if tcp.SeqNum == nil {
 		tcp.SeqNum = Uint32(uint32(conn.LocalSeqNum))
 	}
@@ -159,30 +158,41 @@ func (conn *TCPIPv4) Send(tcp TCP, additionalLayers ...Layer) {
 	}
 	layersToSend := deepcopy.Copy(conn.outgoing).(Layers)
 	if err := layersToSend[tcpLayerIndex].(*TCP).merge(tcp); err != nil {
-		conn.t.Fatalf("can't merge %v into %v: %s", tcp, layersToSend[tcpLayerIndex], err)
+		conn.t.Fatalf("can't merge %+v into %+v: %s", tcp, layersToSend[tcpLayerIndex], err)
 	}
 	layersToSend = append(layersToSend, additionalLayers...)
-	outBytes, err := layersToSend.toBytes()
+	return layersToSend
+}
+
+// SendFrame sends a frame with reasonable defaults.
+func (conn *TCPIPv4) SendFrame(frame Layers) {
+	outBytes, err := frame.toBytes()
 	if err != nil {
 		conn.t.Fatalf("can't build outgoing TCP packet: %s", err)
 	}
 	conn.injector.Send(outBytes)
 
 	// Compute the next TCP sequence number.
-	for i := tcpLayerIndex + 1; i < len(layersToSend); i++ {
-		conn.LocalSeqNum.UpdateForward(seqnum.Size(layersToSend[i].length()))
+	for i := tcpLayerIndex + 1; i < len(frame); i++ {
+		conn.LocalSeqNum.UpdateForward(seqnum.Size(frame[i].length()))
 	}
+	tcp := frame[tcpLayerIndex].(*TCP)
 	if tcp.Flags != nil && *tcp.Flags&(header.TCPFlagSyn|header.TCPFlagFin) != 0 {
 		conn.LocalSeqNum.UpdateForward(1)
 	}
 }
 
