Implement RMCP layer type

layers/layertypes.go

@@ -143,6 +143,7 @@ var (
 	LayerTypeMLDv2MulticastListenerQuery  = gopacket.RegisterLayerType(139, gopacket.LayerTypeMetadata{Name: "MLDv2MulticastListenerQuery", Decoder: gopacket.DecodeFunc(decodeMLDv2MulticastListenerQuery)})
 	LayerTypeTLS                          = gopacket.RegisterLayerType(140, gopacket.LayerTypeMetadata{Name: "TLS", Decoder: gopacket.DecodeFunc(decodeTLS)})
 	LayerTypeModbusTCP                    = gopacket.RegisterLayerType(141, gopacket.LayerTypeMetadata{Name: "ModbusTCP", Decoder: gopacket.DecodeFunc(decodeModbusTCP)})
+	LayerTypeRMCP                         = gopacket.RegisterLayerType(142, gopacket.LayerTypeMetadata{Name: "RMCP", Decoder: gopacket.DecodeFunc(decodeRMCP)})
 )
 
 var (

layers/ports.go

@@ -115,6 +115,7 @@ var udpPortLayerType = [65536]gopacket.LayerType{
 	6081: LayerTypeGeneve,
 	3784: LayerTypeBFD,
 	2152: LayerTypeGTPv1U,
+	623:  LayerTypeRMCP,
 }
 
 // RegisterUDPPortLayerType creates a new mapping between a UDPPort

layers/rmcp.go

@@ -0,0 +1,162 @@
+// Copyright 2019 The GoPacket Authors. All rights reserved.
+//
+// Use of this source code is governed by a BSD-style license that can be found
+// in the LICENSE file in the root of the source tree.
+
+package layers
+
+// This file implements the ASF-RMCP header specified in section 3.2.2.2 of
+// https://www.dmtf.org/sites/default/files/standards/documents/DSP0136.pdf
+
+import (
+	"fmt"
+
+	"github.com/google/gopacket"
+)
+
+// RMCPClass is the class of a RMCP layer's payload, e.g. ASF or IPMI. This is a
+// 4-bit unsigned int on the wire; all but 6 (ASF), 7 (IPMI) and 8 (OEM-defined)
+// are currently reserved.
+type RMCPClass uint8
+
+// LayerType returns the payload layer type corresponding to a RMCP class.
+func (c RMCPClass) LayerType() gopacket.LayerType {
+	if lt := rmcpClassLayerTypes[uint8(c)]; lt != 0 {
+		return lt
+	}
+	return gopacket.LayerTypePayload
+}
+
+func (c RMCPClass) String() string {
+	return fmt.Sprintf("%v(%v)", uint8(c), c.LayerType())
+}
+
+const (
+	// RMCPVersion1 identifies RMCP v1.0 in the Version header field. Lower
+	// values are considered legacy, while higher values are reserved by the
+	// specification.
+	RMCPVersion1 uint8 = 0x06
+
+	// RMCPNormal indicates a "normal" message, i.e. not an acknowledgement.
+	RMCPNormal uint8 = 0
+
+	// RMCPAck indicates a message is acknowledging a received normal message.
+	RMCPAck uint8 = 1 << 7
+
+	// RMCPClassASF identifies an RMCP message as containing an ASF-RMCP
+	// payload.
+	RMCPClassASF RMCPClass = 0x06
+
+	// RMCPClassIPMI identifies an RMCP message as containing an IPMI payload.
+	RMCPClassIPMI RMCPClass = 0x07
+
+	// RMCPClassOEM identifies an RMCP message as containing an OEM-defined
+	// payload.
+	RMCPClassOEM RMCPClass = 0x08
+)
+
+var (
+	rmcpClassLayerTypes = [16]gopacket.LayerType{
+		// RMCPClassASF and RMCPClassIPMI are to implement; OEM layer type (8)
+		// is deliberately not implemented, so we return LayerTypePayload
+	}
+)
+
+// RMCP describes the format of an RMCP header, which forms a UDP payload. See
+// section 3.2.2.2.
+type RMCP struct {
+	BaseLayer
+
+	// Version identifies the version of the RMCP header. 0x06 indicates RMCP
+	// v1.0; lower values are legacy, higher values are reserved.
+	Version uint8
+
+	// Sequence is the sequence number assicated with the message. Note that
+	// this rolls over to 0 after 254, not 255. Seq num 255 indicates the
+	// receiver must not send an ACK.
+	Sequence uint8
+
+	// Ack indicates whether this packet is an acknowledgement. If it is, the
+	// payload will be empty.
+	Ack bool
+
+	// Class idicates the structure of the payload. There are only 2^4 valid
+	// values, however there is no uint4 data type. N.B. the Ack bit has been
+	// split off into another field. The most significant 4 bits of this field
+	// will always be 0.
+	Class RMCPClass
+}
+
+// LayerType returns LayerTypeRMCP. It partially satisfies Layer and
+// SerializableLayer.
+func (*RMCP) LayerType() gopacket.LayerType {
+	return LayerTypeRMCP
+}
+
+// CanDecode returns LayerTypeRMCP. It partially satisfies DecodingLayer.
+func (r *RMCP) CanDecode() gopacket.LayerClass {
+	return r.LayerType()
+}
+
+// DecodeFromBytes makes the layer represent the provided bytes. It partially
+// satisfies DecodingLayer.
+func (r *RMCP) DecodeFromBytes(data []byte, df gopacket.DecodeFeedback) error {
+	if len(data) < 4 {
+		df.SetTruncated()
+		return fmt.Errorf("invalid RMCP header, length %v less than 4",
+			len(data))
+	}
+
+	r.BaseLayer.Contents = data[:4]
+	r.BaseLayer.Payload = data[4:]
+
+	r.Version = uint8(data[0])
+	// 1 byte reserved
+	r.Sequence = uint8(data[2])
+	r.Ack = data[3]&RMCPAck != 0
+	r.Class = RMCPClass(data[3] & 0xF)
+	return nil
+}
+
+// NextLayerType returns the data layer of this RMCP layer. This partially
+// satisfies DecodingLayer.
+func (r *RMCP) NextLayerType() gopacket.LayerType {
+	return r.Class.LayerType()
+}
+
+// Payload returns the data layer. It partially satisfies ApplicationLayer.
+func (r *RMCP) Payload() []byte {
+	return r.BaseLayer.Payload
+}
+
+// SerializeTo writes the serialized fom of this layer into the SerializeBuffer,
+// partially satisfying SerializableLayer.
+func (r *RMCP) SerializeTo(b gopacket.SerializeBuffer, opts gopacket.SerializeOptions) error {
+	// The IPMI v1.5 spec contains a pad byte for frame sizes of certain lengths
+	// to work around issues in LAN chips. This is no longer necessary as of
+	// IPMI v2.0 (renamed to "legacy pad") so we do not attempt to add it. The
+	// same approach is taken by FreeIPMI:
+	// http://git.savannah.gnu.org/cgit/freeipmi.git/tree/libfreeipmi/interface/ipmi-lan-interface.c?id=b5ffcd38317daf42074458879f4c55ba6804a595#n836
+	bytes, err := b.PrependBytes(4)
+	if err != nil {
+		return err
+	}
+	bytes[0] = r.Version
+	bytes[1] = 0x00
+	bytes[2] = r.Sequence
+	bytes[3] = bool2uint8(r.Ack)<<7 | uint8(r.Class) // thanks, BFD layer
+	return nil
+}
+
+// decodeRMCP decodes the byte slice into an RMCP type, and sets the application
+// layer to it.
+func decodeRMCP(data []byte, p gopacket.PacketBuilder) error {
+	rmcp := &RMCP{}
+	err := rmcp.DecodeFromBytes(data, p)
+	p.AddLayer(rmcp)
+	p.SetApplicationLayer(rmcp)
+	if err != nil {
+		return err
+	}
+	return p.NextDecoder(rmcp.NextLayerType())
+}

