124 lines
3.7 KiB
Go
124 lines
3.7 KiB
Go
// Copyright 2012 Google, Inc. All rights reserved.
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// Copyright 2009-2011 Andreas Krennmair. All rights reserved.
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//
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// Use of this source code is governed by a BSD-style license
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// that can be found in the LICENSE file in the root of the source
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// tree.
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package layers
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import (
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"encoding/binary"
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"errors"
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"fmt"
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"github.com/google/gopacket"
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"net"
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)
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// EthernetBroadcast is the broadcast MAC address used by Ethernet.
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var EthernetBroadcast = net.HardwareAddr{0xff, 0xff, 0xff, 0xff, 0xff, 0xff}
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// Ethernet is the layer for Ethernet frame headers.
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type Ethernet struct {
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BaseLayer
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SrcMAC, DstMAC net.HardwareAddr
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EthernetType EthernetType
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// Length is only set if a length field exists within this header. Ethernet
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// headers follow two different standards, one that uses an EthernetType, the
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// other which defines a length the follows with a LLC header (802.3). If the
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// former is the case, we set EthernetType and Length stays 0. In the latter
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// case, we set Length and EthernetType = EthernetTypeLLC.
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Length uint16
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}
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// LayerType returns LayerTypeEthernet
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func (e *Ethernet) LayerType() gopacket.LayerType { return LayerTypeEthernet }
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func (e *Ethernet) LinkFlow() gopacket.Flow {
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return gopacket.NewFlow(EndpointMAC, e.SrcMAC, e.DstMAC)
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}
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func (eth *Ethernet) DecodeFromBytes(data []byte, df gopacket.DecodeFeedback) error {
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if len(data) < 14 {
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return errors.New("Ethernet packet too small")
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}
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eth.DstMAC = net.HardwareAddr(data[0:6])
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eth.SrcMAC = net.HardwareAddr(data[6:12])
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eth.EthernetType = EthernetType(binary.BigEndian.Uint16(data[12:14]))
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eth.BaseLayer = BaseLayer{data[:14], data[14:]}
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eth.Length = 0
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if eth.EthernetType < 0x0600 {
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eth.Length = uint16(eth.EthernetType)
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eth.EthernetType = EthernetTypeLLC
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if cmp := len(eth.Payload) - int(eth.Length); cmp < 0 {
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df.SetTruncated()
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} else if cmp > 0 {
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// Strip off bytes at the end, since we have too many bytes
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eth.Payload = eth.Payload[:len(eth.Payload)-cmp]
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}
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// fmt.Println(eth)
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}
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return nil
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}
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// SerializeTo writes the serialized form of this layer into the
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// SerializationBuffer, implementing gopacket.SerializableLayer.
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// See the docs for gopacket.SerializableLayer for more info.
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func (eth *Ethernet) SerializeTo(b gopacket.SerializeBuffer, opts gopacket.SerializeOptions) error {
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if len(eth.DstMAC) != 6 {
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return fmt.Errorf("invalid dst MAC: %v", eth.DstMAC)
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}
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if len(eth.SrcMAC) != 6 {
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return fmt.Errorf("invalid src MAC: %v", eth.SrcMAC)
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}
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payload := b.Bytes()
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bytes, err := b.PrependBytes(14)
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if err != nil {
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return err
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}
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copy(bytes, eth.DstMAC)
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copy(bytes[6:], eth.SrcMAC)
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if eth.Length != 0 || eth.EthernetType == EthernetTypeLLC {
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if opts.FixLengths {
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eth.Length = uint16(len(payload))
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}
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if eth.EthernetType != EthernetTypeLLC {
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return fmt.Errorf("ethernet type %v not compatible with length value %v", eth.EthernetType, eth.Length)
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} else if eth.Length > 0x0600 {
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return fmt.Errorf("invalid ethernet length %v", eth.Length)
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}
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binary.BigEndian.PutUint16(bytes[12:], eth.Length)
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} else {
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binary.BigEndian.PutUint16(bytes[12:], uint16(eth.EthernetType))
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}
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length := len(b.Bytes())
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if length < 60 {
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// Pad out to 60 bytes.
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padding, err := b.AppendBytes(60 - length)
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if err != nil {
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return err
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}
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copy(padding, lotsOfZeros[:])
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}
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return nil
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}
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func (eth *Ethernet) CanDecode() gopacket.LayerClass {
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return LayerTypeEthernet
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}
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func (eth *Ethernet) NextLayerType() gopacket.LayerType {
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return eth.EthernetType.LayerType()
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}
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func decodeEthernet(data []byte, p gopacket.PacketBuilder) error {
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eth := &Ethernet{}
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err := eth.DecodeFromBytes(data, p)
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if err != nil {
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return err
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}
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p.AddLayer(eth)
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p.SetLinkLayer(eth)
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return p.NextDecoder(eth.EthernetType)
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}
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