+// Send a packet with reasonable defaults and override some fields by tcp.
+func (conn *TCPIPv4) Send(tcp TCP, additionalLayers ...Layer) {
+	conn.SendFrame(conn.CreateFrame(tcp, additionalLayers...))
+}
+
 // Recv gets a packet from the sniffer within the timeout provided. If no packet
 // arrives before the timeout, it returns nil.
 func (conn *TCPIPv4) Recv(timeout time.Duration) *TCP {
 	deadline := time.Now().Add(timeout)
 	for {
-		timeout = deadline.Sub(time.Now())
+		timeout = time.Until(deadline)
 		if timeout <= 0 {
 			break
 		}
@@ -192,6 +202,7 @@ func (conn *TCPIPv4) Recv(timeout time.Duration) *TCP {
 		}
 		layers, err := ParseEther(b)
 		if err != nil {
+			conn.t.Logf("can't parse frame: %s", err)
 			continue // Ignore packets that can't be parsed.
 		}
 		if !conn.incoming.match(layers) {
@@ -215,7 +226,7 @@ func (conn *TCPIPv4) Recv(timeout time.Duration) *TCP {
 func (conn *TCPIPv4) Expect(tcp TCP, timeout time.Duration) *TCP {
 	deadline := time.Now().Add(timeout)
 	for {
-		timeout = deadline.Sub(time.Now())
+		timeout = time.Until(deadline)
 		if timeout <= 0 {
 			return nil
 		}
@@ -243,3 +254,154 @@ func (conn *TCPIPv4) Handshake() {
 	// Send an ACK.
 	conn.Send(TCP{Flags: Uint8(header.TCPFlagAck)})
 }
+
+// UDPIPv4 maintains state about a UDP/IPv4 connection.
+type UDPIPv4 struct {
+	outgoing     Layers
+	incoming     Layers
+	sniffer      Sniffer
+	injector     Injector
+	portPickerFD int
+	t            *testing.T
+}
+
+// udpLayerIndex is the position of the UDP layer in the UDPIPv4 connection. It
+// is the third, after Ethernet and IPv4.
+const udpLayerIndex int = 2
+
+// NewUDPIPv4 creates a new UDPIPv4 connection with reasonable defaults.
+func NewUDPIPv4(t *testing.T, outgoingUDP, incomingUDP UDP) UDPIPv4 {
+	lMAC, err := tcpip.ParseMACAddress(*localMAC)
+	if err != nil {
+		t.Fatalf("can't parse localMAC %q: %s", *localMAC, err)
+	}
+
+	rMAC, err := tcpip.ParseMACAddress(*remoteMAC)
+	if err != nil {
+		t.Fatalf("can't parse remoteMAC %q: %s", *remoteMAC, err)
+	}
+
+	portPickerFD, localPort, err := pickPort()
+	if err != nil {
+		t.Fatalf("can't pick a port: %s", err)
+	}
+	lIP := tcpip.Address(net.ParseIP(*localIPv4).To4())
+	rIP := tcpip.Address(net.ParseIP(*remoteIPv4).To4())
+
+	sniffer, err := NewSniffer(t)
+	if err != nil {
+		t.Fatalf("can't make new sniffer: %s", err)
+	}
+
+	injector, err := NewInjector(t)
+	if err != nil {
+		t.Fatalf("can't make new injector: %s", err)
+	}
+
+	newOutgoingUDP := &UDP{
+		SrcPort: &localPort,
+	}
+	if err := newOutgoingUDP.merge(outgoingUDP); err != nil {
+		t.Fatalf("can't merge %+v into %+v: %s", outgoingUDP, newOutgoingUDP, err)
+	}
+	newIncomingUDP := &UDP{
+		DstPort: &localPort,
+	}
+	if err := newIncomingUDP.merge(incomingUDP); err != nil {
+		t.Fatalf("can't merge %+v into %+v: %s", incomingUDP, newIncomingUDP, err)
+	}
+	return UDPIPv4{
+		outgoing: Layers{
+			&Ether{SrcAddr: &lMAC, DstAddr: &rMAC},
+			&IPv4{SrcAddr: &lIP, DstAddr: &rIP},
+			newOutgoingUDP},
+		incoming: Layers{
+			&Ether{SrcAddr: &rMAC, DstAddr: &lMAC},
+			&IPv4{SrcAddr: &rIP, DstAddr: &lIP},
+			newIncomingUDP},
+		sniffer:      sniffer,
+		injector:     injector,
+		portPickerFD: portPickerFD,
+		t:            t,
+	}
+}
+
+// Close the injector and sniffer associated with this connection.
+func (conn *UDPIPv4) Close() {
+	conn.sniffer.Close()
+	conn.injector.Close()
+	if err := unix.Close(conn.portPickerFD); err != nil {
+		conn.t.Fatalf("can't close portPickerFD: %s", err)
+	}
+	conn.portPickerFD = -1
+}
+
+// CreateFrame builds a frame for the connection with the provided udp
+// overriding defaults and the additionalLayers added after the UDP header.
+func (conn *UDPIPv4) CreateFrame(udp UDP, additionalLayers ...Layer) Layers {
+	layersToSend := deepcopy.Copy(conn.outgoing).(Layers)
+	if err := layersToSend[udpLayerIndex].(*UDP).merge(udp); err != nil {
+		conn.t.Fatalf("can't merge %+v into %+v: %s", udp, layersToSend[udpLayerIndex], err)
+	}
+	layersToSend = append(layersToSend, additionalLayers...)
+	return layersToSend
+}
+
+// SendFrame sends a frame with reasonable defaults.
+func (conn *UDPIPv4) SendFrame(frame Layers) {
+	outBytes, err := frame.toBytes()
+	if err != nil {
+		conn.t.Fatalf("can't build outgoing UDP packet: %s", err)
+	}
+	conn.injector.Send(outBytes)
+}
+
+// Send a packet with reasonable defaults and override some fields by udp.
+func (conn *UDPIPv4) Send(udp UDP, additionalLayers ...Layer) {
+	conn.SendFrame(conn.CreateFrame(udp, additionalLayers...))
+}
+
+// Recv gets a packet from the sniffer within the timeout provided. If no packet
+// arrives before the timeout, it returns nil.
+func (conn *UDPIPv4) Recv(timeout time.Duration) *UDP {
+	deadline := time.Now().Add(timeout)
+	for {
+		timeout = time.Until(deadline)
+		if timeout <= 0 {
+			break
+		}
+		b := conn.sniffer.Recv(timeout)
+		if b == nil {
+			break
+		}
+		layers, err := ParseEther(b)
+		if err != nil {
+			conn.t.Logf("can't parse frame: %s", err)
+			continue // Ignore packets that can't be parsed.
+		}
+		if !conn.incoming.match(layers) {
+			continue // Ignore packets that don't match the expected incoming.
+		}
+		return (layers[udpLayerIndex]).(*UDP)
+	}
+	return nil
+}
+
+// Expect a packet that matches the provided udp within the timeout specified.
+// If it doesn't arrive in time, the test fails.
+func (conn *UDPIPv4) Expect(udp UDP, timeout time.Duration) *UDP {
+	deadline := time.Now().Add(timeout)
+	for {
+		timeout = time.Until(deadline)
+		if timeout <= 0 {
+			return nil
+		}
+		gotUDP := conn.Recv(timeout)
+		if gotUDP == nil {
+			return nil
+		}
+		if udp.match(gotUDP) {
+			return gotUDP
+		}
+	}
+}
diff --git a/test/packetimpact/testbench/dut.go b/test/packetimpact/testbench/dut.go
index 8ea1706d3..f80dbb35f 100644
--- a/test/packetimpact/testbench/dut.go
+++ b/test/packetimpact/testbench/dut.go
@@ -305,6 +305,35 @@ func (dut *DUT) SetSockOptTimeval(sockfd, level, optname int32, tv *unix.Timeval
 	}
 }
 