layers/rmcp_test.go

@@ -0,0 +1,86 @@
+// Copyright 2019 The GoPacket Authors. All rights reserved.
+//
+// Use of this source code is governed by a BSD-style license that can be found
+// in the LICENSE file in the root of the source tree.
+
+package layers
+
+import (
+	"bytes"
+	"encoding/hex"
+	"testing"
+
+	"github.com/google/gopacket"
+)
+
+func RMCPTestDecodeFromBytes(t *testing.T) {
+	b, err := hex.DecodeString("0600ff06")
+	if err != nil {
+		t.Fatalf("Failed to decode RMCP message")
+	}
+
+	rmcp := &RMCP{}
+	if err := rmcp.DecodeFromBytes(b, gopacket.NilDecodeFeedback); err != nil {
+		t.Fatalf("Unexpected error: %v", err)
+	}
+	if !bytes.Equal(rmcp.BaseLayer.Payload, []byte{}) {
+		t.Errorf("payload is %v, want %v", rmcp.BaseLayer.Payload, b)
+	}
+	if !bytes.Equal(rmcp.BaseLayer.Contents, b) {
+		t.Errorf("contents is %v, want %v", rmcp.BaseLayer.Contents, b)
+	}
+	if rmcp.Version != RMCPVersion1 {
+		t.Errorf("version is %v, want %v", rmcp.Version, RMCPVersion1)
+	}
+	if rmcp.Sequence != 0xFF {
+		t.Errorf("sequence is %v, want %v", rmcp.Sequence, 0xFF)
+	}
+	if rmcp.Ack {
+		t.Errorf("ack is true, want false")
+	}
+	if rmcp.Class != RMCPClassASF {
+		t.Errorf("class is %v, want %v", rmcp.Class, RMCPClassASF)
+	}
+}
+
+func serializeRMCP(rmcp *RMCP) ([]byte, error) {
+	sb := gopacket.NewSerializeBuffer()
+	err := rmcp.SerializeTo(sb, gopacket.SerializeOptions{})
+	return sb.Bytes(), err
+}
+
+func RMCPTestSerializeTo(t *testing.T) {
+	table := []struct {
+		layer *RMCP
+		want  []byte
+	}{
+		{
+			&RMCP{
+				Version:  RMCPVersion1,
+				Sequence: 1,
+				Ack:      false,
+				Class:    RMCPClassASF,
+			},
+			[]byte{0x6, 0x0, 0x1, 0x6},
+		},
+		{
+			&RMCP{
+				Version:  RMCPVersion1,
+				Sequence: 0xFF,
+				Ack:      true,
+				Class:    RMCPClassIPMI,
+			},
+			[]byte{0x6, 0x0, 0xFF, 0x87},
+		},
+	}
+	for _, test := range table {
+		b, err := serializeRMCP(test.layer)
+		switch {
+		case err != nil && test.want != nil:
+			t.Errorf("serialize %v failed with %v, wanted %v", test.layer,
+				err, test.want)
+		case err == nil && !bytes.Equal(b, test.want):
+			t.Errorf("serialize %v = %v, want %v", test.layer, b, test.want)
+		}
+	}
+}