Matteo Scandolo | a6a3aee | 2019-11-26 13:30:14 -0700 | [diff] [blame^] | 1 | // Copyright 2012 Google, Inc. All rights reserved. |
| 2 | // |
| 3 | // Use of this source code is governed by a BSD-style license |
| 4 | // that can be found in the LICENSE file in the root of the source |
| 5 | // tree. |
| 6 | |
| 7 | package layers |
| 8 | |
| 9 | import ( |
| 10 | "encoding/binary" |
| 11 | "errors" |
| 12 | "fmt" |
| 13 | |
| 14 | "github.com/google/gopacket" |
| 15 | ) |
| 16 | |
| 17 | // Loopback contains the header for loopback encapsulation. This header is |
| 18 | // used by both BSD and OpenBSD style loopback decoding (pcap's DLT_NULL |
| 19 | // and DLT_LOOP, respectively). |
| 20 | type Loopback struct { |
| 21 | BaseLayer |
| 22 | Family ProtocolFamily |
| 23 | } |
| 24 | |
| 25 | // LayerType returns LayerTypeLoopback. |
| 26 | func (l *Loopback) LayerType() gopacket.LayerType { return LayerTypeLoopback } |
| 27 | |
| 28 | // DecodeFromBytes decodes the given bytes into this layer. |
| 29 | func (l *Loopback) DecodeFromBytes(data []byte, df gopacket.DecodeFeedback) error { |
| 30 | if len(data) < 4 { |
| 31 | return errors.New("Loopback packet too small") |
| 32 | } |
| 33 | |
| 34 | // The protocol could be either big-endian or little-endian, we're |
| 35 | // not sure. But we're PRETTY sure that the value is less than |
| 36 | // 256, so we can check the first two bytes. |
| 37 | var prot uint32 |
| 38 | if data[0] == 0 && data[1] == 0 { |
| 39 | prot = binary.BigEndian.Uint32(data[:4]) |
| 40 | } else { |
| 41 | prot = binary.LittleEndian.Uint32(data[:4]) |
| 42 | } |
| 43 | if prot > 0xFF { |
| 44 | return fmt.Errorf("Invalid loopback protocol %q", data[:4]) |
| 45 | } |
| 46 | |
| 47 | l.Family = ProtocolFamily(prot) |
| 48 | l.BaseLayer = BaseLayer{data[:4], data[4:]} |
| 49 | return nil |
| 50 | } |
| 51 | |
| 52 | // CanDecode returns the set of layer types that this DecodingLayer can decode. |
| 53 | func (l *Loopback) CanDecode() gopacket.LayerClass { |
| 54 | return LayerTypeLoopback |
| 55 | } |
| 56 | |
| 57 | // NextLayerType returns the layer type contained by this DecodingLayer. |
| 58 | func (l *Loopback) NextLayerType() gopacket.LayerType { |
| 59 | return l.Family.LayerType() |
| 60 | } |
| 61 | |
| 62 | // SerializeTo writes the serialized form of this layer into the |
| 63 | // SerializationBuffer, implementing gopacket.SerializableLayer. |
| 64 | func (l *Loopback) SerializeTo(b gopacket.SerializeBuffer, opts gopacket.SerializeOptions) error { |
| 65 | bytes, err := b.PrependBytes(4) |
| 66 | if err != nil { |
| 67 | return err |
| 68 | } |
| 69 | binary.LittleEndian.PutUint32(bytes, uint32(l.Family)) |
| 70 | return nil |
| 71 | } |
| 72 | |
| 73 | func decodeLoopback(data []byte, p gopacket.PacketBuilder) error { |
| 74 | l := Loopback{} |
| 75 | if err := l.DecodeFromBytes(data, gopacket.NilDecodeFeedback); err != nil { |
| 76 | return err |
| 77 | } |
| 78 | p.AddLayer(&l) |
| 79 | return p.NextDecoder(l.Family) |
| 80 | } |