+// RecvWithErrno calls recv on the DUT.
+func (dut *DUT) RecvWithErrno(ctx context.Context, sockfd, len, flags int32) (int32, []byte, error) {
+	dut.t.Helper()
+	req := pb.RecvRequest{
+		Sockfd: sockfd,
+		Len:    len,
+		Flags:  flags,
+	}
+	resp, err := dut.posixServer.Recv(ctx, &req)
+	if err != nil {
+		dut.t.Fatalf("failed to call Recv: %s", err)
+	}
+	return resp.GetRet(), resp.GetBuf(), syscall.Errno(resp.GetErrno_())
+}
+
+// Recv calls recv on the DUT and causes a fatal test failure if it doesn't
+// succeed. If more control over the timeout or error handling is needed, use
+// RecvWithErrno.
+func (dut *DUT) Recv(sockfd, len, flags int32) []byte {
+	dut.t.Helper()
+	ctx, cancel := context.WithTimeout(context.Background(), *rpcTimeout)
+	defer cancel()
+	ret, buf, err := dut.RecvWithErrno(ctx, sockfd, len, flags)
+	if ret == -1 {
+		dut.t.Fatalf("failed to recv: %s", err)
+	}
+	return buf
+}
+
 // CloseWithErrno calls close on the DUT.
 func (dut *DUT) CloseWithErrno(fd int32) (int32, error) {
 	dut.t.Helper()
@@ -330,10 +359,11 @@ func (dut *DUT) Close(fd int32) {
 	}
 }
 
-// CreateListener makes a new TCP connection.  If it fails, the test ends.
-func (dut *DUT) CreateListener(typ, proto, backlog int32) (int32, uint16) {
+// CreateBoundSocket makes a new socket on the DUT, with type typ and protocol
+// proto, and bound to the IP address addr. Returns the new file descriptor and
+// the port that was selected on the DUT.
+func (dut *DUT) CreateBoundSocket(typ, proto int32, addr net.IP) (int32, uint16) {
 	dut.t.Helper()
-	addr := net.ParseIP(*remoteIPv4)
 	var fd int32
 	if addr.To4() != nil {
 		fd = dut.Socket(unix.AF_INET, typ, proto)
@@ -358,6 +388,12 @@ func (dut *DUT) CreateListener(typ, proto, backlog int32) (int32, uint16) {
 	default:
 		dut.t.Fatalf("unknown sockaddr type from getsockname: %t", sa)
 	}
-	dut.Listen(fd, backlog)
 	return fd, uint16(port)
 }
+
+// CreateListener makes a new TCP connection. If it fails, the test ends.
+func (dut *DUT) CreateListener(typ, proto, backlog int32) (int32, uint16) {
+	fd, remotePort := dut.CreateBoundSocket(typ, proto, net.ParseIP(*remoteIPv4))
+	dut.Listen(fd, backlog)
+	return fd, remotePort
+}
diff --git a/test/packetimpact/testbench/layers.go b/test/packetimpact/testbench/layers.go
index 35fa4dcb6..d7434c3d2 100644
--- a/test/packetimpact/testbench/layers.go
+++ b/test/packetimpact/testbench/layers.go
@@ -22,6 +22,7 @@ import (
 	"github.com/google/go-cmp/cmp/cmpopts"
 	"github.com/imdario/mergo"
 	"gvisor.dev/gvisor/pkg/tcpip"
+	"gvisor.dev/gvisor/pkg/tcpip/buffer"
 	"gvisor.dev/gvisor/pkg/tcpip/header"
 )
 
@@ -97,7 +98,7 @@ func equalLayer(x, y Layer) bool {
 	return cmp.Equal(x, y, opt, cmpopts.IgnoreUnexported(LayerBase{}))
 }
 
-// Ether can construct and match the ethernet encapsulation.
+// Ether can construct and match an ethernet encapsulation.
 type Ether struct {
 	LayerBase
 	SrcAddr *tcpip.LinkAddress
@@ -161,7 +162,7 @@ func ParseEther(b []byte) (Layers, error) {
 		return append(layers, moreLayers...), nil
 	default:
 		// TODO(b/150301488): Support more protocols, like IPv6.
-		return nil, fmt.Errorf("can't deduce the ethernet header's next protocol: %v", b)
+		return nil, fmt.Errorf("can't deduce the ethernet header's next protocol: %#v", b)
 	}
 }
 
@@ -173,7 +174,7 @@ func (l *Ether) length() int {
 	return header.EthernetMinimumSize
 }
 
-// IPv4 can construct and match the ethernet excapulation.
+// IPv4 can construct and match an IPv4 encapsulation.
 type IPv4 struct {
 	LayerBase
 	IHL            *uint8
@@ -236,9 +237,11 @@ func (l *IPv4) toBytes() ([]byte, error) {
 		switch n := l.next().(type) {
 		case *TCP:
 			fields.Protocol = uint8(header.TCPProtocolNumber)
+		case *UDP:
+			fields.Protocol = uint8(header.UDPProtocolNumber)
 		default:
-			// TODO(b/150301488): Support more protocols, like UDP.
-			return nil, fmt.Errorf("can't deduce the ip header's next protocol: %+v", n)
+			// TODO(b/150301488): Support more protocols as needed.
+			return nil, fmt.Errorf("can't deduce the ip header's next protocol: %#v", n)
 		}
 	}
 	if l.SrcAddr != nil {
@@ -294,13 +297,19 @@ func ParseIPv4(b []byte) (Layers, error) {
 		DstAddr:        Address(h.DestinationAddress()),
 	}
 	layers := Layers{&ipv4}
-	switch h.Protocol() {
-	case uint8(header.TCPProtocolNumber):
+	switch h.TransportProtocol() {
+	case header.TCPProtocolNumber:
 		moreLayers, err := ParseTCP(b[ipv4.length():])
 		if err != nil {
 			return nil, err
 		}
 		return append(layers, moreLayers...), nil
+	case header.UDPProtocolNumber:
+		moreLayers, err := ParseUDP(b[ipv4.length():])
+		if err != nil {
+			return nil, err
+		}
+		return append(layers, moreLayers...), nil
 	}
 	return nil, fmt.Errorf("can't deduce the ethernet header's next protocol: %d", h.Protocol())
 }
@@ -316,7 +325,7 @@ func (l *IPv4) length() int {
 	return int(*l.IHL)
 }
 
-// TCP can construct and match the TCP excapulation.
+// TCP can construct and match a TCP encapsulation.
 type TCP struct {
 	LayerBase
 	SrcPort       *uint16
@@ -347,12 +356,16 @@ func (l *TCP) toBytes() ([]byte, error) {
 	}
 	if l.DataOffset != nil {
 		h.SetDataOffset(*l.DataOffset)
+	} else {
+		h.SetDataOffset(uint8(l.length()))
 	}
 	if l.Flags != nil {
 		h.SetFlags(*l.Flags)
 	}
 	if l.WindowSize != nil {
 		h.SetWindowSize(*l.WindowSize)
+	} else {
+		h.SetWindowSize(32768)
 	}
 	if l.UrgentPointer != nil {
 		h.SetUrgentPoiner(*l.UrgentPointer)
@@ -361,38 +374,52 @@ func (l *TCP) toBytes() ([]byte, error) {
 		h.SetChecksum(*l.Checksum)
 		return h, nil
 	}
-	if err := setChecksum(&h, l); err != nil {
+	if err := setTCPChecksum(&h, l); err != nil {
 		return nil, err
 	}
 	return h, nil
 }
 
-// setChecksum calculates the checksum of the TCP header and sets it in h.
-func setChecksum(h *header.TCP, tcp *TCP) error {
-	h.SetChecksum(0)
-	tcpLength := uint16(tcp.length())
-	current := tcp.next()
-	for current != nil {
-		tcpLength += uint16(current.length())
-		current = current.next()
+// totalLength returns the length of the provided layer and all following
+// layers.
+func totalLength(l Layer) int {
+	var totalLength int
+	for ; l != nil; l = l.next() {
+		totalLength += l.length()
 	}
+	return totalLength
+}
 
+// layerChecksum calculates the checksum of the Layer header, including the
+// peusdeochecksum of the layer before it and all the bytes after it..
+func layerChecksum(l Layer, protoNumber tcpip.TransportProtocolNumber) (uint16, error) {
+	totalLength := uint16(totalLength(l))
 	var xsum uint16
-	switch s := tcp.prev().(type) {
+	switch s := l.prev().(type) {
 	case *IPv4:
-		xsum = header.PseudoHeaderChecksum(header.TCPProtocolNumber, *s.SrcAddr, *s.DstAddr, tcpLength)
+		xsum = header.PseudoHeaderChecksum(protoNumber, *s.SrcAddr, *s.DstAddr, totalLength)
 	default:
 		// TODO(b/150301488): Support more protocols, like IPv6.
-		return fmt.Errorf("can't get src and dst addr from previous layer")
+		return 0, fmt.Errorf("can't get src and dst addr from previous layer: %#v", s)
 	}
-	current = tcp.next()
-	for current != nil {
+	var payloadBytes buffer.VectorisedView
+	for current := l.next(); current != nil; current = current.next() {
 		payload, err := current.toBytes()
 		if err != nil {
-			return fmt.Errorf("can't get bytes for next header: %s", payload)
+			return 0, fmt.Errorf("can't get bytes for next header: %s", payload)
 		}
-		xsum = header.Checksum(payload, xsum)
-		current = current.next()
+		payloadBytes.AppendView(payload)
+	}
+	xsum = header.ChecksumVV(payloadBytes, xsum)
+	return xsum, nil
+}
+
+// setTCPChecksum calculates the checksum of the TCP header and sets it in h.
+func setTCPChecksum(h *header.TCP, tcp *TCP) error {
+	h.SetChecksum(0)
+	xsum, err := layerChecksum(tcp, header.TCPProtocolNumber)
+	if err != nil {
+		return err
 	}
 	h.SetChecksum(^h.CalculateChecksum(xsum))
 	return nil
@@ -444,6 +471,85 @@ func (l *TCP) merge(other TCP) error {
 	return mergo.Merge(l, other, mergo.WithOverride)
 }
 
+// UDP can construct and match a UDP encapsulation.
+type UDP struct {
+	LayerBase
+	SrcPort  *uint16
+	DstPort  *uint16
+	Length   *uint16
+	Checksum *uint16
+}
+
+func (l *UDP) toBytes() ([]byte, error) {
+	b := make([]byte, header.UDPMinimumSize)
+	h := header.UDP(b)
+	if l.SrcPort != nil {
+		h.SetSourcePort(*l.SrcPort)
+	}
+	if l.DstPort != nil {
+		h.SetDestinationPort(*l.DstPort)
+	}
+	if l.Length != nil {
+		h.SetLength(*l.Length)
+	} else {
+		h.SetLength(uint16(totalLength(l)))
+	}
+	if l.Checksum != nil {
+		h.SetChecksum(*l.Checksum)
+		return h, nil
+	}
+	if err := setUDPChecksum(&h, l); err != nil {
+		return nil, err
+	}
+	return h, nil
+}
+
+// setUDPChecksum calculates the checksum of the UDP header and sets it in h.
+func setUDPChecksum(h *header.UDP, udp *UDP) error {
+	h.SetChecksum(0)
+	xsum, err := layerChecksum(udp, header.UDPProtocolNumber)
+	if err != nil {
+		return err
+	}
+	h.SetChecksum(^h.CalculateChecksum(xsum))
+	return nil
+}
+
+// ParseUDP parses the bytes assuming that they start with a udp header and
+// continues parsing further encapsulations.
+func ParseUDP(b []byte) (Layers, error) {
+	h := header.UDP(b)
+	udp := UDP{
+		SrcPort:  Uint16(h.SourcePort()),
+		DstPort:  Uint16(h.DestinationPort()),
+		Length:   Uint16(h.Length()),
+		Checksum: Uint16(h.Checksum()),
+	}
+	layers := Layers{&udp}
+	moreLayers, err := ParsePayload(b[udp.length():])
+	if err != nil {
+		return nil, err
+	}
+	return append(layers, moreLayers...), nil
+}
+
+func (l *UDP) match(other Layer) bool {
+	return equalLayer(l, other)
+}
+
+func (l *UDP) length() int {
+	if l.Length == nil {
+		return header.UDPMinimumSize
+	}
+	return int(*l.Length)
+}
+
+// merge overrides the values in l with the values from other but only in fields
+// where the value is not nil.
+func (l *UDP) merge(other UDP) error {
+	return mergo.Merge(l, other, mergo.WithOverride)
+}
+
 // Payload has bytes beyond OSI layer 4.
 type Payload struct {
 	LayerBase